Food Absorption

1. Amino acids and glucose. These materials are absorbed into the blood stream through the process of active transport. They diffuse into the blood with the dissolved materials to the hepatic portal vein. The hepatic portal vein takes the blood with the dissolved materials to the liver and then joins the general body circulation.

2. Fatty acids and glycerol. They are absorbed into the lacteals of the villi. They can drain into lymphatic vessel and finally join the body circulation at the vena cava.

NOTE: The wall of the small intestine has numerous finger-like structures called villi (singular villus) which increase the surface area for digestion and absorption of food to take place.

Diagram of villi

Adaptation of ileum to its functions

1. It is long to provide large surface area for digestion and absorption.
2. It is highly coiled to increase the surface area for digestion and absorption.
3. It has villi and micro-villi which increase the surface area for absorption.
4. It has dense network of blood capillaries which facilitate easy diffusion of digested food.

This is the process by which the end products of digestion are incorporated in the cell. Assimilation occurs as follows:

Glucose: some is oxidized during respiration to produce energy (ATP), some is stored as glycogen in muscle, and some is converted to fats and stored as tissue beneath the skin.

Amino acids: Some are used in the synthesis (formation) of proteins, some are used in growth and repair of worn out cells. In absence of glucose and fats they may be oxidized to release energy during respiration.

Fatty acids and glycerol:

1. They are oxidized to release energy during respiration.
2. Stored as adipose tissue beneath the skin. This helps in insulating the body.

1. These have no function in man.
2. In herbivores the caecum and appendix contain bacteria that secrete an enzyme known as cellulase.

The large intestine has four functions:

1. Absorb water from the undigested materials.
2. Absorb small amount of digested food.
3. Glandular lining of the colon produces mucus which lubricates the passage of faeces.
4. It is a temporary storage of faeces up to the time of defecation (egestion).

The undigested materials are known as faeces. The faeces are removed from the body through the anus by the process of egestion.