Body Fluids and Circulations

i. Embolus : It is a clot that forms in one part of body, flows with the blood stream and lodges on a blood vessel at a point some distance from the site of its formation.

ii. Thrombus : It is a blood clot, which stays where it is formed e.g. coronary thrombus.

iii. Thrombophilia : is a condition where the blood has an increased tendency to form clots. 

iv. Vasodilation : refers to the widening of blood vessels. 

v. Thrombocytopenia : deficiency of platelets in the blood. This causes bleeding into the tissues, bruising, and slow blood clotting after injury.

vi. Acapnia : It is the deficiency of C0₂ in the blood.

vii. Pulse pressure : The difference between systolic and diastolic pressure is termed as pulse pressure.

Blood performs the following functions :

1. Transportation of oxygen.

2. Transportation of carbon dioxide.

3. Transportation of various hormones.  

4. Healing up of injured parts : At the point of injury, clotting occurs and thus the blood helps in healing up of the injured part.

5. Transportation of the metabolic waste products : The blood takes metabolic waste products from all cells and supply them to kidneys.

6. Antibodies : The antibodies of plasma neutralize the toxic substances produced by bacteria.

7. Protection from diseases : The neutrophils engulf the foregin bacteria and thus protect human beings from diseases.
8. Distribution of various nutrients throughout the body. 

Blood clotting : It is the natural device to check bleeding. The clot is a reddish brown scum which is formed at the site of a cut or an injury over a period of time. The clot consists mainly of a network of threads called fibrins in which dead and damaged formed elements of blood are trapped.
An injury or a trauma stimulates the platelets in the blood to release certain factors which activate the mechanism of coagulation. Certain
factors released by the tissues at the site of injury also can initiate coagulation. Calcium ions play a very important role in clotting.

i. The fibrins are formed by the conversion of inactive fibrinogens in the plasma by the action of the enzyme thrombin.
ii. Thrombins, in turn are formed from another inactive substance present in the plasma called prothrombin. This reaction is brought about by the enzyme thrombokinase. TThe clot is formed by a series of linked enzymic reactions (cascade process) involving a number of factors present in the plasma in an inactive
state. 

Blood contains formed elements. Erythrocytes, leucocytes, and platelets are collectively known as formed elements. 
i. Erythrocytes - They are also called Red Blood Corpuscles (RBCs). They are the most abundant elements present in the blood. RBCs are formed in the red bone marrow in the adults. They are devoid of a nucleus.
Their main function is the transport of the respiratory gases.
ii. Leucocytes - They are also called White Blood Corpuscles (WBCs). They are nucleated and less abundant as compared to the RBCs. The WBCs are further divided into granulocytes and agranulocytes. The granulocytes are of three types neutrophils, eosinophils and basophils. Monocytes and lymphocytes constitute the agranulocytes. The lymphocytes are further 
The main function is to provide immunity to the body against the pathogenic organisms. 
iii. Platelets -  They are also known as thrombocytes. Platelets are small irregular bodies present in the blood. They contain essential chemicals that help in clotting.
The main function of platelets is to promote clotting.