The heart and mediastinum

Question 1

What other structures are in the superior mediastinum?

Answer 1

Oesophagus
Trachea
Thymus
Thoracic duct

Question 2

What vessels are in the superior mediastinum?

Answer 2

Arch of the aorta - brachiocephalic trunk, L common carotid, L subclavian artery

SVC - brachiocephalic veins, L superior intercostal vein, supreme intercostal vein, azygous veins

Question 3

What are the borders of the superior mediastinum?

Answer 3

Superior - thoracic inlet

Inferior - sternal plane

Anterior - sternum

Posterior - vertebral bodies (T1-T4)

Lateral - pleurae of the lungs

Question 4

What nerves are in the superior mediastinum?

Answer 4

Vague nerve
Phrenic nerve
Cardiac nerves
Sympathetic trunk

Question 5

What are the borders of the anterior mediastinum?

Answer 5

Superior - sternal plane

Inferior - diaphragm

Anterior - body of the sternum

Posterior - pericardium

Lateral - mediastinal pleura

Question 6

What structures are in the anterior mediastinum?

Answer 6

Thymus (in children)

Question 7

What are the borders of the middle mediastinum?

Answer 7

Superior - sternal plane

Inferior - diaphragm

Anterior - pericardium

Posterior - pericardium

Lateral - mediastinal pleura

Question 8

What organs are in the middle mediastinum?

Answer 8

Heart (+ pericardium)
Tracheal bifurcation
Right main bronchi

Question 9

What vessels are in the middle mediastinum?

Answer 9

Ascending aorta
Pulmonary trunk
SVC

Question 10

What nerves are in the middle mediastinum?

Answer 10

Cardiac plexus (vagus, sympathetic nerves T1-4)

Phrenic nerves

Question 11

What are the borders of the posterior mediastinum?

Answer 11

Superior - sternal plane

Inferior - diaphragm

Anterior - pericardium

Posterior - T5-12 vertebrae

Lateral - mediastinal pleura

Question 12

What structures are in the posterior mediastinum?

Answer 12

Oesophagus

Thoracic duct

Question 13

What vessels are in the posterior mediastinum?

Answer 13

Thoracic (descending) aorta - gives off posterior intercostal arteries, bronchial arteries, oesophageal arteries, superior phrenic arteries

Azygous system of veins (azygous vein, hemiazygous vein, accessory hemiazygous vein) - drain into SVC

Question 14

What nerves are in the posterior mediastinum?

Answer 14

Sympathetic trunks

Lower thoracic splanchnic nerves (from the sympathetic trunks)

Question 15

How can the blood supply of the heart prevent necrosis during an MI?

Answer 15

Anastomoses between branches of the L and R coronaries are widespread and can open during an MI to open up blood supply to that area

Question 16

What are the main functions of the fibrous cardiac skeleton?

Answer 16

Mechanical stability
Electrical insulation (meaning that AV node is the only route for signal conduction from the atria to ventricles)  
Attachment point for cardiac muscles and valve cusps

Question 17

How does the structure of the aortic and pulmonary valves aid their function?

Answer 17

Structure = semi-lunar, 3 cusps with a sinus (pocket) behind each cusp 
Function = sinuses fill with blood (from reverse flow) during diastole, closing valves. During systole, the cusps are pushed towards the vessel wall allowing valves to open

Question 18

Where do the coronary arteries arise from?

Answer 18

Coronary sinuses above the cusps of the aortic valve (R coronary artery arises from R sinus and L arises from L sinus)
So main inflow of blood is during diastole (when valves are closed)

Question 19

What is the venous drainage of the myocardium?

Answer 19

Coronary veins (great, middle, small and posterior) drain into the Coronary Sinus which drains into the right atrium

Question 20

Where is the Coronary Sinus?

Answer 20

Posterior portion of the coronary sulcus found on the diaphragmatic surface of the heart

Question 21

What are the 4 key points used to map the surface anatomy of the heart?

Answer 21

1. 2nd left CC (just left of the sternum) - marks left atrium and pulmonary trunk
2. 3rd right CC (just right of sternum) - marks right atrium and SVC
3. 6th right CC (just right of sternum) - marks right atrium and IVC
4. 5th left ICS (just medial to MCL) - marks apex and left ventricle

Question 22

What are the 4 auscultation points of the heart valves?

Answer 22

1. Pulmonary (2nd L ICS, just lateral to sternum)
2. Aortic (2nd R ICS, just lateral to sternum)
3. Mitral (5th L ICS, MCL)
4. Tricuspid (4/5th L ICS, just lateral to sternum)

Question 23

What is the fossa ovalis?

Answer 23

Embryological remnant of the foramen ovale (which allows right to left shunting in the foetal heart to allow blood to bypass the lungs).
Should close in newborns leaving a small oval-shaped depression in the atria walls.
Failure to close = atrial septal defect

Question 24

Which atria has a higher pressure?

Answer 24

Left atrium has higher pressure than the right (so walls of the left atrium are thicker than those on the right)

Question 25

What is the name of the structure between the arch of the aorta and the pulmonary arteries?

Answer 25

Ligamentum Arteriosum | Embryological remnant of the ductus arteriosus (shunt allowing bypass of the lungs)

Question 26

What is the nerve innervation of the heart?

Answer 26

``` Parasympathetic = cardiac branches of vagus (CN X) arising in the thorax - with postganglionic fibres arising from ganglia on heart Sympathetic = fibres from top of sympathetic chain (T1-T4) ```

Question 27

What is the surface marking of the aortic arch?

Answer 27

Starts and finishes on the sternal plane (T4)