What Is Blood?
Blood is one of the essential parts of the body. It is a fluid that circulates in the body. It helps to transport oxygen, and nutrients, to various cells and tissue of the body. Blood consists of plasma, blood cells and platelets. It also transports metabolic waste products away from those same cells. Blood makes up 8% of our body weight.
Physical Properties Of Blood:
pH: Slightly alkaline ( 7.35-7.45).
An average-sized man has about 5-6 litres of blood in his body.
Temperature: 38 ° C ( 100.4 ° F).
Specific Gravity: 1.052-1.062
Functions Of Blood:
- Blood performs the following important functions:
- Transportation of gases (oxygen and carbon dioxide), nutrients, hormones, heat and wastes.
- Regulation of pH, body temperature and water content of cells.
- Protection against blood loss through clotting and against disease through phagocytic activity with blood cells and antibodies.
Components Of Blood:
Blood Plasma- It is a liquid extracellular matrix. Blood plasma consists of 55% of blood.
Formed Element- Formed elements are blood cells and fragments. It consists of 45% of blood.
When a sample of blood is centrifuged it is separated into the following parts: Plasma, Buffy coat and erythrocytes.
Plasma: Plasma is mainly made from water and it is pale yellow in colour. Blood plasma consists of salt, nutrients, water and enzymes. Plasma also contains proteins, sugar and hormones. It transports water and nutrients to other parts of the body. Blood plasma contains 90-92% water and 8-10 % solutes, most of which are protein. Blood plasma also contains small amounts of minerals like ( sodium, calcium, magnesium, bicarbonate, chloride etc.). Plasma also contains proteins like:
1)Albumin: Albumin helps to maintain the colloidal osmotic pressure of the blood. It helps keep fluid from leaking out of blood vessels and into tissues. Albumin also helps to transport many substances like drugs, hormones and fatty acids. A deficiency of albumin causes edema e.g nephrotic syndrome.
2) Globulin: It is of three types-
Alpha globulin or High-Density Lipoprotein (HDL): The role of HDL is to prevent plaque formation by keeping cholesterol in transport within the blood.
Beta Globulin or Low-density Lipoprotein (LDL): Beta globulin helps to transport fat to cells for steroid and cell membrane formation. It also promotes cholesterol plaque formation which is a risk factor for arterial and heart disease.
Gamma Globulin or Immunoglobulins (Antibodies): Antibodies defend the body against viruses, bacteria, fungi and cancer cells. They are produced by the B lymphocytes. Antibodies recognize pathogens by specific receptors and neutralise them by various mechanisms.
Fibrinogen: Fibrinogen is an important soluble plasma clotting factor precursor. It is essential for the coagulation of blood.
Red Blood Cells (RBC) Or Erythrocytes:
RBCs are biconcave cells without a nucleus in humans. RBC is the shape of a flat disk or doughnut. It makes up
about 40% of the blood volume. It contains haemoglobin, an iron-rich protein that gives a red colour to blood. The
main function of RBCs is to carry oxygen from the lungs to other tissue of the body. Oxygen binds with
haemoglobin and takes oxygen from the lungs to other parts of the body. RBCs are produced by the bone
marrow to primarily carry oxygen to the body and carbon dioxide away from it. They have a life cycle of
about 120 days in the human body. One drop of blood contains about 5 million red cells. RBC is also
responsible for the determination of blood group
White Blood Cells (WBC):
White Blood Cells are also known as Leukocytes. They are fewer in number than red blood cells. White blood cells are mainly responsible for the body against infection. There are five types of white blood cells found:
They are normally found in the bloodstream. It is predominant in cells and presents in the pus. It helps in protecting the body against infection by killing bacteria, viruses and fungi by ingesting foreign debris. Around 60-65% of WBC are neutrophils. It has a diameter of 10-12 micrometres. The nucleus is 2-5 lobed. Neutrophils are stained using neutral dyes, hence they are named so. Neutrophils are the first cell of the immune system to respond to an invader. The lifespan of WBCs extends for up to 8 hours and is produced every day in the bone marrow.
They are cells of leukocytes that are present in the immune system. They are small granulocytes. They are produced in the bone marrow. These cells make 2-3 % of white blood cells. These are present in the high concentration of the digestive tract. The main function of eosinophils is not yet clear, but it is linked with allergic diseases and certain infections.
These are the common type of granulocytes. It makes up 0.5-1% of the WBCs. White blood cells have the ability to stain with basic dyes. Hence it is referred to as Basophils. It is also produced in the bone marrow. They secrete serotonin, histamine and heparin. Basophils are part of the immune system.
Lymphocytes play a vital role in producing antibodies. Their size range from 8-10 micrometre. Each tiny lymphocyte has a large nucleus at its centre. Lymphocytes are natural killer cells. They are colourless cells found in lymphoid tissue, hence referred to as lymphocytes. There are mainly two types of lymphocytes: T Lymphocytes and B Lymphocytes. These cells are responsible for human and cell-mediated immunity.
These cells have a large bilobed nucleus. It has a diameter of 10-20 micrometres. The nucleus is generally kidney-shaped or half-moon-shaped. It occupies 6-8 % of WBC. They are a garbage track of the immune system. The main function of the monocyte is to migrate in the tissue and clean up dead cells. They protect against bone marrow pathogens. They move into the sites of infection very quickly.
Platelets are also called thrombocytes. It is smaller than red or white blood cells. The main function of platelets prevention of blood loss ( Haemostasis). Platelets help in the clotting process by gathering at a bleeding site and clumping together to form a plug that helps seal the blood vessel. Wherever a wound occurs the blood vessel sends a signal to platelets. Platelets receive that signal and travel to that area and transform into their active formation. The life span of platelets is 8-10 days. Production of platelets influenced by thromboplastin secreted by the liver and kidney.
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