GI Physiology

Question 1

What is the GI tract

Answer 1

Also known as the Alimentary canal

A group of specialised organs concerned with digestion and absorption

Question 2

What structures make up the GI tract (in order)

Answer 2

the mouth, pharynx, oesophagus, stomach, small intestine (duodenum, jejunum, ileum), large intestine (colon), rectum, anus

Question 3

Givean example of an acessory structure to the GI tract

Answer 3

Salivary glands

Question 4

What do salivary glands secrete

Answer 4

Amylase, lipaseand mucin (a glycoprotein which helps with lubrication and swallowing)

Question 5

What are the names of the three pairs of salivary glands

Answer 5

Sublingual, submandibular and parotid

Question 6

What is mumps

Answer 6

An infection of the (parotid) salivary glands

Question 7

Explain how the mumps virus enters host cells

Answer 7

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

Question 8

What are some complications of mumps

Answer 8

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

Question 9

Which part of the brain is involved in swallowing

Answer 9

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

Question 10

Which nerves are involved in swallowing

Answer 10

Trigeminal, facial, glossopharyngeal, hypoglossal, vagus

Question 11

What do 40-65% of stroke survivors experience

Answer 11

Dysphagia - damage to the nerves involved in swallowing

Question 12

What structres does the oesophagus pass through

Answer 12

The diaphragm, oesophageal hiatus down to the stomach

Question 13

What is a hiatus hernia

Answer 13

Protrusion of the stomach through the oesophageal hiatus. This often results in acid reflux from the stomach into the oesophagus

Question 14

What cells line a healthy oesophagus

Answer 14

squamous epithelial cells

Question 15

What is the lower oesphageal sphincter (cardiac sphincter)

Answer 15

A structure which

Seals stomach
Prevents acid/digestive enzymes getting into the oesophagus
Prevents gastroesophageal reflux (heartburn)

Question 16

What happens when the cells of the oesophagus are exposed to stomach juices

Answer 16

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

Question 17

What is the risk of having the condition Barretts oesophagus

Answer 17

Patients have a higher risk of adenocarcinoma than general population.

Question 18

Name the 4 gastric cell types and what their role is

Answer 18

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

Question 19

How do chief cells utilise a positive feedback system

Answer 19

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

Question 20

Which pumps pump H ions into the stomach lumen

Answer 20

Hplus, Kplus ATPases

Question 21

What stimulates gastrin release

Answer 21

At sight/smell of food, brain signals to stomach to release gastrin from G cells.

Stretching of stomach also stimulates gastrin release.

Question 22

How does gastrin work to pump H ions into the stomach lumen

Answer 22

Gastrin binds to receptor on Parietal cells, stimulating synthesis of H+, K+ ATPase pumps

Question 23

What role does acetylcholine have in stomach acid production (2 ways)

Answer 23

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

Question 24

Which 3 substrates bind to parietal cells to stimulate HCL secretion

Answer 24

Acetylcholine, histamine, gastrin

Question 25

What two ways can we use to decrease gastric acid production

Answer 25

H2 receptor antagonists

Proton pump inhibitors - PPIs

Question 26

How do H2 receptor antagonists work to reduce gastric acid secretion

Answer 26

H2 receptor antagonists bind to histamine receptor and reduce HCl production

Question 27

Give 2 examples of drugs which are H2 receptor antagonists

Answer 27

Cimetidine (Tagamet)

Ranitidine (Zantac)

Question 28

How do PPIs work to reduce gastric acid secretion work to reduce gastric acid secretion

Answer 28

Omeprazole
Irreversibly binds to sulfhydral groups of the H+,K+–ATPase
Hence it blocks the gastric proton pump

Question 29

Give an example of a PPI

Answer 29

Omeprazole

Question 30

What happens during gastric acid secretion (on a elemental level)

Answer 30

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

Question 31

How do proton pump inhibitors prevent gastric acid secretion (on a elemental level)

Answer 31

Proton pump inhibitors block the proton pump and reduce transport of protons into the stomach lumen.