Anatomy 5

Question 1

What does the posterior mediastinum contain?

Answer 1

● descending (thoracic) aorta
● azygos veins
● oesophagus
● thoracic duct
● sympathetic trunk and splanchnic nerves
● posterior intercostal vessels and nerves

Question 2

What does the descending aorta give rise to?

Answer 2

● Posterior intercostal arteries which supply the intercostal spaces
● Bronchial arteries which supply the lungs
● Oesophageal branches which supply the oesophagus
● Pericardial branches which supply the pericardium
● Phrenic branches which supply the diaphragm.

The aorta passes through the diaphragm at the level of T12.

Question 3

Where does the Azygos system of veins arise from?

Answer 3

Arises in the abdomen at the level of L1 / L2 and traverses the diaphragm to enter the posterior mediastinum

Question 4

What does the Azygos System of Veins do?

Answer 4

It drains blood from the posterior thoracic wall and returns it to the superior vena cava

Question 5

What does the Azygos System comprise of?

Answer 5

● an azygos vein on the right side of the vertebral bodies
● a smaller (shorter) hemiazygos vein on the left side of the vertebral bodies
● one or more veins connecting the above veins to each other

Question 6

Where does the Azygos System receive blood from?

Answer 6

The azygos system receives blood from the posterior intercostal veins, oesophageal veins, and bronchial veins.

Question 7

Where is the Oesophagus located?

Answer 7

In the posterior mediastinum, to the right of the aorta

Question 8

What is the Oesophagus supplied by?

Answer 8

It is supplied by oesophageal arteries from the descending aorta

Question 9

What do Oesophageal Veins do?

Answer 9

Return venous blood to the azygos system.

Question 10

What type of muscle cell is found in the walls of the Oesophagus?

Answer 10

Smooth muscle
Under autonomic control

Question 11

What does the oesophagus pass through?

Answer 11

Passes through the oesophageal hiatus in the diaphragm at the level of T10.

The most distal part of the oesophagus lies inferior to the diaphragm.

Question 12

What is the function of the Thoracic Duct?

Answer 12

The thoracic duct returns most of the body’s lymph to the venous system.

Question 13

Where is the Thoracic Duct found?

Answer 13

It lies between the azygos vein and the aorta.

Question 14

What gives rise to the Thoracic Duct?

Answer 14

Cisterna Chyli, a sac-like swelling that gives rise to the thoracic duct, which ascends into the thorax.

● Lymph from the lower limbs, pelvis and abdomen flows towards it

Question 15

Where does the thoracic duct receive lymph from?

Answer 15

The duct receives lymph from the intercostal spaces and lymph nodes

Question 16

Where does the thoracic duct ascend into?

Answer 16

The duct ascends into the neck, receiving lymph from the left side of the head and neck and the left upper limb.

Question 17

Where does the thoracic duct terminate?

Answer 17

It terminates by opening into the venous system at the junction between the left internal jugular vein and the left subclavian vein.

The right side of the head and neck and the right upper limb are drained by lymphatic ducts that enter the venous system at the junction of the right internal
jugular and right subclavian veins.

Question 18

Where are the sympathetic trunks found?

Answer 18

The trunks lie on the posterior thoracic wall, either side of the vertebral column and posterior to the parietal pleura.

They are thin, longitudinal fibre tracts regularly
interspersed with ganglia

Question 19

What is a ganglion?

Answer 19

A collection of cell bodies outside the CNS

Question 20

What is the ganglia in sympathetic trunks sometimes referred as?

Answer 20

Sometimes referred to as ‘paravertebral ganglia’ as they lie alongside the vertebral column.

Question 21

Where does the sympathetic trunk extend from?

Answer 21

Extends from the skull base in the coccynx

Question 22

Where are the cell bodies of preganglionic sympathetic neurons found?

Answer 22

Lie in the thoracic and upper lumbar spinal cord segments (T1-L2/3)

Question 23

Where do sympathetic fibres leave the spinal cord from?

Answer 23

They are visceral fibres, so leave the spinal cord from its ventral aspect

Question 24

How do sympathetic fibres enter spinal nerves?

Answer 24

Enter spinal nerves T1 – L2/3 along with somatic motor nerves, whose cell bodies lie in the ventral grey horn.

Question 25

How do preganglionic sympathetic fibres distribute to all parts of the body?

Answer 25

● Preganglionic sympathetic fibres exit the spinal cord in spinal nerves T1 - L2/3.

● Almost immediately, they separate from the spinal nerves and enter the sympathetic trunk via a short communicating / connecting branch (white ramus
communicans).

● Once in the sympathetic trunk, the preganglionic axon does one of the following:
1. synapses in the ganglion at its level of entry
2. ascends or descends in the trunk before synapsing in a ganglion
3. travels through a ganglion (and the trunk) without synapsing

In scenarios 1 and 2, the postganglionic axons leaving the ganglia:
● enter spinal nerves via a communicating branch (grey ramus communicans).
Through this arrangement, sympathetic fibres enter all 31 pairs of spinal nerves
● form visceral nerves that convey sympathetic fibres to the head
● form visceral nerves that convey sympathetic fibres to the thoracic viscera
(cardiopulmonary splanchnic nerves).

Question 26

What are the abdominopelvic splanchnic nerves?

Answer 26

● Greater splanchnic nerve (sympathetic preganglionic fibres originating from T5-T9 segments of the spinal cord)
● Lesser splanchnic nerve (from T10-11)
● Least splanchnic nerve (from T12)
● Lumbar splanchnic nerves (from L1–L2)

Question 27

Where are the greater, lesser, and least splanchnic nerves formed?

Answer 27

Formed in the Posterior Mediastinum and transverse the diaphragm to enter the abdomen

They ultimately synapse with second neurons in prevertebral ganglia that lie close to major blood vessels in the abdomen.

After synapsing, the postganglionic fibres innervate abdominal viscera

Question 28

What does the posterior intercostal space contain of?

Answer 28

● intercostal muscles
● a posterior intercostal artery (a branch of the thoracic aorta)
● a posterior intercostal vein (which drains to the azygos system)
● a posterior intercostal nerve

Question 29

What do the Cardiopulmonary Splanchnic Nerves convey?

Answer 29

Convey postganglionic sympathetic fibres to the thoracic viscera

Question 30

What do the Vagus Nerves convey?

Answer 30

Convey parasympathetic fibres to the thoracic viscera.

Question 31

What do the Sympathetic and Parasympathetic fibres form around the Thoracic Viscera?

Answer 31

Form Autonomic Plexuses

Question 32

What is the Cardiac Plexus?

Answer 32

Innervates the sinoatrial node of the heart.

Sympathetic fibres increase the heart rate and force of contraction, whilst parasympathetic fibres decrease the heart rate and force of contraction.

Question 33

What is the Pulmonary Plexus?

Answer 33

Innervates the bronchi.

Sympathetic stimulation relaxes the bronchi and parasympathetic stimulation constricts them.

Question 34

What is the Oesophageal Plexus?

Answer 34

Overlies the anterior surface of the oesophagus.

Sympathetic fibres inhibit peristalsis and parasympathetic fibres stimulate peristalsis.

Question 35

What are Visceral Afferents?

Answer 35

Relay sensory information from the thoracic viscera back to the CNS along the paths of the vagus and thoracic splanchnic nerves.

Question 36

What is Cardiac Pain?

Answer 36

Typically (but not always) felt in the central chest, left side of the neck and left arm.

This is an example of referred pain, where pain from one part of the body is felt in another region.

Question 37

What is the heart innervated by?

Answer 37

● Innervated by the cardiac plexus, composed of sympathetic and parasympathetic fibres.

The sympathetic fibres travel to the cardiac plexus and heart from spinal cord segments T1 -T5 via the cardiopulmonary splanchnic nerves.

● The heart is also innervated by visceral sensory nerves, which convey sensory information from the heart back to the CNS - this sensation normally does not reach our conscious perception.

However, if the myocardium is ischaemic this
sensation does reach our conscious perception, and is interpreted as pain, tightness, crushing pressure or burning, which may be severe.

Question 38

Where in the spine does the visceral sensory information enter?

Answer 38

Enters spinal cord segments T1 - T5.

Question 39

Where does somatic sensory information from the skin of the chest wall, neck and arm return?

Answer 39

Returns to spinal cord segments T1 - T5

Painful visceral sensory information from the heart and somatic sensory information from the chest wall both enter spinal cord segments T1 - T5.

For reasons that are not fully understood, the brain interprets the cardiac pain as coming from the chest, neck, and arm

Question 40

What is Aortic Dissection?

Answer 40

Longitudinal tear in the aortic wall that allows
blood to collect between the intima and media.

It can happen in the ascending aorta,
arch, or descending aorta.

It typically presents with sudden onset severe chest and /or back pain.
Instead of flowing through the ‘true’ lumen of the aorta, blood collects in the ‘false’ lumen created by the tear.

Question 41

What is Horner’s Syndrome?

Answer 41

Horner’s syndrome describes the presentation of three signs together:
- a small pupil (miosis),
- a drooping upper eyelid (ptosis)
- lack of sweating (anhidrosis) on one side of the face.

It is caused by an interruption to the sympathetic nerves that innervate the head.
A cancer in the apex of the lung that invades the sympathetic chain can cause Horner’s syndrome on the ipsilateral side of the head.

Question 42

What is Hiatus Hernia?

Answer 42

A hiatus hernia occurs when the abdominal segment of the oesophagus (inferior to the diaphragm) and part of the stomach moves proximally through the oesophageal opening in the diaphragm and into the chest.

Patients may experience symptoms such as heartburn and acid reflux.