Protein digestion
Enzymes involved in protein digestion are called proteolytic enzyme. proteolytic enzymes are two types.
Endopeptidases: the enzymes which breakdown the central peptide bonds and form smaller peptide chains are called endopeptidases. Eg. Pepsin, trypsin
Exopeptidases: the enzymes which breakdown the terminal peptide bonds and form liberate amino acids are called exopeptidases eg. Carboxy peptides, amino peptides
Carbohydrate
The enzymes associated with carbohydrated digestion are called carbohydrates. The common carbohydrates in fish food are-
Glycogen- storage carbohydrate of animals
Starch- storage carbohydrate of plants
Chitin- structural carbohydrate of animals
Cellose- structural carbohydrate of plants
Lipid
- At first emulsification process occurs.
- The lipolytic enzymes secreted from pyloric caeca and intestinal mucosa and pancreas.
- Fat is digested by the enzyme lipase into fatty acids and glycerols.
- No fat digestion occurs in the mouth.
- In stomach very little digestion occurs.
- Most of the fat is digested in the intestine.
Absorption: Absorption is the transfer of digested food materials from the digestive tract into the blood stream and lymphatic system. There are three types of absorption.
Passive diffusion: Does not requires expenditure of energy, Digested food materials aren’t transported by carrier system, smaller molecules are absorbed.
Active transport: requires expenditure of energy, Digested food materials are transported by carrier system, smaller molecules are absorbed.
Pinocytosis: Intake of food materials by fusion & constriction, large molecules are absorbed.
Absorption site:
absorption occurs mainly in intestine. The enterocytes are the absorption cell of the intestinal epithelium. Also, stomach, rectum can be absorption site. The enterocytes form villi and microvilli which provide a large surface are for absorption.
Villi: In the lumen of the intestine, there are many folds which provide for a large surface area for absorption are called villi.
Microvilli: the absorbing cell enterocytes are folded and form a brush like structure is called microvilli. These brush border are faced towards the food materials and are the main absorption site.
Absorption of Carbohydrates, Proteins and Fats:
Absorption of lipid: Free fatty acid, Glycerol, Monoglycerieds
Absorption of protein: Amino acid, Di & tripeptides, polypeptides
Absorption of carbohydrates: nmonosaccharides , they are carried by NA+CO transport system.
