In contrary to open circulatory system where blood flows in open spaces, humans possess closed circulatory system where blood flows through a closed network of blood vessels.
The discovery of blood circulation was done by William Harvey.
There are four parts under it –
(i) Heart
(ii) Arteries
(iii) Veins
(iv) Blood.

Heart :

  • Heart as the pumping organ works in rhythmic cyclic manner with systole(decrease in volume) and diastole (increased in volume).
  • A heart beat consists of both of these and in humans it lasts for 0.8 second.
  •  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 atrium and a left atrium.
  • In the posterior side of the heart there is a right ventricle and a left ventricle persist.
  • Between the right atrium and the right ventricle there is a tricuspid valve.
  • Between the left atrium and left ventricle there is a bicuspid valve.
  • Vein is the vessels which carries the blood from the body towards the heart.
  • In the vein there is impure blood i.e. carbon dioxide mixed blood.
  • Pulmonary vein is the exception which always carries pure blood.
  • Pulmonary vein carries the blood from lungs to left atrium. It has pure blood.
  • Artery is the vessel which carries the blood from the heart towards the body.
  • In artery there is pure blood i.e. oxygen mixed blood.
  • But Pulmonary arteries are exception which always carries the impure blood.
  • 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 is called coronary arteries. Any type of hindrance in it causes heart attack.

Course of circulation:

  • Mammals have double circulation.
  • It mean blood have to cross two times from heart before circulating throughout the body.
  • Right atrium receives impure blood from the body which goes into right ventricle. From here the blood went into pulmonary artery which sends it to the lung for purification. After purification it is collected by pulmonary vein which brings it back to heart in left atrium. From atrium it vent 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:
  • The cardiac cycle is controlled by two pacemakers in the heart:
  • The sino-atrial node (SA node) located in the top wall of the right atrium
  • The atrio-ventricular node (AV node) located in between the right atrium and ventricle.
  • Both pacemakers are types of nervous tissue.

Blood Pressure:

  • The force that blood exerts against the wall of blood carrying tube is called blood pressure.
  • High in tubes which carry blood to the body parts (systolic pressure).
  • Low in tubes which carry blood to the heart (diastolic pressure).
  • The average blood pressure is 120-80mm Hg.
Wireless Artificial Pace maker:
When SA node becomes defective or damaged the cardiac impulses do not generate.
For this we use wireless pacemaker that regulates the heart by wireless pulses of ultrasound from outside the organ.
It is beneficial over conventional pacemaker as the leads can fail and requiring the additional surgery to replace them.
Cardiovascular Diseases:
Arteriosclerosis:
It is the hardening of the arteries due to the formation of plaques and calcification in their walls.
Atherosclerosis:
Deposition of cholesterol in the walls of arteries due which they become narrow and hinder the blood flow across them.

Heart Attack: 

       Heart Attack is caused due to sudden decrease in blood  supply to heart which leads to the damage of heart muscles.