Human Digestive System

Ingestion Mouth –mechanical digestion teeth –breaking up food –chemical digestion saliva –amylase »enzyme digests starch –mucin »slippery protein (mucus) »protects soft lining of digestive system »lubricates food for easier swallowing –buffers »neutralizes acid to prevent tooth decay –anti-bacterial chemicals »kill bacteria that enter mouth with food

mouth break up food digest starch kill germs moisten food

Mouth Chemical and mechanical digestion. Food is chewed (masticated) mechanically. A bolus (lump) is formed with saliva and the tongue.

Swallowing Epiglottis –flap of cartilage –closes trachea (windpipe) when swallowing –food travels down esophagus Peristalsis –involuntary muscle contractions to move food along

Pharynx The back of the throat. Larynx- passage for air, closes when we swallow. Is approximately 15cm long.

Digestive Glands Groups of specialized secretory cells. Found in the lining of the alimentary canal or accessory organs.

Stomach Food is temporarily stored here. Gastric juices are secreted. Has layers of muscle that line the inside. Mechanically and chemically breaks down food.

Stomach Functions –food storage can stretch to fit ~2L food –disinfect food HCl = pH 2 –kills bacteria –chemical digestion pepsin –enzyme breaks down proteins

stomach kills germs break up food digest proteins store food sphincter mouth break up food digest starch kill germs moisten food

Pancreas Digestive enzymes –digest proteins trypsin, chymotrypsin –digest starch amylase Buffers –neutralizes acid from stomach

Liver Function –produces bile bile stored in gallbladder until needed breaks up fats –act like detergents to breakup fats

pancreas produces enzymes to digest proteins & starch stomach kills germs break up food digest proteins store food mouth break up food digest starch kill germs moisten food liver produces bile - stored in gall bladder break up fats

Small intestine Function –chemical digestion major organ of digestion & absorption –absorption through lining over 6 meters! small intestine has huge surface area = 300m 2 (~size of tennis court) Structure –3 sections duodenum = most digestion jejunum = absorption of nutrients & water ileum = absorption of nutrients & water

Large intestines Solid materials pass through the large intestine. Function –re-absorb water –Vitamins K and B are reabsorbed with the water. use ~9 liters of water every day in digestive juices > 90% of water reabsorbed –not enough water absorbed »diarrhea –too much water absorbed »constipation