phys pharm - heart

Question 1

The role of the heart:

Answer 1

• Supplies O2, nutrients to cells, removes CO2, waste products
• Regulates pH of extracellular fluid and osmotic balance
• Signalling function – hormones; Immune function

Question 2

The heart must…

Answer 2

… be able to regulate the amount of blood it pumps to meet the metabolic needs of the body.

It does this in co-ordination with the vascular system.

Question 3

Cardiovascular diseases:

Answer 3

Heart attack,
Angina,
Heart failure, Arrhythmias

Question 4

The heart as a pump:

Answer 4

the left and right heart act as two pumps in series

the output of the left and right ventricles must be equal

the systemic circulation operates at high pressure

the pulmonary circulation operates at low pressure

Question 5

Cardiac output (CO):

Answer 5

= the volume of blood the heart pumps in a given time, normally expressed in litres / min

CO = heart rate x stroke volume

typical resting cardiac output: about 5 litres.min-1

can increase to 20 litres.min-1 in exercise

Question 6

Frank-Starling mechanism:

Answer 6

ensures output from left and right sides of heart is equal

contributes to increased stroke volume in exercise

contributes to postural hypotension

The force of contraction of a cardiac muscle fibre is proportional to its initial length

Question 7

Cardiac contractility:

Answer 7

the peak contractile force at a given initial fibre length (or peak systolic pressure at a given end-diastolic volume)

Question 8

An increase in contractility…

Answer 8

contractility involves both an increase in force or pressure and an increase in the rate of contraction

• caused by sympathetic stimulation (noradrenaline)

= positive inotropic effect

Question 9

electrical activity in heart is…

Answer 9

….myogenic

= sin atrial node acts as pacemaker

Question 10

Cardiac muscle cells are…

Answer 10

…connected at intercalated discs.

The intercalated discs have many gap junctions, allowing electrical conduction.

Thus the action potential spreads from cell to cell throughout the heart muscle.

Question 11

Spread of electrical activity in the heart:

Answer 11

sin atrial node - atrial action potential - atrial ventricular node - bundle of his (conducting system) - ventricular action potential

Question 12

The ventricular action potential:

Answer 12

The membrane potential of ventricular cells is held close to potassium eqbm by a large inward rectifier K+ current at rest.

• ventricular action potential is caused by Ca2+ influx and K+ efflux
• The duration of the action potential ensures enough Ca2+ enters to initiate contraction.

Question 13

Sympathetic nerves (or circulating adrenaline):

Answer 13

• Increase heart rate
• Increase contractility
• Increase automaticity
• Decrease cardiac efficiency

Question 14

Parasympathetic nerves (vagus):

Answer 14

• Decrease heart rate and automaticity
• Decrease contractility in atria
• Slow conduction through the A-V node

Question 15

Cardiac glycosides:

Answer 15

• increase intracellular calcium and contractile force

- decrease heart rate

Question 16

Actions of cardiac glycosides:

Answer 16

1. Na/K ATPase inhibition to raise intracellular Ca2+ and so force
2. Slowing of heart rate and of conduction at A-V node
3. At high concentrations can cause arrhythmias