Absorbing Soluble Substances

Digestion breaks down complex food molecules into smaller, soluble substances that can be absorbed.
Soluble substances are absorbed into the bloodstream during the process of absorption in the small intestine.
The small intestine is specifically adapted for this purpose, as it has a large surface area created by the presence of tiny, finger-like protrusions known as villi.
Each villus is covered in microscopic hair-like extensions, called microvilli, to further improve absorption.
The lining of the small intestine is only one cell thick allowing for easier passage of nutrients into the bloodstream.
After absorption, the soluble molecules enter the circulatory system and are transported to different parts of the body where they are required.
Mainly glucose, amino acids, vitamins, and minerals are absorbed into the bloodstream. Fatty acids and glycerol are absorbed by the lymph.
Additionally, water is also absorbed through osmosis in the large intestine.
Absorption in the gut can be active or passive. Active absorption requires energy as substances are moved against a concentration gradient, while passive absorption does not require any energy.
Substances like glucose and amino acids are actively absorbed, while others, like fatty acids, are passively absorbed.
Only digested food can be absorbed; undigested food cannot be absorbed and is moved along the digestive system to be eliminated.