PHYSIOLOGY OF DIGESTIVE SYSTEM

The gastrointestinal system is primarily involved in reducing food for absorption into the body.This process occurs in 4 main phases:i) Fragmentationii) Digestioniii) Absorptioniv) Elimination of waste products

- Initial fragmentation of food occurs along with the secretions of the salivary glands, in the oral cavity forming a bolus.- Bolus of food is then carried to the esophagus by the action of the tongue and pharynx (deglutition).- Esophagus carries food from mouth to stomach, where fragmentation is completed and digestion initiated.- Digestion is the progressive breakdown of food by enzymes into molecules which are small enough to be absorbed into the circulation (Eg: protein to polypeptides followed by small peptides and amino-acids).- In the stomach food is converted into semi-digested liquid (chyme) which passes through the pylorus, into the duodenum.- Unabsorbed liquid residue enters the cecum through ileo-cecal valve where water is absorbed and become progressively more solid as it passes into the anus.- Mucosal epithelium consists of three types of cells (Enterocyte ; Goblet and Paneth cells) and is replaced every 3-5 days by gradual maturation of basal enterocytes.

- Mucosa of Gastrointestinal tract consists of 4 basic types:i) Protective - squamous type in the oral cavity, pharynx, esophagus and anal canal.ii) Secretory - gastric mucosa consists of tubular glandsiii) Absorptive - intestinal mucosa consists of villi with intervening crypts.iv) Absorptive and protective - mucosa lines the large intestine. This consists of tubular glands to absorb water and goblet cells to secrete mucus to lubricate the passage of faeces.