Ganong 24th ed - Chapter 26 - Digestion and Absorption (2) Flashcards
Where does protein digestion start? Describe the enzyme that digests proteins here.
In the stomach. Gastric acid converts pepsinogen to pepsin, which cleaves off some of the peptide linkages. Pepsins have an optimal pH of about 2.0, which means that they become inactive once the stomach contents move into the duodenum.
Name four enzymes that digest proteins that come from the pancreas.
Trypsin (trypsinogen)
Chymotrypsin (chymotrypsinogen)
Elastase (proelastase)
Carboxypeptidase (procarboxypeptidase)
How do the protein-digesting enzymes of the pancreas get activated?
Upon release into the duodenum, the native enterokinase (on the apical surface of the enterocytes) cleaves trypsinogen into trypsin. Trypsin then converts all the other zymogens into active enzymes (e.g. converts chymotrypsinogen into chymotrypsin).
Where does amino acid absorption take place?
In the duodenum and jejunum.
How do amino acids cross into the enterocytes?
By co-transport mechanisms that depend on ions such as sodium and chloride.
How is most glucose and galactose absorbed into enterocytes?
By secondary active transport. Uses sodium-dependent glucose transporters.
How is fructose absorbed into enterocytes?
By facilitated diffusion. Uses GLUT5.
Where does lipid digestion begin?
In the mouth: lingual lipase.
How is pancreatic lipase activated? What is another lipid-digesting enzyme that is activated in the same way?
By trypsin, in the small intestine. Also activates co-lipase.
In which state (ferrous or ferric) is iron absorbed? Where?
Ferrous (Fe2+). It forms complexes with vitamin C, which enhances its absoprtion in the upper small intestine.
Name three enzymes that digest carbohydrates.
Salivary amylase
Pancreatic amylase
Oligosaccharidases
