Topic 1 CVS Lecture 4 Flashcards
What is the epicardium?
Outer layer of the heart made up of connective tissues and fats.
What is myocardium?
The muscular part of the heart.
What is Endocardium?
The inner walls of the heart made of endothelial cells.
What is the effect of a change in extracellular calcium on cardiac contraction?
The more extracellular calcium there is the higher the force of contraction.
What is cardiac output?
The litres of blood ejected from the heart per minute.
CO = SV x HR
What are the 2 ways that cardiac output can be altered?
Changing heart rate or stroke volume.
What are the 2 mechanisms used to alter stroke volume or force of contraction.
Alter muscle length therefore altering end diastolic volume.
Alter calcium release and therefore contractility.
What is ejection fraction?
The amount (in percentage) of blood ejected from the ventricle. (EDV-ESV)/EDV x 100
Explain the Frank-Starling mechanism.
The mechanism describes the relationship between myocardial stretch and stroke volume.
An increase in EDV (from increased venous return for eg) will lead to increased pressure in the ventricles. This increased pressure will then cause myocardial stretch. The increased length of the stretched muscle fibres allows for an increased force of contraction.
What are the 2 main determinants of EDV?
Venous pressure.
Filling time.
What would happen if the right ventricular cardiac output was 5.05 and the left ventricular cardiac output was 5?
This would increase the pulmonary blood volume which would increase the pressure in pulmonary veins. This would increase the left ventricle filling pressure which would stretch the muscle cells, increasing stroke volume and therefore cardiac output until the cardiac outputs are matched.
How can stroke volume be altered by changing calcium release?
Sympathetic activation of the heart through noradrenaline increases the contractility of the heart by acting on beta receptors on cardiac muscle cells to increase calcium entry and release from the sarcoplasmic reticulum.
More Ca means stronger contraction.
Hormonal adrenaline does the same thing.
