GI Physiology Flashcards
What is the GI tract
Also known as the Alimentary canal
A group of specialised organs concerned with digestion and absorption
What structures make up the GI tract (in order)
the mouth, pharynx, oesophagus, stomach, small intestine (duodenum, jejunum, ileum), large intestine (colon), rectum, anus
Givean example of an acessory structure to the GI tract
Salivary glands
What do salivary glands secrete
Amylase, lipaseand mucin (a glycoprotein which helps with lubrication and swallowing)
What are the names of the three pairs of salivary glands
Sublingual, submandibular and parotid
What is mumps
An infection of the (parotid) salivary glands
Explain how the mumps virus enters host cells
The viral surfact protein hemagglutinin neuraminidase binds to a receptor on the host cell.
The host cell receptor is a trisaccharide containing alpha2,3-linked sialic acid
Upon binding to the hosts receptor the virus enters the host cell
What are some complications of mumps
When the pancreas is infected patients can develop temporary or permanent diabetes
In post adolescent males, the testes can become infected which may lead to sterility
Which part of the brain is involved in swallowing
Receptors in the mouth and throat relay information to the medullar oblongata in the brain stem. On processing the information impusles are sent from the brain to the throat muscle to initiate swallowing
Which nerves are involved in swallowing
Trigeminal, facial, glossopharyngeal, hypoglossal, vagus
What do 40-65% of stroke survivors experience
Dysphagia - damage to the nerves involved in swallowing
What structres does the oesophagus pass through
The diaphragm, oesophageal hiatus down to the stomach
What is a hiatus hernia
Protrusion of the stomach through the oesophageal hiatus. This often results in acid reflux from the stomach into the oesophagus
What cells line a healthy oesophagus
squamous epithelial cells
What is the lower oesphageal sphincter (cardiac sphincter)
A structure which
Seals stomach
Prevents acid/digestive enzymes getting into the oesophagus
Prevents gastroesophageal reflux (heartburn)
What happens when the cells of the oesophagus are exposed to stomach juices
The patient gets erosion of epithelium
Cells replaced with abnormal cells - a pre-cancerous cell type not normally found in the body
Even if reflux is controlled & oesophagus heals the abnormal cells remain
What is the risk of having the condition Barretts oesophagus
Patients have a higher risk of adenocarcinoma than general population.
Name the 4 gastric cell types and what their role is
Mucous-secreting cells (found in the cardiac region of the stomach): release mucus
G-cells (antrum): enteroendocrine type cells - secrete the hormone gastrin which leads to acid production
Chief cells (found in the fundus/body of the stomach): secrete pepsinogen and lipase
Parietal (oxyntic) cells (fundus/body): secrete HCl
How do chief cells utilise a positive feedback system
They secrete pepsinogen (an inactive form of pepsin). This inactive form is known as a zymogen.
When secreted into the stomach it interacts with HCL converting it to the active pepsin. When more pepsinogen is secreted this is also turned into pepsin via a positive feedback loop
Which pumps pump H ions into the stomach lumen
Hplus, Kplus ATPases
What stimulates gastrin release
At sight/smell of food, brain signals to stomach to release gastrin from G cells.
Stretching of stomach also stimulates gastrin release.
How does gastrin work to pump H ions into the stomach lumen
Gastrin binds to receptor on Parietal cells, stimulating synthesis of H+, K+ ATPase pumps
What role does acetylcholine have in stomach acid production (2 ways)
Stomach nerves release acetylcholine. Acetylcholine binds to receptors on Parietal cells, stimulating HCl production
Acetylcholine also binds to enterochromaffin-like ECL cells. ECL cells produce histamine. Histamine binds to receptors on Parietal cells, stimulating HCl production
Which 3 substrates bind to parietal cells to stimulate HCL secretion
Acetylcholine, histamine, gastrin
What two ways can we use to decrease gastric acid production
H2 receptor antagonists
Proton pump inhibitors - PPIs
How do H2 receptor antagonists work to reduce gastric acid secretion
H2 receptor antagonists bind to histamine receptor and reduce HCl production
Give 2 examples of drugs which are H2 receptor antagonists
Cimetidine (Tagamet)
Ranitidine (Zantac)
How do PPIs work to reduce gastric acid secretion work to reduce gastric acid secretion
Omeprazole
Irreversibly binds to sulfhydral groups of the H+,K+–ATPase
Hence it blocks the gastric proton pump
Give an example of a PPI
Omeprazole
What happens during gastric acid secretion (on a elemental level)
Chloride ions are transported into the periatal cell from the blood. Chloride ions diffuse across the cell and exit out of a chloride channel into the stomach lumen. Also, the proton potassium ATPase actively pumps protons into the lumen so the lumen then contains hydrochloric acid
How do proton pump inhibitors prevent gastric acid secretion (on a elemental level)
Proton pump inhibitors block the proton pump and reduce transport of protons into the stomach lumen.
