00:00
Now, first of all,
let’s just try and understand the structure
of the heart. On the right-hand side, you
can see a diagram. This is a diagram explaining
the internal structure of the heart as if
you are looking at a person standing in front
of you. So, look at this slide and just try
to identify, firstly, the left atrium and the
left ventricle, both towards the right-hand
side of this slide. Once you’ve identified
those two chambers of the heart, then move
towards the other side and identify the right
atrium and the right ventricle. Having done
that, you’ll then identify the four chambers
of the heart, which I’ll describe in a moment.
00:55
But then look and see where the aorta lies.
It’s labeled red, and also underneath that
aorta is a blue colored structure. That’s the
pulmonary trunk. They are important structures
that I’ll deal within a moment. Now, try and identify the
SA node or the sinoatrial node, and you can
see very pale lines running from that node
extending into the right atrium and the
left atrium. They’re going to represent part
of the conducting system I’m going to refer
later. And finally, look at the blue circular
structure towards the center of the heart,
towards the center of the diagram. That’s
called the atrioventricular node, and that
initiates also conduction of impulses into
the ventricles. And those impulses travel
through certain bundles that are shown there
in blue. And I’ll again refer to this later on.
02:02
So that is really just to orientate yourself
with this diagram, so you can have some clear
understanding of the structures we’re going
to talk about later on. There are two sorts
of circulation. Firstly, there is a pulmonary
circulation. This is the circulation whereby
the heart receives blood from the rest of
the body and then pumps that blood to the
lungs. It’s the deoxygenated blood. It then
passes through the lung and becomes oxygenated.
02:39
And then it’s returned back to the heart,
to the left side of the heart, where that
oxygenated blood is finally pumped from the
heart to the rest of the body. The pulmonary
circulation just refers to that circulation
of blood to and from the lungs, whereas, the
systemic circulation refers to the circulation
of blood to all the organs of the body from
the left side of the heart. There is also
portal system components in the cardiovascular
system. These are very strange diversions
from the typical supply of blood to blood
to tissues. And again, I won’t mention them
here except to label them on the left hand
side to remind us that there are these different
systems, particularly in the liver, and particularly
later on when we look at the pituitary gland
as part of the endocrine system. Now, I just
want to make sure that we are aware of how
blood flows through the heart. So on this
diagram, again, refresh your memory of the
chambers, and I will just briefly go through
how blood flows through the heart. First of all,
blood passes back to the heart from systemic
tissues and enters either through the superior
vena cava which is labeled 1 here or via the
inferior vena cava which is not labeled or
shown in this diagram. But the essential idea
is that blood passes through these two vena
cava into the right atrium, labeled here
2. And that right atrium then pumps that blood
into the right ventricle through a valve.
04:47
And that right ventricle then contracts and
sends all that blood through the pulmonary
trunk to the lungs, where, as I mentioned
before, it becomes oxygenated. And that blood
then returns nearly oxygenated into the left
atrium, where it passes from the left atrium
directly into the left ventricle of the heart,
and the left ventricle contracts and passes
blood out through the aorta to the rest of
the body. So that’s the sequence of blood
flow through the heart. Remind yourself of
the physiology of the heart and the pumping
of the heart, the atria contracting together,
and the ventricles contracting together.