Human circulatory system consists of blood which is kept in motion or circulation by the pump called the heart and the pipes called blood vessels. The heart is a non stop pump that pushes the blood through the arteries and supplies the body cells oxygen and glucose along with other essential nutrients. The waste from the cells including carbon di-oxide is brought back through the veins and pumped by the heart into the lungs for purification.
In human beings and other multicellular animals the transport of oxygen and nutrients for the cells of the body takes place by a fluid medium called the blood. The blood constantly moves around the body by the circulatory system.
Blood is an important fluid connective tissue and composed of the
· Formed Elements (R.B.C, W.B.C, PLATELETS)
1. R.B.C (Red Blood Cells or Erythrocytes)
· Total Number = 5 million cells/ cubic mm of blood
· Shape = dumbbell shaped
· Nuclei = absent
· Main Constituent= hemoglobin (a red pigment which is made up of
protein and iron)
2. W.B.C. (White Blood Cells or Leucocytes)
· Total Number = 7000-10,000 cells / cubic mm of blood
· Nuclei = present
· Function = WBC consume bacteria, viruses and debris that enter
the body and form special proteins, called antibiotics that protect
3. PLATELETS:- (or Thrombocytes)
· Total Number = 400,000 / cubic mm of blood.
· Function = important role in the formation of a solid plug called
clot at the site of injury to a blood vessel, so as to prevent further
loss of blood.
It is the liquid part of blood into which float different
types of blood cells; i.e. RBC, WBC & platelets;
- It contains several salts, glucose, amino acids, proteins, hormones,
and also digested and excretory products of food.
- Serum is blood plasma from which the blood clotting protein called
fibrinogen is removed.
How The Circulatory System Functions:
The heart is the muscular pump like organ that circulates blood
through the body. The muscles of the heart contract periodically
and cause the heart to pump blood. The heart contracts about 72
times a minute when an adult person is at rest, but this rate increases
to 100 or more during activity or excitement. The total volume of
blood in the system is about 5 to 6 litres. The heart pumps approximately
5 litres of blood out every minute.
The 3 types of blood vessels are arteries, veins and capillaries
and they are all connected to form one continuous closed system.
They are the widest blood vessels having thick and elastic walls;
arteries branch out into thinner tubes called arterioles, which
again branch into thinner capillaries.
Capillaries are tiny blood vessels with walls that are just one
cell thick. These walls are permeable to water and CO2, which are
exchanged with tissues surrounding the capillaries. Capillaries
ultimately joint to form venules and at last veins return blood
to the heart.
Thus, arteries take blood from the heart and supply it to various
tissues via the capillaries and veins return blood from the tissue
to the heart. For maintaining such a unidirectional flow of blood,
large veins have valves in them. The pressure of blood flow opens
them in the directional of flow and closes them otherwise.
Arterial blood is rich in oxygen and dissolved food, while venous
blood carries CO2 and waste material. However, pulmonary artery
and pulmonary vein form two important exceptions to it. Pulmonary
artery supplies lungs CO2 - rich blood and pulmonary vein collects
oxygen - rich blood from lungs and sends it to heart.