Chapter 19: The Heart
How are the papillary muscles, tendinous cords, and atrioventricular valve positioned relative to one another?
AV Valve lies the most superiorand the tendinous cords begins at the inferior edge of the valve attached to the papillary muscles.
What anatomic features slow the conduction rate of the action potential as it passes through the AV node? What is the function of this delay?
AV node and fibrous skeleton. The delay allows the atrium to finish contraction before ventricles contract
Where are the AV valves located within the heart? Where are semilunar valves located within the heart?
AV valves between the atrium and ventricle. Semilunar valves between a ventricle and arterial trunk
What pressure changes cause the closing of the AV valves and the opening of the semilunar valves?
AV valves close due to increase in pressure in ventricles that exceed atrial pressure. Semilunar valves open due to ventricle pressure increasing and exceeding arterial trunk pressure
What is the significance of the extended refractory period in cardiac muscle?
Allows time for sarcomeres of cardiac muscle cells within heart chamber wall to fully contract and relax before being stimulated again. Tetany is not exhibited and myocardium cells both contract and relax after each stimulation.
Explain what is meant by cardiac reserve
An increase in cardiac output above its level at rest. Subtract CO at rest from CO during exercise. Measure of the level and duration of physical effort in which an individual can engage.
Describe the function of the pericardium and the purpose of the serous fluid within the pericardial cavity
Anchors the heart, prevents the chambers from overfilling with blood, and lubricates the serous membranes to minimize heartbeat friction
Which of the great vessels are more visible from the anterior view? From the posterior view?
Anterior: Pulmonary arteriesand aorta/Posterior: VC and Pulmonary vein
Which side of the heart is more visible on the anterior view of the heart? the posterior view?
Anterior: Right/Posterior: Left
What generalization can be made about all arteries? and all veins?
Arteries away, veins towards
List the five phases of the cardiac cycle
Atrial contraction and ventricular filling, isovolumetric contraction, ventricular ejection, isovolumetric relaxation, and atrial relaxation and ventricular filling
Describe the septal defects that may occur during development
Atrial septal defect: postnatal heart still has opening between atrias and blood from left atrium shunted to right and creates enlarged right side. Ventricular septal defects: Incomplete interventricular septum causing tetralogy of Fallot. When aorticopulmonary septum divides the truncus arteriosus unevenly. Patient has a ventricular septal defect, very narrow pulmonary trunk and an aorta that overlaps both ventricles, enlarged right ventricle
What is the path of an action potential through the conduction system of the heart?
Atrium to SA to AV to bundles to purkinje to Ventricles
Describe the atrial reflex, which involves baroreceptors within the atria, the cardiac center, and the heart
Bainbridge reflex: protection from overfilling. Initiated when baroreceptors in atrial walls are stimulated by increase in venous return. Increase in nerve signals relayed along sympathetic neurons to the heart. HR increases so blood moves more quickly through the heart decreasing atrial stretch.
Explain the significance of coronary arteries as functional end arteries
Body tissues served by a single end artery. The left and right coronoary arteries provide blood to myocardium = arterioal anastomosis. ALthough a blockage of one would not shunt enough blood
Where is the heart positioned, and how is it oriented within the thoracic cavity?
Central to the body and within the thoracic cavity, posterior to the sternum, left of the body midline between the lungs within the mediastinum.
Describe the general function of the cardiovascular system
Circulate blood throughout the body to meet the changing needs of the cells 1) continuous delivery of oxygen and nutrients and 2) the removal of carbon dioxide and other waste products
Briefly summarize the mechanical events of muscle contraction
Contraction: Initiated with Ca2+ entry from IF and SR 1) Crossbridge: Myosin heads attached to actin form bridge between thick and thin filaments 2) Powerstroke: Myosin heads swivels, pulling thin filament past thick a short distance to decrease sarcomere width 3) Release of myosin head: ATP binds to myosin head to release the myosin head from actin Reset of myosin head: ATP split by myosin ATPase, energy for reset Relaxation: Closing of Ca2+ channels. Ca2+ released from troponin with subsequent decrease in crossbridges between thin and thick filaments.
What are the three primary sulci of the heart? What structures are within these superficial grooves of the heart?
Coronary: extends around circumfrence of the heart Interventricular: between ventricles, extending inferiorly from coronary sulcus towards apex 2) Anterior 3) Posterior Within are coronary vessels associated with supplying blood to the heart wall
What three electrical events occur at the sarcolemma of cardiac muscle cells? Explain each event
Depolarization/Plateau/Repolarization
Which function of the fibrous skeleton allows the atria to contract separately from the ventricles?
Electrical insulation. preventing propagation of action potentials directly from atria to the ventricles.
Define end-diastolic volume, end-systolic volume, and stroke volume. How are they related?
End diastolic volume: Volume of blood in the heart at rest End systolic volume: Volume of blood after contraction. Stroke volume: Amount of blood pumped out during ventricular contraction (EDV-SV=ESV)
What are the layers of the heart (in order) that a scalpel would pass through during dissection? What are the two names given to the outer layer of the heart wall?
Epi, Myo, Endo Epicardium/Visceral layer of serous pericardium
Name the three layers of the heart wall and the tissue components of each
Epicardium: Simple squamous epithelium and areolar connective tissue Myocardium: Cardiac muscle endocardium: Simple squamous epithelium and areolar
Explain the significance of ventricular balance
Equal amount of blood pumped by the two ventricles through the two circulations. Right ventricle has to pump to lungs but left to the system. Left has to be stronger to pump the same amount of blood as the right.
Discuss how cardiac muscle meets its energy needs
Extensive blood supply, numerous mitochondria, and other structures like myoglobin and creatine kinase. Relies almost exclusively on aerobic cellular respiration. Versatile in using fatty acids, glucose, lactate, amino acids, and ketone bodies.
Define chronotropic agents, and describe how they affect heart rate
Factors that change HR through acting on the SA or AV node. Primarily from ANS and some hormones
Describe the three layers that cover the heart. Where is the pericardial cavity relative to these layers?
Fibrous pericardium: dense irregular connective tissue that encloses the heart but does not attach to it Parietal layer: simple squamous epithelium and an underlying layer of areolar connective tissue Visceral layer of the serous pericardium: simple squamous epithelium and underlying delicate layer of areolar connective tissue
Identify the coronary veins, and describe the specific areas of the heart drained by their major branches
Great cardiac vein within anterior interventricular sulcus Middle cardiac vein within posterior interventricular sulcus Small cardiac vein alongside right marginal artery All drain into the coronary sinus
Compare and contrast the parasympathetic and sympathetic innervation of the heart.
HR and strength of contraction regulated by ANS (cardiac center of cardiovasc c. of medulla oblongata). Innervation merely modifies cardiac activity Parasymp (cardioinhibitory): right/left vagus nerves and brnach into heart. Right vagus for SA and left for AV. Decreases HR but no direct effect on force of contraction. Symp (cardioaccelatory): T1 - T5 segments extend to SA, AV, and myocardium. Increases HR and force of contraction. Also in coronary arteries for dilation.
Explain how post natal heart structures develop from the primitive heart tube
Heart develops from mesoderm. Day 10: paired tubes present in cardiogenic region of embryo and fuse by day 21. Single heart tube bends and folds upon itself on day 22. By day 28, heart tube is S shaped. Week 7, interatrial septum is formed by overlapping septa and foramen ovale is passageway that detours blood away from pulmonary circulation to systemic.
What are the two factors that determine cardiac output?
Heart rate and stroke volume
Summarize the variables that influence cardiac output
Heart rate, stroke volume, and cardiac output
What are the functions of the tendinous cords and papillary muscles?
Holds the AV valves back from inverting into the atriums.
What great veins deliver blood to the right atrium? to the left atrium?
IVC and SVC. Pulmonary veins
If both heart rate and stroke volume increase, does cardiac output (a) stay the same, (b) increase, or (c) decrease? Thus, is the relationship between these two variables and cardiac output direct or inverse?
Increase, meaning there is a direct relationship
Explain the intracellular structures of cardiac muscle
Intercalated discs found at cell to cell junctions linking cells together 1) Desmosomes: protein filaments that anchor into a protein plaque located on the internal surface of the sarcolemma. Prevent pulling apart of muscles 2) Protein pores between sarcolemma of adjacent cells. Low resistance pathway for flow of ions between cardiac cells. Allow action potentials to move continuously along sarcolemma of cardiac muscle cells = simultaneous stimulation and synchronous contraction = functional syncytium
Describe blood flow through the coronary arteries
Intermeittent. Vessels are open when heart is relaxed but compressed when heart contracts-- temporarily interrupting blood flow.
What is the structure that separates the two ventricles? What is the superficial landmark that identifies the location of this structure?
Interventricular septum marked by the interventricular sulci.
Which features of cardiac muscle support aerobic cellular respiration?
Large number of mitochondria and versatile ability to use different fuel molecules
Define cardiac output
Measure of how effective the cardiovascular system is in fulfilling its function. Amount of blood pumped by a single ventricle-- expressed as liters per minute. HR*SV=CO
What is occurring during ventricular ejection?
Movement of blood from ventricles into arterial trunks
Identify the components of an ECG recording
P wave: atrial depolarization in SA node (.08-.1 second) QRS complex: ventricular depolarization (.06-.1 second). Repolarization of atria masked by ventricle activity T wave: Ventricular repolarization
What events in the heart are indicated by each of the following: P wave, QRS complex, and T wave? Identify the two segments of an ECG that reflect the plateau
P-Q segment: Atrial plateau when contracting S-T segment: ventricular plateau when contracting The two segments between the wave correspond with the plateau.
Distinguish the effect of a positive chronotropic agent from that of a negative chronotropic agent on heart rate, and give examples of each
Positive: Increases HR ex) Activation of B1 adrenergic receptors Negative: Decreases HR ex) M2 muscarinic receptors
Describe the location and function of the fibrous skeleton
Provides structural interventricular support, forms supportive rings to anchor valves, provides framework for attachment of cardiac tissue, electrical insulator by preventing propagation of action potentials directly from atria to ventricles.
Compare and contrast pulmonary circulation and systemic circulation of the cardiovasc. system. Trace blood flow through both circulations
Pulmonary: 1) right side of the heart through blood vessels 2) the lungs (right to lungs to left) Systemic: 3) left side of the heart through blood vessels to 4) the systemic cells such as the brain and muscle (right to lungs to left to cells to right)
Identify the coronary arteries, and describe the specific areas of the heart supplied by their major branches
R/L coronary arteries positioned within c. sulcus of the heart to supply the wall. First and only branches of the ascending aorta. Right marginal artery supplies lateral wall of right ventricle Posterior interventricular artery supplies posterior wall of both ventricles Circumflex artery supplies lateral wall of the left ventricle Anterior interventricular artery supply both the anterior wall of the left ventricle and most of the interventricular septum.
Describe a nodal cell at rest
RMP created by electrical charge difference across the plasma membrane. The cytosol is relatively negative compared to IF. Roughly -60 mV established by K+ and Na+ leak channels and NA+/K+ pumps. RMP is not stable
Describe the conditions at the sarcolemma of cardiac muscle cells at rest
RMP value of -90 mV with greater NA+ outside, K+ inside, and Ca2+ outside.
Describe the general structure of cardiac muscle
Relatively short, branched cells that house 1-2 nuclei. Supported by areolar connective tissue (endomysium). Sarcolemma (membrane) invaginates to form T-tubules extending to SR (once per sarcomere and overlie Z discs). SR surrounds bundles of myofilaments-- arranged in sarcomeres create striation. Overlap of thin and thick filaments does not occur when at rest.
What is the function of the coronary sinus?
Returns deoxygenated blood into right atrium
Compare and contrast the structure and function of the two types of heart valves
Right AV valve: triscuspid Left AV valve: bicuspid (mitral) When ventricles contract, the valves close. Atrial inversion prevented from tendinous cords. Pulmonary and aortic: half moon, no cords. They open when ventricles contract and blood force pushes valves open. Close when ventricles relax and catches backward flowing blood.
Characterize the four chambers of the heart and their functions
Right atrium: smooth posteriorly, pectinate muscles anteriorly and within auricle. fossa ovalis. Coronary sinus drains deoxygenated blood from heart wall. Openings of VCs all draining. AV valve separates it from ventricle. Right ventricle: Trabeculae carneae internal wall, with papillary muscles projecting, anchoring collagen fibers/tendinous cords/chordae tendinae attached to right AV valve. Leads to pulmonary trunk through pulmonary semiliunar valve carrying deoxygenated blood to lungs through pulmonary arteries. Left atrium: muscular structure similar to right. Recieves oxygenated blood from pulmonary veins and flows through atrioventricular opening into left ventricle Left ventricle: Similar to right ventricle muscular structure. Two papillary muscles anchored by tendinous cords. Flows to aortic semilunar valve.
What areas of the heart are deprived of blood when there is a blockage in the posterior interventricular artery?
Right side of the heart
Identify and locate the components of the heart's conduction system
SA node: posterior right atrium initiates heartbeat AV node: floor of right atrium AV bundle: extends from AV node into interventricular septum dividing into L/R bundles Purkinje fibers extend from L/R bundles at apex of heart and into ventricle walls
Which autonomic division is associated with the cardio acceleratory center in the brain stem and how does it affect heart activity?
Sympathetic division and affects heart activity through spinal cord connection to nodes and myocardium to increase HR and contraction force + increases blood flow through artery dilation
Why is the SA node referred to as the pacemaker?
The SA node initiates the signal of the heartbeat
List the structural components of the pericardium
The fibrous pericardium, parietal layer, visceral layer
What would be the path of blood flow through the heart if the foramen ovale did not close shortly after birth?
The path of bloodflow through the heart would be from the right atria to the left.
Explain the significance of the plateau phase
This plateau phase allows for a longer muscle contraction and gives time for the nearby cardiac muscle cells to depolarize. This is important in allowing the heart to contract in a steady, uniform and forceful manner.
What is the bony structure that protects both the heart and the lungs?
Thoracic cage
Identify the two processes within the heart that occur due to the pressure changes associated with the cardiac cycle
Unidirectional movement of blood through heart chambers along a pressure gradient Opening/closing of heart valves to ensure that blood continues to move in a "forward" direction without backflow
List the three variables that may influence stroke volume
Venous return (volume of blood returned to heart), Inotropic agents (external agents that alter contractility), and afterload (resistance in arteries)
Differentiate among the three primary types of blood vessels.
arteries (away) veins (toward) capillaries (sites of exhange)
Define perfusion. Why would it be significant if the cardiovascular system failed to mean adequate perfusion?
delivery of blood per unit time per gram of tissue. (milliliters per minute per gram) cell death would occur
Describe the general structure and function of the heart
hollow, four chambered organ that pumps blood through out the body. -two sides: receiving chamber (atrium) and pumping chamber (ventricle) -great vessels: large arteries and veins directly attached to heart (arteries: pulmonary trunk to right v. and aorta from left v) (veins: SVC and IVC drain into right atrium, pulmonary veins drain into left atrium) -valves: AV valves between a and v. semilunar valves between ventricle and an arterial trunk)
Describe the location and position of the heart in the thoracic cavity
posterior to the sternum left of the body midline between the lungs within the mediastinum, slightly rotated such that its right side or border is more anterior and left is more posterior.
Which of the great vessels is an artery and transports deoxygenated blood? Which of the great vessels is a vein and transports oxygenated blood?
pulmonary artery and pulmonary veins
What path does blood follow through the heart and the two circulations? Identify all structures that it passes through. Including each chamber, valve, and great vessel. Begin at the right atrium
right to lungs to left to cells. Right atrium to right ventricle through pulmonary trunk to pulmonary arteries (R/L) to lung capillaries to pulmonary veins (R/L) to left atrium to left ventricle to aorta to systemic capillaries then to IVC and SVC to right atrium.
Where does the right ventricle pump blood? Where does the left ventricle pump blood?
right ventricle pumps to the lungs, left ventricle to the body.
What is the resting membrane potential (RMP) value of nodal cells?
-60 mV
List and describe what occurs during the five phases of the cardiac cycle
1) Atrial Contraction/Ventricular Filling: SA node stimulates atrial wall contraction moving remaining blood into ventricles. Ventricles fill completely when atria is done contracting = End diastolic volume (EDV) > 130mL. Great veins are compressed during contraction. Isovolumetric contraction: No change in ventricular blood volume when ventricles contract. AV valves close. Purkinje fibers stimulate ventricular contraction. Now all heart valves are closed. Ventricular Ejection: Blood goes from ventricles to arterial trunks forcing semilunar valves open. Stroke volume is the amount of blood pumped out during the ventricular contraction > 70 mL. End systolic volume is the remaining blood in ventricle at the end of systole/contraction. Isovolumetric relaxation: Ventricles relax and semilunar valves close. All heart valves are close simultaneously. Atrial relaxation and ventricular filling: Ventricles relax and AV valves open.
Describe the spread of the action potential through the heart's conduction system
1) Both atria: SA node AP first along the cardiac cells in atria and spread between by gap junctions = instantaneous excitation of all cells in atrial walls 2) AV node: AP arrives at AV node and slow conduction rate allowing atria to finish before ventricles contract. Aided by fibrous skeletons which isolate AP to AV node 3) AV bundle: AP to bundle then purkinje fibers 4) Ventricles: Along ventricles and simultaneous stimulation of ventricular walls
List the electrical events of an action potential that occur at the sarcolemma
1) Depolarization: AP through conduction system triggers opening of fast voltage gated Na+ channels in sarcolemma and changes RMP to +30 mV and close. 2) Plateau: Depolarization triggers K+ channels and it leaves cells and slightly repolarizes cell. Ca2+ channels in the sarcolemma open and enters cells. SR is stimulated for Ca2+ release negates K+ effect. 3) Repolarizes: Ca2+ channels close and K+ channels open to completely repolarize.
Describe the steps for SA nodal cells to spontaneously depolarize and serve as the pacemaker cells
1) Reaching threshold: Voltage gated cation channels open (caused by previous repolarization). Na+ flows into nodal cells with Ca2+ through their T type channels and RMP increases. 2) Depolarization: Changing of the membrane potential triggers voltage gated Ca 2+ channels and creates a positive RMP 3) Repolarization: Ca2+ channels close and K+ channels open to return RMP to negative state.
What is the cardiac output at rest and during exercise, and the cardiac reserve, if (a) the heart rate is 75 bpm and stroke volume is 70 mL at rest, and (b) if the heart rate is 150 bpm and stroke volume is 100 mL during exercise?
CO at rest = 5250 mL per minute / CO during exercise = 15000 mL per minute / Cardiac reserve = 9750 mL per minute
In which direction does Ca2+ move in response to the opening of voltage-gated Ca2+ channels: into or out of the cardiac muscle cells?
Ca2+ moves into the cell when channels open
Define autorhythmicity
Capability to depolarize and initiate an action potential spontaneously without an external influence
Discuss how autonomic reflexes alter heart rate
Cardiac center receives sensory input from baroreceptors and chemoreceptors. Cardiac center responds by altering nerve signals that innervate the heart to maintain homeostasis.
Define the refractory period
a period immediately following stimulation during which a nerve or muscle is unresponsive to further stimulation.
Define each of the three variables, and describe the factors that influence each variable and how each variable affects stroke volume
Venous return: Volume of blood returned to the heart via great veins. Determining amount of blood in the ventricle at the end of rest immediately prior to contraction (Preload: stretch of heart wall due to load which cardiac muscle subjected before shortening). Frank-starling law states that volume entering the heart increasing is a greater stretch and therefore a more forceful ventricular contraction and stroke volume increases. VR is affected by change in venous pressur eor increase in time to fill. Inotropic agents: Alter contractility, the force of contraction at a given stretch of the cardiac muscle cells. Change due to change in available Ca2+ in sarcoplasm. Changes in Ca2+ concentration alter crossbridge numbers. Afterload: Resistance in arteries to the ejection of blood by ventricles. Represents the pressure that must be exceeded before blood if ejected from chamber. Artherosclerosis creates narrower arteries-- increasing the resistance to pump blood into arteries and decreasing stroke volume
Which of the following increases stroke volume: (a) increased venous return, (b) increased Ca2+ in sarcoplasm, or (c) afterload? Explain.
a and b