Review for Chapter 17

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Review for Chapter 17 : The Heart Module 17.1: Overview of the Heart  The heart is a two-sided pump that drives blood into blood vessels.  The heart has two superior atria that receive blood from veins and two inferior ventricles that pump blood into arteries.  The right side of the heart is the pulmonary pump, which delivers deoxygenated blood to the pulmonary circuit. The left side of the heart is the systemic pump, which delivers oxygenated blood to the systemic circuit.  The heart also secretes the hormone atrial natriuretic peptide. Module 17.2: Heart Anatomy and Blood Flow Pathway  The heart wall has three layers: the outer fibrous and serous pericardium, the middle myocardium, and the inner endocardium. The serous pericardium is composed of the outer parietal pericardium and the inner visceral pericardium , between which is the serous fluid–containing pericardial cavity.  The coronary circulation consists of the coronary arteries, which supply the myocardium with oxygenated blood, and the coronary veins, which drain deoxygenated blood from the myocardium. The two main coronary arteries are the right coronary artery and the left coronary artery. The coronary sinus is the large vessel that receives blood from the coronary veins and empties it into the right atrium.  The four main great vessels are the venae cavae (superior and inferior), the pulmonary trunk, the pulmonary veins, and the aorta.  Each atrium has an external auricle. The two atria are separated by the interatrial septum.  The two ventricles are separated by the interventricular septum. The left ventricle has a thicker wall than the right because it pumps against higher pressure.  Blood flowing into the ventricles passes through the atrioventricular (AV) valves , including the tricuspid and mitral valves. The cusps of each valve are attached to papillary muscles by chordae tendineae that prevent the cusps from everting when the ventricles contract.  Blood flowing out of the ventricles passes through the semilunar (SL) valves, including the pulmonary and aortic valves. Module 17.3: Cardiac Muscle Tissue Anatomy and Electrophysiology  Cardiac muscle cells contract in response to action potentials via the sliding-filament mechanism. Pacemaker cells are autorhythmic and spontaneously generate action potentials. These action potentials trigger cardiac contractile cells to have action potentials.  Cardiac muscle cells are short, branched, striated cells joined by intercalated discs.  A contractile cell action potential results from a reversal in membrane potential. The stages of the action potential are as follows: rapid depolarization due to sodium ion influx; brief initial repolarization due to potassium ion efflux; a plateau phase due to calcium ion influx and simultaneous potassium ion efflux; and repolarization due to continued potassium ion efflux.

 Pacemaker cells depolarize rhythmically. They reach threshold through nonselective cation influx; depolarization is due to the inflow of calcium ions. Their repolarization and hyperpolarization are due to the outflow of potassium ions.  Three populations of pacemaker cells exist in the heart, collectively called the cardiac conduction system: the sinoatrial ( SA ) node , which is the main pacemaker of the heart; the atrioventricular ( AV ) node , the heart’s backup pacemaker; and the components of the Purkinje fiber system.  An action potential in the heart normally takes the following path: SA node → atrial contractile cells → AV node where it is delayed → AV bundle → right and left bundle branches → Purkinje Module 17.4: Mechanical Physiology of the Heart: The Cardiac Cycle  Mechanical physiology describes the physiology of cardiac pumping.  Pressure changes generated by ventricular contraction and relaxation cause the blood to flow between chambers and the valves to open and close.  The S1 heart sound is caused by the closing of the AV valves at the beginning of isovolumetric contraction. The S2 heart sound is caused by the closing of the SL valves at the beginning of isovolumetric relaxation.  The cardiac cycle is the sequence of events that takes place within the heart from one heartbeat to the next, during which each chamber has a relaxation period ( diastole ) and a contraction period ( systole ).  There are four stages of the cardiac cycle: ventricular filling, isovolumetric contraction, ventricular ejection, and isovolumetric relaxation. The volume of blood in the ventricles at the end of ventricular filling is the end-diastolic volume ( EDV ) ; the volume of ventricular blood after ventricular ejection is the end-systolic volume (ESV).  Blood is pumped out of the ventricles when the pressure in the ventricles is higher than the pressure in the vessels into which they pump the blood. Module 17.5: Cardiac Output and Regulation  Cardiac output is the amount of blood pumped out by each ventricle in 1 minute. It is equal to the heart rate multiplied by the stroke volume.  Stroke volume is the amount of blood ejected from the right or left ventricle with each beat, and is equal to the EDV minus the ESV. Stroke volume is determined by the preload, the degree of stretch imposed on the cardiac muscle cells; contractility, the effectiveness with which the heart pumps; and afterload, the force against which the ventricles must pump.  Heart rate is influenced by chronotropic agents such as the ANS and endocrine system.  Cardiac output is regulated primarily by the endocrine and nervous systems.  Epinephrine and norepinephrine are positive chronotropic and inotropic agents.  Acetylcholine is primarily a negative chronotropic agent.

 The endocrine system releases chronotropic and inotropic hormones, and other hormones that regulate water balance and preload. Access What You Learn Level 1 Check Your Recall 1. Mark the following statements as true or false. If a statement is false, correct it to make a true statement. 1. The heart is located in the mediastinum slightly to the left of the midline. 2. The heart consists of two superior ventricles and two inferior atria. 3. Arteries always carry oxygenated blood away from the heart, and veins always carry deoxygenated blood toward the heart. 4. The pulmonary circuit delivers blood from the right side of the heart to the lungs to become oxygenated. 5. The heart plays a role in the regulation of blood pressure and secretes the hormone atrial natriuretic peptide. 2. The pericardial cavity is located between: 1. the parietal pericardium and the fibrous pericardium. 2. the fibrous pericardium and the myocardium. 3. the parietal pericardium and the visceral pericardium. 4. the epicardium and the endocardium. 3. Which of the following statements is true ? 1. The tricuspid valve is located between the right atrium and the right ventricle. 2. The mitral valve is located between the pulmonary veins and the left atrium. 3. The pulmonary valve is located between the pulmonary artery and the pulmonary veins. 4. The aortic valve is located between the right ventricle and the aorta. 4. Match the following terms with the correct definition. 1. Auricle 2. Aorta 3. Coronary sinus 4. Papillary muscle

5. Fossa ovalis 6. Pectinate muscle 7. Venae cavae 8. Pulmonary trunk 9. Chordae tendineae A. Pulmonary veins Drainage point for the coronary veins B. Extensions that attach papillary muscles to valves C. Remnant of a hole present in the fetal interatrial septum D. Two largest veins of the systemic circuit E. Flaplike extension from the right or left atrium F. Finger-like projections of ventricular muscle G. Main artery of the pulmonary circuit H. Veins that drain the pulmonary circuit I. Largest artery of the systemic circuit J. Ridges of muscle in the atria 5. Fill in the blanks: The coronary arteries are the first branches off the . The right coronary artery becomes the on the posterior side of the heart. The left coronary artery branches into the and the . 6. How do pacemaker cardiac muscle cells differ from contractile cardiac muscle cells? What is autorhythmicity? 7. Cardiac muscle cells are joined by structures called: 1. T-tubules. 2. tight junctions. 3. sarcoplasmic reticulum. 4. intercalated discs. 8. Mark the following statements as true or false. If a statement is false, correct it to make a true statement. 1. The rapid depolarization phase of the contractile cell action potential is due to the opening of voltage-gated potassium ion channels. 2. Pacemaker cells lack a distinct plateau phase. 3. The plateau phase in contractile cells is due to the influx of calcium ions through calcium ion channels. 4. The repolarization phase of the contractile cell is due to the potassium ions rushing into the cell through potassium ion channels. 5. Open sodium ion channels cause hyperpolarization in pacemaker cells, which triggers HCN channels to open and begins a new action potential.

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