Why are enterocytes susceptible to radiation and chemotherapy?
Because they have a turnover rate of only 3 to 6 days.
What is the major mechanism of uptake in the G.I. for protein and fats?
What to essential molecules lose their ability to be absorbed s/p terminal ileum resection?
What does starch initially break down into?
Maltose and 3-9 polymers of glucose.
What do maltose and trehalose breakdown into?
Glucose + Glucose
What does lactose break down into?
Glucose + Galactose
What does sucrose break down into?
Glucose + Fructose
What transporter pulls glucose and galactose from the luminal side of the enterocytes?
What transporters are used to pump glucose, galactose, and fructose out of the basolateral side of the enterocyte into the blood?
Why does consumption of lactose by the lactose intolerant result in bloating and flatulence?
Because the lactose is instead fermented by the commensal flora of the G.I.
How much D-xylose must be present after five hours in order to be considered "normal absorption."
4 g or more.
What is the method of absorption of D-xylose at the dose used in the D-xylose absorption test?
What portion of the digestion of proteins is not essential to maintain homeostasis?
The portion of protein digestion that occurs in the stomach. Namely, the activity of pepsin.
What enzymes are secreted by the pancreas to digest proteins?
Trypsin and chymotrypsin (enteropeptidases).
Carboxypeptidase A and carboxypeptidase B (exopeptidases).
Which of the proteolytic enzymes of the pancreas are responsible for breaking down large proteins into small polypeptides?
Trypsin and chymotrypsin (the endopeptidases).
What converts trypsinogen, chymotrypsinogen, proelastase, procarboxypeptidase A, and procarboxypeptidase B into their active forms?
Besides trypsin, what converts trypsinogen into its active form?
Enterokinase from the brush border.
How do amino acids enter the enterocytes?
Via a Na+-amino acid transporter specific to the type of the amino acid (neutral, acidic, basic, imino).
What happens to dipeptides and tripeptides that enter the enterocytes?
They are either broken down by cytosolic peptidases and secreted as such, or they enter the portal system whole.
How do amino acids exit the basolateral side of the enterocytes?
Via facilitated transport (not using sodium) with a transporter specific to the type of each amino acid (acidic, neutral, basic, imino).
How will chronic pancreatitis or cystic fibrosis affect protein digestion?
It will cause deficiency of all pancreatic enzymes, including all of the proteases (trypsin, chymotrypsin, carboxypeptidase A & B) which are essential for the breakdown of proteins.
What is the basic pathophysiology of cystinuria?
Defect or absence of the dibasic amino acid transporter. This results in a deficiency in the COAL amino acids (cystine, ornithine, arginine, lysine) in the body and their accumulation in the urine. Cystine then forms crystals, presenting like kidney stones.
What is the basic pathophysiology of Hartnup disease?
Deficiency of pancreatic enzymes or defect in transporters of intestinal epithelial cells for neutral amino acids.
Presents like pellagra – dementia, diarrhea, dermatitis.
How would cystic fibrosis result in steatorrhea?
Anything that creates an inability of the duodenum to increase the pH of the chyme will prevent the action of lipases, amylases, and peptidases.
Cystic fibrosis prevents the pancreas from releasing bicarbonate.
What is the primary dietary form of fat?
What serves to emulsify fats in the stomach?
What is the function of colipase?
Colipase binds to pancreatic lipase and displaces bile salts.
Which fat digesting enzymes are secreted in their active form by the pancreas?
Cholesterol ester hydrolyze.
What enzyme is responsible for the breakdown of cholesterol esters?
What organ secretes it?
Cholesterol ester hydrolase.
How does cholecystokinin assist with the absorption of fats?
Delays gastric emptying, stimulates bile salt ejection, and indirectly increases the pH of the lumen via potentiating secretin.