blood components: RBCs, WBCs, Plasma and platelets
An average adult person as about 4 to 6 litre of blood. it forms about 6% to 10% of the body weight and some 30% to 35% of extracellular fluid. the study of blood is known as hematology.
Blood is an opaque, mobile fluid connective tissues, mesodermal in origin. it is somewhat sticky and slightly heavier than water it has saltish is taste and a mild alkali secretion pH about 7.4. it is bright red when oxygenated and purple when deoxygenated.
In this article we know about different types of blood components like red blood cells, white blood cells, blood plasma and blood platelets. Now let us discuss some description about components of blood.
Blood is consist of four types of blood components a watery fluids called as plasma containing certain floating bodies term formed elements. the latter blood components include blood cells or corpuscles and blood platelets. Blood platelets is also known as thrombocytes.
Others blood components forming blood cells consists of red blood cells represented as RBCs and white blood cells represented as WBCs. Red blood cell is also known as erythrocytes and white blood cell is also known as leucocytes.
Formed elements include blood components red blood cells, white blood cells and blood platelets consist of total volume of 45% of blood and blood plasma contents about 55% of the total volume of blood. And now study blood components one by one
Blood components plasma is of yellow slightly alkaline somewhat viscous fluid. it is a complex mixture which is in dynamic equilibrium with the intercellular fluid bathing the cells and the intracellular fluid present within the cells.
And chemical composition of blood plasma consists of about 90% water, 1% inorganic salt in true solution and 7 or 8% proteins in colloidal state and there are over 70 different plasma protein. And remaining 1% or 2% of blood Plasma is formed by food materials, wastage product, disolved gases, regulatory substances, anticoagulant material, cholesterol and antibodies. These substances do not form an integral part of the blood plasma they inter and leave at some intervals. they are being carried by the plasma from one place to another in the body.
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Blood plasma proteins
The blood components plasma contains on number of proteins like serum albumen, serum globulins, properdin, prothrombin and fibrinogen and the plasma protein serve many functions such as follows:-
Functions of blood plasma proteins
1) blood components plasma proteins act as a source of protein for the tissues cells which may synthesise their own proteins from them
2) blood plasma protein act as acid base buffer, its maintain pH of the blood by neutralizing acids and bases.
3) albumin and globulin maintain Osmotic pressure of the plasma so that they later may retain water. fall in the level of blood plasma proteins causes excessive filtering of water from the blood into the tissues this may produce oedema that is swelling of hands and feet in person taking protein deficient diet.
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4) plasma proteins transport certain materials in combination with them. like thyroxin is bound to albumin or a specific globulin, insulin is combined with globulin, fatty acid are joined to albumen for transport in the plasma
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5) some globulin known as immunoglobulin form protective proteins antibodies in response to the entry of foreign agents that is antigen into the body. the antibodies inactivate the antigen. antigens may be microorganisms or their toxins
6) Properdin is a blood plasma protein that can destroyed certain bacteria, neutralizes certain viruses and damages foreign red blood corpuscles.
7) blood plasma protein like prothrombin and fibrinogen play important role in blood clotting
Inorganic cells in blood plasma
The inorganic salts occurs in the blood plasma as ions, Sodium and chloride are the principle cation and anion of blood plasma. The anion bicarbonate and phosphate. and the cation potassium, magnesium, calcium, iron and manganese occur in smaller amounts.
The inorganic salts present in blood plasma some times known as blood electrolytes. the kidney maintain plasma electrolytes at precise concentration that is an example of homeostasis.
Food materials in blood plasma
The food materials present in the plasma are glucose, amino acids, fatty acids and triglycerides. their amount depend upon the digestion of food in the alimentary canal. normally an adult person is 80 to 100 milligram of glucose per 100 ml of blood 12 hours after meal. If blood sugar is reached to 180 mg glucose is excreted in the urine this causing a disease Diabetes mellitus or hyperglycemia and falling blood sugar is known as hypoglycemia.
Wastes product in blood plasma
The wastes products found in blood plasma are urea, uric acid, Ammonia and creatinine. these are removed by the kidney. their axcess amount causes toxic effect known as uremia.
Dissolved gases in blood plasma
The small amounts of dissolved gases like oxygen, carbon dioxide and nitrogen are found dissolved in the blood plasma
Regulatory substances in blood plasma
Regulatory substances included hormones, vitamins and enzymes in blood plasma. There are different types of hormones and enzymes released from endocrine glands systems and their function is very important. There are so many vitamins like vitamin A Vitamin B complex vitamin C vitamin D vitamin E vitamin K are present in blood plasma.
Anticoagulant material in blood plasma
Natural strong anticoagulant material present in the blood plasma is a heteropolysaccharide named antiprothrombin or heparin. it checks clotting of blood in uninjured blood vessels by preventing the conversion of prothrombin into thrombin and heparin is produced in the liver.
Cholesterol in blood plasma
Liver synthesise cholesterol and release it into the blood it is also obsorbed into the blood from the food such as eggs, digested in the intestine. it provides material to the tissues cells for synthesis of membrane lipids, vitamin D, steroid hormones and bile salts. The cholesterol normal ranges from 50 to 180 milligram per 100 ml of blood. rise in the level of cholesterol in blood may causes heart problem.
Red blood corpuscles (RBCs)
Next blood components is red blood cells also known as red blood corpuscles and represented by RBCs. The red blood cells are the most numerous formed elements of the blood. they are the most abundant cells in the human body. unique feature of red blood cell is the presence of red oxygen carrying pigment that is known as hemoglobin in their cytoplasm.
Prawn, crabs and some molluska have blue copper containing pigment known as haemocyanin and some annelids have green iron- containing pigments known as chlorocruorin.
Shape of RBC
The shape of RBC blood components in different vertebrate classes. In fishes and amphibians reptiles and birds RBC are oval, biconvex and nucleated. And in mammals they are circular biconcave and dnucleated disc. Their Central part is thinner than the margin. The shape of RBC provide flexibility and results in a 20 to 30% increase in surface area as compared to sphere.
Camel and llama are exceptional among mammals in having oval RBC.
Size of red blood cells
The Human RBC are smaller than the white blood cells they are 7 to 8 micrometre in diameter and 2 micrometre thick near the rim. small size of RBC provide its greater surface area for diffusion of oxygen into it.
Red blood cells count
The blood components red blood cells are far more numerous than white blood cells a normal healthy adult men and women have about 5 and 4.5 million RBC cell per cubic mm of blood respectively. This is called as total RBC count. The RBC count decrease in anaemia may be caused by loss of blood (hemorrhage), destruction of red blood cells (haemolysis) or faulty formation of blood.
The RBC count increases during exercise to meet the increased demand of Oxygen and at high altitude to cope with the low of oxygen content of the air. An abnormal rise in RBC count is known as polycythemia. And decrease in number of red blood cells known as erythrocytopenia. Causes oxygen shortage in blood and tissues.
Colour of red blood cells
The RBCs look yellowish seen singly and red when you in bulk. They impart red colour to the blood the colour is due to presence of solution of iron containing pregnant known as hemoglobin in them.
Haemoglobin is a conjugated protein, it consists of basic protein globin joined to a non protein group heme, hence the name hemoglobin. Heme is an iron porphyrin ring. A mammalian hemoglobin molecule is complex of 4 heme molecules joined with 4 globin molecules. There is about 1.5 mg of hemoglobin in hundred ml of blood.
Red blood cells has some 280 millions hemoglobin molecules. in the lungs due to high partial pressure of oxygen haemoglobin take up oxygen and change to bright red oxyhemoglobin. Four oxygen molecules loosely join to 4 ferrous ions 4 Fe+2 such like
Hb4 +4 O2 —— Hb4O8
Thus one RBC can carry over billions oxygen molecules. In the tissues due to low partial pressure of oxygen oxyhaemoglobin breaks up into Oxygen and deoxyhemoglobin in this way the RBC carry oxygen from lungs to the tissues.
The red blood cells also carry carbon dioxide from the tissues to the lungs for elimination. It is transported into two forms in combination with the water of RBC forming bicarbonate ions such as
CO2 +H2O —- H2CO3 — H^+ + HCO3-
And partialy red blood cells transfer carbon dioxide in combination with amino group of globin forming carbaminohemoglobin such as follows
HbO2 + CO2 —- HbCO2 + H+ + O2
Structure of red blood cells
Red blood cells is bounded by an elastic and semi permeable plasma membrane this enables it to squeeze through capillaries having a diameter less than its own. Red blood cells loses its plasticity in Sickle Cell anaemia. In Sickle Cell anaemia RBC block the capillaries leading to grave consequences.
Erythrocytes content homogeneous cytoplasm which loses the nucleus, endoplasmic reticulum mitochondria ribosomes and centrioles during the development of corpuscles. This gives a double advantages the corpuscles has more space to hold hemoglobin, its oxygen consumption is very low due to lack of organelles so that it can supply more oxygen carried by hemoglobin to the tissue cells.
And red blood cells cannot reproduce or carry out cellular metabolism due to lack of organelles. besides hemoglobin a red corpuscles also contain several inorganic ions including those of Sodium, Potassium, calcium, magnesium, chloride and phosphate. the adult red blood cells of mammals are described as enucleated as when young they have nucleus that latter disappears.
Formation of red blood cells
Formation of red blood corpuscles is known as erythropoiesis. It occurs in the liver and spleen in the foetus and in the red bone marrow after birth. Proteins and iron are components of haemoglobin and Vitamin B12 and Folic acid stimulate erythropoiesis, deficiency of any of these materials may causes anaemia, excess of RBC are stored in the spleen.
Life span and disposal of RBC
Human red blood cells remain functional in body for about 120 days. And 50 to 70 days rabbits and 100 days in frog. So human red blood cells life span is about 120 days. The worn out or dead RBC are destroyed by phagocytosis in the body itself and in the spleen and liver in the particular. And their iron is return to the red bone marrow for reuse in the synthesis of haemoglobin.
Their pigment is degraded to pigment bilirubbin which is excreated in bile. The pale yellow colour of the plasma is mainly due to presence of bilirubin. Billirubin is not excreated fully the skin and mucous membrane of the person become a yellowish this disorder is known as jaundice.
White blood cells WBCs
White blood corpuscles also known as white blood cells and it is represented by WBCs. And WBC have no haemoglobin content. The shape of WBC are rounded or irregular cells, they can change their shape and are capable of amoeboid movement this enables them to squeeze out of capillaries into the tissues this process is known as diapedesis.
The size of WBC are mostly larger than the red blood cells range from 12 to 20 micrometre. And number of WBC fever then red blood cells number from 5000 to 10000 per cubic ml of blood this number is known as total count of WBC.
WBC count increase or decrease abnormally in certain conditions. in WBC count is rises known as leucocytosis. it is physiological response to infection like pneumonia inflammation such as appendicitis and malignancy such as blood cancer leukaemia.
Fall in WBC count is termed leucopenia occurs in conditions such as Folic acid deficiency , infection of AIDS virus and WBC count is useful in diagnosis disease.
Structure and formation of WBC
Generally WBC are colourless and known as leucocytes are are nucleated cells their cytoplasmic content mitochondria, Golgi apparatus and centrioles besides other organelles and formation of leucocytes is known as leucopoiesis. its occurs in lymph nodes, spleen, thymus and red bone marrow.
Life span and disposal of WBC
White blood cells service for a few 3 to 4 days only in the blood, dead WBC are phagocytized in blood, liver and lymph node.
Types of white blood cells
Generally white blood cells are categorised into two main subtypes granular leucocytes or non granular leucocytes.
Agranulocytes or non granular leucocytes
Agranular white blood cells lack granules in the cytoplasm and have nonlobed, rounded or oval nucleus. Are granulocytes are called as mononuclear cells they have two subtypes monocytes and Lymphocytes. the monocytes arises in the bone marrow and the B and T Lymphocytes are produced in the bone marrow and thymus respectively and mature in spleen and lymph nodes. formation of agranulocytes is termed as agranulopoiesis
Monocytes these are the largest of all types of white blood cells they had large Sub rounded or Bean shaped nucleus and good amount of cytoplasm. they are very motile they are phagocytic in action and engulf bacteria and cellular debris generally they change into macrophages after entering tissues space.
Lymphocytes these are about the size of red blood cells they have very large rounded nucleus and scanty cytoplasm. they are non motile and phagocytic in action. the secrets antibody to destroy microbes and their toxin reject grafting and kill tumor cells. they also help in healing of injuries, the Lymphocytes defferentiates into two main subtype B Lymphocytes and T lymphocytes.
White blood cells content granules in the cytoplasm and have lobed nucleus. they are produced in the red bone marrow their formation is known as granulopoiesis as they have 3 subtypes basophils, eosinophils and neutrophils.
The basophils take up basic stains such as methlene blue they are fairly large and have nearly S shaped nucleus and a few course granules. granules content histamine. the basophils release histamine and heparin by exocytosis in the blood
Eosinophils stain with acidic dyes such as eosin. they are also fairly large and have bilobed nucleus and abundant course granules. the latter content hydrolytic enzymes and peroxidases which are discharge into the phagosome. the eosinophils have antihistamine properties. their number increases in people with allergic condition such as asthma or hay fever there also help in dissolving blood clot.
Neutrophil is stains equaly both basic and acidic dyes. they are quite large and have many lobed nucleus and abundant fine azurophilic granules. the latter represent lysosome with hydrolytic enzymes. The neutrophils are phagocytic in action. they engulf microbes, they are chemotactically attracted to bacterial peptidase.
The blood platelets also lack haemoglobin, and size of platelets are rounded oval disc like bodies but usually become is stellate in extracted blood. And size of platelets are the smallest formed elements of the blood there are only 2 to 5 micrometre wide.
Blood platelets are fewer then the red blood cells and more than white blood cells in number they are about 250000 platelets in cubic ml of blood. increase and decrease in the number of blood platelets is known as thrombocytosis and thrombocytopenia respectively. Colour of blood platelets is colourless like the leucocytes.
Structure of blood platelets
the blood platelets are flate, nucleated fragments of large cells in the bone marrow rather than true cells they are bounded by a membrane and contains few organelles and secretary granules in the cytoplasm. they have at the centre of a group of the basophilic granules which give the appearance of nucleus at the site of injury blood platelets release platelet factors for thromboplastin that help in blood clotting.
Blood platelets are formed in in red bone marrow their formation is known as thrombopoiesis. And life span of blood platelets survive for only 3 to 7 days only and they are disposed of by phagocytosis in the blood itself.
Thrombocytes are biconvex nucleated cells with granular cytoplasm they are found in vertebrate other than mammals the spindle cell add in clotting of blood like the platelets of mammals.
Haemopoiesis is the process of formation of blood known as haemopoiesis. the tissues in which blood is formed are termed haemopoietic tissues. this include red bone marrow and lymphoid tissue such as this spleen, thymus and lymphatic node. The writer of sides likho sides and blood platelets all together arises from common source that is known as pluripotent stem cells in red bone marrow.
The blood plays a vital role in the body and often is known as river of life
Blood plasma functions
1) Blood components plasma helps in transport of food material such as glucose, amino acid, fatty acids, triglycerides, vitamins, minerals are carried by plasma from the alimentary canal and liver to all tissues of body for growth repair at energy.
2) blood plasma helps in transport of oxygen small amount of oxygen is carried by blood plasma in aqueous solution from the lungs to the tissues for oxidation of food
3) functions of Plasma it help in transport of carbon dioxide and plasma collects carbon dioxide from the tissues and carries it to the lungs for elimination from the body
4) blood plasma carriase nitrogenous wastes such as urea, uric acid and creatine from the liver and other tissues to kidney for removal in the urine.
5) blood plasma helps in transport of hormones the endocrine glands secretes their hormone directly into the blood and blood plasma carry to the their target organ
6) blood plasma helps in transport of metabolic intermediates material from one tissues to another for other metabolism for example lactic acid formed in muscles during anaerobic respiration is carried by plasma to the liver where it is partially oxidized and partially change into glycogen.
7) blood plasma help in supply of raw material to the glands for the preparation of their products
8) blood plasma regulate the water balance of the body that supplies water to the tissues and receive the excess water formed in metabolic process
9) blood plasma also helps in regulation of PH, plasma helps to regulate the pH of body Fluids it contains buffer material such as protein and mineral salts which can utilise the acid and base in the blood
10) blood plasma helps in regulation of body temperature plasma carries heat from the heat producing tissues such as muscles and glands to other where no or little heat is produced to the body surface where it can be dissipited
11) antibody present in the blood plasma provide immunity against certain disease
Red blood cell functions
There are following function of RBC
1) RBC help in transport of oxygen erythrocytes carry oxygen bound to haemoglobin as oxyhaemoglobin from the lungs to the tissues for oxidation of food to release energy
2) red blood cells help in transport of carbon dioxide erythrocytes carries a small amount of carbon dioxide as carbaminohemoglobin from the tissues to the lungs or removal from the body
White blood cell functions
The white blood cells act as soldiers Scavenger and builder of the body. Neutrophils and monocytes Defend the body against the attack of microorganisms that collect at the site of infection and in the invenders microorganism this action is known as phagocytosis ,Lymphocytes and eiosinophils destroyed toxin released by the microorganism. Neutrophils and monocytes also function as scavengers and phagocytize the dead cells to clean the body.
And Lymphocytes help in scar formation after injury to heal the wounds. they are also form collagen and elastin fibre they may enter bone marrow and form erythrocytes and neutrophils.
Functions of blood platelets
Blood platelets play a vital role in blood clotting. Blood clotting is nature’s device to check the excessive loss of blood from and injury caused to the body the process of clotting is initiated by blood platelets the injured cells release substance that attract the platelets together at the stick to the injured surface of blood cells are there clumping is enhanced by ADP. The mass of aggregated blood platelets alone may physically plug a cut in a very small vessels
The contact of blood platelets the collagen fibre exposed by the injury causes them to disintegrate and least two substance serotonin and thromboplastin which minimise loss of blood from the injury in two ways
Serotonin materials helps in vasocontraction causes the blood vessel at the site of bleeding, contract this reduce the blood loss and also makes it less likely for the clot formed to plug the injury to be Swept out by the flow of blood
Thromboplastin is lipoprotein helps in cloud formation blood, clot formation occurs in 3 steps
1) thromboplastin helps in the formation of an enzyme prothrombinase this enzyme inactivate heparin and it also convert the inactive plasma protein prothrombin into its active form thrombin both the changes required calcium ions
2) thrombin act as proteolytic enzyme to separate two peptide from the soluble plasma protein fibrinogen molecules to form in soluble fibrin monomer
3) The Fibrinogen monomer polymerized to form long sticky fibres, the fibrin Threads form a fine network over the wound and trape blood corpuscles RBC WBC platelets to form of crust that is clot, and bleeding clot is formed in about 2 to 8 Minute.