The blood
Blood consists of two main parts:
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Plasma (55%)
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Blood cells (45%)
Blood cells mainly consists of red blood cells (99%) containing the matter haemoglobin that ties up oxygen within the blood.
Blood is an exciting universe of various tiny living organisms, each carrying out their own individual role. Some are cleaners, others are waste collectors and others are killers. Whilst you are reading this text, billions and billions of blood cells and blood platelets are floating around in your blood, making sure that everything is all right.
An average adult contains 4-5 litres of blood. Your blood makes up the base that ensures that all the billions of cells contained in your body are able to function. Blood is filled with specialised cells, each carrying out their own individual function. Your blood consists of around 25,000 billion red blood cells, 1,500 billion blood platelets, 35 billion white blood cells and around 2.5 litres of plasma. The blood carries out a variety of functions, including oxygen and nutrient transportation, immune system, fluid balance, temperature regulation, repairs and information transfer.
Plasma
Plasma is a yellow-ish fluid consisting of 95% water and featuring a concentration of salt similar to that of sea water. It also contains a variety of proteins (albumin), fats, sugars, hormones, vitamins and waste products that are transported within the blood.
Red blood cells
Each cubic millimetre (micro litre) of blood contains around 5 million red blood cells. They maintain oxygen transport from the lungs to the tissues where the oxygen is deposited. Once the oxygen has been deposited, the blood cells absorb carbon dioxide, which is then taken back to the lungs to be exhaled. A red blood cell usually survives around 120 days within the bloodstream. Normally, around 1% of the red blood cells is exchanged each day, i.e. each second, around two million die and another two million are created.
White blood cells
The white blood cells defend our body against infections stemming from viruses, bacteria, parasites and fungi as part of inflammatory reactions. White blood cells are larger in size but fewer than red ones.
The white blood cells mainly operate outside the bloodstream. They settle in connective tissues, skin and organs, fighting various attacks on body tissues.
White blood cells are divided into lymphocytes, granulocytes and monocytes.
Lymphocytes are divided into two subcategories:
- B-lymphocytes are white blood cells, which – amongst other things – create antibodies against bacteria and viruses. Some of them are memory cells that are able to remember previous infections, making the immune system react faster once a similar infection occurs again.
- T-lymphocytes are white blood cells that keep the immune system in constant stand-by. It identifies cells that have been invaded by a bacteria or virus.
B- and T-lymphocytes constantly circulate between blood and lymph tissues (lymph glands, spleen and mesentery). In addition, special T-lymphocytes known very dramatically as “killer cells” assist in destroying infected cells.
Granulocytes are divided into three subcategories:
- Neutrofil granulocytes are white blood cells that defend our body against attacks from various micro organisms. Once tissue has been damaged, the neutrofil granulocytes arrive, swallowing up the rest of the damaged cells and bacteria. Dead neutrofil cells make up the majority of the yellow fluid (pus) that pours out of inflamed tissue.
- Basofil granulocytes are the rarest white blood cells. They have an important role to play in terms of allergic reactions (hypersensitivity) by releasing those matters that influence the size of the blood vessels.
- Eosinofil are white blood cells that make up a part of the immune system. They are produced in larger numbers when dealing with allergic illnesses or in case of infection by certain parasites (worms).
Monocytes are white blood cells that function as body ”waste collectors”. They are active within the blood as well as in other tissues, absorbing and destroying micro organisms and overworn cells.
Blood platelets
The smallest cells within the plasma are the blood platelets. They do not take up much space because their diameter only measures 0.003 millimetres . On the other hand, we do contain a lot of them – around 300,000 per cubic meter of blood. They are created within the bone marrow and survive for about nine days. Normally, the blood platelets just float around in your blood; however, if a blood vessel is damaged, the blood platelets come to the rescue to repair it.
