Digestion and defence Flashcards
(43 cards)
enterocyte turnover
3-7 days
stages of carbohydrate digestion
- salivary amylase initiates digestion, hydrolysing starch to maltose, maltotriose and alpha limit dextrin
- pancreatic amylase continues this process
- brush border dissaccharidases further hydrolyse the carbohydrates
four different membrane bound disaccharidases + function
lactase- lactose into glucose and galactose
maltase- maltose or maltotriose into glucose
sucrase- sucrose into glucose and fructose
sucrose-isomaltase- sucrase hydrolyses sucrose into glucose and fructose, isomaltase maltose and maltotriose into glucose
which carbohydrate isomers are absorbed?
D
where are the disaccharidases expressed?
apical membrane of the small intestine
how do carbohydrates move across the apical bilayer?
SGLT1- glucose and galactose across the apical membrane utilising sodium gradient
GLUT2- can be inserted
GLUT5- fructose
how do carbohydrates move across basolateral bilayer?
GLUT2
by which point is carbohydrate absorption completed?
mid jejunum
what happens to unabsorbed carbohydrates?
stimulate colonic motility and secretion, leading to cramps and diarrhea
will be present in stool
explain the components and actions of oral rehydration therpapies
contain isoosmotic solution of salt and glucose
glucose is taken up via SGLT1 alongside sodium
water follows the sodium
leading to less water loss
where are proteins absorbed? + what form?
small intestine, amino acids and peptides
stages of protein digestion
- pepsinogen cleaved in acidic environment to form pepsin, activated by truncation
- pepsin is an endopeptidase that breaks down proteins into smaller peptides in the stomach
- pancreatic endopeptidases further digest proteins to form oligopeptides 2-6aa and amino acids
two pancreatic endopeptidases
trypsin and chymotrypsin
difference between trypsin and chymotrypsin
trypsin selects for basic amino acids, lysine and arginine
chymotrypsin selects for aromatic amino acids, phenylalanine, tryptophan and tyrosine
what activates trypsin?
enteropeptidase
what is enteropeptidase?
a serine protease enzyme produced by the cells of the duodenum that converts the zymogen trypsinogen to its active form trypsin
what digestion occurs at the brush border?
oligopeptide digestion to form tri and di peptides
how are amino acids absorbed ?
by apical carriers, mostly sodium dependent with different classes- neutral, cationic and basic
then move out basolaterally via sodium independent carriers
how are di/tripeptides absorbed?
absorbed by hydrogen dependent apical carrier protein PEPT-1
once within the cell, cytsolic peptidases convert the peptides to amino acids
amino acids then move out basolaterally via sodium independent transporters
where is absorption complete by?
end of the jejunum
where does the majority of lipid digestion take place?
small intestine
stages of lipid digestion
- muscular movements emulsify fats with bile salts
- pancreatic lipase digest triglycerides to monoglycerides and free fatty acids
- pancreatic colipase enables lipase o bind to the emulsion
stages of lipid absorption
- monoglycerides and free fatty acids are incorporated into micelles using bile salts from the liver
- micelles diffuse in the unstirred acidic later adjacent to the apical membrane
- components dissociate at the cell surface
- components are reassembled in the SER
- combine with apolipoproteins in the RER to form chylomicrons
- chylomicrons are then exported by the golgi into the lymphatic capillaries
- lymph drains back into the left subclavian vein via the thoracic duct or lymphatic duct
bile composition
water- 97%
bile salts 0.7%
bilirubin 0.2%
fats 0.51%- cholesterol, fatty acids and lecthinin
