Gastric Function Flashcards
Stomach Functions
- short term storage
- intrinsic factor secretion
- chemical/enzymatic digestion initiated (proteins)
- liquifys food
- slowly releases to SI
Ouabain
“arrow poison” plant derived toxin used in eastern Africa
- Na+/K+ pump - ATPase blocker
- in turn increases intracellular Ca++
- higher cardiac contractility increases cardiac vagal tone
- Cardiac glycoside - treats hypotension/arrhythmias in LOW doses
Atropine
- blocks Ach from binding muscarinic gastric gland (directly secretes HCl-)
- blocks gastrin release
- inhibits parasympathetic nervous system
Gastric Secretions
2 Glands 1) Gastric (oxyntic) HCl pepsinogen intrinsic factor mucus rennin (chymosin) 2) Pyloric gastrin mucus (some pepsinogen)
Antrum
NO ACID SECRETION
part of pylorus in stomach
Gastric Gland - Oxyntic (upper 80%)
3 cells
1) Mucous neck cells (mucus)
2) Chief Cells (peptic)
pepsinogen –> activated
Pyloric Gland (lower 20%)
2 cells
1) G cells
2) mucus neck cells
mucus and some pepsinogen
Acid Secretion
H+/K+ pump required!!!
In mitochondria, requires ALOT of ATP!!! (surface area is active)
Most secretion is salt = Na+ and H+ trade positions (Na+ decreases and H+ increases with Cl-)
increased acid = decreased gastrin
Mechanism? –> H+ into lumen of canaliculus and K+ into parietal cell (requires Mg+)
Calcium Calmodulin Kinase phosphorylates H+/K+ pump to open
Gastric Acid
3 functions
1) bacteriostatic
2) converts pepsinogen –> pepsin
3) begins protein digestion (with pepsin)
Gastric Secretion
Stimulated by neural, paracrine AND endocrine! (G coupled rec)
1) Ach: (from ENS)
HCl secretion, mucus, pepsinogen and gastrin
2) Histamine: direct
HCl secretion (H2 receptor)
3) Gastrin: (direct or indirect)
HCl secretion (1500x more powerful than histamine)
regulation?
+ peptides, aa bind gastrin cell to stimulate gastrin
- protons bind somatostatin cell to inhibit
Vagus Nerve Role
inhibits somatostatin and activates gastrin!!!
vagus binds ENS which
1) DIRECTLY sends signal to gastric gland to produce HCl - atropine blocks
2) INDIRECTLY sends signal to pyloric gland to produce Gastrin - atropine does NOT block
Histamine
Gastrin and ACh stimulate histamine release from ECL cells
which indirectly releases HCl (paracrine)
ECL Cell
entero-chromaffin-like cell
- specialized endocrine cell in gastric mucosa
- proliferation of ECL cells with LOTS of gastrin from tumor or long term therapy from drugs that block acid secretion
Parietal Cell
Does the acid secretion!!!
Phases of Digestion
1) Cephalic (NaCl to HCl when see food!!!)
parasympathetic excites pepsin and acid production
2) Gastric (stomach distention)
local nervous secretary reflexes, vagal reflexes, gastrin-histamine stimulation
3) Intestinal
nervous mechanisms, hormonal mechanisms (enzymes and zygomens)
