Week 8 Intestines Flashcards
What are the basics of absorption?
Need large SA- mucosa folded into villi, surface covered in micro villi (brush border)
Slow movement of content-precise control needed
What are plicae circulares?
Permenant fold in the gut as oppose to rugae which are temp folds
present in proximal part of small intestines and folds get further apart and narrower as goes down
describe intestinal epithelia- cells present, locations, lifespan and purpose?
- epithelial cells- enterocytes
- goblet cells- mucus producing- into intestinal lumen
- enteroendocrine cells- secrete hormones into blood
- paneth cells- innate defence- antibacterial and viral toxins
mucosa is shed constantly- every 3-6days - affected by chemo
- when shed cells are programmed to die (anoikis)
intestinal gland (crypt)- contains stem cells at base that migrate to the surface, maturing as they do- from point into groove of crypt
- cells in villi are very active- secrete enzymes into brush border to breakdown carbs and proteins - where digestion is complete
what the different sizes of carbs called, which can be absorbed by the gut and where?
polysaccharide- long chains of sugars- starch, cellulose
oligosaccharide- short chain of sugars
disaccharide- 2x sugars
monosaccharide- 1x sugar
only monosaccharides can be absorbed by the gut- fructose, galactose and glucose= end products of carb metabolisms
- final enzyme digestion takes place in brush border
What are the functions of the different parts of the bowel?
Absorb nutrients, water and electrolytes- from gut lumen into blood- paracellular or cellular
what is starch made up of?
starch contains:
- amylose- linear chains of glucose (a-1-4 gylcosidic bonds)
- amylopectin- branches glucose chains (a-1-6 bonds)
how are monosaccharides absorbed once starch has been broken down?
present on apical membrane (lumen and enterocyte):
- SGLT1- cotransports Na down conc grad- binding of Na= conformational change-allows glucose/galactose to bind
- GLUT 5- transports fructose into cell by facilitated diffusion
present of basolateral membrane (enterocyte and capillary):
- Na/K ATPase (3Na into capillary/ 2K into enterocyte)- creates osmotic gradient so Na wants to move in from lumen
- GLUT 2- fructose, galactose and glucose all pass through down grad
where does protein digestion start, what are the breakdown products and what can be absorbed?
in stomach pepsinogen released from chief cells- converted to pepsin by HCI- start of protein digestion
- pepsin acts on protein- oligopeptides/ AAs- then moved to S. intestines
only AAs, dipeptides and tripeptides can be absorbed- nothing larger
describe the role of pancreas secretions in protein digestion?
pancreas releases proteases as zymogens
trypsinogen is important- released by the pancreas
- converted to trypsin by enteropeptidase on the brush borders
trysin then activates other proteases
describe the final stage of protein breakdown- role of proteases?
major proteases:
- endopeptidases- hydrolyse interior peptide bonds
- trypsin, chymotrypsin, elastase
- exopeptidases- hydrolyse from C terminal ends
- carboxypeptidases- A & B
how are protein products absorbed once broken down?
both AAs and small peptides are absorbed- in adults protein is not absorbed
brush border enzymes break down oligopeptides further
1. AAs taken up by active and passive processes
- transported into cell similar to glucose- Na, AA cotransporters- different ones- neutral, acidic, basic, imino
2. dipeptides, tripeptides moved by H+ cotransporter- converted to AA once inside cell by cytosolic peptidases
- most protein products ingested as dipeptides/tripeptides
how is starch digested- broken down?
- digestion starts with a-amylase (saliva) and amylase (pancreas) = breaks a-1-4 bonds= results in glucose and maltose from amyloses and alpha dextrins from amylopactins - broken branches into smaller chains but still have a-1-6 bonds
- these processes produce monosaccharides which can then be absorbed - brush border enzymes:
- isomaltase- breaks a-1-6 bonds = glucose
- alpha dextrinase- glucose
- sucrase- glucose and fructose
- lactase- glucose and galactose
What are the mechanisms of absorption of fats in the small intestines?
D
What are the mechanisms of absorption of salts and water in the intestines?
- Na moved by active transport out of cell on basolateral membrane - Na diffuses into epithelial cells, H20 can also move into intracellular space
- osmotic gradient from all absorption leads to uptake of water- fluid absorbed is isosmotic- if cant absorb electrolytes cant absorb water- diarrhoea
describe the role and differences of water/electrolyte absorption in the S and L intestines
large intestine- last bit of water absorption- water absorption is the main job of the L intestines but it actually absorbs less than the S intestines- has a harder job as has to pick up the remainders
- both S and L intestine have Na/K ATPase on basolateral membrane (cell to capillary)
- APICAL MEMBRANE- S intestine Na cotransported, L intestine Na channels as dont need to co transport- induces by aldosterone
