Secretion of saliva: The principle glands of salivations are parotid, submandibular & sublingual with many buccal glands, the daily secretion of saliva is about millilitters. Saliva contain 2 types of secretion: 1- serous secretion contain a-amylase 2- mucous secretion Pariatal glands secrete entirely serous secretion,submandibular &sublingual secret both serous &mucous, buccal gland mainly mucous. PH os salivais about 6&7.

99.5% of saliva is water, 0.5%are solutes, among them are salts of CL, Hco3, phosphate of Na&k, some disolving gases, vareous organic substances,including urea, uric acid, albumin, globulin, mucin,,bacteriolytic enzyme. Water provide a medium for dissolving food, Cl activate salivary amylase, HCO3 &Ph buffer chemicals, urea & uric acid help the body to get rid of waste, mucous lubricate the food so it can be easily turned in the mouth & swallowed, lysozyme distroy bacteria, so protect mucous memnbrane from infection& teeth from decay.

Saliva prevent the harmful effect of bacteria by :1- continuous washing away pathogenic bacteria as well as food particles that provide bacteria with metabolic support. 2- saliva contain many facter that can kill bacteria such as proteolytic enzyme Regulation of salivary secretion : The superior & inferior salivary nuclei located in the brain stem, control secretion by salivary glands, these nuclei interne are controlled mainly by taste impulses & tactile sensory impulses from the mouth, food that have pleasant tast increase salivary secretion, also smooth texture food increase the secretion.

Phases of salivary secretion :] In addition to the salivation that occurs while food in the mouth, salivation can occur even before food enters the mouth, therefore, salivary secretion divided into 3 phases : 1- psychic phase:it makes the mouth ready for food & aid in the secretion of saliva as the food is presented to the mouth 2- gastatory phase : supplies the saliva that mixes with food while one is chewing 3- GI phase :continuous the secretion of saliva even after the food passed for storage in the stomach, this phase is especially likely to be abundant when one has swallwed irritant food because nerve signals from stomach then excite the salivary nuclei, this helps to neutralize the irritant substances thereby relieving the irritation of stomach.

Esophageal secretion : It is entirely mucoid, it provide lubrication for swallwing, the main body of esophagus is lined with many simple mucous glands in the gastric end & in the initial portion of esophagus, the mucous in the upper esophagus prevents mucosal excoriation by the newly entering food, whereas that near esophago-gastric junction protect the esophageal wall from digestion by gastric juice, despite this protection peptic ulcer may occure at the gastric end of esophagus.

Regulation of gastric acid secretion (nervous & hormonal mechanism): Basic facters that stimulate gastric secretion (Ach, gastrin &histamine): The neurotransmitters or hormones that directly gastric secretion are ACH, gastrin &histamine, all function by binding to specific receptors

Gastric secretion : In addition to mucus – secreting cell that line the entire surface of the stomach, it has 2 important types of glands : 1- oxyntic (acid forming ) glands, secrete Hcl, pepsinogen, intrinsic facter&mucus. 2- pyloric gland, secrete mainly mucus for protection pyloric mucosa, some pepsinogen, & gastrin hotrmone.

Stimulation of acid secretion Nervous stimulation : One half on nerve signals to the stomach that cause gastric secretion originate in the dorsal nuclei of the vagi&pass by vagus nerve to the stomach then to the gastric glands other half of signals generated by local reflexes that occure in the enteric nervous system, the type of stimuli that can initiate reflexes are:distention, tactile, chemical stimuli.

Stimulation of acid secretion by gastrin: The nerve signals from vagus nerve&from local enteric reflex, beside causing direct stimulation of glandular secretion of stomach juices, also also stimulate the antral mucosa to secrete gastrin hormone, it will carried by blood to the oxyntic glands in the body of stomach, it will stimulate the pariatal cells to secrets Hcl (8x)which inturn excit local enteric refllex activity which increase Hcl secretion & increase the secretion of enzyme by the peptic cell.