Myocardial mechanics

Question 1

Calcium during cardiac muscle relaxation

Answer 1

0.1uml in sacroplasm, 10nm in SR- so calcium binds to calsequestrin to lower the concentration

Question 2

How is Magnesium involved in cross bridge cycling?

Answer 2

Provides signalling for breaking down ATP

Question 3

Who is the Length-Tension relationship by?

Answer 3

Starling

Question 4

What does Starlings law allow to be measured?

Answer 4

Length is proportional to EDV and tension to systolic pressure- so can make length tension diagram from volume pressure diagram

Question 5

Difference between passive length tension diagrams for skeletal and cardiac muscle and why?

Answer 5

Passive tension begins to rise at a much lower length in cardiac muscle compared to skeletal - because the non contractile components are less destensible

Question 6

Difference between active length tension diagrams between skeletal and cardiac muscle

Answer 6

More rise in tension at longer cardiac muscle lengths due to at longer length (1.8um) there is an increase in calcium sensitivity so more cross bridges form, raising above 1.8um increases the tension on stretch activated calcium channels therefore increasing calcium entry from the ECF thus enhancing calcium induced calcium release. As cardiac length increase above 2.4um active tension decreases rapidly whereas skeletal more slowly

Question 7

Which muscle is there greater regulation of tension and why?

Answer 7

Cardiac muscle as more motor units can’t be added together to increase contraction whereas skeletal muscle can

Question 8

What is the max tension of cardiac muscle?

Answer 8

2.2um

Question 9

What is the maximum length in cardiac brought about by?

Answer 9

10-12mmHg

Question 10

What indicates contractility?

Answer 10

Vmax- the initial velocity of shortening

Question 11

When does change in contractility of the heart occur?

Answer 11

When heart changes its output per beat but the same end diastolic volume

Question 12

What can cause an increase in contractility?

Answer 12

When more cross bridges form per stimulus, quality of actin/ myosin cross bridges

Question 13

What can have positive inotropic and chronotropic effect?

Answer 13

Noradrenaline- which increases the max force and the Vmax

Question 14

Why does an increase in frequency increase tension?

Answer 14

More beats mean more calcium influx during plateau via Cav1.2 L type channels, depolarisation during plateau of an AP causes Na-Ca exchanger to operate in reverse so calcium entered, also increase rate stimulates SERCA2A thereby sequestering the Ca in SR