Mediastinum (Morgan R + lecture slides)

What is the pericardium?

fibroserous sac made of 2 layers that encloses the heart and root of great vessels

What are the 2 layers of the pericardium?

fibrous pericardium and serous pericardium

What is the fibrous pericardium?

the conical sac attached to the diaphragm and above to the root of the great vessels

What is the serous pericardium?

a thin double-layered membrane that is lined by mesothelium (parietal outer layer that is fused with the fibrous pericardium and inner visceral layer that covers the heart)

What allows the heart to move freely in the pericardial sac?

the thin film of fluid in the pericardial cavity between the parietal and visceral layers of serous pericardium

What are the layers of the heart wall?

superficial to deep: epicardium, myocardium, endocardium (continuous with the endothelium of the great vessels)

What are the sinuses of the pericardium?

Areas where the epicardium at the roots of the great vessels arrange to form 2 tubes: the transverse sinus and the oblique sinus

Where is the transverse sinus located in the heart?

it is the horizontal gap behind the ascending aorta and pulmonary trunk (separates them from the vena cava)

Where is the oblique sinus located in the heart?

it is a narrow gap behind the left atrium formed by the reflection of pericardium around the pulmonary veins and vena cava

What is the mediastinum?

the median septum of thorax between the 2 lungs

Describe the location of the superior mediastinum

it extends inferiorly from the superior thoracic aperture to the horizontal plane at the level of the sternal angle and lower border of T4

simplified: structures posterior to the manubrium of the the sternum

What structures make up the superior mediastinum?

- remnants of the thymus gland

- brachiocephalic veins

- superior vena cava

- brachiocephalic artery

- L common carotid artery

- L subclavian artery

- arch of aorta

- phrenic nerves

- vagus nerves

- lymph nodes

- thoracic duct

- sympathetic trunks

- trachea

- esophagus

Describe the location of the inferior mediastinum.

the area between the transverse thoracic plane and diaphragm. It is further subdivided by the pericardium into 3 parts: anterior, middle, and posterior

Where is the anterior mediastinum and what does it contain?

it is part of the inferior mediastinum (below sternal angle) and is between the pericardium and sternum, contains remnants of the thymus gland and lymph nodes

Where is the middle mediastinum and what does it contain?

It is part of the inferior mediastinum (below sternal angle) and contains the pericardium and heart

Where is the posterior mediastinum and what does it contain?

It is part of the inferior mediastinum (below sternal angle) behind the pericardium and it contains the:

- descending thoracic aorta*

- esophagus*

- thoracic duct*

- azygous system of veins

- vagus nerves

- splanchnic nerves

- sympathetic trunks

- lymph noes

Where does the superior mediastinum switch to the inferior mediastinum?

at the sternal angle (below manubrium of sternum) and T4 vertabra

Anastomosis

the union or connection of any branches (vessels or nerves)

Collateral circulation

situated or running side by side, it becomes important when one of the vessels is obstructed; the blood that is blocked in the obstructed vessel can flow through the collateral vessel

End artery

an artery that has no anastomosis

Anatomic end artery

an artery that does not have any anastomoses to any other artery

ex: the central artery of retina

Functional end artery

an artery that has anatomic connections to other arteries but the connections are small and are not able to supply enough blood to satisfy the tissues supplied by the block artery

ex. coronary arteries

Venous portal system

a portal vein connects one capillary bed to another

ex. hepatic portal vein

Thrombus

immobile blood clot that stays where it is formed

ex. coronary thrombosis

Embolus

a plug, composed of a detached thrombus or vegetation, mass of bacteria, or other foreign body, occluding a vessel

ex. blood clot formed in the lower extremity breaks loose and is carried to the lungs where it blocks pulmonary ciruclation

Metastatic tumor cells

transfer of cancer cells from the primary tumor to another site

Diastole

the normal rhythmically occurring relaxation and dilation of the heart cavities during which the cavities are filled with blood

Systole

normal rhythmically occurring contraction of the heart cavities

Edema

excessive accumulation of fluid

What is the superior vena cava and where does it drain?

a large vein formed by the union of the right and left brachiochephalic veins that drains into the right atrium

Describe which veins unite to eventually form the superior vena cava.

the internal jugular and subclavian veins join to form the brachiocephalic vein, and the brachiocephalic veins join to form the SVC

What vein drains into the SVC just before it enters the pericardium?

the azygous vein

What vertebra does the trachea run from?

C6 - T5

What is the carina?

bifurcation of trachea into the right and left bronchus at level T5

Which primary bronchus is more likely to be the site of aspiration of small objects?

the right primary bronchus because it is wider and more vertical (more in line with the trachea)

What is the esophagus and what are its landmarks in the body?

A muscular tube that connects the mouth to the stomach. It extends from the lower border of the cricoid cartilage from vertebra C6 and then descends in front of the vertebral column through both the superior and posterior parts of the mediastinum and pierces the diaphragm at vertebra level T10 and ends in the stomach at the vertebra level T11

Where does the ascending aorta arise from?

the left ventricle

What are aortic sinuses?

3 bulges (dilations) at the root of the ascending aorta located just above the aortic valve, they provide space for aortic valve leaflets to open and close properly, each is connected to an aortic artery so they also have their own blood reservoir to constantly supply the coronary arteries

What branches off of the ascending aorta?

right and left coronary arteries

Where does the arch of aorta begin?

at the second right sternocostal joint, runs upwards, backwards, and left across the left side of the bifurcation of the trachea, ends at the lower border of T4 by becoming the descending aorta

What branches off the arch of aorta?

brachiocephalic (further branches into right common carotid and right subclavian), left common carotid, left subclavian

Where does the the thoracic aorta begin?

the left side of the lower border of T4

Where does the thoracic aorta become the abdominal aorta?

at the lower border of the T12 vertebra

Why does the FDA warn against the use of certain SSRI antidepressants during pregnancy?

they can lead to elevated risks of cardiac birth defects like coarctation of the aorta (narrowing of the aorta)

What is the azygous vein?

The azygous vein runs parallel to the aorta and acts as a drainage for the thoracic wall and upper lumbar region. It also acts as a second passage for veinous drainage other than the vena cava

What forms the azygous vein?

the union of the lumbar azygos, right subcostal and right ascending lumbar veins

Where does the azygous vein terminate?

it ascends up to T4, where it arches forwards over the root of the right lung and terminates in the superior vena cava (mainly on the right side of the body)

What are the azygous vein tributaries?

- right superior intercostal vein

- 4th to 11th right posterior intercostal veins

- hemi azygous vein

- accessory azygous vein

What is the hemiazygous vein?

a vein that is a branch of the azygous vein that is almost equal to the lower half of the azygous vein, joins the azygous vein at T9 after taking a turn to the right (mainly on the left side of the body)

What are the tributaries of the hemiazygous vein?

- left ascending lumbar vein

- lumbar azygous vein

- left subcostal vein

- 9th to 11th left posterior intercostal veins

What is the accessory hemizygous vein and where is it located?

a branch of the azygous vein that runs on the left side of the vertebral column from the medial end of the 4th intercostal space and descends down. It joins the azygous vein at the T8 level. Drains the 5-8 left posterior intercostal veins

Where is the accessory hemizygous vein in relation to the hemizygous vein?

it is superior to it (above it)

How long is the thoracic duct?

38-45 cm

Why does the thoracic duct have a beaded appearance?

due to the many valves in its lumen

Where is the thoracic duct?

it extends from the upper abdomen to the lower neck, crossing both posterior and superior parts of the mediastinum. It begins at T12 and crosses from right to left at T5. In the neck it arches laterally and ends by opening in to an angle of junction between left subclavian and left internal jugular vein

Where is the common duct for most lymph vessels in the body?

the thoracic duct

Where does the thoracic duct empty into?

the left subclavian vein

What does the right lymphatic duct empty into?

right subclavian vein

What does the jugular trunk drain?

the head and neck regions

What does the subclavian trunk drain?

upper extremity

What does the bronchiomediastinal trunk drain?

the thorax

What does the cisterna chyli do?

collects lymph from the lower body and intestines and it dumps it into the thoracic duct

What do the intestinal (prevertebral) trunks drain?

the gut and associated structures

What do the lumbar (paravertebral) trunks drain?

the lower extremities and the pelvis

What do the lumbar and thoracic vessels drain?

the thoracic and abdominal walls, except skin and superficial fascia