Cardiac muscle Flashcards
1
Q
What are some diseases of the heart?
A
- Hypertension-(Inc Cardiac output(CO=HRxForce of contr))
- Ischeamic HD(angina, MI)
- Chronic heart failure-(Red CO)
2
Q
How to target these diseases + arrhythmias?
A
- Hypertension-Red CO-B-blockers
- Ischaemic HD-Red HR-B-blockers
- Chronic heart failure-stimulate contraction-digoxin
- Arrhythmias-cont HR-ion channel modulators
3
Q
What is the structure of cardiac muscle?
A
- Striated like Skeletal muscle
- But, cardiac cells are extensively connected by gap junctions like smooth muscle
- Gap junctions: allow AP to travel from cell to cell
- Contracts as a unit.
See PP fo diag
4
Q
Are cardiac AP long or short>
A
- Broad on graphs
- Long, last for hundreds of milliseconds
5
Q
What is the refractory period?
A
- AP last almost as long as contraction
- Long refractory period prev a 2nd cont too soon
- Allows heart to relax fully and therefore fill up with blood again before next cont
- Even when AP freq is high & sp heart beating fast, RP allows heart to fill
6
Q
How many phases of cardiac AP are there?
A
- 5- 0,1,2,3,4
7
Q
What is phase 0 of Cardiac AP?
A
- Rapid depolarisation-Mem pot reaches critical level (-60mV) at which inward Na+ current becomes large enough to generate all or nothing depolarisation
8
Q
What is phase 1 of Cardiac AP?
A
- Partial repolarisation-Na+ channels close
9
Q
What is phase 2 of Cardiac AP?
A
- Plateau-inward calcium current
10
Q
What is phase 3 of Cardiac AP?
A
- Repolarisation-Ca2+ channels close and the outward K+ current kicks in-delayed outwardly rectifying K+ current
11
Q
What is phase 4 of Cardiac AP?
A
- Pacemaker potential-gradual depolarisation up to -60mV when Na+ current activated again
- Only found in pacemaker cells
12
Q
What cells initiate a Cardiac AP?
A
- Pacemaker cells
- Heart muscle cells in SAN and AVN exhibit pacemaker activity-can generate an AP
13
Q
How is heartbeat triggered?
A
- Heartbeat is triggered by APs generated by pacemaker cells NOT neural input-
- Why heart beats when removed from body-myogenic
- (although Autonomic NS regulates freq and force of contr)
14
Q
How is a cardiac AP conducted?
A
- Conductance of AP across atria=atrial contraction
- Delay (0.1s) at A-V node
- AP passes down purkinje fibres down to bottom of ventricles, then up the sides
- Contraction of ventricles starts from the bottom
15
Q
What is the relationship of AP to contraction? (atrial)
A
- During cardiac relaxation, venous blood flows into atria.
- AV valves open, allowing blood to flow into ventricles.
- On contraction of atria, rest of blood in atria squeezed into ventricles.
- AV delay allows complete filling before ventr contr.
5.(Atrial fibrillation-impaired contr of atria. some blood stays in atria-stasis-clotting.)
