Cardiovascular Systems

Question 1

What is the circulatory system subdivided into?

Answer 1

Pulmonary
Coronary
Systematic - rest of body

Question 2

Describe mechanical coupling

Answer 2

Transverse ion interpolated disks that are highly folded
Small 0.02um gap between adjacent cells filled with connective tissues
Cells bound stronger at desmosomes

Question 3

Describe pacemaker activity

Answer 3

intrinsic, spontaneous time dependent depolarisation of a cell membrane leading to an action potential in an otherwise quiescent cell (does not divide but can proliferate)

Question 4

Describe the Primary, secondary and tertiary pacemaker cells

Answer 4

Primary = SA node -100bpm
Secondary = AV node - 40bpm 
Tertiary = Purkinje fibres - 20bpm

Question 5

Describe the conduction system in the heart

Answer 5

1. From SA node action potential spreads through atrial tissue to AV node via internal tract
2. Cells of AV node transmit action potentials more slowly and delay impulses by 100ms
3. Impulse spreads to ventricles via AV and bundle of his which divides left and right bundle branches
4. Spreads to contractile cells via purkinje fibres

Question 6

Describe parasympathetic effect on pacemaker cells

Answer 6

Release of ACh decreases If - pacemaker potential is slowed and longer to reach threshold
ACh increases K+ permeability of SA node which hyper polarises the maximum diastolic potential therefore decreasing heart rate

Question 7

describe the sympathetic effect of pacemaker cells

Answer 7

Increases If so pacemaker potential rate accelerated, reduction in k+ permeability so most diastolic increases
Increase in L type Ca2+current so upstroke = faster, more action potentials per unit time - tachycardia

Question 8

What is the frank Stirling law?

Answer 8

strength depends on initial degree of stretch within physiological range stretching ventricular muscle leads to increased contraction force

Question 9

Describe extrinsic regulation

Answer 9

Autonomic regulation of sv is under sympathetic control
Effects mediated by beta adrenoceptors increasing Ca2+ influx into ventricular myocytes during action potentials
Increase in contraction force, greater stroke volume from given end diastolic volume myocardial cells
-Contracts more rapidly and relaxes faster

Question 10

What is Darcy’s law?

Answer 10

steady state fluid flows between 2 points - to the difference in pressure between 2 points divided by resistance flow

Question 11

Describe arteriolar resistance

Answer 11

Walls contain a high proportion of smooth muscle - contraction reduces radius
Radius under influence of systematic nervous as wall as metabolic + myogenic auto regulatory
- major autonomic control via alpha adrenoceptors