Download File - CAPE Biology Unit 1 Haughton XLCR 2013

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With aid of diagrams , describe the structure of the human
heart .
Include annotated diagrams of the internal structure and
external structure of the heart and associated blood vessels
and valves.
Compare the human heart to that of a fish and amphibian
(diagrams required)
Describe the structure and function of the cardiac muscle.
The human heart is a fist-sized, muscular organ that
is hollow. Its job is to pump blood through the
body's network of blood vessels. The heart, blood,
and blood vessels are part of the circulatory
system, which supplies all the body's cells with
the oxygen and nutrients they need, and removes
waste products. The heart has chambers, valves,
arteries, and veins -- and a complex electrical
system keeps everything working smoothly and
makes the heart beat.
Right Atrium: The upper right chamber of the heart.
During the normal cardiac cycle, the right atrium
receives deoxygenated blood from the body
(blood from the head and upper body arrives
through the superior vena cava, while blood from
the legs and lower torso arrives through the
inferior vena cava). Once both atria are full, they
contract, and the deoxygenated blood from the
right atrium flows into the right ventricle through
the open tricuspid valve
Left Atrium: The upper left chamber of the heart.
During the normal cardiac cycle, the left atrium
receives oxygenated blood from the lungs through
the pulmonary veins. Once both atria are full, they
contract, and the oxygenated blood from the left
atrium flows into the left ventricle through the
open mitral valve.
Superior Vena Cava: One of the two main veins
bringing deoxygenated blood from the body to the
heart. Veins from the head and upper body feed
into the superior vena cava,which empties into the
right atrium of the heart.
Inferior Vena Cava: One of the two main veins
bringing deoxygenated blood from the body to the
heart. Veins from the legs and lower torso feed
into the inferior vena cava, which empties into the
right atrium of the heart.
Atrial septum: The wall between the two upper
chambers (the right and left atrium) of the
heart.
Aorta: The central conduit from the heart to the
body, the aorta carries oxygenated blood from the
left ventricle to the various parts of the body as
the left ventricle contracts. Because of the large
pressure produced by the left ventricle, the aorta
is the largest single blood vessel in the body and
is approximately the diameter of the thumb. The
aorta proceeds from the left ventricle of the heart
through the chest and through the abdomen and
ends by dividing into the two common iliac
arteries, which continue to the legs.
Pulmonary veins: The vessels that transport
oxygenated blood from the lungs to the left atrium.
The pulmonary veins are the only veins to carry
oxygenated blood.
Pulmonary Valve: One of the four one-way valves
that keep blood moving properly through the
various chambers of the heart. The pulmonary
valve separates the right ventricle from the
pulmonary artery. As the ventricles contract, it
opens to allow the deoxygenated blood collected
in the right ventricle to flow to the lungs. It closes
as the ventricles relax, preventing blood from
returning to the heart.
Aortic Valve: One of the four one-way valves that
keep blood moving properly through the various
chambers of the heart. The aortic valve, also
called a semi-lunar valve, separates the left
ventricle from the aorta. As the ventricles contract,
it opens to allow the oxygenated blood collected
in the left ventricle to flow throughout the body. It
closes as the ventricles relax, preventing blood
from returning to the heart. Valves on the heart’s
left side need to withstand much higher pressures
than those on the right side. Sometimes they can
wear out and leak or become thick and stiff.
Mitral Value: One of the four one-way valves that
keep blood moving properly through the various
chambers of the heart. The mitral valve separates
the left atrium from the left ventricle. It opens to
allow the oxygenated blood collected in the left
atrium to flow into the left ventricle. It closes as
the left ventricle contracts, preventing blood from
flowing backwards to the left atrium and thereby
forcing it to exit through the aortic valve into the
aorta. The mitral valve has tiny cords attached to
the walls of the ventricles. This helps support the
valve’s small flaps or leaflets.
Tricuspid Valve: One of the four one-way valves
that keep blood moving properly through the
various chambers of the heart. Located between
the right atrium and the right ventricle, the
tricuspid valve is the first valve that blood
encounters as it enters the heart. When open, it
allows the deoxygenated blood collected in the
right atrium to flow into the right ventricle. It closes
as the right ventricle contracts, preventing blood
from flowing backwards to the right atrium,
thereby forcing it to exit through the pulmonary
valve into the pulmonary artery.
Atria: The two upper cardiac chambers that collect
blood entering the heart and send it to the
ventricles. The right atrium receives blood from
the superior vena cava and inferior vena cava.
The left atrium receives blood from the pulmonary
veins. Unlike the ventricles, the atria serve as
collection chambers rather than as primary
pumps, so they are thinner and do not have
valves at their inlets.
Ventricles: The two lower cardiac chambers that
collect blood from the upper chambers (atria) and
pump it out of the heart. Because the ventricles
pump blood away from the heart, they have
thicker walls than the atria so that they can
withstand the associated higher blood pressures.
The right ventricle pumps oxygen-poor blood
through the pulmonary artery and to the lungs.
The left ventricle pumps oxygen-rich blood
through the aorta and to the rest of the body.
The fish heart (figure 1a) is much different than the
amphibian/reptile/bird/mammal heart (figures 1b
and c). Hearts are very complex--they're not just a
bunch of random arteries and veins connecting
tissue. Fish hearts simply draw in deoxygenated
blood in a single atrium, and pump it out through a
ventricle. This system is termed "single
circulation", as blood enters the heart, gets
pumped through the gills and out to the body,
Blood pressure is low for oxygenated blood
leaving the gills.
3 and 4 chambered hearts have a pulmonary circuit
(pathways taking blood from heart to lung and
back to heart) that is very complex and must be
set up such that blood can travel from the heart to
become oxygenated in the lungs and then be
properly pumped back the heart and out to the
body. The 3 (and 4) chambered heart has "double
circulation" (figure 1b and c) and is quite different
from "single circulation" (figure 1a) of fishes.
"Double circulation" has an interior circuit within
the heart--blood enters the heart, leaves the
heart and gets oxygenated, enters the heart
again, and then gets pumped out to the body.
Because "Double circulation" allows oxygenated
blood to be pumped back into the heart before
going out to the body, it pumps blood with much
more pressure and much more vigorously than
"single circulation”
Though the 4 chambered heart has 2 atriumventricle pairs, both pairs do not do the same
thing. There are 4 steps involved with blood
entering the heart: 1) oxygen poor blood enters
the first atrium. 2) oxygen poor blood is fed to
the first ventricle, which pumps it out to the
pulmonary circuit (lungs) where it is enriched in
oxygen. 3) Oxygen rich blood just leaving the
lungs is pumped back into the second atria. 4)
Oxygen rich blood is then fed to the second
ventricle, which pumps the oxygen rich blood
out of the heart and back into the body for
usage.
The 4 chambered heart differs from the 3
chambered heart in that it keeps oxygenated
blood completely separate from de-oxygnated
blood, because there is one ventricle for
deoxgynated blood and one for oxygenated
blood. In the 3 chambered heart, a single
ventricle pumps both out of the heart, and there
is some mixing between fresh and old blood.
The 2 ventricle-4 chamber heart prevents mixing
allows the blood leaving the heart to have far
more oxygen than it would otherwise. This is
good for enhancing the more fast paced lifestyle
that birds and mammals tend to have, giving an
advantage to having a 4 chambered heart.
Function of the Cardiac Muscle: The cardiac
muscle functions with the help of its cardiac cells.
These cells are responsible for the contraction of
this muscle and sending blood to the atria and
ventricles. That in turn, reaches the blood vessels
of the circulatory system.
Cardiac Muscle Fibers: The cardiac muscle is not
linear, unlike the striated or smooth muscles. It
forms instead, a complicated and crisscross
network of muscle fibers, in any direction
possible. The reason is that it performs the
action of squeezing, what is called a bulb.
Take an example of a water balloon being applied
pressure on by a belt in a single direction. What
will happen? Well, some amount of water will
still be retained by the balloon. On the contrary,
if you squeeze the balloon in all directions,
there will be no water left in the balloon.
Similarly, the muscle fibers of the cardiac muscle
comprise a mesh, squeezing the chambers of the
heart, forcing the blood either in lungs or
through the entire body.
Metabolism: Believe it or not, our cardiac muscle
does not ever get tired! Imagine the amount of
pressure we put on it, it still goes on working,
unfettered. The secret to it not being tired lies
in the mitochondria. The mitochondria act as
fuel plants for the cardiac cells. They generate
adenosine triphosphate or ATP, a major source of
chemical energy for the muscle. Furthermore,
lactate is converted into fuel by the cardiac
muscles. This implies that even if the rest of the
body is starved, the heart will always have fuel!
This is one of the most striking aspects of the
cardiac muscle function.
Electro Chemical System of the Muscle: If the
heart has to function properly, the cardiac
muscle needs a special electrical system for
sending the correct signals to the corresponding
muscle at the appropriate time. This then means
that without a delay between the atrium and the
ventricles for ensuring that all the blood is
pumped out of the heart, it cannot happen.
To facilitate this, the heart has sinoatrial node (SA
node) for directing the electrical impulses to the
right area of the heart at the right time. In
addition to this, the SA node also maintains a
tension on the muscles all the time. This helps in
maintaining of blood pressure and keeps it ready
for the next contraction
T-Tubules: Interestingly , there are pathways for
electrical stimulation to reach and activate the
muscle. These are called transverse tubules and
even though there are fewer of these in the
cardiac muscle, they are broader and larger. This
facilitates better signal and activation of the
muscle.