Flashcards in Physiology Gastric Motility and Gastric Secretion and Pharmacology Deck (64):
What are the names of the salivary glands?
Parotid - located below the ear over the master muscle
Submandibular - located under the lower edge of the mandible
Sublingual - located in the floor of the mouth under the tongue
What are the functions of saliva?
Neutralisation of acid
Facilitates sucking in infants
Describe the formation of Saliva?
Two staged process. Primary secretion by the Acinus cells and secondary modification by the duct cells
What cells are important for the primary secretion of saliva?
What cells are important for the modification of saliva?
Describe the structure of a saliva duct?
Acinus cells produce the saliva. Saliva moves into the intercalated duct, then to the striated duct and finally to the excretory duct
Describe the composition of saliva after primary production by the acinus cell?
Similar Na+, K+ Cl-, and HCO3- content to plasma. Contains mucus and amylase
Describe the composition of the duct cells after secondary modification of the saliva?
Cells modify the secretion by removing Na+ and CL-
Adds K+ and HCO- to a lesser extent
There is no net movement of water. The overall effect is dilution of the saliva
What is the rate of saliva production?
0.05 ml/min – sleep
0.5 ml/min – resting, awake state
5 ml/min – “actively” salivating
How does the composition of HCO3- vary with flow rate of saliva?
In higher flow there is an increased HCO3-. In lower flow there is reduced HCO3-
What are the two types of neuronal control that controls saliva production?
Simple reflex - Unconditioned reflex. Mechanical receptors
Conditioned reflex - acquired. This is thinking about food etc
Describe the nerve pathway for the simple reflex for salivary secretion?
Chemo receptors and pressure receptors activate in the mouth. This sends an impulse via afferent nerve fibres to the salivary centre in the medulla.
Impulses extrinsic and autnomic nerves to the salivary glands
Increases salivary gland's saliva production
Describe the nerve pathways for the conditioned reflex for salivary production?
cerebral cortex impulsed to salivary glands. Affects extrinsic nerve control. Salivary glands increase production of saliva.
What effect does the parasympathetic system have on saliva production?
(mediated by M3 muscarinic acetylcholine receptors)
By which nerve does the parasympathetic system affect the saliva production?
Glossopharyngeal and facial nerves
By which nerve does the sympathetic system affect the saliva production?
Postgangionic fibres from superior cervical ganglia.
What effect does sympathetic innervation have on the Saliva?
Mediated by Beta 1 - adrenoreceptor
What sympathetic receptor is affected for saliva secretion?
Beta 1 adrenoreceptors
What parasympathetic receptor is affect for saliva secretion?
M3 muscarinic acetylcholine receptors
When is the parasympathetic dominant in saliva production?
Dominant in normal saliva production
When is the sympathetic dominant in saliva production?
Dominant in stressful times.
What is the top of stomach called?
The Fundus - this is a gas layer
What are rugae?
Folds in the stomach that allow it to expand. When the stomach empties the somatic becomes smooth.
What is the sphincter between the oesophagus and the stomach?
The lower oesophageal sphincter
What is the antrum of the stomach?
The pyloric antrum is the initial portion of the pylorus. It is near the bottom of the stomach, proximal to the pyloric sphincter, which separates the stomach and the duodenum. It may temporarily become partially or completely shut off from the remainder of the stomach during digestion by peristaltic contraction of the prepyloric sphincter
What does the stomach produce?
What is the sphincter between the duodenum and the stomach?
Describe how the stomach empties?
There is a peristaltic contraction in the middle of the somatic. The pyloric sphincter opens and chyme enters the duodenum,
Describe how the stomach mixes food?
There is peristaltic contraction around the antrum of the stomach - The pyloric sphincter is closed. This causes mixing of the stomach.
What gastric factors affect the stomach emptying process?
- Emptying to proportional to the volume of chyme in the stomach. Distenion of the stomach increases vagal tone. Vagus nerve innervates for gastrin levels to increase
- Consistency of chyme
What does distension of the stomach cause?
Distension increases motility due to stretch of smooth muscle, stimulation of intrinsic nerve plexuses, increased vagus nerve activity and gastrin increase
What duodenal factors affect stomach emptying?
Neural response: The enterogastic reflex causesa decrease in antral peristalic activity though signals from the intrinsic nerve plexus and autonomic nervous system.
Hormonal response: Release of entergastrones, like secretin and CCK inhibits stomach contraction
What factors affect the neuronal and normal responses of the duodenum in stomach emptying?
Fat levels - increase in fat levels delay the gastric emptying
Acid levels - increase in acid increases bicarbonate secreted from the pancreas. Important for pancreatic digestive enzymes
Hypertonicity - Danger of loosing water
Distension - increases vagal tone and increases levels of gastrin and increases motility
What cells are present in the gastric glands of the pyloric gland area (antrum) ?
D cells - secrete somatostatin
G cells - secrete Gastrin
What is the function of somatostatin?
Inhibits insulin and glucagon secretion and HCl secretion
What is the function of gastrin?
Stimulates the enterchromaffin-like cell to histamine.
Increases H+ content in the stomach.
What cell are present in the mucous of the oxyntic mucosa (In the funds and body) ?
Chief cells - secrete pepsinogen
Enterochromaffin like cell - secrete histamine
Parietal cell - secrete hydrochloric acid and inartistic factor
What is the function of pepsinogen?
Inactive precursor of the peptidase, pepsin. Note: pepsin once formed activates pepsinogen (autocatalytic)
What is the function of HCL in the stomach?
Activates pepsinogen to pepsin
Kills most (not all) micro-organisms ingested with food
What is the function of internist factor?
Binds vitamin B12 allowing absorption in terminal ileum
What is the function of histamine in the stomach?
Stimulates HCl secretion
What is the function of mucus in the stomach?
Used for protection
Where are the gastric parietal cells located?
Present in the gastric glands of the oxyntic mucosa - In gastric pits of the rugae.
How do Parietal cells make HCl in the stomach?
CO2 is combined with H2O - This makes H2CO3- (carbonic acid)
Carbonic anhydrase catalyses the hydrolysis of carbonic acid into H+ and HCO3-
The H+ goes into the Canaliculus of the Gastric parietal cell. Movement of H+ is out of cell by the H+/K+ ATPase pump into the Canaliculus of the gastric parietal cell. The potassium is then recycled.
Cl- taken into the parietal cell by Cl-/HCO- antiporter. Cl- then moves into the canaliculus by Cl- channel.
H+ joins with Cl- to form HCL.
What is the canaliculus?
The canaliculus is a deep fold in the gastric parietal cell of the oxyntic mucosa.
What binds to the parietal cell to initiate the production of HCl?
Histamine - via the H2 receptor
ACh - via the M3 receptor
Gastrin - via the CCK2 receptor
What binds to the parietal cell to inhibit the production of HCl?
Prostaglandin - via the PGE2 receptor
What is a secretagogue?
This is a substance that causes another substance to be secreted
What happens to the parietal cell during the stimulated state?
Extended microvilli in the canaliculus. This allows H+/K+ ATPase trafficking to the apical membrane of the extended microvilli
What are the three phases of gastric secretion?
What occurs in the cephalic phases?
Sight smell of food sends a signal to the medulla oblongata.
Causes Parasympathic stimulation (Increased in vagal activation) causes an increase in HCl, pepsin and gastrin release.
What occurs in the gastric phase?
Food is in the stomach, the stomach is distended. Causes a parasympathic innervation via the vagus nerves to the medulla oblongata. Causes continued secretion of HCl and pepsin from the gastric glands.
What occurs during the intestinal phase?
Chyme enters the duodenum. When chyme contains the lipids or hydrochloric acids and has a pH below 2 there is a signal to the medulla oblongata which inhibits HCl production and pepsin. Releases hormones of Secretin, Gastric inhibitory peptide and Cholecystokinin which inhibits gastric gland secretion.
Secretion of somatostatin resumes.
What is an example of a Muscarinic receptor antagonist and how does it work?
Competitively blocks the M3 ACh receptor and the M1 ACh receptor on the Paracrine cell.
This prevents the production of HCl
What is an example of the Histamine receptor antagonist and how does it work?
Competitively blocks the H2 receptors. This inhibits HCl production
What is an example of a Proton pump inhibitor and how does it work?
Blocks by covalent modification of the H+/K+ ATPase pump (Proton pump). This inhibits HCl production.
Advantage: They are prodrugs and are inactive in a neutral pH
What is an example of a non-steroidal-antiinflammatory drug and how does it work?
Irreversibly blocks cyclo-oxygenase (COX). This reduces the Prostaglandins which reduces the amount of mucus produced. Causes peptide ulcers
How does the body protect the stomach from HCl and Pepsin?
Hydrophoibic monolayer with a mucus gel layer beneath it. There is a pH gradient as you move down the mucus gel layer.
The stomach produces prostalgangins which:
reduce acid secretion
increase mucus and bicarbonate secretion
increase mucosal blood flow
What prostaglandins are secreted by the stomach lining?
PGE2 and PGI2
How do you treat peptic ulcer?
reducing acid secretion
increasing mucosal resistance
Eradicating H. pylori (not covered here)
Drugs that reduce acid secretion are used for what conditions?
Gastro-oesophageal reflux disease
Acid hyper section
How are proton pump inhibitors such as omeprazole activated?
Two step activation that involves protonation
Give two examples of mucosal strengtheners and how they work?
Bismuth chealate (used in combination with ranitidine)
Bind to the ulcer base and form a complex gel with the mucus
Increase the mucosal blood flow, mucus, bicarbonate and prostaglandin production.