Cardiac contraction Flashcards
1
Q
Cardiomyocyte structure overview
A
- Cardiomyocytes: Make up branching of myofibres. Myocytes contain multiple myofibrils composed of repeating sarcomeres.
- T tubules: Invaginations of the sarcolemma that penetrate the centre of cardiac muscle. Cytoplasm between the myofibrils contains the nucleus, mitochondria and sarcoplasmic reticulum. (Intracellular membrane system)
- Sarcomeres: Cause muscle ccontraction when actin and myosin move to each other. Actin-myosin overlap is shown for systole and diastole.
2
Q
Cardiomyocyte function overview
A
- The T tubules have calcium channels - ensure calcium is delivered deep into the cell close to the sarcomere.
- Calcium enters via calcium channels that open in response to depolarisation which travels along the sarcolemma - positive feedback - more and more calcium from sarcoplasmic reticulum and initiate contraction.
- The varying actin-myosin overlap is shown for systole when conc of Ca2+ is maximal, and diastole when conc of Ca2+ is minimal.
- Eventually the Ca2+ leaves through the Na+/Ca2+ exchanger.
3
Q
Rise in intracellular calcium is central to contraction
A
Depolarisation wave goes through the heart, as it reaches each cell it is enough to reach the threshold for Na+ channel opening.
4
Q
How does electrical excitability contract cardiac myocytes?
A
5
Q
Calcium binds tropomyosin complex
A
6
Q
Decrease in calcium & relaxation
A
7
Q
Difference between Starling’s law & contractility (inotropy)
A
8
Q
Control of cardiac contractility
A
9
Q
β1 - adrenoreceptors include increased contractility
A
10
Q
Sympathetic stimulation has multiple actions on heart
A
11
Q
Cardiac glycosides
A
12
Q
Other inotropic agents
A
