Human Physiology

Lesson 19 : Physical Processes Of Digestive System & Stomach Digestion


Secretions: are the products of digestive glands that are rich in digestive enzymes. e.g. gastric juice, bile, saliva etc.

Vomition: is expulsion of stomach contents through mouth.

Peristalsis: is forwarded motility of GI tract which is responsible for pushing the food in forward direction (from mouth to anus).

Belching/eructation: is defined as expulsion of stomach gases into the air through mouth.

Regurgitation: is defined as back flow of ingesta in reverse direction i.e. from intestines to mouth.


The food is ingested into mouth by hands. Once food is in mouth, mastication reflex initiates movement of mandibles (lower jaw) that helps in grinding of food into smaller particles which can pass comfortably through narrow digestive tract. Mixing of saliva during mastication lubricates the food bolus for easy passage. The quantity of saliva produced per day may vary from 0.5 to 1.0 liter. The quantity produced increases with ingestion of dry food and decreases with juicy/ succulent food. Ptyalin or ?-amylase enzymes contributed mainly by parotid salivary glands helps in initial digestion of starch into maltose. Thoroughly masticated and lubricated food is pushed into pharynx and later on into esophagus by the process of swallowing or deglutition. Esophagus, commonly known as food pipe, carries the bolus to stomach where further digestion and temporary storage of food occurs.

Mastication: is an activity by which coarse food particles are converted into finer particles with cutting grinding and crushing action of teeth. Organs involved in this process are teeth, jaw bones and muscles of face. Masticated food can pass easily through oesophagus after a ball like called bolus. Grinding action is achieved by horizontal and vertical movements of lower jaw against immobile upper jaw. Advantages of mastication are:

  1. Finer particles provide greater surface area for better enzyme action.
  2. Masticated food is easily transformed into bolus that smoothly passes through narrow digestive tract.

Salivation: Saliva is a clear secretion discharged into mouth by a set of salivary glands situated around mouth. These are three pairs of glands namely parotid, sub mandibular and sublingual glands. Saliva contains mucin (a polysaccharide having lubricating property, enzyme ptyalin or ?-amylase and dissolved inorganic and organic compounds. Secretion of saliva occurs as a result of reflex action after entry of solid food in mouth or due to mastication activity). Saliva is required for following major functions:

  1. Moistening of food for easy passage.
  2. Lubricating properly for easy swallowing.
  3. Antibacterial
  4. Enzymatic digestion of starch
  5. Taste perception

Swallowing is the act of passage of food from mouth to stomach through oesophagus. This action is partly voluntary and partly involuntary. An initial voluntary effort pushes the bolus from oral cavity to pharynx by backward movement of tongue. From pharynx to esophagus, the bolus is pushed involuntarily through a reflex action called deglutition reflex. Subsequently the bolus moves progressively through oesophagus to stomach by specialized contractile activity of gut wall called peristalsis. Passage of bolus from pharynx to trachea (respiratory tract) is prevented by reflex closure of epiglottis.

Last modified: Tuesday, 10 April 2012, 7:34 AM