Theme 1: Lecture 2 - The Superior Mediastinum Flashcards

1
Q

Where is the mediastinum located?

A

Between the left and right pleural cavities

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2
Q

What are the three names for the junction between the manubrium and sternal body?

A
  • Level T4/5
  • Sternal angle
  • Transverse thoracic plane
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3
Q

What are the divisions of the mediastinum?

A

Superior and inferior

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4
Q

What is the inferior mediastinum further divided into?

A

Anterior, middle and posterior

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5
Q

What is the superior boundary of the superior mediastinum?

A

Superior thoracic aperture (manubrium, 1st rib and costal cartilage, T1 vertebra)

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6
Q

What is the inferior boundary of the superior mediastinum?

A

Transverse thoracic plane or T4/5 or sternal angle

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7
Q

What is the anterior boundary of the superior mediastinum?

A

Manubrium

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8
Q

What is the posterior boundary of the superior mediastinum?

A

T1-T4/5 vertebral bodies

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9
Q

What are the lateral boundaries of the superior mediastinum?

A

Mediastinal pleura`

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10
Q

What is contained in the superior mediastinum?

A
  • Arteries (arch of aorta and branches)
  • Veins (brachiocephalic veins, superior vena cava)
  • Phrenic and Vagus nerves
  • Oesophagus
  • Trachea
  • Thoracic duct
  • Thymus gland (part)
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11
Q

Where is the thymus gland located?

A

Immediately deep to the sternum and superficial to the heart. It is in both the superior and anterior mediastinum

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12
Q

What is the thymus gland?

A
  • It’s a lymphoid organ
  • T and B cells are produced in the bone marrow, T cells mature in the thymus (once they’ve matured they migrate to lymph nodes throughout the body)
  • Lymph drains through the parasternal, brachiocephalic and tracheobronchial nodes
  • Atrophies after puberty and is replaces by fat
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13
Q

Which arteries supply the thymus gland?

A

Internal thoracic arteries (these branch off the subclavian arteries and travel down either side of the sternum on the inside of the thoracic wall)

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14
Q

What are the arteries in the superior mediastinum?

A

The arch of the aorta and its 3 branches:

  • Brachiocephalic trunk (this branches into the right common carotid and subclavian arteries)
  • Left common carotid artery
  • Left subclavian artery
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15
Q

What arteries branch off the ascending aorta?

A

Left and right coronary arteries

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16
Q

What arteries branch off the descending aorta?

A
  • Posterior intercostal arteries (anastomose with anterior intercostal arteries coming from the internal thoracic arteries)
  • Left bronchial arteries
  • Lumbar arteries
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17
Q

What veins are contained in the superior mediastinum?

A
  • Superior vena cava

- brachiocephalic veins

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18
Q

Which veins form the superior vena cava?

A

The union of the left and right brachiocephalic veins

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19
Q

Which veins form the brachiocephalic veins?

A

The union of the internal jugular vein and subclavian vein

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20
Q

What is the ligamentum arteriosum?

A
  • A ligamentous structure that connects the pulmonary trunk to the aorta
  • An embryological remnant of the Ductus Arteriosus
21
Q

What is the Ductus Arteriosus?

A
  • An open duct connecting the pulmonary trunk and the arch of aorta
  • Important in foetal circulation allowing blood to bypass the immature lungs
  • Closes at birth
22
Q

Describe the Trachea

A
  • Tube with C-shaped cartilage rings
  • Trachealis muscle runs posteriorly
  • Runs from larynx to bronchi
23
Q

Describe the oesophagus

A
  • Muscular tube

- Runs from pharynx to stomach

24
Q

Describe the thoracic duct

A
  • Transports lymph to the venous system
  • Starts beneath the diaphragm, travels all the way through the thorax between the vertebral bodies and oesophagus before draining into the venous system at the venous angle
  • Receives multiple branches throughout the thorax
  • Numerous branches associated with thoracic (descending) aorta
25
Where do the phrenic nerves originate from?
Anterior rami of spinal nerves C3, C4 and C5
26
Where do the phrenic nerves travel?
- Enter mediastinum between brachiocephalic veins an subclavian arteries - Pass anterior to the main bronchi
27
What do the phrenic nerves do?
- Provide motor supply to the diaphragm | - Provide sensory supply to the diaphragm (central region) and parietal pleura (diaphragmatic and mediastinal)
28
How many phrenic nerves are there?
2
29
Where do the vagus nerve originate from?
The brainstem (AKA cranial nerves 10)
30
Where do the vagus nerves travel?
- They enter the mediastinum just medial to the phrenic nerves - They continue into the posterior mediastinum coursing posterior to the main bronchi
31
What do the vagus nerve give rise to?
The recurrent laryngeal branch to supply the larynx
32
What do the vagus nerves do?
Provide parasympathetic supply via the pulmonary, cardiac and oesophageal plexi
33
What does the anterior mediastinum contain?
- Thymus gland in children which atrophies in the adult and is replaced by fatty tissue - Pericardial-sternal ligaments - Lymph nodes (parasternal) and vessels - Internal thoracic artery
34
What is the superior border of the anterior mediastinum?
Level T4/5
35
What is the inferior border of the anterior mediastinum?
Diaphragm
36
What is the anterior border of the anterior mediastinum?
Sternum
37
What is the posterior border of the anterior mediastinum?
Pericardial sac
38
How does the heart develop?
- Angiogenic clusters develop in the mesoderm and these canalise (become hollow) to form early blood vessels - Two large blood vessels known as heart tubes form in the cardiogenic area - The paired heart tubes grow and fuse
39
What day do the paired heart tubes grow and fuse?
21 (this is also when the heart starts to beat, this is important as the embryo can no longer satisfy its needs by diffusion alone)
40
What are the regions that the newly formed heart tube are divided into?
- Sinus venosus - Primordial atrium - Primordial ventricle - Truncus arteriosus
41
What is the sinus venosus?
The primitive inflow vessels into the heart tube of an embryo
42
What is the truncus arteriosus?
The primitive inflow vessels into the heart tube of the embryo
43
On which day does the heart tube become too long for the pericardial cavity and start to fold?
Day 23
44
What does folding of the heart result in for the heart's orientation?
- Ventricles and outflow tracks positioned anteriorly | - atria and veins posteriorly
45
What are the two features of the foetal heart that allow blood to bypass the lungs?
- Foramen ovale | - Ductus arteriosus
46
What is the foramen ovale?
Opening between the left and right atria in the foetus and allows oxygenated blood to bypass the lungs
47
What is the fossa ovalis?
The embryological remnants of the foramen ovale which closes after birth
48
Why can blood travel from the right to left atrium through the foramen ovale?
Due to the higher pressure in the right than the left atrium