Term
Excitation-contraction coupler = |
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Definition
free cytosolic calcium:
action potential ------Ca++------>contraction |
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Term
2. Sarcoplamic reticulum (SR) = |
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Definition
major site of calcium storage and major source (95%) of Ca++ for excitation-contraction coupling. Calciquestrin = protein that binds and buffers Ca++ in SR.
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Term
Cardiac muscle requires extracellular calcium (entry via “slow” Ca++ channels) to serve as a trigger for _________. Cytoplasmic side of SR has ___ calcium binding sites linked to a calcium channel - binding of 1 Ca++ to the fast binding site (activation site) causes ________________________.
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Definition
sarcoplamic reticulum (SR) calcium release
2
a conformational change opening the Ca++ channel in the SR membrane - Ca++ diffuses out.
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Definition
| Similar to skeletal muscle, Ca++ binds to the C subunit of Troponin; causing a conformational change in the I subunit of Troponin; pushing the tropomyosin into the groove in the F-actin molecule exposing the myosin binding site on actin; activating the contractile/filament sliding process.) Generally there are more sites for Ca++ binding on C subunits of troponin than free Ca++ ; so more Ca++ release leads to stronger contraction. |
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Definition
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5. Repolarization of myocardial cells is associated with closure of _______________ and transport of Ca++ into _________; additionally, towards the end of the cardiac action potential Ca++ begins to bind to the second site (inactivation or slow binding site) on the SR calcium channel, inactivating the channel and halting exit of Ca++ from the SR. There is a fall in intracellular [Ca++] and then dissociation of Ca++ from both binding sites of the SR Ca++ channel. |
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Definition
cell membrane calcium channels
SR and interstitial fluid |
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Term
_______ contain plentiful mitochondria (35% of cell volume vs 2% in skeletal muscle) suppplying most of energy by _________. |
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Definition
6. Contractile cells
oxidative phosphorylation |
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Definition
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Term
| What is the cardiac cycle? |
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Definition
CARDIAC CYCLE=coordinated sum of all events that occur in the heart from one beat to the next. Effective cardiac contraction leads to ejection of blood from its chambers. Note that all of these events are precisely coordinated. (Note: The cardiac cycle of the right heart is similar to that for the left though pressures are much lower.) |
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| What are the 3 steps in the cardiac cycle |
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Definition
Step 1: Each cycle is initiated by pacemaker (usually SA node) depolarization. Variations in cell membrane ion conductance lead to the characteristic changes in transmembrane potential we refer to as the action potential. The coordinated sum of these action potential leads to an electrical dipole (potential) on the suface we can record (EKG).
Step 2: There is coordinated delivery of the depolarization wave to all cells in the syncytia by the conduction system (Atria first, then a delay, then ventricles.) Because of this cardiac conduction system, all action potentials within a syncytium begin more or less simultaneously (generally within 0.02 - 0.06 seconds).
Step 3: Calcium influx during the plateau of the action potentials leads to myosin/actin interaction and shortening of cardiac cells. The cells begin to contract in the same order in which they were depolarized; therefore the contraction process takes about 0.02-0.06 seconds to be initiated all cells within a syncytium. Initiation of tension development occurs in a coordinated fashion (Atria first, delay, then ventricles.) The cells remain contracted as long as free calcium is available (plateau phase of action potential). Thus contraction within a syncytium lasts about 0.2 to 0.3 seconds; during most of this time all of the contractile cells in that syncytium are simultaneously contracted.
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Term
| Components of atrial function |
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Definition
1. Atrial function:
A. The flow, from veins thru the atria directly to the ventricles, accounts for 75% of the blood that fills the ventricles during each cardiac cycle. Atrial contraction delivers the final 25%.
B. The pressure within the atria is low (0-5 mmHg). There are three pressure waves within the atria.
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| What are the 3 pressure waves within the atria? |
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Definition
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Definition
caused by atrial contraction (atrial systole). Muscle fibers in the atria are roughly arranged in a circular fashion and thus contraction leads to compression (modest) of blood in the ventricle.
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Term
caused by ventricular contraction raising pressure in the ventricular and causing bulging of the closed A-V valves into the atria, compressing the blood in atrium (pressure rises slightly)
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| caused by atrial distention as the atria fill |
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Definition
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Definition
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Definition
this is the period of ventricular relaxation
Early after the last ventricular contraction, blood rushes into the ventricular chamber (PERIOD OF RAPID INFLOW). In the middle third of diastole, there is little additional inflow of blood (DIASTASIS) and during this time, there is little change in the ventricular volume curve. The duration of diastasis decreases during mild to moderate tachycardia. This has little effect on cardiac filling. However, in extreme tachycardia diastasis disappears and the period of rapid inflow is shortened with stroke volume diminishing as a result. The final third of diastole is ATRIAL SYSTOLE, during which time the final minority (25% in an animal at rest) of ventricular filling occurs.
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Term
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Definition
| Muscle fibers in the ventricle are arranged spirally and thus contraction leads to shortening of the apex-base distance and compression of blood in the ventricle. The spiral arrangement is efficient for force generation (like squeezing a sponge). Immediately after ventricular contraction begins, intraventricular pressure rises, exceeds atrial pressure, and the A-V valves close. During this time and soon thereafter, the ventricular pressure rises without appreciable change in volume. This is the period of ISOVOLUMETRIC CONTRACTION. This period ends abruptly with the opening of the semi-lunar valves (aortic and pulmonic) and the beginning of the period of EJECTION. At the end of systole, ventricular relaxation begins, the semi-lunar valves close as ventricular pressure falls. Initially this occurs without appreciable change in ventricular volume (PERIOD OF ISOVOLUMETRIC RELAXATION) and then the intraventricular pressure falls below atrial pressure causing the AV valves to open and the cycle begins again. |
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Term
END DIASTOLIC VOLUME (EDV): |
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Definition
volume of blood in the left ventricle at the end of diastole
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Term
END SYSTOLIC VOLUME (ESV): |
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Definition
the volume of blood in the left ventricle after systole
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Term
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Definition
amount of blood ejected by the left ventricle in one contraction = EDV - ESV
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Term
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Definition
number of cardiac cycles per minute
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Term
EJECTION FRACTION (usually given as a %): |
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Definition
percent of EDV that is ejected = (SV/EDV) X 100%
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Term
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Definition
The amount of blood ejected by the left ventricle per unit time, generally expressed in liters/minute = SV X HR.
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Definition
Amount of blood returned to the right atrium, expressed in liters/minute.
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Term
What is the relationship between cardiac output and venous return?
What is the relationship between cardiac output of the left and right ventricles? |
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Definition
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4. Valvular function and heart sounds: |
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Definition
Blood flow in the cardiovascular system is unidirectional. This is due to pressure gradients in most of the system. However, in some locations within the cardiovascular system (heart and veins), passive unidirectional valves are required because of varying direction of the pressure gradient.
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Term
A. the A-V valves (right AV valve = tricuspid and left AV valve = mitral) |
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Definition
prevent retrograde flow of blood from the ventricle to the atria during ventr. systole
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Term
B. the semilunar valves (right = pulmonic and left = aortic) |
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Definition
prevent retrograde flow of blood from the major arteries during relaxation (a time when arterial pressure exceeds ventricular pressure)
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Definition
| Point of maximal intensity (PMI) for valve sounds (used in clinical medicine). |
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Definition
first heart sound ("lub"), occurring at the onset of systole, due to AV valve closure and semilunar valve opening
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Definition
second heart sound ("dub"), occurring at the onset of diastole, due to semilunar valve closure and AV valve opening
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Definition
third heart sound, occurring in early ventricular diastole, due to rapid inflow of blood into the ventricles
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Definition
4th heart sound, occurring in late diastole, due to turbulence created as atrial contraction pushed blood into the ventricles
Usually only S1 and S2 are heard in dogs and cats, but S1-S4 may be heard in large animals.
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Term
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Definition
are abnormal heart sounds that occur whenever there is turbulent flow of blood. This commonly occurs when heart valves fail to function properly. There are 2 main types of valvular abnormalities. In each of them, a murmur may be heard.
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Term
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Definition
a valve that does not close adequately, thru which retrograde flow occurs (in dogs, usually involves the mitral valve)
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Definition
a valve which does not open adequately, and consequently restricts flow
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Term
When in the cardiac cycle would a murmur be heard in a man with mitral insufficiency?
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Definition
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5. Arterial (aortic) pressure curve:
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Definition
| This is the pressure often referred to as "blood pressure". In dogs, aortic pressure is normally approximately 80 mmHg at the end of ventricular relaxation (diastolic pressure) and 135 mmHg at the peak of ventricular systole (systolic pressure). The notch of the aortic pressure curve (incisura) is caused by backward flow of blood striking the closed aortic valve early in diastole. |
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How can blood pressure by measured |
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Definition
| Blood pressure may be measured directly by cannulation of the aorta or indirectly with ultrasonic, oscillometric, phototplethysmographic, or auscultatory methods. The shape of the aortic pressure curve in an animal at rest indicates that the pressure is nearer to diastolic than systolic pressure for a longer proportion of the cardiac cycle and hence the MAP is closer to diastolic pressure. An appropriate formula for a mammal at rest is: MAP= (1/3 X systolic) + (2/3 X diastolic). |
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Definition
| is the rate of movement of blood within the cardiovascular system. It is a volume of blood passing a given point per unit time and is generally expressed as ml/min or liter/min. Cardiac output is a flow. |
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Definition
| is used to refer to blood flow through a tissue and is expressed as ml/min/gm of tissue. |
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Definition
| is hydrostatic pressure. It varies throughout the systemic circulation and is pulsatile in the arteries and arterioles. |
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Term
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Definition
is the opposition to blood flow offered by a vessel. Both length and diameter of a blood vessel effect the resistance to blood flow. The smaller diameter and longer blood vessels offer more resistance to blood flow. The relationship between resistance to blood flow (R), diameter (D), and length (L) of a single blood vessel is referred to as the Poiseuille's Law:
R= k (L/D4), where k is Poiseuille's constant. |
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