The Digestive System

Function~ Mechanical and chemical breakdown of food Absorption of nutrients Consists of alimentary canal and accessory organs

Characteristics of the Canal Mucosa-protects tissues and carries absorption Submucosa-glands, blood vessels, nerves Muscular Layer-smooth muscle tissue, circular and longitudinal fibers, pushes food (PERISTALSIS) Serosa-(serous layer) visceral perioneum, lubricates surfaces (serous fluid)

Digestion~ Contractions mix food with digestive juices. Peristalsis – pushes food down the tube.

Ingestion~ Mouth mechanical digestion chemical digestion teeth saliva 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

Pharynx and Esophagus~ Pharynx – nasal and oral cavities: nasopharynx, oropharynx, and laryngopharynx Esophagus – moves to the stomach Cardiac sphincter – prevents food and chemicals from moving up out of stomach

mouth break up food moisten food digest starch kill germs

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

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

Small Intestine~ Function Structure major organ of digestion & absorption chemical digestion digestive enzymes absorption through lining over 6 meters! small intestine has huge surface area Structure 3 sections duodenum = most digestion jejunum = absorption of nutrients & water ileum = absorption of nutrients & water

Duodenum~ pancreas liver gall bladder 1st section of small intestines acid food from stomach mixes with digestive juices from accessory glands: pancreas liver gall bladder

Pancreas~ Digestive enzymes Buffers peptidases pancreatic amylase reduces acidity buffers acidity of material from stomach

mouth break up food moisten food digest starch kill germs stomach kills germs break up food digest proteins store food pancreas produces enzymes to digest proteins & starch

Liver~ Digestive System Functions Secretes bile stored in gallbladder until needed breaks up fats maintains blood glucose stores iron and vitamins destroys damaged RBCs removes toxic substances

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

Large Intestine~ Function not enough water absorbed back to body re-absorb water use ~9 liters of water every day in digestive juices > 90% of water reabsorbed not enough water absorbed back to body diarrhea too much water absorbed back to body constipation

Rectum~ salts masses of bacteria undigested materials Last section of colon (large intestines) eliminate feces undigested materials extracellular waste mainly cellulose from plants roughage or fiber salts masses of bacteria

mouth break up food moisten food digest starch kill germs stomach kills germs break up food digest proteins store food liver produces bile - stored in gall bladder break up fats small intestines breakdown food - proteins - starch - fats absorb nutrients pancreas produces enzymes to digest proteins & carbs large intestines absorb water

Ulcers~ Used to think ulcers were caused by stress Coevolution of parasite & host Free of H. pylori Colonized by H. pylori Used to think ulcers were caused by stress tried to control with antacids Now know ulcers caused by bacterial infection of stomach Helicobacter pylori now cure with antibiotics inflammation of stomach inflammation of esophagus H. pylori cell damaging proteins (VacA) inflammatory proteins (CagA) cytokines helper T cells neutrophil cells white blood cells