12-09-22 - Thoracic Cavity 1 Flashcards
Learning outcomes
• Describe the general arrangement of the pleura and pericardium
• Define the term mediastinum and describe the boundaries of its subdivisions
• List the contents of the anterior, middle, superior and posterior mediastina
• Describe the relationships of the structures within the mediastina
• Describe the fibrous and serous pericardium, and pericardial cavity
• Describe the position of the transverse and oblique sinuses of the serous pericardium
• Describe the course and distribution of the right and left phrenic nerves
• Describe why irritation of the phrenic nerve will result in referred pain to the shoulder
• Discuss the clinical conditions that affect the pericardium
• Describe the position of the thymus
• Identify anatomical structures on medical images of the thorax
Body is the function of body cavities?
What are the 2 types of membranes found in body cavities?
Where are they both found?
What are the 3 functions of serous membranes?
• Body cavities confine organs and systems that have related functions
• In body cavities, there are mucous and serous membranes
• Mucous membranes can be found in cavities open to the external environment e.g nasal cavity, oral cavity, tubular structures
• Serous membranes can be found in the thoracic cavity, where it lines the lung and chest wall (serous membrane called pleura) and the heart (serous membrane called pericardium)
• It also lines abdominal and pelvic cavities (serous membrane called peritoneum)
Functions of serous membranes:
1) Allows for movement, expansion, and contraction of organs
2) Compartmentalizes the overall body cavity into smaller parts
3) Provides lubricated potential spaces, which give friction free movement
What are the lungs covered in?
What are the 2 layers of pleura?
How many types of each layer are there?
What 4 places is parietal pleurae firmly attached to?
What is the area in between these 2 layers called?
How is the thoracic cavity divided up?
• The lungs are invaginated in a serous membrane called pleura
• Invagination – be turned inside out or folded back on itself in a cavity or pocket
• The 2 layers of pleura:
1) Visceral pleura - touches the lung tissue (1 visceral pleura)
2) Parietal pleura – not in the contact with lungs, but surround root of lung (3 parietal pleura)
• The parietal pleura is firmly attached to:
1) Thorax wall (costal pleura)
2) The fascia at the thoracic inlet at 1st rib and T1 (covers inner surface of rib – costal pleura)
3) Fibrous pericardium and other mediastinal structures (mediastinal pleura)
4) Diaphragm (diaphragmatic pleura )
• The area in between these 2 layers is called the pleural/thoracic cavity
• The thoracic cavity is divided up into 3 parts:
1) Left pleural cavity
2) Mediastinum – in between independent pleural cavities
3) Right pleural cavity
Label these vessels in the heart
What things 3 is the mediastinum located between?
What property does the mediastinum have that is important for respiration?
What are the structures on the right of the mediastinum related to?
What are 3 of the structures?
What are the structures on the left of the mediastinum related to?
What are 4 of the structures?
What 2 things is the mediastinum divided into?
Where are these divisions located?
• The mediastinum is the space of the thoracic cavity located between:
1) The 2 pleural cavities
2) Sternum and costal cartilages
3) Thoracic vertebrae and diaphragm
• The mediastinum is a highly mobile region, which is important for volume and pressure changes during respiration.
• Structures on the right of the mediastinum are related to right atrium and veins:
1) Superior Vena Cava
2) Arch of the Azygos
3) Inferior Vena Cava
• Structures on the left of the mediastinum are related to left ventricle and arteries:
1) Left common carotid
2) Left subclavian artery
3) Arch of aorta
4) Thoracic aorta
• The mediastinum is divided into:
1) Superior mediastinum
• Located behind the manubrium, between the thoracic inlet and the transverse plane running through the sternal angle (T4/T5 level)
2) Inferior mediastinum:
• Located inferior to the transverse plane through the sternal angle and the diaphragm
• The inferior mediastinum is further subdivided into the anterior, middle, and posterior mediastinum
Structures on the right and left of the mediastinum diagram
• Structures on the right of the mediastinum are related to right atrium and veins:
1) Superior Vena Cava
2) Arch of the Azygos
3) Inferior Vena Cava
• Structures on the left of the mediastinum are related to left ventricle and arteries:
1) Left common carotid
2) Left subclavian artery
3) Arch of aorta
4) Thoracic aorta
Where is the middle mediastinum located?
What 5 things does it contain?
What is the pericardium?
What are 2 functions of the pericardium?
What are the 2 layers of the pericardium?
• The middle mediastinum is located inferior to the sternal angle
• The middle mediastinum contains:
1) Heart
2) Pericardium
3) Great vessel roots (not the full great vessels)
4) Phrenic nerves
5) Branches of vagus nerve
• The pericardium is the fibro-serous sac that encloses the heart and the roots of the great vessels
• Functions of the pericardium:
1) Anchoring the heart to surrounding tissues without compromising cardiac movement
2) Preventing overfilling (overexpansion) of the heart
• Layers of the pericardium:
1) Fibrous pericardium (externally)
2) Serous pericardium (internally)
What does the fibrous-pericardium consist of?
Why is this important?
What is the apex of the fibrous pericardium fused with?
Where does the fibrous pericardium attach anteriorly, posteriorly and inferiorly?
• The fibrous pericardium is made from tough tissue to prevent overfilling of the heart
• The apex of the fibrous pericardium is fused with the adventitia (outer connective tissue layer) of the great vessels, which includes:
1) Aorta
2) Pulmonary trunk
3) Terminal parts of SVC and IVC
• Anteriorly, the fibrous pericardium is attached by the sterno-pericardial ligament to the body of the sternum and 3rd and 6th costal cartilages
• Posteriorly, the fibrous pericardium is related and attached by the pericardiovertebral ligaments to the 5th and 8th thoracic vertebrae
• Inferiorly, the fibrous pericardium blends with the central tendon of the diaphragm (pericardiophrenic ligament)
What are the 2 layers of the serous pericardium?
Where can they be found?
What exists between these 2 layers?
What can be found in this area?
What is it produced by?
What is its function?
• Layers of the serous pericardium:
1) Parietal serous pericardium
• Lines the inner aspect of the fibrous pericardium
• Reflects onto itself around the roots of the great vessels and continues as the visceral layer
2) Visceral serous pericardium (epicardium)
• Between these 2 layers of the serous pericardium exists the pericardial cavity
• In the pericardial cavity, there is 10-15ml of pericardial fluid
• Pericardial fluid is produced by the serous pericardium
• It reduced the friction during the contraction of the heart
How do 2 sinuses form during embryological development?
What are the names of these sinuses?
What is another name for the transverse pericardial sinus?
What is its function?
Where is it located?
Why is the transverse sinus important for surgery?
What is another name for the oblique pericardial sinus?
What is it surrounded by?
• During embryological development, the heart tube folds and invaginates into the serous pericardium, which is within the fibrous pericardium
• This leads to the formation of 2 sinuses in the serous pericardium:
1) Transverse pericardial sinus
• Also known as the sinus of Theile
• Separates the arterial and venous ends of the heart tube, leading to the formation of atria and ventricles
• The transverse pericardial sinus is located posterior to the ascending aorta and pulmonary trunk
• It is anterior to the superior vena cava
• It is superior to the left atrium and pulmonary veins
• During cardiac surgery, the transverse pericardial sinus allows a surgeon to isolate the pulmonary trunk and ascending aorta and apply a temporary ligature or clamp.
• This can allow the heart and lungs to be put on bypass (cardiopulmonary bypass) while surgery is performed on the heart
2) Oblique pericardial sinus
• Also known as Haller’s Cul-de-sac
• Surrounded by the reflection of the serous pericardium around the right and left pulmonary veins and inferior vena cava
Where do the sensory and vasomotor nerves fibres of the pericardium come from?
• The sensory fibres of the pericardium come from the phrenic nerve
• The vasomotor fibres of the pericardium come from vagus nerve parasympathetics or splanchnic nerve parasympathetics
What plexus is the phrenic nerve part of?
What ventral rami does it arise from?
What muscle does it sit over?
How does the phrenic nerve enter the mediastinum?
What structures do the right and left phrenic nerves pass in the mediastinum?
Where does the right phrenic nerve go from here?
What does it innervate?
• The phrenic nerve is a branch of the cervical plexus
• It arises from the ventral (anterior) rami of C3, C4, C5
• The phrenic nerve goes over the scaleneus anterior muscle
• The phrenic nerve enters the mediastinum between the venous (subclavian vein) and arterial planes (subclavian artery)
• In the mediastinum of the thoracic cavity, the right and left phrenic nerve passes anterior to the roots of the lung, and lies between the fibrous pericardium and mediastinal pleura
• Right phrenic nerve
• The right phrenic nerve passes adjacent to the superior vena cava, then the inferior vena cava in the mediastinum
• It passes through the caval opening with the IVC, which is an opening on the central tendon of the diaphragm that allows the right phrenic nerve to move into the abdominal cavity at the level of T8
• From here, it turns around and supplies the inferior surface of the diaphragm and innervates the right hemidiaphragm
• Left phrenic nerve
• The left phrenic nerve crosses the aortic arch and goes over the left ventricle
• It travels between the pericardium and mediastinal pleura
• It descends towards the diaphragm but not into the abdominal cavity
• The left phrenic nerve is distributed on the superior surface of the diaphragm and innervates the left hemidiaphragm
What is a dermatome?
What is a myotome?
• A myotome is a group of muscles innervated by the same spinal nerve
• A dermatome is an area of skin innervated by a single spinal segment
What is the phrenic the sole motor supply of?
What might occur is the phrenic nerve is severed?
What 4 things does the phrenic nerve supply sensory fibres to?
What is the sensory supply to the periphery of the diaphragm?
What is the supraclavicular nerve?
What does it supply?
How can this cause referred pain?
• The phrenic nerve is the sole motor supply of the diaphragm
• If the phrenic nerve is severed, the person can still live, but can’t exercise
• The phrenic nerve supplies sensory fibres to:
1) Mediastinal pleura
2) Diaphragmatic pleura related to the central tendon of the diaphragm (sensory fibres don’t go to the periphery of the diaphragm)
3) Parietal pericardium
4) Peritoneum
• The sensory supply to the periphery of the diaphragm is intercostal nerves
* The supraclavicular nerve is made from nerve roots C3 and C4
• The supraclavicular nerve supplies the skin over the shoulder, which is the C4 dermatome
• This will mean structures with a sensory supply via the phrenic nerve may refer pain to the back of the neck, the supraclavicular region
What is another name for the anterior mediastinum?
What are the 3 boundaries of the anterior mediastinum?
What are 7 contents of the anterior mediastinum?
• The anterior mediastinum can also be called the pre-vascular compartment or pre-vascular mediastinum
• Boundaries of anterior mediastinum:
1) Sternal body and xiphisternum
2) Pericardium
3) Lungs with pleura
• Contents of anterior mediastinum:
1) Internal thoracic vessels
2) Thymus
3) Lymph nodes
4) Connective tissue
5) Fat tissue
6) Lower pole of thyroid (rare)
7) Ectopic parathyroid (lower thyroid glands)
What is the thymus?
Where is it found?
What structures is the thymus related to?
Where does the thymus extend from?
When is the thymus active?
How does it change with age?
What is the function of the thymus?
• The thymus is a bi-loped organ of lymphoid tissue
• The thymus can be found in the upper anterior part of the chest, directly bind the sternum and between the lungs, along both sides of the trachea
• The thymus is related to:
1) Pericardium
2) Superior Vena Cava
3) Aorta
4) Left and right brachiocephalic veins
5) Pleura
6) Phrenic nerves
7) Trachea
• The thymus extends from the jugular notch to the 4th costal cartilage (sometimes below the aortic arch)
• The thymus is active in childhood until puberty
• The infiltration of fibro-fatty tissue in the thymus increases with age
• The thymus us an organ that is critically important to the immune system
• It serves as the body’s defence mechanism, protection against diverse pathogens, tumours, antigens and mediators of tissue damage.
• The primary function of the thymus gland is to train special white blood cells called T-cells or T-lymphocytes to recognise the body’s own proteins
How are structures in the superior mediastinum arranged?
What lies between these planes?
• The structures in the superior mediastinum are arranged in 3 planes:
1) Venous plane
2) Arterial plane
3) Visceral plane - Trachea and Oesophagus
• The vagus and phrenic nerves lie between these planed and pass from the neck into the thoracic cavity through the venous and arterial planes to supply the heart
The venous plane.
What veins form the brachiocephalic?
Where does the left BCV pass anteriorly and posteriorly?
What is the Superior Vena Cava formed by (SVC)?
What joins to the SVC?
Where does the SVC enter into?
• The brachiocephalic veins (BCV) are formed by the internal jugular (IJV) and subclavian veins (ScV)
• The left BCV passes anterior to the arch of the aorta and posterior to the manubrium
• The Superior Vena Cava (SVC) is formed by the right and left brachiocephalic veins
• The arch of azygous vein joins SVC
• The SVC then enters into the right atrium
The arterial plane.
Where is the ascending aorta located?
Where does the ascending aorta turn into the aortic arch?
Where does the aortic arch go from here?
What are the 3 branches of the aortic arch?
Where is the pulmonary trunk found?
Where does it divide?
What does it divide into?
Where these branches located?
• The ascending thoracic aorta with its branches are in the superior mediastinum
• The ascending aorta continues as the aortic arch above the sternal angle (T4/T5 plane)
• The aortic curves up, backwards and slightly left behind the lower half of the manubrium, then continues as the thoracic (descending) aorta in the posterior mediastinum
• Branches of the aortic arch:
1) Brachiocephalic trunk – divides into right subclavian and right common carotid arteries
2) Left common carotid artery
3) Left subclavian artery – posterior and to the left of the trachea
• The pulmonary trunk lies within the pericardium (in the middle mediastinum) to the left of the ascending aorta
• The pulmonary trunk divides at the level of the T4/T5 disc, inferior to the aortic arch
• The pulmonary trunk divides into:
1) Right pulmonary artery – posterior to the ascending aorta and superior vena cava
2) Left pulmonary artery – inferior to the arch of the aorta and anterior to the descending thoracic aorta
Visceral plane.
Where is the trachea located?
Where does it start and end?
Where might the trachea rise and descend to?
• The trachea is an air-transport tube located in the midline of the neck
• The trachea starts at the level of the C6 vertebra
• The trachea ends at the tracheal bifurcation (carina)
• The trachea may rise and descend to the level of T4 and T6 with deep inspiration and expiration
Label this diagram of the C-spine
