The digestive system “ The digestive system takes in food, breaks it down into nutrient molecules and absorbs them into the bloodstream, and then rids the body of the indigestible remains.” -E. Marieb

Consists of 2 “parts” 1. Alimentary canal (gastrointestinal - GI- tract) – path that food travels 2. Accessory organs

Digestive processes (disassembly) (disassembly) 1. Ingestion 2. Propulsion a. Swallowing b. peristalsis 3. Mechanical digestion 4. Chemical digestion 5. Absorption 6. Defecation

MOUTH (oral cavity) Palate: hard Soft uvula Tongue

Salivary glands 1. Cleanses mouth 2. Important for taste 3. Moistens food 4. Contains enzymes

Major salivary glands Parotid gland Submandibular gland Sublingual gland The average person produces ml a day

Teeth Masticate = to chew Baby teeth (deciduous) Full set = 20 teeth Permanent teeth = 32 teeth Incisors Canines Premolars/molars

pharynx Longitudinal & circular layers of muscle  peristalsis

esophagus Propels food using muscles (peristalsis)

stomach

Mostly protein digestion No absorption** Mechanically and chemically digested into chyme Gastric glands produce gastric juice: acidic Walls of stomach lined with mucus so the acid doesn’t “digest itself”

Problems of the stomach Ulcers: a hole in the mucus lining of the stomach Heartburn (acid reflux): contents of stomach move into esophagus

Small Intestine

Small intestine Chemical digestion of carbohydrates, proteins, nucleic acids, and fats Done with enzymes from pancreas and bile (formed in liver). Pancreatic duct and bile duct empty into duodenum

Absorption by small intestine Increased surface area: villi, microvilli

Almost all food absorption All structures increase surface area; decrease in # toward the end. What’s left at end: some water, indigestible food material and large amounts of bacteria

DON’T WRITE: Appendix C (A-5,6) – vitamins and minerals

(DON’T WRITE) 5 basic food groups and their major nutrients FRUITS: carbohydrate, water (vitamins A, C, folic acid, iron, potassium, fiber) VEGETABLES: carbohydrate, water (Vitamins A, C, E, K, B calcium, magnesium, iodine, manganese, phosphorus) GRAINS: carbohydrate, protein, thiamin, niacin (water, fiber, iron, magnesium, selenium) MILK PRODUCTS: protein, fat, riboflavin, B12, calcium, phosphorus, water MEATS/MEAT ALTERNATIVES (eggs, seeds, nuts, soybeans, legumes): protein, niacin, B6, iron, zinc (carbohydrate, fat, B12, B1, water, fiber)

Large Intestine

Function of large intestine: to absorb water eliminate residue as feces Absorb vitamins produced by bacteria Role of bacteria: Digest some nutrients Produce vitamins Produce gas

Action of L. intestine: Peristalsis Mass peristalsis: a strong wave that pushes contents towards rectum Problems: diarrhea and constipation

PANCREAS Releases enzymes into duodenum has an endocrine function

Don’t write: What is bile? Bile is a yellow, brown, or green, watery solution containing bile salts, bile pigments, cholesterol, phospholipids and a variety of electrolytes. pH of 7.6 – 8.6

Liver Produces bile; leaves through common hepatic duct Bile: part waste product, part digestive secretion (mechanical digestion of lipids)

Other liver functions Metabolism of carbs, lipids, and proteins Processing of drugs and hormones Excretion of bilirubin (from heme of old RBCs)

Gallbladder Releases bile in response to fatty food entering duodenum Location: underside of liver gallstones

liver summary… Blood from stomach and intestines passes through liver. When the liver has broken down harmful substances, they are excreted into the bile or blood. Bile by-products enter the intestine and ultimately leave the body in the feces. Blood by-products are filtered out by the kidneys and leave the body in the form of urine.