Circulatory and Respiratory Systems
Vocabulary: pacemaker, atherosclerosis, hemoglobin, platelets, alveoli, nicotine, emphysema
The circulatory system consists of the heart, blood, and blood vessels. There are three types of blood vessels: arteries, veins and capillaries.
The heart is an organ made of cardiac muscle and it acts like a pump. The muscles of the heart contract and pump blood away from the heart (through the aorta) and to the tissues of the body. Diffusion occurs at the tissues, allowing for nutrients and oxygen to enter the cells, and for carbon dioxide and other wastes to be removes from the cells.
Your heart beats when the pacemaker (sinoatrial node located in the right atrium) sends an impulse that causes muscle contractions to occur. The heartbeat is partly controlled by neurotransmitters released by the nervous system.
When your heart pumps, it produces a pressure in your arteries called blood pressure. Your body helps regulate your blood pressure by communicating with the brain. The brain releases neurotransmitters that can raise or lower the blood pressure by relaxing or contracting the smooth muscles of the blood vessels. Your kidneys also play a role in regulating blood pressure by removing water from the blood and releasing it as urine.
High blood pressure can lead to many problems. High blood pressure makes the heart work harder. This can lead to damage or weakening of the blood vessels and heart muscle. Also, if you have high blood pressure, you are more susceptible to heart attack, stroke, coronary artery disease, and other circulatory system diseases.
Atherosclerosis occurs when fatty plaque deposits build up on the walls of blood vessels. If this condition occurs in the coronary arteries, it can block the flow of blood that supplies the heart with oxygen and nutrients. The part of the heart that isn't getting the supply of oxygen it needs can start to die, causing a heart attack. If the plaque buildup causes a blood clot and the clot breaks free, it can get stuck in other blood vessels. If that happens in the brain, it can cause a stroke.
Cardiovascular diseases can be prevented through the avoidance of smoking, regular exercise and balanced diets.
Blood is composed of 55% plasma and 45% red blood cells (RBCs), white blood cells (WBCs) and platelets. Plasma is made up primarily of water, but also contains salts, nutrients, hormones, and many other substances.
Red blood cells transport oxygen. Hemoglobin is a protein located on RBCs that binds to oxygen in the lungs and transports it to the tissues where the oxygen gets released.
White blood cells are produced from stem cells in bone marrow. The number of WBCs in the blood is much less than that of RBCs. When you are sick, the number of WBCs int he blood increases to help fight infection. There are many types of WBCs and they each have a different job (ex: engulfing microorganisms that cause disease, releasing chemicals, etc.). Some WBCs make antibodies to help destroy pathogens ("bad guys") that provides you with immunity to several diseases. WBCs leak out of the circulatory system into the lymphatic system where they are able to provide defense within the tissues of the body.
Platelets are fragments of blood cells that aid in clotting the blood. Platelets circulate around the body and become sticky when they come into contact with broken blood vessels. This causes proteins called clotting factors to be released, which can produce microscopic filaments called fibrins. The strands of fibrin act like a net and form a blood clot, which prevents continued loss of blood from the body. Hemophilia is a genetic disorder that causes defected clotting factor proteins, leading to the inability to clot blood.
The circulatory system has a close interrelationship with the respiratory system. The main organ of the respiratory system is the lungs. The diaphragm is a muscle located underneath the heart and lungs that contracts to pull air into the lungs and relaxes to force air out of the lungs. When the air enters the lungs, it travels through the bronchi to tiny air sacs called alveoli. In the alveoli, oxygen diffuses into the blood stream through capillaries that surround each alveoli. The newly oxygen rich blood then travels back towards the heart, where it will then get pumped to the rest of the body.
Breathing is not a completely voluntary action. The nervous system (medulla oblongata) can regulate breathing by monitoring the levels of carbon dioxide in the blood. If the levels get too high, the brain sends impulses to the diaphragm and chest muscles that increase the breathing rate. This rids the body of the excess carbon dioxide while bringing more oxygen to the blood.
Nicotine, carbon monoxide and tar are just three of the substances that makes smoking dangerous to the body. Nicotine is a stimulant drug that causes an increase in blood pressure and heart rate. Cilia that line the respiratory tract become paralyzed, leaving them unable to sweep mucus away from the lungs.
Many respiratory diseases can be caused by smoking. Chronic bronchitis is when the bronchi become swollen and clogged with mucus. Emphysema is when your lungs lose their elasticity, making it extremely difficult to breathe. Smoking can also lead to lung cancer.
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