The internal jugular vein begins at the jugular foramen at the base of the skull. It continues as part of the sigmoid venous sinus before it meets the subclavian vein and terminates ultimately in the brachiocephalic vein. Upon exiting the base of skull, the internal jugular vein lies lateral to the internal carotid artery and then to the common carotid artery. These two structures, along with the vagus, are enclosed within the fascial compartment termed the carotid sheath. The carotid sheath travels in the anterior triangle of the neck, which is formed by the sternocleidomastoid posteriorly, the mandible superiorly and the mid-line of the neck anteriorly. There are several tributaries of the internal jugular vein, including the facial and lingual veins. Included also are the superior and middle thyroid veins, which are particularly relevant during thyroid surgery as they must be identified and divided in order to prevent bleeding from the internal jugular.

The subclavian vein is a continuation of the axillary vein originating at the lateral border of the first rib and ending medial to the scalenus anterior, where it meets the internal jugular vein. Its only tributary, the external jugular vein, meets the subclavian at the medial third of the clavicle. The left subclavian drains into the left brachiocephalic, where it also receives drainage from the thoracic duct. The right subclavian drains into the right brachiocephalic along with the right lymph duct. The course taken around the manubrium by the left brachiocephalic makes it on average around 6 cm long compared to 3 cm on the right side.

Cannulation of the subclavian is best achieved on a supine patient with the needle inserted at the mid-point of the clavicle aiming towards the sternoclavicular joint. The internal jugular can be identified by lying the patient slightly cephalad and palpating the mid-point between the mastoid process and the sternal notch level with the cricoid cartilage.

The cervical plexus is formed from the anterior rami of the first four cervical vertebrae. The lower branches of C3 and C4 fuse with C5 to form the phrenic nerve, which supplies the diaphragm, parietal pleura, pericardium and the upper border of the peritoneum. The phrenic nerve descends down the neck traversing the scalenus anterior and travelling behind the internal jugular vein. Due to its course, pathology within the pleura or subdiaphragmatic peritoneum can lead to pain perceived in the shoulder tip region. Superficial branches from the cervical plexus include the lesser occipital nerve, greater auricular nerve and supraclavicular nerves, which largely supply structures in the back of the head. Deeper branches of the plexus supply the sternocleidomastoid, trapezius, scalenus medius, serratus anterior and rhomboids.

Cervical plexus blocks conducted for neck surgery provide regional anaesthesia over the neck, shoulder and upper pectoral region. Care should be taken to avoid injection into a phrenic or vagus nerve. Blockade of the sympathetic chain in the cervical region can lead to Horner’s syndrome.

The pharynx is muscular tube originating at the base of skull extending down to the level of the C6 vertebra. It is divided into three components: the nasopharynx, oropharynx and laryngopharynx. The walls of the pharynx are covered in four layers: mucosal, fibrous, muscular and fascial. The mucosal coat is continuous with the nose where it consists of ciliated, columnar epithelium. The rest is stratified squamous epithelium. The muscular layer contains the pharyngeal constrictors: superior, middle and inferior. The muscles have two functional parts, between which pharyngeal pouches can occur. The pharyngeal muscles involved in swallowing are supplied largely by the vagus and accessory nerves. The glossopharyngeal nerve supplies only the stylopharyngeus muscle.

The nasopharynx extends from the base of the skull down through the pharyngeal isthmus, where it connects to the oropharynx. The Eustachian tube enters the nasopharynx just below the two posterior nasal openings, which are termed the nasal choanae.

The adenoids, which are also termed the nasopharyngeal tonsils, are small collections of lymphoid tissue that lie on the roof of the nasopharynx.

The oropharynx then continues from the nasopharynx superiorly down to the upper border of the epiglottis. The fauces within the orophayrnx contain collections of lymphoid tissue, which are the palatine tonsils.

The laryngopharynx begins at the tip of the epiglottis down to the lower border of the cricoid cartilage. The piriform fossae are recesses formed secondary to the bulgings of the larynx into the laryngopharynx. As such, they are well placed to house tiny items of food that have been inadvertently inhaled.

There are nine cartilages in total, three are paired and three exist singly.

The single cartilages are:

1. 
   

   i. Thyroid cartilage: this is the largest and is made up of two plates which join to form the thyroid notch (Adam’s apple).

   
   
2. 
   

   ii. Cricoid cartilage: this is shaped like a signet ring. The lateral surfaces consist of facets which join with the inferior cornu of the thyroid cartilage. The upper border joins with the arytenoid cartilages.

   
   
3. 
   

   iii. Epiglottis: the inferior border extends posteriorly to attach to the thyroid cartilage. The anterior surface is attached to the hyoid bone. The valleculae are two depressions that fall either side of the glossoepiglottic folds, which connect the epiglottis to the posterior tongue.

The paired cartilages are:

1. 
   

   i. Arytenoid cartilages: these are shaped like a three-sided pyramid. The anterior processes attach to the vocal ligaments to form the vocal cords. The muscular process projects laterally and is attached to the posterior and lateral cricoarytenoid muscles.

   
   
2. 
   

   ii. Corniculate and cuneiform cartilages: these are small cartilages that lie on the posterior aryepiglottic folds.

The ligaments within the larynx connect the cartilages and are generally named as a combination of the cartilages that they conjoin.

• 
  

  The aryepiglottic fold (may also be referred to as ligament or membrane) runs from the side of the epiglottis down to the arytenoid cartilage. The inferior border of the fold runs free and is covered by a loose membrane called the vestibular fold. This is known as the false vocal cord.

  
  
• 
  

  The cricothyroid ligament runs from the cricoid cartilage to the thyroid cartilage and is the insertion point for an emergency needle cricothyroidotomy.

  
  
• 
  

  The thyrohyoid membrane connects the thyroid cartilage to the hyoid bone. Through this membrane run the superior laryngeal artery and the internal laryngeal nerve.

  
  
• 
  

  The conus elasticus is a triangular shaped ligament that attaches to the cricoid cartilage inferiorly. The upper border attaches to the arytenoid cartilage and is thickened to form the vocal ligament. This forms the true vocal cord.

Muscles of the larynx can be divided into the extrinsic and intrinsic muscles.

The extrinsic muscles and their respective functions are:

1. 
   

   a. Sternothyroid: depresses the larynx

   
   
2. 
   

   b. Thryohyoid: elevates the larynx

   
   
3. 
   

   c. Inferior constrictor: constricts the pharynx.

The intrinsic muscles and their respective functions are:

1. 
   

   a. Cricothyroid (paired): increases the diameter of the glottis

   
   
2. 
   

   b. Posterior cricoayrtenoid (paired): abducts the vocal cord

   
   
3. 
   

   c. Lateral cricoarytenoid (paired): adducts the vocal cord

   
   
4. 
   

   d. Aryepiglottic (paired): minor constriction of laryngeal inlet

   
   
5. 
   

   e. Thyroarytenoid (paired): relaxation of the vocal cord

   
   
6. 
   

   f. Transverse arytenoids (unpaired): constriction of the glottis.

The arterial supply to the larynx is from the superior and inferior laryngeal arteries, which are respectively the branches of the superior and inferior thyroid arteries.

Venous drainage is via the superior and inferior laryngeal veins, which ultimately drain into the internal jugular vein.

The nerve supply is divided into two; above the vocal cords, innervation is via the internal laryngeal nerve. Below the vocal cords, the muscles are innervated by the recurrent laryngeal nerve. An exception to this is the cricothyroid muscle, which is supplied by the superior laryngeal nerve.

The superior laryngeal artery and the internal laryngeal nerve both traverse the thyrohyoid membrane.

The orbit is pyramidal in shape and houses the globe which is located anteriorly in a superolateral position. The orbit has three posterior openings:

1. 
   

   i. The optic canal: optic nerve and ophthalmic artery

   
   
2. 
   

   ii. The superior orbital fissure: superior and inferior ophthalmic veins

   
   
3. 
   

   iii. The inferior orbital fissure.

The globe itself consists of three layers:

1. 
   

   i. Outer fibrous layer, sclera: covers the entire globe except the cornea

   
   
2. 
   

   ii. Vascular layer: contains the choroid, iris and ciliary body

   
   
3. 
   

   iii. Inner retina: contains photoreceptors. There are approximately 120 million rods and 7 million cones.

Before an image can be processed by the brain it needs to be directed appropriately onto the retina. The pupil constricts and dilates relative to light intensity and is controlled by the action of the smooth muscle fibres in the iris. The lens is crucial in providing accommodation of the image and is altered by tension within the suspensory ligaments. These are controlled by the ciliary muscles.

Images are then projected onto the retina, where they are converted into electrical potentials. These are transmitted onto ganglion cells and reach the optic disc via the axons. The optic nerves from each eye converge at the optic chiasm. Images from the nasal half decussate, whereas images from the temporal half remain ipsilateral. Fibres are then carried to the lateral geniculate nuclei and on to the visual cortex. The superior collicli also intercept some fibres to allow for control of eye movement.

CN III, the oculomotor nerve, carries parasympathetic fibres from the Edinger–Westphal nucleus to cause pupillary constriction.

CN IV, the trochlear nerve, supplies the superior oblique muscle and CN VI, the abducens nerve, supplies the lateral rectus muscle. All the other extraocular muscles are supplied by the oculomotor nerve.

The sensory component of the corneal reflex is mediated by the ophthalmic division of the trigeminal nerve, CN V. The temporal and zygomatic branches of the facial nerve, CN VII, control the action of the ‘blink’. Other branches of the facial nerve include the buccal, mandibular and cervical.

The oral cavity of the mouth contains the hard and soft palates and the tongue. It is separated from the vestibule of the mouth anteriorly by the teeth. The tongue itself is a muscular structure and is controlled by the actions of several intrinsic and extrinsic muscles. The innervation to these muscles is via the glossopharyngeal nerve, CN IX, except for the palatoglossus, which is supplied by CN X, the vagus nerve.

The tongue is superficially divided into an anterior two-thirds and a posterior third. The lingual nerve, which arises from the mandibular branch of the trigeminal nerve, supplies the anterior two-thirds of the tongue, passes through the chorda tympani and joins the facial nerve to reach the nucleus of the tractus solitarius. The posterior third of the tongue is supplied by the glossopharyngeal nerve.

The nose is made up of two nasal cavities, which are separated by the nasal septum. Each cavity is made up of a roof, a floor, a medial wall and a lateral wall.

The roof of the cavity consists of cartilages and bones and also the cribriform plate of the ethmoid bone. The floor is formed by the palatine bone and the palatine process of the maxilla.

The nasal septum makes up the medial wall and is mainly cartilaginous. The lateral wall contains three conchae, which help to increase the surface area: superior, middle and inferior. It receives openings from the paranasal sinuses and the nasolacrimal duct.

Nasal lining is primarily respiratory epithelium, except for the area over and surrounding the superior conchae, which is yellow, olfactory epithelium.

Arterial blood supply to the nose is from the ophthalmic and maxillary arteries. The facial vein drains blood away from the nose into the pterygoid venous plexus.

The thyroid gland consists of two lobes that are connected by a central isthmus. The gland is located at the region of the second and third tracheal rings with the isthmus overlying the trachea. The thyroid lobes contain follicles or acini and it is in the colloid within these that the thyroglobulin and iodine are stored. The parafollicular cells that are located on the outside of the acini are responsible for the production of calcitonin.

The thyroid gland is a vascular-rich organ and receives its blood supply via the superior and inferior thyroid arteries. Venous drainage is via the superior, middle and inferior thyroid veins.

The four parathyroid glands are located in both the two upper and two lower poles of the thyroid gland. They consist of two cell types: the primary chief cells are responsible for the production and storage of the parathyroid hormone (PTH). PTH is a polypeptide hormone that is released into the bloodstream to raise levels of serum calcium. Calcitriol, which is formed by vitamin D, also aids in the increase of serum calcium levels. Calcitonin, released from the parafollicular C cells of the thyroid gland, causes a reduction in the level of serum calcium.

The carotid sheath contains the:

• 
  

  Internal carotid artery

  
  
• 
  

  Internal jugular vein

  
  
• 
  

  Vagus nerve

  
  
• 
  

  Deep cervical lymph nodes.

The relations of the internal jugular vein are:

• 
  

  Anterolateral to the carotid artery (through its most part, but this can vary depending on the level of the neck)

  
  
• 
  

  Anterior to the vagus nerve

  
  
• 
  

  Posterior to the sympathetic chain

  
  
• 
  

  Medial to the hypoglossal and glossopharyngeal nerves

  
  
• 
  

  On the left side, the internal jugular vein lies anterior to the thoracic duct.

Complications associated with a deep cervical plexus block:

• 
  

  Phrenic nerve palsy

  
  
• 
  

  Haematoma

  
  
• 
  

  Intrathecal injection: there may be a dural sleeve surrounding the cervical plexus into which the injection could be placed. This would invariably lead to signs and symptoms of a high spinal injection

  
  
• 
  

  Horner’s syndrome and recurrent laryngeal nerve blockade are commonly seen with superficial cervical plexus block.

Deep or superficial cervical plexus blocks can be undertaken to provide anaesthesia for carotid endarterectomy. Nerves within the cervical plexus include:

• 
  

  Lesser occipital nerve

  
  
• 
  

  Greater auricular nerve

  
  
• 
  

  Transverse cervical nerve

  
  
• 
  

  Supraclavicular nerve.

Often, retraction pain is felt over the submandibular region and therefore branches of the trigeminal nerve also need to be blocked.

The pterygopalatine fossa is often infiltrated with local anaesthetic to provide a maxillary nerve block for oral and maxillofacial surgery.

Structures contained within the fossa include the maxillary nerve, which is a branch of the trigeminal nerve. The pterygopalatine ganglion is also suspended within the fossa. The greater petrosal and deep petrosal nerves contain parasympathetic nerve fibres and form the nerve of the pterygoid canal.

Local anaesthetic will block the maxillary nerve and provide loss of sensation to the maxillary sinus, upper molars, canines and incisor teeth, the cheek and the gums.

A sub-Tenon’s block is delivered by injection using a blunt needle into the sub-Tenon’s space. Topical anaesthesia is applied onto the conjunctiva along with a few drops of aqueous iodine. An incision is then made on the inferomedial aspect of the conjunctiva and the needle is advanced along the posterior aspect of the sclera. Major complications are rare due to the use of a blunt needle and relative distance away from the optic sheath. Subconjuctival haemorrhage and subconjuctival swelling are seen in roughly 40–50% of patients.

Complications associated with a partial thyroidectomy include:

• 
  

  Bleeding leading to haematoma formation. This can cause airway obstruction, which will manifest as stridor. Injury to the recurrent laryngeal nerve can also cause unilateral cord paralysis, which can lead to hoarseness of voice.

  
  
• 
  

  Hypoparathyroidism is more common in a complete thyroidectomy and can cause hypocalcaemia.

  
  
• 
  

  Thyroid storm is a rare, but severe, complication of hyperthyroidism. In the acute setting it manifests as tachycardia, often associated with atrial fibrillation, fever and agitation that may lead to myocardial infarction. In the longer term it causes diarrhoea and vomiting, heart failure and eventually death. It may be caused by uncontrolled/untreated hyperthyroidism or in the acute setting either by intercurrent infection in patients suffering with mild hyperthyroidism or manipulation of a hyperthyroid gland, such as during surgery. The treatment is twofold. Firstly the acute complications of thyroid storm require immediate medical management in parallel with drugs to reduce thyroid hormone secretion. Thus β-blockers, nitrites, paracetamol and manual cooling are employed to treat the atrial fibrillation, hypertension and pyrexia, and antithyroid drugs (e.g. propylthiouracil) are employed to reduce thyroid hormone production. Secondly, the primary cause of the thyroid crisis requires management.

The presence of a goitre can have anatomical manifestations that can affect anaesthetic management.

Compression effects of the goitre on the airway can lead to tracheomalacia, although this is potentially recognized as a postoperative complication.

Pressure on the superior vena cava can lead to oedema in the face and the airway, and also engorgement of the nasopharyngeal veins. This can lead to problems with endotracheal as well as awake nasal fibre-optic intubation.

A decreased venous return will also affect placement of a central venous catheter in the internal jugular veins.

Vocal cord palsy can result due to compression of the recurrent laryngeal nerve. Unilateral involvement causing cord adduction will lead to a hoarse voice and bilateral involvement will lead to stridor.

Recurrent laryngeal nerve injury is a recognized complication of thyroid surgery.

Due to the anatomical orientation of the right recurrent laryngeal nerve, it is more prone to injury than the left. Unilateral injury presents with ipsilateral vocal cord paralysis. The cord is immobile and suspended in a slight abduction away from the mid-line. Unilateral injury presents with hoarseness and a reversible injury may take up to six months to improve. Corrective surgery should only be performed after this period unless there are life-threatening circumstances.

Bilateral nerve injury is more likely in a total thyroidectomy and will lead to a partial airway obstruction presenting as stridor or respiratory distress. As it is often only detected post extubation, treatment consists of emergency reintubation or emergency tracheostomy.

The trachea runs from the lower border of the larynx, at the level of C6, and divides into left and right main bronchi at the level of the sternal angle, approximately T5. Each trachea has 15–20 C-shaped cartilaginous rings that are connected by the trachealis muscle anteriorly, leaving a membranous wall posteriorly, which can collapse when the oesophagus expands. The trachea is lined by pseudostratified ciliated columnar epithelium and goblet cells, which produce mucus.

The trachea lies median in the neck, but deviates slightly to the right towards its lower end. It lies anterior to the oesophagus. Laterally, are the right and left lobes of the thyroid gland, the parathyroid glands (normally two on each side) and the carotid sheath (containing the common carotid artery, the internal jugular vein and the vagus nerve).

Other anterior relations to the trachea include the thyroid ima artery and the inferior thyroid veins. The thyroid ima artery is only present in a small number of people, arises from the brachiocephalic artery and supplies the thyroid isthmus. It can be damaged during thyroid surgery or percutaneous tracheostomy insertion. The inferior thyroid veins drain the lower lobes of the thyroid artery and drain into the brachiocephalic veins.

The arch of the aorta runs anteriorly to the trachea, but then superior to the left main bronchus, once the trachea has bifurcated.

A tracheostomy is normally made between tracheal rings 2 and 4. A transverse incision can be made, dissecting through skin and superficial fat and dividing the infrahyoid muscles (strap muscles) longitudinally in the mid-line. This is retracted laterally. At this point, the operator must ensure they are in the correct position, avoiding the thyroid isthmus, the thyroid ima artery and the inferior thyroid plexus of veins, all of which can be in the mid-line and cause bleeding. In children the thymus may also be present anteriorly. Also, in children, the trachea is small and soft, and care must be taken in dividing it, to ensure the oesophagus is not damaged posteriorly.

Dual antiplatelet therapy is associated with a higher risk of bleeding from the procedure, but is not an absolute contraindication.

Open surgical and percutaneous tracheostomy insertions are widely practised. Each has their own benefits, however certain situations dictate the need for surgical insertion over the percutaneous method.

Absolute contraindications to percutaneous insertion include:

• 
  

  Age below 8 years old

  
  
• 
  

  Abnormal neck anatomy

  
  
  
  
  • 
    

    Tumour

    
    
  • 
    

    Thyromegaly

    
    
  • 
    

    High innominate artery

  
  

Relative contraindications include:

• 
  

  Obesity

  
  
• 
  

  Prolonged bleeding time

  
  
• 
  

  Platelet count <50 000 µl^–1

  
  
• 
  

  Infection at the wound site

  
  
• 
  

  PEEP requirements >20 cmH₂O

Insertion of a tracheostomy can lead to a number of complications.

Early complications include:

• 
  

  Bleeding

  
  
• 
  

  Tracheal cartilage fracture

  
  
• 
  

  Posterior tracheal wall injury

  
  
• 
  

  Pneumothorax

  
  
• 
  

  Infection

Late complications include:

• 
  

  Inadvertant decannulation

  
  
• 
  

  Infection

  
  
• 
  

  Recurrent laryngeal nerve injury leading to vocal cord paralysis

  
  
• 
  

  Tracheal stenosis

  
  
• 
  

  Tracheomalacia

  
  
• 
  

  Tracheoarterial fistula

  
  
• 
  

  Persistent tracheal stoma

The three layers of the muscles in the intercostal space are the external intercostal, inner intercostal and the innermost intercostal (superficial to deep).

The neurovascular bundle contains the intercostal vein, artery and ventral rami of T1– T11 (superior to inferior) and lies in the space between the inner and innermost intercostal muscles, in the intercostal groove of the rib above.

A collateral neurovascular bundle is also present in the space between the inner and innermost intercostal muscles, in the intercostal space, which lies superior to the rib below. Therefore care must be taken of this bundle when performing a pleural tap.

The ventral rami of T1–T11 form the intercostal nerve. However, the dorsal and ventral rami of T1–T12 spinal nerve roots form their respective dermatomes, via multiple cutaneous branches given off by the nerves as they pass anteriorly along the costal groove. A group of muscles also supplied by the intercostal nerves are the myotome.

Rami communicantes connect the intercostal nerves to the sympathetic trunk, which sends fibres with the nerve.

The right main bronchus is shorter, wider and more vertical than the left, making foreign bodies more likely to lodge in it than the left. The right main bronchus passes directly to the root of the lung, accompanied by the pulmonary artery.

The left main bronchus is longer, narrower and more angulated than the right. It passes inferior to the arch of the aorta and anterior to the oesophagus and aorta, before entering the root of the lung, accompanied by the pulmonary artery.

The trachea divides into two main bronchi, left and right. Each main bronchus is accompanied by pulmonary and bronchial vessels, lymph vessels and autonomic and sympathetic nerve fibres into the root of the lung.

The left main bronchus then divides into two secondary bronchi, which supply two lobes, superior and inferior. The right main bronchus divides into three secondary bronchi, which supply three lobes, superior, inferior and middle. Each secondary bronchus divides into tertiary bronchi that supply each bronchopulmonary segment. There are nine bronchopulmonary segments on each side.

The oblique fissure divides the superior and inferior lobes on the left, and divides the middle and inferior lobes on the right. The horizontal fissure divides the superior and middle lobes on the left.

Each lung has three surfaces: costal, mediastinal and diaphragmatic. The costal surface is adjacent to the sternum and ribs, the mediastinal surface is adjacent to the mediastinum and the vertebrae, and the diaphragmatic surface is adjacent to the diaphragm. The root of the lung is on the mediastinal surface, and is the area of continuity of the parietal and visceral layers of pleura. It contains the right and left main bronchi, pulmonary and bronchial vessels, nerves and lymph vessels.

The apex of the lung is the superior aspect of the lung, covered by cervical pleura, and extends through the superior thoracic aperture.

Each lung has three borders: anterior, inferior and posterior (there is no superior border). The anterior border separates the costal and mediastinal surfaces anteriorly. The left side forms the cardiac notch. The posterior border separates the costal and mediastinal surfaces posteriorly. The inferior border encircles the diaphragmatic surface of the lung.

The lung, like the liver, has two sources of blood supply. The first is provided by a single pulmonary artery, which carries deoxygenated blood from the right ventricle. This blood is drained by two pulmonary veins, which carry oxygenated blood to the left atrium. Each pulmonary artery gives off a superior branch prior to entering the hilum. Within the lung, each artery divides into lobar branches.

The bronchial arteries supply the lung with the oxygen and nutrition it requires. These generally arise directly from the thoracic aorta. The drainage of this blood is by the bronchial and pulmonary veins.

The lungs also have two lymphatic plexuses, superficial and deep, each one divided into left and right. The superficial plexus lies deep to the visceral pleura and drains into the bronchopulmonary lymph nodes. The deep plexus lies in the submucosa of the bronchi and drains into the pulmonary lymph nodes. These lymph plexuses drain either into the right or left bronchomediastinal lymph plexuses, which, in turn, drain into the lymphatic duct on the right and the thoracic duct on the left.

The pulmonary plexus is located at the root of the lungs and supplies the lung, the pulmonary arteries and veins, and the visceral pleura. The nerves of the lungs and visceral pleura are derived from the pulmonary plexus. They contain sympathetic and parasympathetic fibres. The sympathetic fibres arise from the sympathetic trunk and the parasympathetic fibres arise from the vagus nerve (CN X). Parasympathetic innervation leads to bronchoconstriction, vasodilatation and increased secretion of the glands of the bronchial tree. Fibres of CN X are also found in the bronchial mucosa and muscles, interalveolar connective tissue, pulmonary arteries and pulmonary veins. Sympathetic innervation leads to bronchodilatation, vasoconstriction and reduced secretion of the glands of the bronchial tree. It is in this context that antimuscarinic agents are useful for bronchospasm.

The intercostal and phrenic nerves supply sensory innervation to the parietal pleura.

See explanation for Question 38.

The pleurae consist of two layers: visceral and parietal. Between them is a potential space called the pleural cavity. The pleural cavity consists of a thin layer of pleural fluid, which lubricates the movements of the lungs during respiration. The visceral pleura invests the lungs and the parietal pleura lines the thoracic wall and diaphragm. The parietal pleura is anatomically divided into costal pleura, mediastinal pleura, diaphragmatic pleura and cervical pleura, depending on the region of the thoracic cavity they are covering. The visceral and parietal pleura become continuous at the root of the lung and form the pulmonary ligament.

The main function of the diaphragm is inspiration, when it descends into the abdomen, increasing the volume of the thorax, therefore reducing the intrathoracic pressure. It is formed by a central tendinous portion, and an outer muscular portion. The central tendinous portion has three main foramina within it to allow structures to pass between the abdomen and thorax, but the diaphragm itself is not continuous with these structures. The diaphragm is, however, lined by parietal peritoneum, which also lines these structures, and it is this that is continuous with these structures.

The outer part of the diaphragm, the muscular portion, forms the attachments of the diaphragm to the body. The attachments can be divided into sternal, costal and lumbar. The sternal part is attached to the xiphoid process and forms two small foramina either side of it. The costal part is attached to the lower surface of the ribs and costal cartilages of ribs 6–12 and the posterior part of the diaphragm is attached to the lumbar vertebrae via the crura, a ligamentous portion of the diaphragm. The right crus is longer and inserts into L1–L3, compared to the left crus which inserts into L1 and L2. The two crura are connected via the median arcuate ligament.

There are three main foramina within the diaphragm:

1. 
   

   1. The aortic hiatus, formed posterior to the diaphragm. It is formed by the median arcuate ligament anteriorly, the left and right crus of the diaphragm laterally and the anterior surface of T12 posteriorly. The thoracic duct, sympathetic trunk, subcostal nerve and azygous duct also pass through the aortic hiatus.

   
   
2. 
   

   2. The vena caval foramen, formed within the central tendinous section of the diaphragm at level of T8. It allows passage of the vena cava, right phrenic nerve and lymph vessels.

   
   
3. 
   

   3. The oesophageal hiatus, formed by the overlapping flaps of the muscular part of the diaphragm posteriorly. With it, the vagus and left gastric vessels also pass.

There are also two small foramina lateral to the sternum, which allow passage of the internal thoracic artery.

The arterial supplies to the superior and inferior surfaces of the diaphragm are from the respective phrenic arteries, via the aorta. The superior surface also has a supply from the musculophrenic and pericardiophrenic arteries via the internal thoracic arteries.

The venous drainage of the superior surface of the diaphragm is via the musculophrenic and pericardiophrenic veins to the internal thoracic veins. The venous drainage of the inferior surface of the diaphragm is via the inferior phrenic veins, which on the right drain into the IVC and on the left drain into the left suprarenal vein.

The lymph drainage of the superior surface of the diaphragm is to the diaphragmatic lymph nodes, to the phrenic, parasternal and posterior mediastinal lymph nodes. The lymph drainage to the inferior surface of the diaphragm is to the superior lumbar lymph nodes. Lymph drainage between the superior and inferior surfaces of the diaphragm communicates freely, which of course has huge ramifications in the spread of infection and tumour between the abdomen and thorax.

Unlike the vascular supply of the diaphragm, the innervation of the diaphragm is the same on both the superior and inferior surfaces. The motor supply is entirely from the phrenic nerve, C3–C5. The sensory supply is divided between the central part, which is supplied by the phrenic nerve, C3–C5, and the peripheral part, which is supplied by the intercostal (T5–T11) and subcostal nerves (T12) in direct relation to that part of the diaphragm.

Because of this split in sensory innervation, referred pain can be felt in two areas. The most common place for referred pain is at the shoulder (dermatome C5), after irritation of the central portion of the diaphragm, supplied by C3–C5. This occurs following laparoscopic intra-abdominal surgery. Alternatively, referred pain can also be felt over the respective dermatomes T5–T12, depending on which part of the peripheral diaphragm is being irritated.

The right atrium forms the entire right border of the heart, as seen on chest X-ray. It receives the inferior and superior vena cava and the coronary sinus, which drains venous blood from the cardiac veins. There are two anatomical parts to the internal wall of the right atrium divided by the crista terminalis; a smooth walled section posteriorly, and a rough, more muscular section anteriorly. The smooth-walled part corresponds to the foramen ovale, found in the fetal heart. As the right system is of lower pressure, the walls of the right side of the heart are thinner, in comparison to the left side. The tricuspid valve lies between the right atrium and the right ventricle.

The left atrium forms the base and superior borders of the heart, as viewed on a chest X-ray. It receives oxygenated blood via the pulmonary vein and pumps it to the left ventricle via the tricuspid mitral valve. The mitral valve is attached to the internal wall of the atrium via muscular extensions, called the papillary muscles, and tendinous extensions called chordae tendinae. The internal wall of the atrium is generally smooth, except for the papillary muscles.

The right ventricle forms most of the anterior and inferior (diaphragmatic) surfaces of the heart.

The right ventricle receives blood from the right atrium, via the right atrioventricular/tricuspid valve and pumps blood via the pulmonary valve and pulmonary artery to the lungs. The pulmonary valve is also a tricuspid valve (formed by three cusps), but the formation of the cusps is very different to that of the right atrioventricular valve. The pulmonary valve is formed by three semi-lunar cusps and the tricuspid valve is formed by three ‘U-shaped’ cusps, attached to the internal wall of the heart via muscular projections, papillary muscles and tendinous insertions, chordae tendineae.

The interventricular septum is composed of a thin membranous section, which forms attachments superiorly and posteriorly, and a muscular part, which forms the centrally located division between the ventricles.

The left ventricle forms the apex, the left surface and the diaphragmatic surfaces. It pumps blood to the systemic circulation via the ascending aorta, which exits superoanteriorly from it. The aortic valve sits at the entry to the aorta. It has three semi-lunar cusps, right, left and posterior. Two aortic sinuses supply the coronary circulation, exiting from the right and left aortic sinuses. There is no aortic sinus from the posterior cusp.

When describing the surface anatomy of the heart, five points need to be addressed:

1. 
   

   1. The apex (left ventricle) is commonly palpated at the fifth intercostal space in the mid-clavicular line, on the left. In hypertrophic diseases of the heart, this is often displaced more inferolaterally.

   
   
2. 
   

   2. The left border runs from the second left costal cartilage to the fifth left intercostal space, mid-clavicular line (apex).

   
   
3. 
   

   3. The right border runs almost vertically, from the third to sixth costal cartilages.

   
   
4. 
   

   4. The superior border runs from the third costal cartilage on the right to the second costal cartilage on the left.

   
   
5. 
   

   5. The inferior border runs from the sixth costal cartilage on the right to the apex.

The mitral valve is posterior to the fourth left costal cartilage, but is auscultated at the apex.

The pulmonary valve is at the level of the third left costal cartilage and can be auscultated at this point.

The tricuspid valve is posterior to the left side of the fifth intercostal space and can be auscultated at this point.

The aortic valve is indeed posterior to the left side of the third intercostal space, but is auscultated at the right parasternal third intercostal space. A referred pulse from the aortic valve can be auscultated at the right carotid in aortic stenosis.

For an explanation, please see Question 53.

The sinoatrial (SA) node is found in the right atrium and is known as the pacemaker of the heart as it generates the initial electrical impulse. From here, the impulse travels to the AV node, which after a delay transmits the electrical impulse via the bundle of His to the left and right ventricles. A delay is required to prevent simultaneous contraction of the atria and ventricles. This delay forms the P-R interval on the ECG. The Purkinje fibers stimulate each muscle fiber individually to contract.

Parts of the ECG and how they relate to cardiac contraction:

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  P-wave: atrial contraction

  
  
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  P-R interval: delay caused by the AV node in transmitting the electrical impulse from atria to ventricles

  
  
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  QRS complex: ventricular contraction

  
  
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  ST segment: depolarization of the ventricles

  
  
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  T-wave: repolarization of the ventricles

For an explanation, see Question 55.

The left and right coronary arteries arise from the ascending aorta, distal to the aortic valve, via the left and right coronary sinuses, respectively.

The right coronary artery runs in the coronary groove (also known as the atrioventricular groove) and divides into:

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  The SA nodal artery (in 60% of cases) to supply the SA node

  
  
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  The right marginal artery, supplying the right ventricle and the apex

  
  
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  The posterior interventricular artery, which supplies both ventricles

  
  
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  The AV nodal artery, which supplies the AV node

The left mainstem artery runs for 1–2 cm in the anterior atrioventricular groove and divides into:

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  The SA nodal artery (in 40% of cases) to supply the SA node

  
  
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  The left anterior descending artery (LAD) to supply the right and left ventricles

  
  
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  The circumflex artery, which supplies the left atrium and ventricle

  
  
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  The left marginal artery, which supplies the left ventricle

The posterior and anterior interventricular arteries form an arch of arteries and the left circumflex also anastomoses with the main right coronary artery.