As you know bood circulation is one of the important topic of human phsiology for competitive exams.under this topic to know about details like Definition of blood circulation ,what is Blood, Functions of blood, composition of blood, plasma protein cellular elements of blood ( RBCs,WBCs,and platelets) clotting of blood, blood groups, Disorder of blood etc.
Definition of blood circulation:
The circulatory system is also known as cardiovascular system that all living cells have to be provided with nutrients, Oxygen and other essential substances.Also, the waste or harmful substances produced. Blood is the medium through which these substances are transported.
What is Blood ?
Blood is a specialised connective tissue which is fluid in nature. The total volume of blood in the body is about 5 litres. Blood is slightly alkaline with a Ph of about 7.4. The specific gravity of blood is about 1.055.
Functions of blood:
Blood serves the following important functions:
1. It transports Oxygen and nutrients to various tissues.
2. Transports waste products to organs of excretion.
3. It up redistributes water from one part of the body to the other.
4. It carries hormones from endocrine glands to various tissues.
5. Clotting of blood protects against haemorrhage.
6. It contains antibodies and white blood cells which protect the body from diseases.
Composition of blood:
Blood contains of fluid called Plasma in which the the cellular elements of blood are suspended.
Plasma:
Plasma contains:
- Water to the extent of 91%.
- Proteins (albumin, globulin, and fibrinogen)
• Serum is obtained from plasma after removing fibrinogen.
(Serum= plasma-fibrinogen)
Blood plasma fig.
Plasma proteins:
Plasma proteins occur in blood to the extent of 7 to 8%. The plasma proteins are:
1.Albumin:
It is present in in very high concentration. It is responsible for osmotic pressure of blood. It is synthesized in the liver.
2.Globulin:
It is of three types alpha beta and gamma. It is produced in lymphoid tissues. It produces antibodies and immune substances.
3.Fibrinogen:
It is responsible for coagulation of blood. It is synthesized in the liver.
Functions of Plasma proteins:
• the transport hormones iron and other substances.
• the exert osmotic pressure and regulate blood volume.
• fibrinogen of Plasma is necessary for clotting.
• they provide viscosity to blood.
• Globulin of plasma is important for the synthesis of immune substances called antibodies.
Cellular elements of blood:
•The cellular elements of blood circulation by three cells -
1.Red blood cells (Erythrocytes)
2.White blood cells(Leucocytes)
3.Platelets( thrombocytes)
Red blood cells(RBC) OR Erythrocytes:
They are the the most abundant of all the cells in blood. A healthy adult man has on an average 5 millions to 5.5 millions of RBCs per mm cube.( mm-3) of blood. RBC are formed in the red bone marrow in the adults. RBC are devoid of nucleus in most of the mammals and are biconcave in shape. They have red coloured iron containing complex protein called hemoglobin hence the colour and name of these cells. A healthy individual h 12 to 16 grams of haemoglobin in every hundred ml of blood. These molecules play play a a significant role in transport of respiratory gases. RBC have an average lifespan of 120 days after which they are destroyed in the spleen .( graveyard of RBCs)
Red Blood cells fig.
Erythropoiesis:
It is the process by which RBCs are formed. In the foetus RBC are formed in the liver spleen and bone marrow. After birth they are formed only in red bone marrow of sternum, ribs ,vertebrae etc.
White blood cells( Leucocytes):
They are colourless due to the lack of haemoglobin. They are nucleated and are relatively lesser in number which averages 6000 to 8000 per mm cube. Leukocytes are generally short lived
We have two main categories of WBCs:
1.Granulocytes which are of three types -
• Neutrophils
•Eosinophils
• Basophils
2.Aranulocytes which are two types-
•Lymphocytes
•Monocytes
•Granulocytes:
20 WBC have granules in the cytoplasm. They have a nucleus which contains to are more lobes. Granulocytes are further divided into the following three types:
1.Neutrophils(polymorphs):
The contain granular cytoplasm which stanins with neutral dyes. the nucleus may contain 2 se 5 lobes. Neutrophils occur to the extent of 65 to 70% of total WBCs.
2.Eosinophils( acidophils):
These cells are slightly larger the neutrophils. The granules are coarse and closely packed. These granules take up acid stain. The nucleus contains two lobes. Normal eosinophil count is 2 to 4 percent of total WBCs.
3.Basophils (mast cells ):
They contain coarse granules as in eosinophils. But these granules stain blue with basic dyes. The nucleus is kidney shaped or lobulated. The basophils contains heparin , histamine and 5 -hydroxy tryptamine normal basophil count is .5 % of total WBC.
• Agranulocytes :
This type of WBC do not have granules. What they have a single nucleus which is not lobed
Agranulocytes are further classified into the following two types.
1.Lymphocytes: They are two types:
(A) Small lymphocytes:
They occur to the extent of 25% of total WBC. They are smaller in size with a nucleus occupying almost the whole of the cell. So the cytoplasm is less.
(B)Large lymphocytes :
They are larger in size containing more cytoplasm.
2.Monocytes :
They are the the largest of WBCs. They are occurred to the extent of 2 to4 percent of WBCs.They contain and eccentric nucleus which is notched in the inner side.
Functions of WBCs:
They are following steps given below-
• protection against infection. This is done by neutrophils and monocytes which engulf bacteria. This process is called as phagocytosis.
• To produce immune substances which defend against diseases. This is done by lymphocytes through the synthesis of Gamma globulin.
• Basophils secrete iron anticoagulant substance called heparin.
•To aid in the repair of injured tissues.
Platelets :
They are also known as thrombocytes. Their cell fragment produced from megakaryocytes (special cells in the bone marrow). Platelets can release a variety of substances most of which are involved in the coagulation or clotting of blood. Reduction in their number can lead to clotting disorders which will lead to excessive loss of blood from the body. Blood normally contains 1,500,00 to 3,500,00 platelets per mm cube.
Functions of platelets :
Following functions given as-
• thromboplastin liberated from platelets is essential for clotting.
• They close minute lesions in the walls of blood vessels.
•They aid in bodies defence mechanism against bacteria.
• They contain histamine and serotonin.
• They contain some artigenic substances also.
Clotting of blood :
They are also known as coagulation of blood. Clotting of blood is Defence mechanism of the body. It prevents loss of blood from the site of injury. If a leak develops in blood vessels A clot is formed and it plugs the leak. This prevents the loss of blood .
Mechanism of clotting :
Clotting of blood occurs in the following stages :
• Thromboplastin is liberated from disintegrated tissues and damaged platelets.
• Thromboplastin converts prothrombin into thrombin. This occurs in presence of calcium ions.
•Thrombin converts fibrinogen to fibrin.
• The insoluble fibrin forms threads. The formed elements of blood get entangaled in this and form the clot.
Clotting factors :
The various factors involved in the scheme of clotting described above are designated by numbers as factors. These factors are:
Factor 1- Fibrinogen
Factor 2- Prothrombin
Factor 3-. Thromboplastin
Factor 4- calcium ions
Factor 5- Quick's labile factor
Factor 6- Existance of this factor not accepted
Factor 7- Quick 's stable factor
Factor 8- Antihemophilic factor
Factor 9-. Christmas factor .
Blood Clotting time:
It is the time taken for the clotting of human blood removed from circulation. The average clotting time varies from 5 to 15 minutes.
Blood Group d :
ABO grouping is based on the presence o r absence of two surface antigens (chemicals that can induce immune response) on the RBCs namely A and B . Similarly the plasma of different individuals contains two natural antibodies. The distribution of antigens and antibodies in the four groups of blood A, B, AB and O .
Universal donar bood group (O) :
A person with blood group ' O' can be donated to persons with any other blood group ' O 'and his group individuals are called universal donors .
Universal Acceptor ( recipients ) blood group ( AB ):
Persons with AB group can accept blood from persons with 'AB 'as well as the other groups of blood. Therefore such persons are called universal recipients.
Disorders of blood :
Disorders of Red blood cells :
Disorders of red blood cells occur in the form of either anaemia or polycythemia.
Anemia :
It is the disease involving deficiency in the number of red blood cells o r deficiency of haemoglobin. Because of anyone of these deficiencies there is a decrease in oxygen carrying capacity of flood. The symptoms of anaemia manifest in the form of Breathless tiredness loss of appetite and Payal pallor skin.
Polycythemia :
In this condition there is an abnormal increase in the number of red blood cells. This increase the the viscosity of blood circulation. This decrease the the rate of flow and increased risk of intravascular clotting.
Disorders of white blood cells :
They may occur in the form of of Leukocytosis o r leucopenia.
Leukocytosis :
It is an increase in the total number of white blood cells beyond 10000 per cubic millimetre.
Disorder of platelets :
They occur in the form of thrombocytopenia.
It is a condition where there is a decrease in platelet count. It reasults in:
1. Increase in bleeding time
2. Defect in the retraction of clot.
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