Digestion of Proteins and Carbohydrates

Protein Digestion

Begins with pepsin in the stomach due to the stomach's acidic environment (pH 1-2).
Pepsin and trypsin (both endopeptidases) break down polypeptides into dipeptides.
Dipeptides move to the Brush Border Enzymes (BBE) on the microvilli.
BBE convert dipeptides into two amino acids.
A sodium-potassium pump (\text{Na}^+ / \text{K}^+ pump) operates in the background, driven by ATP.
Amino acids are cotransported with sodium (\text{Na}^+) via secondary active transport.
Amino acids then exit the enterocyte through facilitated diffusion to the capillary of the villus.
The hepatic portal vein transports the amino acids to the liver.

Begins in the mouth with salivary amylase breaking down carbohydrates.
No carbohydrate digestion occurs in the stomach.
In the small intestine, pancreatic amylase further breaks down carbohydrates into disaccharides.
Brush border enzymes (on microvilli) convert disaccharides into monosaccharides.
A sodium-potassium pump (\text{Na}^+ / \text{K}^+ pump) operates in the background, utilizing ATP.
Monosaccharides are cotransported with sodium (\text{Na}^+) via secondary active transport.
Monosaccharides uses facilitated diffusion to exit into site.
The hepatic portal vein transports the monosaccharides to the liver.

Both involve Brush Border Enzymes (BBE).
Both utilize secondary active transport.
Both result in the transport of nutrients to the liver via the hepatic portal vein.