Bililary System, Salvivary, Pancreatic and Gastric Secretions Flashcards
Where is secretin produces and what does it do?
Produced by S-cells in the duodenum.
It stimulates liver ductal secretion of bile.
Where is bile stored?
In the gallbladder.
Give 2 stimuli which cause the gallbladder to secrete bile into the duodenum.
- Vagal stimulation - causes gallbladder to contract
2. Cholecystokinin causes gall bladder contraction.
What is cholecystonkinin and where is it produced?
Cholecystonkinin is a hormone secreted by cells in the duodenal wall that causes the gallbladder to contract, secreting bile into the duodenum.
What is the composition of bile?
Ions: Na+, K+, Ca2+, Cl-, HCO3-
Bile acids
Bilirubin
Phospholipids, cholesterol, proteins
How is bile concentrated in the gallbaldder?
Reabsorption of water caused by ion pumps created a crystalloid oncotic pressure.
What is the importance of bile salts?
Digestion and absorption of lipids.
Emulsifies fats into lipid droplets (micelles).
Also important as a critical excretory fluid - allows body to dispose of lipid soluble end products of metabolism - the only route to dispose of cholesterol.
Where is bile acid formed?
In hepatocytes of the liver
How does bile travel from the liver into the gallbladder?
Leaves the liver via the hepatic bile duct into the common bile duct. Then passes up the cystic duct to the gallbladder.
Name the 3 salivary glands.
Submandibular
Sublingual glands
Parotid glands
What is the function of saliva?
Lubricates food for swallowing and glycoproteins aid starch digestion.
Speech, keeps teeth healthy
What nervous system is responsible for stimulation of the salivary glands?
Autonomic
Sympathetic - release of pre-stored amylase
Parasympathetic - fluid secretion and blood flow increase.
Cholinergic, adrenergic and peptidergic stimulation cause salivation.
What is the function of acinar cells of the salivary glands?
Produce the primary secretion of saliva.
Primary secretion is isotonic.
What is the function of ductal cells of the salivary gland?
Modify the primary secretion by reabsorption of NaCl and secretion of K+ and HCO-. Produces a hypotonic solution called the final secretion.
How does the sympathetic nervous system stimulate acinar cells?
Sympathetic nerve releases noradrenaline - activates α1 and β1 adrenergic receptors.
Increases cAMP production and increases intracellular calcium.
Leads to watery protein secretion
What causes the watery secretion?
Massive increase in blood flow through microvasculature due to arterial smooth muscle tone relaxation.
Increase in blood flow from 0.5 to 10 ml/g leads to watery secretion.
What are gastric pits and what cells are present in them?
Entrance to tubular gastric glands (oxyntic gland.
Contains chief cells, parietal cells.
What is the function of chief cells in the stomach?
Release pepsinogen which is activated in acid to form pepsin.
What is the function of parietal cells?
Secrete HCl into the stomach.
Secretion is stimulated by gastrin.
Where is gastrin produces?
In the G-cells of the stomach and duodenum.
How is the stomach surface protected from HCl?
By a mucus bicarbonate buffer lining secreted by stomach epithelial cells.
What is the role of blood flow during gastric secretion?
Blood flow increases dramatically during secretion which brings bicarbonate from vasculature to buffer the mucosal surface.
Outline the physiological stimulation of gastric acid secretion.
- Gastrin is released from G-cells in stomach epithelium.
- Gastrin binds to CCK 2 receptors of ECL-cell.
- ECL-cell releases histamine which binds to receptor on parietal cell.
- This trigger HCl secretion from the aprietal cell.
How does the negative feedback mechanism control gastric acid secretion?
HCl activates D-cells which release somatostatin which binds to G-cells, inhibiting gastrin secretion.
