Heart

Question 1

What is the structure of the pericardium?

Answer 1

There are 2 layers to the pericardium:

1. Fibrous pericardium
2. Serous pericardium

Question 2

What are the properties of the fibrous pericardium?

Answer 2

• The fibrous pericardium defines the borders of the middle mediastinum.
• It is conical in shape.
• It is inelastic and does not allow for expansion.
• It is innervated by the phrenic nerve.
• Its blood supply is from the pericardiophrenic vessels of the internal thoracic arteries.

Question 3

What are the attachments of the fibrous pericardium?

Answer 3

• Inferiorly: Diaphragm

- Superiorly: Continuous with the tunica adventitia of the great vessels

Question 4

What is the structure of the serous pericardium?

Answer 4

• Consists of 2 layers:
  1. Parietal layer - Lines inside of fibrous pericardium.
  2. Visceral layer - Lines outside of heart.
• Between the 2 layers is the pericardial cavity containing small amounts of serous fluid. This reduces friction between the 2 layers during contraction.
• The 2 layers are continuous with each other at 2 separate borders around the arteries and veins connecting to the heart.
• The parietal pericardium is innervated by the phrenic nerve.
• The visceral pericardium is innervated by visceral afferents running with sympathetic fibres.

Question 5

What are the pericardial sinuses?

Answer 5

• The transverse sinus is a space formed between the arterial reflection (anterior) and the venous reflection (posterior). It allows for slings to be passed around the great vessels in order to tie them off during surgery.
• The oblique sinus is a space formed between the venous reflections. It is directly posterior to the left atrium and so facilitates its distension.

Question 6

What are the functions of the pericardium?

Answer 6

• Reduces friction during contractions.
• Protects heart from infections of surrounding tissues.
• Fibrous pericardium anchors heart to diaphragm, preventing excess movement (and therefore torsion of great vessels).
• Prevents overdistension of the heart during diastole.

Question 7

What are the surfaces and margins of the heart?

Answer 7

• Anterior surface: 2/3 right ventricle, 1/3 left ventricle.
• Diaphragmatic surface: 1/3 right ventricle, 2/3 left ventricle.
• Right pulmonary surface: Right atrium.
• Left pulmonary surface: Mostly left ventricle, small amount of left atrium.
• Base: Origins of the great vessels.
• Apex: Left ventricle.
• Inferior margin: Mostly right ventricle and some left ventricle.
• Obtuse margin: Mostly left ventricle and some left auricle.

Question 8

What is the structure of the heart?

Answer 8

• The heart is divided into 4 chambers: The right/left atria and the right/left ventricles.
• The atria are divided from the ventricles by the coronary sulcus.
• Left side divided from right side by atrioventricular septum.
• The right atrium/ventricle effectively lie anterior to the left atrium/ventricle.

Question 9

What is the path of the right coronary artery (RCA)?

Answer 9

1. The RCA originates from the right aortic sinus (just above aortic valves) and passes between right auricle and pulmonary trunk.
2. It enters the coronary sulcus and gives off the atrial branch which gives rise to the SA-nodal branch supplying the SAN (in 60% of people).
3. It travels inferiorly and to the right in the right coronary sulcus.
4. It gives off the right marginal branch just before it winds posteriorly onto the diaphragmatic surface.
5. Along the diaphragmatic surface, it gives rise to the posterior interventricular artery (in 90% of people) which descends along the diaphragmatic surface in the interventricular sulcus. It also gives off the AV-nodal branch.

Question 10

What is the path of the left coronary artery (LCA)?

Answer 10

1. The LCA originates from the left aortic sinus and passes anteriorly between the left auricle and pulmonary trunk.
2. It enters the coronary sulcus and bifurcates into the anterior interventricular (left anterior descending) artery and the circumflex artery.
3. The anterior interventricular artery descends on the anterior surface in the anterior interventricular groove.
4. The circumflex artery travels in the coronary sulcus before winding onto the left pulmonary surface, where it gives off the left marginal branch along the oblique margin.
5. It continues onto the diaphragmatic surface, where it terminates.

Question 11

What are the anatomical variations in blood supply of the heart?

Answer 11

• Right dominance (90%): Posterior interventricular artery (and AV-nodal artery) given off by the RCA.
• Left dominance (10%): Posterior interventricular artery (and AV-nodal artery) given off by the circumflex artery.
• Dominance is decided by which artery supplies the AVN, not which one supplies the largest area (since LCA always supplies larger area).
• In 40% of people, SA-nodal branch given off by the LCA.

Question 12

Which parts of the myocardium does the RCA supply?

Answer 12

• Right ventricle
• Right atrium
• Part of left ventricle
• Posterior IV septum

Question 13

Which parts of the myocardium does the anterior IV supply?

Answer 13

• Left ventricle

- Anterior IV septum

Question 14

Which parts of the myocardium does the circumflex artery supply?

Answer 14

• Left atrium

- Left ventricle

Question 15

What type of blood supply does the heart have?

Answer 15

• The coronary arteries are functional end arteries as the areas of the myocardium supplied by them are supplied by no other arteries.
• They have poor anastomoses.

Question 16

What are the advantages of the locations of the RCA and LCA origins?

Answer 16

• They are just above the left ventricles so the blood they receive are richest in O2 and nutrients.
• They are above the aortic valves, so when the heart contracts, they are blocked. This prevents them from being damaged by the high blood pressure of systole due to small diameters, and also allows muscles to be adequately perfused as they are not contracting and blood vessels are distended.

Question 17

What is the nature of the intramural supply of the myocardium?

Answer 17

• Outer 2/3 of myocardium supplied by the coronary artery and branches.
• Inner 1/3 supplied by branches directly off branches from the heart chambers.
• Branches extend into the myocardium are perpendicular and give off more perpendicular branches.
• This is disadvantageous as it creates turbulence and damage to vessels.

Question 18

What are the veins of the heart?

Answer 18

• Great cardiac vein: Closely associated with the anterior IV artery and then the circumflex artery. It enlarges on the diaphragmatic surface to become the coronary sinus draining into the right atrium.
• Middle cardiac vein: Closely associated with the posterior IV artery and drains into the coronary sinus.
• Small cardiac vein: Closely associated with right marginal branch and then the RCA, draining into the coronary sinus.
• Posterior cardiac vein: Just left of middle cardiac vein and drains into great cardiac vein or coronary sinus.
• Anterior cardiac veins: Small veins draining right atrium/ventricle that drain directly into right atrium.
• Venae cordis minimae: Small veins that drain directly into the all chambers (right atrium in particular) and provide 20-30% of drainage.

Question 19

What is the nature of the innervation of the heart?

Answer 19

• Sympathetic fibres that innervate the heart are derived from T1-5 ganglia of sympathetic chain.
• Parasympathetic fibres that innervate the heart are derived from left and right vagus nerve.
• All fibres that innervate the heart are derived from the cardiac plexues.

Question 20

What are the relations of the cardiac plexuses?

Answer 20

• Superficial plexus on inferior aspects of aortic arch between it and pulmonary trunk.
• Deep plexus between aortic arch and tracheal bifurcation.

Question 21

What are the features of the atria?

Answer 21

• Fossa ovalis: In the atrial septum.
• Sinus venosus: Smooth part of atria.
• Cristae terminalis (sulcus terminalis): Division between sinus venosus and auricles, internal and external counterparts.
• Musculi pectinati: Fibrous muscular bands found in the auricles.
• Openings to the great veins.

Question 22

What are the features of the ventricles?

Answer 22

• Papillary muscles: Contract to keep valves shut during systole and prevents inversion of valves.
• Cordae tendinae: Attachments of valve cusps to papillary muscles.
• Septomarginal trabecluae (moderator band): Present in right ventricle only.
• Infundibulum: Smooth part lining entrance to pulmonary trunk. Ensures laminar flow of expelled blood. This is equivalent to the aortic vestibule in the left ventricle.
• Openings to the great arteries.

Question 23

What are the features of the cardiac conduction system?

Answer 23

1. SAN: Located at the junction between the SVC and the right atrium.
2. AVN: Located at the opening of the coronary sinus, just above the tricuspid valve.
3. The bundle of His is a direct continuation of the AVN and travels along the atrioventricular septum for a short distance, before dividing into the right and left bundle branches.
4. The right bundle branch extends down the right side of the interventricular septum and divides into purkinje fibres at the apex of the heart. It sends branches to the moderator band and papillary muscles. Purkinje fibres travel 2/3 the way up the right ventricle.
5. The left bundle branch extends down the left side of the interventricular septum and divides into purkinje fibres at the apex of the heart. These fibres travel 2/3 the way.

Question 24

What is the proposed purpose of the moderator band?

Answer 24

Acts as a short circuit for the conduction system so that the right ventricles contract slightly before the left ventricles. This ensures that the pumping efficiency of the right ventricle is not undermined by the contraction of the left ventricle, which is much more powerful.

Question 25

What are the differences between the right and left ventricles?

Answer 25

• Left ventricle has much thicker walls ( about x3) compared to right ventricle as it pumps against higher resistance.
• Left ventricle has much thinner and more numerous trabeculae carnae compared to right ventricle.
• The left atrium is divided from the left ventricle by the bicuspid valve while the right atrium is divided from the right ventricle by the tricuspid valve.

Question 26

What is the structure of the tricuspid valve?

Answer 26

• There are 3 valve cusps:
  1. Anterior cusp
  2. Posterior cusp
  3. Septal cusp
• Each cusp is attached to 2 separate papillary muscles.
• There are 3 separate papillary muscles named the same way as the cusps.

Question 27

What is the structure of the bicuspid valve?

Answer 27

• There are 2 valve cusps:
  1. Anterior cusp
  2. Posterior cusp
• Each cusp is attached to 2 separate papillary muscles.
• There are 2 separate papillary muscles named the same way as the cusps.

Question 28

What is the structure of the interventricular septum?

Answer 28

There are 2 parts to the septum:

1. Membranous part
2. Muscular part

Question 29

What are the structures of the semilunar valves?

Answer 29

• The ‘cups’ formed by each valve cusp is called a sinus.
• There are 3 cusps to each set of valves.
• For the pulmonary valves, these are:
  1. Anterior
  2. Right
  3. Left
• For the aortic valves, these are:
  1. Posterior
  2. Right
  3. Left

Question 30

what is the cardiac skeleton?

Answer 30

• Figure of eight-shaped connective tissue partitions between the atria and ventricles.
• These act as structural support for the atrioventrcular valves as well as electrical partitions between the myocardium of atria and ventricles to prevent conduction between them.

Question 31

What are the surface markings of the heart?

Answer 31

Right margin: Between the right 3rd and 6th costal cartilages.
Left margin: Between the left 2nd costal cartilage and the 5th intercostal space.

Question 32

What are the auscultation points for the heart?

Answer 32

• Pulmonary valve: 2nd and 3rd left intercostal spaces.
• Aortic valve: 2nd right intercostal space.
• Mitral valve (apical beat): 5th left intercostal space at mid-clavicular line.
• Tricuspid valve: Lower left sternal angle.