GI secretions P1: Salivary & gastric secretions Flashcards
What 3 processes does saliva do to food
Lubrications- moistening mouth, dissolve chemicals in food and easily swallow
Protection- Reduces adverse effects of oral bacteria
Digestion-Began breakdown of carbohydrates & fats via the enzymes alpha-amylase & Lingual lipase
Dysfunction of saliva secretion :
Sjoyrens syndrome-describe it
An autoimmune disease that destroys the exocrine glands and most commonly affects saliva: dry mouth and eyes-Sicca symptoms
Dysfunction of saliva production:
Describe Xerostomia
Dry mouth-Lack adequate saliva, bacterial overgrowth and therefore dental caries
Organisation of salivary glands- acidic or alkaline
Alkaline
What are the 2 types of secretion
Sercus- main type of protein secreted is pyalin-hydrolyses starch
Mucus- Mucin protein-lubricant-
What are 3 major salivary glands & % contribution
Submandibular-70%
Sublingual-5%
Parotid-25%
Structure and Composition: what is acinus
Contains a isotonic solution. Duct cells reabsorb Na+ & Cl- but are impermeable to water and therefore saliva is hypotonic
Na+ leaves via leaky tight junctions and cl- through chloride channels- accompanied by water
Describe func of Ductal cells
Removal of Na+ from saliva is upical Na+ channel
cl- through cl channels
no H20 accompanied as aqua porins aren’t expressed
Central control of salivary glands
Saliva-stim by thought
Efferent nerves-salivary glands via the ACH-muscarinic receptors.
Parasympathetic promotes watery secretion in acini
& increase blood flow
Salivary nuclei in pons & parasympathetic tone
Glossopharygeal and facial nerves
Sympathetic-increase amylase
but decrease blood flow
Gastric secretions: describe some and name
Water and electrolytes: To dissolve & dilute digested food
HCL: hydrolysis, fat & starch, antiseptic-microbes, converts pepsinogen into pepsin & provide optim PH
Pepsins: Secreted as inactive pepsinogens away from stomach, low PH activates it
Mucus+bicarb barrier: Protect surface of epithelial cells
Intrinsic factor: Glycoproteins bind B12, necessary for absorption in ileum; without this can develop anaemia
Origins: Exocrine and endocrine
exocrine- fondus/body-acid
endocrine-hormone-/antrum/gastrin produce
What are the 2 functional regions of the stomach
Exocrine-consist of fundus and body
Endocrine
Structure and func of gastric gland -endocrine
Endocrine:
Mucus cell- protective barrier
Endocrine cell: D cells, somatostatin-inhibit gastrin release/regulates
Chiet cells: Secrete pepsinogen, & activated by gastric acid= Pepsin
G cells- gastrin
Structure and func of gastric gland -exocrine
Parietal- acid secretory & intrinsic factor IF
Histamine cells
Are there a lot of parietal cells in endocrine region
A few
Protection against self & mechanical damage
How?
Mucous layer of polysaccharides & mucoproteins prevent mechanical damage
Mucin has basic side chains & HCO3- secreted from epithelial cells -neutralises H+ ions
Tight junctions-stop acid entry
Continual renewal
Dysfunction of gastric mucosa: Gastritis?
Inflam by bacteria- Helicobacter pylori
Acid secretion -oxyntic cells-describe development of them
Tubulovascular membrane contain H+ K+ ATPASE Pump, responsible for acid secretion
Upon stimulation, tubulovascular mem fuses into canalicular mem
Fusion, then insertion of pump and cl- channel into canalicular mem
Acid Secretion-Parietal cell, describe process
Actively exchanges H+ for K+
Carbonic anhydrase generates H+ & HCO3-. H+ pumped across membrane by H+/K+ ATPase pump.
HCO3- exchanged for cl- in interstit space
Cl- diffuses down gradient helping gastric venous blood to be alkaline
Dsyfunction of proton pump
Inhibitors such as omeprazole, binds irreversibly to H+/K+ ATPase pump
Regulation of secretion-what stimulates secretion p1
Cephalic nerve-neural
Gastric-antral distention,
Interstitial- Proteins present - increase gastrin produce
Regulation: Stim of acid secretion p2: what cells & substances are stimulated
& how are they related
Gastrin- G cells
Histamine - Mast cells-CAMP-Increase intracellular CA2+ in 1
Acetylcholine- from postsynaptic vagal fibres
acts on D cells to inhibit somatostatin
Both 1 and 3 are : ACH stimulates histamine and acid release in parietal cells
ACH and acid amplify histamine release from ECL cells and parietal cells
What are 2 major paracrine inhibitors:
Somatostatin: Antral & oxyntic gland D cells & pancreatic islet cells
Prostaglandins- from mucosal cells- antag histamine, inhib CAMP production, Gastric parietal cells dysfunction.
Autoimmune disease
Autoimmune atrophic gastritis: antibody mediated destruction: leads to hypochlorhydria
What cells release Gastrin & area of cells-anatomy, what type of effect and triggered by
Gcells of pyloris and Duodenum
Endocrine effect
triggered by peptides
What are effects of histamine and by what cells
ECL cells
Local Vasodilation
Paracrine effect
Vagal stimulation - regulation of gastric acid secretion
what does the corpus do
via Ach, increases acid secretion via directly parietal cells, and indirectly via ECL and D cells (ECL increases acid secretion via histamine release, D cells inhibit somatostatin
What do D cells inhibit
Somatostatin
IF PH is high what do D cells release
Somatostatin to inhibit G cells
Gastrin can activate receptors on which cells
D and G cells leading to release of
Antrum?
via GRP, stimulates both G and D cells (increase gastrin, inhibit somatostatin)
Gastrin from antrum promotes acid secretion by two endocrine mechanisms:
Directly via parietal cells
Indirectly via ECL cells
