Cardiovascular Physiology

Question 1

Does the heart fill actively or passively?

Answer 1

Passively

Question 2

What limits the filling of the heart?

Answer 2

It’s limited pressure-volume compliance

Question 3

What is the venous return?

Answer 3

The amount of blood flowing into the right atrium per minute from the systemic circulation

Question 4

What drives venous return?

Answer 4

• Peripheral vein compression from skeletal muscle activity
• Respiration
• Active ventricular contraction

Question 5

How does peripheral vein compression from skeletal muscle activity drive venous return?

Answer 5

It pushes venous blood into vessel segments closer to the heart

Question 6

How does respiration drive venous return?

Answer 6

It produces an alternating pressure gradient between the abdomen and thorax that favours venous return during inspiration

Question 7

What opposes the opposite effect of respiration on venous return during expiration?

Answer 7

The presence of semilunar valves in the veins

Question 8

How does active ventricular contraction drive venous return?

Answer 8

It shifts the atrioventricular border downwards in the direction of the cardiac apex and, as the atrioventricular valves are closed at this point, draws blood from the venae cavae and pulmonary veins into the atria

Question 9

What is stroke volume defined as?

Answer 9

The volume ejected by each ventricle

Question 10

What is the stroke volume in an adult?

Answer 10

About 70ml

Question 11

What is cardiac output defined as?

Answer 11

The total volume of blood pumped out of each ventricle every minute

Question 12

Does cardiac output refer to the volume pumped by the right or left ventricle?

Answer 12

Either, but not total amount pumped by both

Question 13

How is cardiac output calculated?

Answer 13

Stroke volume (L) x heart rate (per min)

Question 14

How can the heart modify its cardiac output?

Answer 14

By adjusting the number of contractions per unit of time, and by moderating the volume of blood pumped by each contraction (stroke volume)

Question 15

How are the mechanisms for the heart modifying its cardiac output brought about?

Answer 15

Through a number of intrinsic biophysical pathways as well as extrinsic control

Question 16

In terms of electrical activity of the heart, how can acceleration of the heart rate be achieved?

Answer 16

By decreasing the time taken to depolarise a pacemaker cell

Question 17

What substances act as positive inotropes?

Answer 17

Catecholamines

Question 18

Give 2 catecholamines?

Answer 18

• Noradrenaline

- Adrenaline

Question 19

What do catecholamines bind to when acting as positive inotropes?

Answer 19

Cardiac ß1-adrenoceptors

Question 20

What is the effect of catecholamine binding to cardiac ß1-adrenoceptors?

Answer 20

It moves the threshold for action potential generation towards a more negative potential

Question 21

What is the result of catecholeamines moving the threshold for action potential generation towards a more negative potential?

Answer 21

It increases the rate of diastolic depolarisation

Question 22

What does acetylcholine bind to in the heart?

Answer 22

Muscarinic M2 receptors

Question 23

What is the effect of acetylcholine binding to M2 receptors in the heart?

Answer 23

It slows the heart rate

Question 24

Give 6 positive inotropic factors

Answer 24

• Sympathetic nerve stimulation and catecholamines
• Increase in extracellular calcium
• Decrease in extracellular sodium
• Increased pH
• Drugs

Question 25

Give 3 drugs that are positive inotropic factors

Answer 25

- Digoxin - Glucagon - L-thyroxine

Question 26

Give 7 negative inotropic factors

Answer 26

- Hypoxia - Hypercapnoea - Decrease in extracellar calcium - Increase in extracellular sodium - Decreased pH - Decreased temperature - Drugs

Question 27

What can cause a decrease in extracellular calcium?

Answer 27

Calcium channel blockers

Question 28

Give 2 drugs with negative inotropic effects?

Answer 28

- Beta blockers | - Anaesthetic agents

Question 29

How are changes in the heart rate initiated?

Answer 29

By the reticular formation in the brainstem

Question 30

Where does the reticular formation in the brainstem receive information from that indicates a need to change the heart rate?

Answer 30

Specialised nerve receptors that are constantly feeding back to the reticular formation

Question 31

Via what does the reticular formation initiate changes in the heart rate?

Answer 31

The glossopharyngeal and vagal nerve supply

Question 32

How are changes in blood pressure detected?

Answer 32

Baroreceptors

Question 33

Where are baroreceptors located?

Answer 33

- Walls of internal carotid arteries | - Arch of aorta

Question 34

How is the amount of oxygen in the blood monitored?

Answer 34

Chemoreceptors

Question 35

Where are chemoreceptors located?

Answer 35

Carotid and aortic bodies

Question 36

What is meant by preload?

Answer 36

The end-diastolic volume loading of the heart

Question 37

What happens to the heart rate when the preload is increased?

Answer 37

It increases

Question 38

Why does the heart rate increase when preload is increased?

Answer 38

The increased preload stretches the sinuatrial (SA) node and increases the heart rate via a reflex pathway and local stretch-activated ion channels

Question 39

How do stretch activated ion channels in the heart work?

Answer 39

They depolarise the pacemaker cells and increase the rate of diastolic depolarisation

Question 40

What happens to the contractility of the myocardium when preload increases?

Answer 40

It increases

Question 41

Why does the contractility of the myocardium increase with an increasing preload?

Answer 41

Due to the Frank-Starling law

Question 42

What describes the relationship between the preload and the contractility of the myocardium?

Answer 42

The Frank-Starling law

Question 43

What is the Frank-Starling law?

Answer 43

The energy of contraction is proportional to the initial length of the cardiac muscle fibre, i.e. length dependent activation

Question 44

How does increasing the preload lead to an increased contractility?

Answer 44

- Increases load experienced by each muscle fibre - Increases affinity of troponin C for calcium - Causes greater number of actin-myosin cross-bridges to form within the muscle fibres

Question 45

What is pre-load affected by?

Answer 45

- Length of diastole - Venous return - Atrial systole - Myocardial compliance

Question 46

Give an example of a cause of increased preload?

Answer 46

Premature ventricular contraction

Question 47

What happens in premature ventricular contraction?

Answer 47

There is early emptying of the left ventricle

Question 48

How does premature ventricular contraction lead to increased preload?

Answer 48

It increases the filling time for the next regular ventricular contraction, and so increases left ventricular end-diastolic volume

Question 49

What is the result of the greater end-diastolic volume when there is a premature ventricular contraction?

Answer 49

The next ventricular contraction will be more forceful, causing the ejection of a larger than normal amount of blood, brining left ventricular end diastolic volume back to baseline

Question 50

What effect might pericardial effusion have on stroke volume?

Answer 50

Decrease it

Question 51

Why might pericardial effusion decrease stroke volume?

Answer 51

It reduces myocardial compliance

Question 52

What does the law of Laplace describe?

Answer 52

The relationship between; - The pressure difference across a wall - The radius of the cavity - The thickness of the cacity

Question 53

What is the law of Laplace?

Answer 53

The greater the pressure difference or larger the radius, the more tension there will be in a wall, but the tension is reduced the thicker the wall

Question 54

How can the law of Laplace be applied to dilated cardiomyopathy?

Answer 54

In dilated cardiomyopathy the heart becomes distended and the radius increases, and so the heart must increase cardiac tension produced by the cardiac muscle. The dilated heart therefore requires more energy to pump the same amount of blood compared to a heart of normal size.

Question 55

What is afterload?

Answer 55

The external load against which the ventricles must pump to eject blood

Question 56

What is the total peripheral vascular resistance determined by?

Answer 56

- Vessel diameter, pressure, and tone - Aortic valve resistance - Ventricular cavity size - Haematocrit

Question 57

Which vessels are most important in determining total peripheral vascular resistance?

Answer 57

Resistance arterioles

Question 58

Why is haematocrit important in determining total peripheral vascular resistance?

Answer 58

Measures blood viscosity

Question 59

Give 5 factors causing constriction of arterioles

Answer 59

- Increased sympathetic activity - Circulating catecholamines - Circulating angiotensin II - Locally released serotonin - Decreased local temperature