Digestion & Absorption-1/26/16 Flashcards
___ digestion refers to digestion resulting from the action of enzymes secreted by the salivary glands, stomach, and pancreas
___ digestion refers to hydrolysis by enzymes synthesized by epithelial cells
Cavital (luminal)
Membrane (contact)
Villi are longest in the ___ of the SI and shortest in the ____ of the SI
Duodenum
Terminal ileum
____ are epithelial cells whose function is digestion, absorption, and secretion. These are susceptible to irradiation and chemotherapy
___ are mucus-secreting cells which provide a physical, chemical, and immunologic protection
___ cells are part of the mucosal defenses against infection and secrete agents that destroy bacteria or produce inflammatory responses
Enterocytes
Goblet cells
Paneth cells
On the enterocyte, where does pinocytosis occur?
At the base of the microvilli. It is a major mechanism in the uptake of protein
If the terminal ileum is resected, absorption of ___ is abolished
Vitamin B-12 and bile salts
Lactase converts lactose to ____
Sucrase converts sucrase to ____
The 3 end-products of carbohydrate digestion are ____
Glucose and galactose
Glucose and fructose
glucosa, galactose, and fructose
List the 3 main carbohydrate transporters on the apical membrane of the SI:
Na-Glucose cotransporter (SLGT1)
Na-Galactose cotransporter (SLGT1)
Fructose transporter (GLUT5)
SLGT1 is secondary active transport and all of these bring Na and the sugar from the lumen into the cell
List the Main transporters on the basolateral (blood) side of the SI:
Na-K ATPase–> creates the energy gradient
GLUT2 brings glucose, galactose, and fructose in individually
How does lactose intolerance cause diarrhea?
Lactase is deficient on the brush-border and lactose remains in the lumen. As a result, undigested lactose holds water in the lumen and causes osmotic diarrhea
Undigested and unabsorbed lactose is fermented into methane and H+ gas, causing flatulence
In the stomach, what converts pepsinogen to pepsin?
Low pH
In the SI, what initially converts trypsinogen to trypsin?
Enteropeptidase (brush-border)
Chymotrypsinogen –> chymotrypsin, Proelastase –> elastase, Procarboxypeptidase a/b –> carboxypeptidase a/b
All of these rxns are catalyzed by ___ in the SI
Trypsin
What are the co-transporters for amino acids and di/tri-peptides on the apical (lumen) side in the SI?
Na-AA co-transporter
H-Di/tri-peptide cotransporter
Both co-transporters bring them from the lumen into the cell
Also a Na-H exchanger –> Na into the cell, H into the lumen
Once di and tri-peptides are co-transported from the lumen into the cell via the H+-Di/tri-peptide cotransporter, what converts the di/tri-peptides into AAs?
Peptidase
How are AA’s absorbed from the cells of the SI into the blood?
Na-K ATPase creates energy gradient
AA’s absorbed via facilitated diffusion
___ is a genetic disorder that occurs when there is a defect or absence of Na+ - AA cotransporters and the transporter for di-basic AAs is absent from the SI and kidneys.
As a result of the intestinal deficiency, AAs are secreted in feces
Cystinuria
___ is a recessive genetic disorder (SLC6A19 gene) where you cannot absorb neutral AAs, such as Trp. Urine samples from these patients reveal an abnormally high excretion of neutral AAs and their by-products
Hartnup disease
Mutations in the ___ is associated with a deficiency of pancreatic enzymes
CFTR (Cystic Fibrosis Transmembrane conductance Regulator)
Triglycerides are converted to monoglyceride and 2 FA’s via these enzymes:
Lingual, gastric, pancreatic lipases
Cholesterol esters are converted to cholesterol and FA via these enzymes:
Cholesterol ester hydrolases
Phospholipids are converted to lysolecithin and FA via this enzyme:
Phospholipase A2
Most lipid digestion occurs in the ___ and ___ emulsifies the lipids in this region
SI
Bile salts
Procolipase is converted to colipase via this enzyme:
Once colipase is activated, it bind to ___ to displace bile salts
Trypsin
Pancreatic lipase
The proenzyme of Phospholipase A2 is activated by ____
Trypsin
The pH optimum for pancreatic lipase is ___
6
List the steps for the mechanism(s) of absorbing lipids:
1) solubilization by micelles
2) diffusion of micellar content across the apical membrane
3) Re-esterification
4) Chylomicron formation
5) Exocytosis of chylomicron
The absence of ApoB on a chylomicron leads to ___
Abetalipoproteinemia–> impaired absorption of dietary lipids
Steatorrhea is a result of ____
Disorder of lipid assimilation
I.e., abnormalities in: pancreatic enzyme secretion,bile acid secretion, emulsification, micelle formation, diffusion of lipids into intestinal epithelial cells, chylomicron formation, transfer of chylomicrons into lymph
___ is the result of a gastrin-secreting tumor of the pancreas that leads to increased H+ secretion by gastric parietal cells and an overload of acid in the duodenum
Zollinger-ellison syndrome
___ leads to impaired HCO3- secretion and impaired enzyme secretion, i.e., lipase and amylase
Pancreatitis
____ is the reduction in the number of intestinal epithelia cells which in turn reduces the microvillar surface area. Cause is unknown and lipid absorption is impaired because the SA for absorption is decreased (steatorrhea). Diarrhea is the main symptom.
Tropical Sprue –> nutritional deficiencies especially Folate and B12. Treatment with Tetracycline and folate for 6 months
____ is an autoimmune disorder thought to begin in childhood with the introduction of wheat gluten. Abs develop against gliadin that leads to destruction of the villi in the SI as well as hyperplasia of the intestinal crypts. Symptoms include abdominal pain, constipation, diarrhea
Non-tropical sprue (celiac sprue)
Malabsorption related to deficiencies in B12, folate, Fe, Ca, Vit D, and Vit A
Most common in caucasians and persons of European ancestry. Women affected more than men
What is the mechanism for the absorption of fat-soluble vitamins (A,D,E,K)?
Same mechanism of absorption as lipids
What is the mechanism of absorption of water-soluble vitamins (B1/2/3/12, Biotin, folic acid, nicotinic acid, pantothenic acid)
Most are absorbed via a Na+-dependent cotransport mechanism in the small bowel
Vitamin B12 forms complexex with these proteins in order to be absorbed:
R Proteins (secreted in salivary juices)
IF (secreted by gastric parietal cells)
Transcobalamin II
____ is a type of vitamin B12 anemia where the stomach does not produce enough IF, which leads to decreased B12
Pernicious anemia
Common causes:
- Atrophic gastritis–> chronic inflamm of stomach mucosa, leads to parietal cell loss
- Autoimmune condition –> IS attacks IF protein or gastric parietal cells
The production of 1,25-dihydroxy-D3 leads to:
___ gut Ca absorption
___ bone calcification
___ bone resorption
All increase
Inadequate Ca2+ absorption leads to:
Rickets (Children)
Osteomalacia (adults)
Describe the cellular path of absorption:
Lumen–> apical membrane –> intestinal epithelial cell–> basolateral membrane–> blood
Transporters in membrane
