Digestion and absorption AAU Flashcards
Digestion of various food is by the process of
hydrolysis
Digestion is?
different types of food are broken in the absorbable units “ principally in the small intestine.
Absorption is ?
the products of digestion and vitamins, minerals and water crosses mucosa and enter the blood or lymph
Carbohydrate Digestion the mouth ?
Salivary α amylase acts on polysaccharides
starches is hydrolyzed into maltose
not more than 5 %of all the starches will have become hydrolyzed
Carbohydrate Digestion In the stomach ?
Salivary α amylase is essentially nonactive once the pH below 4.0.
Carbohydrate Digestion In the intestine?
Pancreatic α amylase
the carbohydrates are almost totally converted into maltose and/or other very small glucose polymers before passing beyond the duodenum or upper jejunum.
Products of starch digestion by α amylase ?(3)
- Disaccharides: maltose.
- Trisaccharides: maltotriose.
- Short polymesr: α dextrins.
enzymes found in the brush border ?(5)
- α dextrinase
- Maltase
- Sucrase
- Lactase
- Trehalase
α dextrinase:
Acts on alpha dextrins, maltose & maltotroise. α dixtrinase also known as isomaltase it hydrolyses 1:6α linkages. along with maltase and sucrase it also breaks down maltotriose and maltose.
Maltase?
Acts on maltose to give glucose -glucose
Sucrase ?
Acts on sucrose to give glucose =fructose
Lactase?
Acts on lactose give glucose + galactose.
Trehalase:
Acts on trehalose to give glucose+glucose
The absorbed units of carbs enter
portal circulation portal vein.
Glucose absorption On luminal membrane
Accomplished by carries for co-transport to inside the cell
Sodium –glucose transports 1 & 2 (SGLT1 & SGLT2).
Glucose absorption On basolateral membrane?
(carriers for facilitated diffusion to the ISF). Glucose transporters 1 & 2 (GLUT1 & GLUT2).
The Glucose transporter sensitive to insulin
GLUT-4
found in fat & muscle cells
Galactose Absorption?
Similar to glucose (i.e.co transported with sodium “secondary active transport”).
Fructose Absorption by
Facilitated diffusion that is Independent of Na
Fructose Absorption To enterocytes by
GLUT5
Fructose Absorption To interstitial by
GLUT2
Pentose Absorption
Absorbed by simple diffusion
Produced from metabolism of nucleic acids.
Protein Digestion In the mouth?
No enzyme for digestion.
Protein Digestion In the Stomach?
Enzymes gelatinase : liquefies gelatin Pepsin : It hydrolysis the bond between aromatic amino acids and a second amino acid Product polypeptides with very divers sizes.
pepsin (activation , inhibition )
Pepsinogen in low pH activated to pepsin
Pepsin activity inhibited by alkaline secretion of the pancreas
Protein Digestion In the intestine?
Enzymes
Pancreatic endopeptidases (Trapsin, chymotrypsin, and elastase)
Pancreatic exopeptidase (Caboxypeptidases A & B)
Product
They produce Di & Tri peptides but not aminoacids( endopeptidases )
Some free aminoacids liberated in the intestinal lumen ( exopeptidase )
Endopeptidases act at
interior peptide bonds.
carboxipeptidases hydrolyses aminoacids at
carboxyl and amino ends.
proteolytic enzyme found in the brush border ?
Aminopeptidases
Carboxipeptidases
Endopeptidases
Dipeptidases
digestion of aminoacids occur in three locations
- Intestinal lumen.
- Brush boarder.
- Cytoplasm of mucosal
Products of Protein Digestion ?
- Free amino acids.
- Dipeptides.
- Tripeptides.
The absorbed units of protein enter
portal circulation
Absorption of free Amino Acids ?
Co transport with sodium (mainly)
Absorption of Dipeptides & Tripeptides?
By a mechanism involving hydrogen ions
absorption Complete Protein Undigested
Occurs in infants for IgA antibodies in milk
by endocytosis
Abnormalities of Protein Digestion & Absorption?
Absorption of foreign proteins induces antibody formation;
Congenital defects in the mechanism of amino acid absorption
Lipid Digestion In the mouth ?
Lingual lipase (acts on triglycerides). Lingual lipase digest as much as 30% of triglycerides
Lipid Digestion In the stomach ?
Gastric lipase. Gastric lipase is of little importance.
Lipid Digestion In the intestine (From the liver) ?
Bile salts, which cause emulsification and micelle formation
Micelle contains ?
- Fatty acids.
- Monoglycerids .
- Cholesterol .
Lipid Digestion In the intestine ( From the pancreas ) ?
Pancreatic lipase & Co lipase .
Pro-colipase activated by ……. to colipase
trypsin
co-lipase act on
emulsified fat
tri-glycerides ( HYDROLYSIS 1& 3bonds easily but 2-bondes slowly )
co-lipase product
- Free fatty acids.
2. 2-monoglycerids.
Bile salt activated lipase act on ?
cholesterol esters, ester of fat soluble vitamins, phospholipids as well as Triglycerides .
The absorbed units of fats enter ?
portal circulation or lymphatics
Fats entering the portal blood have carbons
No answer here
Fats entering the lymphaties have carbons >(10-12)e.g. long chain free fatty acids and cholesterol.
No answer here
Chylomicrons
Before entering the lymphatic’s, the long chain fatty acids and cholesterol are re-esterified within the cytoplasm of intestinal cells and become coated with protein & phospholipids to from it
Chylomicrons are released to lymphatic’s by ?
exocytosis.
Steatorrhoea
Loss of more than 5 grams of fat in stool per day. Steatorhoea is caused by conditions that impairs of Fat Digestion & Absorption
Nucleic acids digestion ?
- Deoxiribonucleases act on DNA and release nucleotides
- Ribonucleases act on RNA release nucleotides
- Then different nucleases releases pyrimidines and purine bases.
