Human Circulatory System : Parts and Functions

Posted on Dec 9 2013 - 12:12pm by

Posted under Category : Health Fundas

The Human Circulatory System Basics:

Each and every cell in the body requires energy to perform various activities. For performing these activities, oxygen and nutrients should be transported to these cells. Waste materials generated by the result of metabolic activities of the cells should be transported to the excretory organs.

For performing these functions a specialized system, namely circulatory system is present.

simplified diagram of the human Circulatory sy...

simplified diagram of the human Circulatory system in anterior view. edited to address several concerns for featured picture nomination process. (Photo credit: Wikipedia)

Parts of the Circulatory System:

The important parts of the circulatory system are

  1. Heart
  2. Blood vessels
  3. Blood

The Human Circulatory System and How it works

1. Heart:

Heart is of the size of the fist and is built with the muscles which is situated in the rib cage between the lungs.

Chambers of the Heart:

It consists of four chambers of which upper two chambers are called as auricles and lower two chambers as ventricles.

Auricles are divided as right and left auricles by a thin membrane know as intra auricular membrane. Similarly ventricles are divided into right and left ventricles by a thick membrane called as intraventricular membrane. Auricles and ventricles are separated by a auriculoventricular membrane. Pacemakers namely sinoauricular node (SA node) and auriculoventricular node (AV node) are present which stimulate the functioning of the heart.

Right auricle receives the deoxygentaed blood from various parts of the body. Oxygentaed blood from lungs is brought to left auricle by the pulmonary vein. Deoxygentaed blood from right auricle is pumped into right ventricle and this blood is pumped to lungs by the pulmonary artery. Oxygentaed blood from left auricle is pumped to left ventricle and this blood is supplied to all body parts.

2. Blood Vessels:

Blood vessels are thin pipe like structures which supply the blood to the heart and receives impure blood from body parts. Blood vessels are of two types namely arteries and veins.


Arteries supply oxygentaed blood from the left ventricle to all parts of the body. These arteries divide into arterioles and end as capillaries in the cells. Pulmonary artery supplies deoxygenated blood from right ventricle to lungs.


Veins collect deoxygenated blood from all parts of the body. They start as capillaries, then to veinlets and to larger veins finally. Pulmonary vein brings oxygenated blood from lungs to left auricle.

3. Blood:

Blood is a fluid connective tissue which is red in colour due to the presence of haemoglobin. Our body contains 5-6 litres of blood. The main components of the blood are plasma and blood cells.


Plasma constitutes 55% of the blood and is light yellow coloured liquid containing water, salts and plasma proteins.

Blood cells:

Blood cells constitute 45% of the blood. They float in plasma and are of three types. They are red blood cells, white blood cells and blood platelets.

Red Blood Corpuscles:

They are also known as erythrocytes. RBC are round in shape and disc shaped with constriction in the middle. They contain a pigment called as haemoglobin. They do not contain nucleus. The life span of RBC is 120 days.

White Blood Corpuscles:

They are also known as leukocytes. They are of differenet shapes. WBC contains nucleus. WBC are classified as granulocytes and agranulocytes based on the presence of granules in their cells. They do not contain haemoglobin and hence are white in colour. They attack the microorganisms which enter our body and protects us from diseases. Their lifespan is 12 days.


Lymohocytes and monocytes belongs to agranulocytes as they do not contain granules in their cells. Kidney shaped nucleus is present in them. Monocytes are called as macrophages.


Eosinophils (acidophils), basophils and neutrophils belong to granulocytes as they contain granules. Their nucleus is lobed.

Blood platelets:

Blood platelets are called as thrombocytes and are small and oval in shape. They do not contain the pigment and are white in colour. The life span is 3 -10 days. Blood platelets are useful for formation of the blood clot during bleeding when wound occurs in the body.