Download Anatomy #01 د.محمد الحيدري 15-3

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‫‪Anatomy‬‬
‫‪#01‬‬
‫د‪.‬محمد الحيدري‬
‫‪15-3-2016‬‬
‫ثائر شحادة وسعد العيطان‬
Today we will start describing the cardiovascular system structurally. As we know
by now, this system is a completely closed system, composed of a pumping station
(the heart) of specialized muscle.
Recall that we have 3 types of
muscles in our body:
1- skeletal (motor control)
2- smooth (autonomic control)
3- cardiac (autonomic control)
From this pumping station, vessels arise to distribute the
blood to different regions of the body by a special
circulation called the “systemic circulation”. Another
smaller circulation aiming at oxygenating the blood after
the consumption of oxygen in different types of tissues in the body is called the
“pulmonary circulation”.
The right atrium of the heart will receive deoxygenated blood from the body via
vena cava and it is passed to the right ventricle which
pumps blood to the pulmonary circulation to be oxygenated,
and the left atrium of the heart will receive oxygenated
blood from the lungs and it passes to the left ventricle to be
pumped outside the heart to the systemic circulation.
So a general rule is: any vessel approaching the heart is
called a vein. Any vessel leaving the heart is called an
artery, Regardless if it was oxygenated or not.
e.g: - The aorta leaves the heart (oxygenated) Artery
Blood flow in the heart
- Pulmonary trunk leaves the heart (deoxygenated) Artery
The whole cardiac muscle with its great vessels are located in the chest region in a
position behind the sternum (retrosternal position). In clinical examination, we are
going to see certain landmarks on the chest of a person and use
them to examine the dimension or certain sounds of the heart.
What is a sternum?...
It’s a part of the axial skeleton, and it has 3 parts:
- manubrium - body - xyphoid process
So behind the sternum we have the whole heart with its coverings.
Sternum
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In the thoracic cavity, the major organs present are the
lungs and the heart with the attached structures to them.
In between the 2 lungs there is a space (imaginary
space) called the mediastinum. And of course, this
space has limits and boundaries.
You may be asking, “How can we examine patients
according to landmarks?”
Well, let’s take the thoracic cage for example. The
sternum is the central portion that receives cartilage
costal attachments from the ribs. How many ribs are
directly attached to the sternum? About 6
The ribs below these 6 are connected indirectly as they
all merge into one subcostal cartilage. And we also
have the last remaining floating ribs that are not
attached to the sternum at all. (see the figure)
Note: you can’t feel the 1st rib
because it is located behind the
clavicle
So assume you want to hear someone’s heart with a stethoscope. You need to
locate the best intercostal space to put your stethoscope on. We know that we have
6 ribs connected directly, but how can we feel them and count them?
We can feel the junction between the body and the manubrium (sternal angle). At
this angle that we could feel, the 2nd costal cartilage articulates, meaning that this is
the 2nd rib. This means what’s above this rib is the 1st intercostal space, below it is
the 2nd intercostal space.
Let’s look at these 2 diagrams for the
mediastinum.
If we take a straight line from the sternal angle to
the vertebral column, we are going to approach the
intervertebral disk between T4-T5. And if we take
another straight line from vertebra T1 to the
jugular notch (at the tip of manubrium superiorly),
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this will mark an oblique line above the thoracic cavity. This will mark a space
which is called the mediastinum.
We know that the diaphragm is a curved muscle sheath that comes from several
attachments. In this sagittal section we can see that the diaphragm comes from the
lower part of the sternum (Xiphisternal junction) and curves backward into a
deeper attachment to the 1st and 2nd lumber vertebrae.
Okay let’s break this diagram into pieces:
The mediastinum!
The lowest point is the diaphragm
The highest point is the oblique line
The line from the sternal angle to T4-T5
divides the mediastinum to superior and
inferior parts.
Inferior: from straight line to diaphragm
Superior: from straight line to oblique line
The Superior mediastinum receives mainly
the great vessels emerging from the heart
Inferior mediastinum is larger and occupies
the heart and pericardium.
let’s talk about the inferior mediastinum now cause it’s waaay more interesting
than the lame superior one.
The inferior mediastinum is subdivided into 3 regions:
Anterior
mediastinum
Slightly deep
Smallest in volume
internal thoracic
(internal mammary)
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Middle
mediastinum
Not deep
largest in volume
Heart and
pericardium
Posterior mediastinum
deepest
large in volume
Descending aorta
So now we have subdivided the mediastinum into 4 regions:
One above the horizontal line
One below the horizontal line (3 parts (anterior, middle, posterior))
The whole heart, like any visceral structure in the body, is surrounded by a serous
membrane for protection. Of course, the lungs also have a protective covering
called the pleura, GIT (stomach to rectum part of it) is surrounded by the
Peritoneum (some parts are not). The one that surrounds the heart is called the
Pericardium.
But, what exactly is this serous membrane?
It is a covering composed of 2 layers, the visceral layer (against the viscera) and
the parietal layer (against the outside).
In between these 2 membranes is a
small space filled with a fluid named
after the name of the membrane (pleural
fluid for lungs, peritoneal fluid for
GIT). So it is called the pericardial fluid
for the heart. This fluid will help in the
movement and minimizes the friction to
protect the heart.
Now let’s make something clear. All these visceral organs in the body have these 2
membranes, but the heart has an extra outer layer (membrane) called fibrous
pericardium. It is tougher than the parietal and visceral membranes and is located
on the outer portion of the heart to protect and limit the expansion of the heart (so
that the heart doesn’t blow up or burst from the pressure inside it).
The fibrous pericardium is attached inferiorly to
the diaphragm, but how is it attached and why?
Well, let’s explain what the diaphragm is first.
The diaphragm is a flat sheet of muscle which is a
muscle of respiration. It acts during respiration by
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If we want to blow a balloon, we
Know it has a thin elastic wall. If you
continue to blow it, it will blow up.
But if you put the balloon in a paper
bag and blow it, it will no.
It will limit itself and you’ll reach a
stage where you can’t blow it
anymore; this is how fibrous
pericardium acts. The balloon is the
heart, and the paper bag is the
fibrous pericardium
contraction and relaxation. It also separates the thoracic and abdominal cavities.
What is it made of? Is it all made of flesh (muscles tissue)?
Nooo, we have a central tendon in the center of it (C shaped) which is not a muscle
tissue, it is a tendinous structure.
Tendinous structures are not a contractile tissue, so if you are running or
performing exercise, the diaphragm moves up and down rapidly for respiration.
But what exactly goes up and down? Only the
fleshy part!! Okay? The tendinous part does
not move up and down or it could at least
slightly move.
So the tendinous part will be fixed.
Now let’s go back to our first question, how is
the fibrous pericardium attached to the
diaphragm? Via the central tendon
Why? To fix the heart in its place and prevent
it from moving up and down.
But, what is the upper attachment for the
fibrous pericardium to fix the heart in its place?
The superior attachment will be to the roots of the great vessels, the “ascending
aorta” and the “pulmonary trunk” to their adventitia (outer layer of the vessel).
THE END
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