Biology b7

Parts of blood

The functions of the four components of blood are as follows

Red blood cells – these cell carry oxygen. They are packed with the red pigment, haemoglobin, which binds with oxygen. To Make more room for the haemoglobin, red blood cells have no nucleus.

Red blood cells have a biconcave shape which increases the surface area for more efficient uptake of oxygen.

White blood cells – these cells fight infections and protect the body from microorganisms

Platelets – they clot together at injury sites to prevent blood loss

Plasma – a liquid that transports nutrients (eg glucose, mineral salts and amino acids) hormones, antibodies and waste (eg carbon dioxide and urea) around the body.

The heart

Most of the heart wall is made of muscle. The left side is more muscular then the right because it pumps blood around the whole body whereas the right side only pumps blood to the lungs.

The heart has 4 chambers

Two atria – the smaller, less muscular upper chambers that receive blood coming back to the heart from the veins.

Two ventricles – the larger more muscular lower chambers that pump blood out of the heart

The heart muscle needs a good blood supply of oxygen and glucose for respiration. This is supplied by the coronary artery, which is a branch from the aorta to the heart muscle.

The double circulatory system

This is the cardiac cycle;

The heart muscles relax and blood flows into the atria through the veins from the lungs and the rest of the body.

The atria contract, squeezing blood into the ventricles

The ventricles contract and blood is forced out of the lower chambers, which carry the blood to the body and lungs

The heart muscles relax and the process starts again.

Valves in the heart and veins ensure that the blood flows in the right direction (i.e. not backwards.)

Humans have a double circulation system, which means that the blood returns to the heart twice on every circuit of the body.

Deoxygenated blood that has travelled around the body enters the heart via the right atrium.

It’s pumped from the heart into the lungs, where haemoglobin binds to the oxygen becoming oxyhaemoglobin.

The oxygenated blood returns to the heart via the left atrium and is then pumped to the rest of the body.

Blood vessles

There are 3 types of blood vessel:

Arteries carry blood away from the heart towards the organs. They have thick, elastic walls to cope with the high pressure of blood coming from the heart. Substances cant pass through the artery walls.

Veins carry blood from the organs back to the heart. They have thinner, less elastic walls and contain valves to prevent the blood flowing backwards. Substances cant pass through the vein walls.

Capillaries connect arteries to veins. They have a narrow, thin wall that is only one cell thick. The exchange of substances between cells and the blood takes place here.

Tissue fluid

The plasma of…