GIT Flashcards
What is the main function of the stomach
Mechanical breakdown of food to produce chyme
What is a gastric mucous cell? What is the function of the mucous it secretes?
Gastric pit cell that secrete mucous. Mucous (controlled by prostaglandins) is slightly alkaline and can protect the stomach lining from the acidic environment.
How do NSAIDs lead to the formation of gastric ulcers?
NSAIDs act on prostaglandins, therefore reducing gastric mucous secretion. Insufficient mucous leads to ulcers
Describe function of parietal cells. How are secretions from parietal cells mediated?
Secrete HCl and intrinsic factor. Secretion is response to histamine release from ECL cells.
What is intrinsic factor? How does it relate to B12
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
What are the 3 enteroendocrine cells and what do they secrete?
G - secretes gastrin, a hormone that promotes the release of histamine from ECL cells
A - secretes glucagon
D - secretes somatostatin
Function of chief cells?
Secretes pepsinogen, the precursor to pepsin (responsible for breaking down proteins)
Explain the release of H+ from the proton pump
Proton pump = active transporter. Pumps H+, K+ and Cl- into the lumen. H+ and Cl- come together in the lumen to form HCL
HCL function in stomach?
- acidic environment allows for pepsinogen to be converted to pepsin
- denatures proteins, exposing them to digestive enzymes
- kills microbes
Name 3 receptors found in small intestine
- muscarinic (ACh)
- alpha 1 and beta 2 (adrenoreceptors)
Gastrin and CCK inhibit gastric motility, whereas somatostatin and GIP (gastric inhibitory peptide) stimulate motility. True or false?
False. It is the opposite. Gastrin and CCK stimulate
Name 2 uses of prokinetic agents
- relieve nausea due to overeating
- IBS
Explain the role of acetylcholine in gastric motility
ACh binds to muscarinic receptors on the smooth muscle cells. This activates the muscle and leads to contraction.
Compare the 5-ht 4 and 5-ht 3 receptors in the GIT
4 - stimulates motility by increasing ACh release
3- mediates nausea and abdominal pain
Explain how D2 and CB1 receptors inhibit gastric motility
D2 = binding of agonist to D2 receptor blocks the releases of ACh CB1 = cannabinoids reduce gut motility ... effect on nervous system maybe?
Compare metoclopramide and domperidone
Metoclopramide = both an antagonist of D2 and agonist at 5-HT4
Domperidone = D2 antagonist
Both increase motility and are antiemetics
Explain the CTZ (chemoreceptor trigger zone) and how it leads to activation of the vomiting centre in the medulla.
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
Explain the process of the inner ear activating vomiting.
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)
Why can’t dopamine antagonists be used for motion sickness?
No dopamine receptors in the labyrinth
What effect do dopamine antagonists have on vomiting and gastric motility?
Vomiting =antiemetic
Motility = increase
List some side effects on dopamine antagonists?
Extrapyramidal / Parkinson’s symptoms (like muscle dystopia, muscle stiffness, tremors) Others: Increased prolactin release Sedation Hypotension
List 2 examples of a dopamine antagonist and muscarinic antagonist.
Dopamine =
- metoclopramide
- promethazine
Muscarinic =
- scopolamine
- hyoscine
How do muscarinic antagonists work as antiemetics
Block muscarinic receptors in vomiting centre and reduce nausea associated with kinetosis (motion sickness)
Can be given transdermally to minimise systemic effects (sludge-bbb)
What does SLUDGE-BBB stand for? Side effects of activating muscarinic receptors.
Salivation, lacrimation, urination, defecation, gastroEmesis, bronchorrhea, bronchospasm, bradycardia
Antagonist of M receptors = opposite effects.
Name for serotonin antagonists is ____
Setrons
Setrons are used to treat acute ekes is caused by xxx and xxx
Radiotherapy / chemotherapy or post op
Example of setrons used as antiemetic?
Ondansetron (note suffix)
3 treatment options for hyperemesis gravidarum?
Severe vomiting during pregnancy
- IV rehydration
- D2 antagonists (metoclopramide)
- Ondansetron
Explain MOA of bulk laxatives
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.
Example of bulk laxative
Methylcellulose
Psyllium
Describe MOA of osmotic laxatives
Non-absorbable sugars which increase the stool osmolarity, which draws fluid in. Onset usually 1-3 days. Can cause bloating or cramping
Describe osmotic laxatives II MOA
More intense osmotic laxatives. Used before surgery. Works in 1-3 hours
Give examples of both osmotic and osmotic II laxatives
Osmotic
- lactulose
- sorbitol
Osmotic II
- epsom salt
Explain MOA of stimulant laxatives
Directly stimulate the myenteric plexus to promote peristalsis and defecation
E.g. senna
Which laxative can lead to dependence with frequent use?
Senna - stimulant laxatives
Explain MOA of faecal softeners
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
Compare the 3 different types of diarrhoea. Secretory, osmotic and exudative
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
Describe MOA of loperamide
Blocks the action of ACh on smooth muscle cells, leading to reduced GIT motility. By slowing down GIT, more time available for water absorption.
Compare D2 and 5-HT4 receptors in GIT
Agonist @ D2 = decreased motility due to block of ACh release
Agonist @ 5-HT = increased motility due to increased ACh release
Describe MOA of metoclopramide. Which receptors does it act on
Increases motility by encouraging ACh release.
Agonist at 5ht4 and antagonist at D2
Do cannabinoids increase or decrease gut motility?
Decrease
What does CRTZ stand for
Chemoreceptor trigger zone
Describe the CRTZ
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.
Name 4 different sources of input into the vomiting centre of the medulla
- labyrinth
- higher cortical centres
- CRTZ
- stomach
Dopamine agonists increase motor control, therefore describe some of the extrapyrimidal side effects of dopamine antagonists
Tremors, muscle stiffness, dystonia (uncontrolled contractions), etc
Name 2 dopamine antagonists and their use
Metoclopramide and promethazine.
Used as anti-emetics. Increases ACh release
Describe MOA of scopolamine and hyoscine, including which receptors they bind to and systemic side effects
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)
How do setrons suppress nausea
Block 5-ht3 receptors in gut and vomiting centre
