Body cavities 1 and 2 Flashcards
What do serous membranes do?
- Compartmentalize
- Allow movement, expansion and contraction of organs
- With a minuscule layer of fluid, create a lubricated potential space which is friction free
What is the thoracic cavity lined by?
(parietal) Pleura
What are the abdominal and pelvic cavities lined by?
The peritoneum
Visceral
Covers the organ
Parietal
Next to the wall
Pleural cavities
In-between the parietal and visceral layers
What are the compartments of the thoracic cavity?
- Left cavity
- Right cavity
- Mediastinum
Describe the covering of the left and right compartments
- Pleura covers the lungs and reflects onto itself around the root of the lung and covers the diaphragm and thoracic wall
- The left and right compartments are completely independent because the pleura is attached firmly to the root
What is the parietal pleura attached to?
- Thoracic wall
- Fascia at the throracic inlet, at the 1st rib and T1 (cervical fascia
- Fibrous pericardium and other mediastinal structures
- Diaphragm
Describe the mediastinum
- Space between the 2 pleural sacs, the sternum and costal cartilages, thoracic vertebrae and the diaphragm (superiorly, nothing)
- Highly mobile region, volume and pressure changes
- Filled with hollow organs
What is the border between the superior and inferior mediastinum?
The sternal angle
Where is the Superior mediastinum?
• Behind the manubrium, between the inlet and the plane between the sternal angle and T4/5
Where is the Inferior mediastinum?
- Inferior to the transverse plane through the sternal angle and the diaphragm
- Further divided into the anterior mediastinum, middle mediastinum and posterior mediastinum
Structures on the right of the mediastinum
- Related to the right atrium and veins
- Superior vena cava
- Arch of the azygos
- Inferior vena cava
Structures on the left of the mediastinum
- Related to the left ventricle and the arteries
- Left common carotid
- Left subclavian
- Arch of the aorta
- Thoracic aorta
Where is the Middle mediastinum and what does it contain
- Centrally located
- Contains the heart and the pericardium (origins of great vessels: ascending aorta, pulmonary trunk, vena cava) (terminal parts of the SVC and IVC)
- Contains phrenic nerves and some of the branches of the vagus
What is the pericardium
• Fibro-serous sac that encloses the heart and roots of the great vessels
What is the function of the pericardium?
- Compartmentalise
- Anchors the heart to the surrounding tissues without compromising cardiac movement
- Prevents the overfilling (over expansion) of the heart
What are the 2 layers of the pericardium?
- Fibrous pericardium (externally)
* Serous pericardium (internally, inside the fibrous)
Describe the fibrous pericardium
- The apex is fused with the adventitia of the great vessels
- Anteriorly, it is related and attached by the sterno-pericardial ligament to the body of the sternum and 3rd-6th costal cartilages
- Posteriorly, it is related to and attached to the pericardiovertebral ligaments to the 5th to 8th thoracic vertebrae
- Inferiorly, it blends with the central tendon of the diaphragm (pericardiophrenic ligament)
What is the purpose of the attachment of the pericardium to the diaphragm?
• Halts the descent of the diaphragm during inspiration because of the suspension of the heart
Describe the serous pericardium
• Two layers: parietal and visceral
• Parietal:
- Lines the inner aspect of the fibrous pericardium
- reflects onto itself around the roots of the great vessels and continues as the visceral layer= epicardium
Describe the pericardial cavity
- Between the parietal and visceral layers of serous pericardium
- Contains pericardial fluid
Describe the pericardial fluid
- 10-15ml
- produced by the serous pericardium
- reduces friction during contraction of the heart
What is pericardial tamponade?
- When fluid in the pericardium builds up, resulting in compression of the heart
- Beck’s triad: distant heart sounds, distended neck veins, decreased pulse pressure
- Hypotension
- Tachycardia
- Tachypnoea
What are the two sinuses in the serous pericardium?
- Transverse pericardial sinus (sinus of Theile)
* Oblique sinus
How do the two sinuses in the serous pericardium form?
During embryological development, the heart tube folds and invaginate into the serous pericardium
Describe the transverse pericardial sinus
- Sinus of Theile
- Separates the arterial and venous ends of the heart tube
- Posterior to the ascending aorta and pulmonary trunk, anterior to the superior vena cava
- Superior to the left atrium and the pulmonary veins
Describe the oblique pericardial sinus
- Haller’s culture de sac
- Surrounded by the reflection of the serous pericardium around the right and left pulmonary veins and inferior vena cava
What is the nerve supply of the pericardium?
- Sensory fibres from the phrenic nerve
* Vasomotor fibres from the vagus nerve (parasympathetic) and the cardiopulmonary splanchnic nerves (sympathetic)
Describe the roots of the phrenic nerve
- Branch of the cervical plexus
* Arises from the ventral rami of C3,4 and 5 (majority from C4)
Describe the route of the phrenic nerve
- Travels over the scalenus anterior muscle
- Enters the mediastinum between the arterial and venous planes (subclavian artery and vein)
- Passes anterior to the root of the lung
- Lies between the fibrous pericardium and the parietal pleura
- Right phrenic nerve enters via the canal opening of the diaphragm
What does the phrenic nerve supply?
- Sole motor supply to the diaphragm
* Sensory fibres to the mediastinal parietal pleura and peritoneum and pleura related to the diaphragm
What is the site of referred pain of the phrenic nerve?
- Supraclavicular nerves C3,4,5
- Lateral supraclavicular
- Structures with a sensory supply via the phrenic nerve may refer pain to the back of neck, supraclavicular region, shoulder tip
What are the boundaries of the anterior mediastinum?
- Sternal body and xiphisternum
- Pericardium
- Lungs with pleura
What is the contents of the anterior mediastinum?
- Thymus
- Internal mammary vessels
- Lymph nodes
- Connective tissue
- Fat cell tissue
- Lower pole end of thyroid
- Ectopic parathyroid
What is the thymus?
• Bi lobed organ of lymphoid tissue
Where is the thymus
Between the manubrium, sternum and pericardium
• It extends from the lower neck (jugular notch) to 4th costal cartilage (sometimes below the aortic arch
Describe the use of the thymus in relation to age
- Active in childhood until puberty
* Increasing fibro fatty infiltration with age
What are the 3 planes of the superior mediastinum?
- Venous plane
- Arterial plane
- Trachea and oesophagus
Venous plane of the superior mediastinum
- Brachiocephalic veins are formed by the internal jugular and subclavian veins
- Left brachiocephalic vein passes anteriorly to the arch of the aorta; posterior to the manubrium
- Superior vena cava is formed by the right and left brachiocephalic veins
- Arch of azygos vein joins the superior vena cava
- Superior vena cava enters the right atrium
Arterial plane of the superior mediastinum
- Ascending aorta with its branches (coronary arteries) are in the middle mediastinum
- Ascending aorta contines as the aortic arch above the sternal angle - T4/5 plane
- Aortic arch curves up, backwards and slightly left behind the lower half of the manubrium
- continues as the thoracic (descending) aorta in the posterior mediastinum
What are the branches of the aortic arch?
• Brachiocephalic trunk which divides into the right subclavian and right common carotid arteries
• Left common carotid artery
• Left subclavian artery
- posterior and the the left of the trachea
Describe the position of the pulmonary trunk
• Within the pericardium, to the left of the ascending aorta
• At the level of T4/5 disc, inferior to the aortic arch, it divides into:
- Right pulmonary artery, posterior to the ascending aorta and superior Vena cava
- Left pulmonary artery, inferior to the arch of the aorta and anterior to the thoracic aorta
What is posterior to the sternoclavicular joint?
- Formation of the brachiocephalic veins by the internal jugular vein and the subclavian veins
- Division of the brachiocephalic trunk divides to its branches on the right side
What is posterior to the 1st right costal cartilage?
Formation fo the superior vena cava by right and left brachiocephalic veins
What is posterior to the 2nd right costal cartilage?
Arch of the azygos vein joins the superior vena cava
What is posterior to the 3rd right costal cartilage?
Superior vena cava enters the right atrium
What is in the posterior mediastinum?
- Vertebral bodies
- Proximal costal segments
- Proximal segments of intercostal nerves
- Sympathetic chain with its ganglia
Position of the thoracic aorta
- Continuation of the aortic arch
- Between the level of the sternal angle and aortic hiatus (T12)
- Lies on the left of the thoracic vertebral bodies but moves to the midline in the lower thorax
Visceral branches of the thoracic aorta
- Oesophageal arteries to the middle third of the oesophagus
- Bronchial arteries, usually 2 on the left and 1 on the right
- Pericardial branches
- Mediastinal branches
- Superior phrenic artery
Position of the trachea
- Starts at C6 vertebra, ends at the tracheal bifurcation (carina)
- May rise and descend to the level of T4 and T6 with deep inspiration and expiration, respectively
Position of the oesophagus
- Starts in the midline as the continuation of the pharynx at C6, inferior border of the cricoid cartilage
- Descends between the trachea and the vertebral column
- Enters the thorax behind the trachea, with he arch arch of aorta to its left in the superior mediastinum
- In the lower posterior mediastinum it swings forwards and to the left
- Pierces the diaphragm at T10
Upper 1/3 histology of the oesophagus
Striated muscle as swallowing is voluntary and rapid
Middle 1/3 histology of the oesophagus
Mixed striated and smooth muscle
Lower 1/3 histology of the oesophagus
Smooth muscle
Cells of the oesophagus
Stratifies squamous epithelium
What are the constrictions of the oesophagus?
- Upper oesophageal sphincter
- Arch of aorta
- Left main bronchus
- Diaphragm
What are the risks associated with the constrictions of the oesophagus?
- They are more likely to cause blockage
- Hinders the passage of instruments
- Slow down the passage of caustic substances which will therefore cause more damage
Where do the veins related to the oesophagus drain to?
Veins of upper and middle thirds:
• Azygos
• Hemiazygos
• Accessory hemiazygos
Lower third:
• Left gastric portal vein
What is the Porto systemic anastomosis?
- Portocaval anastomosis
* Anatomoses of veins of the middle and lower thirds
Give an example of a cause of oesophageal varices
Cirrhotic liver disease causes portal hypertension, forming the oesophageal varices
Where does lymph from around the lung drain to?
Superior and inferior tracheobrachial nodes
Which lymph nodes are located around the brachiocephalic veins?
Anterior mediastinal
Which lymph nodes are located behind the Heart and adjacent to the oesophagus?
Posterior mediasitnal
Where does the thoracic duct start?
• Cisterna chyli
Describe the position of the thoracic duct
- Lies between the aorta and the azygos vein in the posterior mediastinum (pulsation of the aorta promotes lymph flow)
- At T4/5 level it crosses behind the oesophagus to ascend on the left side
- Arches over the apex of the left lung and pleura
- Opens into the left brachiocephalic vein at the junction of the left internal jugular and left subclavian vein (Pirogoffs angle)
