6- Intestines Flashcards
(25 cards)
Describe the state of chyme when it enters the intestines
Isotonic
Neutral
Nearly completely digested
Describe intestinal epithelia
Simple columnar epithelium - enterocytes
Goblet cells
Within intestinal gland:
Enteroendocrine cells
Paneth cells (antibacterial)
Stem cells (cells mature as they migrate to the surface)
How are carbohydrates digested?
Polysaccharides broken down into monosaccharides by brush border enzymes
Monosaccharide absorbed with Na
Describe how starch is broken down
Maltase breaks a1,4 bonds to form maltose (glucose+glucose) and alpha dextrins, strands of amylopectin still with a1,6 bonds in tact
Isomaltase breaks a1,6 bonds to form glucose
Describe how lactose is broken down
Lactase breaks it down into glucose and galactose
Describe how sucrose is broken down
Sucrase breaks it down into glucose and fructose
Describe the structure of starch
Made up of two molecules - straight chained amylose with A1,4 bonds
Branched amylopectin with A1,6
How are monosaccharides absorped?
Basolateral Na/K ATPase maintaines low intraceullular Na
SGLT-1 binds to Na, allows glucose to bind and move into enterocyte
GLUT2 transports glucose out of enterocyte (fructose uses GLUT5)
Why is Na and glucose given in oral rehydration?
Uptake of Na generates an osmotic gradient, water follows
Glucose uptake stimulates Na uptake
Describe protein digestion in the stomach
Pepsinogen released from chief cells
Converted to pepsin by HCl
Pepsin breaks down proteins into amino acids
What happens when trypsinogen is released from the pancreas?
Enteropeptidase converts trypsinogen into trypsin
Trypsin then activates other proteases
Define exopeptidases
Exopeptidases break bonds at the ends of polypeptides to produce dipeptides/single amino acids
Define endopeptidases
Endopeptidases break bonds in the middle of polypeptide to produce shorter polypeptide
Give examples of endo and exopeptidases
Endopeptidases: Trypsin Chymotrypsin Elastase Exopeptidases: Carboxypeptidase A and B
Why are amylase plasma levels tested?
In acute pancreatitis, amylase is released into blood
Describe the absorption of protein products
Amino acids transported into eclls by Na co-transporter
Majority - Dipeptides moved into cell by H+ co-transporter PepT1, when cytosolic peptidases break them down into amino acids
Describe water uptake in the intestines
Both small and large have Na/K ATPase basolaterally
Apically:
Small: Na co-transporter (most reabsorbed here)
Large: Na+ channels, induced by aldosterone, diffuses
Describe the uptake of calcium in the duodenum
When calcium intake is low
Active transcellular transport, Ca enters via facilitated diffusion - Ca ATPase removes Ca from basolateral membrane
Vitamin D activates calbindin (Ca intracellular transport protein) and is activated by parathyroid horomone
When calcium intake is high
Passive paracellular absorption
Where is iron stored in the body?
Half in haemoglobin
Half in ferritin complexes in bone marrow, liver and spleen
How is iron absorbed?
In haem, absorbed across apical membrane by co-transport with H+
Why do proton pump inhibitors affect iron absorption?
Gastric acid cotransporter, so needed to drive reuptake. PPIs inhibit gastric acid secretion
How is iron uptaken when levels are high and low?
High: Iron contained in ferritin complexes within cell, lost when enterocyte is replaced
Low: Iron binds to transferrin, transported to stores
Describe vit b12 uptake and what can affect it
Absorbed in terminal ileum and bound to intrinsic factor, which is secreted by gastric parietal cells.
Gastritis, terminal ileal removal (for Cronn’s disease) and PPIs all decrease absorption
Describe the disease process of coeliac disease
Intolerance of gliadin fraction of gluten
Causes immune response that damages intestinal mucosa:
Lose intestinal villi
Lengthen intestinal crypts
Lymphocytes infiltrate epitheliumm, impairing digestion
