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Table of Contents
- Course Home
- Objectives
- Matching Exercise
- Introduction
- Anatomy: The Heart
- Anatomy: The Vessels
- Physiology: Introduction
- Physiology: Review of Circulation
- Physiology: The Cardiac Cycle
- Physiology: Innervation of the Heart
- Cardiac Electrophysiology: Introduction
- Cardiac Electrophysiology: Electrolytes
- Cardiac Electrophysiology: The Cardiac Conduction System
- Sample Cases
- Case 1: Cardiac Tamponade
- Figure 1: Assessment
- Figure 2: Management
- Case 2: Cocaine Overdose
- Figure 3: Assessment
- Figure 4: Management
- Case 3: Hemorrhagic Shock
- Figure 5: Assessment
- Figure 6: Management
- Conclusion
- References
- Bibliography
Anatomy: The Heart
The Location of the Heart:
The heart, which is about the size of a small fist, is located in the center of the chest, just behind the sternum. Other important structures, which border the heart, include: the diaphragm (located just below the heart), the aorta (just above the heart), the esophagus and vertebral column (just behind the heart), as well as the lungs (on either side of the heart).
The Tissue Layers of the Heart:
The heart is composed of three tissue layers – the pericardium, myocardium, and endocardium.
-The Pericardium:
The pericardium is the outermost layer of the heart and serves as a protective barrier. This layer is divided into the parietal pericardium and visceral pericardium. The parietal pericardium is composed of a thick layer of fibrous tissue and encases the heart, while the visceral pericardium is composed of a thinner cell layer and is adherent to the heart itself. A space exists between the visceral and parietal pericardial layers, which holds a small amount of fluid. This fluid serves as a lubricant and decreases friction between the beating heart and surrounding structures. The pericardial space can also collect fluid, from medical disease or trauma, which can result in life threatening cardiac tamponade and death.
-The Myocardium:
The middle layer of the heart is the myocardium, which is composed of thick muscular tissue. The myocardial cells, which make up this layer, are similar to skeletal muscle cells but are more complex because they can transmit electrical signals.
-The Endocardium:
The innermost most layer of the heart, known as the endocardium, is in contact with the blood.
The Chambers of the Heart:
The heart is basically a four-chambered box, consisting of two upper chambers (the atria) and two lower chambers (the ventricles).
-The Atria:
The atria are thin-walled structures that receive blood from the circulation and pump it into the ventricles. The right atrium receives deoxygenated blood from the body via the inferior and superior vena cavae and empties into the right ventricle. The left atrium receives oxygenated blood from the lungs via the pulmonary veins and empties the blood into the left ventricle.
-The Ventricles:
The ventricles, which have thick, muscular walls, are responsible for generating the contractile force that pumps blood throughout the body. The right ventricle receives deoxygenated blood from the right atrium and pumps it through the pulmonary artery and into the lungs. The left ventricle receives oxygenated blood from the left atrium and pumps it through the aorta and into the vessels that supply the rest of the body. The walls of the left ventricle are considerably thicker than the right ventricle secondary to hypertrophy, which occurs in response to the left ventricle having to pump against higher pressures.
-The Septa:
The right and left chambers of the heart are separated from each other by a layer of tissue known as a septum. The atria are separated from each other by the interatrial septum. Similarly, the ventricles are divided by a layer of tissue called the interventricular septum. In addition to acting as a barrier between the right and left ventricles, the interventricular septum contains conductive tissue that aids in the electrical stimulation of the heart.
The Heart Valves:
The heart has four valves – two atrioventricular valves and two semilunar valves.
-The Atrioventricular Valves:
The valves which control the flow of blood between the atria and ventricles are known as the atrioventricular valves. The right atrioventricular valve is called the tricuspid valve and is named as such because the valve is composed of three leaflets (as the name tri – cusp – id implies). The left atrioventricular valve is called the mitral valve and is composed of only two leaflets.
-The Semilunar Valves:
The semilunar valves permit one way movement of blood between the ventricles and the great arteries. The right semilunar valve, also known as the pulmonic valve, connects the right ventricle to the pulmonary artery. The left semilunar valve, known as the aortic valve, allows oxygenated blood to flow from the left ventricle to the aorta.
