One of the most clearly defined systems in the body, consisting of a long passageway (the digestive tract) and associated glands like the liver and pancreas
Six functions of the digestive system
Ingestion
Mechanical processing
Digestion
Secretion
Absorption
Excretion
Ingestion
Materials enter the digestive tract via the mouth
Mechanical processing
Crushing and shearing to make materials easier to propel along the digestive tract
Digestion
The chemical breakdown of food into small organic fragments for absorption
Secretion
The release of water, acids, enzymes, buffers, and salts by the epithelium of the digestive tract and glandular organs
Absorption
The movement of organic substrates, electrolytes, vitamins, and water across the digestive epithelium tissue into the interstitial fluid
Excretion
The removal of waste products from body fluids, with the process of defecation removing feces
Digestive tract
Also called the gastrointestinal (GI) tract or alimentary canal, a muscular tube extending from the mouth to the anus
The digestive system is vital for our survival, as it is our nutrient feed, main defense system, main elimination route for waste, and the location for a million different vital biochemical processes
Oral cavity
Functions include sensory analysis, mechanical processing, lubrication, and limited digestion
Saliva
Moistens food and begins the process of chemical digestion
Saliva is about 99% water and not only moistens food but cleanses the mouth, dissolves food chemicals so they can be tasted, and contains enzymes that start the chemical breakdown of starchy foods
Salivary glands
Three pairs: parotid, sublingual, and submandibular (submaxillary)
Tongue
Creates a bolus of food so it can travel down the pharynx and esophagus
Peristalsis
Waves of muscular contractions that move a bolus along the length of the digestive tract
Stomach
A muscular-walled, J-shaped sac where food is stored, churned, and mixed with gastric juices
Gastric juices
Include digestive enzymes and hydrochloric acid, which break down food and kill potentially harmful microbes
Liver
Secretes bile to emulsify fats in the small intestine
Gallbladder
Stores and concentrates bile secreted by the liver
Pancreas
Secretes pancreatic juice, a mix of digestive enzymes, water, buffers, and electrolytes
Villi
Line the walls of the small intestine and absorb nutrients into capillaries and lacteals
Ileocecal valve
Allows chyme to pass from the small intestine into the cecum of the large intestine
Defecation
The process of expelling waste products from digestion through the rectum and anus, involving contraction of rectal muscles, relaxation of the internal anal sphincter, and contraction of the external anal sphincter