Digestion and Absorption of Macronutrients Flashcards
Duodenuym and ionic concentrations
ionic concentrations rapidly come to match the ECF concentrations earlly in the dyodenum. Want to bring to isotonic.
Nutrients we ingest are not lipophilic. How do we get them in?
Transporter proteins.
constituent binds. May be coupled with Na or H, or may require ATP
IMPORTANT if we shut down NaK pump, we get problems with absorption
Major plasma ions
Cations= Na, K
anions= Cl, HCO3
special cases Ca, Fe
2 ways to get ions across brush border
Paracellular pathway= tight junctions between cells regulate. cations more soluble than chloride
Transcellular pathway= via pores or transporters
Dont fuck with Cl
CFTR and Cach all depend on what we do with chloride
Na absorption in early duodenum
transcellular
Na absorption in proximal SI
Na/H exchanger,
moves more Na than simple diffusion
Na absorption in distal SI
Secondary active transport dependant on NaK Atpase
Na absorption in ileum to LI
Na/Cl transporter
Cl absorption in distal SI and LI
Na/Cl cotransporter
Cl absorption in proximal GI
Cl/HCO3 antiporter
K absorption
predominatly paracellular in SI
in LI, it is freely diffuseable, but usually results in net secretion
Ca absorption from lumen
strongly controlled by Vit D (which requires the liver, skin, kidneys)
Ca moves through the Ca-ch TRPV
presence of TRPV on membrane is controlled by Vit D.
channel always open, if expressed on cell
In the cell, Calbinding scoops up Ca to keep it from being toxic
Ca from enterocyte to blood
Ca in cell is bound to calbindin to keep it out of trouble.
Ca extruded from cell to blood via Ca-ATPase= primary active pump
absorption of H20
set up by the absorption of ions
need to put a pore on membrane to get it across.
absorption of water predominates later in the GI tract
CHO digestion - amylase
salivary or pancreatic
breaks CHO down to disaccharides
Disaccidases
chop specific disaccharides into monosacharides
Maltase
chops maltose into two glucoses
lactase
lactose to glucose and galactose
sucrase
sucrose to glucose and fructose
Fructose absorption
has its own transporter, facilitated transport, doesnt need active bc we convert it to glucose and use it in the cell, so concentration in cell is lower
Glucose and galactose absorption
coupled to Na cotransporter
cotransport maintained by NaK pump gradient
Cholesterol absorption
absorbed as is
Triglyceride absorption
must be broken down into glycerol backbone and either mono or di glycerides. just cant absorb triglycerides.
Micelle function
Lipids dont have problem getting THROUGH the membrane, its getting TO it that is hard.
we use MICELLES to keep the lipids insolution and keep it from coalescing.
use bile salts - ampipathic
when micelle comes into contact with the cell membrane, it releases the lipids, which can then cross easily into the cell
Chylomicrons
transport fats to lymph and blood
enzymes that cleave peptides in the middle
trypsin
chymotrypsin
chymotryipsin
Carboxypeptidase
cleaves single aa acids from the carboxyl terminal
aminopeptidase
cleaves single aa at the amine terminal
absorption of peptides
di and tripeptides can be brough in with Na cotransporter
single aa have specific transporters
if we have defect in the single aa transporter, we use the di and tripeptide cotransporter as backup
What is important about vitamin absorption
water solubility - Vit B, Vit C, niacin
Fat soluble - Vits A, D, E, K
Absorption of water soluble vitamins
absorbed with cotransporters
one exception= VitB12, which requires IF
absorption of fat soluble vitamins
major requirement is that you need to utilize the micelle.
