Human Anatomy and Physiology The Digestive System

The Digestive System - Function Dissembles food to small molecules that the body can absorb. Components: –Mouth, pharynx, esophagus stomach, small intestine, large intestine –Accessory structures: Salivary glands, pancreas, liver. These add secretions

Digestive System Total length 8-9 meters –2/3 small intestines

Mouth Salivary glands Stomach Pancreas (behind stomach) Large intestine Small intestine Rectum Gallbladder (behind liver) Liver Esophagus Pharynx The digestive system

Upper Digestive System Lips, Mouth (lips, tongue, teeth), salivary glands, pharynx, esophogus,

Mouth Mechanical and Chemical Digestion –Mastication – “chewing” Lips – hold food in Tongue – moves food around Teeth – cut, tear and crush –Salivation – chemical digestion begins Moistens food – salt, water, mucous Amylase – starch breakdown to sugars Lysozyme – breaks down cells (especially pathogens) End result: Bolus –Bolus pushed to esophagus –Tongue and throat muscles

Salivary Glands and Pharynx Salivary glands –Three pairs Parotid Submandibular Sublingual Pharynx Common passage Epiglottis Covering for the glottis (opening to the larynx)

Esophogus – about 25 cm (10 inches) Peristalsis –Movements in the “food tube” that push food to the stomach (voluntary muscle) Can eat in no gravity Can eat lying down Cardiac Sphincter (involuntary) –Ring of muscle between stomach and esophagus –Heartburn; acid reflux Overeating, high acid foods, high caffeine

Stomach Muscular sac Chemical Digestion Mucus – lubricates and protects the stomach wall Hydrochloric acid – provides acidity Pepsin –Activated by HCl –Begins protein digestion (with HCl) Muscular Digestion –Fluids and food mix to form chyme –After ~1 to several hours, goes through pyloric valve to duodenum (1 st part of small intestine)

Ulcers Caused by Helicobacter pylori –Requires antibiotics, not bland diets –Bacteria damage cells of stomach lining, make stomach susceptible to ulcers, acid further irritates.

Duodenum 1 st part of small intestine Most chemical digestion here –Enzymes & digestive juices from pancreas, liver, and duodenum lining

Digestive System Site Mouth Stomach Small intestine (from pancreas) Small intestine Site Mouth Stomach Small intestine (from pancreas) Small intestine Enzyme Role in Digestion Salivary amylase Pepsin Amylase Trypsin Lipase Maltase, sucrase, lactase Peptidase Breaks down starches into disaccharides Breaks down proteins into large peptides Continues the breakdown of starch Continues the breakdown of protein Breaks down fat Breaks down remaining disaccharides into monosaccharides Breaks down dipeptides into amino acids.

Pancreas and Liver As chyme enters duodenum of small intestine, add from: Pancreas –For digestion: Amylase – continued starch breakdown Trypsin – protein; Lipase – fat breakdown Sodium bicarbonate – neutralizes stomach acid –Also: Enzymes that regulate blood sugar levels. Liver –Bile – acts like a detergent Disperses fat into droplets Lipase then breaks down fats Gall bladder – Bile storage area

The liver and pancreas Liver Gallbladder Duodenum Bile duct Pancreas Pancreatic duct To small intestine Section 38-2

Small Intestine Three parts –Duodenum – very short (< 1 meter) –Jejunum (3 meters) –Ileum (3 meters) Role: Absorption of nutrients –Folds -  Villi  Microvilli Contain capillary fields Chyme moved slowly across surface Absorb protein and carbohydrate products –Lacteals Lymph vessels which absorb fatty acids and undigested fats

Small Intestine Villus Circular folds Villi Epithelial cells Capillaries Lacteal Vein Artery

Large Intestine What remains? –Cellulose and undigested materials –Water –Bacteria Purpose: Water absorption –Some vitamins produced here (K) Defecation –Elimination of remaining waste material through rectum. (Solid excretion)

Key Functions of Digestion Mastication (Mechanical) Salivation (Chemical) Peristalsis (Mechanical) Actions of Enzymes/Acid (Chemical) Muscular Digestion (Mechanical) Absorption Defecation