GI 6 Flashcards
Three Major Salivary Glands?
- Parotid
- Mandibular
- Sublingual
Secretion from parotid glands?
watery (serous) saliva
Secretion from mandibular glands?
mixed serous and mucous
Secretion from sublingual glands?
mucous
Do the minor glands in the mucosa secrete mucous or serous saliva?
highly mucous
3 Functions of Saliva
- Lubrication
- Digestion
- Protection (antibacterial)
Is saliva in ruminants acidic or alkaline? Why?
Alkaline - high levels of bicarbonate and phosphate (to neutralize acid generated by fermentation)
Is monogastric saliva hypo-, iso-, or hyper- tonic?
hypotonic (very low conc. of all solutes, including sodium)
Hypotonic solution
lower concentration of solutes outside than inside the cell
Acinar gland
type of salivary gland which secretes mucus, enzymes, water, and electrolytes
Duct epithelium
absorbs electrolytes, sodium and chloride; (Secretes bicarbonate and potassium?)
Is ALL saliva hypotonic?
NO intitally it is isotonic until duct epithelium does its job
Why is water not absorbed by the duct epithelium?
cells are water impermeable
Is saliva secretion under any hormonal control?
No, it is exclusively neural (autonomic)
Is saliva secretion stimulated by sympathetic or parasympathetic?
both (mainly parasympathetic but still both)
What gastric secretions do parietal cells produce?
HCl and intrinsic factor
What gastric secretions do chief cells produce?
pepsinogen
What gastric secretions do surface mucous cells produce?
mucus and bicarbonate
What gastric secretion do enterochromaffin-like cells (ECL) produce?
histamine
What gastric secretions come from G cells?
gastrin
What gastric secretions come from D cells?
somatostatin
What gastric “secretions” (neurotransmitters) come from nerves?
Ach (acetylcholine) and GRP (gastrin-releasing peptide)
Intrinsic factor
produced by parietal cells and absorbs Vitamin B12
Pepsinogen
inactive precursor to pepsin (enzyme) for protein digestion
Histamine
paracrine from ECL cells to promote gastric acid secretion from the parietal cells
Somatostatin
paracrine to inhibit gastrin secretion
Parietal glands
75% of gastric glands in body of stomach, include parietal cells and chief cells
Pyloric glands
in pylorus, made up of mucous cells and G cells
Where do G cells release gastrin?
to the bloodstream
Alkaline Tide
transient alkalization of the blood
4 Steps of HCl Secretion from Parietal Cells
- Carbon dioxide and water undergo rxns to end upwith H+ and bicarbonate
- Proton pump on the lumenal/apical aspect will pump H+ out and pull K+ in
- Cl- follows H+ through channels (diffusion); makes HCl
- Bicarbonate is pumped out into blood and Cl- pulled in at the basolateral membrane
How is alkaline tide reversed?
blood flows into pancreas, pancreas picks up the bicaronate and uses it to neutralize the acid in the intestine
Size of effect of gastric acid production on blood pH?
Small and transient
Is HCl secretion always stimulated by food?
yes
3 Phases for HCl Secretion
- Cephalic
- Gastric
- Intestinal
What % of HCl secretion occurs during the cephalic phase?
30%
What % of HCl secretion occurs during the gastric phase?
60%
Mechanisms of HCl release during Cephalic Phase
CNS can act directly on parietal cells with acetylcholine, or by gastrin-releasing peptde on a G cell to release gastrin which then acts via CCK2 receptor on the parietal cell
What is different about the mechanisms of HCl release in the gastric phase?
includes the vagovagal reflex, involves interneurons within the enteric nervous system in addition to the same signals as the cephalic phase
Direct Mechanism of Gastrin on HCl Secretion
gastrin binds to CCK2 on parietal cells to stimulate HCl secretion
Indirect Mechnism of Gastrin on HCl Secretion
gastrin bind to CCK2 on ECL cells to stimulate histamine release, then histamine can act on parietal cells to stimulate HCl secretion
Synergism of HCl Secretion
when gastrin (endocrine), histamine (paracrine), and Ach (NT) all act on parietal cells simultaneously
Atropine
anticholinergic effect blocking the ACh binding to the M3 receptor on parietal cells
Cimetidine
H2 receptor antagonist; blocks binding of histamine to parietal cells
Omeprazole
proton pump inhibitor to block H+ secretion from the parietal cell into the lumen
Somatostatin and Prostaglandin effect on HCl secretion
binds to its respective receptor on the parietal cell, decreases cAMP, therefore reducing activity of proton pump putting H+ into the lumen
NSAID effect on prostaglandin
inhibits prostaglandin synthesis, therefore removing an inhibitory factor of acid secretion
2 Ways Somatostatin Inhibits HCl Secretion in the Stomach
- Directly on the parietal cells
- Indirectly by inhibiting gastrin release
acts when stomach pH drops below 3.0ish
Can neurons in the duodenum inhibit acid secretion by inhibiting gastrin? What about hormones?
no (they directly act on parietal cells)
Hormones can do both
proenzymes
inactive form of an enzyme that cannot digest protein so the body doesn’t digest itself
Zymogens
name for the proenzymes used in digestion
Peptic Ulcer Disease Causes
mucosal loss on the protective layer, excess H+ and pepsin secretion; due to imbalance of protectiive and damaging factors in gastroduodenal mucosa