Cardiovascular System

      Like the other mammals, primates have a four-chambered heart and a double-

circuit circulatory system and are able to maintain a constant body temperature.

The insulating covering is provided by hair, although in the humans nearly all the

hair is lost, and insulation is now provided by clothing. The cardiovascular system

functions to supply the tissues with oxygen and nutrients by circulating blood

throughout the body. At the same time it removes carbon dioxide and other

metabolic wastes.  The waste products and carbon dioxide move into the blood to

be carried away. The process of the circulation of blood is necessary for continued

life of the cells, tissues, and ultimately the whole organism.


      The heart is made of cardiac muscle, and this is a special type of muscle,

because it adjusts the rate of muscular contraction, letting the heart regulate a

normal pumping rhythm. The parts of the heart include the chambers, the valves,

and the electrical nodes.

Heart Chambers 

     There are two different types of heart chambers.  First is the atrium which

receives blood that returns to the heart through the veins. The right atruium pumps

blood to the right ventricle, and the left atrium pumps blood into the tleft ventricle.

The blood is then pumpted from the atrium into the second chamber that is known

as the ventricle.  The ventricles are larger than the atria and are thicker, muscular

walls that are used for aggressively pumping the blood from the heart to the body

and lungs.


         The valves which are located within the the heart are placed between the atria

and ventricle, and between the ventricles and major arteries. These valves are

opened and closed by changes of pressure inside the chambers they function as a

barrier to prevent backflow of blood.  The vibrations caused by the closing of the

respective valves are what create the "lub-dub, lub-dub" heart sounds that are

heard through a stethoscope.

Electrical Nodes

        There are two different electrical nodes that are located in the cardiac tissue.

The first is the SA, or sinotrial node, which is more commonly called the

pacemaker. The pacemaker is located in the wall of the right atrium. It is a small

patch of tissue that goes through rhythmic excitation.  The impulse rapidly

spreads through the atria which causes a muscular contraction and pumping of

blood from the atria to the ventricles.  The atrioventricular node, or AV, is the

other node which relays the impulse of the SA node to the ventricles like a

message.  The cycle of contraction of heart muscle is also known as the heartbeat.


        A vessel is a hollow tube for transportin something. A blood vessel is a hollow

tube that transports blood. There are three main types of blood vessels:

  • Arteries
  • Capillaries
  • Veins

The role of these blood vessels is to transpost blood through the entire body and

exchange oxygen and nutrients for carbon dioxide and wastes.


        The arteries are what carry blood away from the heart and are under high

pressure because of the the pumping of the heart. In order for them to maintain

structure, they have thick, elastic walls to allow stretch and recoil.  The large

pulmonary artery carries unoxygenated blood from the right ventricles to the

lungs where it releases carbon dioxide and receives oxygen. The largest artery

though is the aorta. It carries oxygenated blood from the left ventricle to the

body. The arteries branch and eventually lead to capillary beds.


        The capillaries are what make up networks of tiny vessels that have extremely

thin, highly permeable walls.  They are present in every major tissue of the body

and have a role in the exchange of gases, nutrients, and fluids between the blood,

body tissues, and alveoli of the lungs.


         On the opposite end of the capillary beds they merge to create veins which

return the blood back to the heart. The veins are under a lot less pressure than

what the arteries are, and therefore have much thinner walls.  The veins contain

one-way valves so it may prevent the blood from flowing the wrong direction in

the absence of pressure.  The pulmonary vein brings back oxygenated blood from

the lungs to the left atria.  The vena cava returns blood from the body to the right

atria.  The blood that is returned to the heart is then recycled through the

cardiovascular system.