6.2 - Introduction to the Heart

Question 1

What are the main components of the heart?

Answer 1

Chambers:

• left atrium ~100 mL
• right atrium ~110 mL
• left ventricle ~ 150 mL
• right ventricle ~ 175 mL

Great vessels:

• aorta: 100-200 mmHg
• pulmonary artery: 10-20 mmHg
• vena cava: 5-10 mmHg
• pulmonary vein(s): 10-15 mmHg
• others: myocardium

Question 2

What is the blood flow through the heart?

Answer 2

• vena cava –> right atrium –> tricuspid valve –> right ventricle –> pulmonary valve –> pulmonary artery –> lungs
• pulmonary veins –> left atrium –> mitral valve –> left ventricle –> aortic valve –> aorta –> body

Question 3

What are the valves of the heart?

Answer 3

RHS of heart:

• tricuspid valve: right atrium –> right ventricle
• pulmonary valve: right ventricle –> pulmonary artery (blue in diagram)

LHS of heart:

• mitral valve: left atrium –> left ventricle
• aortic valve: left ventricle –> aorta (red in diagram)

Question 4

What is the electrical activity of the heart?

Answer 4

• the primary pacemaker signal is generated at the sinoatrial node
• the electrical signal is transmitted across the myocardium of the atrium along the internodal tracts
• the ‘slowing down’ of the electrical signal at the atrioventricular node corresponds to the P-R interval on a surface ECG trace
• transmission of the electrical signal along the Purkinje fibres causes contraction of the ventricles

Question 5

What are the nodes of the heart?

Answer 5

Sinoatrial node (SAN):

• pacemaker of the heart: 60-100 bpm
• junction of crista terminalis - upper wall of right atrium and opening of superior vena cava

Atrioventricular node (AVN):

• has pacemaker activity: slow calcium mediated action potential
• triangle of Koch at base of right atrium

Question 6

What are the tracts of the heart?

Answer 6

Bundles of His & bundle branches:

• specialised myocytes
• AVN: Bundle of His –> branches at intraventricular septum –> apex

Purkinje fibres:

• specialised conducting fibres

Question 7

What are the arteries of the heart?

Answer 7

• coronary artery - left and right
• circumflex artery - major coronary artery that divides off the left main coronary artery (the other branch being the left anterior descending (LAD) artery)
• left anterior descending artery

Question 8

What are the veins of the heart?

Answer 8

• coronary sinus - largest vein of the heart
• great cardiac vein
• middle cardiac vein