1-موضوعات
عامة
2-أشعارى
3-مختارات شعرية و قصصية
4-مقالات أدبية
5-مقالات تاريخية و سياسية
6-شخصيات
7-إسلاميات
8-عروض الكتب
9-القسم الطبى
10-طب الأسنان
11-مدوناتى الخاصة
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THE CIRCULATORY SYSTEM
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Blood
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Plasma is the liquid component of the blood. Mammalian blood
consists of a liquid (plasma) and a number of cellular and cell
fragment components. Plasma is about 60 % of a volume of
blood; cells and fragments are 40%. Plasma has 90% water and
10% dissolved materials including proteins, glucose, ions,
hormones, and gases. It acts as a buffer, maintaining pH near
7.4. Plasma contains nutrients, wastes, salts, proteins, etc.
Proteins in the blood aid in transport of large molecules such as
cholesterol.
Red blood cells, also known as erythrocytes, are flattened,
doubly concave cells about 7 µm in diameter that carry oxygen
associated in the cell's hemoglobin. Mature erythrocytes lack a
nucleus. They are small, 4 to 6 million cells per cubic millimeter of
blood, and have 200 million hemoglobin molecules per cell.
Humans have a total of 25 trillion (about 1/3 of all the cells in the
body). Red blood cells are continuously manufactured in red
marrow of long bones, ribs, skull, and vertebrae. Life-span of an
erythrocyte is only 120 days, after which they are destroyed in
liver and spleen. Iron from hemoglobin is recovered and reused
by red marrow. The liver degrades the heme units and secretes
them as pigment in the bile, responsible for the color of feces.
Each second 2 million red blood cells are produced to replace
those taken out of circulation.
White blood cells, also known as leukocytes, are larger than
erythrocytes, have a nucleus, and lack hemoglobin. They function
in the cellular immune response. White blood cells (leukocytes)
are less than 1% of the blood's volume. They are made from stem
cells in bone marrow. There are five types of leukocytes,
important components of the immune system. Neutrophils enter
the tissue fluid by squeezing through capillary walls and
phagocytozing foreign substances. Macrophages release white
blood cell growth factors, causing a population increase for white
blood cells. Lymphocytes fight infection. T-cells attack cells
containing viruses. B-cells produce antibodies. Antigen-antibody
complexes are phagocytized by a macrophage. White blood cells
can squeeze through pores in the capillaries and fight infectious
diseases in interstitial areas
Platelets result from cell fragmentation and are involved with
clotting. Platelets are cell fragments that bud off megakaryocytes
in bone marrow. They carry chemicals essential to blood clotting.
Platelets survive for 10 days before being removed by the liver
and spleen. There are 150,000 to 300,000 platelets in each
milliliter of blood. Platelets stick and adhere to tears in blood
vessels; they also release clotting factors. A hemophiliac's blood
cannot clot. Providing correct proteins (clotting factors) has been
a common method of treating hemophiliacs. It has also led to HIV
transmission due to the use of transfusions and use of
contaminated blood products.
Water and plasma are forced from the capillaries into intracellular
spaces. This interstitial fluid transports materials between cells.
Most of this fluid is collected in the capillaries of a secondary
circulatory system, the lymphatic system. Fluid in this system is
known as lymph.
Lymph flows from small lymph capillaries into lymph vessels that
are similar to veins in having valves that prevent backflow. Lymph
vessels connect to lymph nodes, lymph organs, or to the
cardiovascular system at the thoracic duct and right lymphatic
duct.
Lymph nodes are small irregularly shaped masses through which
lymph vessels flow. Clusters of nodes occur in the armpits, groin,
and neck. Cells of the immune system line channels through the
nodes and attack bacteria and viruses traveling in the lymph.
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The Heart
The heart is a muscular structure that contracts in a rhythmic pattern to pump blood. Hearts have a variety of forms: chambered hearts in mollusks and vertebrates, tubular hearts of arthropods, and aortic arches of annelids. Accessory hearts are used by insects to boost or supplement the main heart's actions. Fish, reptiles, and amphibians have lymph hearts that help pump lymph back into veins.
The basic vertebrate heart, such as occurs in fish, has two chambers. An auricle is the chamber of the heart where blood is received from the body. A ventricle pumps the blood it gets through a valve from the auricle out to the gills through an artery.
Amphibians have a three-chambered heart: two atria emptying into a single common ventricle. Some species have a partial separation of the ventricle to reduce the mixing of oxygenated (coming back from the lungs) and deoxygenated blood (coming in from the body). Two sided or two chambered hearts permit pumping at higher pressures and the addition of the pulmonary loop permits blood to go to the lungs at lower pressure yet still go to the systemic loop at higher pressures.
Establishment of the four-chambered heart, along with the pulmonary and systemic circuits, completely separates oxygenated from deoxygenated blood. This allows higher the metabolic rates needed by warm-blooded birds and mammals.
The human heart is a two-sided, 4 chambered structure with muscular walls. An atrioventricular (AV) valve separates each auricle from ventricle. A semilunar (also known as arterial) valve separates each ventricle from its connecting artery.
The heart beats or contracts 70 times per minute. The human heart will undergo over 3 billion contraction cycles during a normal lifetime. The cardiac cycle consists of two parts: systole (contraction of the heart muscle) and diastole (relaxation of the heart muscle). Atria contract while ventricles relax. The pulse is a wave of contraction transmitted along the arteries. Valves in the heart open and close during the cardiac cycle. Heart muscle contraction is due to the presence of nodal tissue in two regions of the heart. The SA node (sinoatrial node) initiates heartbeat. The AV node (atrioventricular node) causes ventricles to contract. The AV node is sometimes called the pacemaker since it keeps heartbeat regular. Heartbeat is also controlled by the autonomic nervous system.
Blood flows through the heart from veins to atria to ventricles out by arteries. Heart valves limit flow to a single direction. One heartbeat, or cardiac cycle, includes atrial contraction and relaxation, ventricular contraction and relaxation, and a short pause. Normal cardiac cycles (at rest) take 0.8 seconds. Blood from the body flows into the vena cava, which empties into the right atrium. At the same time, oxygenated blood from the lungs flows from the pulmonary vein into the left atrium. The muscles of both atria contract, forcing blood downward through each AV valve into each ventricle.
Diastole is the filling of the ventricles with blood. Ventricular systole opens the SL valves, forcing blood out of the ventricles through the pulmonary artery or aorta. The sound of the heart contracting and the valves opening and closing produces a characteristic "lub-dub" sound. Lub is associated with closure of the AV valves, dub is the closing of the SL valves.
Human heartbeats originate from the sinoatrial node (SA node) near the right atrium. Modified muscle cells contract, sending a signal to other muscle cells in the heart to contract. The signal spreads to the atrioventricular node (AV node). Signals carried from the AV node, slightly delayed, through bundle of His fibers and Purkinjie fibers cause the ventricles to contract simultaneously.
An electrocardiogram (ECG) measures changes in electrical potential across the heart, and can detect the contraction pulses that pass over the surface of the heart. There are three slow, negative changes, known as P, R, and T. Positive deflections are the Q and S waves. The P wave represents the contraction impulse of the atria, the T wave the ventricular contraction. ECGs are useful in diagnosing heart abnormalities.
Diseases of the Heart and Cardiovascular System
Cardiac muscle cells are serviced by a system of coronary arteries. During exercise the flow through these arteries is up to five times normal flow. Blocked flow in coronary arteries can result in death of heart muscle, leading to a heart attack.
Blockage of coronary arteries is usually the result of gradual buildup of lipids and cholesterol in the inner wall of the coronary artery. Occasional chest pain, angina pectoralis, can result during periods of stress or physical exertion. Angina indicates oxygen demands are greater than capacity to deliver it and that a heart attack may occur in the future. Heart muscle cells that die are not replaced: heart muscle cells do not divide. Heart disease and coronary artery disease are the leading causes of death in the US.
Hypertension, high blood pressure (the silent killer), occurs when blood pressure is consistently above 140/90. Causes in most cases are unknown, although stress, obesity, high salt intake, and smoking can add to a genetic predisposition.
Two main routes for circulation are the pulmonary (to and from the lungs) and the systemic (to and from the body). Pulmonary arteries carry blood from the heart to the lungs. In the lungs gas exchange occurs. Pulmonary veins carry blood from lungs to heart. The aorta is the main artery of systemic circuit. The vena cavae are the main veins of the systemic circuit. Coronary arteries deliver oxygenated blood, food, etc. to the heart. Animals often have a portal system, which begins and ends in capillaries, such as between the digestive tract and the liver.
Fish pump blood from the heart to their gills, where gas exchange occurs, and then on to the rest of the body. Mammals pump blood to the lungs for gas exchange, then back to the heart for pumping out to the systemic circulation. Blood flow is only one directional.
Physiology of Murmurs
Before trying to decipher what may be the underlying cause of a murmur, it is important to first understand what the normal heart sounds are, and what normal variations of these sounds may occur. It is assumed that you already understand the anatomy of the heart, and have read a basic physical examination textbook which describes the standard methods for auscultation.
The most obvious of the heart sounds are the first and second sounds, or S1 and S2, which demarcate systole from diastole. The heart sound playing in the background on the introduction page of this site is a normal sinus rhythm, with a sharp S1 and S2 and no other significant sounds. S1 is the sound which marks the approximate beginning of systole, and is created when the increase in intraventricular pressure during contraction exceeds the pressure within the atria, causing a sudden closing of the tricuspid and mitral, or AV valves. The ventricles continue to contract throughout systole, forcing blood through the aortic and pulmonary, or semilunar valves. At the end of systole, the ventricles begin to relax, the pressures within the heart become less than that in the aorta and pulmonary artery, and a brief back flow of blood causes the semilunar valves to snap shut, producing S2.
Although S1 and S2 are considered to be discrete sounds, you will notice that each is created by the near-instantaneous closing of two separate valves. For the most part, it is enough to consider that these sounds are single and instantaneous. However, it is worth remembering the actual order of the closures, because certain conditions can split these sounds into the separate valve components. During S1, the closing of the mitral valve slightly precedes the closing of the tricuspid valve, while in S2, the aortic valve closes just before the pulmonary valve. Rather than memorize this order, if you remember that the pressure during systole in the left ventricle is much greater than in the right, you can predict that the mitral valve closes before the tricuspid in S1. Similarly, because the pressure at the start of diastole in the aorta is much higher than in the pulmonary artery, the aortic valve closes first in S2. Knowing the order of valve closure makes understanding the different reasons for splitting of heart sounds easier.
When listening to a patient’s heart, the cadence of the beat will usually distinguish S1 from S2. Because diastole takes about twice as long as systole, there is a longer pause between S2 and S1 than there is between S1 and S2. However, rapid heart rates can shorten diastole to the point where it is difficult to discern which is S1 and which is S2. For this reason, it is important to always palpate the PMI or the carotid or radial pulse when auscultating. The heart sound you hear when you first feel the pulse is S1, and when the pulse disappears is S2.
When a valve is stenotic or damaged, the abnormal turbulent flow of blood produces a murmur which can be heard during the normally quiet times of systole or diastole. This murmur may not be audible over all areas of the chest, and it is important to first note where it is heard best and where it radiates to. Next, you should try to discern if the murmur occurs in systole or diastole by timing it against S1 and S2. Then, listen carefully to tell if the murmur completely fills that phase of the cycle (i.e., holosystolic), or if it has discrete start and end points. Regurgitant murmurs, like mitral valve insufficiency, tend to fill the entire phase, while ejection murmurs, like aortic stenosis, usually have notable start and end points within that phase. The quality and shape of the murmur is then noted. Common descriptive terms include rumbling, blowing, machinery, scratchy, harsh, or musical. The intensity of the murmur is next, graded according to the Levine scale:
| I - Lowest intensity, difficult to hear even by expert listeners |
| II- Low intensity, but usually audible by all listeners |
| III - Medium intensity, easy to hear even by inexperienced listeners, but without a palpable thrill |
| IV - Medium intensity with a palpable thrill |
| V - Loud intensity with a palpable thrill. Audible even with the stethoscope placed on the chest with the edge of the diaphragm |
| VI - Loudest intensity with a palpable thrill. Audible even with the stethoscope raised above the chest. |
Finally, it is important to decide if this murmur is clinically significant or not. Just as a murmur can be caused by normal flow through a stenotic valve, it may also be created by high flow through a normal valve. Pregnancy is a common high-volume state where these physiologic flow murmurs are often heard. Anemia and thyrotoxicosis can cause high-flow situations where the murmur is not pathologic itself, but indicates an underlying disease process. Children also frequently have innocent murmurs which are not due to underlying structural abnormalities. How can a physician determine if a murmur is significant?
The most important thing to consider is the clinical scenario. In a population of unreferred young adults, the prevalence of systolic murmurs ranges from 5% to 52%, with 86% to 100% of these patients having normal echocardiograms. Important questions to ask would include the presence of symptoms such as effort syncope, chest pain, palpitations, shortness of breath, or paroxysmal nocturnal dyspnea. In terms of the examination, there is no one way to rule in or out a murmur as being physiologic, but in general, physiologic murmurs tend to be located between the apex and left lower sternal border, have minimal radiation, occur during early to mid-systole, have a crescendo-decrescendo shape, and a vibratory quality. They will usually change intensity with positional maneuvers, becoming quieter on standing and louder with squatting. A Valsalva maneuver will decrease the intensity of the murmur because the increase in intrathoracic pressure will decrease venous return, which will decrease flow through the heart and lessen the turbulence. Additionally, they will not be correlated with additional audiologic findings, such as an S3 or S4.
Examples of some common variations of normal heart sounds without an underlying structural pathology can be found via the links in the menu to the left.
Systolic Murmurs - Aortic Stenosis
One of the most frequent pathologic systolic murmurs is due to aortic stenosis. Most commonly, aortic stenosis arises from one of three conditions. A patient may be born with a congenital stenosis, or acquire the stenosis from secondary conditions such as rheumatic heart disease or idiopathic calcification of the valves. Persons born with an abnormal bicuspid valve are particularly susceptible to calcification later in life.
The murmur of aortic stenosis is typically a mid-systolic ejection murmur, heard best over the “aortic area” or right second intercostal space, with radiation into the right neck. This radiation is such a sensitive finding that its absence should cause the physician to question the diagnosis of aortic stenosis. It has a harsh quality and may be associated with a palpably slow rise of the carotid upstroke. Additional heart sounds, such as an S4, may be heard secondary to hypertrophy of the left ventricle which is caused by the greatly increased work required to pump blood through the stenotic valve. Because the second heart sound is largely generated by the sudden closing of the aortic valve, a poorly mobile and stenotic aortic valve may cause S2 to become quieter or even absent. Although S2 is normally created by the closure of the aortic valve followed by the pulmonary valve, if the closure of the aortic valve is delayed enough, it may close after the pulmonary, creating an abnormal paradoxical splitting of S2.
Aortic stenosis is a progressive disease, with typical symptoms and clinical findings to match its course. A good mnemonic to remember the march of symptoms related to undiagnosed aortic stenosis is ASC, or Aortic Stenosis Complications. One of the early symptoms is Angina, which is usually stable and exertion-related. A more serious and later condition is Syncope, again associated with exercise. Finally, the hypertrophied left ventricle can no longer meet demands, and Congestive heart failure may ensue. On examination, the phase during systole at which the murmur peaks can help to determine the severity of the disease. An early-peaking murmur is usually associated with a less stenotic valve, while a late-peaking murmur has a more severe degree of stenosis. This is because a more stenotic valve takes longer for the ventricle to generate the terrific pressures needed to force the blood past the lesion.
Credits
The Auscultation Assistant was originally conceived early during my fourth year of medical school at UCLA as a unique way to utilize the multimedia capabilities of the Internet to enhance teaching of physical diagnosis to second year medical students. The idea was developed into an individual creative project, and the initial site was first published onto the web at the end of my fourth year. I would like to thank Michael Wilkes, MD, PhD, for his support of this project.
Although some of the graphics and sounds on this site are my own creation, several have also been gathered from a wide variety of sources throughout the Internet. In particular, I would like to thank Dr. Hans Pasterkamp from the University of Manitoba for his generous lending of the breath sounds used on this site. The original breath sounds along with many more can be found at his web site, the R.A.L.E. repository, and I would encourage anyone interested in learning more about breath sounds to visit it.
Because it can be difficult to determine the exact origin of a graphic or sound once it is on a web page, it is possible that some of the sounds not recorded by myself may not be public domain. If the original author of any of the items utilized in this site wishes for them to be removed or would like acknowledgement for the use of the items, please contact me and I will immediately comply.
The following texts were instrumental in creating this site:
| Etchells, Edward, et al., “The Rational Clinical Examination: Does This Patient Have an Abnormal Systolic Murmur?”, Journal of the American Medical Association, February 19, 1997, Vol. 227, No. 7, pp 564-571 |
| Isselbacher, Kurt, et al., Harrison’s Principals of Internal Medicine, Thirteenth edition, McGraw-Hill, Inc, 1994 |
| Swartz, Mark, Textbook of Physical Diagnosis: History and Examination, Second edition, W.B. Saunders Company, 1994 |
One my original inspirations for this site is an amazing program which was written by one of UCLA’s own professors, John Criley, MD. It is titled “The Physiologic Origins of Heart Sounds and Murmurs: The Unique Interactive Guide to Cardiac Diagnosis” and is published on CD-ROM for the PC and Macintosh. This program combines clever graphics, excellent recordings, and detailed text to help medical students understand murmur pathophysiology. Although none of the sounds or graphics from the CD were utilized in making this site, the idea of using the computer as an alternate means of teaching students about murmur physiology was one of the major influences which led to the development of this site.
If you are looking for other excellent sites with heart sounds and murmurs, Agilent has a page devoted to auscultation with many further links.
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مني محمد
MONA25_2010@yahoo.com |
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Anterior Mediastinum
Before studying the heart, I would just like to mention the anterior
mediastinum and what its contents are. This part of the mediastinum
contains connective tissue and fat, as well as, a few blood vessels, maybe
a lymph node or two and, sometimes, the lower end of what used to be the
thymus. It also contains the anterior folds of the pleura, the
costomediastinal folds.
The Pericardium
The heart and its pericardium make up the contents of the middle
mediastinum. The left and right phrenic nerves and their adjacent
arteries (pericardiacophrenic) lie to the left and right of the
pericardium and anterior to the roots of the lungs.
A diagram of the pericardium and its reflections
As you can see, the parietal and visceral pericardium are
continuous. This continuity takes place at the points where
the major blood vessels enter and leave the heart.
You should also be aware that the parietal pericardium has
two inseparable parts, an outer fibrous part and an inner
smooth part, the serous part.
The potential space between the visceral and serous
parietal pericardium is the pericardial cavity. I call
this a potential space because in life there is only a
single layer of fluid between the two layers.
In clinical cases when air is introduced into the
pericardial cavity you have what is known as a
pneumopericardium. This might occur in penetrated wounds
to the thorax.
When blood fills this space, you have a
hemopericardium. Since the pericardial cavity is a
closed space and if it is filled with blood, the heart
can no longer work and the condition is fatal if not
recognized and treated. The term for this syndrome is
cardiac tamponade. This happens after long term
cardiac pathology when the walls become very thin and
weak. The heart virtually blows out and enters the
pericardial cavity.
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Pericardial Sinuses
Within the pericardial cavity, at the points where the visceral
and parietal pericardia are continuous with one another, small
chambers or sinuses are located. In this diagram, the heart has
been removed and you are looking toward the posterior wall of the
pericardial cavity. Although not labeled, you should be able to
identify the superior and inferior venae cavae, the left and right
pulmonary veins and the ascending aorta and pulmonary trunk.
The pericardial sinuses:
| transverse pericardial sinus |
| oblique pericardial sinus |
For those of you who are studying the cadaver, the
transverse pericardial sinus can easily be reached by
sticking your finger between the superior vena cava and the
ascending aorta and pulmonary trunk. This sinus is a
leftover from heart development in the embryo.
Again, for those of you who are studying the cadaver, and
the heart is still in place, slide two or three fingers
under and behind the heart until they reach a dead end.
Your fingers are now in the oblique pericardial sinus.
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The Heart
For those of you studying the cadaver heart, the problem of
orientation invariably crops up. How can you tell the anterior
from the posterior heart surfaces? My technique may not work for
everyone but what I do is first identify two small ruffled
appendages of the left and right auricles. Once I can identify
these, I then know that they will always point to the front of
anterior part of the heart. These cannot be observed from the
back. Once you are oriented, take a look at the various surfaces
and borders of the heart.
The anterior surface of the heart is also known as the
sternocostal surface for obvious reasons. Notice the ruffled
edges of the left (LA) and right (RA) atria. These are the
ones to use for orientation. Since we are looking at the
anterior surface of the heart, they can be seen.
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When the vessels are removed from the heart, certain sulci
(grooves) can be seen and separated the various chambers of the
heart.
From the anterior view of the heart, the anterior
interventricular and coronary sulci can be seen (the darker
brown areas). The anterior interventricular sulcus separates
the right and left ventricles. The anterior part of the
coronary sulcus separates the right atrium from the right
ventricle. |
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From the posterior view of the heart, the posterior part
of the coronary sulcus and the posterior interventricular
sulcus can be seen. From this view, the coronary sulcus can be
seen to separate the left and right atria from the left and
right ventricles. The posterior interventricular sulcus
separated the right ventricle from the left ventricle and if
followed inferiorly, it can be seen to be almost continuous
with the anterior interventricular sulcus. |
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Coronary Arteries and Cardiac Veins
The heart muscle is supplied by the coronary arteries which are
direct branches of the ascending aorta, so the heart muscle gets
the freshest blood possible. The heart muscle is drained by the
cardiac veins. Most of the venous drainage is by was of the
coronary sinus into the right atrium. A small amount of blood
drains directly into the right atrium by way of the anterior
cardiac veins.
The heart is supplied by two major coronary arteries, the
right and left.
The left coronary divides into the anterior interventricular
and circumflex branches almost immediately after it arises
from the left side of the ascending aorta. The anterior
interventricular lies in the anterior interventricular
sulcus and is also known as the left anterior descending
artery. The circumflex branch lies in the coronary sulcus
and forms an anastomosis with the right coronary in the
posterior part of this sulcus.
The anterior interventricular artery is the one most often
involved in coronary occlusions and is often the one that
is bypassed in bypass cardiac surgery.
The right coronary lies in the coronary sulcus and gives
rise to an important branch immediately after leaving
the ascending aorta. This is the anterior right atrial
branch which gives rise to the important nodal artery.
This artery supplies the sinoatrial node (SA node) or
pacemaker of the heart. When this vessels loses its
ability to supply the node, a person usually needs to
have a pace maker placed in their thoracic wall to take
the place of the original pace maker.
The right coronary continues in the coronary sulcus,
giving a branch along the right inferior border of the
heart called the marginal artery.
Finally the right coronary gives rise to the
posterior interventricular (or descending) branch,
and then anastomoses with the circumflex artery from
the left coronary.
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When the heart is viewed from the back, the most obvious
structure lying in the coronary sulcus is the coronary sinus.
This sinus receives most of the venous blood from the heart
and empties into the right atrium. Its tributaries are the
small cardiac vein, the middle cardiac vein and the greater
cardiac vein. There is a small vein that arises along the left
side of the left atrium just beneath the lower left pulmonary
artery (called the oblique vein. This vein is a remnant of the
embryonic left superior vena cava.
The arteries seen in the back of the heart are the
circumflex coronary artery, the terminal part of the right
coronary artery and its posterior interventricular branch.
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Internal Structure of the Chambers of the heart
The right atrium has a forward extension into its auricle.
This space is lined by ridges of muscle called pectinate
muscles and are not shown in the diagram.
Starting with the right atrium, the internal structures are:
| fossa ovalis |
| openings of the superior (SVC) and inferior (IVC)
venae cavae and the coronary sinus opening (CS) The
entrance of the inferior vena cava and coronary sinus may
be covered with small valve leaflets (valve of the
interior vena cava and valve of coronary sinus). |
| The SA node is located at the junction or the superior
vena cava with the right atrium. The AV node is located in
the lower part of the interatrial septum near the opening
of the coronary sinus. |
The right atrium and right ventricle communicate with
each other by way of the tricuspid valve. As the name
implies, it has three leaflets. As you observe the chamber
of the right atrium, notice the following:
| chordae tendineae, attaching the free border of the
valve cusps (leaflets) to either papillary muscles (PM) or
directly to the wall of the heart chamber. Papillary
muscles are only found in the ventricles of the heart.
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| the rough lining of the ventricular wall is called
trabeculae carneae, because of their meaty appearance |
| the anterior papillary that has an attachment to the
interventricular wall known as the septomarginal trabecula
or the moderator band. |
Blood leaves the right ventricle and passes through the
pulmonary trunk to the lungs. Oxygenated blood returns to
the left atrium of the heart from the lung through the
pulmonary veins. The left atrium doesn't have much to talk
about. There is an extension into the small auricles which
have pectinate muscles in its walls.
The left atrium communicates with the left ventricle
through the mitral or bicuspid valve. Just as in the right
ventricle, the valve cusps or leaflets connect to the
papillary muscles (PM) by way of chordae tendineae. The
inner walls of the left ventricle is thrown into folds of
trabeculae carneae just as in the right ventricle. Note,
in particular that the left ventricular has a much thicker
wall than the right ventricle. If the heart is not too
diseased, this is how you can tell the difference between
the two ventricles.
Note the interventricular septum (IVS) between the two
ventricles.
Blood leaves the left ventricle through the ascending
aorta and is then sent to body organs and tissues.
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Heart Valve Positions
This diagram is a special dissection that shows the four
heart valves and their relationship to one another. The view
is from the top after the left and right atria have been
removed.
Start with the right atrioventricular valve (tricuspid
valve). It has an anterior (A), posterior (P) and septal (S)
cusp.
The left atrioventricular valve (mitral valve) has an
anterior (A) and a posterior (P) cusp.
The pulmonary and aortic valves are both tricuspid.
During embryonic development, these two vessels were
one. With rotation of the heart and a separation of the
single channel, the pulmonary trunk ends up anterior and
the ascending aorta ends up posterior. The original
contained four primitive valve cusps, an anterior, left
and right and a posterior. The left and right valves
were divided during the separation so that a left and
right ended up in both the pulmonary (or anterior
channel) and the ascending aorta (or posterior channel).
In the adult, this development results in an anterior
displaced pulmonary trunk with an anterior and a left
and right cusp, while the posterior displaced ascending
aorta has a left and right coronary cusp and a posterior
cusp. The coronary cusps are named because the origins
of the left and right coronary arteries are found
lateral to these cusps.
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