Functions of blood
Transport of oxygen and carbon dioxide: Red blood cells can bind oxygen and carbon dioxide to themselves (with haemoglobin). Oxygen is transported by the blood to the tissues in the body, whereas carbon dioxide is taken away from the tissue and is transported to the lungs, where carbon dioxide will be turned into oxygen again.
Defence against infections caused by viruses, bacteria or parasites: White blood cells protect the body from infections. There are several types of white blood cells that fight intruders. Transport of nutrients, minerals and vitamins: These molecules are transported in the blood plasma, where needed.
Prevention of blood loss after cut: The process is called haemostasis, where platelets or thrombocytes in other words, and other clotting factors prevent an open wound from losing blood as fast as possible.
Regulation of temperature: The ability of animals and humans to regulate their own body temperature is called thermoregulation.
If a human is exercising, he will be making a lot of ATP in order to support his muscles with energy. Thus increases the body temperature and blood is pumped faster during exercise. Blood vessels widen, in order to be closer to the skin and enable the blood to release some heat (this produces sweat to cool down the body).
If the environment is colder than the body temperature, blood vessels narrow. Consequently, the blood loses less heat outwards.
How much blood has a human?
An average human has about 5-6 litres blood (70-80ml per kg bodyweight).
Components of blood (how many there are, shape, function, speciality, place of creation, life expectancy)
The blood is composed out of 4 main components, namely: Plasma, red blood cells (erythrocytes), white blood cells (leukocytes), which have subtypes of white blood cells and platelets.
Function of Blood Plasma
Plasma: The function of the plasma is to create a current so the red blood cells, white blood cells and platelets can actually move through the body. It consists of about 93% of water and 7% of various minerals like Natrium (Na), Potassium (K), Chlorine (Cl) and Calcium (Ca). It makes up 55% of the blood
Functions of Red Blood Cells (RBC)
Red blood cells (erythrocytes): Red blood cells compose 45% of the blood. Their main function it so transport oxygen from the heart / lungs to the rest of the body tissue, where it is needed. Simultaneously, red blood cells take away carbon dioxide from the body tissue and transport it to the lungs, where it will be oxygenated. Their special feature, which enables red blood cells (erythrocytes) to bind oxygen and carbon dioxide, is called haemoglobin. In a cubic millimetre there are 4-5 million red blood cells in women and 5-6 million in men. So, the total amount of red blood cells is about 2-3 trillion (1013). They are produced in the bone marrow and one single circulation through the whole body takes them about 20 seconds. Furthermore, their life expectancy varies from 100 to 120 days.
Functions of White blood cells (leukocytes), T memory cells, natural T killer cells, natural killer cells
White blood cells (leukocytes): White blood cells are the defenders of our body. Their occurrence in an average human body is about 1% and there are about 4’000 to 11’000 white blood cells (leukocytes) per cubic millimetre (mm3). Their diameter is about 7-21 µm and their life expectancy is only 3-4 days. There are different types of white blood cells, which protect our body from viruses, bacteria and parasites.
Granulocytes have little sacs, which contain enzymes in order to digest microorganisms. Granulocytes are released from the bone marrow by the regulatory complement proteins.
Monocytes are stored in the spleen (50% of them). They are also produced in the bone marrow by hematopoietic stem cells (multipotent stem cells that give rise to all blood cells). They fulfill several functions, but one of them is that they can move quite quickly to the sites of infection, where they will differentiate / divide into macrophages and dendritic cells to elicit an immune response.
There are different cell types of lymphocytes.
Natural killer cells (NK cells): Natural killer cells are critical to the innate system. They have similar roles to the cytotoxic T cells. NK cells provide a rapid response to virally infectedcells and tumors and destroy them quite fast, because natural killer cells do not need an activator. They have the ability of recognising cells, which lack a antibodies on their surface and MHC (major histocompatibility complex) markers.
B-cells are able to release antibodies. Their main functions are to create antibodies against antigens, perform the function of anti-presenting cells (APCs) (cells that display the antigen complexes on their surface) and develop into a memory B-cell (by memorizing the antigen complex, they can act faster in case another infection with the same antigens should happen).
T-cells mature in the chest (more exactly in the thymus that is why they have a “T” in their name) and have different physical appearances and therefore, there are several subtypes of T-cells.
One of them is the cytotoxic T-cell (Tc cells). These cells are responsible for destroying infected cells and tumor cells. Moreover, they are implicated in transplant rejection.
T memory cells are a subtype of T killer cells. These cells have memorized the antigens of the virally infected the cells, which they have killed previously, and can endure very long in the blood circulation. Moreover, they react more quickly to infected cells, which have the same antigen structure they have memorized.
Function of Platelets
Platelets (thrombocytes): There are about 150’000 to 450’000 per mm3 in a human being and have a diameter of 2-3 µm. These platelets (or thrombocytes) are irregularly shaped and they are derived from a fragmentation of precursor megakaryocytes. Their main function is blood clotting (they are involved in haemostasis process) and they are involved in inflammations.
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