Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Chapter 16: Anatomy and Physiology of the Cardiovascular System

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Cardiac Muscle Fibers

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Contractile Elements Inside a Sarcomere

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Characteristics of Cardiac Tissue Automaticity: Pacemaker cells generate their own action potential. Conductivity: Cardiac cells receive the electrical signal and pass it from one cell to another. Contractility: Cardiac muscle shortens because of depolarization. Excitability: Cardiac tissue responds to a stimulus and generates an action potential. Rhythmicity: Cardiac cells generate an action potential at a regular rate.

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Question Which of the following terms describes the cardiac tissue function of the sinoatrial node? A. Excitability B. Automaticity C. Conductivity D. Contractility

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer B. Automaticity Rationale: Automaticity is the ability of pacemaker cells to spontaneously make an action potential and depolarize. Excitability is the ability of a cardiac cell to respond to a stimulus and depolarize. Conductivity is the ability of cardiac tissue to respond to a stimulus and generate an action potential. Contractility is the ability of cardiac muscle cells to respond to depolarization by shortening.

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Electrical Events That Occur in the Myocardial Cell

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins The Resting Membrane Potential of Myocardial Cell Inside of the myocardial cell is more negative (-80 mV) compared to the outside of the cell because of ionic pumps. –Determined by concentration of ions on both sides of cell membrane –Ion transport proteins in cell membrane need ATP. Resting state is the time the heart is in diastole.

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Cardiac Action Potential

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Electrical Conduction System

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Comparison of Electrical and Mechanical Events During One Cardiac Cycle

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Measuring Cardiac Function CO = HR (beats/min) x SV (L/beat) Normal adult range: 4 to 8 L/min CI = CO (L/min) BSA (m) Normal adult range: 2.8 to 4.2 L/min

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Effects of the Autonomic Nervous System on the Heart and Vascular System Receptor TypeEffects Alpha-1Vasoconstriction of blood vessels, increased BP, increased contractility of heart Alpha-2Decreased BP (reduced norepinephrine) Beta-1Increased heart rate, increased heart contraction Beta-2Dilation of arteries Muscarinic receptorsDecreased HR, decreased force of contraction

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Role of the Aortic Reflex and Bainbridge Reflex on Heart Rate Aortic Reflex Effects Adjust HR to BP Bainbridge Effects Adjust HR to Handle Venous Return Rise in BP causes decrease in HRIncrease in venous return causes increase in HR Decrease in BP causes increase in HR Decrease in venous return causes decrease in HR

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Starling’s Law of the Heart

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Coronary Arteries

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Coronary Artery Blood Supply for Cardiac Muscle and Conduction System

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Question A client is diagnosed with a 95% occlusion of the right coronary artery (RCA). Which area of the heart’s conduction system is most likely to be affected? A. Bundle branches B. Sinoatrial (SA) node C. Atrioventricular (AV) node D. Purkinje fibers

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer C. Atrioventricular node Rationale: The RCA supplies the AV node in 90% of hearts. The left anterior descending (LAD) supplies the bundle branches. The left circumflex supplies the SA node in 45% of hearts and the AV node in 10% of hearts. The Purkinje fibers are supplied by all of the coronary arteries.

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Question A 19-year-old client with supraventricular tachycardia has a heart rate in the 160s. The client complains of chest pain. The chest pain is most likely a result of which of the following? A. A decrease in diastolic time B. A decrease in atrial kick C. Coronary artery disease D. Decreased oxygen demand

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Answer A. A decrease in diastolic time Rationale: The coronary arteries receive blood flow when the aortic valve is closed (ventricular diastole). Tachycardia decreases diastolic time, resulting in decreased blood flow to the coronary arteries. Chest pain occurs from the decreased coronary perfusion. It is unlikely that a 19-year-old patient has coronary artery disease causing the chest pain. Atrial fibrillation can lead to a loss in atrial kick that would decrease the cardiac output. Tachycardia would lead to increased cardiac workload and increased oxygen demand.

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Central Venous Pressure (CVP) Defined as pressure of the blood measured in mm Hg in the thoracic vena cavae before the entry into the right atrium –CVP is increased when there is an increase in the blood volume; increase due to Valsalva maneuver, change from standing to supine position, or decrease in pumping action of heart –CVP is decreased when there is a decrease in blood volume –Normal range is 3 to 6 mm Hg

Copyright © 2009 Wolters Kluwer Health | Lippincott Williams & Wilkins Influences on Blood Pressure Neuroregulation –Autonomic nervous system Hormonal influences –Renin-angiotensin system Hypercapnia/hypoxia –Vasomotor center Unbound calcium in tunica media –Calcium channel blockers