B4 Organising animals and plants

• fish have a single circulatory system. blood is pumped from the heart, to the gills (where oxygen is collected) and it becomes oxygenated blood. the oxygenated passes from gills to the organs where the oxygen diffuses out of the blood, into the body cells. the blood then goes back to the heart
• a problem with a single circulatory system is that the blood loses a lot of pressure as it passes through the gills before reaching the organs. this means that the blood travels slowly and cannot deliver a large amount of oxygen
• humans have a double circulatory system. de-oxygenated blood goes from the heart to the lungs where it collects oxygen, it the returns to the heart. the heart now pumps the oxygenated blood to the organs where the blood transfers its oxygen to the body cells. the blood then returns to the heart
• the benefit of a double circulatory system is that because the blood travels through the heart twice, it can travel rapidly through the body cells, delivering the oxygen that the body cells need
• the human heart is an organ made mainly of muscle tissue. at the top we have the atria and at the bottom of the heart we have the ventricles. the atria and the ventricles are separated by valves.
• the vena cava brings in deoxygenated blood from the body.
• the blood passes from the heart to the lungs in the pulmonary artery.
• oxygenated blood passes from the lungs to the heart in the pulmonary vein.
• oxygenated blood is pumped from the heart to the body through the aorta
• when blood enters the atria, they contract so blood is then forced into the ventricles. the ventricles now contract and force blood out of the heart. the valves stop the blood from flowing backwards into the atria when the ventricles contract
• the left side of the heart has a thicker muscular wall than the right side. this is because the left ventricle pumps blood around the entire body, so needs to provide a greater force.
• the right ventricle only pumps blood to the lungs so has a thinner muscular wall
• the coronary arteries branch out of the aorta and spread out into the heart muscle. the purpose of these is to provide oxygen to the muscle cells of the heart. the oxygen is used in respiration to provide enough energy for contraction
• the natural resting heart rate is controlled by a group of cells found in the right atrium, called the pacemaker. sometimes the pacemaker can stop working correctly. in this case, doctors can implant an artificial pacemaker.
• an artificial pacemaker is a small electrical device and it corrects irregularities in the heart rate.
• arteries carry very high pressure blood from the heart to the organs in the body. they have a very thick muscular wall, allowing them to withstand the very high pressure of the blood.
• blood travels in surges every time the heart beats, the surge can be felt in your wrist as the pulse. to cope with this, arteries contain elastic fibres that stretch when blood passes through, then they recoil in between the surges which keeps the blood moving
• when blood is in the organs it flows through capillaries. when the blood passes through capillaries, substances like glucose and oxygen diffuse from the blood to the cells. carbon dioxide diffuses out the cells, back into the blood.
• capillaries have very thin walls, so the diffusion pathway is very short. substances can diffuse rapidly.
• blood in the veins travels slowly and at low pressure, meaning that the blood is likely to stop or go backwards.
• veins have a thin walls, because the blood pressure is low, so the wall doesn't need to be thick. veins also contain valves to stop backflow. valves open when travelling in the correct direction, however when the blood starts the flow backwards, they shut
• there are 4 main components of the blood; blood plasma, platelets, red blood cells and white blood cells
• red blood cells and white blood cells are found in the plasma. the plasma is the liquid part of the blood
• blood plasma is the liquid parts of the blood. its job is to transport dissolved substances around the body. plasma transports soluble digestion products e.g. glucose from the small intestine to the other organs. it transports carbon dioxide from the body cells to the lungs to be breathed out. it also transports waste products urea from the liver to the kidneys to be excreted in the urine.
• red blood cells transport oxygen from the lungs to the body cells. they contain haemoglobin, which is an oxygen carrying molecule. it combines with haemoglobin in the lungs, forming the molecule oxyhaemoglobin. in the organs, the oxyhaemoglobin releases the oxygen
• red blood cells have no nucleus, meaning they have more room for haemoglobin. they also have dimples in the centre of the cell, this shape is called a biconcave disc. this shape gives the red blood cells a greater surface area so oxygen diffuses in and out rapidly
• white blood cells form part of the immune system e.g. making antibodies. they contain a nucleus which contains DNA which encodes the instructions that the white blood cells need to do their job.
• platelets are tiny fragments of cells and their job is to help the blood to clot. e.g. when we get a cut, the blood clotting will form a scab.
• donated blood has many uses in medicine: to replace lost blood during injury, some people are given platelets extracted from blood to help in clotting and proteins extracted from the blood can also be useful e.g. antibodies
• in a blood transfusion, we have to make sure the donated blood is the same blood type as the patients otherwise the body's immune system could reject the blood and the patient could die.
• with blood transfusions, there is also a risk of infection. lots of different diseases can be transmitted via blood, however in the UK, blood is now screened for blood so the risk of this is relatively low.
• cardiovascular diseases are diseases of the heart and blood vessels. they are non-communicable so cannot be passed from person to person. e.g. coronary heart disease.
• coronary arteries branch out of the aorta and spread out over the heart muscle. in coronary heart disease, layers of fatty material build up inside the coronary arteries. this causes the coronary arteries to narrow. this then reduces the flow of blood through the coronary arteries, resulting in a lack of oxygen for the heart muscle so it can't contract efficiently. in extreme cases, this can cause a heart attack
• to treat coronary heart disease, we usually use statins or stents.
• statins are drugs that reduce the levels of cholesterol in the blood, slowing down the rate of fatty material build up in arteries. they have been proven to reduce the risk of coronary heart disease so are effective. however they can cause liver problems.
• in some people, coronary arteries can cause an almost total blockage of the artery. these people can be treated using stents.
• a stent is a tube which is inserted into the coronary artery to keep it open. using these, the blood can flow normally through the artery however the stent will not prevent other regions from narrowing and doesn't treat the underlying causes of the disease
• sometimes valves don't fully open so the heart has to pump extra hard to get the blood through, this can cause the heart to enlarge
• valves that are leaky can cause the patient to be fatigued and tired
• when heart valves are faulty, we can replace them either with the mechanical valves made from metal or a biological valve from an animal e.g. a pig.