Absorbing Soluble Substances

Absorption predominantly occurs in the small intestine, which is lined with millions of tiny, finger-like projections called villi.
Villi increase the internal surface area of the intestinal walls making absorption more efficient.
Each villus is equipped with a network of capillaries and a single lacteal, which are used for transporting different types of absorbed nutrients.
Soluble substances such as sugars, amino acids, vitamins, and minerals are absorbed directly into the bloodstream via the capillaries in the villi.
This absorption process is predominantly driven by active transport, where nutrients move against a concentration gradient with the aid of carrier proteins and energy.
Fats are broken down into glycerol and fatty acids, which are then recombined into triglycerides in the cells of the villi. These are coated with proteins to form chylomicrons, which are absorbed into the lacteal, a lymphatic vessel in an individual villus.
End products of carbohydrate digestion (glucose/fructose) and protein digestion (amino acids) are absorbed by facilitated diffusion and active transport.
Water is absorbed passively following an osmotic gradient in the large intestine.
Absorbed substances are transported to the liver by the hepatic portal vein to be processed, stored, or distributed to other parts of the body.
Any waste products remaining after nutrient and water absorption are then passed into the large intestine, where they are converted into feaces and finally excreted through the rectum.