Absorption In Nutrition In Animals - High School Biology

- This is the process through which the soluble end products of digestion diffuse into the cellular lining of the villi.
- Absorption of micronutrients such as water soluble vitamins, mineral salts and alcohol are absorbed at the stomach.
Alcohol is equally absorbed here without undergoing digestion. - Most absorption of end products of digestion occurs in the ileum.
- Molecules of amino acids and glucose pass through the epithelial lining and capillary walls into the blood system by active transport.


- The capillaries drain into the hepatic portal vein where the absorbed products are transported to the liver before they are circulated to other body parts.
- The fatty acids are absorbed into the lacteals of the villi which drain into the lymphatic vessels.
- The lymphatic vessels later join the blood circulatory system which transports them to other body parts. - The ileum is adapted to absorption in many ways

• It is long to provide a large surface area for absorption.
• It has a narrow lumen so as to bring the digested food into close contact with the walls of the ileum for easier absorption
• It is highly coiled to slow down movement of food thus allowing more time for digestion and absorption of food.
• The inner surfaces have numerous villi and microvilli to increase surface area for absorption of end products of digestion.
• The epithelial lining is one cell thick to reduce the distance through which digested food diffuses.
• Has a dense network of blood capillaries into which digested food materials diffuse to increase transport and thus maintain a steep concentration gradient.
• Have lacteal vessels in the villi for absorption of fatty acids and glycerol.

This is the process through which the undigested and indigestible food substances are eliminated from the body.

- While these have no roles in man, they play vital roles in the ruminant animals and other herbivores.
- They contain some bacteria which secrete cellulose enzyme.
- These enzymes digest cellulose since most digestive systems cannot secrete cellulose digesting enzyme.
- The bacteria and the herbivores are in a symbiotic relationship.

- This is process of incorporation of the end products of digestion into the cell metabolism.
- It involves utilization of the end products of digestion into various uses.

a) Glucose
- Oxidized to release energy
- Excess glucose is stored under the skin to provide heat insulation
- Glucose is used to synthesize complex polysaccharide such as cellulose that is an important structural compound in plants.
b) Fatty acids and glycerol
- Oxidized to release energy
- Combine to form neutral fats stored under the skin to provide heat insulation
- Used to build structures
c) Amino acids
- Used to synthesize proteins for general body growth
- Oxidized during starvation to release energy.

- These are organic chemical compounds that are essential for a healthy body.
- Some are synthesized in the body through the action of some microorganisms while some are also obtained in fresh fruits and vegetables.
- Vitamins are destroyed when foods are excessively cooked. They are required in small quantities.

- They play vital roles in metabolic reactions.
- Some act as co-enzymes while some influence the intake of certain substances. In particular, vitamin C influences uptake of iron while vitamin D influences absorption of calcium ions in the gut.
- Lack of vitamins in the body results into abnormalities that manifest through various deficiency diseases.
- These deficiency diseases can be corrected by inclusion of the deficient vitamins in the diet or taking the vitamin supplements
- There are two classes of vitamins owing to their solubility:

• Fat soluble vitamins- They dissolve in fats and are often stored in the liver. Include Vitamins A, D, E, K.
• Water soluble vitamins- Dissolve in water. Include vitamins B1, B2, B5, B12 and C.

- These are important inorganic compounds containing elements required for essential body functioning. Depending on body requirements, mineral salts are of two classes:

• Macro-nutrients: Nutrients required in large quantities. These include nitrogen, sulphur, phosphorous, calcium, sodium, iron and magnesium.
• Micro-nutrients: Nutrients required in small quantities. Include copper, manganese, boron, iodine and cobalt.

- This is the indigestible material in food. Mainly composed of cellulose from plant cell walls.
- They are found in full cereals, fresh fruit fibres like lemons, oranges, mangoes and vegetables.

Importance of Roughage

1. It rubs against the walls of the alimentary canal stimulating secretion of digestive enzymes and mucus to lubricate the epithelial lining.
2. Roughage enhance peristalsis since as they rub against the walls of the alimentary canal, they stimulate contraction and relaxation of the muscles.
3. Roughage is an absorbent; it extracts water from the alimentary canal making the fecal matter bulky and moist hence can be easily propelled by peristaltic movements. This prevents constipation.

Factors affecting energy requirements in humans

- Discuss how the following factors affect energy requirements in humans:

• Basal metabolic rate
• Occupation
• Health of an individual
• Age
• Sex
• Body size
• Environmental temperature