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The heart. The beating within your chest
every second of
your life. Sometimes
slower, sometimes faster. Let's say you're up north at the cottage,
relaxing on the dock, soaking up the sun. It's probably not beating too
quickly.
But what if at the cottage out of the trees
there appears a bear. Well your heart will undoubtedly go from its resting
state of around 70 beats per minute
to more than three times that. The heart is an amazing organ.
It is dynamic and it can use a ton of different fuel sources
and it can adaptively grow in size. One thing is for sure though,
it is constantly working the pump blood throughout your body
and get oxygen and nutrients to the tissues. So in this video
we'll be talking about the heart. We will be looking at why we need the heart,
what it does, its overall goals. We'll also be looking at the anatomy of the heart
from the inside and the outside. To start, what is the heart?
Well it's a muscular organ and it's found in the
anterior portion of the chest wall. It's not positioned
exactly in the center of the body either. It's
slightly rotated to the left and it's also found slightly left
of the midline of the body. Let's discuss the borders of the heart
On the top or the superior border
you'll find the base. On the bottom left
or where the inferior border meets the left border
is where the apex is found. This seems opposite to what you might initially think
so don't get confused. Now I mentioned borders.
The base forms the superior border as I said.
The right border is formed by the right atrium.
The left border is formed by the left ventricle
as well as the left atrium and finally
the inferior border is formed mainly by the inferior portion
the right ventricle. A typical adult heart
is about 12 to 13 centimeters long extending from the apex
to the base. Normally
its weight is around 300 grams ranging
from 250 to 350 grams depending on gender.
As I had mentioned before, the heart is rotated to left and sits slightly to the left of
the midline.
The apex of the heart is found usually between the 5th and 6th
costal cartilages, about 7 or 8 centimeters
to the left at the midline. The heart is comprised of
three different layers. The first
is the epicardium. The second is the myocardium.
And the third is the endocardium.
The most external
or superficial layer the heart is the epicardium. Actually
it is also known as the visceral pericardium. It is a serous membrane
that forms the inner part the pericardial sac which is a fluid-filled
double membrane
that surrounds the heart. The epicardium
is directly attached to the middle layer of the heart which is known as the
myocardium.
The myocardium is the muscular layer of the heart.
It is formed of layers and layers of cardiac muscle cells
otherwise known as cardiomyocytes. The myocardium makes up the atria
and the ventricles and it's responsible for the contraction of the heart
during a heartbeat. Finally
the endocardium is the deepest layer of the heart. It covers the inner surfaces
of the chambers
as well as the heart valves. Alright,
we have looked at some of the external anatomy of the heart
now let's take a look at what's on the inside.
So, here is a frontal section the heart and we're looking at it from an anterior
view.
There are four chambers of the heart the right atrium,
the right ventricle, the left atrium,
and the left ventricle.
Between the chambers we have valves
on the right side of the heart as the tricuspid valve otherwise known as
the right
atrioventricular valve. On the left side we have the bicuspid valve
or the left atrioventricular valve. Now
the heart is pretty complicated one way to remember the names of these two
valves is to think about buying a car.
If you think about the way blood flows in the body
it returns through the venous system to the right atrium and into the right
ventricle
via the tricuspid valve. Then it goes to the lungs
and comes back to the heart to the left atrium and into the left ventricle
via the bicuspid valve. The blood is then pumped into the aorta
and into the system. So, to remember the names of the valves
as I said before think about it like a car. Before you buy a car
you have to test it out or try it out. So,
you tri before you bi. These aren't the only valves in the heart.
There are two other valves as well that lead away from the actual heart itself.
The first is the pulmonary valve which opens
and leads into the pulmonary trunk. We'll get more into the functions of this
later
but right now we will just cover the anatomy. The other valve
is the aortic valve and, as the name suggests, blood passing through this
valve
enters the aorta. So,
coming back to the heart, let's take a look once again at the ventricles.
Notice a difference between the right and the left? The left ventricular muscle
is much thicker than the right. Why would this be? The
answer is that there is a much greater force
needed to push the blood from the left ventricle to the aorta
rather than from the right ventricle to the pulmonary trunk.
In order for the pulmonary and aortic valves to open and allow blood out
there must be a greater pressure within the ventricle
then there is in the following vessel. For example,
in order for the blood to move from the left ventricle
into the aorta, pressure within the ventricle
has to exceed the pressure in the aorta. This is done
by ventricular contraction. The pressure in the aorta
is called the afterload. So the left ventricular myocardium
is very thick so that it can contract forcefully
and create greater pressure than the afterload allowing the blood to be pushed into the
aorta.
Alright, so we've looked at some of the basic anatomy of the heart.
Now let's focus on how the blood moves in and out of the heart.
Blood coming back to the heart comes through veins.
The blood in the veins has already perfused through the tissues
and has unloaded its oxygen. So the blood coming back to the right side of the
heart
is called deoxygenated blood. It is generally a darker color of red than
oxygenated blood. All of the veins draining to the heart
eventually lead to the superior and inferior vena cava.
These large veins drain into the right atrium.
As I mentioned before the blood in the right atrium
then moves through the tricuspid valve into the right ventricle.
After contraction of the right ventricle,
the blood is then moved into the pulmonary trunk, through the pulmonary
arteries
to the lungs. It is here where the deoxygenated blood
picks up oxygen that we breathe in. The newly oxygenated blood
then travels back to the heart through the pulmonary veins
and reaches the left atrium. After left
atrial contraction, the blood moves through the bicuspid valve
into the thick, strong left ventricle. Contraction of the left ventricle
then causes the aortic valve to open where the blood is pushed
into the aorta. From here
the oxygenated blood. Then is delivered throughout the body
to reach all of the different tissues including organs,
bones, skeletal muscles, and other tissues.
This is represented in the following diagram.
So in summary, the heart is an extremely important organ
and has to work very hard every second of our lives.
It is dynamic and can adapt to changes very quickly.