VPB 121: Veterinary Physiology - II (2+1)

PHYSIOLOGY OF DIGESTION AND ABSORPTION

• Digestion is the process of breakdown of complex food into simpler form by the activities of the alimentary tract and glandular secretions for absorption of nutrients and the rejection of their residues.

Food

• Food is a complex mixture of substances like carbohydrates proteins, fats, vitamins, inorganic salts and water to meet the nutritive requirements of an animal.
• Herbivorous animals (Cattle, sheep, horse, goat etc.,) derive their nutritive requirements from plant sources.
• Carnivorous animals (dog, cat etc.,) obtain their food from animal sources.
• Omnivorous animals (man, pig, etc) get their foods from both animals and plants sources.

Alimentary tract

• It extends from the lips, mouth, pharynx, oesophagus, stomach, small intestine (Duodenum, jejunum and ileum), large intestine (Caecum, colon and rectum) and anus .
• In carnivores, alimentary tract is small and simple.
• The simple stomach herbivores(horse, rabbit), are also referred as hind-gut digesters because they have relatively simple stomach portion,but  the large intestine is much more complex and voluminous than the carnivores.
• In ruminants (cattle, sheep and goat), the stomach is extensively large and complex, whereas the large intestine is relatively small , hence they are known as fore-gut digesters.

Functions of GI tract

• To assist in the acquisition of nutrients.
• To prepare nutrients for digestion.
• To digest the nutrients.
• To felicitate absorption of products of digestion.
• Absorbtion of water.
• As excretory organs to help in elimination of waste products.
• As an endocrine gland to influence digestion and other metabolic functions.
• Motility of the GI tract.

Prehension of food

• Prehension is the seizing and conveying of food into the mouth. In bipeds (Primates) the hands are the prehensile organs. Dogs and Cats hold their pray with the forelimbs which is passed into the mouth by the head and jaw movements. In horse, upper lip, tongue and the incisor teeth are the main prehensile organs to collect the food. The clefted upper lip in sheep favours close grazing, on contrast the unclefted upper lip in goat. In cattle, large strong, rough protrudeable tongue and incisor teeth of the lower jaw are the prehensile organs. The pointed lower lip functions as a prehensile organ in swine.