Digestive System

Oral Cavity (Mouth) Teeth, tongue and salivary glands begin mechanical and chemical digestion

Salivary Glands Made up of 2 types of secretory cells Serous cells produce a watery secretion containing enzymes, ions and a tiny bit of mucin Mucous cells produce a stringy, viscous solution called mucous

Composition of Saliva Slightly acidic (pH 6.75-7.00) 98% water Electrolytes (Na+, K+, Cl-, PO4-, HCO3-) Salivary amylase – digests carbs Mucin – lubricates food Lysozyme – inhibits bacterial growth IgA - antibodies Metabolic Wastes – urea and uric acid

Esophagus Peristalsis – muscular contractions that push bolus to stomach

Stomach Muscular sac where protein digestion begins Has volume of 50 ml empty to 4L (1 gallon) full

Gastric Bypass Surgery

What happens in the stomach? Churning action mechanically breaks down food HCl denatures proteins to prepare for digestion Pepsin chemically digests proteins Intrinsic factor is secreted – needed for vit. B12 absorption in small intestine Food is changed into a creamy paste called chyme

Pyloric Sphincter Controls Chyme Delivery to Small Intestine Slow delivery of chyme is necessary because… Chyme is very hypertonic Chyme has low pH

Accessory Organs for Digestion Liver – makes bile which emulsifies fats Gallbladder – stores bile and delivers it to small intestine Pancreas – creates digestive enzymes to complete digestion and secretes bicarbonate to neutralize the acidic contents of the stomach

What is Bile?? Bile salts emulsify fats (makes small droplets) and helps fat absorption Bilirubin is the breakdown product of hemeglobin (green). The breakdown product of bilirubin gives feces its brown color. The liver produces 500-1000 ml daily

Small Intestine Duodenum – (25cm) bile duct and pancreatic duct attach here Jejunum (2.5m) Ileum (3.6m) Chemical digestion is completed and absorption of nutrients occurs here It takes 3-6 hours for chyme to travel through

Segmentation – mixes and moves the chyme

Intestinal surface area for absorption is 200m2 Villi

Large Intestine Absorbs water from indigestible food residue and eliminates semisolid feces. Subdivisions: Cecum Appendix Colon Rectum Anal canal

Bacterial Flora Colonize the colon and ferment indigestible carbohydrates like cellulose Synthesize B complex vitamins and Vitamin K

USDA – United States Department of Agriculture My Pyramid Plan

MEAT & BEANS EXERCISE VEGGIES GRAINS OILS MILK FRUITS