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Lecture 30

PHYSIOL 201 Lecture Notes - Lecture 30: Calcitriol, Skeletal Muscle, LipoproteinPremium

6 pages20 viewsWinter 2015

Department
Physiology
Course Code
PHYSIOL 201
Professor
Elizabeth Rust
Lecture
30

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Lecture 30: Small Intestine
Slide 2
When we look at the wall, there are folds called villi and epithelial cells whose
membranes are also folded
-Lots of folding
-The folding of the cells are called the brush border
Blood vessels in the submucosa will go up the villi
As things are being absorbed across the epithelial cells, they can enter the capillaries
or enter lymph duct called lacteral
Slide 5
Length varies depending on how tall you are
You can live without some parts of the small intestine but one major part is the
ileum that you can’t live without
Slide 6
The ileum has transporters that are only present in the ileum for the absorption of
vitamin B12 and recycling of the bile salts that come from the liver
So you end up with some nutritional deficiency when someone doesn’t have an
ileum
-B12 is important for red blood cells production
-So these individuals can’t make read blood cells
-Bile salts help increase the breakdown of fats so without the bile salts going back
into the liver, we decrease efficiency of fat digestion
Slide 8
In order to absorb carbohydrates, we have to break them down to their
monosaccharide form
We have an enzyme that comes from the pancreas called pancreatic amylase
-Amylase breaks carbs down into a disaccharide called maltose and then into chains
called dextrins
The brush border expresses these enzymes that will do the rest of the breaking
down of carbs
-Dextrinase and glucoamylase breakdown the dextrins into maltose, sucrose and
lactose (these are three disaccharides)
-Then three other enzymes break down the disaccharides: maltase, sucrase, and
lactase
-These products can be absorbed; the other things before cannot be absorbed
There is a Na cotransporter for glucose and galactose
On the basolaterial side we have facilitated diffusion
-Fructose crosses the apical membrane using facilitated diffusion
Slide 10
GLUT is what transports glucose into our cells and also fructose into the cell through
facilitated diffusion
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GLUT is a facilitated transporter
SGLT (sodium, glucose cotransporters) use secondary active transport
Na/K pump generates a Na gradient which can be used as an energy source for the
transporters
Slide 11
Pancreatic enzymes come from the pancreas
-As CCK levels go up, CCK stimulates the acinar cells to release all these enzymes
-Amylase was one
-Trypsinogen, trypsin, and procarboxypeptidase are all coming from the pancreas
-They are not active when they are released because when released, if active, they
would be digesting the proteins inside the cell
-Released in the inactive form and are activated in the intestinal lumen
What they do:
Trypsin and chymotrypsin split proteins into smaller peptides (not all the way down
to the single amino acid)
Carboxypeptidase splits peptides into amino acids from the carboxy end
Brush border enzymes express aminopeptidases (so they don’t come from the
pancreas) and they split peptides in to amino acids from the amino end
Slide 12
From the pancreas into the lumen, we have trypsinogen, chymotrypsinogen and
procarboypeptidase
Then we have these two brush border enzymes
-Enterokinase and it’s job is to take trypsinogen and break it down to trypsin
-Trypsin then activates chymotrypsinogen and procarboxypeptidase
Slide 13
With amino acids, we can absorb individual amino acids or small peptides (two or
three amino acids together)
We have at least 7 different amino acid transporters to transport the 20 amino acids
-These are all Na coupled
Short chains are absorbed by active transport coupled to H+ gradient
Only the basolateral membrane can move amino acids using facilitated diffusion
Slide 14
We have the Na coupled amino transport and the brush border enzymes and the
pancreatic enzymes
Across the basolateral membrane we have facilitated diffusion transporters
We also have H+ being secreted and it moves back into the cell via this H/Peptide
transporter
-So we’re not adding hydrogen, keeps coming back in
-This gradient is used to move the peptides
-So this is a hydrogen active coupled transporter that moves the di and tri peptides
into the cell
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