Organs of the Digestive Tract

Liver

– produces bile
-bile emulsifies fats in the small intestine; increases surface area of fat particles

Gall Bladder

– stores bile between meals
– releases bile when food moves into the small intestine

Pancreas

– manufactures and releases bicarbonate to neutralize acid coming out of the stomach
– basic environment inactivates pepsin
– releases many enzymes that complete the chemical digestion of many food substances:
– lipases chemically digest lipids
– carbohydrases chemically digest sugars and starches
– proteases chemically digest proteins

Oral Cavity (mouth)

– teeth and tongue mechanically digest food
– salivary glands secrete saliva (mucus, water and salivary amylase)
– mucus and water moisten and lubricate food
– amylase chemically digests starch > dissaccharides

Esophagus

– moves food from the oral cavity and pharynx to the stomach for further digestion
– moves the food down by peristalsis; series of coordinated muscular contractions

Stomach

– sphincters control the movement of food into and out of the stomach
– churn and squeeze food (mechanical digestion)
– gastric glands secretes gastric juices (hydrochloric acid, mucus, pepsin)
– hydrochloric acid kills bacteria and converts pepsinogen into it’s active form pepsin
– pepsin chemically digests protein molecules
– mucus protects stomach lining from corrosive HCl

Small Intestine

– inside walls are folded and have small fingerlike projections called villi and micro villi (extremely high surface area)
– composed of three sections duodenum (beginning), jejunum (middle) and ileum (end)
– major site of chemical digestion and absorption
– peristalsis mixes contents and propels contents further along
– contains secretions the liver and pancreas that assist in digestion
– active transport and diffusion move nutrients through the intestinal walls and into the circulatory system

Large Intestine

– reabsorb water, vitamins and to hold and compact the unabsorbed material from the small intestine
– contains bacteria cultures that breakdown indigestible material and release vitamins
– the rectum controls defecation; elimination of waste