Digestion and Absorption Flashcards
Two types of digestive enzymes are?
Luminal and Membranous
Luminal enzymes are pretty self-explanatory
Membranous enzymes are those which are inserted into the membranes of cells linng the gut
What are some of the barriers to absorption in the gut?
1) Unrestricted water layer
2) Glycocalyx
3) Microvilli membrane
4) Cytoplasm
5) Basolateral membrane
6) Basement membrane
7) Capillary Fenestrae
Basal cells of the gut lie where?
In crypts…..stem cells move up the villi and differentiate as they do. How do the stem cells divide?——Assymetrically, one stays in the crypt to be another stem cell and one matures.
Gut lining is sloughed off every 3 days
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50% of calories in the American Diet are what
Carbs
What starts carb digestion?
Salivary Amylase
Salivary amylase does what
Hydrolyzes alpha 1,4 linkages to yield disaccharides (maltose, Maltotriose, and alpha limit dextrins (1,4 and 1,6))
Alpha 1,6 dextrins are digested by what membrane proteins?
Glucoamylase (5%)
Isomaltase (95%)
Alpha 1,4 dextrins are digested by what membrane proteins
Glucoamylase (60%)
Sucrase (20)
Isomaltase (20)
Maltotrose digested by what membrane proteins
Basically the same as alpha 1,4 dextrin because it is also a 1,4 linkage
G- 25
Sucrase- 25
I_ 50
Lactose carb digested by
Lactase
Sucrose carb digested by
Sucrase
Trehalose found in
Mushrooms….digested by trehalase
KNOW…all of these carbs turn into glucose at least partially. Which ones also turn into galactose and Fructose
Lactose— glucose and galactose
Sucrose— glucose and fructose
Glucose is absorbed primarily by what method?
Active transport
The fact that glucose is absorbed by active transport means what about its abosorption in the absence of oxygen
Not much of it happens.
SGLT-1
Luminal glucose absorption
How does SGLT-1 work?
It binds 2 sodiums and either a glucose or a galactose and brings them into the cell. The sodium is then exported out of the enterocyte by a Na K ATPase, if this doesn’t work, SGLT-1 doesn;t work.
Glut-5 brings in?
Fructose
Most common carb enzyme deficiency?
Lactase
Glut-2
transports glucose through the blood
What starts protein digestion?
Pepsin
Pepsin does what
Its an endopeptidase so it cleaves peptide linkages
Trypsinogen is converted to trypsin by what enzyme>
Enterokinase
What does it mean to say that trypsin is auto-catalytic
Once it is activated it activates more of itself
Pepsin and pancreatic proteases break down protein into what three things:
Di and Tri- peptides, Large Peptides and Free Amino Acids
Large peptides are then shunted to either the Di and tri peptides or free amino acid
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Lipid soluble amino acids may leave via?
SImple diffusion
Triglycerides are broken down by pancreatic lipase into
2 monoglyceride + 2 FFA
What the hell does colipase do?
It is secreted with pancreatic lipase, it is not an enzyme. It allows pancreatic lipase to get in close enough to an emulsion droplet in order to act on it. Binds to the emulsion droplet and displaces the bile acid, then binds to the pancreatic lipase and anchors it to the droplet.
What activates pro-colipase
Trypsin
Micelles contain what
cholesterol, fatty acids, monoglycerides.
The order of fat absorption
CCK—> Micelle—> Triglyceride re-esterification —> Chylomicron —> Lacteal
What is a lacteal
Lacteals are the lymph vessels that take up fat
Two routes by which water and electrolytes are absorbed
Transcellular and paracellular (tight junctions)
All of the mechanisms for sdium absorption depend on what?
Na K ATPase
Some chloride absorption is linked to HCO3- secretion. THis process occurs where
Colon
Water absorbed mostly in small or large bowel
Small- leaky tight junctions here
POMC signals for what and via what
POMC stimulation leads to low food intake and high metabolism.
Stimulated via alpha MSH
Hunger stimulates — and —– to increase food intake
NPY and AGRP
Leptin does what
released from fat cells to downregulate food intake….fat people make a ton of leptin but they are insensitive to it. Leptin usually stimulates POMC (no more eating) and blocks NPY (hunger).
Ghrelin secreted by
Stomach . It increases apetite.
Peptide YY (PYY)
stimulates POMC
Intestinal smooth muscle contraction stimulated by
Ach
