GIT Functions (ppt) - Dr. Nobleza Flashcards
Largest portion of the stomach:
Body or corpus
Most anterior part of the stomach:
Fundus
The muscles of the stomach are arranged in such a way for ________ and _________.
Churning
Peristaltic motion
Consists of a simple columnar epithelium that produces an alkaline carpet of mucus that covers the interior surfaces of the stomach and protects epithelial cells against the acid and enzymes in the gastric lumen.
Mucosa
- Lamina propria
- Muscularis mucosae
Structures under muscularis externa:
Oblique muscle
Circular muscle
Longitudinal muscle
The ______ allow the stomach to have a larger surface area.
Folds
Secretions of the stomach secrete ______.
2 L/day
*Isotonic with plasma
Made up of basal secretionL
Sodium rich (non-parietal cells)
Stimulated secretion:
H+ rich (Parietal cells)
Acid secretion
Pepsinogen
Intrinsic factor
Corpus
Acid
IF
Parietal cells or oxyntic cells
Secrete pepsinogen not acid
Chief or peptic cells
If chief or peptic cells reach pH <3 activated to:
Pepsins
Mucus secreting cells
Chief or peptic cells
Endocrine cells
Chief or peptic cells
No parietal cells and no acid secretion
Antrum
G cells produce:
Gastrin
- Gastric acid secretion
- Trophic effect
D cells produce:
Somatostatin
Inhibit gastrin release and parietal acid secretion
Somatostatin
______ are present throughout the fundus and body, branched, tubular gastric glands.
Glands
- Mucous neck cells
- Chief cells
- Parietal cells
- Stem cells
- Enteroendocrine cells
Secretes mucus
Surface mucous cell and mucous neck cell
Secretes hydrochloric acid and intrinsic factor
Parietal cell
Secretes pepsinogen and gastric lipase
Chief cell
Secretes the hormone gastrin
G cell
Also secretes bicarbonate and protects the lining.
Mucous neck cell
Large triangular cell, inc mitochondria, intracellular tubulovesicular membrances
Parietal cell
Secretes mucus
Surface mucus cells
Secretes mucus and pepsinogen
Mucus neck cells
Secrete pepsinogen
Peptic or chief cells
Secrete HCl intrinsic factor
Oxyntic or parietal cell
Secretes hormones
Endocrine
Enterochromaffin like cells:
Histamine
In BASAL state, the rate of acid secretion is _____.
Low
Tubolovesicular membrane present in resting nonstimulated parietal cell has __________
H-K pump
Responsible for acid secretion
Pump
In basal state, luminal pH of stomach is ______ and the rate of acid secretion is _____.
4-6
Low
With stimulation the pH of gastric secretion is ______
<2
Ach, Gastrin, Histamine _______ stimulate acid secretion by acting on different receptors.
Directly
Ach and gastrin also _____ stimulate by actin on ECL cell.
Indirectly
Large polypeptide
Gastrin
More active
Antral G cells
G-17
Slower degradation
Duodenal G-cells
G-34
Stimulation of acid secretion by parietal cells
Gastrin
Release of histamine by ECL cells
Gastrin
Regulation of mucosal growth (trophic effect) on corpus
SI and LI
Gastrin
Polypeptide hormone
Somatostatin
D cells corpus (endocrine) is triggered by _____ and ______ mechanism
Neural
Hormonal
D cells antrum (paracrine) is stimulated by ____ intraluminal pH
Low
Delta cells of pancreas and hypothalamus
Somatostatin
GI predominant form in somatostatin
SS-28
SS-14
Somatostatin
Inhibits gastric acid secretion
Somatostatin
Fat, acid and hyperosmolar solution
Enteric hormones
Potent inhibitor of gastric acid secretion
Enteric hormones
Most potent inhibitor
Lipid
S cells duodenum
Secretin
Inhibition of release of gastrin from antrum
Secretin
Stimulation of somatostatin release
Secretin
Direct down regulation of parietal H release
Secretin
Triggered by low pH because too much acid may cause duodenal ulcers.
S cells
Stomach can handle an acidic environment because of its:
Gastric diffusion barrier
Gastric diffusion barrier is composed of:
- Apical membrane and epithelial tight junctions
- Bicarbonate layer (produces bicarbonate)
- Mucuous layer (20-50 micro meter)
How come Gastric Acid is still produced by cells that are being covered?
Viscous fingering
From the time that your HCl acid is released, it passes through 3 barriers (______, _______ and _______) in a straight finger like fashion, eventually extruded out.
apical
bicarbonate
mucous
Gastric inhibitory peptide (GIP) DIRECTLY inhibits:
Parietal cell acid secretion
GIP INDIRECTLY inhibits:
Antral gastrin release
I cells in duodenum/jejenum release:
CCK - Cholecytoskinin
The feedback inhibition directly reduces gastric acid secretion by parietal cells
CCK
Inhibits histamine activation
Prostaglandins (PGE2)
Common ingredients in the action of enteric hormones
G-alpha
Acts on IP3 directly, then calcium or through adenylyl cyclase
G-alpha
Can stimulate or not stimulate the secretion of hormones, depending on the increase or decrease of adenylyl cyclase or calcium
G-aplha
What can trigger acid secretion?
- Taking medicines like NSAIDS
- Stress (neural stimulation can increase acid secretion)
- Alcohol intake
- H. pylori infection
Initiate hydrolysis of ingested proteins in the stomach
Pepsins
Secreted from base of glands in corpus of stomach
Group 1 pepsinogen
Chief cells and mucus neck cells of cardia, corpus and antral areas
Group 2 pepsinogens
Basal secretion of pepsinogen is _____ of maximal secretion after stimulation.
20%
Fusion of secretory granules with plasma membrane and other secretory granules
Compound exocytosis
Emptying of liquids
Smooth muscle (Proximal part)
Emptying of solids
Antral smooth muscles