The main components of cardiovascular systems

HEART

The heart plays a vital role in the body because it is thepump that drives the cardiovascular system.

The main parts of the heart :

The chambers 

There are two different types of heart chambers :

The atrium ( plural is atria ), which receives bloodreturning to the heart through the veins. The right atrium pumps blood to theright ventricle, and the left atrium pumps blood into the left ventricle. Thisblood is then pumped from the atrium into the second chamber called theventricle.

The ventricles are much larger than the atria and theirthick, muscular walls are used to forcefully pump the blood from the heart tothe body and lungs.

The valves

The valves found within the heart are situated between theatria and ventricles, and also between the ventricles and major arteries. Thesevalves are opened and closed by pressure changes within the chambers, and actas a barrier to prevent the backflow of blood. The characteristic "lub-dub, lub-dub"heart sounds heard through a stethoscope are the result of vibrations caused bythe closing of the respective valves.

The electrical Nodes

There are two different electrical nodes, or groups ofspecialized cells, located in the cardiac tissue ;

The sinoatrial ( SA ) node, commonly called the pacemaker.The pacemaker is embedded in the wall of the right atrium. This small patch oftissue experiences rhythmic excitation and the impulse rapidly spreadsthroughout the atria, causing a muscular contraction and the pumping of bloodfrom the atria to the ventricles.

The atrioventricular ( AV ) node, relays the impulse of theSA node to the ventricles. It delays the impulse to prevent the ventricles fromcontracting at the same time as the atria, thus giving them time to fill withblood.

The cycle of contraction of the heart muscle is called aheartbeat, the rate of which varies greatly between organisms.

BLOOD VESSELS

A vessel is a hollow tube for transporting something, like agarden hose transporting water. A blood vessel is a hollow tube fortransporting blood. These main blood vessels function to transport bloodthrough the entire body and exchange oxygen and nutrients for carbon dioxideand wastes.

There are three main types of blood vessels:

Arteries

The arteries carryblood away from the heart, and are under high pressure from the pumping of theheart. To maintain their structure under this pressure, they have thick,elastic walls to allow stretch and recoil. The arteries branch and eventuallylead to capillary beds. The types of artery :

The large pulmonary artery carries unoxygenated blood fromthe right ventricles to the lung, where it gives off carbon dioxide andreceives oxygen.

The aorta is the largest artery. It carries oxygenated bloodfrom the left ventricle to the body.

Capillaries

The capillaries makeup a network of tiny vessels with extremely thin, highly permeable walls. Theyare present in all of the major tissues of the body and function in theexchange of gases, nutrients, and fluids between the blood, body tissues andalveoli of the lungs.

Veins

At the opposite side of the capillary beds, the capillariesmerge to form veins, which return the blood back to theheart. The veins are under much less pressure than the arteries and thereforehave much thinner walls. The veins also contain one-way valves in order toprevent the blood from flowing the wrong direction in the absence of pressure. 

The types of vein :

The pulmonary vein returns oxygenated blood from the lungsto the left atria.

The vena cava returns blood from the body to the rightatria. The blood that is returned to the heart is then recycled through thecardiovascular system.

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