Digestion and Absorption of Macronutrients

Question 0

Duodenuym and ionic concentrations

Answer 0

ionic concentrations rapidly come to match the ECF concentrations earlly in the dyodenum. Want to bring to isotonic.

Question 1

Nutrients we ingest are not lipophilic. How do we get them in?

Answer 1

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

Question 2

Major plasma ions

Answer 2

Cations= Na, K
anions= Cl, HCO3
special cases Ca, Fe

Question 3

2 ways to get ions across brush border

Answer 3

Paracellular pathway= tight junctions between cells regulate. cations more soluble than chloride
Transcellular pathway= via pores or transporters

Question 4

Dont fuck with Cl

Answer 4

CFTR and Cach all depend on what we do with chloride

Question 5

Na absorption in early duodenum

Answer 5

transcellular

Question 6

Na absorption in proximal SI

Answer 6

Na/H exchanger,

moves more Na than simple diffusion

Question 7

Na absorption in distal SI

Answer 7

Secondary active transport dependant on NaK Atpase

Question 8

Na absorption in ileum to LI

Answer 8

Na/Cl transporter

Question 9

Cl absorption in distal SI and LI

Answer 9

Na/Cl cotransporter

Question 10

Cl absorption in proximal GI

Answer 10

Cl/HCO3 antiporter

Question 11

K absorption

Answer 11

predominatly paracellular in SI

in LI, it is freely diffuseable, but usually results in net secretion

Question 12

Ca absorption from lumen

Answer 12

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

Question 13

Ca from enterocyte to blood

Answer 13

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

Question 14

absorption of H20

Answer 14

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

Question 15

CHO digestion - amylase

Answer 15

salivary or pancreatic

breaks CHO down to disaccharides

Question 16

Disaccidases

Answer 16

chop specific disaccharides into monosacharides

Question 17

Maltase

Answer 17

chops maltose into two glucoses

Question 18

lactase

Answer 18

lactose to glucose and galactose

Question 19

sucrase

Answer 19

sucrose to glucose and fructose

Question 20

Fructose absorption

Answer 20

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

Question 21

Glucose and galactose absorption

Answer 21

coupled to Na cotransporter

cotransport maintained by NaK pump gradient

Question 22

Cholesterol absorption

Answer 22

absorbed as is

Question 23

Triglyceride absorption

Answer 23

must be broken down into glycerol backbone and either mono or di glycerides. just cant absorb triglycerides.

Question 24

Micelle function

Answer 24

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

Question 25

Chylomicrons

Answer 25

transport fats to lymph and blood

Question 26

enzymes that cleave peptides in the middle

Answer 26

trypsin
chymotrypsin
chymotryipsin

Question 27

Carboxypeptidase

Answer 27

cleaves single aa acids from the carboxyl terminal

Question 28

aminopeptidase

Answer 28

cleaves single aa at the amine terminal

Question 29

absorption of peptides

Answer 29

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

Question 30

What is important about vitamin absorption

Answer 30

water solubility - Vit B, Vit C, niacin

Fat soluble - Vits A, D, E, K

Question 31

Absorption of water soluble vitamins

Answer 31

absorbed with cotransporters

one exception= VitB12, which requires IF

Question 32

absorption of fat soluble vitamins

Answer 32

major requirement is that you need to utilize the micelle.