Circulatory System
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Circulatory System
What is the Circulatory System?
Blood transports various substances from one part of the
body to another by continuous flowing through a closed system of blood vessels
known as the circulatory system. The blood flow is known as blood circulation.
Blood is moving by means of an organ known as the heart, which is a muscular
pump that draws blood in when it relaxes and pushes it out at great force when
it contracts. Circulation is begins at early fetal life and it is estimated that
a given portion of blood would take 30 seconds to complete one course of
circulation around the body. An average of 5 liters of blood is traveling by
means of the circulatory system at any one given point in time.
There are three distinct parts of the circulatory system :
Pulmonary Circulation
Pulmonary circulation is the movement of blood from the
heart to the lungs and back to the heart again. The veins bring waste-rich blood
excreted from bodily processes such as cellular respiration to the heart. It
enters the right atrium through two large veins - the superior vena cava (common
anterior) and the inferior vena cava (posterior).
Deoxygenated blood from the upper body, the head, neck
and arms is returned to the right atrium by means of the superior vena cava.
Deoxygenated blood from the rest of the body is brought back by the inferior
vena cava. When the right ventricle is filled with deoxygenated blood, it
contracts, pushing the blood through a one-way valve into the right ventricle.
This valve is known as the tricuspid valve, consisting of three muscular flaps.
These flaps are attached to the wall by muscle tendons called chordae tendineae.
These flaps point downwards hence allowing only a uni-directional flow of the
blood downwards from the atrium to the ventricle. When the right ventricle
contracts, pressure from the blood closes the flaps. This prevents a backflow of
blood back into the atrium. The flaps are prevented from being reverted in the
opposite direction by the chordae tendineae when the right ventricle contracts.
The blood now leaves the right ventricle by the pulmonary arch.
Through this, the blood leaves the heart and divides
into the two pulmonary arteries, each leading to one lung. In the lung
capillaries, the exchange of carbon dioxide and oxygen takes place.
Oxygenated blood from the lungs is brought back by way
of the pulmonary veins re-entering through the left atrium. The oxygen-rich
blood passes through a one-way valve known as the bicuspid or mitral valve. It
is similar to the tricuspid valve except for the fact that it has two flaps
instead of three. When the left ventricle contracts, it will exit the heart
through the aortic arch. The aortic arch is a U-shaped tube curved upwards.
Semi-lunar valves prevent backflow of blood back to the left ventricle. Blood
enters the aortic arch at high pressure, hence giving it enough force to
circulate around the body and pushing streams of blood in front.
The right ventricle has considerably thinner walls than
the left ventricle this gives the blood sufficient time for the diffusion of
gases (gaseous exchange) that occurs in the lungs.
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Coronary Circulation
Coronary circulation is the means by which the heart
tissues are themselves supplied with nutrients and oxygen free from waste
products of the body. There are 2 coronary arteries branching out from the
aortic arch. Myocardial blood supply is from the right and left coronary
arteries, running over the surface of the heart giving braches to the
endocardium. The right coronary artery follows the coronary sulcus around the
heart and branches off into the marginal branch which extends along the right
border. The left coronary artery splits into two major braches. The circumflex
branch goes to the left around the coronary sulcus. The anterior
inter-ventricular branch goes around the pulmonary trunk and runs along the
surface of the inter-ventricular sulcus. The blood is then passed onto the
coronary capillaries when the exchange of substances occurs. This intricate
network of blood vessels enables the arteries to provide a relatively constant
flow of blood to the cardiac muscles of the heart. These connections are known
as anastomoses.
The great and middle cardiac veins carry blood away from
the coronary capillaries. The blood is then drained into the coronary sinus and
eventually sent back to the right atrium.
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Systemic Circulation
Systemic circulation supplies nourishment to all of the
other tissues located throughout your body. It plays an integral role in the
overall circulatory system. The arteries carry oxygenated blood away from
the heart leaving through the aortic arch. It branches out to form smaller
arteries that run throughout the body. The internal layer of an artery is smooth
allowing blood to flow quickly while the outer layer is strong to withstand the
great pressure of the blood flow from the heart.
These smaller arteries will branch out again into
capillaries where the exchange of substances occur and oxygen and nutrients from
the blood are released. The endothelium, a selectively permeable membrane of
single layer cells is found in the capillaries allowing for faster diffusion and
transfer. The great number of branches is to increase the cross-sectional
surface area of the tissues. This also helps to lower the blood pressure in the
capillaries where the flow of blood is slowed out to give more time for the
exchange of substances.
During the systemic circulation blood is passed through the kidneys. This phrase
is known as renal circulation where the kidneys filter much of the waste from
the blood. Blood also passes through the small intestines through the portal
circulation where it is passed through the liver and the sugars filtered stored
for use later. The remaining blood will be returned to the heart by the
veins.
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