Download Laboratory Exercise 12 Anatomy of the Heart

Laboratory Exercise 12: Anatomy of the Heart
The circulatory system consists of the heart, which is a double pump, and tubes, the blood vessels.
Each side of the heart has two chambers. The upper chambers, the atria, receive blood from the body.
The lower chambers, the ventricles, pump the blood through the body.
The right side of the heart pumps deoxygenated blood to the lungs, where it is oxygenated. This is the
pulmonary division of the circulatory system.
The left side of the heart pumps the oxygenated blood to the tissues of the body. At the level of the body
tissue cells, the oxygenated blood releases the O2 to the cells and the blood becomes deoxygenated this is the
systemic division of the circulatory system.
A. Histology - Pericardium and Heart Wall
The heart lies in the mediastinum of the thoracic cavity. The heart is surrounded by the two layer pericardium.
Each layer consists of simple squamous epithelium. The outer layer, the parietal pericardium is a serous
membrane. The inner layer, the visceral pericardium (epicardium) is the external layer of the heart wall. It is
also a serous membrane. Between the visceral and parietal layers is the pericardial cavity into which the
pericardial membranes secrete serous fluid for lubrication.
The myocardium composed of cardiac muscle tissue, makes up the bulk of the heart wall. The
endocardium is the endothelial layer internal to the myocardium that lines the heart’s chambers and
valves. The endothelium is a type of squamous epithelium.
B. Anatomy
The External Features of the Heart
In normal position, the base of the heart is superior, the conical tip or apex is inferior and points to the
left.
The base is continuous with the blood vessels. Definition of blood vessels: The veins carry blood
toward the heart while the arteries transport blood away from the heart no matter if the blood is
oxygenated or deoxygenated.
The anterior aspect of the heart has a diagonal groove, the anterior interventricular sulcus. It is a line
of demarcation between the left and right ventricles. The blood vessel within the sulcus is the left
anterior descending or interventricular artery, a major branch of the left coronary artery. In the
coronary (horizontal) sulcus between the ventricles and the atria is the proximal part of the left and
right coronary arteries. From the left and right coronary arteries a capillary network supplies the heart
muscle with oxygenated blood. The coronary veins return the deoxygenated blood from the heart
muscle to the right atrium.
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The Chambers and Great Vessels of the Heart
Veins to the Heart
The right atrium receives two large systemic veins, the inferior and superior venae cavae. The left atrium
receives blood from the four pulmonary veins, two from the left lung and two from the right lung.
Arteries from the Heart
The ventricles are connected to two large arteries.
The aorta, from the left ventricle has three regions ascending aorta, aortic arch and descending aorta. The
aorta arches from right to left before it descends through the thoracic and abdominal cavities. From the base
of the ascending aorta emerge the left and right coronary arteries. From the aortic arch arise three major
branches which direct blood to the arms and head. From right to left: brachiocephalic artery, which in turn
branches into the right subclavian and right common carotid arteries; left common carotid artery and left
subclavian artery.
The pulmonary artery or trunk from the right ventricle is to the left of the aortic arch and passes
diagonally beneath it. The pulmonary artery branches into left and right pulmonary arteries a short
distance from its origin.
Cardiac Cycle
During a cardiac cycle, the atria are input chambers; they receive incoming venous blood and then
transmit this blood to the ventricles, the output chambers. The ventricles then pump the blood to body.
The force of ventricular contraction powers the flow of blood through the arteries. The ventricles relax
(diastole) and fill with blood as the atria contract. The filled ventricles then contract (systole) and eject
blood into the systemic and pulmonary arteries while the atria relax and fill. To pump effectively, the
atria and ventricles must contract in this precise sequence.
The Internal Features of the Heart
The contractile force developed by the ventricles is related to the thickness of the ventricular
myocardium. The efficiency of this force is maximized by a series of one-way valves which prevent
the backflow of blood. The atrioventricular (AV) valves are located between the atria and ventricles.
On the left is the bicuspid (mitral) valve and on the right is the tricuspid valve. The valves are
supported by the chordae tendineae and papillary muscle.
The papillary muscles contract with the ventricles tightening the chordae. The taut chordae prevents
the AV valves cusps from everting. This ensures that blood does not flow back into the atria during
ventricular systole.
The pulmonic and aortic semilunar valves consist of 3 valves each; guard the openings of the right and
left ventricles. The semilunar valves prevent regurgitation of blood into the ventricles during
ventricular diastole.
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