GI System 2 Roane Flashcards
Carbohydrates in food:
Polysaccharides: Starch (fiber non digestible starch), Glycogen, Cellulose
Disaccharides: Sucrose, Lactose, Maltose
Monosaccharides: Glucose, fructose,…
How are carbohydrates digested?
Know the enzymes
3 groups of carbohydrate enzymes:
1) Salivary amylase (ptyalin) - inactivated in the stomach due to acid
2) Pancreatic amylase: yields short-chained carbohydrates in the SI
3) Saccharidases on the intestinal brush border: yield monosaccharides (few dissacharides) -> absorbed from the lumen
Absorption of carbohydrates:
Secondary active transport
After breakdown into monosaccharides, they are reabsorbed through transporters: Glucose with Na+ symporter and Fructose with GLUT5
How are proteins digested?
Know the enzymes
1) Pepsin released from the stomach
2) Pancreatic enzymes: Trypsin and Chymotrypsin
the chyme (partly digested food moves to the small intestine -> protein fragments
3) Luminal enzymes: carboxypeptidase and aminopeptidase in the brush border produce amnio acids
Absorption of amino acids:
1) Amino acids are transported through Na+ linked transporter and some small peptides through the H+ transporter
2) Amino acid transporter on the basolateral side transport amino acids to the interstitium
dependent on Na+K-pump (ATP needed)
How are fats absorbed?
Fats are not water-soluble in a waterlike lumen -> so it has to be emulsified -> by Bile salt
What are bile salts?
Modified cholesterol with hydrophilic (OH) portion on the D-ring
What does Bile consist of?
Lecithin, phospholipids, bilirubin, cholesterol, minerals, and bicarbonate stored in the gall bladder
What are gallstones?
Insoluble rocks of bile salt, blocks the cystic duct of gall bladder
How is emulsification possible?
Bile salts have a non-polar side attracted to fats and a polar side attracted to water
smaller particles (droplets) are pulled out of the fat and wrapped around with bile salts
Digestion of fats:
Most of the fat we eat is present in triglycerides:
Lipases pull out the triglycerides out of the emulsion droplet and break them into monoglycerides and two fatty acids
What is the consequence of taking Orlistat (drug)
Fat will be emulsified but not digested and it will get to the large intestine and gets excreted
(fat usually doesn’t get into the large intestine, it gets absorbed by 100%)
What happens to the monoglycerides and fatty acids?
They diffuse into epithelial cells and reform into triglycerides again (in ER) and leave the cells on the basolateral side and form chylomicrons -> they enter the Lacteal (lymphatic system in intestine)
Where does the fat go after it enters the lymph?
The lymph goes up to the thoracic duct and enters the bloodstream through the subclavian vein
What happens with used bile salts?
Enterohepatic circulation: important because drugs can be trapped in this circulation
Sequence: comes out of the liver or gall bladder -> goes to the small intestine -> emulsifies fat -> in the Ileum it enters portal circulation (blood) through active transporter -> back to the liver
