Human body systems, Year 10: the heart, blood vessels and blood

right ventricle

提示It is one of the two lower chambers, on the side that receives blood back from the body.

为什么The heart is two pumps side by side. The right side sends blood on the short loop to the lungs to collect oxygen. The left side sends it on the long loop round the rest of the body. Ventricles pump blood out; atria receive it.

aorta

提示It is the largest artery in the body, and its name begins with the first letter of the alphabet.

为什么The left ventricle pumps oxygenated blood into the aorta, which branches to supply every organ except the lungs. The first branches are the coronary arteries, which supply the heart muscle itself.

vena cava; vein

提示One has a two-word Latin name; the other is the general word for a vessel that carries blood towards the heart.

为什么Both of these vessels bring blood back to the heart. The vena cava carries deoxygenated blood into the right atrium. The pulmonary vein carries oxygenated blood from the lungs into the left atrium, which makes it unusual among veins.

atrium

提示It is one of the two upper chambers, which receive blood coming back to the heart.

为什么This small group of cells sends out regular electrical signals that make the heart muscle contract. It sets the natural resting heart rate. The heart keeps beating without being told to by the brain, although the rate can be adjusted.

To correct an irregular heart rate

提示It does the job that a small group of cells in the right atrium normally does.

为什么An artificial pacemaker is a small electrical device placed under the skin with a wire to the heart. It sends electrical signals to keep the heartbeat regular when the natural pacemaker does not.

To withstand the high pressure of the blood pumped out by the heart

提示Think how forcefully the ventricles squeeze with each beat.

为什么Arteries carry blood away from the heart, so the blood in them is under the highest pressure. The thick wall is strong, and its elastic fibres stretch with each surge and spring back, which helps to keep the blood moving.

valves

提示Similar flaps are found between the chambers of the heart.

为什么Blood in veins is at low pressure, and in the legs it has to travel upwards. These flaps let blood pass one way only, towards the heart. Veins also have thinner walls and a wider channel than arteries.

Substances can diffuse quickly between the blood and the body's cells

提示Think about the distance that oxygen has to cross.

为什么Capillaries are where exchange happens: oxygen and glucose pass out to the cells, and carbon dioxide and other wastes pass in. A very thin wall gives a short diffusion path, so exchange is fast.

300

提示A rate is an amount shared out over the time taken.

为什么Rate of blood flow = volume of blood ÷ time = 600 ÷ 2. The unit is a volume per unit of time, here millilitres per minute.

Capillaries

提示They link the smallest arteries to the smallest veins.

为什么Arteries divide into smaller and smaller vessels until they form networks of capillaries inside every tissue. No cell is far from one. The capillaries then join up again to form veins.

plasma

提示It is straw-coloured and is mostly water.

为什么Blood counts as a tissue because it is a group of cells working together. The liquid part carries the cells and also transports dissolved substances such as glucose, carbon dioxide and urea.

Platelets

提示The name sounds like "little plates".

为什么When a blood vessel is cut, platelets gather at the damage and start the clotting process. The clot dries to a scab, which stops bleeding and keeps pathogens out.

To defend the body against pathogens

提示They are part of the immune system.

为什么White blood cells are far fewer than red cells, and unlike red cells they have a nucleus. Some surround and digest microorganisms; others make antibodies or antitoxins. The details belong to the topic on the body's defences.

It gives a large surface area for taking in oxygen

提示Compare the outside of a flattened ball with that of a round one holding the same amount.

为什么The biconcave shape gives more surface for the cell's volume, and no part of the inside is far from the surface, so oxygen diffuses in and out quickly. The cell is also flexible enough to squeeze through capillaries.

haemoglobin

提示Its name starts with the Greek for "blood", as in "haemorrhage".

为什么Haemoglobin picks up oxygen in the lungs and releases it in the tissues. A red blood cell has no nucleus, which leaves more room for it. It contains iron, which is why too little iron in the diet can cause tiredness.