Chapter 24 Flashcards
(216 cards)
1
Q
Digestive system
A
Consists of a group of organs that break down the food we eat into smaller molecules that can be used by body cells.
2
Q
What two groups of organs compose the digestive system? Describe them:
A
- Gastrointestinal (GI) tract (alimentary canal): a continuous tube that extends from the mouth to the anus through the thoracic and abdominopelvic cavities. Organs of the gastrointestinal tract include the mouth, most of the pharynx, esophagus, stomach, small intestine, and large intestine.
- Accessory digestive organs: include the teeth, tongue, salivary glands, liver, gallbladder, and pancreas.
3
Q
Tonus
A
A state of sustained contraction.
4
Q
What are the six basic processes that the digestive system performs? Describe them:
A
- Ingestion: taking food into mouth.
- Secretion: release of water, acid, buffers, and enzymes into lumen of GI tract.
- Motility: churning and movement of food through GI tract.
- Digestion: mechanical and chemical breakdown of food.
- Absorption: passage of digested products from GI tract into blood and lymph.
- Defecation: elimination of feces from GI tract.
5
Q
What is the difference between mechanical digestion and chemical digestion? Describe them:
A
Mechanical digestion: the teeth cut and grind food before it is swallowed, and then smooth muscles of the stomach and small intestine churn the food to further assist the process. As a result, food molecules become dissolved and thoroughly mixed with digestive enzymes.
Chemical digestion: large carbohydrate, lipid, protein, and nucleic acid molecules in food are split into smaller molecules by hydrolysis. Digestive enzymes produced by the salivary glands, tongue, stomach, pancreas, and small intestine catalyze these catabolic reactions.
6
Q
From deep to superficial, what are the four layers of the GI tract?
A
- Mucosa
- Submucosa
- Muscularis
- Serosa
7
Q
Mucosa
A
Is the inner lining of the GI tract, and is a mucous membrane.
8
Q
What are the three layers of the mucosa? Describe them:
A
- Epithelium: is in direct contact with the contents of the GI tract. Contains enteroendocrine cells.
- Lamina propria: a layer of connective tissue. Contains majority of the cells of the mucosa-associated lymphatic tissue (MALT).
- Muscularis mucosae: a thin layer of smooth muscle.
9
Q
Enteroendocrine cells
A
Cells that secrete hormones. Are located among the epithelial cells.
10
Q
Mucosa-associated lymphatic tissue
(MALT)
A
Lymphatic nodules that contain immune system cells that protect against disease. Is present all along the GI tract, especially in the tonsils, small intestine, appendix, and large intestine.
11
Q
Submucosa
A
Consists of areolar connective tissue that binds the mucosa to the muscularis. Contains many blood and lymphatic vessels that receive absorbed food molecules. Contains the submucosal plexus, and may also contain glands and lymphatic tissue.
12
Q
Muscularis
A
Consists of skeletal muscle and smooth muscle. Skeletal muscle can be found in the mouth, pharynx, and superior and middle parts of the esophagus, which produces voluntary swallowing. Skeletal muscle can also be found in the external anal sphincter, which permits voluntary control of defecation. Smooth muscle can be found throughout the rest of the GI tract, and its involuntary contractions help break down food, mix it with digestive secretions, and propel it along the tract. The smooth muscle can generally be found in two sheets: an inner sheet of circular fibers and an outer sheet of longitudinal fibers. The muscularis contains the myenteric plexus.
13
Q
Serosa (visceral peritoneum)
A
Is a serous membrane composed of areolar connective tissue and simple squamous epithelium (mesothelium).
14
Q
Adventitia
A
A single layer of areolar connective tissue that forms the superficial layer of the esophagus as it lacks a serosa.
15
Q
Enteric nervous system (ENS)
A
The “brain of the gut”. Consists of about 100 million neurons that extend from the esophagus to the anus.
16
Q
What two plexuses are the neurons of the ENS arranged into? Describe them:
A
- Myenteric plexus (Plexus of Auerbach): located between the longitudinal and circular smooth muscle layers of the muscularis. Mostly controls GI tract motility (movement), particularly the frequency and strength of contraction of the muscularis.
- Submucosal plexus (Plexus of Meissner): found within the
submucosa. Controlling the secretions of the organs of the GI tract.
17
Q
What two major types of sensory receptors does the wall of the GI tract contain? Describe them:
A
- Chemoreceptors: respond to certain chemicals in the food present in the lumen.
- Mechanoreceptors: activated when food distends (stretches) the wall of a GI organ.
18
Q
What do parasympathetic nerves that supply the GI tract do?
A
In general, stimulation of the parasympathetic nerves that innervate the GI tract causes an increase in GI secretion and motility by increasing the activity of ENS neurons.
19
Q
What do sympathetic nerves that supply the GI tract do?
A
In general, the sympathetic nerves that supply the GI tract cause a decrease in GI secretion and motility by inhibiting the neurons of the ENS. Emotions such as anger, fear, and anxiety may slow digestion because they stimulate the sympathetic nerves that supply the GI tract.
20
Q
GI (gastrointestinal) reflex pathways
A
Regulate GI secretion and motility in response to stimuli present in the lumen of the GI tract. Starts off with sensory receptors that are associated with the sensory neurons of the ENS. The axons of these sensory neurons can synapse with other neurons located in the ENS, CNS, or ANS, informing these regions about the nature of the contents and the degree of distension (stretching) of the GI tract. The neurons of the ENS, CNS, or ANS subsequently activate or inhibit GI glands and smooth muscle, altering GI secretion and motility.
21
Q
Peritoneum
A
The largest serous membrane of the body. Consists of a layer of simple squamous epithelium (mesothelium) with an underlying supporting layer of areolar connective tissue.
22
Q
What can the peritoneum be divided into? Describe them:
A
Parietal peritoneum: lines the wall of the abdominal cavity.
Visceral peritoneum: covers some of the organs in the cavity and is their serosa.
23
Q
Peritoneal cavity
A
The slim space containing lubricating serous fluid that is between the parietal and visceral portions of the peritoneum.
24
Q
Ascites
A
When the peritoneal cavity becomes distended by the accumulation of several liters of fluid. Occurs in certain diseases.
25
Retroperitoneal
Organs that lie on the posterior abdominal wall and are covered by peritoneum only on their anterior surfaces; they are not in the peritoneal cavity. Include the kidneys, ascending and descending colons of the large intestine, duodenum of the small intestine, and pancreas.
26
What are the five major peritoneal folds?
1. Greater omentum
2. Falciform ligament
3. Lesser omentum
4. Mesentery
5. Mesocolon
27
Greater omentum
The longest peritoneal fold. Normally contains a considerable amount of adipose tissue. Its adipose tissue content can greatly expand with weight gain, contributing to the characteristic “beer belly” seen in some overweight individuals. The many lymph nodes of the greater omentum contribute macrophages and antibody-producing plasma cells that help combat and contain infections of the GI tract.
28
Falciform ligament
Attaches the liver to the anterior abdominal wall and diaphragm. The liver is the only digestive organ that is attached to the anterior abdominal wall.
29
Lesser omentum
Connects the stomach and duodenum to the liver. It is the pathway for blood vessels entering the liver and contains the hepatic portal vein, common hepatic artery, and common bile duct, along with some lymph nodes.
30
Mesentery
Binds the jejunum and ileum of the small intestine to the posterior abdominal wall. Is the most massive peritoneal fold and is typically laden with fat, which contributes extensively to the large abdomen in obese individuals. Together, the mesentery and mesocolon hold the intestines loosely in place, allowing movement as muscular contractions mix and move the luminal contents along the GI tract.
31
Mesocolon
Two separate folds of peritoneum that bind the transverse colon (transverse mesocolon) and sigmoid colon (sigmoid mesocolon) of the large intestine to the posterior abdominal wall. Also carries blood and lymphatic vessels to the intestines. Together, the mesentery and mesocolon hold the intestines loosely in place, allowing movement as muscular contractions mix and move the luminal contents along the GI tract.
32
Mouth (oral or buccal cavity)
Helps with the functioning of the tongue, salivary glands, and teeth, all of which are in the mouth. Additionally, the lips and cheeks keep food between the teeth during mastication, and buccal glands lining the mouth produce saliva.
33
What is the activity and result of the cheeks?
Activity: keeps food between teeth.
Result: foods uniformly chewed during mastication.
34
What is the activity and result of the lips (labia)?
Activity: keeps food between teeth.
Result: foods uniformly chewed during mastication.
35
Labial frenulum
A midline fold of mucous membrane that attaches the inner surface of each lip to its corresponding gum.
36
Oral vestibule
The space bounded externally by the cheeks and lips and internally by the gums and teeth.
37
Oral cavity proper
The space that extends from the gums and teeth to the fauces.
38
Fauces
The opening between the oral cavity and the oropharynx (throat).
39
Palate
A wall or septum that separates the oral cavity from the nasal cavity, and forms the roof of the mouth. This important structure makes it possible to chew and breathe at the same time.
40
Hard palate
The anterior portion of the roof of the mouth. Is formed by the maxillae and palatine bones and is covered by a mucous membrane; it forms a bony partition between the oral and nasal
cavities.
41
Soft palate
The posterior portion of the roof of the mouth. Is an arch-shaped muscular partition between the oropharynx and nasopharynx that is lined with mucous membrane. During swallowing, the soft palate and uvula are drawn superiorly, closing off the nasopharynx and preventing swallowed foods and liquids from entering the nasal cavity.
42
Uvula
A fingerlike muscular structure that hangs from the free border of the soft palate. During swallowing, the soft palate and uvula are drawn superiorly, closing off the nasopharynx and preventing swallowed foods and liquids from entering the nasal cavity.
43
Palatoglossal arch
A muscular fold that runs down the lateral sides of the soft palate. Is anterior. Extends to the side of the base of the tongue.
44
Palatopharyngeal arch
A muscular fold that runs down the lateral sides of the soft palate. Is posterior. Extends to the side of the pharynx.
45
What is the activity and result of the salivary gland?
Activity: secrete saliva.
Result: lining of mouth and pharynx moistened and lubricated.
Saliva softens, moistens, and dissolves food and cleanses
mouth and teeth. Salivary amylase splits starch into smaller
fragments (maltose, maltotriose, and α-dextrins).
46
Small salivary glands
What a small amount of saliva is secreted by. Open directly, or indirectly via short ducts, to the oral cavity. Include labial, buccal, and palatal glands in the lips, cheeks, and palate, respectively, and lingual glands in the tongue.
47
Major salivary glands
What most saliva is secreted by. Lie beyond the oral mucosa into ducts that lead to the oral cavity.
48
What are the three pairs of major salivary glands? Describe them:
1. Parotid glands: secretes saliva into the oral cavity via a parotid duct.
2. Submandibular glands: secretes saliva into the oral cavity via a submandibular duct.
3. Sublingual glands: secretes saliva into the oral cavity via a lesser sublingual duct.
49
Saliva
99.5% water and 0.5% solutes.
50
What is the source, substrates, and products of salivary amylase?
Source: salivary glands.
Substrates: starches (polysaccharides).
Products: maltose (disaccharide), maltotriose (trisaccharide), and α-dextrins.
51
Salivation
The secretion of saliva. Is controlled by the autonomic nervous system. Amounts of saliva secreted daily vary considerably but average 1000–1500 mL (1–1.6 qt).
52
Tongue
Maneuvers food for mastication, shapes food into a bolus, maneuvers food for deglutition, detects sensations for taste, and initiates digestion of triglycerides.
53
What is the activity and result of the extrinsic muscles of the tongue?
Activity: move tongue from side to side and in and out.
Result: food maneuvered for mastication, shaped into bolus, and maneuvered for swallowing.
54
What is the activity and result of the intrinsic muscles of the tongue?
Activity: alter shape of tongue.
Result: swallowing and speech.
55
Lingual frenulum
A fold of mucous membrane in the midline of the undersurface of the tongue. Is attached to the floor of the mouth and aids in limiting the movement of the tongue posteriorly.
56
Papillae
Projections of the lamina propria covered with stratified squamous epithelium. Cover the dorsum (upper surface) and lateral surfaces of the tongue. Some papillae contain taste buds, and some contain receptors for touch and increase friction between the tongue and food, making it easier for the tongue to move food in the oral cavity.
57
What is the activity and result of the taste buds?
Activity: serve as receptors for gustation (taste) and presence of food in mouth.
Result: secretion of saliva stimulated by nerve impulses from taste buds to salivatory nuclei in brain stem to salivary glands.
58
What is the activity and result of the lingual glands?
Activity: secrete lingual lipase.
Result: triglycerides broken down into fatty acids and diglycerides.
59
What is the source, substrates, and products of lingual lipase?
Source: lingual glands in tongue.
Substrates: triglycerides (fats and oils) and other lipids.
Products: fatty acids and diglycerides.
60
What is the activity and result of the teeth (dentes)?
Activity: cut, tear, and pulverize food.
Result: solid foods reduced to smaller particles for swallowing.
61
Gingivae
AKA gums. Cover the alveolar processes. Extend slightly into each socket.
62
Periodontal ligament (Periodontal membrane)
Helps anchor the tooth to the underlying bone.
63
Crown
The visible portion above the level of the gums.
64
Roots
Embedded in the socket. One to three of them.
65
Neck
The constricted junction of the crown and root near the gum line.
66
Dentin
Calcified connective tissue. Makes up the majority of the tooth.
67
Enamel
Made up of calcium salts. Protects the tooth from wear and tear. Is the hardest substance in the body.
68
Cementum
A bone-like substance that attaches the root to the periodontal ligament.
69
Pulp cavity
Contains pulp (connective
tissue containing nerves and blood vessels).
70
Root canal
An extension of the pulp cavity that contains nerves and blood vessels.
71
Apical foramen
An opening at the base of a root canal through which blood vessels, lymphatic vessels, and nerves enter a tooth.
72
What is the difference between endodontics, orthodontics, and periodontics?
Endodontics: a branch of dentistry that is concerned with the prevention, diagnosis, and treatment of diseases that affect the pulp, root, periodontal ligament, and alveolar bone.
Orthodontics: a branch of dentistry that is concerned with the prevention and correction of abnormally aligned teeth.
Periodontics: a branch of dentistry concerned with the treatment of abnormal conditions of the tissues immediately surrounding the teeth, such as gingivitis (gum disease).
73
Dentitions
Sets of teeth that humans have.
74
What are the two dentitions? Describe them:
1. Deciduous teeth (primary teeth, milk teeth, or baby teeth): 20 teeth; begin to erupt at about 6 months of age, and approximately two teeth appear each month thereafter, until all 20 are present. All of the deciduous teeth are lost between ages 6 and 12 years.
2. Permanent teeth (secondary teeth): 32 teeth; erupt between ages 6 and adulthood.
75
Identify where the central incisors, lateral incisors, canines, first deciduous molars, and second deciduous molars are:
76
Mastication
Chewing.
77
Bolus
A soft, flexible, easily swallowed mass.
78
What two enzymes contribute to chemical digestion in the mouth?
1. Salivary amylase
2. Lingual lipase
79
Pharynx
AKA throat; receives a bolus from the oral cavity and passes it into the esophagus.
80
Esophagus
Receives a bolus from the pharynx and moves it into the stomach; this requires relaxation of the upper esophageal sphincter and secretion of mucus.
81
Esophageal hiatus
An opening where the esophagus pierces the diaphragm through, and ends in the superior portion of the stomach.
82
From deep to superficial, what are the four layers of the esophagus?
1. Mucosa
2. Submucosa
3. Muscularis
4. Adventitia
83
What makes the layers of the esophagus different from the layers of the GI tract?
The GI tract has the serosa as its superficial layer, and the esophagus has the adventitia as its superficial layer.
84
Upper esophageal sphincter (UES)
Formed by the muscularis. Consists of skeletal muscle. Regulates the movement of food from the pharynx into the esophagus.
85
Lower esophageal (cardiac) sphincter (LES)
Formed by the muscularis. Consists of smooth muscle and is near the heart. Regulates the movement of food from the esophagus into the stomach.
86
Deglutition
AKA swallowing; is facilitated by the secretion of saliva and mucus and involves the mouth, pharynx, and esophagus.
87
What are the three stages of swallowing? Describe them:
1. Voluntary stage: the voluntary passage of the bolus into the oropharynx.
2. Pharyngeal stage: the involuntary passage of the bolus through the pharynx into the esophagus.
3. Esophageal stage: the involuntary passage of the bolus through the esophagus into the stomach.
88
Deglutition center
In the medulla oblongata and lower pons of the brain stem. Receives impulses from receptors in the oropharynx that the bolus stimulates. The impulses caused the soft palate and uvula to move upward to close off the nasopharynx, which prevents swallowed foods and liquids from entering the nasal cavity. In addition, the epiglottis closes off the opening to the larynx, which prevents the bolus from entering the rest of the respiratory tract. The bolus moves through the oropharynx and the laryngopharynx. Once the upper esophageal sphincter relaxes, the bolus moves into the esophagus.
89
Stomach
Mixing waves combine saliva, food, and gastric juice, which activates pepsin, initiates protein digestion, kills microbes in food, helps absorb vitamin B12, contracts the lower esophageal sphincter, increases stomach motility, relaxes the pyloric sphincter, and moves chyme into the small intestine.
90
What are the four main regions of the stomach?
1. Cardia
2. Fundus
3. Body
4. Pyloric part
91
What are the three regions of the pyloric part? Describe them:
1. Pyloric antrum
2. Pyloric canal
3. Pylorus
92
Rugae
Large folds.
93
What is the activity and result of the pyloric sphincter (valve)?
Activity: opens to permit passage of chyme into duodenum.
Result: regulates passage of chyme from stomach to duodenum; prevents backflow of chyme from duodenum to stomach.
94
Lesser curvature
The concave medial border of the stomach.
95
Greater curvature
The convex lateral border of the stomach.
96
From deep to superficial, what are the four layers of the stomach?
1. Mucosa
2. Submucosa
3. Muscularis
4. Serosa
97
What is the activity and result of the muscularis?
Activity: mixing waves (gentle peristaltic movements).
Result: churns and physically breaks down food and mixes it with gastric juice, forming chyme. Forces chyme through pyloric sphincter.
98
Surface mucosa cells
A layer of simple columnar epithelial cells found at the surface of the mucosa.
99
Gastric pits
Where secretions from several gastric glands flow into to enter the lumen of the stomach.
100
What three types of exocrine gland cells do gastric glands contain? Describe their activites and results:
1. Mucous neck cells:
Activity: secrete mucus.
Result: forms protective barrier that prevents digestion of stomach wall.
2. Chief cells (zymogenic cells):
Activity: secrete pepsinogen.
Result: pepsin (activated form) breaks down proteins into peptides.
Activity: secrete gastric lipase.
Result: splits triglycerides into fatty acids and monoglycerides.
3. Parietal cells:
Activity: secrete intrinsic factor.
Result: needed for absorption of vitamin B12 (used in red blood cell formation, or erythropoiesis).
Activity: secrete hydrochloric acid.
Result: kills microbes in food; denatures proteins; converts pepsinogen into pepsin.
101
Gastric juice
The secretions of the mucous, parietal, and chief cells. Totals 2000–3000 mL (roughly 2–3 qt) per day.
102
What is the activity and result of the G cell?
Activity: secrete gastrin.
Result: stimulates parietal cells to secrete HCl and chief cells to secrete pepsinogen; contracts lower esophageal sphincter, increases motility of stomach, and relaxes pyloric sphincter.
103
Propulsion
The process of each peristaltic wave moving gastric contents from the body of the stomach down into the antrum.
104
Retropulsion
The process of gastric contents being moved back into the body of the stomach. This process occurs because most food particles in the stomach initially are too large to fit through the narrow pyloric sphincter - it will repeat until the food particles are small enough to fit through the pyloric sphincter.
105
Chyme
A souply liquid made up of gastric contents mixed with gastric juice.
106
Gastric emptying
The process of gastric contents, now in the form of chyme, being passed through the pyloric sphincter. Is a slow process: only about 3 mL of chyme moves through the pyloric sphincter
at a time.
107
Proton pumps
Proton pumps that are powered by ATP actively transport H+ into the lumen while bringing potassium ions (K+) into the cell. At the same time, Cl− and K+ diffuse out into the lumen through Cl− and K+ channels in the apical membrane.
108
What three things can stimulate HCl secretion by parietal cells?
1. Acetylcholine (ACh) released by parasympathetic neurons.
2. Gastrin secreted by G cells.
3. Histamine, which is a paracrine substance released by mast cells in the nearby lamina propria.
109
What is the source, substrates, and products of pepsin?
Source: stomach chief cells.
Substrate: proteins.
Products: peptides.
110
Pepsinogen
An inactive form of pepsin. In this form, pepsin cannot digest the proteins in the chief cells that produce it. Pepsinogen is not converted into active pepsin until it comes in contact with hydrochloric acid secreted by parietal cells or active pepsin molecules. This keeps pepsin from digesting the protein in stomach cells along with the food.
111
What is the source, substrates, and products of gastric lipase?
Source: stomach chief cells.
Substrates: triglycerides (fats and oils).
Products: fatty acids and monoglycerides.
112
Pancreas
Pancreatic juice buffers acidic gastric juice in chyme, stops the action of pepsin from the stomach, creates the proper pH for digestion in the small intestine, and participates in the digestion of carbohydrates, proteins, triglycerides, and nucleic acids.
113
What three parts does the pancreas consist of?
1. Head
2. Body
3. Tail
114
Pancreatic duct (duct of Wirsung)
Convey secretions into the small intestine. The larger of the two ducts.
115
Hepatopancreatic ampulla (Ampulla of Vater)
A dilated common duct.
116
Major duodenal papilla
An elevation of the duodenal mucosa which lies about 10 cm (4 in.) inferior to the pyloric sphincter of the stomach.
117
Sphincter of the hepatopancreatic
ampulla (Sphincter of Oddi)
A mass of smooth muscle that regulates the passage of pancreatic juice and bile through the hepatopancreatic ampulla into the duodenum of the small intestine.
118
Accessory duct (duct of Santorini)
Leads from the pancreas and empties into the duodenum about 2.5 cm (1 in.) superior to the hepatopancreatic ampulla.
119
Acini
Clusters of glandular epithelial cells.
120
Pancreatic islets (islets of Langerhans)
Make up about ~1% of the acini. Form the endocrine portion of the pancreas. Secrete the hormones glucagon, insulin, somatostatin, and pancreatic polypeptide.
121
Pancreatic juice
A clear, colorless liquid consisting mostly of water, some salts, sodium bicarbonate, and several enzymes. Each day the pancreas produces 1200–1500 mL (about 1.2–1.5 qt) of
pancreatic juice.
122
What is the source, substrates, and products of pancreatic amylase?
Source: pancreatic acinar cells.
Substrates: starches (polysaccharides).
Products: maltose (disaccharide), maltotriose (trisaccharide), and α-dextrins.
123
What are the sources, substrates, and products of trypsin, chymotrypsin, carboxypeptidase, and elastase?
Source: pancreatic acinar cells.
Substrate: proteins.
Products: peptides.
124
What is the source, substrates, and products of pancreatic lipase?
Source: pancreatic acinar cells.
Substrates: triglycerides (fats and oils) that have been emulsified by bile salts.
Products: fatty acids and monoglycerides.
125
What is the source, substrates, and products of ribonuclease?
Source: pancreatic acinar cells.
Substrate: ribonucleic acid.
Products: nucleotides.
126
What is the source, substrates, and products of deoxyribonuclease?
Source: pancreatic acinar cells.
Substrate: deoxyribonucleic acid.
Products: nucleotides.
127
Trypsinogen
An inactive form of trypsin.
128
Trypsin inhibitor
A protein that combines with any trypsin formed accidentally in the pancreas or in pancreatic juice and blocks its enzymatic activity.
129
Enterokinase
An activating brush-border enzyme that splits off part of the trypsinogen molecule to form trypsin when the trypsinogen reaches the lumen of the small intestine.
130
Chymotrypsinogen
Inactive precursor of chymotrypsin.
131
Procarboxypeptidase
Inactive precursor of carboxypeptidase.
132
Proelastase
Inactive precursor of elastase.
133
Liver
Produces bile, which is required for the emulsification and absorption of lipids in the small intestine.
134
Gallbladder
Stores and concentrates bile and releases it into the small intestine.
135
What two principal lobes can the liver be divided into?
1. Right lobe (large)
2. Left lobe (small)
136
What two lobes is the right lobe believed to include?
1. Quadrate lobe (inferior)
2. Caudate lobe (posterior)
137
Ligamentum teres (Round ligament)
A remnant of the umbilical vein of the fetus; this fibrous cord extends from the liver to the umbilicus.
138
Coronary ligaments
Narrow extensions of the parietal peritoneum that suspend the liver from the diaphragm.
139
From inferior to superior, what are the three parts of the gall bladder?
1. Fundus
2. Body
3. Neck
140
What three parts is the liver histologically composed of?
1. Hepatocytes
2. Bile canaliculi
3. Hepatic sinusoids
141
Hepatocytes
The major functional cells of the liver and perform a wide array of metabolic, secretory, and endocrine functions. Are specialized epithelial cells with 5 to 12 sides that make up about 80% of the volume of the liver. Secrete bile.
142
Hepatic laminae
Complex three-dimensional arrangements formed by hepatocytes. Grooves in the cell membranes between neighboring hepatocytes provide spaces for canaliculi into which the hepatocytes secrete bile.
143
Bile canaliculi
Small ducts between hepatocytes that collect bile produced by the hepatocytes.
144
What is the route of bile from the bile canaliculi to the duodenum of the small intestine to participate in digestion?
Bile canaliculi -> bile ductules -> bile ducts -> left and right hepatic ducts -> common hepatic duct (which joins the cystic duct) -> common bile duct - > duodenum
145
Hepatic sinusoids
Highly permeable blood capillaries between rows of hepatocytes that receive oxygenated blood from branches of the hepatic artery and nutrient-rich deoxygenated blood from branches of the hepatic portal vein.
146
Stellate reticuloendothelial cells (hepatic macrophages)
Fixed phagocytes that destroy worn-out white and red blood cells, bacteria, and other foreign matter in the venous blood draining from the gastrointestinal tract.
147
Portal triad
Together, what a bile duct, branch of the hepatic artery, and branch of the hepatic vein are referred to as.
148
The hepatocytes, bile duct system, and hepatic sinusoids can be organized into anatomical and functional units in three different ways. What are they? Identify them:
1. Hepatic lobule
2. Portal lobule
3. Hepatic acinus (model most accepted today)
149
Cystic duct
Where the contents of the gallbladder get ejected into when the smooth muscle fibers of the gallbladder contract.
150
What two sources does the liver receive blood from?
1. Hepatic artery (receives oxygenated blood)
2. Hepatic portal vein (receives deoxygenated blood)
151
What is the route of hepatic blood flow (path through the liver and return to the heart)
Oxygenated blood from the hepatic artery + nutrient-rich, deoxygenated blood from the hepatic portal vein -> hepatic sinusoids -> central vein -> hepatic vein -> inferior vena cava -> right atrium of the heart
152
Bile
Yellow, brownish, or olive-green liquid. Consists mostly of water, bile salts, cholesterol, a phospholipid called lecithin, bile pigments, and several ions. Secreted by hepatocytes (800–1000 mL (about 1 qt) of bile per day).
153
Bilirubin
Principal bile pigment. Derived from the heme of red blood cells (RBCs).
154
Stercobilin
A product of bilirubin when it is broken down in the intestine. Gives feces its normal brown color.
155
Emulsification
The breakdown of large lipid globules into a suspension of small lipid globules. Carried out by bile salts (sodium salts and potassium salts of bile acids).
156
In addition to secreting bile, which is needed for absorption of dietary fats, the liver performs nine other vital functions. What are they?
1. Carbohydrate metabolism
2. Lipid metabolism
3. Protein metabolism
4. Processing of drugs and hormones
5. Excretion of bilirubin
6. Synthesis of bile salts
7. Storage
8. Phagocytosis
9. Activation of vitamin D
157
Small intestine
Segmentation mixes chyme with digestive juices; peristalsis propels chyme toward the ileocecal sphincter; digestive secretions from the small intestine, pancreas, and liver complete the digestion of carbohydrates, proteins, lipids, and nucleic acids; circular folds, villi, and microvilli help absorb about 90% of digested nutrients.
158
What three regions can the small intestine be divided into?
1. Duodenum
2. Jejunum
3. Ileum
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Ileocecal sphincter
A smooth muscle sphincter where the ileum joins the large intestine.
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From deep to superficial, what are the four layers of the small intestine?
1. Mucosa
2. Submucosa
3. Muscularis
4. Serosa
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Absorptive cells
Digest and absorb nutrients.
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Goblet cells
Secrete mucus.
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Intestinal glands (Crypts of Lieberkuhn)
Secrete intestinal juice to assist absorption.
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Paneth cells
Secrete lysozyme (bactericidal enzyme), and phagocytosis.
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Enteroendocrine cells (S, CCK, K)
Secrete secretin, cholecystokinin, and glucose-dependent insulinotropic peptide.
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Solitary lymphatic nodules
Most numerous in the distal part of the ileum.
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Aggregated lymphatic follicles (Peyer's patches)
Groups of lymphatic nodules. Present in the ileum.
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Duodenal glands (Brunner's glands)
Secrete alkaline fluid to buffer stomach acids and mucus for protection and lubrication.
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Circular folds (Plicae circulares)
Folds of mucosa and submucosa that increase surface area for digestion and absorption.
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Villi
Fingerlike projections of mucosa that are sites of absorption of digested food and increase surface area for digestion
and absorption.
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Lacteal
A lymphatic capillary which absorbed nutrients can pass through to enter blood or lymph. Found in villi.
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Microvilli
Microscopic, membrane-covered projections of absorptive epithelial cells that contain brush-border enzymes and that increase surface area for digestion and absorption.
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Brush border
A fuzzy line formed by microvilli that extend into the lumen of the small intestine. Can be seen when looking through a light microscope - can see this rather than individual microvilli because they are too small to be seen individually. Also contain several brush-border enzymes that have digestive functions.
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Intestinal juice
A clear yellow fluid secreted by the small intestine, that contains water and mucus. Together, pancreatic and intestinal juices provide a liquid medium that aids the absorption of substances from chyme in the small intestine.
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Brush-border enzymes
Enzymes in microvilli of the plasma membrane. Include four carbohydrate-digesting enzymes called α-dextrinase, maltase, sucrase, and lactase; protein digesting enzymes called peptidases (aminopeptidase and dipeptidase); and two types of nucleotide-digesting enzymes, nucleosidases and phosphatases.
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What is the source, substrates, and products of α-Dextrinase?
Source: small intestine.
Substrates: α-Dextrins.
Products: glucose.
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What is the source, substrates, and products of maltase?
Source: small intestine.
Substrates: maltose.
Products: glucose.
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What is the source, substrates, and products of sucrase?
Source: small intestine.
Substrates: sucrose.
Products: glucose and fructose.
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What is the source, substrates, and products of lactase?
Source: small intestine.
Substrates: lactose.
Products: glucose and galactose.
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What is the source, substrates, and products of enterokinase?
Source: small intestine.
Substrates: trypsinogen.
Products: trypsin.
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What is the source, substrates, and products of aminopeptidase?
Source: small intestine.
Substrates: amino acid at amino end of peptides.
Products: amino acids and peptides.
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What is the source, substrates, and products of dipeptidase?
Source: small intestine.
Substrates: dipeptides.
Products: amino acids.
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What is the source, substrates, and products of nucleosidases and phosphatases?
Source: small intestine.
Substrates: nucleotides.
Products: nitrogenous bases, pentoses, and phosphates.
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What are the two main type of movements of the small intestine? Describe them:
1. Segmentation: type of peristalsis; alternating contractions of circular smooth muscle fibers that produce segmentation and resegmentation of sections of small intestine; mixes chyme with digestive juices and brings food into contact with mucosa for absorption.
2. Migration motility complex (MMC): type of peristalsis; waves of contraction and relaxation of circular and longitudinal smooth muscle fibers passing the length of the small intestine; moves chyme toward ileocecal sphincter.
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Lipases
Enzymes that split triglycerides and phospholipids.
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Why are bile salts said to be amphipathic?
Because each bile salt has a hydrophobic (nonpolar) region and a hydrophilic (polar) region.
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Micelles
Tiny spheres formed by bile salts that surround large short-chain fatty acids, long-chain fatty acids, monoglycerides, and other large hydrophobic molecules. Surround them to make them more soluble. Act as ferry's and transport large short-chain fatty acids, long-chain fatty acids, monoglycerides, and other large hydrophobic molecules from the interior of the small intestinal lumen to the brush border of the absorptive cells.
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Chylomicrons
Large spherical masses made from long-chain fatty acids and monoglycerides that have recombined to form triglycerides once inside the absorptive cells. Leave the absorptive cells via exocytosis.
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Lipoprotein lipase
An enzyme that is attached to the apical surface of capillary endothelial cells that breaks down triglycerides in chylomicrons and other lipoproteins into fatty acids and glycerol.
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Enterohepatic circulation
The cycle of bile salt secretion by hepatocytes into bile, reabsorption by the ileum, and resecretion into bile.
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Large intestine
Haustral churning, peristalsis, and mass peristalsis drive the colonic contents into the rectum; bacteria produce some B vitamins and vitamin K; absorption of some water, ions, and vitamins occurs; defecation.
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What are the four main regions of the large intestine?
1. Cecum
2. Colon
3. Rectum
4. Anal canal
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Appendix (vermiform appendix)
A twisted, coiled tube, measuring about 8 cm (3 in.) in length.
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Mesoappendix
The mesentery of the appendix that attaches the appendix to the inferior part of the mesentery of the ileum.
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What four parts does the colon divide into?
1. Ascending colon
2. Transverse colon
3. Descending colon
4. Sigmoid colon
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Right colic (hepatic) flexure
Formed by the ascending colon.
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Left colic (splenic) flexure
Formed by the transverse colon
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Anal columns
Longitudinal folds containing networks of arteries and veins that makes up the mucous membrane of the anal canal.
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Anus
Opening of the anal canal to the exterior.
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What two structures guard the anus and keep it closed except during the elimination of feces? What kind of muscle are they?
1. Internal anal sphincter: smooth muscle (involuntary)
2. External anal sphincter: skeletal muscle (voluntary)
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From deep to superficial, what are the four layers of the large intestine? What kind of tissue does each consist of?
1. Mucosa: consists of simple columnar epithelium, lamina propria (areolar connective tissue), and muscularis mucosae (smooth muscle).
2. Submucosa: consists of areolar connective tissue.
3. Muscularis: consists of an external layer of longitudinal smooth muscle and an internal layer of circular smooth muscle.
4. Serosa
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What two kinds of cells does the epithelium of the mucosa contain? Why are they important?
The epithelium contains mostly absorptive and goblet cells. The absorptive cells function primarily in water absorption; the goblet cells secrete mucus that lubricates the passage of the colonic contents.
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Teniae coli
Three conspicuous bands that run most of the length of the large intestine.
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Haustra
Pouches of the colon. Formed by tonic contractions of the teniae coli.
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Omental (fatty) appendices
Small pouches of visceral peritoneum filled with fat that are attached to teniae coli.
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Gastroileal reflex
Immediately after a meal, this reflex intensifies peristalsis in the ileum and forces any chyme into the cecum. The hormone gastrin also relaxes the sphincter. Whenever the cecum is distended, the degree of contraction of the ileocecal sphincter intensifies.
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Gastrocolic reflex
This reflex within the colon initiates mass peristalsis, which usually takes place three or four times a day, during or immediately after a meal. This reflex is initiated by food in the stomach.
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Flatulence
Excessive flatus (gas) in the colon.
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Feces
Consists of water, inorganic salts, sloughed-off epithelial cells from the mucosa of the gastrointestinal tract, bacteria, products of bacterial decomposition, unabsorbed digested materials, and indigestible parts of food.
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What is the activity of the lumen of the large intestine and its function(s)?
Activity: bacterial activity.
Function(s): breaks down undigested carbohydrates, proteins, and amino acids into products that can be expelled in feces or absorbed and detoxified by liver; synthesizes certain B vitamins and vitamin K.
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What is the activity of the mucosa of the large intestine and its function(s)?
Activity: secretes mucus.
Function(s): lubricates colon; protects mucosa.
Activity: absorption.
Function(s): water absorption solidifies feces and contributes to body’s water balance; solutes absorbed include ions and some vitamins.
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What is the activity of the muscularis of the large intestine and its function(s)?
Activity: haustral churning.
Function(s): moves contents from haustrum to haustrum by muscular contractions.
Activity: peristalsis.
Function(s): moves contents along length of colon by contractions of circular and longitudinal muscles.
Activity: mass peristalsis.
Function(s): forces contents into sigmoid colon and rectum.
Activity: defecation reflex.
Function(s): eliminates feces by contractions in sigmoid colon and rectum.
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What are the three phages of digestion? Describe them:
1. Cephalic phase: the smell, sight, thought, or initial taste of food activates neural centers in the cerebral cortex, hypothalamus, and brain stem. The brain stem then activates the facial (VII), glossopharyngeal (IX), and vagus (X) nerves. The facial and glossopharyngeal nerves stimulate the salivary glands to secrete saliva, while the vagus nerves stimulate the gastric glands to secrete gastric juice. The purpose of the cephalic phase of digestion is to prepare the mouth and stomach for food that is about to be eaten.
2. Gastric phase: begins once food reaches the stomach. Neural and hormonal mechanisms regulate this phase to promote gastric secretion and gastric motility.
3. Intestinal phase: begins once food enters the small intestine. Reflexes in this phase have inhibitory effects that slow the exit of chyme from the stomach. This prevents the duodenum from being overloaded with more chyme than it can handle. In addition, responses occurring during this phase promote the continued digestion of foods that have reached the small intestine. The activities of this phase of digestion are regulated by neural and hormonal mechanisms.
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What is the stimulus and site of secretion and actions of gastrin?
Stimulus and site of secretion: distension of stomach, partially digested proteins and caffeine in stomach, and high pH of stomach chyme stimulate gastrin secretion by enteroendocrine G cells, located mainly in mucosa of pyloric antrum of stomach.
Actions:
Major effects: promotes secretion of gastric juice, increases gastric motility, promotes growth of gastric mucosa.
Minor effects: constricts lower esophageal sphincter, relaxes pyloric sphincter.
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Enterogastric reflex
Initiated by the presence of chyme which causes distension of the duodenum.
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What is the stimulus and site of secretion and actions of secretin?
Stimulus and site of secretion: acidic (high H+ level) chyme that enters small intestine stimulates secretion of secretin by enteroendocrine S cells in the mucosa of duodenum.
Actions:
Major effects: Stimulates secretion of pancreatic juice and bile that are rich in HCO3 − (bicarbonate ions).
Minor effects: Inhibits secretion of gastric juice, promotes normal growth and maintenance of pancreas, enhances effects of CCK.
