Cardiac physiology Flashcards
Which law does each belong to;
1) The tension on the wall of a sphere is the product of the pressure times the radius of the chamber and the tension is inversely related to the thickness of the wall
2) The stroke volume of the left ventricle will increase as the left ventricular volume increases due to the myocyte stretch causing a more forceful systolic contraction
3) The pressure of an incompressible and Newtonian fluid in laminar flow through a long cylindrical pipe will drop as the cross section increases
4) Wall tension is directly proportional to pressure
1) Laplace
2) frank-starling
3) Poisuille
4) Laplace
Which of the following describes the frank starling relationship?
1) The tension on the wall of a sphere is the product of the pressure times the radius of the chamber and the tension is inversely related to the thickness of the wall
2) The stroke volume of the left ventricle will increase as the left ventricular volume increases due to the myocyte stretch causing a more forceful systolic contraction
3) The pressure of an incompressible and Newtonian fluid in laminar flow through a long cylindrical pipe will drop as the cross section increases
4) Wall tension is directly proportional to pressure
it is 2
What are the three types of heat liberated by muscle?
- Maintenance = slow liberation of heat that is unrelated to contraction
- Activity related heat
-> Initial heat – appears during contraction due to:
- Tension-independent heat: caused by membrane depolarisation and repolarisation, Ca2+ cycling in the SR, Ca2+ binding to troponin I, conformational changes in the thin filament, ion transport via the sodium/potassium pump, and oxidative reactions that rephosphorylate ADP
- Tension-dependent heat: (aka shortening heat, tension time heat): caused by contractile protein interactions, muscle shortening and cross-bridge turn over.
-> Recovery heat – liberated once contraction has reached its peak, caused by ADP rephosphorylation by the Mch potential energy degraded to hear as tension falls during relaxation.
How does myosin ATPase concentration affect heat generation in muscle?
Crossbridge cycling rate occurs at rate that is proportional to myosin ATPase activity. Muscles with low Myosin ATPase activity waste less heat as tension-time heat because crossbridge cycling is low. The opposite is true for mm with high myosin ATPase activity.
what is the main energy source of the heart ?
Fasted state; FAs become the main energy source. Use of lipids account for 60-70%of the oxygen uptake in the heart where as CHOs account for <20%.
Fed state; CHO and insulin levels are high, circulating fatty acid concentration is low. The uptake of FAs by the heart is inhibited and glucose becomes the major fuel of the heart. CHOs account for 50% - 75% of the oxygen uptake.
How much of the glucose is converted into energy in the heart?
The rates of glucose oxidation only account to ¼- ½ of the the chemical glucose uptake, the rest may be converted to glycogen.
What shift occurs in energy metablism due to ischaemia?
In ischaemia oxidative metabolism decreases and glycolysis is stimulated but iscahemia results in inhibition of pyruvate dehydrogenase and so glucose cannot enter the TCA cycle. because of this FFAs are better able to capture the residual oxygen uptake. This is inefficient however as FFAs waste oxygen.
what receptors are responsible for glucose uptake into the cardyomyocytes?
What is the hormone which increases uptake of glucose?
GLUT-1 and GLUT-4 – glucose specific transporters
Insulin
what are insulins effects in the cardiomyocyte?
- Reduce FFA release (removing the inhibition to gluc uptake)
- Increase GLUT transporter translocation from the nucleus:
a. Insulin binds to the alpha subunit = autophosphrylation
b. Activation of peptide kinases = phosphorylation of tyrosine
c. Increased activity of insulin receptor subtype 1
d. Activation of IP3
e. Activation of PKB (Akt)
