Mediastinum

Question 1

Mediastinum

Answer 1

part of thoracic cavity that lies between the lungs- extends from the superior thoracic aperture superiorly to the diaphragm inferiorly and from the sternum anteriorly to the thoracic vertebrae posteriorly

Question 2

How is the mediastinum divided

Answer 2

superior and inferior compartment (the line runs from the sternal angle anteriorly to the T4/T5 junction posteriorly)

Question 3

How is the inferior mediastinum divided

Answer 3

Inferior mediastinum is divided into anterior (contains thymus gland), middle (contains the heart, pulmonary trunk and ascending aorta) and posterior

Question 4

3 parts of aorta

Answer 4

1. Ascending aorta- short, first part that gives rise to the coronary arteries that supply the myocardium
2. Arch of aorta- curves posteriorly and lies in the superior mediastinum
3. Descending aorta- descends through the posterior mediastinum and into the abdomen posterior to the diaphragm

Question 5

3 branches of aorta arch

Answer 5

1. Brachiocephalic trunk- bifurcates into right common carotid artery (which supplies the right side of head and neck, including the brain) and right subclavian artery (supplies right upper limb)
2. Left common carotid artery (supplies left side of head, neck and brain)
3. Left subclavian artery (supplies left upper limb)

Question 6

Aortic bodies

Answer 6

arch of aorta contains the aortic bodies where chemoreceptors are located- monitor arterial oxygen and carbon dioxide, visceral sensory information travels to CNS along vagus nerve and results in reflex response that regulates ventilation

Question 7

What does the brachiocephalic trunk supply

Answer 7

bifurcates into right common carotid artery (which supplies the right side of head and neck, including the brain) and right subclavian artery (supplies right upper limb)

Question 8

What does the left common carotid artery supply

Answer 8

supplies left side of head, neck and brain

Question 9

What does the left subclavian artery supply

Answer 9

Left upper limb

Question 10

Ligamentum arteriosum

Answer 10

fibrous, cord-like connection between pulmonary trunk and arch of aorta
• remnant of ductus arteriosus- a foetal circulatory shunt which diverts most of blood entering the pulmonary trunk directly tot the aortic arch as gas exchange occurs at placenta not in lungs (some blood circulates through lungs for development). When baby uses lungs, ductus arteriosus closes and blood in pulmonary trunk enters the lungs

Question 11

Superior vena cava

Answer 11

returns blood to heart from head, neck and upper limbs
• SVC domed by union of the left and right brachiocephalic veins
• Each brachiocephalic vein is formed by union of the internal jugular vein (which drains the head and neck) and subclavian vein (which drains the upper limb)

Question 12

What veins join to form brachiocephalic veins

Answer 12

internal jugular vein (which drains the head and neck) and subclavian vein (which drains the upper limb)

Question 13

Inferior vena cava

Answer 13

returns blood to heart from all regions inferior to the diaphragm

Question 14

Trachea

Answer 14

semi-rigid due to C-shaped incomplete rings of cartilage in its walls
• Extends from the larynx into the superior mediastinum and is palpable just superior of the suprasternal notch
• Terminates at level of sternal angle by bifurcating into left and right main bronchi

Question 15

Oesophagus

Answer 15

muscular tube that extends from pharynx to stomach
• Peristalsis- waves of smooth muscle contraction to move swallowed food and fluid distally
• Lies in midline of thorax, posterior to trachea, descends into posterior mediastinum

Question 16

Phrenic nerves

Answer 16

Left and right phrenic nerves (formed by fibres from the C3, C4 and C5 spinal nerves) innervate the diaphragm
• Somatic nerves and contain motor and sensory fibres
• Descend through neck and enter thorax through superior thoracic aperture
• Course over pericardium and pierce diaphragm

Question 17

Vagus nerves

Answer 17

left and right vagus nerves (CN X) arise from brainstem
• Contains sensory, somatic motor and parasympathetic fibres
• Innervate structures of thorax, abdomen, head and neck
• The vagus nerves descend in the thorax posterior to the root of the lung.
• contribute parasympathetic fibres to the heart, lungs, and oesophagus.
• They traverse the diaphragm and convey parasympathetic fibres to most of the abdominal viscera.

Each give rise to recurrent laryngeal nerve (RLN)- ascend back up neck to innervate muscles of larynx

Question 18

Left recurrent laryngeal nerve

Answer 18

loops under arch of aorta before ascending back up the left side of the neck (alongside the trachea) to the larynx.

Question 19

right recurrent laryngeal nerve

Answer 19

right recurrent laryngeal nerve descends anterior to the right subclavian artery and then loops under the inferior border of the artery before ascending back up the right side of the neck (between the trachea and oesophagus) to the larynx.

Question 20

Thoracic duct

Answer 20

major channel for lymphatic drainage from most regions of the body
• ascends through the posterior mediastinum and into the superior mediastinum, where it empties into the venous system at the union of the left internal jugular vein and left subclavian vein

Question 21

Thymus gland

Answer 21

lymphoid organ
• Lies anteriorly in superior mediastinum
• Important in children but atrophies with age, eventually becoming fatty

Question 22

Pericardium

Answer 22

tough, fibrous sac that encloses the heart- loose to allow movement of heart within it

Question 23

2 continuous layers of pericardium

Answer 23

1. tough, outer fibrous layer that is attached superiorly to the great vessels and inferiorly to the central tendon of the diaphragm
2. thin, inner serous layer which has two parts: the parietal layer lines the inner aspect of the fibrous pericardium, and the visceral layer covers the surface of the heart

Question 24

Pericardial cavity

Answer 24

narrow space between the two layers of serous pericardium- contains a small amount of pericardial fluid that lubricates the serous membranes and allows them to slide over each other with movements of the heart

Question 25

Which nerves innervate the pericardium

Answer 25

left and right phrenic nerves give rise to sensory branches that innervate the fibrous pericardium.