(a) Absorption of amino acids and glycerol takes place in the small intestine.

(b) The faeces in the rectum initiate a neural reflex causing an urge for its removal.

(c) Skin and eyes turn yellow in liver infection.

(d) Rennin is a proteolytic enzyme found in infants gastric juice.

(e) Pancreatic juice and bile are released through hepato-pancreatic duct. (f) Dipeptides, disaccharides and glycerides are broken down into simple substances in the region of small intestine called duodenum.

Gastric glands process three major types of cells namely

(i) Mucous neck cells (Goblet cells) These cells are present throughout the epithelium of gastrointestinal tract and are involved in the secretion of mucus.

(ii) Peptic or Chief cells (Zymogenic cells) These cells are usually basal in location and are involved in the secretion of gastric digestive enzymes such as proenzymes pepsinogen and prorennin.

(iii) Parietal or oxyntic cells These cells are large and most numerous present on the side walls of the gastric glands. They are involved in the secretion of HCl and Castlis Intrinsic Factor (CIF). (factor essential for the absorption of vitamin- $\mathrm{B}_{12}$ in ileum).

The mucus secreted by the goblet cells along with the bicarbonates from the pancreas play an important role in lubrication and protection of the mucosal epithelium from excoriation by the highly concentrated hydrochloric acid.

The activities of the Gastro-Intestinal Tract (GIT) are under neural and hormonal control for proper coordination amongst different parts. The gastrointestinal tract is innervated by intrinsic nerves as well as by extrinsic nerves.

The intrinsic neural system, also called the enteric neural system consists of (i) Meissner's plexus situated in the submucosa and (ii) Auerbach's plexus situated in the muscular layer. The enteric neural system controls most of the gastrointestinal functions like secretion and motility.

The extrinsic innervation of the gut consists of parasympathetic and sympathetic nerves which can modify the activity of intrinsic neural system in response to reflex activity initiated by GIT or from other body parts.

The sight, smell and the presence of food in the oral cavity can stimulate the secretion of the saliva through vagus nerve. Gastric and intestinal secretions are also stimulated by neural signals. The muscular activity of different parts of the alimentry canal can also be moderated by neural mechanisms, both local and through CNS.

Hormonal control of the secretions of digestive juice is carried out by the local hormones produced by the gastric and intestinal mucosa. These include gastrin (stimulate release of gastric juice), enterogastrone (inhibits gastric secrection and motility), secretin (decreases gastric secretion), duodocrinin (stimulate Brunner's gland) etc.

Constipation is characterised by small amounts of hard, drybowel movements usually fever than three times a week. In constipation, the faeces are retained within the rectum as the bowel movement occurs irregularly. The causes for constipation involve water deficiency, lack of roughage in diet, spasm of colon, lack of exercise, emotional stress and certain drugs.

Indigestion is the condition in which the food is not properly digested leading to a feeling of fullness. The cause of indigestion are inadequate enzyme secretion, anxiety, food poisoning, over eating and spicy food consumption.