Science en anglais : le coeur humain

The Heart The blood Blood carries oxygen for various tissues to use, nutrients to provide energy, removes waste products and even helps you warm up or cool down. Blood Vessels Arteries and veins form the plumbing system of the human body, carrying blood through a complex system of different sized and shaped pipes, from the large elastic aorta down to tiny, one cell thick capillaries. Blood is carried in vessels, of which there are two main different types : arteries and veins. Arteries carry blood away from the heart and deal with high pressures. In these vessels, blood is what the body use for energy, blood oxygen rich. Veins carry blood back towards the heart and deal with lower pressures, so have thinner walls. After it has been used, this oxygen depleted blood is returned for recycling and is dark red. Also, tiny capillaries connect arteries and veins together. Components of blood Blood is a mix of solids and liquids, a blend of highly specialized cells and particles suspended in a protein rich fluid, called plasma. Plasma : Plasma is a straw coloured watery fluid that carries all of the cells and proteins in blood, including the vital clotting factors. Plasma is composed of 92% of water. Platelets : are tiny fragments of blood that are crucial in stopping bleeding, along with clotting factors, by forming a platelet plug. Red Blood Cells : are the most abundant cells in blood and give it red colour. They carry oxygen from the lungs around the body, bound to a protein called haemoglobin. White Blood Cells : are your infection-fighting cells, they circulate in the blood so they can quickly multiply and be transported to an area where there's an infection flaring. These cells are the immune system's best weapon, searching out and destroying bacteria, producing antibodies against viruses. They are five different type of white blood cells, all with distinct functions. There is monocyte (the largest type), granulocyte, lymphocytes ... Red blood cells dominate the mix : to give an approximate idea, for every 600 red blood cells, there is a single white blood cells. It means that the blood is composed of 54% of plasma, 1% of white blood cells and 45% of red blood cells. Roughly 2 million red blood cells are born every second. Blood types and transfusion The ABO blood grouping system. In this blood group system, each individual has inherited alleles, receiving one allele from each parents during the conception. There are three different blood types, alleles A, B, and O, therefore possible genotypes AA, AO, AB, BB, BO, OO. AA and AO are expressed as a phenotype A, BB and Bo, as B, and OO is expressed as O. An individual will generally have the same blood group for life. Blood type is classified by the presence or absence of antigens on the surface of red blood cells. O group is universally accepted by other blood types. Blood transfusion A blood transfusion takes place when a patient is given components of blood from a donor when their own blood levels are too low. Having enough blood is essential because it carries oxygen around the body and returns carbon dioxide to the lungs to be exhaled as a waste product. In blood transfusion, doctors have to be careful with the ABO grouping system : blood can't be mix ! During the transfusion, the patient is attached to a drip and the donor blood is transfused through this. Typically, an arm vein is normally used. Dessiner au tableau le système des deux boucles (Coeur/poumons ; Coeur/autres organes)