Chapter 38Digestive 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