Circulatory System

Circulatory System

The discovery of blood circulation was done by William. Harvey in the year 1628.
There are four parts under it
(a) Heart
(b) Arteries
(c) Veins
(d) Blood


It remains safe in the pericardial membrane. Its weight is approximately 300 grams. Heart of the human is made up of four chambers. In the anterior side there is a right auricle and a left auricle. In the posterior side of the heart there is a right ventricle and a left ventricle persist.
» Between the right auricle and the right ventricle there is a tricuspid valve.
» Between the left auricle and left ventricle there is a bicuspid valve.
» The blood vessels carrying the blood from the body towards the heart is called vein.
» In the vein there is impure blood i.e. carbon dioxide mixed blood, Its exception is pulmonary vein, which always carry pure blood.
» Pulmonary vein carries the blood from lungs to left auricle. It has pure blood.
» The blood vessels carrying the blood from the heart towards the body is called artery.
» In artery there is pure blood i.e. oxygen mixed blood. Its exception is pulmonary artery.
» Pulmonary artery carries the blood from right ventricle to lungs. It contains impure blood.
» In the right part of the heart, there remains impure blood i.e. carbon dioxide mixed blood and in the left part of the heart there remains pure blood i.e. oxygen mixed blood.
» The artery carrying blood to the muscles of the heart are called coronary arteries. Any type of hindrance in it causes heart attack.

Course of circulation

Mammals have double circulation. It mean blood haveto cross two times from heart before circulating throughout the body.
  Right auricle receive impure blood from the body which goes into right ventricle. From here the blood went into pulmonary artery which send it to the lung for purification. After purification it is collected by pulmonary vein which bring it back to heart in left auricle. From auricle it went into left ventricle. Now this purified blood is went into aorta for different organ of body.
» This circulation is done is a cardiac cycle.

Cardiac cycle

Rhythmic systole (Contraction) and diastole (relaxation) of auricle and ventricle constitutes a cardiac cycle.

Heart beat

Heart keeps beating rhythmically throughout the life. There is a node from which originate contraction of heart.
1. Sino auricular node (S A node) : It is a specialized area of cardiac muscle fibre in right auricle. SA node is also known as pacemaker as it generates each wave of cardiac impulse.

2. Auriculo Ventricular node (AV node) : AV node is present close to the interatrial septum near the right AV aperture. Wave of contraction is picked up by AV node which spread through.

» Wave of excitation is picked up by AV node which spread through AV bundle of muscles fibers present on inter arterial septum as well as inter-ventricular septum.

Artificial pacemaker

When SA node becomes defective or damaged, the cardiac impulses do not generate. This can be cured by surgical grafting of an artificial pacemaker an electric device in the chest of the patient. It stimulate the heart electrically at regular intervals.
» Systole and diastole of the heart are collectively called heartbeat. In the normal condition the heart of the human beats 72 times and in a single beat it pumps approximately 70 ml blood.
» The blood pressure of a normal human is 120 / 80. (Systolic -120 and Diastolic -80).
» Blood pressure is measured by sphygmomanometer.
» Thyroxin and adrenaline are the hormones which independently controls the heartbeat.
» The CO2 present in the blood accelerates the heart beat by reducing the pH.