BLOOD CIRCULATORY SYSTEM:

DEFINITION:

The circulatory has to ensure that the materials reach all the cells of the body and in time. 
‘’The system involved in the transport of various substances within the body of an animal is called circulatory system’’.  

TYPES OF BLOOD CIRCULATORY SYSTEM:x

There are two types of blood circulatory system:
  •  Open circulatory system.
  •  Closed circulatory system.

OPEN CIRCULATORY SYSTEM:

  • The blood enters and circulates in the interestial spaces (space between the tissues).
  • The exchange of materials between the cells and the blood is done directly.
  • The blood vessels are open- ended as they open into the common cavities called the HOEMOCOEL. For example: Insects.
  • The blood does not flow inside the blood vessels, instead it remains filled in the open spaces called SINUSES, so the tissues of the body are virtually floating in the direct contact with the blood.
  • After exchange of materials with the tissues, it enters the HEART which pumps the blood into the blood vessels.
  • This vessel again drains out the blood into sinuses; hence it is kept in CIRCULATION.

CLOSED CIRCULATORY SYSTEM:

  • In mammals there is a closed circulatory system, because the blood during flowing always remains inside the blood vessels and never comes in direct contact with the cells.
  • The materials enter and exit the blood vessels through the walls.
  • The blood flows in the blood vessels under high pressure such that it reaches all the parts of the body in good time.

COMPONENTS OF CLOSED CIRCULATORY SYSTEM:

There are three main components of the closed circulatory system in ma are:

BLOOD: A fluid that can carry all the materials to be transported (blood).

HEART: A pumping organ that can push the fluid through the body.

BLOOD VESSELS: Many tubes through which the fluid can flow through the body.

How arteries, veins and capillaries look like.There are three types of blood vessels:
  • Arteries.                      

  • Veins.

  • Capillaries.

ARTERIES:

  • The blood vessel that carry blood from the heart to various organs are called arteries.
  • They carry oxygenated blood (except pulmonary artery that carries de-oxygenated blood) and lie deep in the body.
  • The colour of fresh blood drawn from the arteries is bright red.
  • When an artery enters in the corresponding organ, it divides up into smaller branches or arterioles which eventually divides in to fine capillaries.
  • The walls of an artery is composed of three layers; an inner layer layer of endothelial cells, a thick middle layer of smooth muscles and elastic fibres, and an outer layer of elastic fibers and connective tissues.

Blood circulation
VEINS:

  • Veins carry deoxygenated blood except for pulmonary vein that carries oxygenated blood from the lungs.
  • The blood drawn from the veins is dark red in colour. 
  • The capillaries join together to form venioles.  
  • The venioles join together to form veins.
     
  • The walls of the veins are not a thick as those of arteries.
     
  • All the veins of the upper body joins, except the pulmonary vein, and form the inferior vena cava.
     
  • The pulmonary veins bring the blood to the heart from the lungs.
  • Thus, the blood vessels that brings the blood to the heart are called the veins. 

CAPILLARIES:

  • These are microscopic vessels where exchange of various substances occurs between blood and the surrounding tissues
  • Each capillary is composed of only a single layer of endothelial cells.
  • Internally, its diameter is slightly larger that of Red Blood Cells.
  • They are connected on one side and venioles on the other side.