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Summary Human Anatomy and Physiology
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Human Anatomy and Physiology
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HAP1 Monday, 6 September 2021Anatomy of the Heart
POSITION OF THE HEART
The sternum is bone which protects your heart. The
sternum consists of three parts, the manubrium, body and xiphoid process (top to bottom)
The connection between the manubrium and the corpus is called the sternal angle. The
position of the heart begins at a sternal angle.
The right side of the heart is located at the 5th intercostal space parasternal on the right
side. The apex of the heart, also known as the left bottom of the heart, is located at the 5th
intercostal space midclavicular on the left.
MEDIASTINUM
The mediastinum is the area between the right pleural
cavity (right lung) and the left
pleural cavity (left lung). The mediastinum is bordered
anteriorly by the sternum, and posteriorly by the vertebrae.
It is also bordered inferiorly by the diaphragm and
superiorly by the thoracic inlet. The thoracic inlet is located
at the top of the ribcage, and here the first ribs, vertebrae
and sternum are connected.
The mediastinum consists of two parts, known as the
superior (upper) and inferior (bottom) mediastinum. The
inferior mediastinum consists of three parts: the front
part is called the anterior mediastinum, the middle part is
called the middle
mediastinum, and the back part is called the posterior
mediastinum.
Superior mediastinum
In the superior mediastinum, the thymus can be found. The thymus is part of the lymphoid
tissue. When becoming an adult, the thymus shrinks into a fat deposit-like structure.
There are also nerves located in the superior mediastinum. The most important are the
vagal nerves, which are wondering through the human body. The vagal nerve is the
parasympathetic branch of the autonomous system, which telles the organs to relax.
The left recurrent laryngeal nerve is a branch from the vagus nerve. It curls around the aortic
arch, in order to head up along the trachea. This nerve is responsible for the control of the
vocal cords and breathing ability.
Phrenic nerves come from the cervical plexus, and go between the lungs and the heart,
anterior to the hilum of the lung. It enters the diaphragm, with causes control of contraction
and relaxation of the diaphragm.
There is also the sympathetic trunk. It is a pearl necklace-like structure which connects
multiple nodes alongside the vertebrae and between the pleura.
Last, there is the thoracic duct. The superior
vena cava collects blood from the
subclavian and the jugular vein, which
causes pressure buildup in the vena cava.
In the angle of these veins, the thoracic
duct is located. The thoracic duct collects
fat from the digestive system, bringing it to
the left side of the body. On the left side, a
small branch is located, which only collects
from the left arm and head space.
Anterior mediastinum
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In the anterior mediastinum, two arteries can be found, one on each side of the body. They
are located parasternal and come from the subclavian artery. These arteries also have their
responding veins, and they are known as the internal thoracic arteries and veins (aa. and vv.
thoracicae internae)
Posterior mediastinum
In the posterior mediastinum, the same structures can be found as in the superior
mediastinum. The only difference is that in the superior mediastinum, the trachea is located,
while not in the posterior mediastinum.
THE PERICARDIUM
When the heart is just located in the thorax while beating
alongside the movement of the lungs, their surfaces will rub
together. This cause inflammation and damage to both
organs. Therefore, the heart has a protective layer known as
the pericardium. The pericardium is attached to the heart
itself, curls around, and goes around the heart another time.
This results in a pericardial cavity, which contains of air. The
pericardial cavity allows the heart to move freely without
any friction with other tissues.
The pericardium consists of two layers. The visceral
pericardium, also known as the epicardium, is attached to
the heart closely. The parietal pericardium is attached to its
surrounding, like loose tissues and the diaphragm.
The pericardial cavity
As mentioned before, the pericardial cavity provides less friction and free movement of the
heart in the chest cavity. When there is fluid inside the cavity dues to trauma or pericarditis,
cardiac tamponade can occur. Cardiac tamponade causes the heart to compress.
Pericard
The transverse sinus is a little cavity located between the major vessels of the heart. This
sinus is often used during surgery to clip off the aorta or pulmonary artery for clipping on
the heart-lung bypass machine. Within the transverse sinus, the transition from the visceral
to parietal pericardium occurs.
The oblique sinus is a small cavity between the big veins entering the left atrium.
The border between the left and the right ventricle is the interventricular sulcus which is a
groove of fat and vessels. This sulcus goes down from the auricle of the left atrium.
Between the atriums and the ventricles there is also a big groove called the coronary sulcus
which is a groove of fat and vessels. At the height of the coronary sulcus on the inside we
find the coronary sinus where are the venus blood used by the heart is collected and comes
back at the right atrium where the inferior vena cava also enter the right atrium. From the
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aorta there are three big branches: the brachiocephalic trunk, the left common carotid
artery, and the left subclavian artery.
The brachiocephalic trunk is a little bit bigger than the other two since it gives the arms and
the head its blood supply.
The left common carotid artery only goes to the head whereas the left subclavian artery
only goes to the arms.
Between the arch of the aorta and the pulmonary trunk there is a ligament which is called
the ligamentum arteriosum. The ligamentum arteriosum was open in the embryonic period
of the heart. There are four pulmonary veins coming in of the left atrium.
ATRIA AND VENTRICLES
Right and Left Atrium
The right auricle is the muscular part of the
atrium. The auricle contains pectinate muscles
on its inside. These muscles have other origin
in embryonic state than the smooth muscle of
the heart between the atria and on the
posterior side of the heart. Between the atria
lies the intertribal septum, which is also made
from the smooth muscle tissue. This septum
contains the oval fossa, which is a small dent-
like structure. This is a remnant of the
embryonic stage of the heart where the left and
right atria were connected.
Entering the atria is the superior and inferior
vena cava. Besides the orifice (opening) of the inferior vena cava, lies the orifice of the
coronary sinus.
Between the right atrium and the right ventricle lies an orifice combined with a valve (right
atrioventricular valve) to prevent back flow of the blood when it entered the ventricle.
The crista terminalis is a small ridge dividing the smooth part of the atrium and the
pectinate muscular part of the atrium.
The left atrium has the same structure as the right atrium, only here the blood comes back
from the lungs instead from the entire body.
Heart valves
In the atrioventricular valves, the papillary muscles tuck on the chordae tendinae to avoid
blood prolapse into the atria. The semilunar valves are located at the base of the pulmonary
artery and the aorta. The valves are composed of nodules. When these come together, the
valve is rounded and closed off. There are no muscles connected to the valves, as these
valves need less force because of their structure. The inside of the aortic valve can be
distinguished from the pulmonary valve by the orifices to the coronary arteries inside the
aortic valve. During diastole your heart get blood through the left and right coronary artery,
and during systole it does not get any blood.
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Right ventricle
If the ventricle contracts, it has to make sure
the cusps of the valve don’t flap back into the
atrium. This is done with chordae tendineae,
which are little tendon-like strings connected
to the valve cusps, but also to the papillary
muscles lying in the ventricle. Besides the AV
valve, there is also the pulmonary valve to
avoid refill of the ventricle after contaction.
The pulmonary valve is a semilunar structure,
composed of 3 ‘shapes’, which collects all the
‘falling’ blood. This causes the blood to move
to the lungs.
In the right ventricles, there are trabeculae
carneae, which are irregular muscle columns.
It is surrounded by conducted muscle tissue
in order to obtain fast contraction of the
muscle. The trabeculae carneae are more rough in the right ventricle than in the left
ventricle.
Left Ventricle
The wall of the left ventricle is thicker than
the right wall. This is because the left
ventricle uses more force to pump the
blood, as it needs to go through the whole
body. The trabeculae are more subtle and
less fleshy than the right ventricle. The left
ventricle has a bicuspid valve, while in the
right ventricle it is tricuspid. The left AV
valve is also known as the mitral valve. The
left ventricle pumps blood through the
ascending aorta, which is ‘protected’ with
the aortic valve. The inter ventricular
septum is also muscular and membranous,
because of the high force the blood is
pumped with to the body.
Heart Skeleton
If you squeeze the valves, the integrity of the circle is
broken and the valves will leak. Therefore, the heart
has a ‘skeleton’ made of connective tissue to make the
valves and the heart firmer. The left fibrous anules lies
around the left ventricle, and the right annulus around
the right ventricle. The heart skeleton is composed of
rings, which will ensure the chambers and arteries
maintain their round shape to avoid leaking. The
fibrous ring of aortic valveis around the aorta, and
between those three rings there is an opening for the
bundle of His. The bundle of his is part of the heart
conducting system. Therefore, the skeleton also has
plays a role in the isolation of electrical stimulation.
This is to ensure that diastole and systole don’t
happen simultaneously.
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