Anatomy 3 & 4 Flashcards
Where does the mediastinum extend from?
Superior thoracic aperture superiorly to the diaphragm inferiorly
Sternum anteriorly to the thoracic vertebrae posteriorly
What does the mediastinum contain?
Heart and pericardium (the fibrous sac around the heart)
Great vessels that enter and leave the heart
Veins that drain the chest wall
Trachea and main bronchi
Oesophagus
Nerves (somatic and autonomic)
Lymphatics
Thymus gland
Where does the line between the superior and inferior compartments in the mediastinum run from?
Run from the sternal angle anteriorly to the T4/T5 junction posteriorly
What is the inferior mediastinum divided into?
● The anterior mediastinum lies between the posterior aspect of the sternum and the anterior aspect of the pericardial sac. It is a narrow space that contains the thymus gland in children and its remnant in adults.
● The middle mediastinum contains the heart inside the pericardial sac, the pulmonary trunk, and the ascending aorta.
● The posterior mediastinum lies between the posterior aspect of the pericardial sac and the vertebrae.
What are the main contents of the superior mediastinum?
● arch of the aorta and its three branches
● superior vena cava and its tributaries - the left and right brachiocephalic veins
● trachea
● oesophagus
● phrenic nerves (left and right) and vagus nerves (left and right)
● thoracic duct
● thymus gland
What are the 3 parts of the aorta?
● The ascending aorta is the short, first part. It gives rise to the coronary arteries, which supply the myocardium.
● The arch of the aorta curves posteriorly. It lies in the superior mediastinum.
● The descending (thoracic) aorta descends through the posterior mediastinum
and into the abdomen posterior to the diaphragm.
What are the 3 major branches that the arch of the aorta give rise to?
● First, the brachiocephalic trunk. It bifurcates into the right common carotid artery which supplies the right side of the head and neck, including the brain, and the right subclavian artery which supplies the right upper limb.
● Second, the left common carotid artery, which supplies the left side of the head, neck, and brain.
● Third, the left subclavian artery, which supplies the left upper limb.
What does the arch of the aorta contain?
Contains aortic bodies where chemoreceptors are located.
These receptors constantly monitor arterial oxygen and carbon dioxide.
This visceral sensory information travels back to the CNS along the path of the vagus nerve and results in reflex responses that regulate ventilation.
What is the ligamentum arteriosum?
The ligamentum arteriosum is a fibrous, cord-like connection between the pulmonary trunk and the arch of the aorta.
It is the remnant of the ductus arteriosus, a foetal circulatory shunt. In the foetus, gas exchange occurs at the placenta, not in the lungs.
The ductus arteriosus diverts most of the blood entering the pulmonary trunk directly to the aortic arch (only a small amount of blood circulates through the foetal lungs; enough for them to develop).
When a baby starts to use their lungs at birth, the ductus arteriosus closes, and blood in the pulmonary trunk enters the lungs.
What two veins carry deoxygenated blood to the right atrium?
● The superior vena cava (SVC) returns blood to the heart from the head, neck,
and upper limbs. The SVC and its tributaries lie in the superior mediastinum.
● The SVC is formed by the union of the left and right brachiocephalic veins (brachium = arm; cephalic = head).
● The union of the internal jugular vein (which drains the head and neck) and the subclavian vein (which drains the upper limb) forms each brachiocephalic vein.
● The inferior vena cava (IVC) returns blood to the heart from all regions inferior to the diaphragm (abdomen, pelvis, and lower limbs). The thoracic part of the IVC is very short - as soon as it enters the thorax (the inferior mediastinum) through the diaphragm it enters the right atrium.
What does the trachea do?
The trachea conducts air to and from the left and right main bronchi. It is semi-rigid due to C-shaped, incomplete rings of cartilage in its walls.
Where does the trachea extend from and terminate?
● It extends from the larynx in the midline of the neck into the superior mediastinum and is palpable just superior to the suprasternal notch.
● It terminates at the level of the sternal angle (and junction between the T4 and T5 vertebrae) by bifurcating into the left and right main bronchi.
What is the oesophagus?
The oesophagus is a muscular tube that extends from the pharynx in the midline of the neck to the stomach.
‘Waves’ of contractions of smooth muscle in the oesophageal wall move swallowed food and fluid distally (peristalsis).
What is the position of the oesophagus?
In the superior mediastinum, the oesophagus lies in the midline of the thorax, posterior to the trachea.
It descends into the posterior mediastinum, and we will learn more about the oesophagus when we look at the posterior mediastinum.
What are the phrenic nerves formed from?
The left and right phrenic nerves, formed by fibres from the C3, C4 and C5 spinal nerves, innervate the diaphragm.
What are the phrenic nerves and where are they found?
They are somatic nerves and contain motor and sensory fibres.
They descend through the neck and enter the thorax through the superior thoracic aperture.
They course over the pericardium and pierce the diaphragm.
What are the vagus nerves?
The left and right vagus nerves (CN X) arise from the brainstem and contain somatic sensory, somatic motor and parasympathetic fibres. They innervate structures of the thorax and abdomen, in addition to the head and neck.
Where are the vagus nerves found?
They descend through the neck alongside the internal carotid artery and internal jugular vein and enter the thorax via the superior thoracic aperture.
What do the vagus nerves give rise to?
They each give rise to a recurrent laryngeal nerve (RLN), which ascend back up into the neck to innervate the muscles of the larynx.
● The left recurrent laryngeal nerve loops under the arch of the aorta before ascending back up the left side of the neck (alongside the trachea) to the larynx.
● The 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.
Where do the vagus nerves descend into?
Into the thorax posterior to the root of the lung
What do the vagus nerves contribute?
They contribute parasympathetic fibres to the heart, lungs, and oesophagus.
● They traverse the diaphragm and convey parasympathetic fibres to most of the
abdominal viscera.
What is the thoracic duct?
The thoracic duct is a major channel for lymphatic drainage from most regions of the body.
It 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.
What is the thymus gland?
The thymus is a lymphoid organ. It lies anteriorly in the superior mediastinum.
It is important in children, but atrophies with age, eventually becoming fatty.
We will not see the thymus in the cadavers.
What is the pericardium?
The pericardium is a tough, fibrous sac that encloses the heart like a loose-fitting bag; it is loose to allow for the movement of the heart within it.
What two layers is the pericardium composed of?
● a tough, outer fibrous layer that is attached superiorly to the great vessels and inferiorly to the central tendon of the diaphragm
● a 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.
The two layers are continuous with each other.
What is the narrow space between the two layers of serous pericardium?
Pericardial cavity
It 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.
The left and right phrenic nerves give rise to sensory branches that innervate the fibrous pericardium.
What is the apex?
‘Point’ of the heart, which projects to the left of the sternum towards the left lung
What are the surfaces of the heart?
● base – it ‘faces’ posteriorly, so is also called the posterior surface.
● inferior surface – it lies on the central tendon of the diaphragm, so is also called
the diaphragmatic surface.
● anterior surface – it ‘faces’ the sternum and ribs, so is also called the sternocostal surface.
● The left and right sides of the heart ‘face’ the lungs and are referred to as the pulmonary surfaces.
What do the heart surfaces correspond to?
● Base / posterior surface = left atrium, part of the right atrium
● Inferior / diaphragmatic surface = left ventricle, part of the right ventricle
● Anterior / sternocostal surface = right ventricle
● Left pulmonary surface = left ventricle
● Right pulmonary surface = right atrium
What is the apex formed by?
The apex is formed by the left ventricle.
It lies at the left 5th intercostal space in the midclavicular line and the apex beat is palpable here.
What do the borders of the heart correspond to?
● Right border = right atrium
● Left border = left ventricle
● Inferior border = right ventricle and part of the left ventricle.
Where are the borders of the heart located?
● Right border = lies lateral to the right sternal edge, from the right 3rd costal cartilage to the right 6th costal cartilage.
● Left border = extends from the left 2nd intercostal space to the left 5th intercostal space in the midclavicular line (i.e. the apex).
● Superior border = lies along the line connecting the superior extents of the right and left borders (i.e. from the right 3rd costal cartilage to the left 2nd intercostal space).
● Inferior border = lies along the line connecting the inferior end of the right border with the apex (mostly formed by the right ventricle).
What are auricles (auricular appendages)?
So named because of their ear-like appearance
They are outpouchings from the walls of the right and left atria.
What is coronary circulation?
The arteries and veins that supply the heart are visible on its external surface.
The major arteries lie in grooves on the external surface called sulci (singular = sulcus; Latin for groove or furrow).