Different classes of nutrients are absorbed through distinct mechanisms:
Carbohydrates
Carbohydrates are broken down into monosaccharides like glucose, fructose, and galactose. Glucose and galactose are absorbed via
active transport using the sodium-glucose linked transporter (SGLT1), while fructose is absorbed through
facilitated diffusion by the GLUT5 transporter.
Proteins
Proteins are digested into amino acids and small peptides. The amino acids are absorbed through various transporters, while dipeptides and tripeptides are absorbed via the H+-dependent transporter, PepT1. Inside the enterocyte, these peptides are further broken down into amino acids.
Lipids
Fats are emulsified by bile salts and broken down into fatty acids and monoglycerides. These lipids form micelles, which facilitate their diffusion into enterocytes. Inside the cells, they are re-esterified into triglycerides and packaged into
chylomicrons for transport via the lymphatic system.
Vitamins and Minerals
Water-soluble vitamins (e.g., B-complex and C) are absorbed through specific transporters, while fat-soluble vitamins (A, D, E, and K) are absorbed along with dietary fats. Minerals like calcium and iron have specialized absorption mechanisms tightly regulated by the body.
