Digestive System 1B Flashcards
what gets absorbed in the stomach
small, non polar substances like lipid-soluble alcohol and aspirin
what is intrinsic factor
substance made and released by the parietal cells in the stomach
required for the absorption of vitamin B12
lack of it causes pernicious anemia
where is B12 absorbed and what is it important for
ileum of the small intestine
maturation of red blood cells
what are the four regions of the stomach
cardia
fundus
body
pylorus
what are some features of the cardia of the stomach
portion right below the esophagus at the cardiac orifice
cardiac orifice has inferior esophageal sphincter
what are some features of the pylorus
opens into the duodenum at the pyloric orifice
pylorus is surrounded by pyloric sphincter
what are the purpose of rugae in the stomach
folds that allow the stomach to expand (only seen when stomach is not stretched)
what is the stress-relaxation response in the stomach
when the stomach stretches, it initially contracts
after a while of being stretched however, it will relax
allows us to keep eating
what are the two serous membranes of the stomach
greater and lesser omentum
what are some features of the greater omentum
extends inferiorly from the greater curvature of the stomach and drapes over the intestine, spleen, and transverse colon
has fat deposits and lymph nodes
what are some features of the lesser omentum
extends superiorly from the lesser curvature of the stomach and duodenum to attach them to the liver
what is significant about the inner lining of the stomach
mucosa - simple columnar epithelium which are replaced often due to the acid
lots of gastric pits
gastric glands which help expels secretions when it contracts
what are the three layers of the muscularis of the stomach and what are their function
inner oblique, middle circular, and outer longitudinal
oblique helps with churning and blending
all do mechanical digestion
where are the 5 types of glands found in your stomach
1.) surface mucous cells
2.) mucous neck cells
3.) parietal cells
4.) chief cells
5.) G-cells
what do surface mucous cells do
most superifical cell that lines stomach and gastric pits
secrete alkaline product containing mucin
mucous protects from ulcers and abrasions
what do mucous neck cells do
deep to surface mucous cells
deep to base of gastric pit
found among parietal cells
produce acidic mucin to help maintain acidic conditions
what are the two secretions of parietal cells
intrinsic factor and hydrochloric acid components
what does hydrochloric acid do
responsible for low pH of stomach
components (H+ and Cl-) secreted by parietal cell
explain how hydrochloric acid is formed from parietal cells
1.) CO2 from the stomach lumen and H2O from the parietal cell combine to form carbonic acid (catalyzed by carbonic anhydrase)
carbonic acid dissociates into H+ and bicarbonate
H+ is pumped into lumen of the stomach by hydrogen/potassium pump
2.) bicarbonate is transported out of the parietal cell into the blood
chloride is transported into the cell then the lumen of the gastric gland (chloride shift)
chloride is pumped into the stomach lumen
3.) chloride forms with hydrogen to form hydrochloric acid
what are the 5 things that the low pH created by HCl facilitates in the stomach
1.) food breakdown
2.) protein denaturation
3.) pepsin activation
4.) enhanced enzymatic activity
5.) protection
explain pepsin activation
pepsinogen from chief cells is converted to pepsin
explain enhanced enzymatic activity of the stomach
hydrochloric acid creates optimal pH environment for enzymatic activity of both pepsin and acidic lipases
explain protection of the stomach
low pH protects us against infectious agents
what are some features of chief cells of the stomach
most numeous secretory cells, 4th layer deep
produce and secrete zymogen granules and gastric lipase
what do zymogen granules do
contain pepsinogen which is activated by hydrochloric acid and other pepsin molecules
once activated, pepsin can digest denatured proteins
what does gastric lipase do
digests 10-15% of ingested fats
what are some features of G-cells
deepest cell
type of enteroendocrine cells (hormone producing)
secrete gastrin into the blood which stimulates stomach secretions and motility
what are the two main functions of the smooth muscle within the stomach wall
mix bolus with gastric juice to form chyme
emptying chyme from the stomach to the small intestine
define retropulsion
reverse flow of some contents back towards stomach
what do the pacemaker cells (interstitial cells of cajal) do
cells in the GI tract wall
found in the longitudinal layer of smooth muscle in the stomach
spontaneously depolarize less than four times a minute to establish muscular contraction rhythm
what does parasympathetic (vagus nerve) stimulation do to secretion of gastric glands
increases it
what does sympathetic stimulation do to secretion of gastric glands
decrease it
what are the three phases of the regulation of the digestion process
cephalic phase
gastric phase
intestinal phase
what are the features of the cephalic phase
cephalic reflex is triggered by something like aroma, taste, sight, and thought
signals go to the hypothalamus then medulla oblongata
increases vagal simulation of the stomach to increase motility and secretly activity
stomach growls
what are the features of the gastric phase
starts once the bolus reaches stomach
gastrin is released into blood and gets to the stomach
baroreceptors detect stretch which initiates gastric reflex
chemoreceptors detect protein and increased pH
these signals go to medulla
more motility and secretory activity (parasympathetic)
contraction of pyloric sphincter to slow stomach emptying
what are some features of the intestinal phase
chyme reaches small intestine
intestinal reflex triggered
chyme in duodenum signals to medulla to decrease motility and secretory activity of stomach
cholecystokinin (CCK) and secretion also decrease motility and secretory activity of stomach - slows emptying
what is gastritis
inflammation of stomach lining caused by anything that breaches stomach’s mucosal barrier
what are peptic ulcers
erosion of portion of stomach or duodenum
can erode and cause perforation
usually caused by helicobacter pylori or NSAIDS
what is vomiting (emesis)
rapid expulsion of gastric contents through oral cavity because of stomach muscle contraction
controlled by vomiting center in the medulla
nasal passageways close
too much can cause dehydration and imbalances
what is gastric bypass
surgical treatment for obesity where small part of stomach is sectioned off and the duodenum is bypassed
less nutrients absorbed and reduce appetite
altered hormonal response to insulin
glands in which parts of the stomach produce the most gastric juice
fundus and body
what causes the pyloric sphincter to open
peristalsis contractions build the pressure gradient until it’s high enough to open the pyloric sphincter
what regulates the muscular contractions of the stomach wall
nervous reflexes and hormones
regulate force but not rate of contraction
how do hormones affect gastric secretions
gastrin (hormone) stimulates HCl secretion
therefore sitmulates digestion
gastrin antagonist hormones from small intestine stop HCl secretion
therefore stopping digestion
