Session 1.2g - Gray's Anatomy for Students - Thorax - Regional anatomy - Mediastinum (Part I) Flashcards
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What is the mediastinum?
A broad central partition that separates the two laterally placed pleural cavities (Fig. 3.50).
Where does the mediastinum extend?
- from the sternum to the bodies of the vertebrae, and
- from the superior thoracic aperture to the diaphragm (Fig. 3.51)
What is the superior border of the mediastinum?
Superior thoracic aperture
What is the inferior border of the mediastinum?
Diaphragm
What is the anterior border of the mediastinum?
Sternum
What is the posterior border of the mediastinum?
Vertebral bodies (thoracic)
What does the mediastinum contain?
- thymus gland
- pericardial sac
- heart
- trachea
- major arteries and veins
What does the mediastinum serve as a passageway for?
Structures such as the:
- oesophagus
- thoracic duct
- various components of the nervous system
The mediastinum serves as a passageway for structure that ___?
Traverse the thorax on their way to the abdomen.
How is the mediastinum subdivided?
For organisational purposes, it is subdivided into several smaller regions.
Where is the mediastinum separated into the superior and inferior mediastinum?
A transverse plane extending from the sternal angle (the junction between the manubrium and the body of the sternum) to the intervertebral disc between vertebrae TIV and TV
A transverse plane from the sternal angle to the intervertebral disc between vertebrae TIV and TV separtes the mediastinum into the:
SUPERIOR MEDIASTINUM and INFERIOR MEDIASTINUM
How is the inferior mediastinum further partitioned?
Into the ANTERIOR, MIDDLE and POSTERIOR MEDIASTINUM
How is the inferior mediastinum partitioned into the anterior, middle and posterior mediastinum?
By the pericardial sac.
Where is the anterior mediastinum?
The area anterior to the pericardial sac and posterior to the body of the sternum. (Fig. 3.52)
Where is the posterior mediastinum?
The region posterior to the pericardial sac and the diaphragm and anterior to the bodies of the vertebrae. (Fig. 3.52)
Where is the middle mediastinum?
The area in the middle, which includes the pericardial sac and its contents. (Fig. 3.52)
What is centrally located in the thoracic cavity?
The MIDDLE MEDIASTINUM.
What does the middle mediastinum contain?
The pericardium, heart, origins of the great vessels, various nerves, and smaller vessels.
What is the pericardium?
The PERICARDIUM is a fibroserous sac surrounding the heart and the roots of the great vessels.
What components does the pericardium consist of?
Two components; the fibrous pericardium and the serous pericardium (Fig. 3.53).
Name the layers between the fibrous pericardium to the heart.
From superficial to deep
- Fibrous pericardium
- Junction between fibrous pericardium and adventitia of great vessels
- Serous pericardium:
- —– Parietal layer of serous pericardium
- —– Pericardial cavity
- —– Visceral layer of serous pericardium
What is the fibrous pericardium?
The FIBROUS PERICARDIUM is a tough connective tissue outer layer that defines the boundaries of the middle mediastinum.
What type of tissue is the fibrous pericardium?
Tough connective tissue
Which pericardium defines the boundaries of the middle mediastinum?
The fibrous pericardium (the outer layer)
Describe the serous pericardium
The SEROUS PERICARDIUM is thin and consists of two parts
What are the two parts of the serous pericardium?
The PARIETAL LAYER and the VISCERAL LAYER (EPICARDIUM)
Where is the parietal layer of serous pericardium?
The PARIETAL LAYER of serous pericardium lines the inner surface of the fibrous pericardium
What is the visceral layer of serous pericardium also known as?
EPICARDIUM
Where is the visceral layer of serous pericardium?
The VISCERAL LAYER (EPICARDIUM) of serous pericardium adheres to the heart and forms its outer covering.
Where are the parietal and visceral layers of serous pericardium continuous?
At the roots of the great vessels
What is the narrow space created between the two layers of serous pericaridum called?
PERICARDIAL CAVITY
What does the pericardial cavity contain?
A small amount of fluid
What is the function of the pericardial cavity?
This potential space allows for the relatively uninhibited movement of the heart.
Describe the shape and borders of the fibrous pericardium.
The FIBROUS PERICARDIUM is a cone-shaped bag with its base on the diaphragm and its apex continuous with the ADVENTITIA of the great vessels (Fig. 3.53).
Where, generally, is the base of the fibrous pericardium?
The diaphragm
Where is the apex of the fibrous pericardium?
Continuous with the ADVENTITIA (the outermost layer of a wall of a blood vessel) of the great vessels.
What is the base of the fibrous pericardium attached to?
The CENTRAL TENDON OF THE DIAPHRAGM and to a small muscular area of the diaphragm on the left side.
What is the fibrous pericardium attached to anteriorly?
The posterior surface of the sternum
How is the fibrous pericardium attached to the sternum?
By STERNOPERICARDIAL LIGAMENTS
What is the function of the sternopericardial ligaments?
These attachments help to retain the heart in its position in the thoracic cavity.
As well as the pericardial sac aiding movement of the heart, what else does it do?
The sac also limits cardiac distension.
What innervates the fibrous pericardium?
The phrenic nerves, which innervate the diaphragm and originate from spinal cord levels C3 to C5.
They pass through the fibrous pericardium from the point of origin to the diaphragm (their final destination). (Fig. 3.54).
Where is the location of the phrenic nerves in the fibrous pericaridium?
Their location, within the fibrous pericardium, is directly related to the embryological origin of the diaphragm and the changes that occur during the formation of the pericardial cavity.
What vessels supply the fibrous pericardium?
The PERICARDIACOPHRENIC VESSELS
Where are the pericardiacophrenic vessels found?
Located within and supply the fibrous pericardium as they pass through the thoracic cavity.
Where are the parietal and visceral layers of serous pericardium continuous?
Around the roots of the great vessels.
Where do the reflections of serous pericardium occur?
In two locations:
- one superiorly, surrounding the arteries, the aorta and the pulmonary trunk;
- one more posteriorly, surrounding the veins, the superior and inferior vena cava and the pulmonary veins.
What does the superior reflection of the serous pericardium surround?
The arteries, the aorta and the pulmonary trunk.
What does the more posterior reflection of the serous pericardium surround?
The veins, the superior and inferior vena cava and the pulmonary veins.
The zone of reflection from the serous pericardium surrounding the veins is what shape?
J-shaped
Where is the oblique pericardial sinus?
The zone of reflection from the serous pericardium surrounding the veins is J-shaped, and the cul-de-sac formed within the J, posterior to the left atrium, is the OBLIQUE PERICARDIAL SINUS.
What is the passage between the two sites of reflected serous pericardium called?
The TRANSVERSE PERICARDIAL SINUS
Where is the transverse pericardial sinus?
This sinus lies posterior to the ascending aorta and the pulmonary trunk, anterior to the superior vena cava, and superior to the left atrium.
What is the transverse pericardial sinus’ anterior border?
Ascending aorta and the pulmonary trunk
What is the transverse pericardial sinus’ posterior border?
The superior vena cava
What is the transverse pericardial sinus’ inferior border?
The left atrium
What is the clinical significance of the transverse sinus?
When the pericardium is opened anteriorly during surgery, a finger placed in the transverse sinus separates arteries from veins.
Where does the pericardium need to be opened to access the transverse sinus?
Anteriorly during surgery
How can the transverse sinus separate the arteries from veins?
A finger can be placed there during surgery.
How can the oblique sinus be accessed during surgery?
A hand placed under the apex of the heart and moved superiorly slips into the oblique sinus.
How can the transverse and oblique sinuses be accessed during surgery?
Transverse - open the pericardium anteriorly and place a finger in the transverse sinus to separate arteries from veins
Oblique - A hand placed under the apex of the heart and moved superiorly
What supplies the pericardium?
The pericardium is supplied by branches from the - internal thoracic - pericardiacophrenic - musculophrenic - inferior phrenic arteries, and the - thoracic aorta
Where do veins from the pericardium enter?
- the azygos system of veins
- internal thoracic v.
- superior phrenic v.
What nerves supply the pericardium?
Nerves supplying the pericardium arise from the
- vagus nerve [X]
- sympathetic trunks
- phrenic nerves
Where is the source of somatic sensation (pain) from the parietal pericardium from?
Somatic sensation (pain) is carried by somatic afferent fibres in the phrenic nerves.
Where might pain related to a pericardial problem be referred to?
The supraclavicular region of the shoulder or lateral neck area dermatomes for spinal cord segments C3, C4 and C5.
Why might pain be referred to the supraclavicular region of the shoulder or lateral neck area?
The source of somatic sensation (pain) from the pericardium is carried by somatic afferent fibres in the phrenic nerves.
This may lead to referred pain in the dermatomal spinal cord segments C3, C4 and C5.
Somatic sensation from the pericardium is carried by somatic ______ fibres from which nerves?
Afferent; phrenic nerves
What is the general shape and orientation of the heart?
Cardiac orientation is that of a pyramid that has fallen over and is resting on one of its sides.
Where is the apex of the heart?
Placed in the thoracic cavity, the apex of the heart projects forward, downward, and to the left.
Where is the base of the heart?
Opposite the apex and faces in a posterior direction (Fig. 3.56).
What direction does the base of the heart face?
Posteriorly (Fig. 3.56).
What do the sides of the pyramid consist of?
- Diaphragmatic surface
- Sternocostal surface
- Right pulmonary
- Left pulmonary
What is the inferior surface of the heart?
A diaphragmatic (inferior) surface on which the pyramid rests
What is the anterior surface of the heart?
An anterior (sternocostal) surface oriented anteriorly
What is the right surface of the heart?
A right pulmonary surface
What is the left surface of the heart?
A left pulmonary surface
Describe the base of the heart?
The BASE (posterior surface) OF THE HEART is quadrilateral and directed posteriorly.
What does the base of the heart consist of?
- The left atrium
- A small portion of the right atrium
- Proximal parts of the great veins
Which atrium does the base of the heart mainly consist of?
The left atrium
Which atrium does the base of the heart consist of a small portion of?
The right atrium
Which parts of the great veins does the base of the heart contain?
The proximal parts