FULL UNIT 8 REVISION Flashcards
what is bilirubin
- Yellow bile pigment produced through haemolysis
types of bilirubin
conjugated and unconjugated
unconjugated bilirubin
insoluble in water, only travel in the bloodstream if bound to albumin
conjugated bilirubin
soluble in water, can be directly excreted
stages of bilirubin metabolism
creation
conjugation
excretion
creation stages of bilirubin metabolism
- Haem is broken down into iron and biliverdin catalysed by haem oxygenase
- Iron gets recycled
- Biliverdin is reduced to created unconjugated bilirubin
conjugation stages of bilirubin metabolism
- Unconjugated bilirubin will bind to albumin to transport to the lvier
- Glucuronyl transferase adds glucuronic acid to unconjugated bilirubin
- Conjugated bilirubin can be excreted into the duodenum in bile
excretion stages of bilirubin metabolism
- Colonic bacteria deconjugate bilirubin into urobilinogen
- Further oxidised to make sterocobilin
- Excreted in faeces
- Minority of urobilinogen is reabsorbed into the bloodstream in enterohepatic circulation, oxidised in the kidneys to urobilin and excreted in the urine
digestion in the mouth
- Mechanical :mastication
- Reduces size of ingested particles
- Mixes food with saliva, exposing to digestive enzymes
- Increases surface area of the ingested material - Chemical
- Alpha amylase, ptyalin: cleaves internal alpha 1,4-glycosidic bonds in starch, maltos, maltotriose and alpha limit dextrins produced
- Linguinal lipase: hydrolysis of dietary lipids, 3 fatty acids and 1 glycerol
stomach acid secretion
- Gastrin and acetylcholine activate phospholipase C
- PLC catalyses the formation of inositol triphosphate IP3
- IP3 causes release of intracellular Ca2+ and activates calmodulin kinase
- Calmodulin kinase phosphorylates variety of proteins leading to H+ secretion
- ECL cells have cholecystokinin receptors for gastrin
- Gastrin stimulates ECL cells to release histamine
- Histamine activates adenylate cyclase to form cyclic AMP
- Protein kinase A phosphorylates variety of proteins leading to H+ secretion
H+ secretion stomach
- H+ pumped actively into the lumen in exchange for K+ through ATPase
- Cl- enters cells across basolateral membrane in exchange for HCO3-
protein digestion in the stomach
proteins stimulate the G cells to secrete gastrin into the blood
- Gastrin stimulates the ECL cells in the lamina propria to release histamine
- Histamine stimulates acid secreting parietal cells
- Gastrin stimulates parietal cells to release HCl and intrinsic factor and the chief cells to release pepsinogen
- Pepsinogen converted to pepsin which cleaves the protein
- Negative feedback: low antral pH causes D cells to release somatostatin to inhibit G cells to prevent over secretion of acid
digestion of fats in the stomach
- Gastric lipase produced by chief cells in the fundus
- Stimulated by neurohormonal stimuli e.g. gastrin and cholinergic mechanisms
- Inhibited by cholecystokinin and glucagon like peptide GLP-1
digestion of carbohydrates in the stomach
- Salivary amylase is inactivated due to low pH
- Chemical activity is low
- Mechanical breakdown is ongoing
- Strong peristaltic contractions of the stomach mix into chyme via propulsion and retropulsion
duodenum inhibiting gastric emptying
- CCK increases distensibility of the orad stomach
- Acid inhibits motility and emptying
- Secretin and GIP inhibit
carbohydrate digestion in the small intestine
- Pancreatic amylase released following stimulus of secretin and CCK
- Starch digested into maltose, maltotriose and alpha limit dextrins
- Oligosaccharides and disaccharides digested at the brush border by lactase, sucrase, isomaltase and maltase
fat digestion in the small intestine
- Bile acts as an emulsifier to increase the surface area
- Lipase converts lipids to fatty acids and glycerides
- Bile salts envelop the fatty acids and monoglycerides to micelles and at the brush border they will diffuse out of the micelles to absorptive cells
protein digestion in the small intestine
- Proteases: trypsin and chymotrypsin
- Brush border enzymes: peptidases hydrolyse dipeptides and amino acids
absorption of monosaccharides across the intestinal wall
- SGLT1 for glucose uptake
- Energised by the electorchemical Na+ gradient
- Maintained by the extrusion of Na+ across by the Na-K pump by secondary active transport
- Facilitated diffusion mediated by GLUT5 for fructose absorption to the enterocyte
- Facilitated diffusion by GLUT2 across basolateral membrane to interstitial space
glycaemic index
cells in the small intestine
metabolism
catabolism
anabolism
catabolism
breakdown of complex molecules to release energy, glucose and adrenaline
anabolism
use of energy to construct molecules, insulin