L5.2 Heart muscle: specialised structure and function Flashcards
1
Q
Difference b/w physiological and pathological hypertrophy
A
- Physiological hypertrophy: Hypertrophy in response to physiological stimuli
- Pathological hypertrophy: Hypertrophy in response to pathological stimuli (e.g. hypertension)
2
Q
What is the heart muscles arranged in a spiral
A
allows squeezing of blood up from apex
3
Q
What are intercalated discs
A
Intercalated discs attaches one myocyte to another
4
Q
What is the ultrastructure of the cardiomyocytes
A
- 100microns by 20microns
- ↑↑[mito] → cardiomyocytes are always contracting
- More than skeletal muscles
- Myofilaments: Cardiomyocytes < skeletal muscles
5
Q
Length tension relationship of the cardiomyocytes
A
- Frank-starling curve
- Proportional to myofilament (actin/myosin) overlap
- ALWAYS on the ascending part of curve (always able to cope with amount of blood)
6
Q
What is the function of the T-tubules
A
- Allows integration of the extracellular space into myocyte
- Allows myocyte to contract at the same time
7
Q
EC coupling of cardiomyocytes
A
- CA ENTERS DURING AP PLATEAU PHASE
- Ca induced Ca release - unique to cardiac muscle
- Triggers release of Ca from SR (binding to RyR)
- Ca binds to troponin-C
- Cross-bridge cycling
- Cell shortens
- MOST Ca pumped back into SR (SERCA pumps)
- CA EXIT CELL BY NA-CA EXCHANGER & THROUGH SARCOLEMMAL CA PUMPS
- 3 Na in for every Ca out - unique to cardiac muscle
8
Q
Difference b/w skeletal and cardiac EC coupling
A
9
Q
What is the fuzzy space?
A
restricted diffusional region b/w SL & SR
10
Q
Things going wrong in the fuzzy space
A
- Misalignment with RyR & L-type channel
- Not efficiently stimulating Ca release
- L-type channels becomes leaky or hypersensitive to Ca
- Space gets wider → ↓effectiveness
- Disruption in junctophilin (JP2) which is responsible for binding of L-type channels to T-tubules
- Caused by Ca overload → Activating calpains
