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AS Biology Circulatory System Overview SPRING BREAK HW Name: __________________________________________________________ Class: _______________ Directions: 1) Read over the following article, annotating it for important information. 2) Create a “One-Pager” summary sheet of the information. FOLLOW THESE 5 STEPS 1. Select 2 quotes from the text that stood out to you in the reading. 2. Illustrate your interpretation. (Literally draw, use clip art, cut our magazines, etc.…) This can be a small scale or a big scale image. 3. Write at least four single words or thoughts that express the function/purpose of the human circulatory system 4. Make a 5-sentence summary of the reading. 5. Ask/Write 2 questions you have after reading the text. The goal is to complete all 5 steps into ONE PAGE, hence a One Pager. Have fun! **This will be 10 points in your quarter 4, standards-based grade. Circulatory systems and the cardiac cycle Article Sources: www.bbc.co.uk/schools/gcsebitesize/science/triple_ocr_21c/further_biology/circulation/revision/1/ and http://www.bbc.co.uk/schools/gcsebitesize/science/triple_ocr_gateway/the_living_body/circulatory_systems_cardia c/revision/6/ Summary: Circulatory systems can be open (as in insects) or closed (as in fish and mammals). Closed circulatory systems may be single circulatory systems with a two-chambered heart, or double circulatory systems with a four-chambered heart. The contractions of the heart muscles are controlled by groups of cells called pacemakers. The circulatory system in mammals transports essential chemical substances to and from all of the cells in our bodies. The heart pumps blood along a network of blood vessels to reach our cells, while the lungs replace the oxygen used during respiration. Open and closed circulatory systems Living cells need to absorb nutrients and oxygen, and to release waste products, such as carbon dioxide. Some animals – such as the single-celled amoeba - are small enough to do this by diffusion from their surface, and do not require a circulatory system. But larger, multicellular animals need a circulatory system to transport substances to and from their cells. A. Open circulatory systems Some animals, such as insects, have an open circulatory system. Their blood flows freely through their body cavity, carrying nutrients to their cells. Oxygen is delivered directly to the insect’s tissues through tiny tubes that open to the outside. B. Closed circulatory systems Vertebrates have closed circulatory systems. Their blood flows through blood vessels (arteries, veins and capillaries) and they have a heart to push the blood around their body. The human circulatory system is a closed system. Single and double circulatory systems Fish have a single circulatory system, but mammals have a double circulatory system. A. Single circulatory system In the circulatory system of a fish, the blood travels from the heart to the gills, where it absorbs oxygen and releases carbon dioxide. It then flows from the gills to the organs and tissues in the rest of the body, and back to the heart. There is just one circuit from the heart. B. Double circulatory system In the circulatory system of a mammal, there are two circuits from the heart: 1. Blood passes from the heart to the lungs - where it absorbs oxygen and releases carbon dioxide then back to the heart 2. Blood passes from the heart to the organs and tissues in the body, and back to the heart Blood pumps through the heart twice during a complete journey around the body. Some blood is sent to the lungs and some blood is sent to the rest of the body each time the heart beats. The blood in each circuit is kept separate. This is called double circulation and is a more efficient way of delivering oxygen to the tissues than single circulation. Compared to a single circulatory system, blood in a double circulatory system is under higher pressure - which allows materials to be transported more quickly around the body. Figure 1: The double circulation of mammals The double circulatory system in humans Arteries, veins and capillaries Arteries are blood vessels that carry blood away from the heart. (It’s easy to remember this – ‘arteries away’.) Because arteries have to withstand the high pressure of the blood during each heart beat, they have thick, elastic walls which substances cannot pass through Veins carry blood towards the heart. Veins have thinner walls that are less elastic, because the blood they transport is under lower pressure. They still do not allow substances to pass through their walls. Veins contain one-way valves that prevent blood flowing backwards. Capillaries are very thin blood vessels that have walls that are only one cell thick. This means that substances such as glucose, oxygen, water and carbon dioxide can diffuse through between the blood and the tissues. How does the circulatory system work? 1. The left side of the heart pumps oxygenated blood from the lungs, through the aorta to the body tissues 2 (excluding the lungs). 2. Deoxygenated blood returns from the body tissues to the right side of the heart, via the vena cava. 3. It is then pumped to the lungs, via the pulmonary artery where it is oxygenated. 4. Blood returns to the left side of the heart, via the pulmonary vein and is pumped to the body tissues again. The heart The heart is mainly made from muscle. The left ventricle of the heart has a thicker muscle wall because it needs to pump blood further, and at a higher pressure, around the body. The right ventricle is under less pressure, as it only needs to pump blood to the lungs. The cardiac cycle The atria are the top chambers of the heart. They collect blood as it flows back to the heart through the veins. The blood is then pumped into the lower chambers called the ventricles -, which are more muscular. When the ventricles contract, blood is forced out of the heart through the arteries. Sets of valves exist between each atrium and ventricle, preventing blood from flowing backwards into the atria. Another set of valves exists between the ventricle and arteries, preventing blood flow back into the ventricles. Veins also have one-way valves stopping blood flowing backwards between each heartbeat. Deoxygenated blood Deoxygenated blood passes through these blood vessels, valves and parts of the heart: 1. Vena cava 2. Right atrium 3. Tricuspid valve 4. Right ventricle 5. Semilunar valve 6. Pulmonary artery It then moves on to the lungs. 3 Oxygenated blood Oxygenated blood passes through these blood vessels, valves and parts of the heart: 1. Pulmonary vein 5. Semilunar valve 2. Left atrium 6. Aorta 3. Bicuspid valve It then moves on to the rest of the body. 4. Left ventricle The coronary artery The heart needs a continuous supply of oxygen and glucose for respiration. The coronary artery is a branch of the aorta that transports blood to the heart muscle itself. A blockage in one of the branches of the coronary artery can severely interrupt blood flow and is called a heart attack. Blood pressure You should be able to interpret pressure changes in arteries, capillaries and veins. The chart shows how the pressure changes in the circulatory system - starting at the aorta leading from the left ventricle to the rest of the body, and back to the vena cava leading to the right atrium. Figure 2: Pressure changes in the circulatory system Note - the pressure is greatest in the arteries. The regular rise and fall in arterial pressure is due to the action of the heart. The systolic pressure is the pressure in the arteries when the heart is contracting, and the diastolic pressure is when the heart’s chambers are refilling with blood. 4 Controlling heart beat The heart is made of powerful muscles. The coronary artery supplies these muscles with oxygen and food substances such as glucose. The heart needs a constant supply of glucose and oxygen so that its muscle cells can respire and continue to contract. The pulse The pulse is a measure of the heartbeat – the muscle contractions that put the blood under pressure. The pulse can be felt at various places on the body, including the ear, wrist and temple. Controlling heart rate Heart rate is linked to activity. The body’s cells need more glucose and oxygen during exercise, and the blood supplies this. The heart rate increases as activity increases, and this is detected as a faster pulse rate. The hormone adrenaline increases heart rate. The action of the heart can be investigated using: Electrocardiograms (ECGs) - which measure the heart’s electrical activity Echocardiograms - which use ultrasound to show possible heart defects Figure 3: An ECG of a normal heart Pacemakers The muscles in the heart are stimulated to contract by small electric currents. These are produced by groups of cells called pacemakers, which naturally control the heartbeat. Some people have a heart rate that is too fast, too slow, or irregular. They may have an artificial pacemaker fitted to control their heartbeat. Pacemaker cells Two groups of pacemaker cells coordinate the contractions of the heart muscles: Impulses from the SAN (sinoatrial node) cause the atria to contract, and stimulate the AVN Impulses from the AVN (atrioventricular node) cause the ventricles to contract ECG (electrocardiograms) traces show these impulses. 5 Blood and blood cells The blood transports many useful chemicals around the body. For example, all cells for aerobic respiration need glucose and oxygen. Carbon dioxide and water are the waste products of respiration and need to be transported to the lungs so that they can be excreted. Blood is made from four components: Plasma - the liquid part of blood. It transports nutrients (e.g. glucose), amino acids, antibodies and hormones to tissues that need them. It also transports waste substances: carbon dioxide and water to the lungs, and water and urea to the kidneys. Red blood cells - they transport oxygen, which is bound to hemoglobin. White blood cells - they are part of the body’s immune system and fight infection. Platelets - they stick together when a blood vessel is damaged in order to help form a clot. Red blood cells Red blood cells are highly specialized. They are the only cells in the body that do not have a nucleus. This gives them more room inside to carry hemoglobin that is the red pigment that binds oxygen (to form oxyhemoglobin). Red blood cells are a biconcave shape. This kind of shape (which is disc like) gives them an increased surface area for oxygen exchange. Tissue fluid By the time blood reaches the capillary beds from an artery, it is at high pressure and this forces blood plasma out. The plasma leaves the capillary and becomes tissue fluid. As the blood plasma moves through the capillary bed towards the vein, pressure drops and stops plasma being squeezed out. Figure 4: Tissue fluid, blood, and lymph Tissue fluid acts as a bridge in the diffusion of chemicals between the capillaries and the cells of the tissue. Oxygen and glucose diffuse from the blood into the tissue fluid and then into the cells. Carbon dioxide and urea diffuse from the cells into the tissue fluid and then into the blood. 6