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.
Which cell secretes somatostatin and what is its function?
D-cells in the stomach.
Somatostatin inhibits further gastrin secretion by G-cells.
What does Omeprazole do?
Forms disulphide link with H+/K+ ATPase - blocking enzyme irreversibly.
Inhibits gastric HCl secretion.
Therapy for peptide ulcer.
What can occur if the mucus layer of the stomach is damage?
HCl can destroy epithelium and activate mast cells.
Mast cells secret histamine and damage blood stream epithelium
Causes a peptic ulcer
Name the 3 phases of gastric secretion in order.
Cephalic phase
Gastric phase
Intestinal phase
What occurs during the cephalic phase of gastric secretion?
Salivary secretions.
Sight/thought of food or stimulation of taste/smell receptors stimulates the hypothalamus/medulla oblongata. Sends action potential via vagus nerve to stimulate salivary secretion.
What occurs during the gastric phase of gastric secretion?
Stomach distension activates stretch receptors which acts via local reflexes or via vagovagal reflexes to cause gastric secretion in the stomach
What occurs during the intestinal phase of gastric secretion?
Presence of low pH and partially digested foods in the duodenum stimulates intestinal gastrin release into the blood stream which stimulates secretory activity.
What are the constituents of pancreatic secretion?
Rich in HCO3- -neutralises duodenal content.
Proteolytic enzymes - trypsinogen, chymotrypsinogen, procarboxypolypeptidase, ribonuclease, deoxribonucelase.
Amylase and lipase
How is pancreatic secretion produced?
Active process of ATPase and tritransporter enables accumulation of Cl- in the acinar lumen which creates an NaCl rich fluid.
Na+ can flow though gap junctions along with H2O
What is a zymogen granule?
Specialised storage organelle in the exocrine pancreas that allows sorting, packaging and regulating apical secretion of digestive enzymes.
