Q11

What factors regulate gastric secretion?

Neural and hormonal OR

Cephalic, Gastric and intestinal

Cephalic; food in mouth -> vagus,

psychologic states eg anger hostility -> hypersecretion


Gastric:
food in stomach, local receptors eg to amino acid and protein digestions -> post ganglionic neurons -> parietal cells -> acid secretion
Intestinal: fats, carbohydrates, and acid in duodenum inhibit gastric acid secretion and pepsin secretion as well as motility by neural and hormonal mechanisms Eg peptide YY


Neural
: Vagal increases gastrin secretion in G cells by GRP. Gastrin stimulates gastric acid and pepsin secretion as well as motility.

Hypoglycaemia via vagus to stimulate acid and pepsin secretion

Also alcohol and caffeine stimulate gastric secretion

Pass: Need to name both and give an example of each (vagus, hormonal eg: gastrin)


Q12

Describe the composition of pancreatic juice.

Composition: cations, anions, HCO3-, Digestive enzymes — Proenzyme trypsinogen converted to trypsin by enteropeptidase (enterokinase) from brush border. Trypsin converts chymotrypsinogens, proelastase, procarboxypeptidases to active enzymes. Digestive enzymes in zymogen granules in acinar cells in alveolar glands, discharged by exocytosis into pancreatic ducts.

Describe the regulation of secretion of pancreatic juice.

Secretin — HCO3-, 1500m1/day; bile secretion. CCK — releases zymogen granules (also vagal acetylcholine)


Q13

List the principal functions of the liver.

  • Bile formation (500mL/day)
  • Synthesis – protein, coagulation factors, albumin
  • Inactivation/detoxicification – drugs, toxins, active circulating substances
  • Nutrient vitamin absorption, metabolism/control (e.g. glucostat), amino acids, lipids, fat soluble vitamins
  • Immunity (especially gut organisms) – Kupffer/macrophages in sinusoid endothelium

Pass Criteria:

  • 3/5 bold + example to pass

Describe the metabolism of bilirubin.

  • Formed by breakdown of Hb
  • Bound to albumin in the blood
  • In liver – actively transported (OATP) as dissociates – binds to cytoplasmic proteins
  • Conjugated by glucoronyl-transferase in endoplasmic reticulum  with glucuronic acid to H2O soluble bilirubin-diglucoronide
  • Bilirubin diglucoronide active transport (MDRP2) against concentration gradient to bile caniliculi – to gut (<5% bil/bdg reflux to blood)
  • Intestinal mucosa relatively impermeable
  • Gut bacteria act/convert most to urobilinogens
  • Some bile pigments/urobilinogens/unconjugated bilirubin reabsorbed in portal circulation – most resecreted = enterohepatic circulation
  • Small amoutns urobilinogen in blood excreted in urine – urobilinogen and faeces – stercobilinogen

Pass Criteria:

  • Bold to pass

Q14

Describe the metabolism of bilirubin.

  • Formed by breakdown of Hb
  • Bound to albumin in the blood
  • In liver – actively transported (OATP) as dissociates – binds to cytoplasmic proteins
  • Conjugated by glucoronyl-transferase in endoplasmic reticulum  with glucuronic acid to H2O soluble bilirubin-diglucoronide
  • Bilirubin diglucoronide active transport (MDRP2) against concentration gradient to bile caniliculi – to gut (<5% bil/bdg reflux to blood)
  • Intestinal mucosa relatively impermeable
  • Gut bacteria act/convert most to urobilinogens
  • Some bile pigments/urobilinogens/unconjugated bilirubin reabsorbed in portal circulation – most resecreted = enterohepatic circulation
  • Small amoutns urobilinogen in blood excreted in urine – urobilinogen and faeces – stercobilinogen

Pass Criteria:

  • Bold plus one more concept to pass

What are the causes of jaundice?

  • Excess production of bilirubin (e.g. haemolytics anaemia)
  • Decreased uptake of bilirubin into hepatic cells
  • Disturbed intracellular protein binding or conjugation
  • Disturbed secretion of conjugated bilirubin into the bile canniliculi
  • Intra- or extra-hepatic bile duct obstruction

NB. First three causes liberate free bilirubin; last two causes result in elevated conjugated bilirubin in blood.

Pass Criteria:

  • Bold to pass