Absorption

Most nutrients are absorbed in the small intestine. This is due to its large surface area and specialized structures like villi that enhance absorption.

Most water is absorbed in the small intestine. Some water is also absorbed in the colon, which helps in forming solid waste.

Villi and microvilli greatly increase the internal surface area of the small intestine. This increased surface area allows for more efficient absorption of nutrients into the bloodstream.

One adaptation is the presence of villi, finger-like projections that increase the surface area for absorption. Each villus contains capillaries and a lacteal to transport absorbed nutrients.

Capillaries in the villi absorb water-soluble nutrients such as glucose and amino acids. These are then transported via the bloodstream to other parts of the body.

Lacteals in the villi absorb fats and fat-soluble vitamins. These are transported via the lymphatic system before entering the bloodstream.

A villus is a finger-like projection of the small intestine lining containing a network of capillaries, a lacteal (lymph vessel), and a single layer of epithelial cells with microvilli.

Fats (lipids) and fat-soluble vitamins are absorbed into the lacteals. These are transported via the lymphatic system.

Glucose (a simple sugar) and amino acids are absorbed into the capillaries within the villi. These nutrients are then carried away in the blood.

Active transport allows the absorption of nutrients against a concentration gradient.

Diffusion allows the absorption of fatty acids and glycerol into the epithelial cells lining the small intestine. These molecules move from a region of high concentration (lumen of the small intestine) to a region of low concentration (epithelial cells).