Blood Vascular System

The blood and lymphatic vascular systems are classified as specialized connective tissue.

The main functions of the blood are to transport oxygen, nutrients and hormones to the tissues and to collect the waste products (carbon dioxide and waste metabolites) for removal from the body via the excretory system.

The cardiovascular system consists of the:

• Heart (muscular pump)
  
• Pulmonary circulation (system of blood vessels to and from the lungs)
  
• Systemic circulation (system of blood vessels bringing blood to and from all the other organs of the body).
  
• Arteries are classified into two main groups:
  
• Conducting (Elastic Arteries).
  
• These are large arteries closest to the heart (aorta, renal artery) with very high blood pressure and flow (320mm/sec in the aorta).
  

Distributing (Muscular Arteries).
These are smaller diameter arteries with a slower blood flow.

The arteries lead to smaller vessels, the arterioles, which lead to the capillaries. The capillaries are present in the form of microcirculation networks (capillary beds) in the organs and tissues. Exchange of metabolites and transport through the vessel wall is only possible in the capillaries, as only here the blood flow is sufficiently reduced (about 0.3mm/sec) and the vessel wall sufficiently thin.

On the return route to the heart the blood flows in venules, small veins and large veins.

Arterial blood in the Systemic Circulation is richly oxygenated, whereas the venous blood has little oxygen. In the Pulmonary Circulation the arterial blood is poorly oxygenated, whereas the venous blood, are highly oxygenated (having replenished its oxygen supplies in the lungs).