Week 1 - Cardiovascular System

Question 1

What are the 3 layers of the heart

Answer 1

Outer- epicardium, myocardium and inner-endocardium

Question 2

What is the myocardium?

Answer 2

The muscular wall of the heart containing cardiac muscle tissue, vasculature and nerves

Question 3

What are the two human vascular circuits?

Answer 3

•A pulmonary circuit to oxygenate the blood and remove CO2
•A systemic circuit which supplies cells with O2 and nutrients and removes CO2 and waste

Question 4

How does the right atrium receive blood?

Answer 4

Through the systemic circuit through the superior and inferior vena cava as well as the coronary sinus

Question 5

How does the left atrium receive blood?

Answer 5

•Receives blood from the pulmonary circuit via four pulmonary veins
▫Two left pulmonary veins
▫Two right pulmonary veins

Question 6

Physical characteristics of the right ventricle

Answer 6

Thicker myocardium compared to atria (2-3mm compared to 4-5mm)
Similar internal volume to atria
Interior surface containing trabeculae carneae
Cone shaped papillary muscles extend from ventricular base

Question 7

Physical characteristics of left ventricle

Answer 7

•Thickest heart chamber
▫10-15 mm thick
•Myocardium required to generate high pressure to force blood through the systemic circuit
•Inner surface contains trabeculae carneae
•Similar papillary muscles as seen in the right ventricle
▫Anchor the chordae tendineae of the left atrioventricular valve (bicuspid/mitral valve)

Question 8

Two key components of atrioventricular valves

Answer 8

1. Cusps that open and close
2. Chordae tendineae (tendinous cords) that prevent the cusps from eversion

Question 9

Method of Atrioventricular valves

Answer 9

When open, they permit ventricular filling
▫Cusps projects downwards into the ventricle
When ventricular contraction occurs, the pressure of blood forces the cusps closed

Question 10

The two semilunar valves

Answer 10

Aortic valve (at base of aorta)
Pulmonary valve (at base of pulmonary trunk)

Question 11

How do semilunar valves work?

Answer 11

Semilunar valves open when blood pressure in the two ventricles is higher than that in the aorta and pulmonary trunk

Question 12

What factors does heart muscle rely on for activation?

Answer 12

1. Auto-rhythmic fibres
2. Special cell junctions

Question 13

Characteristics of heart muscle fibers

Answer 13

•Heart muscle fibres connected to others via intercalated disks
•Contain desmosomes
▫Used for attachment of sarcolemmas of neighbouring muscle fibres
•Also contain gap junctions
▫Permit the passage of ions
▫Used to facilitate the conduction of action potentials from one muscle fibre to the next

Question 14

Autorhythmic heart fibres general function

Answer 14

These specialised cardiac muscle fibres spontaneously generate action potentials that spread via gap junctions to neighbouring fibres

Question 15

How do autorhythmic heart fibres contribute to heart function?

Answer 15

•Autorhythmic fibres act as pacemakers
▫Set the rhythm of electrical activity of the heart
•Collectively form the heart’s conduction system
▫Activate the heart’s contractile muscle fibres
▫Ensuring each section of myocardium contracts at the appropriate time
▫Essential for ensuring the heart’s blood pumping ability

Question 16

Steps of Intrinsic Conduction System

Answer 16

1. Sinoatrial Node (SA node)
2. Atrioventricular node
3. AV bundle- bundle of His
   4.Bundle branches
4. Purkinje fibres

Question 17

Role of SA node in intrinsic conduction system

Answer 17

Autorhythmic fibres repeatedly depolarise and repolarise. Each action potential created spreads across both right and left atria via muscle fibre gap junctions which results in contraction of myocardium in both atria at the same time.

Question 18

Role of AV node in intrinsic conduction system

Answer 18

Cell structure creates ‘bottleneck’ effect for the conduction pathway (results in delay). This delay allows the ventricles to fill with blood.

Question 19

What is the role of the AV bundle (Bundle of His)

Answer 19

Vital for conduction of action potentials from the atria to ventricles (heart’s fibrous skeleton electrically insulates the atria from the ventricles.

Question 20

What is the role of bundle branches?

Answer 20

Represent a left and right division of the AV bundle.

Question 21

What is the role of purkinje fibres?

Answer 21

Large diameter fibres that rapidly conduct the action potential resulting in ventricular contraction.

Question 22

What part of the intrinsic conduction system depolarises the quickest?

Answer 22

1. SA node- 100 times per minute
2. AV node - 40-60 times per minute
3. Rest of system - 20-35 times per minute.

Question 23

Autorhythmic cell action potential

Answer 23

Depolarisation (slower than neuron)- caused by Ca ++
Repolarisation - effluent of K+ (Ca++ channels close)

Question 24

How is the electrochemical gradient restored in Autorhythmic cells?

Answer 24

Via Na/Ca exchanger and Na/K pump

Question 25

Cardiac Contractile Fibres depolarisation

Answer 25

Depolarisation is initiated by neighbouring cells (via gap junctions). This causes the opening of fast voltage gated Na channels. Na influx down the electrochemical gradient results in rapid depolarisation.

Question 26

Cardiac contractile fibres plateau phase

Answer 26

After depolarisation. Depolarisation is maintained which is caused by opening of slow Ca channels (slow ca entry matched by K influx.

Question 27

Cardiac contractile fibres repolarisation

Answer 27

Repolarisation via rapid efflux of K due to opening of voltage gated K channels. Contraction is similar to skeletal muscle ie. Ca binds to troponin, moving tropomyosin and permitting binding of actin and myosin.

Question 28

ECG Trace

Answer 28

P wave- atrial depolarisation
QRS wave- ventricular depolarisation
T wave - Ventricular repolarisation

Question 29

Parasympathetic control of heart rate

Answer 29

Parasympathetic activity via the vagus nerve releases acetylcholine (reduces HR)

Question 30

Sympathetic control of heart rate

Answer 30

Sympathetic activity via the cardiac accelerator nerves releases norepinephrine which increases depolarisation rate in SA and AV nodes and increases contractility via heightened Ca entry into contractile fibres.