Human circulatory system consists of centrally located muscular pump called heart, circulating fluid (blood, tissue fluid and lymph) and blood vessels, which are tube-like structures, connected to the heart.
Blood vessels are of three kinds:
Arteries: Carry blood from heart to various parts of body.
Veins: Bring blood from various parts of body to the heart.
Capillaries: Thin vessels between the artery and the vein. The capillaries allow the exchange of materials between blood and tissues.
Heart is a powerful muscular organ lying between lung. It is four-chambered - two (right and left) atria (also called auricles), and two (right and left) ventricles.
The heart is made of specialised muscle cells, also called cardiac muscle fibers, which contract and relax all the time without getting tired. The contraction and relaxation follows a rhythm called heartbeat. Heart pumps blood into the blood vessels.
Rhythmic heart beat results in the proper transport of substances to the various organs by means of blood. In one minute, normal human heart beats about 72 times. Abnormalities in heartbeat can be seen by taking ECG or Electrocardiogram.
The oxygen laden blood from the left ventricle gets pumped into a large artery called aorta. It carries oxygenated blood to all parts of the body.
Veins bring oxygen depleted and carbon dioxide laden blood to the heart and arteries take oxygen laden blood away from the heart. But there are two exceptions - the pulmonary artery carries carbon dioxide laden blood and the pulmonary vein carries oxygen laden blood.
It is the force with which blood pushes against the walls of the arteries. It is generally measured in terms of how high it can push a column of mercury. When ventricles contract, pressure of blood inside the arteries is highest.
In a healthy young human being, it is about 120 millimetres of mercury (120 mm Hg). When the ventricles relax, pressure of blood inside the arteries is comparatively less It is about 80 millimetres of Hg (80 mm Hg) in a healthy young man. Thus, a healthy young man has a normal blood pressure of 120/80 mm of Hg. The instrument used to measure blood pressure is called sphygmomanometer.
The systemic contraction of the heart can be felt as a jerk in certain arteries like the radial artery in the wrist and neck artery below the jaw which are superficial in position. This is called arterial pulse. Pulse rate is the same as the rate of heartbeat.
Our body has three different types of fluids:
Blood - found in heart and blood vessels (arteries, veins and capillaries)
Tissue fluid - found in spaces between cells in organs
Lymph - found in lymph vessels and lymphatic organs (spleen and tonsils)