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Respiratory System As you learned, the circulatory system was responsible for the transport of materials throughout the body, the most important being oxygen. In order for your body to get the oxygen needed for cellular respiration, you need to breathe. Breathing exchanges the gases needed for respiration. You inhale the O2 you need and exhale the CO2 you don’t need. The O2 is then used to obtain energy from chemical respiration. Without oxygen, your body is not able to make ATP. Breathing is not respiration. Breathing just gives you the gases needed for respiration. Air enters the respiratory system when you inhale through your nose or mouth. Inhalation occurs when the diaphragm underneath and other muscles around the chest area contract and expand the rib cage. Inhaled air passes through a series of tubes to reach the lungs. Within each lung, the tubes carry the air into smaller and smaller tubes called bronchioles (see diagram). The smallest bronchioles end in groups of tiny air sacs called alveoli, which are surrounded by blood vessels. The exchange of gases takes place across thin moist membranes of the alveoli. O2 leaves the alveoli and enters the blood; CO2 leaves the blood and enters the alveoli. Excretory System The human body uses the process of excretion to remove liquid and gaseous wastes that are produced by its chemical reactions. By removing wastes and toxic chemicals, excretion enables the body to maintain homeostasis. When you sweat, your skin excretes excess water, salts, and some nitrogen wastes. CO2 and water are excreted as you exhale. The liver is responsible for filtering toxins and dead red blood cells from the blood. The blood also carries other cellular wastes to the kidneys, the primary organs of excretion. Your kidneys are responsible for filtering your blood and reabsorbing nutrients. They are able to complete this through a series of structures called nephrons (see diagram). After the blood is filtered by the nephrons in the kidneys, the resulting solution is called urine. It is made up of urea – a nitrogen containing waste product released into the blood by the liver. Urine also includes excess water, salts, amino acids, and glucose. The urine produced by the kidneys flows through a tube called the ureter, which leads to the urinary bladder. This is a muscular organ responsible for storing urine until it exits the body from the urethra (see diagram). Copy and complete the following in your notebook: 1. Explain the importance of the respiratory system. 2. Explain the importance of the excretory system.