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25 Cards in this Set

  • Front
  • Back
What are normal absorption (quantities) in SI ?
300 g CHO, 100 g fat, 75 g amino acids, 75 g ions, 8 L water

-Several fold more for max
How is water absorbed in SI?
Via diffusion/osmosis. Water is always in isoosmotic equilibrium with chyme, so it can move in either direction
How much sodium is secreted each day? How much ingested in the diet? How much reabsorption needs to occur to stay homeostatic? Why do we need sodium homeostatic?
30 g secreted, 5 ingested. Must reabsorb 25 to stay homeostatic, which is important for absorbing other nutrients among other things.
What is the mechanism of sodium transport into the intestinal epithelium?
Intestinal epithelium cells normally have low sodium levels. This is because Active transport through the basolateral membrane keeps sodium at low levels. Since the concentration of Na in the chyme is much higher than the cell, it moves down the gradient and into the epithelial cell cytoplasm. There are also cotransporters (Na/AA, Na/Glucose) and exchanger (Na/H)
How does aldosterone work to increase sodium absorption?
When one is dehydrated, the cortices of the adrenal gland secrete aldosterone. This increases activation of transport mechanisms for Na absorption by intestinal epithelium. This is particularly important in the large intestine. Na+ absorption causes secondary Cl- and water absorption.
How is chloride absorbed in the small intestine?
Cl- absorption is rapid and is a consequence of diffusion (Na+ absorption causes Cl to folow).
How is bicarbonate absorbed in the duodenum and jejunum?
Large pancreatic and bile secretions necessitate absorption of HCO3. One mechanism for absorbing Na involves exchanging for H+ ions- these ions combined with bicarbonate to form carbonic acid, which then dissociates to form CO2 and H20.The CO2 diffuses into the blood.
Where does simultaneous secretion of bicarbonate and absorption of Cl occur? How?
This happens in the large intestine and ileum. These cells secrete bicarbonate into the intestine in exchange for absorption of chloride ions. This neutralizes acidic bacterial products and absorbs Cl ion.
How is calcium absorbed?
Calcium is absorbed from the duodenum. PTH activates vitamin D, and the activated vitamin D enhances calcium absorption.
Why absorb fe++ from the intestine?
Iron absorption is necessary for Hb.
How are other ions absorbed?
Monovalent ions like K+ actively absorbed. Bivalent ions are only absorbed based on need.
In what forms are carbohydrates absorbed?
Carbohydrates are mainly absorbed as monosaccharides (some as disaccharides). 80% of the carbohydrates are absorbed as glucose. The remaining is galactose and fructose.
How is glucose absorbed?
1) Sodium is first pumped out via active transport into the blood
2) Sodium and glucose are brought in via secondary active transport (cotransort).
Glucose then is free to diffuse out of the cell into capillaries.
How is galactose transported into the intestinal epithelium?
Galactose is transported via the same mechanism as glucose.
How is fructose transported into the intestinal epithelium?
Fructose is transported by facilitated diffusion and IS NOT coupled with sodium transport.Upon entering the cell, much of fructose is phosphorylated and converted to glucose. Its rate of import into the cell is only half of galactose/glucose since its not cotransported.
How are proteins absorbed into the intestinal epithelial cells?
As dipeptides most frequently, but also tripeptides and single AAs. Through a sodium cotransport mechanism, a peptide binds along with a Na, and both are transported into the cell. Again, some peptides can move in via facilitated diffusion too but this is less common.
How many types of transport proteins have been identified for AAs and peptides?
At least 5.
How are fats absorbed?
Recall that TAGs are digested to form monogllyceride and free fatty acids that then float in bile micelles. These two products are then carried to surfaces of microvilli and penetrate into the recesses, agitating microvilli- They then diffuse out of the micelles (bile micelles remain in chyme and can be reused). The fats can then diffuse into the epithelium cells.
Once the MAG and FA enter the intestinal epithelial cell, what happens?
At this point the smooth ER then takes up the fatty acids and monoacylglycerides.They are then used to form new triglycerides that are then released as chylomicrons to flow through the thoracic duct and into the circulating blood.
How can some FA be absorbed directly into portal blood?
Some short and medium chain fatty acids (more water soluble) can be absorbed directly into the portal blood rather than going through lympatics - they are not reconverted into TAGs by ER.
Of all the water and electrolytes that pass into the large intestine, is most reabsorbed?
Yes, the large intestine absorbs most of the water and electrolytes that passes into it (90%) but remember the SMALL INTESTINE still absorbs more volume of water than the large intestine.
How is the mucosa of LI similar to and different than SI?
similar- contains mechanisms for active transport of sodium; secretes bicarbonate in response for Cl- absorption just like SI
different- much tighter tight junctions of small intestine= especially true during aldosterone presence.

The absorption of Na+ and Cl- creates a gradient for water absorption.
What kind of bacteria do we have in the colon?
Colon bacilli
What kind of bacterial action do the colon bacteria have
Can digest small amounts of cellulose
Results in formation of vitamin K, B12, thiamin, riboflavin and some
gases (carbon dioxide, hydrogen and methane)
Vitamin K is vitally important, as daily ingestion is insufficient to
maintain adequate blood coagulation
What is the composition of feces?
75 water, 25% solid matter.
Solid matter made of dead bacteria, 10-20% fat, 2-3% protein, 30% undigested roughage. Brown color of feces caused by stercobilin and urobilin- odor caused by bacterial action (indole, skatole, mercaptans, h2s)