The Digestive System

• Mouth

Functions:
    -mastication
    -deglutition
    -start of digestion (starch)
    -self-cleaning
    -holding food

Secretions:
    -Saliva from salivary glands (parotid, sublingual,  
     submandibular)- prepare food for swallowing, prevent mouth 
     from drying, and start the breakdown of starch
    -Amylase- digests starch

Histology: stratified squamous epithelium 

• Stomach

Functions:

     -temporary food storage

     -mechanical breakdown of food

     -breakdown of chemical bonds by acids and enzymes

     -production of intrinsic factor needed for vitamin B12
      absorption

     -begins the breakdown of proteins 

Secretions:

      -mucous- protects the stomach lining

      -gastric juices- softens meat and bones, kills bacteria in food,
       activates protein-digesting pepsinogen 

      -Hydrochloric acid

Histology: simple columnar epithelium with mucous cells

• Small Intestine

Functions: 

      -completes the digestion of food

      -absorbs end products into blood and lymph

      -secretes hormones that help control production of pancreatic 
       juice, intestinal juice, and bile

      -controls the amount of fluid and electrolytes lost from the 
       body 

Secretions:

      -paptidase- digest proteins

      -maltase, sucrase, lactase- digest disaccharides

      -lipase- digest lipids 

      -bicarbonate ions- act as emulsifying agents

      -secretin- stimulates the pancreas to secret a fluid high in 
       bicarbonate ions that help neutralize chyme

      -CCK- stimulates the release of bile from the gallbladder and 
       the secretion of digestion enzymes from the pancreas

Histology: simple columnar epithelium 

• Liver

Functions:

      -produces bile and plasma proteins

      -detoxifies blood

Secretions:

      -bile- lowers the surface tension of fats, forming small droplets

Histology: dense connective tissue

• Gallbladder

Functions: store and secrete bile into the small intestine in the  
       presence of fatty acids

Secretions: bile

Histology: simple columnar epithelium 

• Pancreas

Functions: 

      -secretes enzymes into the cavities and blood

      -neutralizes chyme

Secretions:

      -amylase- digest starch into maltose

      -trypsin- digest proteins

      -lipase- digest lipids

      -nucleases- digest nucleic acids

      -sodium bicarbonate ions- neutralize chyme

Histology: simple cuboidal epithelium

• Large Intestine

Functions: 

      -reabsorb water

      -store wastes

Secretions: none

Histology: simple columnar epithelium 

• Rectum

Function: temporarily stores feces

Secretions: none

Histology: smooth muscle

• Anus

Functions: helps feces to exit the body

Secretions: none

Histology: simple columnar epithelium