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Chapter 16 – Digestive System GENERAL • In your body the food is converted to nutrients. • The body needs nutrients in the form of carbohydrates, proteins, fats, vitamins, minerals, and water for growth, repair of tissues, and energy – to maintain homeostasis • The energy in the food is measured in units called Calories. Depending on your level of physical activity, age, sex, and growth rate you need a certain number of Calories daily to meet the body’s energy needs. • We need to eat more complex carbohydrates (starch) than sugars because complex ones give you more and long-term energy source as well as other nutrients. Fiber is a complex carbohydrate of plant origin that is not broken down in the body but is needed to move the food down the digestive system more efficiently. Eat a variety of vegetables and fruits to get all the essential amino acids, vitamins, and minerals. Limit salt. Limit saturated fats from animal origins since they contain cholesterol and lead to heart disease. • The Food Guide Pyramid was developed by nutritionists to help people eat a healthy diet. It includes 6 food groups (bread, vegetables, fruits, meat, dairy, and the oil/sweet) and indicates the number of servings from each group that should be eaten every day. • Food labels allow you to evaluate a single food as well as compare the nutritional value of two foods. They list the serving size, fat calories, ingredients, and Percent Daily Values (how the nutritional content of one serving fits into the diet of a person who consumes a total of 2,000 Calories/day). THE DIGESTIVE SYSTEM • Functions: - digestion- breaking down of food into molecules the body can use; this is done in two ways, mechanical (physically breaking the food through biting, cutting, chewing) and chemical (breaking down the food by the help of chemicals like enzymes which are proteins that speed up the chemical reaction) - absorption of molecules into the blood - elimination of wastes and undigested material like fiber from the body • Mouth - The teeth (cut, tear), tongue (move the food around and back), and saliva (moisten the food) take part in mechanical digestion. - The enzyme Amylase in saliva chemically breaks down carbohydrates into sugar (a cracker tastes sweet after being in your mouth for few seconds). • Esophagus - A muscular tube connecting your mouth to the stomach - is lined with a slippery thick substance called mucus that helps the food be swallowed easier - moves the food down by peristalsis (involuntary waves of muscle contractions). The epiglottis – flap of tissue which seals off the windpipe to prevent food entering it while swallowing. • Stomach - J-shaped muscular pouch for food storage - Most mechanical digestion happens here by churning motion (squeezing food and mixing with fluids) - Chemical digestion is done by the help of the enzyme Pepsin which breaks down proteins with the help of hydrochloric acid. The acid also kills bacteria in the food. The acid does not burn the lining of the stomach since it also contains mucus and the cells of the lining of the stomach are quickly replaced if damaged. The food now is a thick liquid. • Small Intestine (small in diameter) - Most chemical digestion and absorption happens here with the help of enzymes and secretions of the small intestine, pancreas, and liver (the largest and heaviest organ inside the body that makes bile to break up fats; bile is stored in the gall bladder before it empties into the small intestine) - The inner lining of the small intestine is lined with villi that increase its surface area for easy absorption of nutrients through the blood vessels. • Large Intestine (colon) Has good bacteria (make vitamins) that feed on the material passing through it, namely water that gets absorbed back into the blood and undigested food like fiber that will be compressed into solid in the end part of the large intestine, the rectum and then eliminated through the anus, the end part of the rectum. Chapter 17 – Cardiovascular (Circulatory) System (heart, blood vessels, and blood) • Carries needed substances like oxygen and glucose to cells • Carries wastes like carbon dioxide away from cells • The blood also contains cells to fight disease. HEART • muscular organ containing all types of tissues • pumps blood by pushing it into blood vessels with each beat • size of a fist • 2 upper, receiving chambers – atria/auricles (A) 2 lower, pumping chambers – ventricles (V) In between the atria and ventricles and ventricles and arteries, there are valves which are flaps of tissue to prevent blood from flowing backwards. • the heart works in the following way: - the heart muscle relaxes, atria fill with blood atria contract, blood goes to ventricles through valve ventricles contract, valve between aria and ventricles close, “lub” sound is heard blood goes to blood vessels; valve between ventricles and blood vessels snap shut, “dup” sound is heard this whole process takes less than a second - the blood moves in 2 loops (the heart is made of 2 pumps); in one loop the blood goes from RA to RV to lungs to LA; in the second loop the blood goes from LA to LV to aorta (largest artery) which branches into arteries to take blood to upper body, lower body, and heart itself, and then returns to RA again. The whole process takes less than a minute. • pacemaker – group of cells in RA that receive messages about the body’s oxygen needs and send signals to make the heart muscle contract. This way the heart rate is adjusted. In some people, the pacemaker gets damaged as a result of accident/disease. This causes irregular/slow heartbeat. An artificial battery-operated pacemaker will be inserted in the heart to regulate the beats. BLOOD VESSELS • Arteries: carry blood away from the heart; thicker, strong, flexible • Capillaries: take blood from the arteries and exchange materials between the blood and cells by diffusion; tiniest • Veins: carry blood back to the heart after receiving it from the capillaries Pulse – caused by alternating expansion (as blood moves in) and relaxation of the artery wall. The pulse rate determines how fast your heart is beating. Blood Pressure – force with which ventricles contract; it is lower as blood moves away from the heart; highest in the arteries; measured by sphygmomanometer; normal value for adult is 120/80 (the first number is obtained when the ventricles contract and send blood to the arteries and the second number is obtained when the ventricles relax between heartbeats). BLOOD • Plasma: clear, yellow liquid part of the blood; carries materials like digested food molecules, vitamins & minerals, chemical messengers, and wastes; 90% water • 45% of the blood are the blood cells which are denser and dark red in color - red blood cells are made in the red marrow, are flexible, donutshaped, and thin; its hemoglobin (iron-containing protein) binds with oxygen to make the blood bright red and able to carry oxygen - white blood cells are also made in the red marrow; fight disease; fewer than the red blood cells but bigger; live for months; have nuclei - platelets are cell fragments that help in clotting by releasing chemicals which produce a protein (fibrin) to trap blood cells and form a clot. Dried clot on the skin is called a scab. LYMPHATIC SYSTEM As blood travels in the capillaries, some leak out into the surrounding tissues. It carries materials that the cells in the tissues need. Afterwards, this fluid (now called lymph) moves into the lymphatic system (vein-like vessels that return the fluid into the blood). The lymph moves slowly because the lymphatic system does not have a pump. Lymph nodes – as lymph flows through the lymphatic system, it passes through small knobs of tissue called lymph nodes which filter the lymph trapping bacteria and other germs. That’s why they enlarge. CARDIOVASCULAR HEALTH Cardiovascular disease is the leading cause of death in US: • atherosclerosis – artery wall thickens because of fat build up; blood flow is decreased; leads to heart attack when blood flow to part of the heart muscle is blocked; heart is damaged • hypertension – high blood pressure; heart works harder and blood vessel walls are damaged; “silent killer” because it does not have symptoms usually To keep your cardiovascular system healthy: • exercise regularly • eat a balanced diet low in fat, cholesterol, and salt • avoid smoking