CR1.1 The heart and mediastinum

Question 1

Describe the boundaries of the superior mediastinal cavity.

Answer 1

From thoracic inlet superiorly to transthoracic plane inferiorly.

Question 2

List 7 structures found in the posterior part of the inferior mediastinum.

Answer 2

1. Azygos vein
2. Hemiazygos vein
3. Thoracic aorta
4. Thoracic duct
5. Lymphatic trunk
6. Vagus nerve (CN-X)
7. Oesophagus

Question 3

Describe the pathway of the phrenic nerve including origin and innervation.

Answer 3

Each phrenic nerve originates from anterior rami of C3,4,5. The left and right nerves enters the medistinum through the thoracic inlet and closely follows the pericardium of the heart. The nerves innervate the left and right domes of the diaphragm.

Question 4

Describe the condition that may result from excessive accumulation of fluid in the pericardial cavity.

Answer 4

Pericardial effusion. When excessive pericardial effusion accumulates in the pericardial space it does not allow full expansion of the heart. This limits the amount of blood reaching the heart in diastole and reduces cardiac output.

Question 5

List the three functions of the fibrous pericardium.

Answer 5

1. Protects the heart against sudden overfilling.
2. Fixes the heart in position.
3. Provides a physical barrier from infection.

Question 6

Describe the pathway of the vagus nerve in the mediastinum.

Answer 6

Enters the superior mediastinum through the thoracic inlet with the common carotid artery. The superior laryngeal and recurrent laryngeal branches innervate the larynx. The anterior vagal trunk tracks posteriorly to lie directly on top of the oesophagus as the oesophageal plexus. It exists the mediastinum through the oesophageal hiatus (~T10) of the diaphragm.

Question 7

List the three structures found in the anterior mediastinum.

Answer 7

1. Internal thoracic vessels
2. Thymus
3. Sternopericardial ligaments

Question 8

Trace the following boundaries on the normal chest radiograph; trachea, thoracic cavity width, diaphargm, heart and aorta, breast tissue.

Answer 8

Question 9

Explain why the site of auscultation for valves is different to the anatomical location of the valves.

Answer 9

Movement of blood flow occurs away from the valve and sound propogates in the direction of blood flow.

Question 10

On a normal chest x-ray the apex of the heart can be found ____________ .

Answer 10

in the fifth left intercostal space approximately 7-9 cm from the midline.

Question 11

Describe the three attachments of the fibrous pericardium to other structures in the thoracic cavity.

Answer 11

1. Inferiorly is continuous with the central tendon of the diaphragm.
2. Anteriorly attaches to the posterior surface of the sternum by sternopericardial ligaments.
3. Posteriorly it attaches by loose connective tissue to structures in the posterior mediastinum.

Question 12

List three functions of the pericardium.

Answer 12

1. Protects the heart against sudden overfilling; it is unyielding
2. Fixes the heart in position
3. Physical barrier from infection

Question 13

When extensive pericardial effusion fills the pericardial space it does not allow full expansion of the heart.

Answer 13

Cardiac tamponade results from pericardial effusion.

Question 14

Formed by the folding of visceral and parietal pericardium back upon themselves around the great vessels of the heart.

Answer 14

Pericardial Sinuses.

1. Oblique Sinus; blind-ended space formed behind heart.
2. Transverse Sinus; seperates arteries and veins used to clamp great vessels during cardiac operations.

Question 15

Define pericarditis and outline how it may present clinically.

Answer 15

Inflammation within the pericardial space. May cause a pericardial rub (friction between the layers of serous pericardium due to inflammation).

Question 16

Explain the embryological origin of muscular striations and smooth walls in respect to the internal walls of the atrium.

Answer 16

Muscular striations is called pectinate muscle and is developed from the muscle of the heart. The smooth walls develop from the great vessel walls.

Question 17

Label this diagram.

Answer 17

Question 18

Describe the opening and closing of the semilunar and atrioventricular valves.

Answer 18

The atrioventricular valves are open during diastole as blood is recieved in the atrium. Semilunar valves open during systole when ventricles contract. All valves are closed during the end of systole.