The Digestive System

The principal structure of the digestive system Alimentary canal gastrointestinal (GI) tract -Irregular tube open at 2 ends About 29 feet long Food is broken down and then absorbed through the walls Mechanical & Chemical digestion

Main and Accessory Organs of the Digestive System Mouth Pharynx Esophagus Stomach Small intestine Large intestine Teeth & tongue Salivary glands Liver Gallbladder Pancreas Veriform appendix

Mouth/oral cavity Lined with mucous membrane Roof has hard (front) and soft (rear) palates Uvula prevents food/liquid from entering nasal cavity Teeth for physical digestion Salivary glands -secrete saliva w/ enzymes

Pharynx Functions in respiration and digestion 5 inches long Serves as hallway for food and air 3 segments - see diagram

Esophagus Connects to stomach 10 inches long Peristalsis - pushing food toward stomach Epiglottis prevents food from entering windpipe

Stomach Pouch for food to enter after chewed Enters thru the esophageal sphincter (rings of muscle tissue) Muscle fibers run lengthwise, around and obliquely (STRONG) -Contraction mixes food with gastric juice into chyme (mechanical digestion) Gastric glands secrete juice and HCl

Stomach

Small intestine 20 ft long 3 segments, duodenum, jejunum, ileum Mucous layer contains 1000’s of microscopic glands that secretes digestive juice Interior is not smooth - circular folds called plicae covered w/ 1000s of villi

Close up of small intestine Villi project into interior of intestine Inside rich in blood capillaries - why? Microvilli greatly increase surface area & absorption of nutrients

Liver & Gall Bladder Liver secretes bile into gall bladder ducts Bile breaks down fats to smaller molecules (emulsify) When lipid enters duodenum it initiates mechanism that contracts gall bladder and forces bile into sm. Int.

Pancreas Lies behind stomach Gland secretes pancreatic juice into ducts Pancreatic juice contains enzymes that digest many types of foods. Also contains sodium bicarbonate, alkaline, to neutralize stomach acid

Large Intestine 1.5 m/5 ft. long Undigested food and unabsorbed food Bacteria acts on food here which allows some nutrient absorption Water and salt are reabsorbed here Waste excreted