lecture 25 - carbohydrate & protein absorption Flashcards
What are the adaptions of the small intestine that give it a large surface area for absorption?
Villi, microvilli
Are sugars water or lipid soluble?
Highly Water soluble
What are the 2 types of transport of sugars across GI epithelial cell membranes?
Active transport and facilitative transport
What are the 2 glucose transporters that transport glucose across the intestinal epithelia?
SGLT 1 (sodium glucose linked transporter 1), GLUT 2
What type of transport is done by SGLT1?
Secondary active transport of glucose across the intestinal epithelia
What type of transport is done by GLUT 2?
Facilitative transport (down concentration gradient) of glucose across the intestinal epithelia
Where are SGLT 1 membrane transporters found?
On the apical surface (lumen side) of intestinal epithelial cells
Where are GLUT 2 membrane transporters found?
On the basolateral membrane of epithelial cells in the intestines
What symport is involved in SGLT 1 transport?
Sodium and glucose symport/cotransport
What membrane protein creates a concentration gradient for SGLT 1 symport?
Na+/K+ ATPase pumps Na+ out of the epithelial cell to maintain low intracellular [Na+] to ensure a concentration gradient so that Na+ can diffuse through SGLT 1, facilitating glucose transport
What creates the concentration gradient needed for GLUT 2?
SGLT 1 transports glucose into the epithelial cell, creating a high concentration that pushed glucose out via GLUT 2 passively.
What is the ratio of Na+ and K+ transported in/out of the cell by Na+/K+ ATPase?
For every 3 Na+ transporters out of the ell, 2 K+ are transported into the cell.
How does Na+/K+ ATPase work to actively transport?
Hydrolysis of ATP and the subsequent phosphorylation of the transport lead to conformational change that enables the transport of the Na+, followed by the K+.
How is glucose taken up by tissues once in the blood circulation?
Taken up by different glucose transporters (GLUT 1,2,3 or 4)
What glucose transporter is used for glucose uptake in the liver, pancreas, kidney and intestinal epithelia?
GLUT 2
What glucose transporter is used for glucose uptake in the brain?
GLUT 3
What glucose transporter is used for glucose uptake in muscle and adipose tissue?
GLUT 4
What is the ubiquitous (found everywhere) glucose transporter?
GLUT 1
What is the size of peptides that absorbed in the GI tract?
di- and tri-peptides
What membrane transporter is used to transport di- and tri - peptides into the epithelium of the small intestine?
PepT1 - uses cotransport with H+ ions
At what point in protein digestion are di and tri peptides finally converted to amino acids and absorbed?
Di- and tri-peptides are digested into individual amino acids by cytoplasmic peptidases in epithelial cells in the small intestine
What system is used to transport amino acids from the lumen of the small intestine into the epithelial?
Semi-specific Na+-dependent transport system
What do Na+-dependent carriers transport
Na+ and an amino acid - via cotransport
Why are there different types of Na+-dependent amino acid carriers?
Carriers are amino acid side chain specific - different for neutral, acidic, basic, etc.
In what scenario in newborn mammals are intact proteins absorbed from the GI tract?
The uptake of immunoglobulins in colostrum milk to acquire passive immunity
What is pancreatitis?
Disease that leads to inappropriate activation of zymogens/proenzymes resulting in ‘self-digestion’ of the pancreas
What is the cause of peptic or stomach ulcers?
The breakdown of mucosa that normally protects against protease action
What is the effect of cystic fibrosis on digestion and absorption?
Causes thick pancreatic secretions that block the pancreatic duct from secreting digestive enzymes preventing absorption
What is the body’s reaction to gluten for those with coeliac disease?
Antibodies react with transglutaminase
What is the result of coeliac disease on the small intestine?
Villi are flattened so that nutrients cannot be properly absorbed
What is the first stage in the breakdown of dietary nucleic acid polymers?
DNA and RNA are subject to partial acid hydrolysis in the stomach
What enzymes hydrolyse phopshodiester bonds in nucleic acid polymers in the small intestine?
Endonuclease enzymes
What is the role of exonuclease enzymes in dietary nucleic acid polymer digestion?
Release individual nucleotides - nucleoside mono phosphates
