Body Fluids and Circulation

Vertebrates transport essential substances to the cells and carry waste substances from there with the help of “fluid connective tissues”.

The two major fluid connective tissues are: Blood and lymph.

Blood consists of fluid matrix, plasma and formed elements.

Plasma is a liquid component constituting nearly 55% of the blood, in contrast to water and proteins.

Red blood cells, white blood cells and platelets constitute the formed elements.

Erythrocytes are anucleated and contain haemoglobin.

Leukocytes possess nuclei and are classified into two groups: granulocytes (Neutrophils, eosinophils and basophils) and agranulocytes (lymphocytes and monocytes).

Thrombocytes form of blood clots.

Blood of humans are grouped into A, B, AB and O systems.

 ‘O’ group individuals are called ‘universal donors’ while persons with ‘AB’ group are called ‘universal recipients’.

Another blood grouping is also done on the basis of the presence or absence of another antigen called Rhesus factor (Rh) on the surface of RBCs.

Coagulation of blood helps to stop the excess blood flow from the body in case of an injury by forming a clot or coagulum on the wound.
•    A clot consists of a network of threads, called fibrins.
•    Fibrins are formed by the enzyme thrombin.
•    Thrombin, in turn is formed from the prothrombin.
•    An enzyme complex, thrombokinase, is required for the above reaction.


Another fluid connective tissue is called lymph (tissue fluid). It is similar to blood except for the protein content and the formed elements.

Circulatory patterns are of two types: Open or closed circulatory system

Human heart has a double walled membranous covering called as pericardium.
It has four chambers, two atria and two ventricles.
The right and the left atria are completely separated by interatrial septum.
The left and the right ventricles are separated by interventricular septum.
The atrio-ventricular septum separates the atrium and the ventricle.
The valves present in heart are: the tricuspid valve, the bicuspid or mitral valve and the semilunar valves.
Cardiac cycle refers to the sequence of events, which occur from the beginning of one heartbeat to the beginning of the next heartbeat.
The two phases of cardian cycle are: systole and diastole.
Two heart sounds that constitute a heartbeat are: lub and dub.
The graphical representation of the electrical potentials produced by the excitation of the cardiac muscles is called as Electrocardiogram.

The instrument used to measure this, is electrocardiograph.

A normal electrocardiogram has the following waves: P wave (represents depolarisation of atria), QRS complex represents depolarisation of ventricles) and T wave (repolarisation).

Human heart follows two circulatory pathways: Pulmonary and systemic.

Human heart is auto regulated, hence it is myogenic.

Though it is auto regulated, its functions can be moderated by neural and hormonal mechanisms.

Some disorders of circulatory system are: Hypertension, Coronary Artery Disease, Angina, Heart failure.

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