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Name: Date: Period: Directions: Complete the descriptions of the digestive and excretory systems using vocabulary terms from this unit. During Ingestion food is placed into the mouth and digestion begins. In the mouth, both chemical and mechanical digestion occur. In chemical digestion, salivary amylase from the salivary glands/saliva starts to break down starch into sugar. Mechanical digestion also occurs, chewing breaks foods into smaller pieces. Now the food is considered a bolus and is swallowed. Peristalsis moves the bolus down the esophagus by relaxing and contracting smooth muscles. Once the bolus enters the stomach, mechanical and chemical digestion occur. Stomach muscles churn the contents of the stomach during mechnical digestion, mixing the gastric juices with the food. Meanwhile, during chemical digestion the enzyme pepsin breaks down proteins into amino acids, and stomach acid, works to break down everything in the stomach. The food, now referred to as chime (or “acid chime”), moves into the small intestines. The acid in the chyme is neutralized by sodium bicarbonate produced in the pancreas. In the small intestines, chemical digestion and absorption take place. During chemical digestion, enzymes from the pancreas, including, pancreatic amylase, trypsin and lipase, break down starches into sugars, proteins into amino acids, and lipids (fats) into fatty acids. To help with the digestion of lipids/fats, the liver produces bile, which separates lipids/fats for more efficient digestion. In addition to these enzymes, the small intestine produces several enzymes of its own. These enzymes include maltase, sucrase, and lactase, which break down starch (complex sugars) into sugar (simple sugars), and protease which finishes breaking down protein into amino acids. The final stages of the digestive process include the small intestines absorbing nutrients and the large intestines absorbing water and eliminating indigestible material. Now that the nutrients and water have been absorbed into the blood stream any nitrogenous wastes, such as ammonia formed from the breakdown of proteins, are converted into a less toxic form, urea, by the liver. Once these toxins are converted they are filtered out of the blood by the kidneys, along with any excess water or salt. In the kidneys the functional units, known as nephrons, complete three functions to maintain homeostasis. The first function starts when blood enters the glomerulus. In the glomerulus, toxins, excess water and salt are pushed through the membrane of the capillaries and captured by the bowman’s capsule. The filtered out water, salts and toxins, now known as filtrate, proceeds down the Loop of Henle, where any salt or water the body needs is reabsorbed. After reabsorption, the filtrate moves to the collecting duct, where remaining liquids now become urine. This is the third function of the kidney, known as urine excretion. The urine now moves down two tubules known as ureters, to the bladder, where it is stored until it is moved out of the body, via the urethra in a process called excretion.