ciculatory system

Circulatory system

Blood circulatory system of man consists of following components:
Blood
Blood vessels
Heart

BLOOD
Functions of Blood
1. Transport of nutrients
2. Transport of respiratory gases
3. Transport of waste products
4. Transport of hormones
5. Transport of water, inorganic ions and elements.
6. Regulation of body temperature
7. Protection from diseases

Composition of blood
i) IT is red coloured fluid connective tissue that circulates in the body.
ii) It looks red in colour due to pigment hemoglobin present in red blood cells.
iii) It has two components:
a. Plasma
b. Cells

Blood plasma: It is a pale yellow fluid that forms 55% of blood. It contains water, plasma proteins, inorganic compounds, food waste, hormones, enzymes and other compounds.

Blood Cells: There are three types of blood cells.
i. Red blood cells or erythrocytes i. White blood cells or leucocytes
ii. Blood platelets or thrombocytes

All blood cells together form about 45% of blood and float in the blood plasma.


Red blood cells :

1. Circular and biconcave shape


2. Without nucleus


3. Cytoplasm has hemoglobin, a red pigment that gives red colour to these cells.


4. Transport oxygen from lungs to tissues and help in transport of carbon dioxide from tissues to lungs. Protect the body against diseases and infections.


5. Number varies from 4.5-5 million /cubic mm.

White blood cells :

• Round or irregular shape


• Distinct nucleus


• 3.Cytoplasm is colourless without hemoglobin.


• Protects the body against diseases and infections.


• Number is much less than red blood cells. Varies from 7000-10,000/cubic mm.




• 
  Blood platelets
  1. Irregularly shape, fragments of cells
  2. Without nucleus
  3. Cytoplasm is colouless
  4. Help in clotting of blood.
  5. Number is around 2,50,000/cubic mm.
  
  In infants red blood cells are formed in the red bone marrow of stem cells. In adults red blood cells are formed in the red bone marrow of stem cells of the bones of skull, ribs, sternum, vertebrae and pelvic bones. Life span of red blood cells is about120 days after which they are destroyed in spleen or liver.