Blood pressure , structure , functions & Mechanism of blood clotting

From Online Sciences - December 18, 2017

Blood is the principal medium in the transport process , Its colour is red viscous liquid , PH equals 7.4 ( weak alkaline ) , Volume is 56 liters of blood on average , The structure of blood : connective tissue consists of Plasma , Red blood cells , White blood cells and Blood platelets .


Plasma is the tissue fluid of blood , It represents 54 % of the blood volume , It contains 90 % water , 1 % inorganic salts such as Ca++, Na+, Cl and ( HCO3 ) , 7% proteins as albumin , globulin and fibrinogen , 2 % other components as the absorbed food ( sugars and amino acids ) , hormones , enzymes , antibodies and wastes ( urea ) .

RBCsRed blood cells ( Erythrocytes )

They are the most abundant blood cells , they are nearly about 4 : 5 million cell/mm in males , 4 : 4.5 million cell/mm in females , Their shape is round corpuscles and biconcave , They produced in the bone marrow of backbone .

Each cell is destroyed after 120 days , They circulate about 172,000 circulations , They are destroyed in the liver , spleen and bone marrow , They are enucleated cells contain haemoglobin ( protein + iron ) which gives the blood its red colour .


WBCsWhite blood cells ( Leucocytes )

The number of white blood cells is 7000 cell/mm , this number increases during diseases , Their shape is colourless and nucleated with many shapes , They are formed in the bone marrow , spleen and lymphatic system , some of their kinds live for 1320 days .

Functions : They are produced in many types , each type with a specific function , but the main function is the protection of body against the infectious diseases through the following :

They circulate continuously in the blood vessels , attack the foreign particles , destroy and engulf them , Some of them produce antibodies .

Blood platelets

The number of blood platelets is 250 , 000 platelet /mm , Their shape is non-cellular and very small in size , Their size is one fourth of the RBCs , They are produced from the bone marrow , They live for about 10 days , They play a role in blood clot after the injury .

Blood clot

Blood clot occurs when a blood vessel is cut , The importance of clotting : Blood forms a clot to prevent the bleeding before it leads to shock followed by death .

Factors of coagulation ( clotting ) of blood :

Mechanism of blood clotting

In case of the presence of blood clotting factors , the steps are shown as the following :

The blood platelets together with the destroyed cells from a protein called thromboplastin .

Platelets + Destroyed cellsThromboplastin in presence of ( clotting factors in blood )

In the presence of calcium ions ( Ca++ ) and blood clotting factors in the plasma , thromboplastin activates the conversion of prothrombin into thrombin .

Prothrombin Thrombin ( Active enzyme ) , in the presence of Thromboplastin ,Ca++ , clotting factors

Where Prothrombin is a protein that is secreted in the liver with the help of vitamin K and is passed directly into the blood .

Thrombin catalyzes the conversion of fibrinogen ( soluble protein in plasma ) into fibrin ( insoluble protein )

Fibrinogen ( Soluble protein ) Fibrin ( Insoluble protein )in the presence of Thrombin

Reasons of the non-clotting of blood inside the blood vessels

Functions of blood

Blood Pressure

Measurement of blood pressure


Method of measurement


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