Gastrointestinal Physiology Flashcards
What are the 6 main functions of the liver?
- Maintain BSL (gluconeogenesis and glyconeogenesis)
- Protein metabolism (catabolism, ammonia conversion to urea)
- Fat metabolism (converts FFAs to ketones, formation/secretion of bile)
- Inactivation (chemical modification of steroids, makes things less lipophilic, toxins)
- Immunity (Kupffer cells)
- Other shit (plasma proteins, clotting factors, acute phase proteins)
Why do we find abnormally high blood ammonia levels in end stage hepatic failure?
- porto-systemic shunting
- reduced conversion from ammonia to urea
- bacterial production of ammonia in the gut
How is ammonia formed? How much of it gets excreted by kidneys?
What is its relationship to Urea?
Ammonia formed by converting glutamine to glutamate (catalysed by glutaminase in renal tubular cells)
50% excreted by kidneys
Ammonia converted to urea in liver. Kidney does not produce urea but EXCRETES it.
Where is the space of disse?
Between basolateral membrane of hepatocytes and the sinusoids flowing towards the central vein.
Which structures compose the portal triad?
Portal vein
Hepatic Artery
Bile duct
What are the two phases of metabolism in the liver?
Phase 1: hydroxylation/oxidation via CYP450
Phase 2: esterification to allow for hydrophilic excretion
What makes up bile?
Bile salts: Na, K of bile acids cholic acid (50%), chenodeoxycholic acid (30%), deoxycholic acid (15%), lithocholic acid
Bile pigments: glucuronides, bilirubin, biliverdin
Other substances: cholesterol, FFA, lecithin, fat, inorganic salts
Describe the handling of bilirubin by hepatocytes
(fig 28-5 Ganong’s)
- Albumin bound bilirubin enters space of disse
- bilirubin selectively ransported into hepatocyte by OATP
- UDGPG conjugates the bilirubin
- Congugates secreted into bile by MRP2
- some unconjugated and conjugated bili refluxes back into plasma
How much bilirubin in the small intestine re-circulates to liver in enterohepatic circulation?
How much bili is converted to urobilinogen?
How much urobilinogen is excreted in urine?
UNconjugated bilirubin is IMpermeable to intestinal mucosa
conjugated bilirubin passes and about 10% is re-circulated
50% of bili is converted into urobilinogen
5% urobilinogen excreted in urine, rest gets absorbed by intestinal mucosa, re-excreted by liver back into gut
How is uric acid formed? What is the usual plasma level of uric acid?
Breakdown of purines
0.2-0.4 mmol/L
What mechanisms cause true visceral pain? (4)
Ischaemia: due to acidic metabolites
Chemcial stimuli: eg. gastric juices and widespread damage
Spasm: widespread stimulation and diminished blood flow
Overdistension: overstretch collapsing blood vessels and causing ischaemic pain
What are the 3 key enzymes at the brush border of intestines for carbohydrate metabolism?
Maltase - > glucose
Sucrase - > glucose + fructose
Lactase - > glucose + galactose
Describe the ingestion to absorption pathway of vitamin B12
- B12 found in red meats
- source broken down by pepsin and acidic environment breaks it into B12 itself
- B12 binds to transcobalamin and once it goes into duodenum, trypsin break down transcobalamin
- Free B12 binds to intrinsic factor and absorbed in terminal ileum
Which amino acids are “conditionally essential”?
Arginine and histidine (histidine is only AA to have 3 nitrogen molecules)
required during times of rapid growth/recovery
How and where does glycine act as a neurotransmitter?
Hyperpolarises by affecting chloride channels in spinal cord and brain stem. Primarily inhibitory.
