Cardiovascular Physiology

Question 1

Describe the cardiovascular system of birds + mammals

Answer 1

= closed
= 2x circuit
= separate systemic + pulmonary circuits
= O2 + CO2 don’t mix
= 4 chambered heart
= compact myocardium [spongy for embryos]
= high flow + high pressure pump: endotherms have high metabolic rate and high perfusion rate

Question 2

What is the difference between systemic + pulmonary circulation

Answer 2

Systemic: heart → body
O2 blood leaves heart
de-O2 blood comes back

Pulmonary: heart → lungs
de-O2 blood leaves heart
O2 blood comes back

Question 3

What is the difference between diffusion and perfusion?

Answer 3

Diffusion: passive movement over short distances → gas exchange across surfaces
* alveoli → capillaries
* capillary → cell

Perfusion: Convective/ bulk flow of substances under pumping action of the heart → gas movement around body

Question 4

What is the difference between the dynamic, chronic and evolutionary demand on the cardiovascular systems?

Answer 4

Dynamic: immediate response in individual

Chronic: Takes time → phenotypic plasticity in individual (genotype can change so that the phenotype can change to meet demands)

Evolutionary: Takes forever → species adaptation dependent (scaling analysis)/ independent (residual variation of scaling analysis) of body mass.

Question 5

How is cardiac output (CO) measured?

Answer 5

volume of blood pumped per unit time

mL/s

Question 6

How is stroke volume (SV) measured?

Answer 6

volume of blood pumped per contraction

mL

Question 7

How is heart rate measured?

Answer 7

contractions/ unit time

s-1/ b.p.s

Question 8

What does systole mean?

Answer 8

Contraction of cardiac chambers

Question 9

What does diastole mean?

Answer 9

Relaxation of cardiac chambers

Question 10

What is contractility and how is it measured?

Answer 10

Strength of contracting ventricles i.e. force + velocity of contraction

ΔP/Δt or SV/EDV (e.g. mmHg s-1or%)

Question 11

What is compliance and how is it measured?

Answer 11

Degree of “stiffness” of the relaxing ventricles/ vessels i.e. ease of stretch

ΔV/ΔP (e.g. mL mmHg-1)

Question 12

What is preload?

Answer 12

Force on ventricle at end-diastole
(end-diastolic blood volume)

Question 13

What is afterload?

Answer 13

Force on ventricle during systole (arterial pressure)

Question 14

Chronotrophy (+/-)?

Answer 14

heart rate

Question 15

Inotrophy (+/-)?

Answer 15

contractility

Question 16

Lusitropy (+/-)?

Answer 16

relaxation

Question 17

Dromotropy (+/-)?

Answer 17

conduction velocity

Question 18

Bathmotropy(+/-)?

Answer 18

excitablity

Question 19

Describe the orientation of the heart as it is situated in the body

Answer 19

Heart is in the mediastinum space of the thoracic cavity:

1.Cranial end is at the base of the heart:
↕
base shifted to the right

2.Caudal end is at the apex of the heart:
↕
apex formed by left ventricle
↕
apex sits more ventrally to the left

Question 20

What is the structure of the pericardium

Answer 20

1. Fibrous pericardium
2. Serous Pericardium
   i) Parietal layer
   ii) Visceral layer = epicardium
   [layers slide past each other when
   heart beats,
   pericardial fluid between them)

*fibrous pericardium + Parietal layer of serous pericardium = pericardial sac

Question 21

Briefly explain the path of blood flow

Answer 21

Pulmonary circulation:

body → De-O2 blood → Venae cavae → Right Atrium → right AV valve → Right ventricle → pulmonary semilunar valve → pulmonary artery → lungs

Systemic circulation:

lungs → O2- blood → pulmonary veins → left atrium → left AV valve → left ventricle → aortic semilunar valve → aorta → body

Question 22

Briefly explain the cardiac cycle

Answer 22

same thing happens at the same time on both sides

1. Ventricular filling phase:
   - ventricular P < Atrial pressure
   - AV valves open
   - passive blood flow from A → V
   - semilunar valves closed
   = both atria + ventricles in DIASTOLE
2. Atria contract (SYSTOLE): blood flows forcefully from A → V [top-up]
   - ventricles = DIASTOLE
   [reach end-diastole]

AV valves = open
Semilunar valves = closed

3. Isovolumetric contraction phase:
   - No blood flow to/from ventricles
   - AV + semilunar valves = closed
   - Atria = DIASTOLE
   - Ventricles = SYSTOLE
   [ventricles are contracting → increasing pressure without changing volume]
4. Ventricular ejection phase:
   - Blood: V → major arteries
   [ventricular P > Arterial P]
   - AV valves = closed
   - semilunar valves = open
   - Atria = DIASTOLE
   - Ventricles = SYSTOLE
   [V are contracting while changing blood volume]
5. Isovolumetric relaxation phase:
   - No blood flow to/from V
   - AV + semilunar valves = closed
   - A = DIASTOLE
   - V = DIASTOLE
   [V = relaxing + decreasing pressure without changing volume]

CYCLE REPEATS

Question 23

What could be the reason for extra heart sounds?

Answer 23

The 2 AV valves/ 2 semilunar valves aren’t closing simultaneously

Question 24

What two scenarios could produce a heart murmur?

Answer 24

1. Valvular insufficiency: valves aren’t closing completely → blood flows in wrong direction e.g. LV → LA = turbulent blood flow = murmur
2. Valvular stenosis: valves aren’t closing completely → e.g. blood prevented from flowing LA → LV= turbulent blood flow = murmur

Question 25

What is the Law of Laplace

Answer 25

An increase in volume/ pressure load on the ventricles, places greater stress (N/m2) on the walls and this induces an increase in wall thickness to normalise wall stress and vice versa Wall stress (σ) = r × P / 2X Wall thickness (X) = r × P / 2σ σ = wall stress (N m-2), r = lumen radius (cm), P = the blood pressure (N m-2) X = wall thickness (cm)

Question 26

Differentiate between the meaning of preload and afterload VS volume loading and pressure loading

Answer 26

1. ‘Preload’ and ‘afterload’ are used in reference to dynamic changes in demand that invoke an immediate response within an individual 2. ‘Volume loading’ and ‘pressure loading’ are analogous terms used to describe chronic (i.e. phenotypic plasticity within an individual) and evolutionary (i.e. adaptation of a species) changes in demand that invoke a genetic-based response within an individual or a species

Question 27

What are "pacemaker" cells and what is their function?

Answer 27

Specialised collection of cardiomyocytes > sinoatrial (SA) node in the wall of RA- that set heart rate by propagating their elec. impulses to all the cardiomyocytes of the myocardium. They are auto-rhythmic = create their own rhythmic spontaneous contractions (depolarization) and relaxations ( repolarisations) > intrinsic rhythm

Question 28

What is the pathway for electrical impulses from SA node pacemaker to all the cardiomyocytes of the heart

Answer 28

AP generated by SA node pacemaker > internodal pathway > atrioventricular (AV) node [in atrioventricular septum] > spreads cell-to-cell via gap junctions> atria contracts > impulse > bundle of His [ L + R branches in ventricular septum] > from heart apex > heart base [via Purkinje fibres] > cell-to- cell across the ventricles > ventricles contract (depolarisation of cardiomyocytes)

Question 29

Which ventricle is thicker and why

Answer 29

The wall of the left ventricle is thicker because it is responsible for systemic circulation of blood and thus needs more pressure to overcome more resistance