Gastric Physiology Flashcards
what are the 3 goals of the stomach?
- receive and store food
- control rate of delivery to small intestines
- control consistency of content delivered to small intestines
what are the 3 functions of the stomach?
- storage prior to entry into small intestines
- enzymatic breakdown of feed via pepsin to chyme
- muscular walls to churn and breakdown food
list and describe the 4 cells of the stomach
- parietal cells that release HCl
- chief cells that release pepsinogen that is activated to pepsin by HCl and pepsin degrades protein
- mucous cells that release mucin
- endocrine cells
what volume can the human stomach hold?
4 liters
list and describe the 2 motor units of the stomach
- proximal motor unit: located in the fundus and body, function is storage to accomplish receptive relaxation of the stomach
- distal motor unit: located in the antrum and pylorus, function is mixing, propulsing, and empyting stomach contents to small intestine
what is one of the most important functions of the stomach, especially for predators, and why?
receptive relaxation, super important for predators who eat their prey really fast and then go to safety to digest
list and describe the 2 types of digestion
- Mechanical: Mobility/peristalsis; accomplished by the Myenteric plexus at the Musculosa
- chemical: utilizes Secretions (GI enzymes and GI hormones); accomplished by the Submucosal plexus and local blood flow control
generally describe contractions of the stomach
alternating relaxation and contraction of musculature of stomach, in a wave-like motion called peristalsis that is UNIDIRECTIONAL
describe stomach contraction strength in the fundus versus the distal stomach
starts in the fundus, which has weak muscles and weak contractions; contraction is much stronger in the distal stomach
describe contraction in the distal stomach/moving to small intestines (4)
- increased luminal pressure in the pylorus
- pyloric sphincter relaxes to allow contents into duodenum
- mixing of contents allows smaller pieces through first
- mixing and emptying occurs until stomach is empty
when does the pyloric sphincter relax
when the stomach contracts to allow chyme to flow from stomach to small intestine
what defense do predators who eat bones have against the undigestible bones?
vomiting
what are interstitial cells of cajal, where are they located, and what do they do?
located throughout the entire muscularis of the stomach; are pacemaker cells like the SA node of the heart that initiate the oscillations in membrane potential that occur in smooth muscle cells (between circular and longitudinal layers of t. muscularis)
what causes the action potential of the interstitial cells of cajal? what does the number of action potentials depend on?
hormone release opens calcium channels in these cells, allowing calcium to flow into the muscle cell and induce contractions; number of APs depends on neural and hormonal effects
how does the autonomic nervous system innervate the stomach?
paraympathetic: via the vagus nerve (CNX)
sympathetic: via the greater splanchnic nerve (from the thoracic spine)
give the origin, supply, function, outcome, and hormone of the parasympathetic nervous system on the enteric nervous system and GI tract
origin: vagus nerve
supply: smooth muscles of GI wall
function: increased GI motility and secretions (rest and digest)
outcome: activate enteric nervous system
hormone: acetylcholine
give the origin, supply, function, outcome, and hormone of the sympathetic nervous system on the enteric nervous system and GI tract
origin: greater splanchnic nerve
supply: to smooth muscles of GI wall and smooth muscles of blood vessels
function: decreased motility and secretions (fight or flight)
outcome: inhibit enteric nervous system
hormone: norepinephrine
what determines the rate of emptying of stomach contents?
the strength of stomach contractions
what controls strength of stomach contraction? (2) explain
- neural control: activation by vagal nerve releases acetylcholine, leading to more expansion of the stomach and greater contractions
- hormonal control: secretion of the hormone gastrin, which stimulates contractions and produces gastric juice
what are the 2 influences of the duodenum on stomach emptying?
- inhibits stomach from contracting
- increases tension from pyloric sphincter
what drives duodenal influence on stomach emptying
- pressure on duodenal lumen
- high fat concentrations
- low pH (from HCl)
how is stomach emptying stopped? (2) describe
- neural control: sympathetic control to inhibit stomach contraction
- hormonal control: duodenum releases secretin, CCK, and gastric inhibitory peptide in response to high fat content in duodenum or decreased pH in duodenum to stop stomach emptying contents into duodenum so duodenum can digest
when does most gastric secretion occur? give one exception
2-3 hours after a meal; pigs are the exception because they are constantly producing gastric juices
describe secretion of HCl (the cells it comes from and 3 functions)
secreted by parietal cells
functions:
1. activates pepsinogen to pepsin to allow for hydrolysis
2. prevents fermentation of food (no fridge in tummy)
3. degrades connective tissue/muscle from food
describe biochemically how HCl is secreted (5)- maybe less important bc not strictly related to a LO
- CO2 enters chief cells, combines with H2O via carbonic anhydrase and makes carbonic acid
- carbonic acid dissociates into bicarbonate and H+
- H+ is pumped out of cell via a proton pump, and potassium is forced into the cell (one out one in) using energy, but immediately flows back down its concentration gradient out of the cell
- as bicarb is pumped out of the cell, a chloride is pumped into the cell via the bicarb-chloride antiporter, but the chloride immediately flows out of the cell via the chloride ion channel
- the H+ and Cl- combine outside the cell into HCl
describe secretion of pepsinogen (give 2 functions)
secreted by chief cells; is the inactive form of pepsin; is converted to pepsin by HCl and then
functions:
1. degrades proteins into peptides
2. peptides stimulate secretions of HCl
why is pepsinogen produced, stored, and excreted in an inactive form?
to protect the stomach from digesting itself
describe secretion of mucous; give its function and what would happen if there was a decrease in mucous cells?
mucin-producing cells produce mucous, which protects gastric mucosa from HCl; if there was a decrease in these cells, the mucosa would be disrupted and ulcers would form
how is secretion regulated? (2) describe
- neural reflexes: parasympathetic increases; sympathetic decreases
- hormonal control: gastrin and histamine
describe the 2 endocrine cells that regulate gastric secretion
- G cells: gastrin-producing cells, release gastrin into blood, which increases HCl secretion and gastric motility
- ECL-cells: enterochromafin-like cells; produce histamine that acts like a paracrine hormone that stimulates HCl secretion by binding to receptors on parietal cells
where are ulcers most commonly found in the equine stomach?
in the less-protected margo plicatus or nonglandular stomach
