Blood and the Circulatory System

 Objectives   Describe the functions of components of the blood and name the different blood vessels.   Explain how red blood cells are adapted to their function and describe the role of arteries, veins and capillaries in the transport of blood.

The Circulatory System  The circulatory system consists of the heart, arteries, veins capillaries and blood.  Arteries transport blood away from the heart.  Veins transport blood towards the heart.  Capillaries join arteries to veins, materials such as oxygen are exchanges between capillaries and body tissue.

Red Blood Cells  These cells transport oxygen around the body. They contain haemoglobin which oxygen joins to become oxyhaemoglobin.  Red blood cells have no nucleus, this means they can carry more oxygen.  They are disc shaped, this means there is more surface area for oxygen to move in and out. They are small so they can get to all parts of the body.

White Blood Cells These cells destroy microbes. They wrap around microbes and engulf them. They are small cells so that they can squeeze through capillary walls to reach microbes.

Plasma Liquid in the blood to transport dissolved substances such as, water, hormones, antibodies and waste around the body.

Blood Vessels There are three types of blood vessels:  Arteries go away from the heart.  Veins go towards the heart.  Capillaries join the arteries to the veins.  Substances (oxygen and glucose) are exchanged between capillaries and the body tissue. These are very small blood vessels. The beating of the heart squeezes the blood through blood vessels called arteries.

Adaptations of Blood Vessels Arteries  They have a thick muscular and elastic wall to help it withstand high blood pressure as blood leaves the heart. Veins  They have a large lumen to help blood flow at low pressure. Valves stop blood flowing the wrong way. Capillaries  They have thin, permeable walls to allow exchange of material with body tissue.