Exam 3: Chapter 24: Digestive System

Question 1

Digestive tract
Accessory organs

Answer 1

Digestive System Consists Of

Question 2

oIs a tube extending from the mouth to the anus
oIt is also called the gastrointestinal tract and the alimentary canal

Answer 2

Digestive Tract (GI Tract)

Question 3

oThe associated ______ include the tongue, teeth, salivary glands, liver, gallbladder, and pancreas
oThese organs include glands that secrete fluids into the digestive tract

Answer 3

Accessory Organs

Question 4

o1.Oral cavity, including the tongue, teeth, and salivary glands as accessory organs
o2.Pharynx
o3.Esophagus
o4.Stomach
o5.Small intestine, consisting of the duodenum, jejunum, and ileum, with the liver, gallbladder, and pancreas as accessory organs
o6.Large intestine, including the cecum, colon, rectum, anal canal, and anus

Answer 4

The Digestive Tract and Associated Accessory Organs Include the Following

Question 5

Ingestion and Mastication
Propulsion and Mixing
Secretion
Digestion
Absorption
Elimination

Answer 5

Major Functions of the Digestive System Include

Question 6

*Is the intake of solids or liquids
*The normal route of _____ is through the oral cavity
*Is the process by which the teeth chew food in the mouth to begin the process of digestion
*Digestive enzymes cannot easily penetrate solid food particles and are effective only on the outer surface of food particles
*It is vital, therefore, that solid foods be mechanically broken down by _____ to increase total surface area for digestion

Answer 6

Ingestion and Mastication

Question 7

*Is the movement of food from one end of the digestive tract to the other
*Is the movement of food back and forth in the digestive tract, without forward movement
*The total time it takes food to travel the length of the digestive tract is usually about 24-36 hours
*Each segment of the digestive tract is specialized to assist in moving food undergoing digestion from its oral end to its anal end
*The ______ movements begin with swallowing, followed by peristalsis, and finally mass movements

Answer 7

Propulsion and Mixing

Question 8

*Swallowing or deglutition, moves liquids or a soft mass of food and liquid, called a bolus, from the oral cavity into the esophagus
*Peristalsis propels material through most of the digestive tract
*Peristaltic waves are muscular contractions consisting of a wave of
*Mass movements are contractions that move material in the distal parts of the large intestine to the anus
*Mixing contractions blend food with digestive fluids in the stomach and small intestine
*These contractions aid with mechanical digestion

Answer 8

Characteristics of These Propulsive Movements Are

Question 9

*Are muscular contractions consisting of a wave of relaxation of the circular muscles in front of the mass of undigested food (now called chyme)
*This is followed by a wave of strong contraction of the circular muscles behind the mass of chyme, which force the bolus along the digestive tract
*Each _______ travels the length of the esophagus in about 10 seconds
*______ in the small and large intestines usually travel only short distances

Answer 9

Peristaltic waves

Question 10

*Mixing waves are gentle contractions in the stomach that churn the food with gastric secretions
*Ingested food is stored and mixed in the stomach, from where it is slowly released into the small intestine as chyme
*Segmental contractions mix food particles with digestive secretions in the small intestine

Answer 10

There are Two Major Types of Mixing Contractions

Question 11

*A mass of chyme within the tract begins at one location
*Segments of the digestive tract alternate between contraction and relaxation
*The mass of chyme spreads out in both directions

Answer 11

Sequence of Segmental Contractions

Question 12

*Are added to lubricate, liquefy, buffer, and digest the food as it moves through the digestive tract
*Mucus, secreted along the entire digestive tract, lubricates the food and the lining of the tract
*The mucus coats and protects the epithelial cells of the digestive tract from mechanical abrasion, stomach acid, and digestive enzymes
*The ______ also contain large amounts of water, which liquefies the food, making it easier to digest and absorb
*Water also moves into the intestine by osmosis
*Liver ______ break large lipid droplets into much smaller droplets, which makes the digestion and absorption of lipids possible
*Enzymes secreted by the oral cavity, stomach, small intestine, and pancreas break down large food molecules into smaller molecules that can be absorbed by the intestinal wall

Answer 12

Secretion

Question 13

*Is the breakdown of large organic molecules into their individual components
*Consists of mechanical _______ which involves the mastication and mixing of food, and chemical _______, which is accomplished by digestive enzymes secreted along the digestive tract
*Large organic molecules must be digested into their individual components before they can be absorbed by the digestive tract
*Carbohydrates are broken into monosaccharides
*Proteins are broken into amino acids, and triglycerides into fatty acids and glycerol
*Minerals and water are not broken down before being absorbed
*Vitamins are also absorbed without digestion; in fact, they lose their function if their structure is altered by digestion

Answer 13

Digestion

Question 14

*Is the movement of molecules out of the digestive tract and into the blood or into the lymphatic system
*The mechanism by which _______ occurs depends on the type of molecule involved
*Molecules pass out of the digestive tract by diffusion, facilitated diffusion, active transport, symport, or endocytosis

Answer 14

Absorption

Question 15

*Is the process by which the waste products of digestion are removed from the body
*During this process, which occurs primarily in the large intestine, water and salts are absorbed, changing the material in the digestive tract from liquefied to semisolid
*These semisolid waste products, called feces, are stored in the distal large intestine, and then eliminated by the process of defecation

Answer 15

Elimination

Question 16

Mucosa
Submucosa
Muscularis
Serosa or adventitia

Answer 16

There are Four Major Layers of the Digestive Tract

Question 17

*The innermost tunic
*The epithelium extends deep into the lamina propria in many places to form intestinal glands and crypts
*Two types of specialized cells in the ______ are mechanoreceptors involved in peristaltic reflexes and chemoreceptors that detect the chemical composition of food

Answer 17

Mucosa

Question 18

Mucous epithelium
Lamina propria
Muscularis mucosae

Answer 18

The Mucosa, or Mucous Membrane, Consists of Three Separate Layers

Question 19

*The inner ________, which is nonkeratinized stratified squamous epithelium in the mouth, oropharynx, esophagus, and anal canal and simple columnar epithelium in the remainder of the digestive tract

Answer 19

Mucous Epithelium

Question 20

*A loose connective tissue called the _______

Answer 20

Lamina Propria

Question 21

*A thin outer layer of smooth muscle called the _________

Answer 21

Muscularis Mucosae

Question 22

*Beneath the mucosa lies the submucosa, a thick connective tissue layer
*This tunic contains nerves, blood vessels, lymphatic vessels, and small glands

Answer 22

Submucosa

Question 23

*A network of neurons and glial cells in the submucosa forms a portion of the enteric nervous system called the _______ or Meissner plexus
*Axons from the _______ extend to cells in the epithelial intestinal glands, stimulating their secretion
*The esophagus and stomach lack a _________, but the plexus is extensive throughout the rest of the digestive tract

Answer 23

Submucosal Plexus

Question 24

*The next tunic is the ______, a muscular layer

Answer 24

Muscularis

Question 25

*The muscularis consists of an inner layer of circular smooth muscle

Answer 25

Inner Circular Layer

Question 26

*The muscularis consists of an outer layer of longitudinal smooth muscle *Two exceptions are the upper esophagus, where the muscles are skeletal, and the stomach, which has three layers of smooth muscle

Answer 26

Outer Longitudinal Layer

Question 27

*Between the two muscle layers is a second portion of the enteric nervous system called the ______, or Auerbach plexus *The ________ is much more extensive than the submucosal plexus and controls the motility of the intestinal tract *This function is in contrast with the submucosal plexus, which controls secretions *Within the ________, specialized interstitial cells form a network of pacemakers, which promote rhythmic contractions of smooth muscle along the digestive tract *These cells also help transmit signals from neurons to muscles to regulate movement *Dysfunction of these pacemakers decreases motility in the digestive tract *Together, the submucosal and _________ constitute the enteric nervous system (ENS) or the enteric plexus, which is extremely important in controlling secretion and movement

Answer 27

Myenteric Plexus

Question 28

*The fourth layer of the digestive tract is either a ________ or an ______, depending on the structure of the layer *Parts of the digestive tract located within the peritoneal cavity have a _______ as the outermost layer *This ______, or serous membrane, is called the visceral peritoneum *It consists of a thin layer of connective tissue and a simple squamous epithelium *When the outer layer of the digestive tract is derived from adjacent connective tissue, the tunic is called the adventitia and consists of a connective tissue covering that blends with the surrounding connective tissue *These areas include the esophagus and the retroperitoneal organs

Answer 28

Serosa or Adventitia

Question 29

*Most of the nervous regulation of the digestive tract is under local control by the enteric nervous system *The __________ (ENS) is an extensive network of neural tissue and consists of 1.the submucosal plexus and 2.the myenteric plexus *This network of neurons and associated glial cells is a division of the autonomic nervous system *The ENS contains more neurons than the spinal cord *In addition to local reflexes within the ENS, there is also control mediated by autonomic innervation from the CAN *This innervation is largely by the parasympathetic division of the ANS through the vagus nerves and to a lesser extent by sympathetic nerves

Answer 29

Enteric Nervous System

Question 30

*The ENS functions through local reflexes to control activities within specific, short regions of the digestive tract *The ENS is capable of controlling the complex peristaltic and mixing movements, as well as blood flow to the digestive tract, without any outside influences *Although the ENS can control the activities of the digestive tract independently of the CNS, the two systems normally work together *Autonomic innervation from the CNS can increase or decrease ENS activity *Control of the digestive system by the CNS occurs when reflexes are activated by stimuli originating either in the digestive tract or the CNS *From within the digestive system, action potentials are carried by sensory neurons in the vagus and sympathetic nerves to the CNS, where the reflexes are integrated

Answer 30

Enteric Nervous System

Question 31

*Reflexes within the CNS can be activated by the sight, smell, or taste of food; for example, the smell of your neighbor’s cookout increases the secretion of both saliva and pancreatic fluids *All of these reflexes influence activity in parasympathetic neurons of the CNS *Parasympathetic neurons extend to the digestive tract through the vagus nerves to control responses or alter the activity of the ENS and local reflexes *Some sympathetic neurons inhibit muscle contraction and secretion in the digestive system and decrease blood flow to the digestive system *Local reflexes control short regions of digestive tract *ANS modulates ENS activity

Answer 31

Enteric Nervous System

Question 32

Submucosal plexus Myenteric plexus

Answer 32

Enteric Nervous System Consists of

Question 33

Within the walls of the digestive tract

Answer 33

Submucosal Plexus

Question 34

Within the walls of the digestive tract

Answer 34

Myenteric plexus

Question 35

Enteric sensory neuron Enteric motor neuron Enteric interneuron

Answer 35

Types of Enteric Neurons

Question 36

Detect changes in the chemical composition of the digestive tract contents or detect mechanical changes, such as stretch of the digestive tract wall

Answer 36

Enteric Sensory Neuron

Question 37

Stimulate or inhibit smooth muscle contraction and glandular secretion in the digestive system

Answer 37

Enteric Motor Neuron

Question 38

Connect enteric sensory and motor neurons

Answer 38

Enteric Interneuron

Question 39

*Over 30 _______ are associated with the ENS *Two major ENS ________ are acetylcholine and norepinephrine *In general, acetylcholine stimulates and norepinephrine inhibits digestive tract motility and secretions *Another major ENS _________ is serotonin, which stimulates digestive tract motility *In addition to neural release, serotonin is also produced by endocrine cells within the digestive tract wall *Over 95% of the serotonin in the body is found in the digestive tract, so drugs that increase serotonin levels and function, such as antidepressants, and chemotherapeutics used for cancer treatment, can also affect digestive tract activity *An unintended consequence of many cancer therapies is nausea, due to increased serotonin release from endocrine cells in the digestive tract *Serotonin binds to a subset of serotonin receptors on sensory terminals of the vagus nerves, which stimulates the vomiting center in the brain *This results in the nausea and vomiting associated with chemotherapy and radiotherapy *Serotonin receptor blockers, such as ondansetron are commonly used to alleviate nausea

Answer 39

Neurotransmitters of the ENS

Question 40

*A number of _______, such as gastrin and secretin, are secreted by endocrine cells in the digestive system and are carried through the blood to target organs of the digestive system or to target tissues in other systems *These ________ help regulate many digestive tract functions, as well as the secretions of associated glands, such as the liver and pancreas *In addition to the _______ produced by the digestive system that enter the blood, other paracrine chemicals, such as histamine, are released locally within the digestive tract, where they influence the activity of nearby cells *These localized chemical regulators help local reflexes within the ENS control local digestive tract environments, such as pH levels

Answer 40

Hormones of the ENS

Question 41

*The walls and organs of the abdominal cavity are lined with a continuous serous membrane sheet called the peritoneum *Serous membranes are very smooth and secrete serous fluid, which provides lubricating film between the layers of the membranes *The membrane and fluid reduce friction as organs move within the abdominal cavity

Answer 41

Serous Membrane Associated with the Peritoneal Cavity

Question 42

Visceral Parietal

Answer 42

Two Portions of the Peritoneum

Question 43

*(covers the organ) oThe portion of the peritoneum that covers the organs is the ______ oMerges with parietal peritoneum

Answer 43

Visceral Peritoneum

Question 44

*(lines the cavity) oCovers the interior surface of the wall of the abdominal cavity

Answer 44

Parietal Periotenum

Question 45

*Is a potentially life-threatening inflammation of the peritoneum *The inflammation can result from chemical irritation by substances, such as bile, that have escaped from a damaged digestive tract or from infection originating in the digestive tract, as when the appendix ruptures *The main symptoms of ______ are acute abdominal pain and tenderness that are worsened by movement *An accumulation of excess serous fluid in the peritoneal cavity, called ascites, can occur in _______ *Ascites can also accompany starvation, alcoholism, or liver cancer

Answer 45

Peritonitis

Question 46

*All digestive organs within the abdominal cavity are held in place by a structure called the ________ *The _______ is a continuous, double layer of epithelial tissue (mesothelium) attached along its full length to the posterior abdominal wall *The _______ extends from the junction between the esophagus and stomach to the rectum *The point where the _______ attaches to the posterior abdominal wall is called the mesenteric root *The mesenteric root corresponds to the location where the superior mesenteric artery branches from the aorta *The _______ is subdivided into multiple regions, which are named for the portion of the digestive tract with which they are associated *Continuous, double layer epithelial tissue *Hold abdominal structures in place *Attached to posterior abdominal wall

Answer 46

Mesentery

Question 47

Mesentery of small intestine Right mesocolon Transverse mesocolon Left mesocolon Mesosigmoid Mesorectum

Answer 47

Regions of Adult Mesentery

Question 48

This region is mobile and attaches portions of the jejunum and ileum to the posterior abdominal wall

Answer 48

Mesentery of Small Intestine

Question 49

This region is a continuation of the small intestine mesentery and is anchored to the posterior abdominal wall At the hepatic (right colic) flexure, it continues as the transverse mesocolon

Answer 49

Right Mesocolon

Question 50

This is mobile and runs along the transverse colon until it continues at the splenic flexure

Answer 50

Transverse Mesocolon

Question 51

This region is also anchored to the posterior abdominal wall and extends from the splenic (left colic) flexure to the mesosigmoid

Answer 51

Left Mesocolon

Question 52

The _____ is both anchored and mobile The mobile region is attached to the sigmoid colon

Answer 52

Mesosigmoid

Question 53

The ______ is formed by the convergence of the mobile and anchored portions of the mesosigmoid The _______ anchors the rectum as it descends through the pelvic floor

Answer 53

Mesorectum

Question 54

Mesenteric domain Nonmesenteric domain

Answer 54

Regions of Abdominal Cavity Relative to Mesentery

Question 55

The _______ correlates to the visceral peritoneum This is the location where all of the abdominal digestive organs are embedded and interconnected

Answer 55

Mesenteric Domain

Question 56

The _________ correlates to the parietal peritoneum and includes structures that are posterior to the mesentery such as the inferior vena cava, kidneys, and ureters Nonmesenteric structures have traditionally been referred to as retroperitoneal (behind the peritoneum)

Answer 56

Nonmesenteric Domain (Retroperitoneal)

Question 57

Lesser omentum Greater omentum Coronary ligament Falciform ligamnet

Answer 57

Other Specific Regions of Mesentery

Question 58

The portion of the mesentery connecting the lesser curvature of the stomach and the proximal end of the duodenum to the liver and diaphragm is called the ______

Answer 58

Lesser Omentum

Question 59

The region of the mesentery extending as a fold from the greater curvature of the stomach and then to the transverse colon is called the _______ Forms a long, double fold of mesentery that extends inferiorly from the stomach over the surface of the small intestine Because of this folding, a cavity called the omental bursa forms between the two layers of mesentery Can house a large amount of adipose tissue as well as many B and T lymphocytes Has considerable mobility in the abdomen

Answer 59

Greater Omentum

Question 60

Attaches the liver to the diaphragm Unlike other regions of the mesentery, the ______ has a wide space in the center, the bare area of the liver, where no peritoneum exists

Answer 60

Coronary Ligament

Question 61

Attaches the liver to the anterior abdominal wall

Answer 61

Falciform Ligament

Question 62

1.the vestibule is the space between the lips or cheeks and the teeth 2.the oral cavity proper lies medial to the teeth

Answer 62

The oral cavity, or mouth, is divided into two regions

Question 63

*Is lined with nonkeratinized stratified squamous epithelium, which protects against abrasion

Answer 63

Oral Cavity

Question 64

*Are important in mastication and speech *They help manipulate food and hold it in place within the oral cavity *They also help form words when we speak *A large number of the muscles of facial expression are involved in moving the _______ *The _____, or labia, form the anterior boundary of the vestibule *They are muscular structures formed mostly by the orbicularis oris muscle and connective tissue *The skin on the outer surfaces of the upper and lower lips is not highly keratinized and is more transparent than the epithelium over the rest of the body *The underlying blood vessels give the _____ a reddish tint *At the internal margin of the ______, the epithelium is continuous with the nonkeratinized stratified squamous epithelium of the mucosa in the oral cavity *Each _____ has a central mucosal fold called the labial frenulum by which it is attached to the gingiva in its portion of the vestibule * Form the lateral walls of the oral cavity *They are lined with nonkeratinized stratified squamous epithelium and covered by the skin *Within each ______ are the buccinator muscle, which flattens the _______ against the teeth, and the buccal fat pad, which acts as a gliding pad for the muscles of mastication *The buccal fat pads change considerably throughout a person’s lifetime, especially during weight gain or loss

Answer 64

Lips and Cheeks

Question 65

*The roof of the oral cavity is called the _____ *The _____ separates the oral and nasal cavities and prevents food from passing into the nasal cavity during chewing and swallowing *The _____ consists of two parts: 1.the hard ______, the anterior, bony part; and 2.the soft _____, the posterior nonbony part consisting of skeletal muscle and connective tissue *The uvula is a posterior projection from the soft _______ *The posterior boundary of the oral cavity is the fauces, which is the opening into the pharynx, or throat *The palatine tonsils are in the lateral wall of the fauces

Answer 65

Palate

Question 66

*Is a large, muscular organ that occupies most of the oral cavity proper when the mouth is closed *A groove called the terminal sulcus divides the _____ into two parts: 1.the body and 2.the root *The anterior body is found within the oral cavity and is relatively free, except for attachment to the floor of the mouth by a thin fold of tissue called the lingual frenulum *The body is covered by nonkeratinized stratified squamous epithelium and papillae, some of which contain taste buds *The root of the ______ is found within the oropharynx and contains a few scattered taste buds and the lingual tonsil

Answer 66

Tongue

Question 67

Intrinsic muscles Extrinsic muscles

Answer 67

Muscles of the Tongue

Question 68

oAre within the tongue itself and are largely responsible for changing the shape of the tongue, such as flattening and elevating it during drinking and swallowing

Answer 68

Intrinsic Muscles

Question 69

oAre outside the tongue but are attached to it oThese muscles protrude and retract the tongue, move it from side to side, and change its shape

Answer 69

Extrinsic Muscles

Question 70

*The tongue moves food into the mouth, and in cooperation with the lips and gums, holds the food in place during mastication *It also plays a major role in swallowing *In addition, the tongue is the location of the taste buds and one of the primary organs of speech *Moves food around in mouth *Holds food in place during mastication *Location of many taste buds *Organ of speech

Answer 70

Functions of the Tongue

Question 71

*Collectively called the dentition, function to masticate (chew) food in the oral cavity and assist in speech *Adults normally have 32 _____, which are distributed into dental arches: the maxillary arch and the mandibular arch *The _____ in the right and left halves of each dental arch are roughly mirror images of each other *As a result, the _____ are apportioned into four quadrants: 1.right upper, 2.left upper, 3.right lower, and 4.left lower *The _______ in each quadrant include one central and one lateral incisor; one canine; first and second premolars; and first, second, and third molars

Answer 71

Teeth

Question 72

*Each tooth consists of 1.a crown, 2.a neck, and 3.a root *Crown *Root *Dentin *Pulp Cavity *Root Canal *Periodontal ligament *Enamel

Answer 72

Structure of the Tooth

Question 73

o Is the part of the tooth exposed in the oral cavity and covered by enamel oCan have one or more cusps (points)

Answer 73

Crown

Question 74

o Is the largest region of the tooth oIt anchors the tooth in the bone oThe nerves and blood vessels of the tooth enter and exit the pulp through a hole at the point of each _____ called the apical foramen oIt is common to see ____ of molars that are noticeably curved rather than straight

Answer 74

Root

Question 75

oThe pulp cavity is surrounded by living, cellular, calcified tissue called _____ oThe surface of the _____ in the root is covered with a bonelike substance called cementum, which helps anchor the tooth to the periodontal ligament in the jaw

Answer 75

Dentin

Question 76

oWithin the center of the tooth, in the neck and root, is a ______, which is filled with pulp, a collection of blood vessels, nerves, and connective tissue

Answer 76

Pulp Cavity

Question 77

oThe portion of the pulp cavity within the root is called the _____ oIt is common to have branches of a _____ rather than one single _____

Answer 77

Root Canal

Question 78

oSecure the teeth in the alveoli

Answer 78

Periodontal Ligament

Question 79

oThe dentin of the tooth crown is covered by an extremely hard, nonliving, acellular substance called _______, which protects the tooth against abrasion and acids produced by bacteria in the mouth

Answer 79

Enamel

Question 80

*The teeth in each quadrant include one central and one lateral incisor; one canine; first and second premolars; and first, second, and third molars *Incisors *Cuspids *Bicuspids *Molars

Answer 80

Types of Teeth

Question 81

oOne of the anterior, cutting teeth

Answer 81

Incisors

Question 82

oCanine teeth

Answer 82

Cuspids

Question 83

oPremolars

Answer 83

Bicuspids

Question 84

oThe posterior three teeth of each dental arch oTricuspid tooth oThe third _____ are often called wisdom teeth because they usually appear in the late teens or early twenties, when a person is old enough to have acquired some wisdom oIn people with small dental arches, the third ____ may not have room to erupt into the oral cavity and remain embedded within the jaw oEmbedded wisdom teeth are referred to as impacted and may cause pain or irritation oUsually, the impacted wisdom teeth are surgically removed

Answer 84

Molars

Question 85

*Baby teeth or deciduous teeth *The deciduous teeth erupt (the crowns appear within the oral cavity) between about 6 months and 24 months of age *Lost during childhood

Answer 85

Primary Dentition

Question 86

*Permanent teeth *The teeth of the adult mouth are called permanent teeth, or secondary teeth *Most of them are replacements for deciduous teeth, which are lost during childhood *The permanent teeth begin replacing the deciduous teeth at about 5 years, and the process is completed by about 11 years

Answer 86

Secondary Dentition

Question 87

*Food taken into the mouth is masticated, or chewed, by the teeth *The anterior teeth (the incisors and the canines) primarily cut and tear food, whereas the premolars and molars primarily crush and grind it *Breaks large food particles into smaller ones, creating a much larger total surface area of the food *Because digestive enzymes digest food molecules only at the surface of the particles, _______ increases the efficiency of digestion

Answer 87

Mastication

Question 88

*Temporalis *Masseter *Medial pterygoid *Lateral pterygoid

Answer 88

Muscles of Mastication

Question 89

oAct to close the jaw oRetracts the jaw

Answer 89

Temporalis

Question 90

oAct to close the jaw oAccomplish protraction and lateral and medial excursion of the jaw

Answer 90

Masseter

Question 91

oAct to close the jaw oAccomplish protraction and lateral and medial excursion of the jaw

Answer 91

Medial Pterygoid

Question 92

oActs to open the jaw oAccomplish protraction and lateral and medial excursion of the jaw

Answer 92

Lateral Pterygoid

Question 93

*A considerable number of ______ are scattered throughout the oral cavity *Numerous small, coiled, tubular ________ are located 1.deep to the epithelium of the tongue (lingual glands), 2.in the palate (palatine glands), 3.in the cheeks (buccal glands), and 4.in the lips (labial glands) *All of the major large ______ are compound acinar glands, which are branching glands with clusters of acini resembling grapes *They produce thin serous secretions or thicker mucous secretions *Saliva is a combination of serous and mucous secretions from the various salivary glands

Answer 93

Salivary Glands

Question 94

*Or chewing reflex, is integrated in the medulla oblongata and controls the basic movements of chewing *The presence of food in the mouth stimulates sensory receptors, which activate a reflex that relaxes the muscles of mastication *As the mandible is lowered, the muscles stretch and activate a reflex that causes the muscles of mastication to contract *Once the mouth is closed, the food again stimulated the muscles of mastication to relax, and the cycle repeats *Descending pathways from the cerebrum strongly influence the ________ so that chewing can be consciously initiated or stopped *The rate and intensity of chewing movements can also be influenced by the cerebrum

Answer 94

Mastication Reflex

Question 95

Parotid salivary glands Sublingual salivary glands Submandibular salivary glands

Answer 95

Three Pairs of Salivary Glands

Question 96

*The largest salivary glands, the _______, are serous glands, which produce mostly watery saliva; they are located just anterior to the ear on each side of the head *Each parotid duct exits the gland on its anterior margin, crosses the lateral surface of the masseter muscle, pierces the buccinator muscle, and enters the oral cavity adjacent to the second upper molar

Answer 96

Parotid Salivary Glands

Question 97

*The _______, the smallest of the three large, paired salivary glands, are mixed glands containing some serous acini but consisting primarily of mucous acini *They lie immediately below the mucous membrane in the floor of the oral cavity *These glands do not have single, well-defined ducts like those of the submandibular and parotid glands *Instead, each ________ opens into the floor of the oral cavity through 10-12 small ducts

Answer 97

Sublingual Salivary Glands

Question 98

*The ________ are mixed with glands with more serous than mucous acini *Each gland can be felt as a soft lump along the inferior border of the posterior half of the mandible *A submandibular duct exits each gland, passes anteriorly deep to the mucous membrane on the floor of the oral cavity, and opens into the oral cavity beside the frenulum of the tongue

Answer 98

Submandibular Salivary Glands

Question 99

*Is composed of fluid and proteins and had three main roles: 1.it helps keep the oral cavity moist, which is needed for normal speech and for tasting food; 2.it has protective functions; and 3.it begins the process of digestion *Approximately 1-1.5 L/day of _____ are secreted *The serous portion of ____, secreted primarily by the parotid and submandibular glands, provided the moistening function of ______ *Salivary gland secretion is stimulated by both the parasympathetic and sympathetic nervous systems, but the parasympathetic system is more prevalent *Salivary nuclei in the brainstem increase salivary secretions by sending action potentials through parasympathetic fibers of the facial (VII) and glossopharyngeal (IX) cranial nerves in response to a variety of stimuli, such as tactile stimulation in the oral cavity or certain tastes, especially sour *Higher centers of the brain also affect salivary gland activity *Odors that trigger thoughts of food or the sensation of hunger can increase saliva secretion as well

Answer 99

Saliva

Question 100

oThe mucous secretions of the submandibular and sublingual glands contain a large amount of ________, a proteoglycan that gives a lubricating quality to saliva

Answer 100

Mucin

Question 101

oSaliva contains the proteins ______ and immunoglobulin A oIs an enzyme that has a weak antibacterial action, and immunoglobulin A helps prevent bacterial infection

Answer 101

Lysozyme

Question 102

oThe serous part of saliva contains a digestive enzyme called _________ , which breaks the covalent bonds between glucose molecules in starch and other polysaccharides to produce the disaccharides maltose and isomaltose

Answer 102

Salivary Amylase

Question 103

oIn addition to carbohydrate digestion, there is a small amount of lipid digestion initiated by _______ in saliva

Answer 103

Lingual Lipase

Question 104

oThe large volume of saliva helps prevent bacterial infection in the mouth by continually washing the oral surface oBicarbonate ions (HCO3-) in saliva act as a buffer to neutralize the acids produced by oral bacteria oThis reduces the harmful effects of bacterial acids on tooth enamel oThe mucous in saliva helps protect the digestive tract from physical irritation and enzymatic digestion oAny reduction in salivary gland secretion increases the risk for ulceration and infection of the oral mucosa and for caries (cavities) in the teeth

Answer 104

There are Several Protective Functions of Saliva

Question 105

*The _______ consists of three parts: 1.nasopharynx, 2.oropharynx, and 3.laryngopharynx *Normally, only the oropharynx and laryngopharynx transmit food *The oropharynx communicated with the nasopharynx superiorly, with the larynx and the laryngopharynx inferiorly, and with the mouth anteriorly *The laryngopharynx extends from the oropharynx to the esophagus and is posterior to the larynx *The epiglottis covers the opening of the larynx and keeps food and drink from entering the larynx *The posterior walls of the oropharynx and laryngopharynx consist of three muscles: the superior, middle, and inferior pharyngeal constrictors, which are arranged like three stacked flowerpots, one inside the other *The oropharynx and the laryngopharynx are lined with nonkeratinized stratified squamous epithelium, and the nasopharynx is lined with ciliated pseudostratified columnar epithelium *Common passageway for the digestive and respiratory system

Answer 105

Pharynx

Question 106

*The _______ is the part of the digestive tract that extends between the pharynx and the stomach *It is about 25cm long and lies in the mediastinum, anterior to the vertebrae and posterior to the trachea *It passes through the _______ hiatus (opening) of the diaphragm and ends at the stomach *Transports food from the pharynx to the stomach *Has thick walls consisting of the four tunics common to the digestive tract: 1.mucosa, 2.submucosa, 3.muscularis, and 4.adventitia *The muscularis has an outer longitudinal layer and an inner circular layer, as is true of most parts of the digestive tract *Differs from other regions by having skeletal muscle fibers in the superior one-third, and smooth muscle fibers in the inferior one-third *An upper _______ sphincter and a lower _______ sphincter, at the upper and lower ends of the ______, respectively, regulate the movement of materials into and out of the ________ *The mucosal lining of the _______ is nonkeratinized stratified squamous epithelium *Numerous mucous glands in the submucosal layer produce a thick, lubricating mucus, which passes through ducts to the surface of the _______ mucosa *Muscular tube that connects the pharynx to the stomach

Answer 106

Esophagus

Question 107

*Swallowing, or deglutition, is divided into three phases: 1.voluntary, 2.pharyngeal, and 3.esophageal *Over 20 separate muscles are involved in swallowing

Answer 107

Swallowing Phases

Question 108

*Bolus of food is pushed into the oropharynx; voluntary processes *During the _______, a bolus of food is formed in the mouth and pushed by the tongue against the hard palate, until it is forced toward the posterior part of the mouth and into the oropharynx

Answer 108

Voluntary Phase

Question 109

*Presences of the bolus of food in the oropharynx initiates the swallowing reflex; pharyngeal muscles push the bolus of food towards the esophagus *The ______ of swallowing is a reflex initiated by the stimulation of tactile receptors in the area of the oropharynx *Sensory action potentials travel through the trigeminal (V) and glossopharyngeal (IX) nerves to the swallowing center in the medulla oblongata *There, they initiate action potentials in motor neurons, which pass through the trigeminal (V), glossopharyngeal (IX), vagus (X), and accessory (XI) nerves to the soft palate and pharynx *This phase of swallowing begins with the elevation of the soft palate, which closes the passage between the nasopharynx and oropharynx *The pharynx elevates to receive the bolus of food from the mouth and moves the bolus down the pharynx into the esophagus *The superior, middle, and inferior pharyngeal constrictor muscles contract in succession, forcing the food through the pharynx *At the same time, the upper esophageal sphincter relaxes, the elevated pharynx opens the esophagus, and food is pushed into the esophagus *This phase of swallowing is controlled involuntarily, even though the muscles involved are skeletal *The ________ of swallowing lasts about 1-2 seconds *During the _________, the vestibular folds and vocal cords close, and the epiglottis is tipped posteriorly, so that the epiglottic cartilage covers the opening into the larynx, and the larynx is elevated *These movements prevent food from passing into the larynx

Answer 109

Pharyngeal Phase

Question 110

*Peristaltic waves in the esophagus push the bolus towards the stomach *The _______ of swallowing, which takes about 5-8 seconds, is responsible for moving food from the pharynx to the stomach *Muscular contractions in the wall of the esophagus occur in peristaltic waves *Gravity helps move liquids and watery food through the esophagus *However, the peristaltic contractions in the esophagus are forceful enough to allow a person to swallow even while doing a headstand or floating in the zero-gravity environment of space *As the peristaltic waves and the food bolus approach the stomach, the lower esophageal sphincter in the esophagus relaxes *This sphincter is not anatomically distinct from the rest of the esophagus, but it can be identified physiologically because it remains tonically constricted to prevent the reflux of stomach contents into the lower part of the esophagus *The presence of food in the esophagus stimulates the myenteric plexus, which controls the peristaltic waves *Food in the esophagus also stimulates tactile receptors, which send sensory impulses to the medulla oblongata through the vagus nerves *Motor impulses, in turn, pass along the vagal efferent fibers to the skeletal and smooth muscles within the esophagus, thereby stimulating their contractions and reinforcing the peristaltic contractions

Answer 110

Esophageal Phase

Question 111

*Bulk storage of ingested food *Mechanical breakdown *Chemical breakdown *Produces glycoproteins necessary for vit B12 absorption

Answer 111

Functions of the Stomach

Question 112

1.Cardia 2.Fundus 3.Body 4.Pylorus

Answer 112

Four Regions of the Stomach

Question 113

*The esophagus opens into the _____ of the stomach at the gastroesophageal opening *The lower esophageal sphincter, also called the _____ sphincter, surrounds the opening. *Although this is an important structure in the normal function of the stomach, it is a physiological constrictor only and cannot be seen anatomically

Answer 113

Cardia

Question 114

*The part of the stomach to the left of the cardia, the ______ is actually superior to the cardiac opening

Answer 114

Fundus

Question 115

*The largest part of the stomach is the ______, which turns to the right, creating a greater curvature and a lesser curvature

Answer 115

Body

Question 116

*The body narrows to form the funnel-shaped ______ of the stomach *The wider part of the funnel, toward the body of the stomach, is the ______ antrum *The narrow part of the funnel is the _____ canal *The ______ canal opens through the _______ orifice into the small intestine *The _______ orifice is surrounded by the _______ sphincter, a relatively thick ring of smooth muscle that helps regulate the movement of gastric contents into the small intestine *Hypertrophic ______ stenosis is a common defect of the stomach in infants, in which the ______ sphincter is greatly thickened and thus interferes with normal stomach emptying

Answer 116

Pylorus

Question 117

*Extra layers of muscle in muscularis externa and muscularis mucosa; strengthens walls and helps in mixing chyme *The mucous lining of the stomach is simple columnar epithelium. *The epithelium forms numerous, tublike invaginations called gastric pits *Gastric pits are the openings for the gastric glands that secrete acid and other substances *There are five types of epithelial cells of the stomach: surface mucous cells, mucous neck cells, parietal cells, chief cells, and endocrine cells *All but the surface mucous cells are found in the gastric cells

Answer 117

Histology of Stomach

Question 118

*Or visceral peritoneum, is the outermost tunic of the stomach *It consists of an outer layer of simple squamous epithelium and an inner layer of connective tissue

Answer 118

Serosa

Question 119

*The ______ of the stomach consists of three layers: 1.an outer longitudinal layer, 2.a middle circular layer, and 3.an inner oblique layer *The inner oblique layer is unique to the stomach wall *This layer helps generate the strong stomach contractions that physically break down ingested food into smaller particles *In some areas of the stomach, such as the fundus, the three layers blend with one another and cannot be separated

Answer 119

Muscularis

Question 120

oDeep to the muscularis are the submucosa and the mucosa, which are arranged in large folds called _____ when the stomach is empty oThese folds allow the mucosa and submucosa to stretch, and the folds disappear as the stomach volume increases as it is filled

Answer 120

Rugae

Question 121

*Surface mucous cells *Mucous neck cells *Parietal cells *Chief cells *Endocrine cells

Answer 121

Gastric Gland Cells

Question 122

oAre found on the surface around the gastric pit oThese cells protect the stomach wall from being damaged by acid and digestive enzymes oThe cells produce an alkaline mucus on their surface that neutralizes the acid and is a barrier to the digestive enzymes oThe surface of mucous cells are connected by tight junctions, which provide an additional barrier that prevents acids and enzymes from reaching deeper tissues oIn addition, when surface mucous cells are damaged, they are rapidly replaced

Answer 122

Surface Mucous Cells

Question 123

oAre located near the openings of the glands and produce mucus

Answer 123

Mucous Neck Cells

Question 124

oProduce hydrochloric acid and intrinsic factor

Answer 124

Parietal Cells

Question 125

oProduce the enzyme pepsinogen oThey also produce the enzyme gastric lipase, which can digest lipids in the stomach

Answer 125

Chief Cells

Question 126

oProduce regulatory hormones and paracrine factors oThere are several types of endocrine cells oEnterochromaffin-like cells produce histamine, which stimulates acid secretion by parietal cells oGastrin-containing cells secrete gastrin, and somatostatin-containing cells secrete somatostatin, which inhibits gastrin and insulin secretion

Answer 126

Endocrine Cells

Question 127

*Once food enters the stomach, it is mixed with stomach secretions to form a semifluid material called _____ *The primary function of the stomach is to store and mix the ______

Answer 127

Chyme

Question 128

*Hydrochloric acid (HCl) *Intrinsic factor *Pepsinogen *Gastric lipase

Answer 128

Secretions of the Stomach Include

Question 129

oParietal cells in the gastric glands of the pylorus secrete a concentrated solution of hydrochloric acid oProduces the low pH of the stomach’s contents, which is normally between 1 and 3 oThe key player in the formation of gastric acid is a H+ -K+ exchange pump that is commonly called the proton pump oThe proton pump actively transports H+ across the mucosal surface of the parietal cell into the lumen of the stomach

Answer 129

Hydrochloric Acid (HCl)

Question 130

oA major function of _____ is to kill bacteria that are ingested with essentially everything humans put into their mouths oHowever, some pathogenic bacteria have an outer coat that resists stomach acids, and one type of bacteria is normally present in many human stomachs oThe low pH of the stomach’s contents has additional functions oStomach acid denatures many proteins, so that proteolytic enzymes can reach internal peptide bonds oThe acid environment provides the proper pH for the activation and function of pepsin oThe acid also stops carbohydrate digestion by inactivating salivary amylase

Answer 130

Hydrochloric Acid (HCl)

Question 131

The process begins with H+ derived from CO2 and water, which enter the parietal cell from its serosal surface (the side opposite the lumen of the gastric pit) Inside the cell, the enzyme carbonic anhydrase catalyzes the reaction between CO2 and water to from carbonic acid Some of the carbonic acid molecules then dissociate to form H+ and HCO3- While H+ is pumped into the stomach lumen, HCO3- moves down it concentration gradient from the parietal cell into the extracellular fluid *During this process, HCO3- is exchanged for Cl- through an antiporter, which is located in the plasma membrane, and the Cl- subsequently moves into the cell *This results in an elevated blood pH in the veins that carry blood away from the stomach, called the alkaline tide *An alkaline tide normally occurs after eating a meal Drugs that block the proton pump are used to lower gastric acid levels *The pump moves H+ by active transport against a steep concentration gradient, and Cl- diffuses from the cell through ion channels in the plasma membrane Diffusion of Cl- into the gastric gland duct balances the positively charged H+ to reduce the amount of energy needed to transport the H+ against both a concentration gradient and an electrical gradient

Answer 131

Steps for Hydrochloric Acid Transport

Question 132

oIn addition to hydrochloric acid, parietal cells secrete ________ oIs a glycoprotein that binds with vitamin B12, making the vitamin more readily absorbed in the ileum of the small intestine oVitamin B12 is important in deoxyribonucleic acid (DNA) synthesis, which is especially important for continual red blood cell production oA lack of vitamin B12 absorption leads to pernicious anemia oDeficiency of vitamin B12 also leads to neurological symptoms, including peripheral neuropathy because vitamin B12 is required for maintaining myelin in the peripheral nervous system

Answer 132

Intrinsic Factor

Question 133

oChief cells within the gastric glands secrete ______ oIs packaged in zymogen granules, which are released by exocytosis when pepsinogen secretion is stimulated oZymogen is the term for an inactive enzyme oOnce ______ enters the lumen of the stomach, hydrochloric acid and previously formed pepsin molecules convert it to pepsin oPepsin exhibits optimal enzymatic activity at a pH of 3 or less oPepsin catalyzes the cleavage of some covalent bonds in proteins, thus breaking them into smaller peptide chains

Answer 133

Pepsinogen

Question 134

oChief cells also secrete the enzyme ______, which can digest lipids even in an acidic environment

Answer 134

Gastric Lipase

Question 135

*Approximately 2-3 L of gastric secretions (gastric juice) are produced each day *The amount and type of food entering the stomach and small intestine dramatically affect the quantity of gastric secretions, but up to 700mL are secreted as a result of a typical meal *Both nervous and hormonal mechanisms regulate gastric secretions *The neural mechanisms involve reflexes integrated within the medulla oblongata and local reflexes integrated within the ENS *In addition, higher brain centers influence the reflexes *The chemical messengers that regulate stomach secretions include the hormones gastrin, secretin, and cholecystokinin, as well as the paracrine chemical messenger histamine

Answer 135

Regulation of Stomach Secretion

Question 136

Site of Production: Gastrin Method of Stimulation: Distension; partially digested proteins, autonomic stimulation, ingestion of alcohol or caffeine Secretory Effects: Increases gastric secretion Motility Effects: Causes a minor increase in gastric motility

Answer 136

Stomach

Question 137

Site of Production: Secretin Method of Stimulation: Acidity of chyme Secretory Effects: Decreases gastric secretion; stimulates pancreatic and bile secretions high in HCO3- Motility Effects: Decreases gastric motility

Answer 137

Duodenum

Question 138

Cephalic ("get started") phase Gastric ("go for it") phase Intestinal ('slow down") phase

Answer 138

Three Phases of Stomach Secretion

Question 139

*Can be viewed as the “get started” phase, when stomach secretions are increased in anticipation of incoming food *Is the brain phase of stomach secretion *It is controlled by the CNS *It begins even before the bolus of food enters the stomach *Several types of stimuli act on the centers within the medulla oblongata to influence gastric secretions *These stimuli include the taste and smell of food, the stimulation of tactile receptors during the process of chewing and swallowing, and pleasant thoughts of food *Action potentials are sent from the medulla oblongata along parasympathetic neurons within the vagus (X) nerves to the stomach *Within the stomach wall, the preganglionic neurons stimulate the postganglionic neurons in the ENS *The postganglionic neurons, which are primarily cholinergic, stimulate secretory activity in the cells of the stomach mucosa *Parasympathetic stimulation of the stomach mucosa results in the release of the neurotransmitter acetylcholine, which increases the secretory activity of both the parietal and the chief cells and stimulates the secretion of gastrin and histamine from endocrine cells

Answer 139

Cephalic ("Get Started") Phase

Question 140

*The ______ released into the circulation travels to the parietal cells, where it stimulates additional hydrochloric acid and pepsinogen secretion *In addition, ______ stimulates enterochromaffin-like cells to release histamine, which stimulates parietal cells to secrete hydrochloric acid

Answer 140

Gastrin

Question 141

*Acts as both a local paracrine chemical messenger and a hormone in the blood to stimulate gastric gland secretory activity *Acetylcholine, ______, and gastrin working together cause a greater secretion of hydrochloric acid than any of them does separately *Of the three, ______ has the greatest stimulatory effect *Drugs that block the actions of ______ are used to lower acid levels

Answer 141

Histamine

Question 142

*This is followed by the “go for it” ______, when most of the stimulation of secretion occurs *The ______ of stomach secretion produces the greatest volume of gastric secretions *The presence of food in the stomach initiates the ______ *The primary stimuli are distension of the stomach and the presence of amino acids and peptides in the stomach *Distension of the stomach wall, especially in the body or fundus, stimulates mechanoreceptors *Action potentials generated by these receptors initiate reflexes that involve both the CNS and the ENS *These reflexes result in acetylcholine release and the cascade of events that increase secretion, as in the cephalic phase *The presence of partially digested proteins or moderate amounts of alcohol or caffeine in the stomach also stimulates gastrin secretion *When the pH of the stomach contents falls below 2, increased gastric secretion produced by distension of the stomach is blocked *This negative-feedback mechanism limits the secretion of gastric juice

Answer 142

Gastric ("Go For It") Phase

Question 143

*Is the “slow down” phase, during which stomach secretion decreases *The _____ of gastric secretion inhibits gastric secretions *It is initiated by acidic chyme entering the duodenum of the small intestine, which activates both neural and hormonal mechanisms *Secretions are inhibited when the pH of the chyme entering the duodenum drops to 2 or below *In addition, when chyme contains lipid digestion products, gastric secretions are inhibited *There are two hormones involved in the_____ : 1.secretin and 2.cholescystokinin

Answer 143

Intestinal ("Slow Down") Phase

Question 144

*Is released in response to acidic solutions in the duodenum *Inhibits gastric secretions by inhibiting both parietal and chief cells

Answer 144

Secretin

Question 145

*Is released in response to fatty acids, other lipids, and to a lesser degree protein digestion products in the duodenum and the proximal jejunum *Inhibits gastric secretions *The inhibition of gastric secretion is also under nervous control *The enterogastric reflex consists of a local reflex and a reflex integrated within the medulla oblongata that reduce gastric secretion *Distension of the duodenal wall, the presence of irritating substances in the duodenum, reduced pH, and hypertonic or hypotonic solutions in the duodenum activate the enterogastric reflex

Answer 145

Cholecystokinin

Question 146

Mixing waves Peristaltic waves

Answer 146

Movements of the Stomach

Question 147

oAre contractions that occur about every 20 seconds proceeding from the body of the stomach toward the pyloric sphincter oRoughly 80% of the contractions are ______ oRelatively weak contractions result in _____, which thoroughly mix ingested food with stomach secretions to form chyme oIn the _______, the more fluid part of the chyme is pushed toward the pyloric sphincter, whereas the more solid center moves back toward the body of the stomach

Answer 147

Mixing Waves

Question 148

oOccur less frequently, are significantly more powerful than mixing waves, and force the chyme near the periphery of the stomach toward the pyloric sphincter oThe more solid material near the center of the stomach is pushed superiorly toward the cardia for further digestion oRoughly 20% of the contractions are ______ oStronger contractions result in _____, which force the chyme toward and through the pyloric sphincter oAgain, the more fluid part of the chyme is pushed toward the pyloric region, whereas the more solid center of the chyme squeezes past the peristaltic constriction back toward the body of the stomach oEach peristaltic contraction is sufficiently strong to cause partial relaxation of the pyloric sphincter and to pump a few millimeters of chyme through the pyloric opening and into the duodenum, Increased motility leads to increased emptying

Answer 148

Peristaltic Waves

Question 149

Usually remains closed because of mild tonic contraction

Answer 149

Pyloric Sphincter

Question 150

*The entire small intestine averages 6m in length, although there are reports of as much as 9m in length *Two major accessory glands, the liver and the pancreas, release their secretions into the duodenum *The small intestine is where the greatest amount of digestion and absorption of nutrients and water occurs *Within the small intestine, the duodenum and jejunum are the major sites of nutrient absorption, although some absorption occurs in the ileum *Most of the water is absorbed by osmosis, along with the absorbed nutrients in the duodenum and jejunum *Over 90% of the water is absorbed before the large intestine

Answer 150

Primary Site of Digestion and Absorption

Question 151

Circular Folds Villi Microvilli (brush border)

Answer 151

Modifications to Increase Surface Area

Question 152

oThe mucosa and submucosa form a series of folds called the _____, or plicae circulares, which run perpendicular to the long axis of the digestive tract

Answer 152

Circular Folds

Question 153

oTiny, fingerlike projections of the mucosa form numerous ______, which are 0.5-1.5mm in length oEach ____ is covered by simple columnar epithelium and contains a blood capillary network and a lymphatic capillary called a lacteal

Answer 153

Villi

Question 154

oMost of the cells that make up the surface of the villi have numerous cytoplasmic extensions (about 1 µm long) called _______, which further increase the surface area oThe combined ______ on the entire epithelial surface form the _______

Answer 154

Microvilli (Brush Border)

Question 155

Absoprtive cells Goblet cells Granular cells Endocrine cells

Answer 155

Cells of the Small Intestine

Question 156

oAre cells with microvilli that produce digestive enzymes and absorb digested food

Answer 156

Absorptive cells

Question 157

oProduce a protective mucus

Answer 157

Goblet Cells

Question 158

oOr Paneth cells, may help protect the intestinal epithelium from bacteria

Answer 158

Granular Cells

Question 159

oProduce many regulatory hormones oFor example, the hormones secretin and cholecystokinin stimulate hepatic and pancreatic secretions

Answer 159

Endocrine Cells

Question 160

Duodenum Jejunum Ileum

Answer 160

Three subdivisions of the Small Intestine

Question 161

*The region connected to the stomach, the _____, is about 25cm long *The _____ is the shortest part of the small intestine *The structure of the _____ begins with a nearly 180-degree arc from where it leaves the stomach and curves around the head of the pancreas within the abdominal cavity *This short, superior part ends in a sharp bend, where it joins the jejunum *Within the descending portion of the ______ are two small projections: 1.the major duodenal papilla, and 2.the minor duodenal papilla *These papillae are the location of ducts from the liver and the pancreas

Answer 161

Duodenum

Question 162

*The duodenum merges with the _______, which constitutes about two-fifths of the total length of the small intestine, and is about 2.5m long *Is similar in structure to the duodenum *Progressing from the duodenum through the ileum, there are gradual decreases in the diameter of the small intestine, the thickness of the intestinal wall, the number of circular folds, and the number of villi

Answer 162

Jejunum

Question 163

*The jejunum merges with the ____, which constitutes three-fifths of the small intestine, and is about 3.5m long *Merges with the large intestine *Is similar in structure to the duodenum *Progressing from the duodenum through the ____, there are gradual decreases in the diameter of the small intestine, the thickness of the intestinal wall, the number of circular folds, and the number of villi *Lymphatic nodules called Peyer patches are numerous in the mucosa and submucosa of the ______ *Peyer patches and other mucosa-associated lymphoid tissue in the digestive tract initiate immune responses against microorganisms that enter the mucosa from ingested food *Connects to the large intestine at a region of the large intestine called the cecum *The site where they merge is called the ileocecal junction *The junction is a ring of smooth muscle, the ileocecal sphincter, and a one-way ileocecal valve *Together, the sphincter and valve allow intestinal contents to move unidirectionally from the ____ into the cecum

Answer 163

Ileum

Question 164

*Is secreted form the duodenal glands, intestinal glands, and goblet cells *It protects the wall of the intestine from the irritating effects of acidic chyme and from the digestive enzymes that enter the duodenum from the pancreas *Secretions are released from the duodenal glands in response to vagus nerve, stimulation, the hormone secretin, and chemical or tactile irritation of the duodenal mucosa *Chemical and tactile stimulation of the mucosa also stimulate goblet cells to produce ______

Answer 164

Mucus (Secretions of the Small Intestine)

Question 165

*Secretion of ______ and water from the intestinal epithelium keeps the chyme in an aqueous solution, which facilitates the digestive process by pancreatic enzymes and small intestine enzymes

Answer 165

Electrolytes (Secretions of the Small Intestine)

Question 166

*Break down disaccharides to monosaccharides

Answer 166

Disaccharidases (Secretions of the Small Intestine)

Question 167

*Hydrolyze the peptide bonds between small amino acid chains *The large surface area of the intestinal epithelium brings these enzymes into contact with the chyme *Small molecules, which are breakdown products of digestion, are absorbed through the microvilli and enter the circulatory or lymphatic system

Answer 167

Peptidases (Secretions of the Small Intestine)

Question 168

*Mix the intestinal contents *These contractions both mix and propel substances through the small intestine as the wave of contraction proceeds *The contractions move at a rate of about 1cm/min *It usually takes 3-5 hours for chyme to move from the pylorus to the ileocecal junction

Answer 168

Segmental Movements (Movement in the Small Intestine)

Question 169

*Primarily propel the intestinal contents along the digestive tract *Are generally propagated for only short distances, but a few may proceed the entire length of the intestine *Frequently, intestinal peristaltic contractions are continuations of peristaltic contractions that begin in the stomach *These contractions both mix and propel substances through the small intestine as the wave of contraction proceeds *The contractions move at a rate of about 1cm/min *It usually takes 3-5 hours for chyme to move from the pylorus to the ileocecal junction

Answer 169

Peristalsis (Movement in the Small Intestine)

Question 170

*The liver is the largest internal organ of the body, weighing about 1.36kg (3 pounds) *It is in the right-upper quadrant of the abdomen, tucked against the inferior surface of the diaphragm *The liver consists of four lobes, 1.the right lobe, 2.the left lobe, 3.the caudate lobe, and 4.the quadrate lobe

Answer 170

Anatomy of the Liver

Question 171

oSeparated from left lobe by a connective tissue septum, the falciform ligament

Answer 171

Right Lobe

Question 172

oSeparated from right lobe by a connective tissue septum, the falciform ligament

Answer 172

Left Lobe

Question 173

oCan be seen from an inferior view, along with the porta hepatis

Answer 173

Caudate Lobe

Question 174

oCan be seen from an inferior view, along with the porta hepatis

Answer 174

Quadrate Lobe

Question 175

Common hepatic duct Cystic duct Common bile duct

Answer 175

Ducts of the Liver and Gall Bladder

Question 176

oThe right and left hepatic ducts first unite to form a single ______

Answer 176

Common Hepatic Duct

Question 177

oThe _____ from the gallbladder joins the common hepatic duct to form the common bile duct oBile can flow from the gallbladder through the _____ into the common bile duct, or it can flow back up the ______ into the gallbladder

Answer 177

Cystic Duct

Question 178

oJoins the pancreatic duct at the hepatopancreatic ampulla, which is an enlargement where the two ducts merge

Answer 178

Common Bile Duct

Question 179

*A connective tissue capsule and visceral peritoneum cover the liver, except for the bare area, a small area on the diaphragmatic surface that lacks a visceral peritoneum and is surrounded by the coronary ligament *At the porta hepatis, the connective tissue capsule sends a branching network of septa (walls) into the substance of the liver to provide its main support *Vessels, nerves, and ducts follow the connective tissue branches throughout the liver *The liver is divided into hepatic lobules *Hepatic lobules are hexagon-shaped regions surrounded by connective tissue septa and defined by a portal triad at each corner and a central vein in the center of the lobule *The portal triads are so named because three structures- the 1.hepatic portal vein, 2.hepatic artery, and 3.hepatic duct-are located in them *Hepatic nerves and lymphatic vessels, often too small to be seen easily in light micrographs, are also located in these areas

Question 180

*A connective tissue capsule and visceral peritoneum cover the liver, except for the bare area, a small area on the diaphragmatic surface that lacks a visceral peritoneum and is surrounded by the coronary ligament *At the porta hepatis, the connective tissue capsule sends a branching network of septa (walls) into the substance of the liver to provide its main support *Vessels, nerves, and ducts follow the connective tissue branches throughout the liver *The liver is divided into hepatic lobules *Hepatic lobules are hexagon-shaped regions surrounded by connective tissue septa and defined by a portal triad at each corner and a central vein in the center of the lobule *The portal triads are so named because three structures- the 1.hepatic portal vein, 2.hepatic artery, and 3.hepatic duct-are located in them *Hepatic nerves and lymphatic vessels, often too small to be seen easily in light micrographs, are also located in these area

Answer 180

Histology of the Liver

Question 181

*The central vein collects the blood as it leaves the lobule *Central veins of the lobules unite to form hepatic veins, which exit the liver on its posterior and superior surfaces and empty into the inferior vena cava *Hepatic cords are strings of cells that radiate out from the central vein of each lobule like the spokes of a wheel *The hepatic cords are composed of hepatocytes, the functional cells of the liver *Hepatocytes take up nutrients from the portal blood *The nutrients are stored, detoxified, or used to synthesize new compounds before being released into the hepatic sinusoids or into the bile canaliculi *Hepatic sinusoids are blood channels in the spaces between the hepatic cords *The sinusoids are lined with a very thin, irregular squamous endothelium consisting of two cell populations: 1.extremely thin, sparse endothelial cells and 2.hepatic phagocytic cells called Kupffer cells *The bile canaliculus is a cleftlike lumen that lies between the cells within each cord

Answer 181

Histology of the Liver

Question 182

oThe hepatic artery carries oxygenated blood from the aorta through the porta hepatis of the liver Hepatic artery branches become part of the portal triads Blood from the hepatic artery branches enters the hepatic sinusoids and supplies hepatocytes in the hepatic cords with O2 oThe hepatic portal vein carries nutrient-rich, deoxygenated blood from the small intestine through the porta hepatis of the liver Hepatic portal vein branches become part of the portal triads Blood from the hepatic portal vein branches enters the hepatic sinusoids and supplies hepatocytes in the hepatic cords with nutrients oBlood in the hepatic sinusoids that comes from the hepatic artery and hepatic portal vein picks up plasma proteins, processed molecules, and waste products produced by the hepatocytes of the hepatic cords oThe hepatic sinusoids empty into central veins The central veins connect to hepatic veins, which connect to the inferior vena cava oBile produced by hepatocytes in the hepatic cords enters bile canaliculi, which connect to hepatic duct branches that are part of the portal triads oThe hepatic duct branches converge to form the left and right hepatic ducts, which carry bile out of the porta hepatis of the liver

Answer 182

Flow of Blood and Bile Through the Liver

Question 183

*The liver produces and secretes about 600-1000mL of bile each day *Bile is a complex solution that contains 1.bile salts, 2.bile pigments, 3.cholesterol, 4.lipids, 5.lipid-soluble hormones, and 6.lecithin (a mixture of phospholipids) *Bile contains no digestive enzymes, but it plays a role in digestion because it neutralizes stomach acid and emulsifies lipids *The relative alkaline pH of bile helps neutralize the acidic chyme entering the duodenum *This is important because the pancreatic enzymes cannot function at the acidic pH of the chyme leaving the stomach *Bile salts emulsify lipids, which is necessary for subsequent digestion by lipase *Bile pigments are not required for any digestive function but rather are excretory products *Bile pigments have greenish-yellow to brown colors and give feces their characteristic color *One common bile pigment is bilirubin, which results from the breakdown of hemoglobin *Both neural and hormonal signals stimulate the secretion and release of bile

Answer 183

Bile Production (Functions of the Liver)

Question 184

oParasympathetic stimulation through the vagus nerves increases bile secretion from the liver oTwo hormones released from the duodenum increase bile in the digestive tract: 1.secretin and 2.cholecystokinin Secretin stimulates bile secretion from the liver, primarily by increasing the water and HCO3- content of bile oCholecystokinin stimulates gallbladder contractions to release bile into the duodenum oBile salts increase bile secretion through a positive feedback system Over 90% of bile salts are reabsorbed in the ileum and carried in the blood by the hepatic portal circulation Upon their return to the liver, the bile salts stimulate further bile secretion and are once again secreted into the bile This recycling process reduces the loss of bile salts in the feces Bile secretion into the duodenum continues until the duodenum empties

Answer 184

Regulation of Bile Secretion and Release from the Gall Bladder

Question 185

*Hepatocytes can remove glucose from the blood and store it in the form of glycogen *They can also store lipids, vitamins (A, B12, D, E, and K), copper, and iron *This storage function is usually short-term, and the amount of stored material in the hepatocytes-hence their size- fluctuates during the day *Hepatocytes help maintain blood glucose levels within very narrow limits *If a large amount of glucose enters the general circulation after a meal, it will result in hyperglycemia *Under normal conditions, this is prevented because the blood from the small intestine passes through the hepatic portal vein to the liver, where hepatocytes remove glucose and other substances from the blood, store them, and then secrete them back into the circulation when needed

Answer 185

Storage of Nutrients (Functions of the Liver)

Question 186

*The processing, or interconversion, of nutrients is another important function of the liver *Our food choices are not always in line with the nutrient requirements of the body (candy bars for breakfast, for example) *If this is the case, the liver can convert some nutrients into others *For example, if a person is on a diet that is excessively high in protein, an oversupply of amino acids and an undersupply of lipids and carbohydrates may be delivered to the liver *The hepatocytes break down the amino acids and cycle many of them through metabolic pathways so that they can be used to produce ATP, lipids, and glucose *Hepatocytes also transform substances that cannot be used by most cells into more readily usable substances *For example, they combine ingested dietary fats with choline and phosphorus in the liver to produce phospholipids, which are essential components of plasma membranes *In addition, vitamin D is hydroxylated in the liver hepatocytes *The hydroxylated form of vitamin D, which is the major circulating form of vitamin D, is transported through the blood to the kidneys, where it is again hydroxylated to form active Vitamin D3, a hormone regulating Ca^2+

Answer 186

Processing of Nutrients (Functions of the Liver)

Question 187

*Many ingested substances are harmful to body cells *In addition, the body itself produces many by-products of metabolism that, if accumulated, are toxic *The liver forms a major line of defense by altering the structure of many of these harmful substances to make them less toxic or to make their elimination easier *Ammonia, for example, a by-product of amino acid metabolism, is toxic and not readily removed from the blood by the kidneys *Hepatocytes remove ammonia from the blood and convert it to urea, which is less toxic than ammonia *Urea is then secreted into the blood and eliminated by the kidneys in the urine *The liver hepatocytes also remove other substances from the blood and excrete them into the bile *Hepatic phagocytic cells (Kupffer cells), which lie along the sinusoid walls of the liver, phagocytize “worn-out” and drying red and white blood cells, some bacteria, and other debris that enters the liver through the blood vessels

Answer 187

Detoxification (Functions of the Liver)

Question 188

*The liver can produce its own new compounds, including plasma proteins such as albumins, fibrinogen, globulins, heparin, and clotting factors, which are released into the blood *In addition, the liver is the major site of cholesterol synthesis *Cholesterol is important for plasma membrane structure and steroid hormone synthesis, for example

Answer 188

Synthesis of New Molecules (Functions of the Liver)

Question 189

*Site of bile storage and modification of bile concentration *Is a saclike structure for bile storage *It is on the inferior surface of the liver; it is about 8cm long and 4cm wide *Three tunics from the _____ wall: 1.an inner mucosa folded into rugae that allow the _______ to expand; 2.a muscularis, which is a layer of smooth muscle that allows the ______ to contract; and 3.an outer covering of serosa *The cystic duct connects the ______ to the common bile duct *The function of the ______ is to store and concentrate bile *The live continually secretes bile, which flows to the _______, where 40-70mL of bile are stored *While the bile is in the _____, water and electrolytes are absorbed *Thus, bile salts and pigments become as much as 5-10 times more concentrated than when secreted by the liver

Answer 189

Gall Bladder

Question 190

*Bile is released from the ______ by contractions stimulated by cholecystokinin and, to a lesser degree, by vagal stimulation *In this way, large amounts of concentrated bile are dumped into the small intestine shortly after a meal *Gallstones are insoluble aggregates formed in the _____ *They are often caused by precipitation of excess cholesterol, which can be the result of a high-cholesterol diet or other causes *Cholesterol is not soluble in water and is ordinarily kept in solution by bile salts *Occasionally, a gallstone passes out of the ______ and enters the cystic duct, blocking the release of bile *This condition interferes with normal digestion, and often the gallstone must be surgically removed *If the gallstone moves far enough down the duct, it can also block the pancreatic duct, resulting in pancreatitis

Answer 190

Gall Bladder

Question 191

*The pancreas is a complex organ composed of both endocrine and exocrine tissues that perform several functions *The pancreas is located behind the stomach *The head of the pancreas is nestled within the curvature of the duodenum *The body and tail extend to the spleen

Answer 191

Anatomy of the Pancreas

Question 192

Endocrine Exocrine

Answer 192

Two Distinct Functions of the Pancreas

Question 193

*The _____ part of the pancreas consists of pancreatic islets, or islets of Langerhans *The islet cells produce three hormones: 1.insulin, 2.glucagon, and 3.somatostatin *Insulin and glucagon are very important in controlling the blood levels of nutrients, such as glucose and amino acids *Somatostatin regulated insulin and glucagon secretion and may inhibit growth hormone secretion

Answer 193

Endocrine

Question 194

*Pancreatic juices *The _____ part of the pancreas is a compound acinar gland *Acinar cells within the acini produce digestive enzymes *Clusters of acini form lobules that are separated by thin septa *______ secretions flow from the pancreas to the small intestine via a series of ducts *Secretions from the acini first flow into small intercalated ducts, then into intralobular ducts, which leave the lobules to join interlobular ducts between the lobules *The interlobular ducts attach to the main pancreatic duct, which joins the common bile duct at the hepatopancreatic ampulla, or Vater’s ampulla *The hepatopancreatic ampulla empties into the duodenum at the major duodenal papilla *A smooth muscle sphincter, the hepatopancreatic ampullar sphincter, or sphincter of Oddi, regulates the opening of the ampulla *In most people, an accessory pancreatic duct opens at the minor duodenal papilla *The ducts are lined with simple cuboidal epithelium, and the epithelial cells of the acini are pyramid-shaped *A smooth muscle sphincter surrounds the pancreatic duct where it enters the hepatopancreatic ampulla

Answer 194

Exocrine

Question 195

*The exocrine secretions of the pancreas, called ______, have 1.an aqueous component, and 2.an enzymatic component *Is delivered to the small intestine through the pancreatic ducts, where it functions in digestion *The aqueous _____ is rich in bicarbonate ions (HCO3-) *Bicarbonate ions are a major part of the aqueous ______ *They are actively secreted by columnar epithelial cells that line the smaller ducts of the pancreas *The aqueous juice contains Na+ and K+ in about the same concentration found in extracellular fluid, and water flows passively to make ______ isotonic *The HCO3- ions of the aqueous ______ neutralize the acidic chyme that enters the small intestine from the stomach *The neutralized pH caused by pancreatic secretions in the duodenum stops pepsin digestion *More importantly, however, the neutralized pH is required for the functions of pancreatic and brush-border enzymes *The neutralized pH also prevents damage to the duodenum by the acid from the stomach

Answer 195

Pancreatic Juice

Question 196

*The production of HCO3- in the pancreas is similar to the production of H+ in the gastric gland *The major difference is that an alkaline solution is produced in the pancreas, whereas an acidic solution is produced in the stomach *The enzyme-rich ______ contains enzymes that digest all major classes of food *This enzyme-rich secretion is produced by the acinar cells of the pancreas *Without the enzymes produced by the pancreas, lipids, proteins, and carbohydrates cannot be adequately digested *Enzyme-rich _______ also contains other enzymes that digest carbohydrate, lipids, and nucleic acids *In addition to lipase, the pancreas also secretes the enzyme cholesterol esterase, which digests cholesteryl esters (the dietary form of cholesterol) into cholesterol and free fatty acids *Deoxyribonucleases and ribonucleases are enzymes that degrade DNA and RNA, respectively

Answer 196

Pancreatic Juice

Question 197

oThe enzyme carbonic anhydrase is present in duct epithelial cells oCarbonic anhydrase forms carbonic acid, which dissociated into H+ and HCO3- oThe H+ are exchanged for Na+, which are removed from the cell by the Na+-K+ pump The Na+-K+ pump is an ATPase that moves NA+ out and K+ into the cell It generates a Na+ gradient that is important in many cellular processes, including intestinal nutrient and water absorption oThe HCO3- are then transported into the intercalated duct in exchange for Cl- The result is an aqueous pancreatic juice rich in HCO3-

Answer 197

Cellular Mechanism Responsible for the Secretion of HCO3-

Question 198

*The enzyme ______ continues the polysaccharide digestion initiated in the oral cavity

Answer 198

Pancreatic Amylase

Question 199

*The lipid-digesting enzyme ______ breaks down lipids into monoglycerides and free fatty acids

Answer 199

Pancreatic Lipase

Question 200

*The three major _______ are 1.trypsin, 2.chymotrypsin, and 3.carboxypeptidase *In the same manner as pepsin, these protein-digesting enzymes are secreted in inactive forms, whereas many of the other enzymes are secreted in active form * he inactive forms are called trypsinogen, chymotrypinsogen, and procarboxypeptidase *They are activated by proteolytic removal of certain peptides from the precursor proteins *The ______ enterokinase, which is attached to the brush border of the small intestine, activates trypsinogen *Trypsin then activates more trypsinogen, as well as chymotrypsinogen and procarboxypeptidase *This process of releasing inactive enzymes is necessary because if the enzyme were produced in their active forms, they would start to digest the pancreas itself

Answer 200

Proteolytic Enzymes

Question 201

*Inappropriate activation causes ______, which is a painful inflammation of the pancreas *Can result from alcoholism, the use of certain drugs, pancreatic duct blockage, cystic fibrosis, viral infection, or pancreatic cancer *Symptoms can range from mild abdominal pain to systemic shock and coma

Answer 201

Pancreatitis

Question 202

*Is the portion of the digestive tract extending from the ileocecal junction to the anus *Normally, 18-24 hours are required for material to pass through the _____, in contrast to the 3-5 hours required for chyme to move through the small intestine *Thus, the movements of the ______ are more sluggish than those of the small intestine *While in the large intestine, chyme is converted to feces *The formation of feces involves the absorption of water and salts, secretion of mucus, and extensive action of microorganisms *Stores the feces until they are eliminated by defecation *About 1500mL of chyme enter the cecum each day, but more than 90% of the volume is reabsorbed, so that only 80-150mL of feces are normally eliminated by defecation

Answer 202

Large Intestine

Question 203

*Is the proximal end of the large intestine, where it meets the small intestine at the ileocecal junction *Extends inferiorly about 6cm past the ileocecal junction in the form of a blind sac *The vermiform appendix is smaller, blind tube about 9cm long attached to the ____ *The walls of the appendix contain many lymphatic nodules, which contribute to immune functions

Answer 203

Cecum (Anatomy of the Large Intestine)

Question 204

*About 1.5-1.8m long, consists of four parts: 1.ascending ____, 2,transverse ____, 3.descending ____, and 4.sigmoid ____ *The ascending ______ extends superiorly from the cecum and ends at the right colic flexure, or hepatic flexure, near the right inferior margin of the liver *The transverse _____ extends from the right colic flexure to the left colic flexure, or splenic flexure, and the descending ______ extends from the left colic flexure to the superior opening of the true pelvis, where it becomes the sigmoid ______ *The sigmoid _____ forms an S-shaped tube that extends into the pelvis and ends at the rectum *The muscularis of the _____ differs from that of the small intestine *While the circular muscle layer of the _____ is complete, the longitudinal muscle layer is incomplete *Rather than completely enveloping the intestinal wall, the longitudinal layer forms three bands, called the teniae coli

Answer 204

Colon

Question 205

*The teniae coli run the length of the _____ *Contractions of the teniae coli cause pouches called haustra to form along the length of the _____, giving it a puckered appearance *Small, lipid-filled connective tissue pouches called omental appendages are attached to the outer surface of the _____ along its length *The mucosa lining of the large intestine consists of simple columnar epithelium *This epithelium is not formed into folds or villi like that of the small intestine but has numerous, straight, tubular glands called crypts *The crypts, which are somewhat similar to the intestinal glands of the small intestine, are composed of three cell types: 1.absorptive, 2.goblet, and 3.granular *The major difference is that, in the large intestine, goblet cells predominate, and the other two cell types are greatly reduced in number

Answer 205

Colon

Question 206

*Is a straight, muscular tube that begins at the distal end of the sigmoid colon and ends at the anal canal *The mucosal lining of the _____ in simple columnar epithelium, and the muscular tunic is relatively thick, compared with the rest of the digestive tract

Answer 206

Rectum

Question 207

*The last 2-3cm of the digestive tract is the ______ *It begins at the inferior end of the rectum and ends at the anus *The smooth muscle layer of the ______ is even thicker than that of the rectum and forms the internal anal sphincter at its superior end *Skeletal muscle forms the external anal sphincter at the inferior end of the canal *The epithelium of the superior part of the ______ is simple columnar, and that of the inferior part is stratified squamous *Rectal veins that supply the ______ can become enlarged or inflamed, a condition known as hemorrhoids *Hemorrhoids cause pain, itching, and bleeding around the anus *They can usually be treated by changes in diet or medications

Answer 207

Anal Canal

Question 208

*The major secretion product of the large intestine is mucus *Mucus is secreted from the numerous goblet cells scattered along the length of the mucosa of the large intestine *In addition, there are numerous crypts lined almost entirely with goblet cells *Little enzymatic activity is associated with secretions of the large intestine *Mucus lubricates the wall of the large intestine and helps the fecal matter stick together *Tactile stimuli and irritation of the large intestine wall trigger local enteric reflexes that increase mucous secretion *Parasympathetic stimulation also increases the secretory rate of the goblet cells *The feces that leave the digestive tract consist of water, solid substances, microorganisms, and sloughed-off epithelial cells *An abnormally frequent discharge of watery feces is called diarrhea *Numerous microorganisms inhabit the large intestine, and are referred to as normal microbiota of the gut *They reproduce rapidly and ultimately constitute about 30% of the dry weight of the feces

Answer 208

Secretions of the Large Intestine

Question 209

*An important function of normal microbiota is to synthesize vitamin K, which is passively absorbed in the large intestine *Acids are secreted by normal microbiota as metabolic by-products *An antiporter exchanges HCO3- for Cl- in epithelial cells of the large intestine in response to acid produced by the normal microbiota *Another antiporter exchanges Na+ for H+ *Movement of Na+ into the epithelial cells via this exchanger and other Na+ channels is driven by the Na+ gradient established by the Na+-K+ pump *Water leaves the lumen of the large intestine through osmosis as Na+ and Cl- move into the epithelial cells *Normal microbiota also break down a small amount of cellulose to glucose *However, the glucose cannot be absorbed in the large intestine *Bacterial actions in the large intestine produce gases called flatus *The amount of flatus depends partly on the specific bacterial population in the large intestine and partly on the type of food consumed

Answer 209

Secretions of the Large Intestine

Question 210

*Segmental mixing movements occur in the large intestine much less often than in the small intestine *Peristaltic waves are largely responsible for moving chyme along the ascending colon *At widely spaced intervals (normally three or four times each day), large parts of the transverse and descending colon undergo several strong contractions, called mass movements *Each mass movement contraction extends over a much longer part of the digestive tract (≥ 20 cm) than does a peristaltic contraction and propels the large intestine contents a considerable distance toward the anus *Mass movements are very common after meals because they are initiated by the presence of food in the stomach or duodenum *Mass movements are most common about 15 minutes after breakfast *They usually persist for 10-30 minutes and then stop for perhaps half a day *Mass movements are coordinated by two reflexes in the ENS: 1.gastrocolic and 2.duodenocolic *Gastrocolic reflexes are initiated by distension in the stomach, and duodenocolic reflexes are initiated by distension in the duodenum

Answer 210

Movement in the Large Intestine

Question 211

*The gastrocolic and duodenocolic reflexes promote peristalsis of the small and large intestines, including mass movements *These reflexes are mediated by parasympathetic reflexes, local reflexes, and hormones, such as cholecystokinin and gastrin *The thought or smell of food, distention of the stomach, and the movement of chyme into the duodenum can stimulate them *During defecation, the contractions that move feces toward the anus must be coordinated with the relaxation of the internal and external anal sphincters *Parasympathetic reflexes are responsible for most of the defecation reflex *The internal and external anal sphincters prevent defecation *Resting sphincter pressure results from tonic muscle contractions, mostly of the internal anal sphincter *In response to increased abdominal pressure, reflexes mediated through the spinal cord cause contractions of the external anal sphincter

Answer 211

Movement in the Large Intestine

Question 212

*The untimely expulsion of feces during coughing or exertion is avoided *There is also conscious control of the defecation reflex *Action potentials from the sacral spinal cord are propagated to the brain, where parts of the brainstem and hypothalamus inhibit or facilitate reflex activity in the spinal cord *In addition, action potentials are also propagated to the cerebrum, where awareness of the need to defecate is realized *The external anal sphincter is composed of skeletal muscle and is under conscious cerebral control *If this sphincter is relaxed voluntarily, feces are expelled *On the other hand, increased contraction of the external anal sphincter prevents defecation *The defecation reflex persists for only a few minutes and quickly declines *Generally, the reflex is reinitiated after a period that may be as long as several hours *Mass movements in the large intestine are usually the reason for reinitiation of the defecation reflex *The defecation reflex consists of local and parasympathetic reflexes *Local reflexes cause weak contractions of the distal colon and rectum and relaxation of the internal anal sphincter

Answer 212

Movement in the Large Intestine

Question 213

*Defecation can be initiated by voluntary actions that stimulate a defecation reflex, called the Valsalva maneuver *This “straining” includes a large inspiration of air, followed by closure of the larynx and forceful contraction of the abdominal muscles *As a consequence, the pressure in the abdominal cavity increases and forces feces into the rectum *Stretch of the rectum initiates a defecation reflex, and input from the brain overrides the reflexive contraction of the external anal sphincter stimulated by increased abdominal pressure *The increased abdominal pressure also helps push feces through the rectum *The Valsalva maneuver is also employed during urination and childbirth *Individuals with heart disease are discouraged from initiating the Valsalva maneuver as it can decrease heart rate due to the release of acetylcholine from the vagus nerves

Answer 213

Movement in the Large Intestine

Question 214

oDistension of the rectum by feces stimulates local defecation reflexes that cause contractions of the large intestine and rectum, which move feces toward the anus oDistension of the rectum stimulates parasympathetic reflexes Action potentials are propagated to the defecation reflex center Input from the defecation reflex center causes contraction of the large intestine and rectum, but causes relaxation of the internal anal sphincter oVoluntary control of the external anal sphincter from motor nerve fibers contracts it or relaxes it, depending on whether defecation is initiated

Answer 214

Steps of Movement in the Large Intestine

Question 215

*Is the breakdown of food to molecules small enough to be absorbed into the blood

Answer 215

Digestion

Question 216

*Breaks large food particles apart into smaller ones, such as during chewing

Answer 216

Mechanical Digestion

Question 217

*Is the breaking of covalent chemical bonds in organic molecules by digestive enzymes *Carbohydrates break down into monosaccharides, lipids break down into fatty acids and monoglycerides, and proteins break down into amino acids *Some molecules (e.g., vitamins, minerals, and water) are not broken down *A relatively small amount of digestion begins in the oral cavity, and some occurs in the stomach, but the vast majority of digestion occurs in the proximal end of the small intestine, especially in the duodenum

Answer 217

Chemical Digestion

Question 218

*Is the means by which molecules are moved out of the digestive tract into the blood for distribution throughout the body *Nearly all _____ of nutrients occurs in the duodenum and jejunum of the small intestine *Some _____ also occurs in the ileum *A few chemicals, such as nitroglycerin, can be absorbed through the thin mucosa of the oral cavity below the tongue *Some small molecules (e.g., alcohol and aspirin) can diffuse through the stomach epithelium into the blood *Some molecules can be absorbed by diffusion, whereas others must be transported across the intestinal wall *Transport requires transport proteins, which work by facilitated diffusion, active-transport, or secondary-transport mechanisms, such as symport and antiport *The epithelial cells that form the intestinal wall have two distinct sides with different transport proteins on each side *The side that faces the digestive tract lumen is called the apical membrane, and the side that faces the blood vessels is called the basolateral membrane *The transport proteins in these membranes are responsible for the one-way movement of molecules from the digestive tract to the rest of the body

Answer 218

Absorption

Question 219

oWater, ions, and water-soluble digestion products, such as glucose and amino acids, enter the hepatic portal system and travel to the liver oThe products of lipid metabolism are coated with proteins and transported into lymphatic capillaries called lacteals oThe lacteals are connected by lymphatic vessels to the thoracic duct, which empties into the left subclavian vein oThe protein-coated lipid products then travel in the blood to adipose tissue or to the liver

Answer 219

Once the Digestive Products have been Absorbed, they are Transported to Other Parts of the Body by Two Routes

Question 220

*Ingested _____consist primarily of polysaccharides, such as starches; disaccharides, such as sucrose (table sugar) and lactose (milk sugar); and monosaccharides, such as glucose and fructose (the sugar found in many fruits) *During digestion, polysaccharides break down first into smaller chains and some disaccharides and monosaccharides *Disaccharides then break down into monosaccharides *A minor amount of _____ digestion begins in the oral cavity with the partial digestion of starches by salivary amylase *Digestion continues in the stomach until the food is well mixed with acid, which inactivates salivary amylase * _____ digestion is resumed in the small intestine by pancreatic amylase *Pancreatic amylase in the small intestine is responsible for the majority of ______ digestion *Many of the digested _____ at this point are disaccharides, which cannot be absorbed *The final step in _____ digestion is performed by a series of disaccharidases that are bound to the microvilli of the intestinal epithelium *Disaccharides generate three important monosaccharides: 1.glucose, 2.galactose, and 3.fructose *The major monosaccharide is glucose

Answer 220

Carbohydrates (Macromolecule Digestion)

Question 221

oThe monosaccharides glucose and galactose are taken up into intestinal epithelial cells by symport, powered by a Na+ gradient oThe Na+ gradient is generated by the Na+-K+ pump located on the basolateral membrane Diffusion of Na+ down its concentration gradient provides the energy to transport glucose or galactose across the plasma membrane In contrast to glucose and galactose, the monosaccharide fructose is taken up by facilitated diffusion oOnce inside the intestinal epithelial cell, monosaccharides are transported by facilitated diffusion to the capillaries of the intestinal villi oThe monosaccharides are then carried by the hepatic portal system to the liver, where the nonglucose monosaccharides are converted to glucose Glucose enters the cells through facilitated diffusion The rate of glucose transport into most types of cells is greatly influenced by insulin and may increase 10-fold in its presence

Answer 221

Steps of Process of Glucose Transport

Question 222

*Are molecules that are insoluble or only slightly soluble in water *They include triglycerides, phospholipids, cholesterol, steroids, and fat-soluble vitamins *Triglycerides are the most common type of ____ and are often referred to as fats *They consist of three fatty acids bound to glycerol *Lipase enzymes digest _____ molecules *The primary products of lipase digestion are free fatty acids and monoglycerides *There are three lipases released into the digestive tract: 1.pancreatic lipase, 2.lingual lipase, and 3.gastric lipase *The vast majority of lipase is pancreatic lipase, which is secreted by the pancreas and digests _____ in the small intestine *A minor amount of lingual lipase is secreted in the oral cavity and swallowed with food *It digests a small amount (<10%) of lipid in the stomach *The stomach also produces very small amounts of gastric lipase *Lingual and gastric lipase are most important in neonatal infants, while pancreatic lipase is the major enzyme in adults *Pancreatic lipase alone cannot efficiently digest ______ *A key step in ____ digestion is emulsification, by which bile salts transform large ____ droplets into much smaller droplets *Bile salts mix with lipids and act as detergents to disrupt ____ droplets *By decreasing the droplet size, emulsification increases the surface area of the ____ exposed to lipase and other digestive enzymes *This is necessary because lipase is water-soluble and can digest _____ only at the surface of the droplets *The bile salts are secreted by the liver and stored in the gallbladder until needed in the duodenum *Lingual and gastric lipase, which work in the acidic environment of the stomach, do not require bile salts

Answer 222

Lipids (Macromolecule Digestion)

Question 223

*Before entering adipocytes, triglycerides break back down into fatty acids and glycerol, which enter the adipocytes and are once more converted to triglycerides *Triglycerides are stored in adipose tissue until an energy source is needed elsewhere in the body *In the liver, the chylomicron ____ are stored, converted into other molecules, or used as energy *The chylomicron remnant, minus the triglyceride, is conveyed through the blood to the liver, where it breaks up *Because _____ are either insoluble or only slightly soluble in water, they are transported through the blood in combination with proteins, which are water-soluble *____ combined with proteins are called lipoproteins and are categorized as high-or low-density *Are less dense than water and tend to float in water *Proteins, which are denser than water, tend to sink in water *A lipoprotein with a high ____ content has a very low density, whereas a lipoprotein with a high lipid content has a very low density, whereas a lipoprotein with a high protein content has a relatively high density

Answer 223

Lipids (Macromolecule Digestion)

Question 224

*Chylomicrons, which are made up of 99% lipid and only 1% protein, are lipoproteins with an extremely low density *The other major transport lipoproteins are very low density lipoprotein (VLDL), which is 92% lipid and 8% protein; low-density lipoprotein (LDL), which is 75% lipid and 25% protein; and high-density lipoprotein (HDL), which is 55% lipid and 45% protein *About 15% of the cholesterol in the body is digested in the food we eat *Eating foods containing saturated fatty acids can raise plasma cholesterol levels by stimulating LDL production and inhibiting LDL receptor production *Conversely, ingesting unsaturated fatty acids lowers plasma cholesterol *Replacing fats with carbohydrates in the diet can also reduce blood cholesterol *The remaining 85% is manufactured in body cells, mostly in the liver and intestinal mucosa *Most of the cholesterol and other ____ taken into or manufactured in the liver leave the liver in the form of VLDL *Most of the triglycerides are removed from the VLDL to be stored in adipose tissue; as a result, VLDL becomes LDL.

Answer 224

Lipids (Macromolecule Digestion)

Question 225

*The cholesterol in LDL is critical for the production of steroid hormones and bile salts in the liver *It is also an important component of plasma membranes *Abnormally low cholesterol levels may lead to weakened blood vessel walls and an increased risk for cerebral hemorrhage *Cells not only take in cholesterol and other lipids from LDLs but also make their own cholesterol *When the combined intake and manufacture of cholesterol exceeds a cell’s needs, a negative-feedback system reduces the amount of LDL receptors and cholesterol manufactured by the cell *Excess ____ are also packaged into HDLs by the cells *These are transported back to the liver for recycling or excretion in bile *LDL is commonly considered “bad” because, when in excess, it deposits cholesterol in arterial walls *On the other hand, HDL is considered “good” because it transports cholesterol form the tissues via blood to the liver for removal from the body in the bile *A high HDL/LDL ratio in the blood is related to a lower risk for heart disease *Low HDL levels are linked to obesity, and weight reduction increases HDL levels *Aerobic exercise can decrease LDL levels and increase HDL levels

Answer 225

Lipids (Macromolecule Digestion)

Question 226

oOnce lipids are digested in the intestine, bile salts aggregate around the small droplets Lipid droplets surrounded by bile salts are called micelles The hydrophobic ends of the bile salts are directed toward the free fatty acids, cholesterol, and monoglycerides at the center of the micelle; the hydrophilic ends are directed outward toward the water environment oWhen a micelle comes in contact with the epithelial cells of the small intestine, the lipid contents of the micelle pass by simple diffusion through the plasma membrane of the epithelial cells The bile salts are not absorbed until they reach the epithelium of the distal ileum oWithin the smooth endoplasmic reticulum of the intestinal epithelial cells, free fatty acids are combined with monoglyceride molecules to form triglycerides Proteins synthesized in the epithelial cells attach to droplets of triglycerides, phospholipids, and cholesterol called chylomicrons Chylomicrons contain about 90% triglyceride, 5% cholesterol, 4% phospholipid, and 1% protein The chylomicrons leave the epithelial cells by exocytosis and enter the lacteals of the lymphatic system within the villi oChylomicrons enter the lymphatic capillaries rather than the blood capillaries because the lymphatic capillaries lack a basement membrane and are more permeable to large particles, such as chylomicrons, which are about 0.3mm in diameter They travel through the lymphatic system via the thoracic duct to the bloodstream and then by the blood to adipose tissue

Answer 226

Steps of the Process by which Lipids are Absorbed

Question 227

*Are taken into the body from a number of dietary sources *Digestion of ____ begins in the stomach *Pepsin secreted by the stomach catalyzes the cleavage of covalent bonds in _____ to produce smaller polypeptide chains *Pepsin digests as much as much as 10-20% of the total ingested protein *Once the ______ and polypeptide chains leave the stomach, pancreatic proteases continue the digestive process to produce small peptide chains *There are three major pancreatic proteases: 1.trypsin, 2.chymotrypsin, and 3.carboxypeptidase *The protein digestion products are finally broken down into tripeptides, dipeptides, and amino acids by peptidases bound to the microvilli of the small intestine *Each peptidase is specific for a certain peptide chain length or for a certain amino acid sequence *Amino acids are relatively transported into the various cells of the body *This transport is stimulated by growth hormone and insulin *Most amino acids serve as building blocks to form new _____, but some amino acids may be used for energy

Answer 227

Proteins (Macromolecule Digestion)

Question 228

oBasic, acidic, and neutral amino acids are transported into the epithelial cells by separate carrier molecules oAcidic and most neutral amino acids enter by symport with a Na+ gradient, similar to the mechanism used for glucose transport Basic amino acids enter the epithelial cells by facilitated diffusion Dipeptides and tripeptides enter intestinal epithelial cells by a H+ symport mechanism analogous to Na+ symport The total amount of each amino acid that enters the intestinal epithelial cells as dipeptides or tripeptides is considerably more than the amount that enters as single amino acids Once inside the cells, dipeptidases and tripeptides split the dipeptides and tripeptides into their component amino acids oIndividual amino acids then leave the epithelial cells oAmino acids then enter the hepatic portal system, which transports them to the liver The amino acids may be modified in the liver or released into the bloodstream and distributed throughout the body

Answer 228

Steps of the Process of Amino Acid Transport