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Chapter 21
The Digestive System
79
Physiology
Undergraduate 3
11/18/2015

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Term
4 things that make up the gastrointestinal tract (GI tract)
Definition
1. esophagus
2. stomach
3. small intestine
4. large intestine
Term
gut
Definition
the portion of the GI tract running from the stomach to the anus
Term
chyme
Definition
the soupy mixture of food & secretions
Term
3 pairs of salivary glands

*where the first stages of digestion begin in the oral cavity with chewing & the secretion of saliva*
Definition
1. sublingual glands (under the tongue)
2. submandibular glands (under the mandible)
3. parotid glands (near the hinge of the jaw)
Term
esophagus
Definition
the narrow tube that travels through the thorax to the abdomen that swallowed food passes through
Term
stomach
Definition
a baglike organ that can hold as much as 2 liters of food & fluid when fully expanded; lies just below the diaphragm; where the esophagus ends
Term
3 sections of the stomach
Definition
1. upper fundus
2. central body
3. lower antrum
Term
pylorus
Definition
the opening between the stomach & the small intestine that is guarded by the pyloric valve
Term
3 sections of the small intestine
Definition
1. duodenum
2. jejunum
3. ileum
Term
After digestion finishes in the small intestine & nearly all digested nutrients & secreted fluids have been absorbed, how much chime per day passes into the large intestine?
Definition
1.5 liters
Term
colon
Definition
the proximal section of the large intestine where watery chime becomes semisolid feces as water & electrolytes are absorbed out of the chime & into the ECF
Term
rectum
Definition
the terminal section of the large intestine where feces are propelled into; has a defecation reflex triggered by distension of the rectal wall
Term
anus
Definition
where feces leaves the GI tract via its external anal sphincter which is under voluntary control
Term
villi
Definition
small fingerlike extensions in which the intestinal mucosa projects into the lumen
Term
What is the difference between "gastric glands" & "crypts"?
Definition
gastric glands = invaginations in the stomach

crypts = invaginations in the small intestine
Term
submucosal glands
Definition
secretory glands formed by the deepest invaginations that open into the lumen through ducts
Term
4 layers of the gut wall
Definition
1. an inner mucosa facing the lumen
2. submucosa
3. muscularis externa (layers of smooth muscle)
4. serosa (a covering of connective tissue)
Term
3 layers of the mucosa (inner lining of the GI tract)
Definition
1. mucosal epithelium (a single layer facing the lumen)
2. lamina propria (subepithelial connective tissue that holds the epithelium in place)
3. muscularis mucosae (a thin layer of smooth muscle)
Term
Peyer's patches
Definition
larger visible bumps in the mucosa formed from collections of lymphoid tissue adjoining the epithelium
Term
What tissue is majorly made up of lymphoid aggregations such as Peyer's patches?
Definition
gut-associated lymphoid tissue (GALT)
Term
submucosa
Definition
the middle layer of the gut wall
Term
What system is the submucosal plexus (part of the submucosa) a major nerve network for?
Definition
the enteric nervous system
Term
muscularis externa
Definition
the outer wall of the GI tract; consists of 2 layers of smooth muscle (and inner circular layer & an outer longitudinal layer)
Term
myenteric plexus
Definition
the second nerve network of the enteric nervous system; lies between the longitudinal & circular muscle layers of the muscularis externa
Term
serosa
Definition
the outer covering of the entire digestive tract; a connective tissue membrane that is a continuation of the peritoneal membrane that lines the abdominal cavity
Term
mesentery
Definition
sheets of the peritoneum that holds the intestines in place so that they do not become tangles as they move
Term
digestion
Definition
the chemical & mechanical breakdown of foods into smaller units that can be taken across the intestinal epithelium into the body
Term
absorption
Definition
the movement of substances from the lumen of the GI tract to the ECF
Term
motility
Definition
movement of material in the GI tract as a result of muscle contraction
Term
3 significant challenges faced by the digestive system
Definition
1. avoiding autodigetion
2. mass balance
3. defense
Term
mucins
Definition
glycoproteins that primarily make up the viscous secretion that is mucus
Term
phasic contractions
Definition
contraction-relaxation cycles lasting only a few seconds; ex) in the posterior region of the stomach & in the small intestine
Term
slow wave potentials (slow waves)
Definition
cycles of depolarization & repolarization associated with cycles of smooth muscle contraction & relaxation
Term
interstitial cells of Cajal (ICCs)
Definition
a network of cells where slow waves originate
Term
migrating motor complex
Definition
a pattern that is a "housekeeping" function that sweeps food remnants & bacteria out of the upper GI tract & into the large intestine
Term
peristalsis
Definition
progressive waves of contraction that move from one section of the GI tract to the next
Term
bolus
Definition
a mass of food behind which circular muscles contract in peristalsis
Term
segmental contractions
Definition
short segments of intestine alternately contract & relax
Term
5 features the ENS shares with the CNS
Definition
1. intrinsic neurons
2. neurotransmitters & neuromodulators
3. glial support cells
4. diffusion barrier
5. integrating center
Term
intrinsic neurons
Definition
neurons that lie completely within the wall of the gut
Term
short reflexes
Definition
reflexes that originate within the enteric nervous system & are integrated there without outside input
Term
long reflexes
Definition
digestive reflexes integrated in the CNS regardless where they originate
Term
cephalic reflexes
Definition
reflexes that originate in the brain
Term
cholecystokinin (CCK)
Definition
the GI hormone that enhances satiety (the feeling that hunger has been satisfied)
Term
2 hormones in the gastrin family
Definition
1. gastrin
2. CCK
Term
glucose-dependent insulinotropic peptide
Definition
a hormone that stimulates insulin release in response to glucose in the intestinal lumen
Term
What family is the hormone glucagon-like peptide-1 (GLP-1) in?
Definition
the secretin family
Term
cephalic phase
Definition
the feedforward response created by the long reflexes that begin in the brain
Term
4 important functions of saliva
Definition
1. soften & moisten food
2. digestion of starch
3. taste
4. defense
Term
3 parts of the mouth that contribute to the mastication of food to create a softened, moistened mass that can be easily swallowed
Definition
1. lips
2. tongue
3. teeth
Term
acini
Definition
grape-like clusters of the secretory epithelium of salivary exocrine glands
Term
deglutition
Definition
swallowing; a reflex action that pushes a bolus of food or liquid into the esophagus
Term
What does the epiglottis do as the bolus moves down toward the esophagus?
Definition
folds down to complete closure of the upper airway & prevent food & liquid from entering the airways
Term
3 general functions of the stomach
Definition
1. storage
2. digestion
3. defense
Term
vagal reflex
Definition
a cephalic phase reflex that begins digestive activity in the stomach before food even arrives
Term
gastric phase
Definition
when food enters the stomach & stimuli in the gastric lumen initiates a series of short reflexes
Term
Where do gastric glands lie?
Definition
deep within the mucosal layer
Term
G cells
Definition
cells deep in the gastric glands that secrete the hormone gastrin into the blood
Term
gastrin-releasing peptide
Definition
an ENS neurotransmitter that mediates short reflexes
Term
parietal cells
Definition
cells deep in the gastric glands that secrete gastric acid into the lumen of the stomach
Term
pepsin
Definition
carries out the initial digestion of proteins
Term
chief cells
Definition
cells in the gastric glands that secrete pepsin as the inactive enzyme pepsinogen
Term
histamine
Definition
a paracrine signal secreted by enterochromaffin-like cells (ECL cells) in response to gastrin or ACh stimulation
Term
When does the intestinal phase of digestion begin?
Definition
once chime passes into the small intestine
Term
brush border
Definition
the surface of the intestinal epithelium; names because of the bristle-like appearance of the microvilli
Term
bile
Definition
a nonenzymatic solution secreted from hepatocytes (liver cells)
Term
3 key components of bile
Definition
1. bile salts (facilitate enzymatic fat digestion)
2. bile pigments (the waste products of hemoglobin degradation)
3. cholesterol (excreted in the feces)
Term
What makes up bile salts which act as detergents to make fats soluble during digestion
Definition
steroid bile acids combined with amino acids
Term
gallbladder
Definition
stores & concentrates the bile solution after it is secreted by hepatocytes & has travelled here via the hepatic ducts
Term
common bile duct
Definition
the duct through while the gallbladder sends bile into the duodenum via contractions during a meal that includes fats
Term
lipases
Definition
enzymes that remove two fatty acids from each triglyceride molecule & therefore carry out enzymatic fat digestion
Term
colipase
Definition
a protein co-factor secreted by the pancreas & is necessary for fat digestion
Term
5 things that form small disk-shaped micelles as enzymatic mechanical digestion proceeds
Definition
1. fatty acids
2. bile salts
3. mono- & diglycerides
4. phospholipids
5. cholesterol
Term
disaccharidases
Definition
intestinal brush-border enzymes that break down maltose & other disaccharides
Term
endopeptidases (proteases)
Definition
attack peptide bonds in the interior of the amino acid chain & break a long peptide chain into smaller fragments
Term
3 proteases
Definition
1. pepsin (secreted in the stomach)
2. trypsin (secreted by the pancreas)
3. chymotrypsin (secreted by the pancreas)
Term
exopeptidases
Definition
release single amino acids from peptides by chopping them off the ends, one at a time
Term
Why is vitamin B12 also known as cobalamin?
Definition
it contains the element cobalt
Term
colonocytes
Definition
the epithelial cells on the luminal surface of the colon that absorb Na+
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