Lesson 15-17 - Digestive System Flashcards
(460 cards)
1
Q
digestive system
A
organ system that processes food, extracts nutrients, and eliminates residue
2
Q
five stages of digestion
A
- ingestion
- digestion
- absorption
- compaction
- defecation
3
Q
five stages of digestion: ingestion
A
selective intake of food
4
Q
five stages of digestion: digestion
A
mechanical and chemical breakdown of food into a form usable by the body
5
Q
five stages of digestion: absorption
A
uptake of nutrient molecules into the epithelial cells of the digestive tract and then into blood and lymph
6
Q
five stages of digestion: compaction
A
absorbing water and consolidating the indigestible residue into feces
7
Q
five stages of digestion: defecation
A
elimination of feces
8
Q
mechanical digestion
A
the physical breakdown of food into smaller particles
9
Q
three processes of mechanical digestion
A
- cutting and grinding action of the teeth
- churning action of the stomach and small intestines
- the above exposes more food surface to digestive enzymes
10
Q
chemical digestion
A
a series of hydrolysis reactions that breaks dietary macromolecules into their monomers
11
Q
how is chemical digestion carried out?
A
by digestive enzymes produced by salivary glands, stomach, pancreas, and the small intestine
12
Q
digestive enzymes break down polysaccharides into…
A
monosaccharides
13
Q
digestive enzymes break down proteins into…
A
amino acids
14
Q
digestive enzymes break down fats into…
A
monoglycerides and fatty acids
15
Q
digestive enzymes break down nucleic acids into…
A
nucleotides
16
Q
what happens to nutrients that are already in usable forms?
A
the are directly absorbed without being digested
17
Q
nutrients that can be directly absorbed (5)
A
- vitamins
- amino acids
- minerals
- cholesterol
- water
18
Q
the digestive system has two subdivisions
A
- digestive (alimentary) tract
- accessory organs
19
Q
the digestive tract includes these structures (6)
A
mouth, pharynx, esophagus, stomach, small intestine, large intestine
20
Q
the gastrointestinal tract refers to…(2)
A
the stomach and intestines
21
Q
accessory organs of the digestive system include (6)
A
teeth, tongue, salivary glands, liver, gallbladder, and pancreas
22
Q
four layers of the digestive tract
A
- mucosa
- submucosa
- muscularis externa
- serosa
23
Q
four layers of the digestive tract: mucosa (3)
A
the innermost layer comprised of epithelium, lamina propria, and muscularis mucosae
24
Q
four layers of the digestive tract: muscularis externa (2)
A
an inner circular layer and outer longitudinal layer of smooth muscle
25
the epithelial layer of the digestive mucosa consists mostly of what cell type?
simple columnar
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in the epithelial layer of the mouth through the esophagus and in the lower anal canal, what cell type is there?
stratified squamous
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lamina propria of the digestive tract
a loose connective tissue layer found between the epithelium and muscularis mucosae
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muscularis mucosae
a thin layer of smooth muscle that tenses the mucosa, creating grooves and ridges that enhance surface area contact with food
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what is the purpose of the muscularis mucosae?
it improves the efficiency of digestion and nutrient absorption
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mucosa-associated lymphatic tissue (MALT)
lymphocytes and lymph nodules of the digestive tract
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submucosa
thick layer of loose connective tissue
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the MALT extends into the _____ in some parts of the GI tract
submucosae
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the submucosa contains...(3)
- blood vessels
- lymphatic vessels
- a nerve plexus
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in some places of the submucosa, there are _____-_____ glands that dump lubricating _____ into the lumen
mucus-secreting, mucus
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in some places, which layer of the muscularis externa thickens to form valves (sphincters)? what do they do?
inner circular smooth muscles; regulate the passage of material through the tract
36
what is responsible for the motility that propels food and residue through the digestive tract?
the muscularis externa
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the serosa is composed of...(2)
a thin layer of areolar tissue topped by simple squamous mesothelium
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where does the serosa being? where does it end?
beings 3-4cm of the esophagus and ends just before the rectum
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some organs have no serosa but are surrounded by the _____
adventitia
40
adventitia
fibrous connective tissue layer that binds and blends adjacent organs
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where can you find the adventitia? (3)
the pharynx, most of the esophagus, and the rectum
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enteric plexus
nervous network that regulated digestive tract motility, secretion, and blood flow
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where is the enteric plexus? (3)
- esophagus
- stomach
- intestines
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the enteric plexus can/cannot function independently of the CNS
can; but the CNS usually exerts influence on its action
45
the enteric plexus is composed of two neuronal networks
1. submucosal plexus
2. myenteric plexus
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submucosal plexus (2)
controls glandular secretions of the mucosa, and movements of the muscularis mucosae
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where is the submucosal plexus found?
submucosa
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myenteric plexus
ganglia and nerve fibers that control peristalsis and other contractions of the muscularis externa
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where is the myenteric plexus found?
between the two layers of the muscularis externa
50
the enteric plexus includes sensory neurons that monitor...
tension in the gut wall and conditions in the lumen
51
the enteric plexus is often considered part of what section of the nervous system?
autonomic nervous system
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mesentery
connective tissue sheet that suspends the stomach and intestines from the abdominal wall
53
the looseness of the mesentery allows for...
the stomach and intestines to undergo strenuous contractions with freedom of movement in the abdominal cavity
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the mesentery prevents the intestines from...
becoming twisted and tangled by changes in body position and by its own contractions
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the mesentery holds...
the viscera in proper relationship to each other
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the mesentery provides a passage for...
blood vessels and nerves that supply the digestive tract
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the mesentery contains many....(2)
lymph nodes and lymphatic vessels
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depending on their relationship to the mesentery, digestive organs are...(3)
intraperitoneal or retroperitoneal
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intraperitoneal
when and organ is enclosed by mesentery (serosa) on all sides
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portions of the digestive tract that are intraperitoneal (8)
- stomach
- liver
- jejunum
- ileum
- appendix
- cecum
- transverse colon
- sigmoid colon
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retroperitoneal
when an organ lies against the posterior body wall and is covered by peritoneum on its anterior side only
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retroperitoneal organs are considered to be...
outside the peritoneal cavity
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retroperitoneal organs of the digestive tract (5)
- duodenum
- pancreas
- ascending colon
- descending colon
- rectum
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motility and secretion of the digestive tract are controlled by....(3)
neural, hormonal, and paracrine mechanisms
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neural controls over the digestive tract (2)
- short (myenteric) reflexes
- long (vagovagal) reflexes
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short (myenteric) reflexes (2)
- stretch or chemical stimulation acts through the myenteric
- stimulated peristaltic contractions of swallowingl
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long (vagovagal) reflexes
- parasympathetic stimulation of digestive motility and secretion
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examples of hormones that stimulate the digestive tract (2)
gastrin and secretin
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hormones secreted into the blood stimulate _____ parts of the digestive tract
distant
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paracrine secretions stimulate _____ target cells
nearby
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the mouth is also known by these two other names
- oral cavity
- buccal cavity
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functions of the mouth (7)
- ingestion
- taste/other sensory responses to food
- chewing/chemical digestion
- swallowing
- speech
- respiration
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functions of the cheeks and lips of the mouth (3)
- retain food and push it between teeth
- involved in speech
- essential for sucking and blowing actions (including suckling for infants)
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tongue
muscular, bulky, but agile and sensitive organ
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functions of the tongue (2)
- manipulates food between teeth
- senses taste and texture of food
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lingual papillae of the tongue
bumps and projections that are the sites of most taste buds
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body of the tongue
anterior two-thirds of the tongue
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what portion of the tongue occupies the oral cavity?
the body
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root of the tongue
posterior third of the tongue
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what portion of the tongue occupies the oropharynx?
the root
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vallate papillae
a V-shaped row of papillae that mark the boundary between the body and root of the tongue
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intrinsic muscles of the tongue
produce subtle tongue movements of speech
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where are intrinsic muscles of the tongue found?
contained entirely within the tongue
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extrinsic muscles of the tongue
produce stronger movements of food manipulation
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lingual glands (2)
serous and mucous glands within the tongue; secrete a portion of the saliva
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where are extrinsic muscles of the tongue found?
with attachments outside the tongue
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where are lingual glands of the tongue found?
amid the extrinsic muscles
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lingual tonsils of the tongue are located...
contained in the root
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palate
separates the oral cavity from the nasal cavity
90
what makes it possible to breathe while chewing food?
the palate
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hard (bony) palate
anterior portion that is supported by the palatine processes of the maxillae and the palatine bones
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the hard palate has....
palatine rugae
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palatine rugae
transverse ridges that help the tongue hold and manipulate food
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soft palate
posterior to the hard palate with more spongy texture
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uvula
concial medial projection visible at the rear of the mouth
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function of the uvula
helps retain food in the mouth until one is ready to swallow
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the 32 adult teeth are referred to as...
dentition
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functions of the dentition (3)
- break down food into smaller pieces
- make food easier to swallow
- expose more surface area for enzymes (speeding chemicial digestion)
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mastication
chewing
100
what is the first step in mechanical digestion?
mastication
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function of mastication (2)
breaks food into smaller pieces to be swallowed and expose more surface area to digestive enzymes
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food within the mouth stimulates...
oral receptors that trigger an involuntary chewing reflex
103
what muscles elevate the lower teeth to crush food? (2)
- masseter
- temporalis
104
functions of saliva (6)
1. moistens mouth
2. begins starch and fat digestion
3. cleanses teeth
4. inhibits bacterial growth
5. dissolves molecules so they can stimulate taste buds
6. mositens foods and binds it together into a soft mass (bolus) to aid in swallowing
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saliva contains the following solutes (6)
- mucus
- electrolytes
- lysozyme
- IgA
- salivary amylase
- lingual lipase
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electrolytes found in saliva (5)
- Na+
- K+
- Cl-
- phosphate
- bicarbonate
107
what enzyme begins starch digestion in the mouth?
salivary amylase
108
what enzyme begins fat digestion in the mouth? (but mainly after the food is swallowed)
lingual lipase
109
two kinds of salivary glands
- intrinsic (minor) salivary glands
- extrinsic (major) salivary glands
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intrinsic (minro) salivary glands
small glands dispersed amid other oral tissues that secrete saliva at a constant rate
111
extrinsic (major) salivary glands
three pairs of larger, more discrete organs connected to the oral cavity but ducts
112
the extrinsic salivary glands include...(3)
- parotid glands
- submandibular glands
- sublingual glands
113
where are the parotid glands located?
located beneath the skin anterior to the earlobe
114
where are the submandibular glands located?
located halfway along the body of the mandible
115
where are the sublingual glands located?
located in the floor of the mouth
116
the sublingual gland has multiple...
ducts that empty posterior to the papilla of the submandibular duct
117
about how much saliva do extrinsic salivary glands secrete in one day?
1-1.5L
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the salivary nuclei in the _____ _____ and _____ respond to signals generated by the presence of food
medulla oblongata, pons
119
the salivary nuclei are excited by...(3)
tactile, pressure, and taste receptors
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these three things can stimulate salivation
odor, site, or thought of food
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how does the salivary nuclei send signals to glands?
by way of the autonomic fibers in the facial and glossopharyngeal nerves
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parasympathetic fibers stimulate salivary glands to produce...
an abundance of thin, enzyme rich saliva
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sympathetic fibers stimulate salivary glands to produce...
less, and thicker, saliva with more mucus
124
pharynx
muscular funnel connecting the oral cavity to the esophagus and the nasal cavity to the larynx
125
where do the digestive and respiratory tracts intersect?
the pharynx
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the pharynx has a deep layer of...
longitudinal skeletal muscle
127
the pharynx has a superficial layer of circular skeletal muscles that form?
pharyngeal constrictors (superior, middle, and inferior)
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what do the pharyngeal constrictors do?
force food downward during swallowing
129
upper esophageal sphincter
the inferior pharyngeal constrictor that excludes air from the esophagus
130
esophagus
straight muscular tube between the pharynx and the stomach
131
the esophagus extends from...
the pharynx to the cardiac orifice of the stomach before passing through the esophageal hiatus in the diaphragm
132
the lower esophageal sphincter is located..
at the inferior end of the esophagus
133
function of the lower esophageal sphincter (2)
- prevents stomach contents from regurgitating into the esophagus
- protects esophageal mucosa from erosive stomach acid
134
heartburn
burning sensation produced by acid reflux into the esophagus
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deglutition
swallowing
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deglutition is...
a complex action involving over 22 muscles in the mouth, pharynx, and esophagus
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deglutition is coordinated by the...
swallowing center
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swallowing center
a pair of nuclei in the medulla oblongata
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the swallowing center communicated with...
muscles of the pharynx and esophagus
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swallowing occurs in three phases
1. oral phase
2. pharyngeal phase
3. esophageal phase
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swallowing: oral phase
the tongue forms a food bolus and pushes it into the laryngopharynx
142
where in the mouth does the food bolus accumulate?
in the oropharynx in front of the epiglottis
143
during the oral phase of swallowing, what happens with the epiglottis?
it tips posteriorly and the food bolus slides around it and into the laryngopharynx
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swallowing: pharyngeal phase
the palate, tongue, vocal cords, and epiglottis block the oral and nasal cavities and airway while the pharyngeal constrictors push the colus into the esophagus
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swallowing: esophageal phase
peristalsis drives the bolus downward and relaxation of the lower esophageal sphincter admits it into the stomach
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how does peristalsis move the food bolus down the esophagus?
circular muscles constricts above the bolus and relaxes below it
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what happens to food when you swallow when upright?
food and liquid drops through the esophagus by gravity faster than peristalsis can keep up with it
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explain what movements occur during the pharyngeal phase of swallowing (3)
- muscle pull larynx to epiglottis and cover it
- vocal cords adduct/close to stop breathing
- the upper esophagus widens
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esophageal peristalsis is controlled by...(2)
the swallowing center and the myenteric plexus
150
stomach
a muscular sac in the superior left abdominal cavity immediately inferior to the diaphragm
151
what is the primary function of the stomach?
a food storage organ
152
chyme
acidic, soupy mixture of semi-digested food that passes on to the small intestine
153
other functions of the stomach (3)
- mechanically breaks up food particles
- liquifies the food
- begins chemical digestion of proteins and fat
154
four portions of the stomach
- cardiac part
- fundic region (fundus)
- body
- pyloric part
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stomach regions: cardiac part (2)
- small area within about 3cm of the cardiac orifice
- entry point of material from esophagus
156
stomach regions: fundic region (fundus)
dome superior to the esophageal attachment
157
stomach regions: body
makes up the greatest part distal to the cardiac orifice
158
stomach regions: pyloric part
narrower pouch at the inferior end
159
the pyloric part of the stomach is subdivided into... (3)
- funnel-like atrium
- narrower pyloric canal
- terminating at the pylorus
160
pylorus
narrow passage to duodenum
161
pyloric sphincter
ring of smooth muscle around the pylorus
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function of the pyloric sphincter
regulates the passage of chyme into the duodenum
163
the stomach mucosa is covered with what cell type?
simple columnar epithelium
164
the apical regions of the stomach mucosa cells are filled with _____
mucin
165
mucin
swells with water and becomes mucus after it has been secreted
166
when the stomach is empty, the mucosa and submucosa form longitudinal wrinkles called _____ _____
gastric rugae
167
the muscularis externa of the stomach has three layers
- outer longitudinal layer
- middle circular layer
- inner oblique layer
168
mucous cells
secrete mucus
169
regenerative (stem) cells
divide rapidly and produce continual supply of new cells to replace cells that die
170
parietal cells (3)
secrete hydrochloric acid (HCl), intrinsic factor, and ghrelin during hunger
171
chief cells
secrete gastrin and pepsinogen
172
enteroendocrine cells
secrete hormones and paracrine messengers that regulate digestion
173
which glandular cell is most common?
chief cells
174
gastric pits
depressions in gastric mucosa, lined with the same columnar epithelium as the surface
175
gastric juice (3)
mainly a mixture of water, hydrochloric acid, and pepsin
176
how much gastric juice is produced per day?
2-3 L
177
functions of hydrochloric acid (3)
- activates pepsin and lingual lipase
- breaks up connective tissues and plant cell walls helping to liquify food and form chyme
- contributes to innate immunity by destroying most ingested pathogens
178
pepsin
digests dietary protein into shorter peptides
179
pepsin is released by _____ cells as the inactive form _____
chief, pepsinogen
180
zymogen
inactive until removal of some amino acids causes it to become active
181
hydrochloric acid from _____ cells converts pepsinogen to pepsin
parietal
182
autocatalytic effect of pepsin
as some pepsin is formed, it converts more pepsinogen into more pepsin
183
where is protein digestion started? where is it finished?
started in the stomach and completed in the small intestine
184
what two enzymes play a minor role in digesting dietary fats?
gastric and lingual lipase
185
where is the digestion of fat completed?
the small intestine
186
gastric lipase is secreted by _____ cells
chief
187
intrinsic factor
a glycoprotein secreted by parietal cells
188
what is essential to absorption of vitamin B12 by the small intestine?
intrinsic factor
189
how does intrinsic factor contribute to B12 absorption?
it bind to B12 and then intestinal cells absorb this complex by receptor mediated endocytosis
190
vitamin B12 is needed to synthesize _____
hemoglobin
191
vitamin b12 deficiency causes what kind of anemia?
pernicious anemia
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what is the only indispensable function of the stomach?
secretion of intrinsic factor
193
_____ and _____ glands have a variety of cells that produce a variety of chemical messengers
gastric and pyloric
194
gut-brain peptides include...(6)
- substance P
- vasoactive intestinal peptide (VIP)
- secretin
- gastric inhibitory peptide (GIP)
- cholecystokinin
- neuropeptide Y (NPY)
195
during swallowing, food stimulates...
mechanoreceptors in the pharynx and they transmit signals to the medulla
196
the swallowing center of the _____ _____ signals the stomach to _____
medulla oblongata, relax
197
the vagus nerve relays messages from the medulla and activates....
the receptive-relaxation response in the stomach
198
receptive-relaxation response
the stomach resists stretching briefly but relaxes it to hold more food
199
the stomach will show a rhythm of peristaltic contractions controlled by...
enteric pacemaker cells
200
where are the enteric pacemaker cells of the stomach found?
the longitudinal layer of muscularis externa
201
describe peristalsis of the stomach (3)
- a ring of constriction every 20 seconds
- becomes stronger at the pyloric part
- eventually very strong after 30 minutes
202
what acts as a strong pump that breaks up semi digested food and prepares it for the intestine?
thick muscularis of the antrum
203
_____ _____ come in waves that churn and break up the chyme into small particles
antral contractions
204
why is only 3ml of chyme released into the duodenum? (2)
- neutralize the stomach acid
- digest nutrients little by little
205
what happens if the duodenum is overfilled?
it inhibits gastric motility
206
a typical meal is emptied from the stomach in...
in 4 hours
207
vomiting
forceful ejection of stomach and intestinal contents from the mouth
208
vomiting is usually preceded by...(2)
nausea and retching
209
mechanical process of vomiting
thoracic expansion and abdominal contraction creating a pressure difference that dilates the esophagus and forces open the upper esophageal sphincter
210
vomiting involves the _____ center in the _____ _____
emetic; medulla oblongata
211
how does the emetic center function in vomiting?
integrates strong abdominal contractions combined with reverse peristalsis of gastric antrum and duodenum
212
vomiting is induced by...(4)
- overstretching of the stomach or duodenum
- chemical irritants such as alcohol and bacterial toxins
- visceral trauma
- intense pain or physiological and sensory stimuli
213
_____ and _____ enzymes partially digest protein and lesser amounts of starch and fat in the stomach
salivary, gastric
214
most digestion and nearly all absorption occur after...
the chyme has passed into the small intestine
215
the _____ does not absorb any significant amount of nutrients
stomach
216
the stomach does absorb...(2)
aspirin and some lipid-soluble drugs
217
alcohol is absorbed mainly by the...
small intestine
218
the stomach is protected in three ways from harsh acidic and enzymatic environment
1. mucous coat
2. tight junctions
3. epithelial cell replacement
219
stomach: mucous coat
thick, highly alkaline mucus resists action of acid and enzymes
220
stomach: tight junctions
between epithelial cells prevent gastric juice from seeping between them and digesting deeper tissue
221
stomach: epithelial cell replacement
- sloughed off into the chyme and digested with food
- replaced rapidly by cell division in gastric pits
222
cells of the stomach epithelial live only...
3-6 days
223
breakdown of the protective layers of the stomach can result in...
inflammation and peptic ulcers
224
gastritis
inflammation of the stomach
225
gastritis can lead to peptic ulcers as...
pepsin and hydrochloric acid erodes the stomach wall
226
most ulcers are caused by...
Helicobacter pylori
227
how can Helicobacter pylori be treated? (2)
antibiotics and pepto-bismol
228
risk factors for stomach ulcers (4)
- psychological stress
- hypersecretion of acid, pepsin sometimes involved
- smoking
- using of aspirin and other NSAIDs
229
gastric secretion and motility is regulated by...
nervous and endocrine systems
230
gastric activity is divided into three phases
1. cephalic phase
2. gastric phase
3. intestinal phase
231
gastric activity: cephalic phase
stomach being controlled by brain
232
gastric activity: gastric phase
stomach controlling itself
233
gastric activity: intestinal phase
stomach being controlled by small intestine
234
in the cephalic phase, the stomach responds to...(4)
sight, smell, taste, or thought of food
235
in the cephalic phase, sensory and mental inputs converge on the _____
hypothalamus
236
in the cephalic phase, the hypothalamus relays signals to...
medulla oblongata
237
_____ nerve fibers from the medulla stimulate the _____ nervous system of the stomach, stimulating gastric secretion
vagus, enteric
238
40% of the stomach's acid secretion occurs when?
the cephalic phase
239
the gastric phase is the period in which...
swallowed food and semi-digested protein activate gastric activity
240
two-thirds of gastric secretion and one half of acid secretion occurs in this phase
gastric phase
241
ingested food stimulates gastric activity in two ways
1. stretching the stomach
2. increasing the pH of the stomach lumen
242
ingested food stimulation: stretching the stomach (2)
- activates the short reflex mediated through the myenteric plexus
- activates long reflex mediated through the vagus nerves and the brainstem
243
gastric secretion by stimulated by three chemicals
1. acetylcholine
2. histamine
3. gastrin
244
acetylcholine is secreted by....
parasympathetic nerve fibers of both reflexes
245
histamine is a _____ secretion from _____ cells in the gastric glands
paracrine, enteroendocrine
246
gastrin is a hormone produced by the enteroendocrine _____ cells in _____ glands
G, pyloric
247
acetylcholine, histamine, and gastrin all stimulate _____ cells to secrete _____ and _____ _____
parietal, HCl, intrinsic factor
248
_____ and _____ stimulate chief cells to secrete pepsinogen
gastrin, ACh
249
in the intestinal phase, the duodenum responds...
responds to arriving chyme and moderates gastric activity through hormones and nervous reflexes
250
stretching of the duodenum does what?
accentuates vagovagal reflex that stimulates the stomach
251
in the intestinal phase, peptides and amino acids in chyme stimulate _____ cells of the _____ to secrete _____ _____, further stimulating the stomach
G, duodenum, intestinal gastrin
252
in the intestinal phase, acids and fats trigger the _______ reflex
enterogastric
253
enterogastric reflex
duodenum sends inhibitory signals to the stomach by way of enteric nervous system
254
in the intestinal phase, the duodenum also signals the _____ to inhibit _____ _____
medulla; vagal nuclei
255
inhibiting vagal nuclei...
reducing vagal stimulation of the stomach
256
in the intestinal phase, the duodenum stimulates _____ neurons to _____ stomach activity
sympathetic; slow
257
sympathetic neurons send _____ signals to the stomach
inhibitory
258
in the intestinal phase, chyme also stimulates _____ _____ cells to release the hormones _____ and _____
duodenal enteroendocrine, secretin, cholecystokinin
259
secretin and cholecystokinin stimulate the pancreas to release....
pancreatic fluid and gallbladder to release bile, but suppress gastric secretion
260
as gastric secretion declines, the pyloric sphincter...
contacts tightly to limit chyme entering duodenum
261
enteroendocrine cells also secrete _____-_____ _____ _____ (GIP)
glucose-dependent insulinotropic peptide (GIP)
262
what does glucose-dependent insulinotropic peptide (GIP) do?
stimulates insulin secretion in preparation for processing nutrients about to be absorbed by small intestine
263
liver
reddish-brown gland located immediately inferior to the diaphragm
264
what is the body's largest gland?
liver
265
what is the one function of the liver contributes to digestion?
the secretion of bile
266
where does the gallbladder adhere?
a depression on the inferior surface of the liver
267
hepatocytes
cells in the lobules of the liver
268
after a meal hepatocytes absorb what from the blood? (5)
- glucose
- amino acids
- iron
- vitamins
- other nutrients for metabolism and storage
269
between meals, hepatocytes break down stored _____ and release ____ into the blood
glucogen, glucose
270
hepatocytes remove and degrade... (4)
- hormones
- toxins
- bile pigments
- drugs
271
hepatocytes secretes these into the blood (4)
- albumin
- lipoproteins
- clotting factors
- angiotensinogen
272
the liver receives a mixture of....
(1) nutrient-laden venous blood from the intestines and (2) freshly oxygenated arterial blood from the celiac trunk
273
after filtering through the liver, blood..
leaves the liver through the hepatic veins and drains into the inferior vena cava
274
bile canaliculi
narrow channels into which the liver secretes bile which then drains into the right and left hepatic ducts
275
common hepatic duct
formed from the convergence of the right and left hepatic ducts on the inferior side of the liver
276
cystic duct
joins the common hepatic duct leading to the gallbladder
277
bile duct
formed from the union of the cystic and common hepatic duct descending towards the duodenum
278
near the duodenum, the bile duct joins the duct of the pancreas where it forms the _____ _____.
hepatopancreatic ampulla
279
hepatopancreatic sphincter
regulates passage of bile and pancreatic juice into the duodenum from the ampulla
280
between meals, the hepatopancreatic sphincter is...
closed and prevents the release of bile into the intestines
281
when does the hepatopancreatic sphincter open?
when cholecystokinin (CCK) is released by enteroendocrine cells from the duodenum during a meal
282
gallbadder
pear-shaped sac on the underside of the liver that stores and concentrates bile by absorbing H2O and electrolytes
283
bile (6)
fluid secreted by the liver containing minerals, cholesterol, neutral fats, phospholipids, bile pigments, and bile acids
284
the color of bile is _____ when secreted by the liver, but becomes intense _____ when concentrated in the gallbladder
yellow-green, green
285
bilirubin
primary bile pigment
286
where does the body get bilirubin?
hemoglobin decomposition
287
bacteria in the intestine metabolize bilirubin to...
urobilinogen
288
half of urobilinogen is converted to _____
urobilin
289
where is urobilinogen converted to urobilin? where does it go?
the kidney, excreted in urine
290
the rest of urobilinogen is converted to _____ (not urobilin)
stercobilin
291
where is urobilinogen converted to stercobilin? where does it go?
the intestine, brown color of feces
292
how does bile enter the gallbadder?
by first filling the bile duct then overflowing into the gallbladder
293
what happens to about 80% of bile acids?
they are reabsorbed in the ileum and returned to the liver where hepatocytes absorb and resecrete them
294
what happens to the remaining 20% of bile acids?
are excreted in feces
295
what is the body's only way of eliminating excess cholesterol?
through bile in feces
296
the liver synthesizes new bile acids from _____ to replace those lost in feces
cholesterol
297
gallstones
hard masses in either the gallbladder or bile duct
298
what are gallstone composed of? (3)
- cholesterol
- calcium carbonate
- bilirubin
299
how are gallstones usually removed?
laparoscopic surgery
300
cholelithiasis
presence of gallstones
301
cholelithiasis is most common in...
obese women over 40
302
when can cholelithiasis occur?
when cholesterol becomes too concentrated, and it precipitates as crystals that grow in size
303
cholelithiasis results in...(3)
- jaundice
- poor fat digestion
- impaird absorption of fat-soluble vitamins
304
pancreas
flattened, spongy retroperitoneal gland posterior to greater curvature of the stomach
305
the pancreas is both an _____ and _____ gland
exocrine, endocrine
306
endocrine portion of the pancreas
pancreatic islets secrete insulin and glucagon
307
where is the endocrine portion of the pancreas concentrated?
the tail of the gland
308
exocrine portion of the pancreas
99% of the organ, where it secretes pancreatic juice
309
where does the pancreatic duct run?
lengthwise through the middle of the gland
310
where does the pancreatic duct join the bile duct?
hepatopancreatic ampulla
311
the hepatopancreatic sphincter controls release of both _____ and _____ _____ into the duodenum
bile, pancreatic juice
312
accessory pancreatic duct
is a smaller duct that branches from the main pancreatic duct
313
what is the function of the accessory pancreatic duct?
it bypasses the sphincter and allows pancreatic juice to be released into the duodenum even when bile is not
314
pancreatic juice
an alkaline mixture of water, enzymes, zymogens, sodium bicarbonate, and other electrolytes
315
what portion of the pancreas secretes the enzymes and zymogens of pancreatic juice?
acini
316
what portion of the pancreas secretes the sodium bicarbonate?
the ducts
317
what is the function of bicarbonate in pancreatic juice?
it buffers the HCl arriving from the stomach, raising the pH to 7
318
pancreatic zymogens include...(3)
- trypsinogen
- chymotrypsinogen
- procarboxypeptidase
319
trypsinogen is secreted where?
the intestinal lumen
320
trypsinogen is converted to trypsin by _____
enteropeptidase
321
enteropeptidase is secreted by...
the brush border of the duodenum
322
trypsin is autocatalytic meaning...
it converts trypsinogen into more trypsin
323
what converts chymotrypsinogen and procarboxypeptidase into their active forms?
trypsin
324
trypsin plays a role in...
dietary protein digestion
325
pancreatic amylase digests...
starch
326
pancreatic lipase digests...
fat
327
ribonuclease and deoxyribonuclease digest...
RNA and DNA respectively
328
three stimuli are chiefly responsible for the release of pancreatic juice and bile
1. acetylcholine
2. cholecystokinin (CCK)
3. secretin
329
how does acetylcholine stimulate release of pancreatic juice and bile?
from the vagus and enteric nerves
330
acetylcholine stimulates _____ to secrete enzymes during the _____ phase of gastric control even before food is swallowed
acini, cephalic
331
after acetylcholine stimulation, enzymes released remain in _____ and _____ until chyme enters the _____
acini, ducts, duodenum
332
how does CCK stimulate the release of pancreatic juice and bile?
it is secreted by the mucosa of the duodenum in response to the arrival of fats in the small intestine
333
cholecystokinin stimulates...(2)
- pancreatic acini to secrete enzymes
- induces contractions of the gallbladder and relaxation of the hepatopancreatic sphincter to discharge bile and pancreatic juice into the duodenum
334
how doe secretin stimulate the release of pancreatic juice and bile?
it is released from the duodenum in response to acidic chyme arriving from the stomach
335
secretin stimulates the ducts of both ______ and _____ to secrete more sodium bicarbonate
liver, pancreas
336
after stimulating the liver/pancreas, the release of secretin causes....
the pH to rise to the level required for activity of the pancreatic intestinal digestive enzyme (7)
337
what is the site of nearly all chemical digestion and nutrient absorption?
the small intestine
338
what is the longest part of the digestive tract?
the small intestine
339
the small intestine is drained by the _____ veins, which converge to the _____ _____ vein which then joins the _______ vein and flows into the ______ ______ system to the liver with its load of nutrients
mesenteric, superior mesenteric, splenic, hepatic portal
340
small intestine
a coiled tube filling most of the abdominal cavity inferior to the stomach and liver
341
three regions of the small intestine
- duodenum
- jejunum
- ileum
342
where does the duodenum of the small intestine begin?
at the pyloric valve
343
most of the duodenum is _____peritoneal
retro
344
the duodenum receives...(3)
stomach contents, pancreatic juice, and bile
345
what is the function of the duodenum? (3)
- neutralizes stomach acids
- emulsified fats
- inactivates pepsin (elevated pH)
346
when do pancreatic enzymes take over digestion?
in the duodenum
347
the jejunum has tall, large, closely spaces _____ _____
circular folds
348
the wall of the jejunum is...(2)
relatively thick and muscular
349
what gives the jejunum a red color?
the rich blood supply
350
where in the small intestine does most digestion and nutrient absorption occur?
jejunum
351
where is the location of the final digestion and absorption of carbohydrates, lipids, proteins, and nucleic acids
jejunum
352
compared to the jejunum, the ileum is..(4)
- thinner
- less muscular
- less vascular
- a pale pink vs. red
353
aggregated lymphoid nodules
prominent lymphatic nodules in clusters on the side opposite to the mesenteric attachment
354
aggregated lymphoid nodules become _____ near the large intestine
larger
355
ileocecal junction
end of the small intestine where the ileum joins the cecum of the large intestine
356
the small intestine tissues are similar to those in the _____ and _____, but is specialized for _____ _____ and _____
esophagus, stomach; nutrient digestion, absorption
357
the lumen of the small intestine is lined with what kind of cells?
simple columnar epithelium
358
the muscularis externa of the small intestine has...(2)
- thicker inner circular layer
- thinner outer longitudinal layer
359
the jejunum and ileum are _____peritoneal
intra - covered with serosa
360
why does the small intestine have a large internal surface area? (3)
three types of folds/projection
- circular folds
- villi
- mircovilli
361
circular folds of the small intestine increase surface area by..
a factor of 2-3
362
the villi of the small intestine increase surface area by...
a factor of 10
363
microvilli of the small intestine increase surface area by...
a factor of 20
364
circular folds
transverse to spiral ridges up to 1 cm high
365
what are the largest folds of the intestinal wall?
circular folds of the small intestine
366
where do circular folds occur?
from the duodenum to the middle of the ileum
367
the circular folds are not found in what portion of the small intestine?
the distal half of the ileum
368
by what point in the small intestine is most nutrient absorption complete?
by the distal portion
369
what is the function of the circular folds in the small intestine? (2)
- causes chyme to flow in a spiral fath causing more contact with the mucosa
- promotes more thorough mixing and nutrient absorption
370
villi are covered with two types of cells
- absorptive cells (enterocytes)
- goblet cells
371
what makes the digestive mucosa look fuzzy?
villi
372
the epithelia of the digestive system is joined together by _____ _____ that prevent digestive enzymes from seeping between them
tight junctions
373
the core of a villus is filled with...
areolar tissue of the lamina propria
374
the core of the villus contains...
- arteriole
- blood capillaries
- venule
- lacteal
375
lacteal
a lymphatic vessel that absorbs dietary fats that the blood cannot absorb
376
microvilli
small plasma membrane extensions that form a fuzzy brush border on the apical surface of each enterocyte
377
what is the purpose of microvilli?
increase absorptive surface area and contain brush border enzymes
378
brush border enzymes
enzymes contained in the plasma membrane of microvilli (not released into intestinal lumen)
379
what enzymes carry out some of the final stages of enzymatic digestion?
brush border enzymes
380
contact digestion
chyme must contact the brush border for digestion to occur
381
duodenal glands
neutralize stomach acid and shield the mucosa from its erosive effects
382
what do the duodenal glands secrete?
an abundance of bicarbonate-rich mucus
383
what does the mucus of the duodenal glands contain?
signaling molecules that influence immune cells to tolerate food antigens and beneficial bacteria
384
where can a large number of lymphocytes be found within the digestive tract? what do they do?
- throughout the lamina propria and submucosa
- intercept pathogens before they can invade the bloodstream
385
between the bases of villi are _____ _____
intestinal crypts
386
intestinal crypts
pores that open into tubular glands on the floor of the small intestine
387
how far into the intestinal wall can intestinal crypts go?
as far as the muscularis mucosae
388
intestinal crypts secrete...
intestinal juice
389
what does intestinal juice contain? (3)
water, mucus, but little enzyme
390
intestinal juice is secreted in response to... (3)
- acid
- hypertonic chyme
- distension of the intestine
391
most enzymes that function in the small intestine are found...(2)
- brush border
- pancreatic juice
392
contractions of the small intestine serve three functions
- to mix chyme with intestinal juice
- to churn chyme and bring it in contact with mucosa for contact digestion/nutrient absorption
- to move residue toward the large intestine
393
segmentation
movement in which stationary ring-like constrictions appear in several places along the intestine, then relax as new constritions form elsewhere
394
what is the most common kind of intestinal contraction?
segmentation
395
what does segmentation do?
kneads and churns the intestinal contents
396
what sets the rhythm for segmentation?
enteric pacemaker cells in the muscularis externa
397
when does segmentation decline and peristalsis begin?
when most nutrients has been absorbed and little remains but undigested residue
398
peristalsis
rhythmic contractions that move remaining contents of the small intestine toward the colon
399
migrating motor complex
successive, overlapping waves of contraction
400
food in the stomach triggers _____ reflex
gastroileal
401
ileal papilla aka...
ileocecal valve
402
what does the gastroileal reflex do?
enhances segmentation in the ileum and relaxes the ileal papilla to release material from the small intestine to the large intestine
403
are vitamins digested?
no, they are absorbed unchanged
404
what happens if vitamins are ingested without fat-containing food?
they are not absorbed at all but are passed into the feces and wasted
405
fat-soluble vitamins (4)
A, D, E, and K
406
water soluble vitamins (2)
B complex (B12) and C
407
how are water soluble vitamins absorbed?
simple diffusion
408
parathyroid hormone is secreted in response to...
a drop in blood calcium levels to increase calcium absorption in duodenum
409
what does parathyroid hormone stimulate?
the kidney to synthesize vitamin D from precursors made by epidermis and liver
410
most absorbed calcium is from...
meat and dairy
411
how does the digestive system absorb water?
by osmosis following the absorption of salts and organic nutrients
412
diarrhea
occurs when the large intestine absorbs too little water
413
when can diarrhea occur? (2)
- feces pass through too quickly if intestine is irritated
- feces contain high concentrations of a solute
414
constipation
occurs when fecal movement is slow and too much water gets reabsorbed, causing feces to become hardened
415
where does the large intestine begin?
as the cecum inferior to the ileal papilla
416
where is the appendix?
attached to the lower end of the cecum
417
appendix
densely populated with lymphocytes and is a significant source of immune cells
418
colon
portion of the large intestine between the ileocecal junction and the rectum
419
four parts of the colon
- ascending colon
- transverse colon
- descending colon
- sigmoid colon
420
sigmoid colon
s-shaped portion leading down into the pelvic cavity
421
rectum
portion ending at the anal canal
422
the rectum has three curved and three infoldings called...
transverse rectal folds (rectal valves)
423
anal canal
final 3 cm of the large intestine
424
hemorrhoids
permanently distended veins that protrude into the anal canal or bulge outside the anus
425
large _____ veins from the superficial plexus in anal columns around the orifice
hemorrhoidal
426
why are the veins around the anus subject to hemorroids?
they lack valves and are subject to distension
427
the muscularis externa of the colon is different, as it has these components (2)
- taenia coli
- haustra
428
taenia coli
longitudinal fibers concentrated in three thickened, ribbon-like strips
429
haustra
pouches in the colon caused by the muscle tone of the taeniae coli
430
in the rectum and anal canal, longitudinal muscles are in a continuous sheet meaning..
they have no haustra
431
the anus is regulated by two sphincters
- internal anal sphincter
- external anal sphincter
432
internal anal sphincter
smooth muscle of the muscularis externa
433
external anal sphincter
skeletal muscle of the pelvic diaphragm
434
the large intestine mucosa has what cell type? except in what location?
simple columnar epithelium; except the lower half of the anal canal
435
the lower half of the anal canal has what cell type? why?
non-keratinized stratified squamous epithelium; resists abrasion from the passage of feces
436
in the large intestine, the intestinal crypts are _____ than in the small intestine and have _____ density of goblet cells
deeper, greater
437
the large intestine does not have these two features of the small intestine
circular folds or villi
438
the lamina propria and submucosa layers of the large intestine have a lot of _____ tissue
lymphoid
439
the lymphoid tissue in the large intestine is for...
protection from large population of bacteria in large intestine
440
gut microbiome (microbiota)
more than 1000 species of bacteria, yeasts, viruses, and other microbes that populate the large intestine
441
bacteria in the large intestine digest (3)
- cellulose
- pectin
- other carbohydrates which out cells lack enzymes
442
the gut microbiome helps synthesize what vitamins? (2)
B and K
443
flatus
intestinal gas that is expelled
444
flatus consists of...(3)
- hydrogen sulfide
- indole
- skatol
produce odor
445
how long does the large intestine take to reduce residue to feces?
36 - 48 hours
446
where does residue spend the most time?
in the transverse colon
447
what does the large intestine reabsorb? (2)
water and electrolytes
448
the solids of feces consists of? (4)
- 30% bacteria
- 30% undigested fiber
- 10-20% fat
- small amounts of mucus, proteins, salts, digestive secretions, and sloughed epithelial cells
449
colonic motility includes..(2)
- haustral contractions
- mass movements
450
haustral contractions (2)
- distention of a haustrum stimulates it to contract
- churns and mixes residue promoting water and salt absorption
451
mass movements
stronger contractions that occur one to three times day moving residue several centimeters
452
what triggers mass movements? (2)
the gastrocolic and duodenocolic reflexes
453
what stimulates motility of the colon?
filling of the stomach and duodenum
454
stretching of the rectum stimulates two defecation reflexes
- intrinsic defecation reflex
- parasympathetic defecation reflex
455
intrinsic defecation reflex
stretching signals travel through plexus to the muscularis, causing it to contract and the internal sphincter to relax
456
how does the intrinsic defecation reflex work?
entirely within the myenteric plexus to produce relatively weak response
457
the parasympathetic defecation reflex involves...
the spinal cord
458
how does the parasympathetic defecation reflex work? (2)
- stretching of the rectum sends sensory signals to the spinal cord
- pelvic nerves return signals, intensifying peristalsis and relaxing the internal anal sphincter
459
defecation only occurs if...
the external anal sphincter and puborectalis muscles are voluntarily relaxed
460
what increases abdominal pressure and compresses the rectum?
abdominal contractions (valsalva maneuver)
