33.2: Digestive System
• Digestion begins in the mouth as teeth grind food up to increase surface area and enzymes in saliva start to break down food.
• Food moves down the esophagus by a muscle action called peristalsis.
• Pepsin and hydrochloric acid are added in the stomach to help break things down.
• Muscle action by the stomach also helps break down food.
• An ulcer is when the stomach lining is exposed to the harsh acids.  It’s caused by bacteria.
• Pepsin breaks down proteins.
• Digestion is completed in the small intestines.  
• Carbohydrates are broken down into simple sugars.
• Fats are broken down into short chains of carbon and hydrogen molecules.
• Proteins are broken down into amino acids.
• Nutrients are absorbed into the blood through the villi of the small intestines and are stored in the liver.
• Bile, produced in the liver and stored in the gall bladder, helps to break down fats.
• Pancreatic juices also help to break down food into smaller particles.
• Undigested materials then go through the large intestines, where water, salts, and vitamin K is absorbed.
• Undigested materials are compacted and eliminated at the end of the large intestines.

33.3: Excretory System
• The liver combines ammonia with carbon dioxide to make urea, a nitrogen-containing waste eliminated by the kidneys and sweat glands.
• Nephrons in the kidneys filter the blood by removing urea and other waste products.  This removal from the blood is called filtration.  
• Each kidney has over 1 million nephrons.
• As the liquid moves through the nephron, much of the water is reabsorbed by the tubules.
• The hormone ADH (made in the brain) makes the tubules reabsorb more water as needed.
• The resulting liquid is more concentrated in waste product and is called urine.
• Kidney disorders include: kidney stones (which block the flow of urine) and kidney failure (treated by hemodialysis or kidney transplant).
• Hemodialysis is the process of filtering the blood in a machine outside of the body (done twice a week).