Lecture 33 - Monogastric Lipid digestion and absorption Flashcards
what is the most important enzymatic reaction in digestion?
hydrolysis: the breaking of a chemical bond by the addition of a water molecule
protein digestion begins in the:
Stomach
describe how proteins are digested in the stomach
Pepsin is converted from pepsinogen with the help of HCl from parietal cells. Pepsin then breaks down proteins into smaller peptide fragments, so that when they leave the stomach and enter the SI, they are 25-100 aa long
what is the enzyme produced by chief cells that is especially important for digestion of casein in neonates?
Rennin
to aid in protein digestion in the lumen of the SI, the pancreas secretes:
proteases, including trypsin
what facilitates the conversion of peptides into smaller peptides and free amino acids?
peptidases on the brush border of the small intestine
are the brush border peptidases integral membrane proteins, or soluble enzymes?
integral membrane proteins
Pancreatic exocrine secretion is strongly stimulated by:
food entering the stomach and small intestine
CCK and vagal stimulation increase the production and secretion of what organ’s enzymes?
the pancreas
CCK acts on villous enterocytes and causes them to secrete ______, which converts trypsinogen to the active trypsin
enteropeptidase
food entering the small intestine will result in the release of _____, which increases alkaline (bicarbonate) secretion to neutralize the low pH contents entering the lumen from the stomach
Secretin
What is the function of trypsin in protein digestion?
trypsin cleaves off portions of all other inactive pancreatic enzymes, thus activating them in the intestinal lumen
what do single amino acids use to cross the apical membrane of the lumen into the enterocyte?
Sodium dependent amino acid transporters
Once inside the enterocyte, dipeptides and tripeptides are converted into single amino acids by:
intracellular peptidases
what do dipeptides and tripeptides use to be transported across the apical membrane?
Special peptide proteins that do not require sodium (ie. PEPT1)
what happens after cytosolic peptidases in the enterocyte have converted all of the peptides into free amino acids?
transporters on the basolateral membrane facilitate the diffusion of the amino acids into the extracellular fluid
Why can some drugs be taken orally, while others can’t?
Some drugs cannot survive the enzymes or acid in the stomach, or are broken down before being able to enter the extracellular fluid. However, there is potential to make any drug a substrate for PEPT1, the peptide transporter on the apical membrane of the enterocytes.