Digestive and Excretory System Chapter 38 Digestive and Excretory System

38-1 Food and Nutrition Calorie—The energy stored in food is measured in Calories (with a capital C!). 1 Calorie = 1000 calories. Nutrients the body needs are: Carbohydrates, fats, proteins, vitamins, and minerals The most important nutrient the body needs is water.

38-2 Process of Digestion Mouth—Converts food to a clump called a bolus. Chewing—Begins mechanical digestion. Amylase—Found in saliva, begins chemical digestion. Teeth—Responsible for the majority of mechanical digestion. Salivary glands—Secrete Amylase. Pharynx Back of “throat”. Esophagus—Transports bolus to stomach. Peristalsis—Muscle contractions that squeeze the bolus down into the stomach. Stomach—Continues mechanical and chemical digestion. Contains mucus, hydrochloric acid, and the enzyme pepsin. Pepsin—Breaks down proteins into small fragments. Chyme—Mixture produced by the combination of all the stomach’s fluids and food as it churns and mixes its contents.

Small Intestine – Site of most chemical digestion and absorption. Duodenum—The first of three parts of the small intestine. Receives chyme from the stomach and digestive fluids from the ACCESSORY STRUCTURES OF DIGESTION. Villi—Fingerlike projections that increase absorption in the small intestine. Accessory Structures of Digestion Pancreas—Produces: Hormones—regulate blood sugar. Enzymes—Break down macromolecules. Sodium Bicarbonate—Neutralizes stomach acid. Liver Produces bile—dissolves fat. Large Intestine – removes excess water from leftover food. Transports excess waste material to the rectum. Rectum—Site of waste elimination.

38-3 Excretory System Normal metabolic wastes include excess salts, carbon dioxide, and urea Organs of excretion Skin – rid body of salts, and some urea Lungs – rid body of carbon dioxide Liver – converts amino acids into nitrogen wastes, which it then converts to urea Kidneys – remove waste products from blood, maintain pH, regulate water content, and blood volume

In the Kidneys Nephrons – Functional units of the kidney. Each nephron has its own blood supply! Filtration—Removal of wastes from the blood. Takes place in glomerulus—small network of blood vessels located in the upper end of each nephron. Bowman’s Capsule—Encases the blood vessels of the glomerulus and absorbs waste from the blood, called Filtrate. Filtrate—Composed of water, urea, glucose, salts, amino acids, and vitamins. Reabsorption—Process of the filtrate making its way back into the blood. Water, amino acids, fats, and glucose are reabsorbed back into the bloodstream. The remaining waste is called urine. Kidneys (nephrons) Ureter  Urinary bladder  Urethra Excreted