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52 Cards in this Set
- Front
- Back
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What does the heart really consist of?
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2 Separate pumps that are coupled together in series.
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How does the heart maintain a state of mass balance so the same volume of blood that enters the right heart gets pumped out of the left heart?
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By nature of the length tension diagram of the heart - Starling's Law of the Heart.
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What are 2 ways that the right and left heart are separate from each other?
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1. Mechanical isolation
2. Electrical isolation |
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What are the structures that are the basis of mechanical isolation?
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1. Septa
2. Valves |
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What do the AV and semilunar valves do?
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Prevent backflow
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What do Papillary muscles do?
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Prevent prolapse of valves during ventricular contraction.
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What connects the papillary muscles to the valves?
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Chordae tendineae
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Which side of the heart has a bigger wall? Why?
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The left heart - because it has to pump blood through the entire systemic circulation.
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How are Cardiac and Skeletal muscle similar?
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They are both striated and contain fairly uniform arrangements of their sarcomeres.
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How are Cardiac and Skeletal muscle different?
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-Skeletal myocytes contract independently
-Cardiac myocytes contract as a syncytium |
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What allows cardiac myocytes to contract all together as a syncytium?
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Intercalated disks which are gap junctions.
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What features of gap junctions allow syncytial contractions of cardiac muscle?
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-Low electrical resistance
-Free diffusion of ions between cells -Spread of APs from cell to cell |
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So what happens when one area of the heart depolarizes?
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It spreads throughout the entire heart and induces contraction.
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So what SEPARATES cardiac myocytes? What connects them?
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-Intercalated discs separate
-Gap junctions connect |
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Is the entire heart all one syncytium?
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No; it is separated into Atrial and Ventricular Synctia
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What is the thing that separates the Atrial syncytia from Ventricular?
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The AV Bundle
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What is the AV bundle?
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A fibrous ring that prevents Action potentials from passing from the atrial muscles to the ventricles without passing through a specific bundle of conductive fibers
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What is the result of the AV bundle's regulation of APs passing from the atrium to ventricle?
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It allows the atria to contract ahead of the ventricles.
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What is the fundamental difference in Cardiac muscle action potentials compared to skeletal muscle?
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It has a very long plateau at the top of the action potential
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Why do Cardiac muscle action potentials have such a long plateau?
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To prevent repeated contractions of the muscle - tetany of the heart is very bad.
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What allows for cardiac muscle to not contract during the plateau?
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It is refratory to repeated stimulation.
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What is the rate of propagation of action potentials around the heart?
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Relatively slow
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What is the amplitude of a cardiac muscle action potential? What is its range of magnitude?
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Amplitude = 105 mV
Magnitude: from -85 to +20 |
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How long is the plateau of a cardiac muscle AP compared to skeletal muscle?
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15X longer
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How long does atrial muscle remain depolarized? Ventricular? Skeletal muscle?
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Atrial: 0.2 sec
Ventricle: 0.3 sec Skeletal: much shorter time |
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How does the length-tension relationship for cardiac muscle affect its function?
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At optimal sarcomere lengths caused by degree of filling of the ventricles, the muscle will contract with more force.
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How does crossbridge cycling occur in cardiac muscle?
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By the same mechanism as in skeletal muscle - the sliding filament mechanism.
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What does the degree of filling of the heart ventricles determine?
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The amount of passive force that is in the muscle prior to contraction.
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What limits cardiac muscle from stretching beyond its normal physiologic lengths at which active force would drop off?
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The pericardium
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What is the nature of the slope of the length tension curve for cardiac muscle within the normal physiologic range?
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Steep - so slight changes in length (heart filling) have pretty significant effects in the force generated during contraction.
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What is the major portion of work that is done by the heart?
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Stroke work output - Volume-Pressure work.
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What is the minor portion of work that is done by the heart?
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The work of acceleration of blood to its velocity of ejection.
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What is Preload?
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End diastolic pressure
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What is Afterload?
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Systolic pressure
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What is meant by the term Preload?
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The amount of blood that is coming into the heart - the "prestretch" of blood returning to the heart
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What is meant by the term Afterload?
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The force that the heart is pumping into.
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What is generated when you allow the heart to fill, clamp the aorta, and measure the pressure in the left ventricle with subsequent cycles of filling and isovolumic contraction?
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The left ventricular isovolumic pressure-volume curve
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What does the isovolumic pressure volume curve demonstrate?
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That increasing preload enables the heart to generate more force
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What does increasing afterload at a fixed preload do to the heart?
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Decreases stroke volume
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What will increasing preload do to the heart? What is this called?
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Increase stroke volume - called the Frank Starling mechanism.
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What will increasing contractility do to the heart? What accomplishes this?
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Increase stroke volume, but NOT preload - just pumps more out.
Accomplished via Epi/NE and the sympathetic nervous system. |
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What is the relationship between compliance and distensibility?
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As compliance increases, distensibility does as well.
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How does increasing compliance affect the heart?
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It makes it easier for the ventricles to fill so volume increases more.
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what is the detrimental effect of decreased compliance?
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The heart can't fill up with volume; hence it can't generate force to pump out either.
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What are the 2 main types of regulation of heart pumping?
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1. Intrinsic regulation
2. Autonomic neural regulation |
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What does Intrinsic regulation refer to?
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The frank-starling mechanism
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What is the Frank Starling Mechanism?
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Within physiological limits the heart pumps all of the blood that comes into it without allowing excessive damming of blood in the vein.
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What is Autonomic neural regulation composed of? (3 things)
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-Sympathetic innervation
-Vagal innervation -Circulating epinephrine |
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What happens to CO as BP increases to about 160 mm Hg?
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CO remains constant
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Above 160 mm Hg what happens to CO?
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It decreases - afterload is just too much.
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Which side of the heart does more work? How much more?
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The left ventricle - does 10X more work than the right ventricle.
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Why does the left Ventricle do 10X more work than right?
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Because it's pumping agains MAP which is 100 mm Hg, compared to pulmonary pressure which is like 15 mm Hg.
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