GIT

Question 1

What is the main function of the stomach

Answer 1

Mechanical breakdown of food to produce chyme

Question 2

What is a gastric mucous cell? What is the function of the mucous it secretes?

Answer 2

Gastric pit cell that secrete mucous. Mucous (controlled by prostaglandins) is slightly alkaline and can protect the stomach lining from the acidic environment.

Question 3

How do NSAIDs lead to the formation of gastric ulcers?

Answer 3

NSAIDs act on prostaglandins, therefore reducing gastric mucous secretion. Insufficient mucous leads to ulcers

Question 4

Describe function of parietal cells. How are secretions from parietal cells mediated?

Answer 4

Secrete HCl and intrinsic factor. Secretion is response to histamine release from ECL cells.

Question 5

What is intrinsic factor? How does it relate to B12

Answer 5

Vitamin B12 is only taken up by the ileum when it is a complex with intrinsic factor. B12 is important for fatty acid metabolism and DNA synthesis

Question 6

What are the 3 enteroendocrine cells and what do they secrete?

Answer 6

G - secretes gastrin, a hormone that promotes the release of histamine from ECL cells
A - secretes glucagon
D - secretes somatostatin

Question 7

Function of chief cells?

Answer 7

Secretes pepsinogen, the precursor to pepsin (responsible for breaking down proteins)

Question 8

Explain the release of H+ from the proton pump

Answer 8

Proton pump = active transporter. Pumps H+, K+ and Cl- into the lumen. H+ and Cl- come together in the lumen to form HCL

Question 9

HCL function in stomach?

Answer 9

• acidic environment allows for pepsinogen to be converted to pepsin
• denatures proteins, exposing them to digestive enzymes
• kills microbes

Question 10

Name 3 receptors found in small intestine

Answer 10

• muscarinic (ACh)

- alpha 1 and beta 2 (adrenoreceptors)

Question 11

Gastrin and CCK inhibit gastric motility, whereas somatostatin and GIP (gastric inhibitory peptide) stimulate motility. True or false?

Answer 11

False. It is the opposite. Gastrin and CCK stimulate

Question 12

Name 2 uses of prokinetic agents

Answer 12

• relieve nausea due to overeating

- IBS

Question 13

Explain the role of acetylcholine in gastric motility

Answer 13

ACh binds to muscarinic receptors on the smooth muscle cells. This activates the muscle and leads to contraction.

Question 14

Compare the 5-ht 4 and 5-ht 3 receptors in the GIT

Answer 14

4 - stimulates motility by increasing ACh release

3- mediates nausea and abdominal pain

Question 15

Explain how D2 and CB1 receptors inhibit gastric motility

Answer 15

D2 = binding of agonist to D2 receptor blocks the releases of ACh 
CB1 = cannabinoids reduce gut motility ... effect on nervous system maybe?

Question 16

Compare metoclopramide and domperidone

Answer 16

Metoclopramide = both an antagonist of D2 and agonist at 5-HT4

Domperidone = D2 antagonist
Both increase motility and are antiemetics

Question 17

Explain the CTZ (chemoreceptor trigger zone) and how it leads to activation of the vomiting centre in the medulla.

Answer 17

CTZ is an area of the brain where the BBB is not developed. Allows brain to measure / detect what is in the blood stream. If opioids, chemo drugs, etc are detected, the vomiting reflex can be activated

Question 18

Explain the process of the inner ear activating vomiting.

Answer 18

Labyrinth in the inner ear detects info about posture, movement, etc. it can induce vomiting when rapid movement (kinetosis) is detected = motion sickness. Info is carried to medulla via Cholinergic pathway (muscarinic receptors and ACh)

Question 19

Why can’t dopamine antagonists be used for motion sickness?

Answer 19

No dopamine receptors in the labyrinth

Question 20

What effect do dopamine antagonists have on vomiting and gastric motility?

Answer 20

Vomiting =antiemetic

Motility = increase

Question 21

List some side effects on dopamine antagonists?

Answer 21

Extrapyramidal / Parkinson’s symptoms (like muscle dystopia, muscle stiffness, tremors)
Others:
Increased prolactin release 
Sedation 
Hypotension

Question 22

List 2 examples of a dopamine antagonist and muscarinic antagonist.

Answer 22

Dopamine =

• metoclopramide
• promethazine

Muscarinic =

• scopolamine
• hyoscine

Question 23

How do muscarinic antagonists work as antiemetics

Answer 23

Block muscarinic receptors in vomiting centre and reduce nausea associated with kinetosis (motion sickness)
Can be given transdermally to minimise systemic effects (sludge-bbb)

Question 24

What does SLUDGE-BBB stand for? Side effects of activating muscarinic receptors.

Answer 24

Salivation, lacrimation, urination, defecation, gastroEmesis, bronchorrhea, bronchospasm, bradycardia
Antagonist of M receptors = opposite effects.

Question 25

Name for serotonin antagonists is ____

Answer 25

Setrons

Question 26

Setrons are used to treat acute ekes is caused by xxx and xxx

Answer 26

Radiotherapy / chemotherapy or post op

Question 27

Example of setrons used as antiemetic?

Answer 27

Ondansetron (note suffix)

Question 28

3 treatment options for hyperemesis gravidarum?

Answer 28

Severe vomiting during pregnancy 1. IV rehydration 2. D2 antagonists (metoclopramide) 3. Ondansetron

Question 29

Explain MOA of bulk laxatives

Answer 29

Contains non-absorbable carbs and fibre supplements are aren’t digested. They swell with water, and the presence of the large bulk promotes peristalsis and initiates defecation reflex.

Question 30

Example of bulk laxative

Answer 30

Methylcellulose | Psyllium

Question 31

Describe MOA of osmotic laxatives

Answer 31

Non-absorbable sugars which increase the stool osmolarity, which draws fluid in. Onset usually 1-3 days. Can cause bloating or cramping

Question 32

Describe osmotic laxatives II MOA

Answer 32

More intense osmotic laxatives. Used before surgery. Works in 1-3 hours

Question 33

Give examples of both osmotic and osmotic II laxatives

Answer 33

Osmotic - lactulose - sorbitol Osmotic II - epsom salt

Question 34

Explain MOA of stimulant laxatives

Answer 34

Directly stimulate the myenteric plexus to promote peristalsis and defecation E.g. senna

Question 35

Which laxative can lead to dependence with frequent use?

Answer 35

Senna - stimulant laxatives

Question 36

Explain MOA of faecal softeners

Answer 36

Anionic surfactant that lowers the surface tension of the stool, making it easier to pass. Typically combined with other laxative types as it s quite weak alone E.g. docusate

Question 37

Compare the 3 different types of diarrhoea. Secretory, osmotic and exudative

Answer 37

``` Secretory = stimulating substance have increased secretions. Osmotic = poor absorption of water in the colon Exudative = caused by inflammation or infection. Mucous present in stool. Due to reduction in contact time with the Small intestine, meaning not enough time to extract water ```

Question 38

Describe MOA of loperamide

Answer 38

Blocks the action of ACh on smooth muscle cells, leading to reduced GIT motility. By slowing down GIT, more time available for water absorption.

Question 39

Compare D2 and 5-HT4 receptors in GIT

Answer 39

Agonist @ D2 = decreased motility due to block of ACh release Agonist @ 5-HT = increased motility due to increased ACh release

Question 40

Describe MOA of metoclopramide. Which receptors does it act on

Answer 40

Increases motility by encouraging ACh release. | Agonist at 5ht4 and antagonist at D2

Question 41

Do cannabinoids increase or decrease gut motility?

Answer 41

Decrease

Question 42

What does CRTZ stand for

Answer 42

Chemoreceptor trigger zone

Question 43

Describe the CRTZ

Answer 43

area of the brain located near 4th ventricle where the BBB is not developed, allowing the brain to measure / sense what is in the blood stream. When chemotherapy drugs, opioids, etc, are detected, the vomiting reflex can be activated.

Question 44

Name 4 different sources of input into the vomiting centre of the medulla

Answer 44

- labyrinth - higher cortical centres - CRTZ - stomach

Question 45

Dopamine agonists increase motor control, therefore describe some of the extrapyrimidal side effects of dopamine antagonists

Answer 45

Tremors, muscle stiffness, dystonia (uncontrolled contractions), etc

Question 46

Name 2 dopamine antagonists and their use

Answer 46

Metoclopramide and promethazine. | Used as anti-emetics. Increases ACh release

Question 47

Describe MOA of scopolamine and hyoscine, including which receptors they bind to and systemic side effects

Answer 47

Bind to muscarinic receptors in the vomiting centre. They reduce nausea associated with motion sickness Given transdermal to avoid side effects. (Opposite of sludge-bbb)

Question 48

How do setrons suppress nausea

Answer 48

Block 5-ht3 receptors in gut and vomiting centre