Ch. 39 Notes “Digestive and Excretory Systems”
I. Digestion-Process of breaking down food into molecules the body can use. • A. Functions of the digestive system • 1. Takes in food • 2. Break down food • 3. Gets rid of undigested molecules and wastes
B. Parts of the digestive system • 1. Mouth-begins mechanical and chemical digestion. • Saliva-moistens and lubricates food • Amylase-enzyme in saliva that begins digestion of carbohydrates.
2. Pharynx-area in the back of the mouth that serves as a passage from the mouth to the esophagus. • Epiglottis-flap of cartilage that covers the trachea when food is swallowed to prevent choking.
3. Esophagus-food tube connecting the mouth to stomach. • Food is moved down the esophagus by peristalsis; series of wavelike contractions.
4. Stomach-temporarily stores food mechanically and chemically digests food. Gastric juice made up of hydrochloric acid (HCl) and pepsin break down proteins. Mucus coats stomach lining.
5. Small intestine-Digestion continues as secretions are received from several organs: • A. liver-secretes bile, which breaks down fats. • B. gallbladder-stores bile • C. pancreas-secretes lipase, which digests fats. • After digestion, most absorption of nutrients into the bloodstream occurs in this organ.
6. Large Intestine-(colon) undigestable wastes move into this organ. • Bacteria in the colon aid in producing vitamins B and K.
7. Liver-not an organ of the digestive system, but aids in digestion by releasing bile, maintaining bloodsugar levels, and detoxifies poisons, such as ammonia which is converted to a less toxic form call urea. Bile-bitter yellow or green fluid secreted by the liver, made of water cholesterol, bile salts, and bile pigments.
II. Excretion-the process of eliminating metabolic wastes. • A. Organs involved in excretion: • 1. lungs-excrete CO2 and water vapor • 2. Skin-excretes wastes in the form of sweat. • 3. Kidneys-excretes nitrogenous wastes, salts, water, and other substances in the form of urine. Kidneys regulate the amount of water and salts in the blood of plasma.
a. nephrons-microscopic blood filtering tubes in the kidney. Three phases occur as the blood flows through a nephron: Filtration, reabsorption, secretion.
b. urine-liquid waste formed from water, urea, and salts. c. ureters-tubes that carry urine from the kidney to the urinary bladder. d. urethra-tube through which urine exits the body.
B. Damage to the Kidneys • 1. Kidneys play a role in maintaining homeostasis, so disease of the kidneys can be life threatening. • 2. Most common of kidney failure are infection, diabetes, high blood pressure, and damage from the body’s immune system. • 3. If 1 kidney is lost, the other may enlarge and do the work of both. • 4. If both kidneys fail, there are only 2 treatment options: • Dialysis • Transplants