SPLATS about circulation and blood
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Circulation and blood
Our body is made up of a number of systems which get matter and energy to where it is needed. When these systems do not work properly, we become ill.
Blood is the main circulatory fluid in large animals, and is essential for their survival, as diffusion only works over small distances in animal tissue.
Blood is pumped around our bodies by the heart. It is pumped to the lungs to get oxygen and lose carbon dioxide, and to the rest of the body to exchange gases.
The heart operates as a two-stage pump, with a thinner-walled atrium filling a muscular ventricle which then forces the blood around the body.
Oxygen and carbon dioxide are carried around in the blood by haemoglobin, a complex chemical to which the oxygen and carbon dioxide molecules can attach.
Blood carries food molecules to where they are needed. It also carries waste material away from the cells of our body, to where they can be disposed of.
The blood circulation carries oxygen around the body from the lungs, carries carbon dioxide away from cells back to the lungs, and food to cells.
Around 170, Galen speculated that blood might get from one side of the heart to the other through very fine pores, too small to be seen with the naked eye.
By 1574, the anatomist Fabricius had observed and described the valves that may be found in veins, and saw that they would stop blood from pooling in the feet.
In 1628, William Harvey published his detailed description of the circulation of the blood around the body, but he could only infer that capillaries exist.
In 1666 Richard Lower demonstrated the transfusion of blood between two dogs, and the experiment appeared to be successful, given that the dogs did not die.
In 1667 Jean-Baptiste Denys transfused lamb's blood into a 15-year-old boy who was apparently unharmed, or at the worst, did not die as a result of the transfusion.
Around 1680, Marcello Malpighi saw capillary blood vessels for the first time, establishing the missing link in our picture of the body's blood circulation.
In 1689, Anton van Leeuwenhoek began his studies of capillary vessels in frogs' feet, bats' wings, rabbits' ears, and eels' tails, all under the microscope.
Human blood contains a variety of distinctive proteins that 'type' it. Each human belongs to a specific blood group, based on those proteins in the blood.
In 1910, Epstein and Ottenberg discovered that human blood groups (A, B, O) were inherited on Mendelian principles, leading to later paternity testing.
In 1927, Karl Landsteiner discovered the M and N blood groups. In 1940, Landsteiner and Alexander Wiener both discovered the Rh blood factor.
The heart and the veins have valves to force blood to flow in one direction only: out along the arteries under pressure, back through the veins.
Arteries lead to arterioles and then to capillaries which trickle blood into venules which feed into veins, which carry the blood passively back to the heart.
The arteries are elastic, which means they are able to absorb the shock of the pressure wave as blood is pumped from the heart with great force.
The pulmonary system carries blood to the lungs where concentration differences mean the haemoglobin loses carbon dioxide and picks up oxygen.
Hardening of the arteries means that rather than being absorbed by the arteries, pressure surges are carried on to finer blood vessels and damage them.
An artery usually carries oxygenated blood, unless it is the artery that carries blood to the lungs. The pulmonary vein carries oxygenated blood.
Arterial blockages may be cleared by angioplasty, a procedure similar to blowing up a small balloon inside the artery, which clears the blockage.
Normal body movements compress veins, especially in the legs, and each compression pushes blood along, with the valves directing the flow one way.
Very small animals like flatworms do not need a circulatory system: simple diffusion from the nearest surface is enough to provide oxygen to all their tissues.
Large plants need water transport systems to move sugars, minerals and water from the leaves and roots to other parts of the organism where they are needed.
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