Chapter 19 The Cardiovascular System: The Heart Flashcards
(19 cards)
Position of the Heart in the Thorax
The heart is located within the thoracic cavity, medially between the lungs in the mediastinum. it is about the size of a fist, is broad at the top (called the base), and tapers toward the apex.
Dual System of the Human Blood Circulation
Blood flows from the right atrium to the right ventricle, where it is pumped into the pulmonary circuit. The blood in the pulmonary artery branches is low in oxygen but relatively high in carbon dioxide. Gas exchange occurs in the pulmonary capillaries (oxygen into the blood, carbon dioxide out), and blood high in oxygen and low in carbon dioxide is returned to the left atrium.
External Anatomy of the Heart
Inside the pericardium, the surface features of the heart are visible.
Heart Musculature
The swirling pattern of cardiac muscle tissue contributes significantly to the heart’s ability to pump blood effectively
Differences in Ventricular Muscle Thickness
The myometrium in the left is significantly thicker than that of the right ventricle. Both ventricles pump the same amount of blood, but the left ventricle must generate a much greater pressure to overcome greater resistance in the systemic circuit.
Internal Structures of the Heart
The presence of the pulmonary trunk and aorta covers the interatrial septum, and the atrioventricular septum is cut away to show the atrioventricular valves.
Internal Structures of the Heart
The anterior view of the heart shows the four chambers, the major vessels and thier early branches, as well as the valves.
The presence of the pulmonary trunk and aorta covers the interatrial septum, and the atrioventricular septum is cut away to show the atrioventricular valves.
Blood Flow from the Left Atrium to the Left Ventricle
(a) A transverse section through the heart illustrates the four heart valves. The two atrioventricular valves are open; the two semi lunar valves are closed. The atria and vessels have been removed.
(b) A frontal section through the heart illustrates blood flow through the mitral valve. When the mitral valve is open, it allows blood to move from the left atrium to the left ventricle. The aortic semilunar valve is closed to prevent backlog of blood from the aorta to the left ventricle.
Blood Flow from the Left Ventricle to the Great Vessels
(a) A transverse section through the heart illustrates the four heart valves during ventricular contraction. The two atrioventricular valves are closed, but the two semilunar valves are open. The atria and vessels have been removed. (b) A frontal view shows the closed mitral (bicuspid) valve that prevents backflow of blood into the left atrium. The aortic semilunar valve is open to allow blood to be ejected into the aorta.
Coronary Circulation
The anterior view of the heart shows the prominent coronary surface vessels. The posterior view of the heart show the coronary surface vessels.
Atherosclerotic Coronary Arteries
In this coronary angiogram (X-ray), the dye makes visible two occluded coronary arteries. Such blockages can lead to decreased blood flow (ischemia) and insufficient oxygen (hypoxia) delivered to the cardiac tissues. If uncorrected, this can lead to cardiac muscle death (myocardial infarction).
Cardiac Muscle
(a) Cardiac muscle cells have myofibrils composed of myofilaments arranged in sarcomeres, T tubules to transmit the impulse from the sarcolemma to the interior of the cell, numerous mitochondria for energy, and intercalated discs that are found at the junction of of different cardiac muscle cells. (b) A photomicrograph of cardiac muscle cells shows the nuclei and intercalated discs. (c) An intercalated disc connects cardiac muscle cells and consists of desmosomes and gap junctions.
Conduction System of the Heart
Specialized conducting components of the heart include the sinoatrial node, the intermodal pathways, the atrioventricular node, the atrioventricular bundle, the right and left bundle branches, and the Purkinje fibers.
Cardiac Conduction
(1) The sinoatrial (SA) node and the remainder of the conduction system are at rest. (2) The SA node initiates the action potential, which sweeps across the atria. (3) After reaching the atrioventricular node, there is a delay of approximately 100 ms that allows the atria to complete pumping blood before the impulse is transmitted to the atrioventricular bundle. (4) Following the delay, the impulse travels through the atrioventricular bundle and bundle branches to the Purkinje fibers, and also reaches the right papillary muscle via the moderator band. (5) The impulse spreads to the contractile fibers of the ventricle. (6)Ventricular contraction begins.
Action Potential at the SA Node
The prepotential is due to a slow influx of sodium ions until the threshold is reached followed by a rapid depolarization and repolarization. The prepotential accounts for the membrane reaching threshold and initiates the spontaneous depolarization and contraction of the cell. Note the lack of a resting potential.
Action Potential in Cardiac Contractile Cells
(a) Note the long plateau phase due to the influx of calcium ions. The extended refractory period allows the cell to fully contract before another electrical event can occur.
(b) The action potential for heart muscle is compared to that of skeletal muscle.
Standard Placement of ECG Leads
In a 12-lead ECG, six electrodes are placed on the chest, and four electrodes are placed on the limbs.
Electrocardiogram
A normal tracing shows the P wave, QRS complex, and T wave. Also indicated are the PR, QT, QRS, and ST intervals, plus the P-R and S-T segments.
Common ECG Abnormalities
(a) In a second-degree or partial block, one-half of the P waves are not followed by the QRS complex and T waves while the other half are.
(b) In atrial fibrillation, the electrical pattern is abnormal prior to the QRS complex, and the frequency between the QRS complexes has increased.
(c) In ventricular tachycardia, the shape of the QRS complex is abnormal.
(d) In ventricular fibrillation, there is no normal electrical activity.
(e) In a third-degree block, there is no correlation between atrial activity (the P wave) and ventricular activity (the QRS complex).
