The suprapleural membrane, also known as Sibson’s fascia, is located above the pleural cavity. The scalenus anterior muscle is positioned in front of the subclavian vein, while the subclavian artery is situated behind it.

Thoracic Outlet: Where the Subclavian Artery and Vein and Brachial Plexus Exit the Thorax

The thoracic outlet is the area where the subclavian artery and vein and the brachial plexus exit the thorax and enter the arm. This passage occurs over the first rib and under the clavicle. The subclavian vein is the most anterior structure and is located immediately in front of scalenus anterior and its attachment to the first rib. Scalenus anterior has two parts, and the subclavian artery leaves the thorax by passing over the first rib and between these two portions of the muscle. At the level of the first rib, the lower cervical nerve roots combine to form the three trunks of the brachial plexus. The lowest trunk is formed by the union of C8 and T1, and this trunk lies directly posterior to the artery and is in contact with the superior surface of the first rib.

Thoracic outlet obstruction can cause neurovascular compromise.

Normal Gap Acidosis can be remembered using the acronym HARDUP, which stands for Hyperalimentation/hyperventilation, Acetazolamide, and R (which is currently blank).

Disorders of Acid-Base Balance

The acid-base nomogram is a useful tool for categorizing the various disorders of acid-base balance. Metabolic acidosis is the most common surgical acid-base disorder, characterized by a reduction in plasma bicarbonate levels. This can be caused by a gain of strong acid or loss of base, and is classified according to the anion gap. A normal anion gap indicates hyperchloraemic metabolic acidosis, which can be caused by gastrointestinal bicarbonate loss, renal tubular acidosis, drugs, or Addison’s disease. A raised anion gap indicates lactate, ketones, urate, or acid poisoning. Metabolic alkalosis, on the other hand, is usually caused by a rise in plasma bicarbonate levels due to a loss of hydrogen ions or a gain of bicarbonate. It is mainly caused by problems of the kidney or gastrointestinal tract. Respiratory acidosis is characterized by a rise in carbon dioxide levels due to alveolar hypoventilation, while respiratory alkalosis is caused by hyperventilation resulting in excess loss of carbon dioxide. These disorders have various causes, such as COPD, sedative drugs, anxiety, hypoxia, and pregnancy.

The process of lung expansion relies on the negative pressure in the intrapleural space between the visceral and parietal pleura, which is present throughout respiration. This negative pressure pulls the lung towards the chest wall, allowing it to expand. However, if air enters the intrapleural space, the negative pressure is lost and the lung cannot fully reinflate. It is important to note that the intrapleural space is a potential space between the pleural surfaces, and there is typically no actual space present under normal circumstances.

Management of Pneumothorax: BTS Guidelines

Pneumothorax is a condition where air accumulates in the pleural space, causing the lung to collapse. The British Thoracic Society (BTS) has published guidelines for the management of spontaneous pneumothorax, which can be primary or secondary. Primary pneumothorax occurs without any underlying lung disease, while secondary pneumothorax is associated with lung disease.

The BTS recommends that patients with a rim of air less than 2 cm and no shortness of breath may be discharged, while those with a larger rim of air or shortness of breath should undergo aspiration or chest drain insertion. For secondary pneumothorax, patients over 50 years old with a rim of air greater than 2 cm or shortness of breath should undergo chest drain insertion. Aspiration may be attempted for those with a rim of air between 1-2 cm, but chest drain insertion is recommended if aspiration fails.

Patients with iatrogenic pneumothorax, which is caused by medical procedures, have a lower likelihood of recurrence than those with spontaneous pneumothorax. Observation is usually sufficient, but chest drain insertion may be required in some cases. Ventilated patients and those with chronic obstructive pulmonary disease (COPD) may require chest drain insertion.

Patients with pneumothorax should be advised to avoid smoking to reduce the risk of further episodes. They should also be aware of restrictions on air travel and scuba diving. The CAA recommends a waiting period of two weeks after successful drainage before air travel, while the BTS advises against scuba diving unless the patient has undergone bilateral surgical pleurectomy and has normal lung function and chest CT scan postoperatively.

In summary, the BTS guidelines provide a comprehensive approach to the management of pneumothorax, taking into account the type of pneumothorax and the patient’s individual circumstances. Early intervention and appropriate follow-up can help prevent complications and improve outcomes.

The medullary rhythmicity area in the medullary oblongata controls the basic rhythm of breathing through its inspiratory and expiratory neurons. During quiet breathing, the inspiratory area is active for approximately 2 seconds, causing the diaphragm and external intercostals to contract, followed by a period of inactivity lasting around 3 seconds as the muscles relax and there is elastic recoil. Additional brainstem regions can be stimulated to regulate various aspects of breathing, such as extending inspiration in the apneustic area (refer to the table below).

The Control of Ventilation in the Human Body

The control of ventilation in the human body is a complex process that involves various components working together to regulate the respiratory rate and depth of respiration. The respiratory centres, chemoreceptors, lung receptors, and muscles all play a role in this process. The automatic, involuntary control of respiration occurs from the medulla, which is responsible for controlling the respiratory rate and depth of respiration.

The respiratory centres consist of the medullary respiratory centre, apneustic centre, and pneumotaxic centre. The medullary respiratory centre has two groups of neurons, the ventral group, which controls forced voluntary expiration, and the dorsal group, which controls inspiration. The apneustic centre, located in the lower pons, stimulates inspiration and activates and prolongs inhalation. The pneumotaxic centre, located in the upper pons, inhibits inspiration at a certain point and fine-tunes the respiratory rate.

Ventilatory variables, such as the levels of pCO2, are the most important factors in ventilation control, while levels of O2 are less important. Peripheral chemoreceptors, located in the bifurcation of carotid arteries and arch of the aorta, respond to changes in reduced pO2, increased H+, and increased pCO2 in arterial blood. Central chemoreceptors, located in the medulla, respond to increased H+ in brain interstitial fluid to increase ventilation. It is important to note that the central receptors are not influenced by O2 levels.

Lung receptors also play a role in the control of ventilation. Stretch receptors respond to lung stretching, causing a reduced respiratory rate, while irritant receptors respond to smoke, causing bronchospasm. J (juxtacapillary) receptors are also involved in the control of ventilation. Overall, the control of ventilation is a complex process that involves various components working together to regulate the respiratory rate and depth of respiration.

Slowing the decrease in FEV1 in COPD can be most effectively achieved by quitting smoking.

The National Institute for Health and Care Excellence (NICE) updated its guidelines on the management of chronic obstructive pulmonary disease (COPD) in 2018. The guidelines recommend general management strategies such as smoking cessation advice, annual influenzae vaccination, and one-off pneumococcal vaccination. Pulmonary rehabilitation is also recommended for patients who view themselves as functionally disabled by COPD.

Bronchodilator therapy is the first-line treatment for patients who remain breathless or have exacerbations despite using short-acting bronchodilators. The next step is determined by whether the patient has asthmatic features or features suggesting steroid responsiveness. NICE suggests several criteria to determine this, including a previous diagnosis of asthma or atopy, a higher blood eosinophil count, substantial variation in FEV1 over time, and substantial diurnal variation in peak expiratory flow.

If the patient does not have asthmatic features or features suggesting steroid responsiveness, a long-acting beta2-agonist (LABA) and long-acting muscarinic antagonist (LAMA) should be added. If the patient is already taking a short-acting muscarinic antagonist (SAMA), it should be discontinued and switched to a short-acting beta2-agonist (SABA). If the patient has asthmatic features or features suggesting steroid responsiveness, a LABA and inhaled corticosteroid (ICS) should be added. If the patient remains breathless or has exacerbations, triple therapy (LAMA + LABA + ICS) should be offered.

NICE only recommends theophylline after trials of short and long-acting bronchodilators or to people who cannot use inhaled therapy. Azithromycin prophylaxis is recommended in select patients who have optimised standard treatments and continue to have exacerbations. Mucolytics should be considered in patients with a chronic productive cough and continued if symptoms improve.

Cor pulmonale features include peripheral oedema, raised jugular venous pressure, systolic parasternal heave, and loud P2. Loop diuretics should be used for oedema, and long-term oxygen therapy should be considered. Smoking cessation, long-term oxygen therapy in eligible patients, and lung volume reduction surgery in selected patients may improve survival in patients with stable COPD. NICE does not recommend the use of ACE-inhibitors, calcium channel blockers, or alpha blockers

Arterial carbon dioxide stimulates them, but it takes longer to reach equilibrium compared to the carotid peripheral chemoreceptors. They are not as responsive to acidity because of the blood-brain barrier.

The Control of Ventilation in the Human Body

The control of ventilation in the human body is a complex process that involves various components working together to regulate the respiratory rate and depth of respiration. The respiratory centres, chemoreceptors, lung receptors, and muscles all play a role in this process. The automatic, involuntary control of respiration occurs from the medulla, which is responsible for controlling the respiratory rate and depth of respiration.

The respiratory centres consist of the medullary respiratory centre, apneustic centre, and pneumotaxic centre. The medullary respiratory centre has two groups of neurons, the ventral group, which controls forced voluntary expiration, and the dorsal group, which controls inspiration. The apneustic centre, located in the lower pons, stimulates inspiration and activates and prolongs inhalation. The pneumotaxic centre, located in the upper pons, inhibits inspiration at a certain point and fine-tunes the respiratory rate.

Ventilatory variables, such as the levels of pCO2, are the most important factors in ventilation control, while levels of O2 are less important. Peripheral chemoreceptors, located in the bifurcation of carotid arteries and arch of the aorta, respond to changes in reduced pO2, increased H+, and increased pCO2 in arterial blood. Central chemoreceptors, located in the medulla, respond to increased H+ in brain interstitial fluid to increase ventilation. It is important to note that the central receptors are not influenced by O2 levels.

Lung receptors also play a role in the control of ventilation. Stretch receptors respond to lung stretching, causing a reduced respiratory rate, while irritant receptors respond to smoke, causing bronchospasm. J (juxtacapillary) receptors are also involved in the control of ventilation. Overall, the control of ventilation is a complex process that involves various components working together to regulate the respiratory rate and depth of respiration.

The azygos vein’s arch is located within the middle mediastinum.

The mediastinum is the area located between the two pulmonary cavities and is covered by the mediastinal pleura. It extends from the thoracic inlet at the top to the diaphragm at the bottom. The mediastinum is divided into four regions: the superior mediastinum, middle mediastinum, posterior mediastinum, and anterior mediastinum.

The superior mediastinum is the area between the manubriosternal angle and T4/5. It contains important structures such as the superior vena cava, brachiocephalic veins, arch of aorta, thoracic duct, trachea, oesophagus, thymus, vagus nerve, left recurrent laryngeal nerve, and phrenic nerve. The anterior mediastinum contains thymic remnants, lymph nodes, and fat. The middle mediastinum contains the pericardium, heart, aortic root, arch of azygos vein, and main bronchi. The posterior mediastinum contains the oesophagus, thoracic aorta, azygos vein, thoracic duct, vagus nerve, sympathetic nerve trunks, and splanchnic nerves.

In summary, the mediastinum is a crucial area in the thorax that contains many important structures and is divided into four regions. Each region contains different structures that are essential for the proper functioning of the body.

Streptococcal organisms are the most frequent cause of bacterial tonsillitis, which can lead to quinsy.

Understanding Acute Tonsillitis

Acute tonsillitis is a condition that is characterized by pharyngitis, fever, malaise, and lymphadenopathy. It is caused by bacterial infections in over half of all cases, with Streptococcus pyogenes being the most common organism. The tonsils become swollen and may have yellow or white pustules. It is important to note that infectious mononucleosis may mimic the symptoms of acute tonsillitis.

Treatment for bacterial tonsillitis involves the use of penicillin-type antibiotics. Failure to treat bacterial tonsillitis may result in the formation of a local abscess known as quinsy.

The larynx is located in the front of the neck, specifically at the level of the vertebrae C3-C6. This area also includes important anatomical landmarks such as the Atlas and Axis vertebrae (C1-C2), the thyroid cartilage (C5), and the pulmonary hilum (T5-T7).

Anatomy of the Larynx

The larynx is located in the front of the neck, between the third and sixth cervical vertebrae. It is made up of several cartilaginous segments, including the paired arytenoid, corniculate, and cuneiform cartilages, as well as the single thyroid, cricoid, and epiglottic cartilages. The cricoid cartilage forms a complete ring. The laryngeal cavity extends from the laryngeal inlet to the inferior border of the cricoid cartilage and is divided into three parts: the laryngeal vestibule, the laryngeal ventricle, and the infraglottic cavity.

The vocal folds, also known as the true vocal cords, control sound production. They consist of the vocal ligament and the vocalis muscle, which is the most medial part of the thyroarytenoid muscle. The glottis is composed of the vocal folds, processes, and rima glottidis, which is the narrowest potential site within the larynx.

The larynx is also home to several muscles, including the posterior cricoarytenoid, lateral cricoarytenoid, thyroarytenoid, transverse and oblique arytenoids, vocalis, and cricothyroid muscles. These muscles are responsible for various actions, such as abducting or adducting the vocal folds and relaxing or tensing the vocal ligament.

The larynx receives its arterial supply from the laryngeal arteries, which are branches of the superior and inferior thyroid arteries. Venous drainage is via the superior and inferior laryngeal veins. Lymphatic drainage varies depending on the location within the larynx, with the vocal cords having no lymphatic drainage and the supraglottic and subglottic parts draining into different lymph nodes.

Overall, understanding the anatomy of the larynx is important for proper diagnosis and treatment of various conditions affecting this structure.

The oesophagus is expected to remain within the thoracic cavity and situated in the posterior mediastinum at this point.

The mediastinum is the area located between the two pulmonary cavities and is covered by the mediastinal pleura. It extends from the thoracic inlet at the top to the diaphragm at the bottom. The mediastinum is divided into four regions: the superior mediastinum, middle mediastinum, posterior mediastinum, and anterior mediastinum.

The superior mediastinum is the area between the manubriosternal angle and T4/5. It contains important structures such as the superior vena cava, brachiocephalic veins, arch of aorta, thoracic duct, trachea, oesophagus, thymus, vagus nerve, left recurrent laryngeal nerve, and phrenic nerve. The anterior mediastinum contains thymic remnants, lymph nodes, and fat. The middle mediastinum contains the pericardium, heart, aortic root, arch of azygos vein, and main bronchi. The posterior mediastinum contains the oesophagus, thoracic aorta, azygos vein, thoracic duct, vagus nerve, sympathetic nerve trunks, and splanchnic nerves.

In summary, the mediastinum is a crucial area in the thorax that contains many important structures and is divided into four regions. Each region contains different structures that are essential for the proper functioning of the body.

Surgical resection is the preferred treatment for pleomorphic adenoma, a benign tumor of the parotid gland that may undergo malignant transformation. Chemotherapy and radiotherapy are not effective in managing this condition. Additionally, salivary stone removal is not relevant to the treatment of pleomorphic adenoma.

Understanding Pleomorphic Adenoma

Pleomorphic adenoma, also known as a benign mixed tumour, is a non-cancerous growth that commonly affects the parotid gland. This type of tumour usually develops in individuals aged 40 to 60 years old. The condition is characterized by the proliferation of epithelial and myoepithelial cells of the ducts, as well as an increase in stromal components. The tumour is slow-growing, lobular, and not well encapsulated.

The clinical features of pleomorphic adenoma include a gradual onset of painless unilateral swelling of the parotid gland. The swelling is typically movable on examination rather than fixed. The management of pleomorphic adenoma involves surgical excision. The prognosis is generally good, with a recurrence rate of 1-5% with appropriate excision (parotidectomy). However, recurrence may occur due to capsular disruption during surgery. If left untreated, pleomorphic adenoma may undergo malignant transformation, occurring in 2-10% of adenomas observed for long periods. Carcinoma ex-pleomorphic adenoma is the most common type of malignant transformation, occurring most frequently as adenocarcinoma.

The subclavian artery gives rise to the thyrocervical trunk, which emerges from the first part of the artery located between the inner border of scalenus anterior and the subclavian artery. The thyrocervical trunk branches off from the subclavian artery after the vertebral artery.

Thoracic Outlet: Where the Subclavian Artery and Vein and Brachial Plexus Exit the Thorax

The thoracic outlet is the area where the subclavian artery and vein and the brachial plexus exit the thorax and enter the arm. This passage occurs over the first rib and under the clavicle. The subclavian vein is the most anterior structure and is located immediately in front of scalenus anterior and its attachment to the first rib. Scalenus anterior has two parts, and the subclavian artery leaves the thorax by passing over the first rib and between these two portions of the muscle. At the level of the first rib, the lower cervical nerve roots combine to form the three trunks of the brachial plexus. The lowest trunk is formed by the union of C8 and T1, and this trunk lies directly posterior to the artery and is in contact with the superior surface of the first rib.

Thoracic outlet obstruction can cause neurovascular compromise.

The patient’s hearing exam results indicate normal hearing. The Rinne test showed more air conduction than bone conduction in both ears, which is typical for normal hearing. The Weber test also showed equal results in both ears, indicating no significant difference in hearing between the ears.

Rinne’s and Weber’s Test for Differentiating Conductive and Sensorineural Deafness

Rinne’s and Weber’s tests are used to differentiate between conductive and sensorineural deafness. Rinne’s test involves placing a tuning fork over the mastoid process until the sound is no longer heard, then repositioning it just over the external acoustic meatus. A positive test indicates that air conduction (AC) is better than bone conduction (BC), while a negative test indicates that BC is better than AC, suggesting conductive deafness.

Weber’s test involves placing a tuning fork in the middle of the forehead equidistant from the patient’s ears and asking the patient which side is loudest. In unilateral sensorineural deafness, sound is localized to the unaffected side, while in unilateral conductive deafness, sound is localized to the affected side.

The table below summarizes the interpretation of Rinne and Weber tests. A normal result indicates that AC is greater than BC bilaterally and the sound is midline. Conductive hearing loss is indicated by BC being greater than AC in the affected ear and AC being greater than BC in the unaffected ear, with the sound lateralizing to the affected ear. Sensorineural hearing loss is indicated by AC being greater than BC bilaterally, with the sound lateralizing to the unaffected ear.

Overall, Rinne’s and Weber’s tests are useful tools for differentiating between conductive and sensorineural deafness, allowing for appropriate management and treatment.

The correct answer is that metabolic acidosis shifts the oxygen dissociation curve to the right. This is seen in the condition described in the question, diabetic ketoacidosis, which is associated with metabolic acidosis. Acidosis causes more oxygen to be unloaded from haemoglobin, leading to a rightward shift in the curve. The other answer options are incorrect, as they either describe a different type of acidosis or an incorrect direction of the curve shift.

Understanding the Oxygen Dissociation Curve

The oxygen dissociation curve is a graphical representation of the relationship between the percentage of saturated haemoglobin and the partial pressure of oxygen in the blood. It is not influenced by the concentration of haemoglobin. The curve can shift to the left or right, indicating changes in oxygen delivery to tissues. When the curve shifts to the left, there is increased saturation of haemoglobin with oxygen, resulting in decreased oxygen delivery to tissues. Conversely, when the curve shifts to the right, there is reduced saturation of haemoglobin with oxygen, leading to enhanced oxygen delivery to tissues.

The L rule is a helpful mnemonic to remember the factors that cause a shift to the left, resulting in lower oxygen delivery. These factors include low levels of hydrogen ions (alkali), low partial pressure of carbon dioxide, low levels of 2,3-diphosphoglycerate, and low temperature. On the other hand, the mnemonic ‘CADET, face Right!’ can be used to remember the factors that cause a shift to the right, leading to raised oxygen delivery. These factors include carbon dioxide, acid, 2,3-diphosphoglycerate, exercise, and temperature.

Understanding the oxygen dissociation curve is crucial in assessing the oxygen-carrying capacity of the blood and the delivery of oxygen to tissues. By knowing the factors that can shift the curve to the left or right, healthcare professionals can make informed decisions in managing patients with respiratory and cardiovascular diseases.

The referred pain to the shoulder in this case is likely caused by Dressler’s syndrome, a type of pericarditis that occurs after a heart attack. The scratchy sound heard during auscultation is a pericardial friction rub, which is a common characteristic of pericarditis. The phrenic nerve, which supplies the pericardium, travels from the neck down through the thoracic cavity and can cause referred pain to the shoulder in cases of pericarditis.

The axillary nerve is responsible for innervating the teres minor and deltoid muscles, and dysfunction of this nerve can result in loss of sensation or movement in the shoulder area.

While the accessory nerve does innervate muscles in the neck that attach to the shoulder, it has a purely motor function and is not responsible for sensory input. Additionally, the referred pain in this case is not typical of musculoskeletal pain, but rather a result of pericarditis.

Injuries involving the long thoracic nerve often result in winging of the scapula and are commonly caused by axillary surgery.

Although the vagus nerve does supply parasympathetic innervation to the heart, it is not responsible for the referred pain in this case, as the pericardium is innervated by the phrenic nerve.

The Phrenic Nerve: Origin, Path, and Supplies

The phrenic nerve is a crucial nerve that originates from the cervical spinal nerves C3, C4, and C5. It supplies the diaphragm and provides sensation to the central diaphragm and pericardium. The nerve passes with the internal jugular vein across scalenus anterior and deep to the prevertebral fascia of the deep cervical fascia.

The right phrenic nerve runs anterior to the first part of the subclavian artery in the superior mediastinum and laterally to the superior vena cava. In the middle mediastinum, it is located to the right of the pericardium and passes over the right atrium to exit the diaphragm at T8. On the other hand, the left phrenic nerve passes lateral to the left subclavian artery, aortic arch, and left ventricle. It passes anterior to the root of the lung and pierces the diaphragm alone.

Understanding the origin, path, and supplies of the phrenic nerve is essential in diagnosing and treating conditions that affect the diaphragm and pericardium.

Understanding Lung Compliance in Respiratory Physiology

Lung compliance refers to the extent of change in lung volume in response to a change in airway pressure. An increase in lung compliance can be caused by factors such as aging and emphysema, which is characterized by the loss of alveolar walls and associated elastic tissue. On the other hand, a decrease in lung compliance can be attributed to conditions such as pulmonary edema, pulmonary fibrosis, pneumonectomy, and kyphosis. These conditions can affect the elasticity of the lungs and make it more difficult for them to expand and contract properly. Understanding lung compliance is important in respiratory physiology as it can help diagnose and manage various respiratory conditions. Proper management of lung compliance can improve lung function and overall respiratory health.

It is rare for a foreign object to become lodged in the left mainstem bronchus due to its greater angle compared to the right mainstem bronchus. A tracheal obstruction would cause reduced breath sounds bilaterally, not just on one side. The right superior lobar bronchus is also unlikely to be affected due to its angle and direction. Therefore, foreign bodies typically get stuck in the right mainstem bronchus in adults because of its wider diameter and lesser angle.

Anatomy of the Lungs

The lungs are a pair of organs located in the chest cavity that play a vital role in respiration. The right lung is composed of three lobes, while the left lung has two lobes. The apex of both lungs is approximately 4 cm superior to the sternocostal joint of the first rib. The base of the lungs is in contact with the diaphragm, while the costal surface corresponds to the cavity of the chest. The mediastinal surface contacts the mediastinal pleura and has the cardiac impression. The hilum is a triangular depression above and behind the concavity, where the structures that form the root of the lung enter and leave the viscus. The right main bronchus is shorter, wider, and more vertical than the left main bronchus. The inferior borders of both lungs are at the 6th rib in the mid clavicular line, 8th rib in the mid axillary line, and 10th rib posteriorly. The pleura runs two ribs lower than the corresponding lung level. The bronchopulmonary segments of the lungs are divided into ten segments, each with a specific function.

The oval window is where the stapes connects with the cochlea, and it is the most inner of the ossicles. The stapes has a stirrup-like shape, with a head that articulates with the incus and two limbs that connect it to the base. The base of the stapes is in contact with the oval window, which is one of the only two openings between the middle and inner ear. The organ of Corti, which is responsible for hearing, is located on the basilar membrane within the cochlear duct. The round window is the other opening between the middle and inner ear, and it allows the fluid within the cochlea to move, transmitting sound to the hair cells. The helicotrema is the point where the scala tympani and scala vestibuli meet at the apex of the cochlear labyrinth. The tectorial membrane is a membrane that extends along the entire length of the cochlea. A female in her third decade of life with unilateral conductive hearing loss and a family history of hearing loss is likely to have otosclerosis, a condition that affects the stapes and can cause severe or total hearing loss due to abnormal bone growth and fusion with the cochlea.

Anatomy of the Ear

The ear is divided into three distinct regions: the external ear, middle ear, and internal ear. The external ear consists of the auricle and external auditory meatus, which are innervated by the greater auricular nerve and auriculotemporal branch of the trigeminal nerve. The middle ear is the space between the tympanic membrane and cochlea, and is connected to the nasopharynx by the eustachian tube. The tympanic membrane is composed of three layers and is approximately 1 cm in diameter. The middle ear is innervated by the glossopharyngeal nerve. The ossicles, consisting of the malleus, incus, and stapes, transmit sound vibrations from the tympanic membrane to the inner ear. The internal ear contains the cochlea, which houses the organ of corti, the sense organ of hearing. The vestibule accommodates the utricule and saccule, which contain endolymph and are surrounded by perilymph. The semicircular canals, which share a common opening into the vestibule, lie at various angles to the petrous temporal bone.

The pulmonary ligament extends from the pleural reflections surrounding the hilum of the lung and covers the pulmonary vessels and bronchus. However, it does not contain the azygos vein.

Anatomy of the Lungs

The lungs are a pair of organs located in the chest cavity that play a vital role in respiration. The right lung is composed of three lobes, while the left lung has two lobes. The apex of both lungs is approximately 4 cm superior to the sternocostal joint of the first rib. The base of the lungs is in contact with the diaphragm, while the costal surface corresponds to the cavity of the chest. The mediastinal surface contacts the mediastinal pleura and has the cardiac impression. The hilum is a triangular depression above and behind the concavity, where the structures that form the root of the lung enter and leave the viscus. The right main bronchus is shorter, wider, and more vertical than the left main bronchus. The inferior borders of both lungs are at the 6th rib in the mid clavicular line, 8th rib in the mid axillary line, and 10th rib posteriorly. The pleura runs two ribs lower than the corresponding lung level. The bronchopulmonary segments of the lungs are divided into ten segments, each with a specific function.

The right vagus nerve gives rise to the right recurrent laryngeal nerve at a more proximal location, which then curves around the subclavian artery in a posterior direction. Therefore, out of the given structures, it is the least susceptible to injury.

The mediastinum is the area located between the two pulmonary cavities and is covered by the mediastinal pleura. It extends from the thoracic inlet at the top to the diaphragm at the bottom. The mediastinum is divided into four regions: the superior mediastinum, middle mediastinum, posterior mediastinum, and anterior mediastinum.

The superior mediastinum is the area between the manubriosternal angle and T4/5. It contains important structures such as the superior vena cava, brachiocephalic veins, arch of aorta, thoracic duct, trachea, oesophagus, thymus, vagus nerve, left recurrent laryngeal nerve, and phrenic nerve. The anterior mediastinum contains thymic remnants, lymph nodes, and fat. The middle mediastinum contains the pericardium, heart, aortic root, arch of azygos vein, and main bronchi. The posterior mediastinum contains the oesophagus, thoracic aorta, azygos vein, thoracic duct, vagus nerve, sympathetic nerve trunks, and splanchnic nerves.

In summary, the mediastinum is a crucial area in the thorax that contains many important structures and is divided into four regions. Each region contains different structures that are essential for the proper functioning of the body.