Blood is a fluid tissue which provides a link between all the other tissues and organs of the body.
It has the capacity to carry essential items around the body.
- Oxygen from lungs to body cells
- Carbon dioxide from body to lungs
- Waste products and water from cells to kidneys
- White blood cells to sites of infection
- Platelets to damaged capillary areas
- Glucose and nutrients from digestive system to cells
- Hormones from glands to where they are needed
- Heat from warmer to cooler parts of the body
Blood is pumped out of the heart under pressure.
Pressure is calculated by measuring the pressure needed to stop the flow of blood through an artery.
Two readings are taken, the systolic pressure when the heart contracts and the diastolic pressure when the heart relaxes.
This is given as a number.
120/80 is the average reading for a young adult.
Blood pressure can be used as an indicator of general health.
Constant high blood pressure is known as hypertension and has become associated with a number of cardiovascular diseases.
This is usually caused by a restriction of blood through the arteries making the heart work harder to move blood around the body.
Red blood cells
Red blood cells contain haemoglobin that is a compound of protein and iron.
Haemoglobin combines readily with oxygen to form a compound called oxyhaemoglobin.
It will combine with oxygen where oxygen is plentiful and yet readily lose it where oxygen is scarce, as in the body tissue.
Red blood cells are produced in the red marrow of bones such as the sternum, ribs and vertebrae.
They have no nuclei and wear out in 3 - 4 months.
White blood cells
White blood cells form a mobile guard and repair system to keep disease from the body.
They are made in the bone marrow, the lymph nodes and the spleen.
They are 3 - 4 times the size of red cells. They can change shape, move against the blood flow and squeeze through the walls of blood vessels into the surrounding tissue.
There are several kinds of white blood cells; some fight and destroy bacteria, some are involved in tissue repair, while some actually produce chemicals to protect against infection.
Platelets are tiny structures that do not have nuclei.
They are formed from detached lining cells if blood vessels and help to produce clotting when a blood vessel is damaged.
There is also a substance called fibrinogen in the blood. When bleeding occurs a chemical reaction changes fibrinogen into fibrin - thread like strands that help to form a clot.
Plasma is a pale, straw coloured, liquid.
It is 92% water.
The remaining 8% consists of food substances.
It also maintains the correct balance of chemicals, water content and temperature levels within the body.