Anatomy of the heart and organisation of the nerves in the thorax

Question 1

Describe the pericardium

Answer 1

Fibroserous sac surrounding heart and its great vessels (roots)
consists of 2 layers
Fibrous and Serous- fibrous defines the boundaries of the middle mediastinum
Serous has 2 parts
Parietal – lines fibrous
Visceral – adheres to heart and forms its outer covering

Question 2

Describe the fibrous pericardium

Answer 2

Cone-shaped bag with its base on the central tendon of the diaphragm and its apex continuous with the adventitia of the great vessels.
Anteriorly it is attached to the posterior surface of the sternum by sternopericardial ligaments- which retains the heart’s position in the thoracic cavity and limits cardiac distension.
Innervated by C3,4 and 5

Question 3

Describe the serous pericardium

Answer 3

The parietal layer of serous pericardium is continuous with the visceral layer around the roots of great vessels. These reflections occur in two locations:
one superiorly, surrounding the arteries, aorta and pulmonary trunk
one posteriorly, surrounding the veins- oblique pericardial sinus- posterior to left atrium
the transverse pericardial sinus- passage between two sites of reflections- lies posterior to aorta, anterior to the SVC, pulmonary trunk and superior to the left atria.

Question 4

Describe the transverse pericardial sinus

Answer 4

Separates arteries from veins

Important in cardiac surgery to limit outflow of heart- can clamp the aorta and pulmonary trunk off.

Question 5

Describe the oblique pericardial sinus

Answer 5

Where the visceral layer reflects onto the parietal layer- can’t get more superior because of the fold.

Question 6

Why are these sinuses important clinically.

Answer 6

Important in infection and passage of parcels of blood

Question 7

Describe the formation of the pericardial sinuses

Answer 7

The primordial heart is a vertical tube in a pericardial sac- veins one end, arteries the other
Heart loops ventrally
Primordial arterial and venous ends brought together- forming the transverse pericardial sinus
As the veins expand the pericardial reflection is carried out around them to form the oblique pericardial sinus.

Question 8

Describe the base of the heart

Answer 8

Quadrilateral posterior surface of the heart.
Consists of:
Left atrium
Small portion of the right atrium
proximal parts of the great veins.
From the base the heart projects forward, downward and to the left.
The apex of the heart is formed by the inferolateral part of the left ventricle and is positioned deep to the 5th intercostal space.

Question 9

What is the consequence of the great veins entering the base of the heart

Answer 9

The base is fixed posteriorly to the pericardial wall opposite the bodies of T5-T8 (T6-9) when standing.
The oesophagus lies immediately posterior to the base.

Question 10

Describe the anterior surface of the heart

Answer 10

Faces anteriorly and consists mostly of the right ventricle, with some of the right atrium on the right and some of the left ventricle on the left.

Question 11

Describe the diaphragmatic surface of the heart

Answer 11

What the heart rests on in its anatomical position
Consists of left ventricle and a small portion of the right ventricle separated by the posterior interventricular groove
Faces inferiorly
Separated from the base by the coronary sinus
Extends from base to apex

Question 12

Describe the pulmonary surfaces of the heart

Answer 12

left- faces left lung, is broad and convex, consists of left ventricle and portion of left atrium
right- faces right lung, broad and complex, consists of right atrium.

Question 13

Describe the margins of the heart

Answer 13

right and left- same as right and left pulmonary surfaces
inferior- sharp edge between anterior and diaphragmatic surfaces
Formed mostly by right ventricle and a small portion of left ventricle near the apex
obtuse margin- separates anterior and left pulmonary surface- round and extends form left auricle to apex, formed mostly by left ventricle and superiorly by a small portion of left ventricle.

Question 14

Describe the chambers of the heart

Answer 14

Right atrium
Blood returns via superior and inferior venae cavae (body) and coronary sinus (heart)
Left atrium
Blood returns via pulmonary veins
Right ventricle
Outflow to the pulmonary trunk
Left ventricle
Outflow to the ascending aorta

Question 15

Describe the right atrium

Answer 15

SVC enters upper posterior portion
IVC and coronary sinus enters lower posterior portion
Enters RV through atrioventricular orifice which is closed by tricuspid valve in ventricular contraction.
Forms the right border of the heart
Contributes to the right part of the anterior surface

Question 16

Describe the left atrium

Answer 16

Forms most of the base
Posterior part receives the 4 pulmonary veins
Anterior part is continuous with the left auricle and the interaterial septum is a part (faces forward and to the right as left atrium is posterior and to the left of the right atrium).

Question 17

Describe the foramen ovale

Answer 17

Area of depression on the interarterial septum
Important part of foetal circulation- allows oxygenated blood entering the right atrium to pass directly to the left atrium and so bypass the lungs which are nonfunctional in the foetus
Fossa ovalis (bordered by limbus fossa ovalis) marks its location.

Question 18

Describe the right ventricle

Answer 18

Forms most of the anterior surface of the heart and a portion of the diaphragmatic surface
RA is to the right and behind the RV, thus blood moves into the RV in a horizontal and forward direction.

Question 19

Describe the tricuspid valve

Answer 19

3 cusps (anterior, septal and posterior) relative to the RV.
The free margins of the cusps are attached to the chordae tendineae, which arise from the tips of the papillary muscles.
During filling of the right ventricle, the tricuspid valve is open, and the three cusps project into the ventricle
During ventricular contraction, contraction of the capillary muscles prevents eversion of the cusps into the RA- keeping the valves closed.

Question 20

Why do chordae tendineae from two papillary muscles attach to each cusp

Answer 20

Helps prevent separation of the cusps during ventricular contraction.

Question 21

Describe the pulmonary valve

Answer 21

Consists of 3 semilunar cusps (left, anterior and right) with 3 edges projecting upwards into the lumen of the pulmonary trunk.
The free superior edge of each cusp has a middle, thickened position (nodule) and a thin lateral portion (lunula)
Each cusp forms a pulmonary sinus, after ventricular contraction, blood recoils into these pulmonary sinuses, forcing the cusps closed.

Question 22

Describe the left ventricle

Answer 22

Lies anterior to the left atrium
Contributes to anterior, diaphragmatic and left pulmonary surfaces of the heart, and forms the apex.
Blood flows in a forward direction
Conical chamber, which is longer and has a thicker myocardium than the right.
The outflow tract to the aorta is posterior to the outflow track of the RV to the Pulmonary trunk.

Question 23

Describe the mitral valve

Answer 23

Two cusps (anterior and posterior)

Question 24

Describe the aortic valve

Answer 24

Similar to the Pulmonary valve
Has right, left and posterior sinuses.
The right and left coronary arteries originate from the right and left aortic sinuses.
Because of this the posterior cusp is referred to as the noncornary aortic sinus and cusp.

Question 25

What is the difference between cardiac arrest and MI

Answer 25

Cardiac arrest- electrical issue and arrest of the beat of the heart
MI- Ischaemia (blood supply issue)

Question 26

Describe the right coronary artery

Answer 26

Arises from the right aortic coronary sinus of the aorta
Passes anteriorly and descends vertically in the coronary sulcus (between RA and RV)
On reaching the inferior margin it turns posteriorly and continues into the sulcus onto the diaphragmatic and base of the heart- several branches arise.

Question 27

What are the branches of the right coronary artery

Answer 27

Early atrial branch passes in the groove between the right auricle and ascending aorta and gives of the sinu-atrial nodal branch (posterior to the IVC to supply the SAN)
Right marginal branch- inferior margin of the heart and continues to the apex
As it continues on the base/diaphragmatic surface- supplies a small branch of AV node before giving off the posterior interventricular branch, which lies in the posterior interventricular sulcus.

Question 28

What does the right coronary artery supply

Answer 28

Right atrium and ventricle
SA and AV nodes
Interarterial septum
Portion of left atrium
portion of the posterior part of LV
postoinferior part of the septum (1/3)

Question 29

Describe the left coronary artery

Answer 29

Originates from the left aortic sinus- it passes between the pulmonary trunk and left auricle before entering the coronary sulcus
emerging from behind the pulmonary trunk , the artery divides into its two terminal branches, the circumflex and the anterior interventricular.

Question 30

Describe the branches of the left coronary artery

Answer 30

Circumflex- courses towards the left and onto the base/diaphragmatic surface and usually ends before reaching the posterior interventricular sulcus.
Left marginal branch usually arises from this and continues across the rounded obtuse margin of the heart

Anterior interventricular branch- continues around the left side of the pulmonary trunk and descends obliquely toward the apex of the heart. During its course, one or two large diagonal branches may arise and descend diagonally along the anterior surface of the left ventricle.

Question 31

What does the left coronary artery supply

Answer 31

Most of the LA and LV, most of the interventricular septum, including the AV bundle and its branches.

Question 32

Describe variations in the patterns of the coronary arteries

Answer 32

More common variation – right dominant coronary artery - posterior interventricular branch arises from the right coronary artery
Less common variation – left dominant coronary artery - posterior interventricular branch arises from the left coronary artery
Sometimes the AV and SA node are supplied from branches of the circumflex artery

Question 33

Describe the cardiac veins

Answer 33

Receives four major tributaries: the great, middle, small and posterior cardiac veins.

Question 34

Describe the great cardiac vein

Answer 34

Begins at the apex, ascends into the anterior interventricular sulcus (often termed anterior interventricular vein here)
Reaches the coronary sulcus where it turns to the left and continues onto the base/ diaphragmatic surface of the heart enlarges to form the coronary sinus.

Question 35

Describe the middle cardiac vein

Answer 35

Posterior interventricular vein
Begins near the apex and ascends in the posterior interventricular sulcus towards the coronary sulcus
associated with the right or left posterior interventricular coronary artery branch.

Question 36

Describe the small cardiac vein

Answer 36

Begins in the lower anterior section of the coronary sulcus and continues onto the base/diaphragmatic surface of the heart where it enters the coronary sinus at its atrial end (it may also receive the right marginal vein, if not drains directly into the right atrium).

Question 37

Describe the posterior cardiac veins

Answer 37

lies on the posterior surface of the left ventricle just to the left of the middle cardiac vein- either drains into the great cardiac vein or coronary sinus.

Question 38

Summarise the conduction system of the heart

Answer 38

Excitation begins in sinu atrial (SA) node
Spreads across atria causing contraction
Concurrently wave stimulates atrioventricular (AV) node
Travels through the bundle of His
Then along bundle branches, through Purkinje fibres, causing ventricular contraction

Question 39

Where is the SA node found

Answer 39

The superior end of the crista terminalis at the junction of the SVC and right atrium.

Question 40

Where is the AV node found

Answer 40

Near the opening of the coronary sinus, close to the attachment of the septal cusp of the tricuspid valve and within the atrioventricular septum.

Question 41

What is the AV bundle

Answer 41

Continuation of the AV node- follows along the membranous part of the interventricular septum before splitting into the right and left bundles.

Question 42

Describe the right bundle branch

Answer 42

Continues on the right side of the interventricular septum toward the apex of the right ventricle.
From the septum it enters the septomarginal trabecula to reach the base of the anterior papillary muscle, where it is continuous with the purkinje fibres which spread throughout the right ventricle to supply the ventricular musculature and papillary muscles.

Question 43

Describe the left bundle branch

Answer 43

Passes to the left side of the muscular interventricular septum and descends on the apex of the left ventricle. Along its course it gives off branches that become continuous with the purkinjie fibres.

Question 44

Where is Bachman’s bundle found

Answer 44

Inner wall of the left atrium