O level Notes : Food Technology Design - Kitchen - Absorption

Absorption

Absorption is the process whereby the products of digestion pass through the walls of the digestive tract into the blood stream, it occurs in the small intestines, however alcohol is the only substance that can be absorbed elsewhere in the stomach. There are thousands of tiny finger like projections called villi that line the small intestine. Each villus is surrounded by a wall of single cells through which the nutrients pass to reach the lacteal.The lacteal that is connected to the lymphatic system and is surrounded by tiny blood capillaries, which are connected to larger blood vessels. Glucose, amino acids and other monosaccharides together with water-soluble and minerals are absorbed into the blood capillaries. Glycerol and fatty acids pass into the lacteal then into the lymphatic system. Fat-soluble vitamins are absorbed with the fats and are taken to the liver through the hepatic portal vein.

Large intestine

The large intestine is very rich with bacteria and does not contain any digestive juices. After the process of digestion has been completed in the small intestines the remains are passed into the large intestines whilst in their liquid state water is absorbed along the large intestines hence making the food residues more solid. This process may take up to twelve hours. What determines the texture of the faeces is the amount of dietary fibre or roughage that one takes in her diet. If the amount of dietary fibre is taken adequately, the faeces would be soft, bulky and would pass out of the body in minimal time but if the diet lacks dietary fibre, the faeces would be hard and difficult to excrete. The faeces move by peristalsis into the rectum, where they are stored, to be passed out of the body at regular intervals. The process of excretion is assisted by Non Starch Polysaccharides in the food.

Metabolism

Metabolism refers to the complete set of all the chemical changes that occur in living cells and tissues resulting in growth and repair. The release of energy and its use by the cells to promote all their activities, using the nutrients obtained from digested foods together with oxygen taken in by the lungs.

Monosaccharides

Glucose is transported by the bloodstream to the body cells where it is used for the provision of energy. Excess glucose is stored in the liver as glycogen until required.

Fats

These are oxidized to produce energy with water and carbon dioxide as by products, Fats are deposited in cells under the skin as adipose tissue. 

Amino acids

These are used in cell building and in various other repair jobs in tissues of the body. Excess amino acids are eliminated, Nitrogen is removed.

Here is what we discussed in this topic

• Carbohydrates: They are partly broken down by saliva in the mouth. In the small Intestine, the carbohydrate is split into simple sugars. It is then absorbed through the walls of the small intestine into the blood. Excess is stored as glycogen.

• Proteins: They  pass  through  the  mouth  chemically  unchanged meaning that there is no chemical digestion of protein in the mouth. The process of change to amino acids takes place in the small intestines. The proteins are absorbed in the small intestine, and then they pass through the walls into the blood and are carried to the liver, where any excess is removed.
• Fats: They pass through the mouth and the stomach unchanged then they are finally divided into fatty acids and glycerol and emulsified in the small intestine. It is broken into fatty acids and glycerol and is absorbed through the walls of the small intestine into the lymph. Excess is stored as adipose tissue
• Vitamins: The water-soluble vitamins B and C are absorbed in the stomach and the small intestine into the blood stream. Fat soluble A and D are absorbed in the small intestine into the blood. Excess is stored in the liver.
• Liquids: The stomach absorbs some and some are absorbed through the small intestine into the blood stream. Excess is withdrawn by the kidneys automatically to maintain the proper composition of blood.