Mediastinum Flashcards
(25 cards)
Mediastinum
part of thoracic cavity that lies between the lungs- extends from the superior thoracic aperture superiorly to the diaphragm inferiorly and from the sternum anteriorly to the thoracic vertebrae posteriorly
How is the mediastinum divided
superior and inferior compartment (the line runs from the sternal angle anteriorly to the T4/T5 junction posteriorly)
How is the inferior mediastinum divided
Inferior mediastinum is divided into anterior (contains thymus gland), middle (contains the heart, pulmonary trunk and ascending aorta) and posterior
3 parts of aorta
- Ascending aorta- short, first part that gives rise to the coronary arteries that supply the myocardium
- Arch of aorta- curves posteriorly and lies in the superior mediastinum
- Descending aorta- descends through the posterior mediastinum and into the abdomen posterior to the diaphragm
3 branches of aorta arch
- Brachiocephalic trunk- bifurcates into right common carotid artery (which supplies the right side of head and neck, including the brain) and right subclavian artery (supplies right upper limb)
- Left common carotid artery (supplies left side of head, neck and brain)
- Left subclavian artery (supplies left upper limb)
Aortic bodies
arch of aorta contains the aortic bodies where chemoreceptors are located- monitor arterial oxygen and carbon dioxide, visceral sensory information travels to CNS along vagus nerve and results in reflex response that regulates ventilation
What does the brachiocephalic trunk supply
bifurcates into right common carotid artery (which supplies the right side of head and neck, including the brain) and right subclavian artery (supplies right upper limb)
What does the left common carotid artery supply
supplies left side of head, neck and brain
What does the left subclavian artery supply
Left upper limb
Ligamentum arteriosum
fibrous, cord-like connection between pulmonary trunk and arch of aorta
• remnant of ductus arteriosus- a foetal circulatory shunt which diverts most of blood entering the pulmonary trunk directly tot the aortic arch as gas exchange occurs at placenta not in lungs (some blood circulates through lungs for development). When baby uses lungs, ductus arteriosus closes and blood in pulmonary trunk enters the lungs
Superior vena cava
returns blood to heart from head, neck and upper limbs
• SVC domed by union of the left and right brachiocephalic veins
• Each brachiocephalic vein is formed by union of the internal jugular vein (which drains the head and neck) and subclavian vein (which drains the upper limb)
What veins join to form brachiocephalic veins
internal jugular vein (which drains the head and neck) and subclavian vein (which drains the upper limb)
Inferior vena cava
returns blood to heart from all regions inferior to the diaphragm
Trachea
semi-rigid due to C-shaped incomplete rings of cartilage in its walls
• Extends from the larynx into the superior mediastinum and is palpable just superior of the suprasternal notch
• Terminates at level of sternal angle by bifurcating into left and right main bronchi
Oesophagus
muscular tube that extends from pharynx to stomach
• Peristalsis- waves of smooth muscle contraction to move swallowed food and fluid distally
• Lies in midline of thorax, posterior to trachea, descends into posterior mediastinum
Phrenic nerves
Left and right phrenic nerves (formed by fibres from the C3, C4 and C5 spinal nerves) innervate the diaphragm
• Somatic nerves and contain motor and sensory fibres
• Descend through neck and enter thorax through superior thoracic aperture
• Course over pericardium and pierce diaphragm
Vagus nerves
left and right vagus nerves (CN X) arise from brainstem
• Contains sensory, somatic motor and parasympathetic fibres
• Innervate structures of thorax, abdomen, head and neck
• The vagus nerves descend in the thorax posterior to the root of the lung.
• contribute parasympathetic fibres to the heart, lungs, and oesophagus.
• They traverse the diaphragm and convey parasympathetic fibres to most of the abdominal viscera.
Each give rise to recurrent laryngeal nerve (RLN)- ascend back up neck to innervate muscles of larynx
Left recurrent laryngeal nerve
loops under arch of aorta before ascending back up the left side of the neck (alongside the trachea) to the larynx.
right recurrent laryngeal nerve
right recurrent laryngeal nerve descends anterior to the right subclavian artery and then loops under the inferior border of the artery before ascending back up the right side of the neck (between the trachea and oesophagus) to the larynx.
Thoracic duct
major channel for lymphatic drainage from most regions of the body
• ascends through the posterior mediastinum and into the superior mediastinum, where it empties into the venous system at the union of the left internal jugular vein and left subclavian vein
Thymus gland
lymphoid organ
• Lies anteriorly in superior mediastinum
• Important in children but atrophies with age, eventually becoming fatty
Pericardium
tough, fibrous sac that encloses the heart- loose to allow movement of heart within it
2 continuous layers of pericardium
- tough, outer fibrous layer that is attached superiorly to the great vessels and inferiorly to the central tendon of the diaphragm
- thin, inner serous layer which has two parts: the parietal layer lines the inner aspect of the fibrous pericardium, and the visceral layer covers the surface of the heart
Pericardial cavity
narrow space between the two layers of serous pericardium- contains a small amount of pericardial fluid that lubricates the serous membranes and allows them to slide over each other with movements of the heart
