Study Guide - Cardiovascular (Week 4).pdf

Study Guide Cardiovascular System (Week 4) A. General cardiac anatomy and its relation to function 1. Trace the path of a drop of blood as it travels from the vena cava through the heart and into the aorta. Thi...

Study Guide Cardiovascular System (Week 4) A. General cardiac anatomy and its relation to function 1. Trace the path of a drop of blood as it travels from the vena cava through the heart and into the aorta. This should include the chambers, and the valves it passes through. i. Right Atrium ii. Tricuspid Valve iii. Right Ventricle iv. Pulmonary Valve (Semilunar) v. Pulmonary Artery vi. Lungs vii. Pulmonary Vein viii. Left Atrium ix. Mitral Valve x. Left Ventricle xi. Aortic Valve (Semilunar) xii. Aorta 2. Compare and contrast the histology of cardiac muscle to skeletal muscle i. Both are striated with actin and myosin ii. Cardiac muscle has intercalated discs iii. Cardiac muscle has splitting, syncytial arrangement 3. Describe the function of intercalated discs in relation to electrical conduction within the heart i. Communication between cells (rapid diffusion of ions) 4. Describe the function of the papillary muscles and chordae tendinae i. Papillary muscles attach to AV valves by chordae tendinae (a) Prevent bulging towards atria to prevent regurgitation 5. Compare the properties to the semilunar valves and the AV valves, and relate them to their function i. AV valves are thin, semilunar valves are built stronger ii. Faster velocity through semilunar valves (a) Semilunar valves have more mechanical abrasion iii. Semilunar valves function passively (high pressure in arteries) without the need for chordae tendinae B. Briefly Describe Blood Flow Distribution at Rest 1. ~15% to Brain i. Absolute volume remains constant ii. Percentage decreases during exercise 2. ~5% to Coronary Arteries i. Absolute volume increases proportionately during exercise (a) Myocardium is working harder, so it needs more blood ii. Percentage remains at 5% during exercise 3. ~25% to Kidneys  i. Key site for adjusting vascular resistance, at rest and exercise 4. ~25% to GI tract i. Substantially reduced during exercise 5. ~25% to Skeletal muscle i. Appreciate just how much goes to muscles at rest! ii. Increases dramatically during exercise (a) Working muscles get greatest blood flow 6. 5% to Skin i. Varies based on temperature (a) Vasoconstriction during cold temperatures (b) Vasoconstriction initially during exercise (before body temperature increases) (c) Vasodilation during hot temperatures, and to eliminate heat during exercise C. Cardiac muscle contractility 1. Name the two general mechanisms that cause the plateau in the action potential in cardiac muscle (but differ in skeletal muscle) i. 1 (a) Skeletal muscle – caused by rapid increase in opening of fast sodium channels (b) Cardiac muscle – additional activation of L-type calcium channels (slow calcium channels), which remain open longer and allow greater inflow of Na+ and Ca2+ to prolong depolarization, thus causing the plateau in the action potential ii. 2 (a) Decreased permeability for potassium ions (decreased outflow of positive potassium ions to prevent repolarization back to a resting negative potential 2. Explain how slow calcium channels cause the action potential in cardiac muscle to be different than that of skeletal muscle i. See above 3. Compare the relative velocity of signal conduction in cardiac muscle fibers to Purkinje fibers i. Purkinje fiber conduction is MUCH faster than cardiac muscle conduction, thus the spread of the conduction signal is sufficiently fast to allow spread throughout the heart 4. Describe the difference between absolute and relative refractory periods in cardiac muscle, and how they relate to cardiac contraction i. Absolute refractory period is when the heart cannot be stimulated to contract at all ii. Relative refractory period is when it cannot be excited by normal signal, but can be by an especially strong signal. 5. Briefly describe why extracellular calcium concentration is of greater relevance for cardiac muscle contraction compared to skeletal muscle contraction i. Calcium used in cardiac muscle contraction is derived from the extracellular fluid, rather than the sarcoplasmic reticulum. The t-tubules connect to extracellular space. D. Cardiac cycle 1. Describe the relationship between heart rate, the duration of the action potential, duration of cardiac cycle duration, and the relative durations of systole and diastole i. Increased heart rate means (a) Shorter action potential plateau (b) Decreased time in systole  (c) Decreased time in diastole (d) Increased ratio of systole to diastole (a) Less relative filling time 2. Explain how ventricular volume, atrial pressure, aortic pressure, and left ventricular pressure change over the course of the cardiac cycle, and relate this to the electrocardiogram and phonocardiogram (Figure 9-7). i. See figure 3. Describe the role of atrial contraction in the cardiac cycle, including its relative contribution to ventricular filling i. Atria contract slightly before the ventricles to pump blood in before contraction ii. ~20% of ventricular filling accounted for by ventricles 4. Explain the mechanisms behind the “period of rapid filling of the ventricles” i. Increased atrial pressure pushes AV valves open to flow into the low-pressure ventricles 5. Describe why isovolumetric contraction occurs before the period of ejection i. Sufficient pressure in the ventricles must be built up to overcome the pressure in the aorta and pulmonary artery 6. Differentiate between the “period of rapid ejection” and the “period of slow ejection” i. Pressure is greatest in the first third of systole, thus more blood is ejected out of the heart during that time 7. Explain what the ejection fraction is, including how it is calculated, and state the normal value for ejection fraction at rest in healthy individuals i. Fraction of the EDV that is ejected ((EDV-ESV)/EDV); 60% 8. Compare the pressures between the right and left ventricles during systole i. Right sided heart pressures are only 1/6th that of the left 9. Relate the concepts of “preload” and “afterload” to ventricular volume and blood pressure fluctuations which occur during the cardiac cycle i. Preload: end diastolic pressure when ventricle is filled (a) Degree of tension when heart begins to contract (b) Pressure during the filling ii. Afterload: Pressure in the aorta (resistance in circulation) (a) The ventricles must overcome the afterload to get the blood out (a) Aortic diastolic blood pressure is the afterload (b) For example, if one person has an arterial blood pressure of 120/80 and another has an arterial blood pressure of 140/90, the one with the higher diastolic pressure is experiencing a greater afterload (b) A higher afterload means the ventricles need to work harder (a) Ventricles that work harder require more ATP to do so 10. Briefly describe the two key factors underlying the Frank-Starling mechanism i. Greater amount of blood in the heart yields greater contractile force and thus stroke volume ii. Greater stretch means greater elastic energy, thus greater contractile strength (a) More ideal actin and myosin overlap iii. Greater atrial stretch means greater ANS stimulation of heart rate E. General anatomy of the conductive system of the heart 1. Trace the pathway of electrical conduction from the SA node through the epicardial surface  i. Sinoatrial node ii. Internodal Pathways (and Inter-atrial fibers) iii. Atrioventricular (AV) Node iv. Atrioventricular Bundle v. Bundle Branches (which branch into smaller and smaller Purkinje fibers) vi. Ventricular muscle F. Automaticity (self-excitation) 1. Compare the intrinsic rhythmical rates of the sinus note, atrio-ventricular node, and the Purkinje fibers and relate this to pacemaker control of the normal heart, and the concept of ectopic beats and escape beats [Note – don’t get too caught up in the exact numbers, just recognize that the SA node is the fastest, and therefore sets the rhythm for the rest of the heart.] i. SA node = 70-80/min ii. AV node = 40-60/min iii. Purkinje fibers (in ventricles)= 15-40/min iv. Ecotopic beats = originate from non-SA node v. Escape beats = occur when ventricle has not received stimulus from elsewhere. Rate of supraventricular impulses is slower than intrinsic rate of ventricles 2. Define the intrinsic heart rate, and state what it is i. Rate that heart beats at when it is not being affected by the autonomic nervous system (a) If all of the nerves supplying the heart are cut, it will still continue to beat, due to automaticity ii. Approximately 70 to 90 beats per minute (a) Anything faster than this indicates there is sympathetic nervous system stimulation (b) Anything slower than this indicates there is parasympathetic nervous system stimulation G. Autonomic Regulation of Heat Rhythmicity and Impulse Conduction 1. Compare the distribution of the sympathetic and parasympathetic nerves to anatomic regions within the heart i. Sympathetic (a) All parts ii. Parasympathetic (a) SA Node and AV junctional fibers, also a bit to the atria (b) Cause hyperpolarization (slow down action potential process) 2. Name the nerve which supplies parasympathetic function to the heart i. Vagus 3. Name the neurotransmitters released by the sympathetic and parasympathetic nerves to the heart i. Sympathetic (a) Release NE (a) Increase SA node discharge (b) Increased conduction rate of impulse (c) Increased contractile force ii. Parasympathetic (a) Release ACh  4. Identify why the sympathetic nervous system is able to increase contractile force of cardiac muscle i. Beta adrenergic receptor stimulation (a) Increased calcium ions (thus, greater contractility) H. Heart Rate Terminology 1. Define the basic terms used to describe heart rate i. Tachycardia (a) Faster than normal heart rate AT REST (b) During exercise, heart rate increases – this is NOT tachycardia ii. Bradycardia (a) Slower than normal heart rate at rest 2. Recognize that tachycardia and bradycardia MAY or MAY NOT indicate underlying pathology i. In other words, these terms simply describe heart rate – they are not a diagnosis