Cardiac muscle Flashcards
1
Q
Describe the flow of ox and de ox blood through the major blood vessels of the heart
A
- Dexoxygenated blood goes into the vena cava and leaves through the pulmonary artery to the lungs (pulmonary circuit)
- Oxygenated blood from the lungs enters through the pulmonary vein and leaves through the aorta to the entire body (systemic )
2
Q
What is cardiac muscle called?
A
Myocardium
3
Q
Describe the structure of cardiac muscle
A
- Striated - repeated sarcomeres
- one or two central nuclei
- adjacent cells connected though intercalated disks (desmosomes)
- has troponin and tropomyosin like skeletal muscle
- branched cells (myocytes)
4
Q
What is the func of intercalated disks?
A
- provide strong anchorage
- for electrical communication
5
Q
Why does the left side of heart have a thicker myocardium?
A
- needs much more force than RHS as it is pumping blood around the body
6
Q
Describe the term pacemaker potential
A
- no steady RMP
- instead it undergoes a slow depolarisation called a pacemaker potential
- brings MP to threshold where AP’s are generated
7
Q
What are nodal cells?
A
- Cells that produce an electrical impulse through a pacemaker potential
- eg the SA node in the right atrium of the heart
- the hearts natural pacemaker cell - constantly produces AP’s
8
Q
Describe the excitation - contraction coupling in the myocardium - generation of AP
A
- Na+ entry into cell causes depolarisation
- this depolarisation causes L type Ca2+ channels to open in T tubules
- Trigger Ca2+ enters cytosol and binds to the ryanodine receptor on SR
- Ca2+ then flows into cytosol
- Ca2+ binds to troponin and cross bridge cycle begins - sliding flilament mech
9
Q
What controls cardiac muscle ?
A
- Spontaneous electrical activity
- ANS - sympathetic increases heart rate and parasympathetic decreases heart rate
- note hormonal secretions and stretch have effect to
10
Q
What is phase 0 of ventricular AP?
A
- when the AP reaches the myocyte & depolarization begins
- fast Na+ voltage gated channels open but they inactivate rapidly
11
Q
What is phase 1 of ventricular AP?
A
- after Na+ channels become inactivated, there is a period of brief repolarization
- K+ channels open and outward flow of K+
12
Q
What is phase 2 of ventricular AP?
A
- consists of a plateau period where Ca2+ enters the cell through L type (long opening) voltage gated Ca2+ channels
13
Q
What is phase 3 of ventricular AP?
A
- as the plateau progresses, K+ efflux increases due to the opening of voltage gated K+ channels
- these channels are called slowed rectifier K+ channels
14
Q
What is phase 4 of ventricular AP?
A
- the resting membrane is re- established
- 75-90% of the raised Ca2+ in the cytosol is pumped back to the sarcoplasmic reticulum via the Ca2+- ATPase