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56 Cards in this Set

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For carbs what is the:
-Normal daily absorption
-Maximum daily absorption
Normal = 300 g
Max = 3 Kg
For lipids what is the:
-Normal daily absorption
-Maximum daily absorption
Normal = 100 g
Max = 500 g
For proteins what is the:
-Normal daily absorption
-Maximum daily absorption
Normal = 75 g AA
Max = 600 g AA
How much water and ions do we normally absorb daily?
Water = 8L
Ions = 75 g
Max amt of water we can absorb:
>20 L
How is water absorbed?
Entirely by diffusion - under the usual laws of osmosis.
How is water absorbed from the enterocyte into the bloodstream?
By ONCOTIC movement - based on the amt of proteins in the blood.
What governs whether water will be absorbed by the small intestinal villi?
The osmolarity of chyme - if hyperosmotic, water will not be absorbed.
What will result from hypo-osmolarity of chyme?
Water will be reabsorbed more.
How much sodium is excreted in tubular secretions daily?
20-30 g
What is the nature of tubular secretions in general?
-isosmotic to ECF
How do we prevent net loss of sodium in excretions of feces?
By reabsorbing ~25 g daily
What is sodium reabsorption essential for?
glucose and amino acid absorption
How is water reabsorption different in the small intestine compared to large?
Tight junctions in small intestine are freely permeable to water, so it is not pulled into the blood unless enough oncotic pressure. Not so in large intestines, so osmosis is what causes water reabsptn there.
What causes water intake into the bloodstream at the large intestine?
The movement of sodium from the paracellular space into blood; leaves behind a hypotonic solution so water then follows.
What happens to water and sodium reabsorption by the small intestine when a person becomes dehydrated?
Aldosterone is released by the adrenal cortex to increase water and sodium reabsorption.
What part of intestinal sodium reabsorption is especially effected by Aldosterone?
Large intestine
How is chloride reabsorbed?
Very rapid diffusion due to electropositivity generated by Sodium in the paracellular space and EN in the enterocyte.
Why is bicarb reabsorbed?
Because much is secreted in bile and pancreatic secretions.
How is bicarb reabsorbed?
1. Na/H exchanger puts H+ in chyme
2. H + HCO3 -> H2CO3 -> H2O CO2
3. Blow off CO2; H2O stays in chyme for reabsorption via osmotic pressure (follow NaCl)
How does the intestine treat Bicarb differently based on site?
-Upper intestine reabsorbes it

-Lower intestine secretes it
Why does Bicarb get secreted at the ilium and lg intestine?
In exchange for chloride - to retain electroneutrality and neutralize acidity of bacterial byproducts.
Where is calcium absorbed?
Duodenum
What stimulates calcium absoption?
Vit D + PTH
What type of transport allows reabsorption of Calcium, Iron, Potassium, etc?
Active transport
What ions are more easily absorbed? Which are less?
Easiest = monovalent
Least = bivalent
So 3 types of things have to be absorbed; what are they?
-Water
-Ions
-Nutrients
What is the most abundant carb that gets absorbed? How much?
Glucose - 80%
What is the remaining 20% of carbs that get reabsorbed?
Galactose + Fructose
(milk) (cane sugar)
What is essential for glucose uptake by enterocytes?
Sodium - for cotransport
How does glucose get from the enterocyte to the blood?
Via simple diffusion
How is galactose absorbed?
In the same way as glucose
How is fructose absorbed?
Also by facilitated transport, but independent of Sodium AT.
How does fructose absorption compare to glucose?
50% slower; converts fructose to glucose during the process.
How are proteins absorbed?
By 2ndary active transport - sodium driven.
How are fats absorbed by the small intestine?
-Bile salts make micelles
-Ferry to brush border
-Release lipids - diffuse into enterocytes
What happens to lipid absorption if bile salts are not available?
Lipid absorption is reduced to 45% of normal.
What happens to the monoglyceride and FFA taken up by enterocytes?
Sent to smooth ER and remade into triglycerides, then packaged into chylomicrons
What happens to chylomicrons?
Transport into lymph, to thoracic duct, then to circulation.
What is unique about short/med chain fatty acids?
Some can be absorbed directly into the portal system - will see if you spin a sample.
What allows for short/med chain FAs to be reabsorbed direclty into the bloodstream?
They are more soluble in aqueous ECF so aren't directed to the smooth ER.
Where is the bloodvessel that absorbs all these things?
In the villus
What happens to cholesterol in the diet?
Packaged into chylomicrons in same way as other lipids, taken to lymphatics, to circulation.
What happens to chylomicrons in circulation?
Delivered to muscle and organs for energy metabolism.
Where does most cholesterol synthesis in the body occur?
At the peripheral tissues; HDL then returns it back to the liver and is acted on by PLTP and CETP.
What is mostly absorbed in the large intestine?
Water and electrolytes
What is excreted in exchange for chloride absorption? Why?
Bicarb - to neutralize the byproducts of bacteria.
How is chloride able to be reabsorbed?
By the driving energy of sodium Active Transport and absorption.
How are the tight junctions of the large intestine different from small intestine?
Much tighter; water reabsorption is permanent and achieved via osmosis.
What increases water and sodium reabsorption at the large intestine?
Aldosterone
Proximal colon =

Distal colon =
Prox = absorbing colon

Distal = storage colon
Main thing that occurs in large colon:
Formation of feces
What is the result of bacterial action on feces?
-Smll amts of cellulose digested
-Formation of VITAMIN K
-Some b23, other b vitamins, gas
What is especially significant about bacterial action in lg intestines?
Formation of Vitamin K - b/c nutritional ingestion is insufficient to maintain adequete blood coagulation!
What is the main component of feces?
Water - 75%
Why is feces brown?
Stercobilin / urobilin derivitives of bilirubin