LV Function as a Pump Flashcards
- Describe the cellular ultrastructure of the myocardium important for the contraction.
a myofibers is composed of interconnected myocytes
myocytes have contractile myofibrils in which each sarcomere has coupled actin and myosin fibers that produce the force of contraction
energy is required for the “cocking” of the myosin head and continued cycling and relaxation (cross bridge cycling)
- Explain the process of calcium activation and its control of contraction of the myocyte.
troponin I and T molecules regulate the binding alternation of myosin heads on actin fibers
contraction is initiated by Ca2+ induced Ca2+ influx whereas calcium can than bind to Troponin I and cause movement of Troponin T so the active site for binding with myosin head is revealed
- Discuss how the effects of length changes on myocardial cellular force development and whole chamber force development.
with more strength there can be more force generation, so increased preload means greater contractility (ionotropic)
*titin anchors myosin to the Z line and limits the amount of stretching and contraction that myocytes are capable of (1.7-2.2 micron range)
- Describe the Frank-Starling mechanism of who heart performance and how it helps explain ventricular function.
when a heart myocyte or chamber is stretched, it is able to produce more contractile strength (within a range) given ability for more overlap between actin and myocytes
How does calcium levels within the cell contribute to muscle force development.
many theories:
increases xbridge cycling
activate more troponin control
greater response of ATPase or light chain phosphorylation
bottom line is increased Ca++ within limits, leads to greater contractility
- Describe the concept of preload at the cellular level and at the whole heart level.
as you stretch the fibers and chamber of the heart, it is able to produce more contractility, and this is seen with increased pre-systolic filling
increasing preload increases the stroke volume and increases CO
- Describe the concept of after load at the cellular level and at the whole heart level.
after load decreases the velocity of contraction (longer isovolumetric contraction time)
ejection against a greater pressure, the amount of blood that can be ejected is reduced causing preload to build and improving SV through this mechanism
- Explain what adrenergic stimulation does to myocardial function.
B receptor agonists increase the force generated, increasing contractility of the heart by setting of a Ga second messenger cascade to allow a greater amount of Ca into the cell, further increasing CICR
overall increases the rate of contraction, the force of contraction and rate of relaxation; can handle a bigger load and at faster velocities, within limits
- How do adrenergic stimulation affect pressure volume loops and Frank-Sterling curves.
B system can augment the force generation against an after load with, sending yourself to a higher inotropic curve
Describe the motion of the heart as it contracts.
complex layers of muscle contract, wringing out, as if a it were a towel
fibers are positioned in counter-wound helices that change orientation based on trasmural location endocardial R hand helix and epicardial L handed; surface long axis and midway circumferential and as a whole are bound together in sheets
- Describe the pressure volume loop and what conditions change the pressure volume loop.
X axis- LV volume
Y axis LV pressure
chart the development of pressure through conduction with the area within the curve significant for representing the SV
factors that can change the curve/loop include preload, after load, contractility and ejection fraction
How is preload and after load clinically measured?
preload: LV end diastolic volume, ventricular filling pressure
after load: systolic blood pressure is crude measurement, calculating systemic vascular resistance and peak systolic wall stress are more sophisticated measures
- Define the concept of ejection fraction and how it relates to the time volume curve of performance of the left ventricle?
ejection fraction, or the amount of blood that flows into the heart that is pumped out of the heart and it contributes directly to preload stretching but also relates directly to the contractility of the heart (its functionality)
- List ways that cardiac function changes: global, region and synchronous
we have discussed the heart on a global scale but it is important to remember that regional areas of the heart can effect muscle in a heterogenous way ie. ischemia, surrounding cells can be put at increased stress and change the architecture of the cells
electrical damage can cause dyssynchrony, which can reduce pump performance due to non-inform force generation and timing issues
