Download What is the Circulatory System and What Does It Do? The circulatory

What is the Circulatory System and What Does It Do?
The circulatory system is like a circular network of roads on which traffic travels in only
one direction. Every part of the body is connected through the network of blood vessels
making up the circulatory system. The blood flowing in these vessels is composed of blood
cells floating in a fluid called plasma.
Red blood cells possess a chemical called hemoglobin, which is responsible for carrying
oxygen from the lungs to the individual cells of the body. Why do cells need oxygen? In
return, the hemoglobin trades its oxygen for carbon dioxide, a waste product of the cell,
and carries it back on its circular route to the lungs to be expelled.
The fluid portion of the blood, the plasma, is responsible for carrying all other
nutrients (water, electrolytes, food, etc.) to the cells and in return, removing wastes. The
plasma also carries chemical messengers, such as hormones, from the cells that produce and
store the chemical messenger to the cells that it affects.
The circulatory system also acts as a cooling and heating system to maintain body
temperature. Also, the circulatory system helps to maintain a balance of electrolytes and
water between the cells and their environment.
Anatomy of the Circulatory System
The circulatory system is made up of miles and miles of blood vessels, branching from the
large superhighways of the major arteries and veins that come off the heart, to smaller
highways that supply individual organs. Blood only travels in one direction along these vessels
and so makes a circular trip through the body. Vessels carrying blood away from the heart
are called arteries; vessels carrying blood to the heart are called veins.
Inside organs, the vessels continue to branch into smaller and smaller vessels. The smallest
of these vessels are called capillaries. Just as many apartment buildings have back roads or
alleys connecting them to main roads, the capillaries provide individual cells access to the
bloodstream. The capillary walls are so thin that nutrients can easily pass from the blood to
adjacent cells. Likewise, products manufactured by the cell can also pass through the
capillary wall and travel to other parts of the body where they are needed. The cell's waste
products can also pass from the cell into the capillaries and travel to the lungs, skin,
kidneys, and other organs, that specialize in removing waste, to be expelled.
Anatomy of the Human Heart
Blood is kept moving along its circular route by the pumping action of the heart. The heart
consists of four chambers. The upper two chambers are the right and left atria. The right
and left atria are thin-walled sacs, which receive blood from the body and the lungs,
respectively. In both atria the upper half of their inside wall is smooth and forms the
sinuses of the great veins that empty into it. The lower half of the inside surfaces of the
atria is very rough.
The lower two chambers of the heart are the right and left ventricles. The ventricles
have thick walls made up of cardiac muscle. Cardiac muscle is also present in the walls of the
atria. This specialized type of muscle tissue is found only in the heart; its fibers branch in
such a way that when they all contract, they squeeze the heart chamber and force blood out
of it. The inner surfaces of both ventricles are covered with ridges called trabeculae.
Irregular muscle bundles called papillary muscles give rise to chords which anchor the heart
valves. Both the trabeculae and the papillary muscles make the inside walls of the ventricles
very rough.
In humans, the chambers of the atria are joined to their adjacent ventricles by valves.
The tricuspid valve lies between the right atrium and right ventricle and the bicuspid valve
lies between the left atrium and left ventricle. There are also valves between the
ventricular chambers and the great arteries which they feed. The pulmonary valve lies
between the right ventricle and the pulmonary artery. The aortic valve lies between the left
ventricle and the aorta. The valves prevent blood from being forced back into the chamber
from which it was expelled, and thus keep the blood flowing in one direction.
The right atrium and ventricle receive oxygen-poor blood from the body and send it to
the lungs; they are therefore considered the pulmonary side of the heart. The left atrium
and ventricle receive oxygenated blood from the lungs and pump it back into the body; they
are therefore considered the systemic side of the heart.
The pacemaker of the heart (SA node) is located in the upper right atrium near the
opening of the vena cava. The pacemaker sets the normal rhythmic beat of the heart by
coordinating the contractions of the heart chambers. The pacemaker first sends a signal
along specialized cardiac muscle fibers in the walls of both atria to make them contract
simultaneously. The signals then converge on another bundle of specialized cardiac muscle
fibers, the atrioventricular node (AV node) located in the wall separating the two ventricles.
The AV node sends the signal on to the walls of the ventricles to make them contract
simultaneously.
Pulmonary Side of the Heart:
Blood (low in oxygen and high in carbon dioxide) enters the right atrium from the superior
and inferior vena cava. The superior vena cava is the large vein that returns blood to
the heart from the upper half of the body and the inferior vena cava is the large
vein that returns blood to the heart from the lower half of the body.
At this point the tricuspid valve, the valve separating the right atrium from the right
ventricle, is open and blood begins to fill the right ventricle. The right atrium
contracts to force the rest of the blood into the right ventricle.
When the right ventricle is full and begins to contract, the tricuspid valve is forced shut.
(lub)
The right ventricle contracts and pumps the blood through the pulmonary artery to the
lungs. When the right ventricle relaxes, the blood in the pulmonary artery forces
the pulmonary valve shut. (dub)
In the lungs, the blood from the body trades its carbon dioxide for oxygen.
Systemic Side of the Heart:
Now rich in oxygen, the blood returns from the lungs to the left atrium of the heart via
the pulmonary veins.
The oxygen rich blood fills the left ventricle. The left atrium contracts to force the rest
of the blood into the left ventricle.
When the left ventricle is full and begins to contract, the bicuspid valve is forced shut.
(lub)
The left ventricle contracts and pumps the blood through the aortic valve into the aorta.
The aorta is the main artery supplying oxygen-rich blood to the body. When the left
ventricle relaxes, the blood in the aorta forces the aortic valve shut. (dub)
The right and left atria contract at the same time. The tricuspid and bicuspid valves shut at
the same time creating the "lub" sound. The right and left ventricles contract at the same
time. And the pulmonary and aortic valves shut at the same time creating the "dub" sound.
Like the human heart, the chicken heart has four chambers - a right atrium and ventricle
which receives deoxygenated blood from the body and sends it to the lungs and a left
atrium and ventricle which receives oxygenated blood from the lungs and sends it to the
body.
Birds have a much higher metabolic rate than humans. The average body temperature of
a chicken is 41-45 degrees C, compared to a human's average body temperature of 37
degrees C. The pulse rate of a chicken can reach as high as 400 beats/min. All of these
factors place a great demand on the chicken's heart which has to work much harder than a
human heart.
The chicken's heart is adapted to handle the increased stress placed on it by its high
metabolic rate. The size of the heart in relation to body mass is larger in birds (about 0.8%)
than in mammals (about 0.6%). The inside walls of the atria and ventricles are much
smoother than those of the human. And the valves, though present, are much simpler. The
smoother walls and simpler valves of the bird's heart reduces friction as the blood is
pumped through; less friction means less work.
The ventricles of the bird heart have more muscle mass and less chamber space than
those of a human. Externally, the ventricles appear more slender and pointed than in a
human heart.
Heart Development in the Chicken.