BIOLOGY: Digestive System

Digestive System

Digestion – process by which food are broken down into usable form

Functions

1.    Ingestion – taking in of food

2.    Motility – movement of food through digestive tract

3.    Digestion – breakdown of food into smaller molecules

4.    Secretion – adds substances to digestive tract to enhance digestion

5.    Absorption – transfer of nutrients from GI tract

STRUCTURES

Mouth
- integral part of digestion
- tongue pushes food down pharynx
- teeth
    a. canine – tearing
    b. incisors – cutting
    c. molars – crushing

Esophagus
- muscular tube that accommodates food into stomach
- has sphincter which controls the passage of chime
     a. cardiac – bet. Esophagus & stomach
     b. pyloric – near the duodenum

Stomach
- left side of body, under diaphragm
- muscular sac like organ that connects the esophagus & small intestine
- absorbs some water, electrolytes, certain drugs, alcohol
- mucin (mucus)
- rugae (gastric folds) – expands to accommodate more food

Small Intestine ( > 6m)
- most digestion takes place
- rhythmic contraction of muscular walls moves the food along while bile & others break it down
- mucosa (inner lining)
- villi (fingerlike projections w/c increases absorptive surface)
- 3 parts
     a. ileum
     b. jejunum
     c. duodenum

Large Intestine
- anchored in the abdomen
- final section of digestive tract
- undigested material passes from the small intestine as liquid & fiber

Accessory Organs

Salivary gland
- salivary amylase (ptyalin)
- 3 glands:
    a. sublingual – under tongue
    b. subbmandibular – under lower jaw
    c. parotid – front of ear

Liver
- largest internal organ
- has 500 known functions
   a. synthesis of proteins
   b. immune & clotting factors
   c. oxygen & fat carrying substances
- Chief digestive function: Secretion of bile solution
- Converts excess amino acids into useful forms & filters drugs from bloodstream
- has 2 main lobes located under the diaphragm on the right side of body

Gall Bladder
- located under & attached to liver
- reservoir for bile
- bile passes to gallbladder through a small tube called cystic duct
- muscular walls absorb excess water

Pancreas
- gland that secretes pancreatic fluid (aids in digestion. Mixture of enzyme & sodium bicarbonate)

segmentation – mixing of partly digested food & enzymes