Short note thorax

1. Pulmonary pleura: Supplied by bronchial vessels.
2. Parietal pleura: Receives blood from intercostal, internal thoracic, and musculophrenic arteries, with corresponding veins draining the pleura.

The right conus artery is usually the first branch of the right coronary artery and supplies the infundibulum of the right ventricle. In some cases, it may arise directly from the anterior aortic sinus, in which case it is referred to as the 3rd coronary artery. It anastomoses with the left conus artery and the circumflex branch of the left coronary artery.

The right coronary artery:

1. Arises between the root of the pulmonary trunk and the right auricle.
2. Courses downwards and to the right in the right anterior atrioventricular groove.
3. Extends to the inferior border of the heart at the junction of the right and inferior borders.
4. Winds around the inferior border and goes left in the right posterior atrioventricular groove.
5. Terminates by anastomosing with the left coronary artery near the crux of the heart.

The sinu-atrial nodal artery is part of the atrial rami and is responsible for supplying the sinoatrial node. It arises from the initial segment of the right coronary artery in 65% of cases, while in 35% of subjects, it arises from the circumflex branch of the left coronary artery.

The intercostal space is the space between two adjacent ribs, and there are 11 intercostal spaces on each side of the thorax.

The 3rd, 4th, 5th, and 6th intercostal spaces are considered typical because the intercostal nerves and vessels are confined to the thoracic wall, with their contents limited within the thorax.

The boundaries of the intercostal spaces are:

• Superior: lower margin of the upper rib including costal groove & its costal cartilage
• Inferior: upper margin of the lower rib & its cartilage
• Anterior: lateral border of sternum
• Posterior: body of the corresponding thoracic vertebra

The contents of the intercostal spaces include:

• Intercostal muscles
• Intercostal arteries
• Intercostal veins
• Intercostal nerves

The external intercostal muscle originates from the lower border of the upper rib above and inserts into the outer lip of the upper border of the rib below.

The fibers of the external intercostal muscle run downward, forward, and medially.

Helps in inspiration by elevating the ribs.

Origin: Arises from the floor of costal groove of upper rib.
Insertion: Intermediate part of superior border of lower rib.

They act synergistically with external intercostal muscles to help in inspiration.

Helps in expiration by depressing the ribs.

1. Sternocostalis
2. Intercostalis intimus
3. Subcostalis

They occupy the middle 2/4th of a typical intercostal space and are absent in the 1st and 2nd spaces.

The sternocostalis muscle is related anteriorly to the internal thoracic artery.

The subcostalis muscles arise from the inner surface of the rib near its angle and insert into the inner surface of the upper border of the lower ribs after crossing one or two spaces.

The main action of the intercostal muscles is to prevent retraction during inspiration and bulging during expiration of the intercostal spaces.

The arterial supplies to the thoracic wall from the ventral midline include:

1. Internal thoracic artery
2. Superior epigastric artery
3. Inferior epigastric artery

The anterior and posterior intercostal arteries in each space anastomose with each other at the junction of the anterior 1/3rd and posterior 2/3rd at the level of the costo-chondral junction.

Veins do not follow the arteries in the thoracic wall's venous drainage.

A venous network radiates from the umbilicus draining upward into the lateral thoracic vein, which then drains into the axillary vein. Below the umbilicus, veins drain into the great saphenous vein. Additionally, the thoraco-epigastric vein connects the lateral thoracic vein with the superficial epigastric vein, becoming prominent in cases of inferior vena cava obstruction.

Lymph channels above the umbilicus drain into the axillary lymph nodes, while those below drain into the superficial inguinal lymph nodes. Specifically, lymph from the anterior body wall drains into the anterior (pectoral) group of axillary lymph nodes, and lymph from the posterior body wall drains into the posterior (subscapular) group.

Above the second rib and manubrio-sternal joint, the supraclavicular nerves provide nerve supply. Below the second rib:

1. Ventral midline: Anterior cutaneous branches of the second thoracic to the first lumbar spinal nerves.
2. Laterally: Lateral cutaneous branches of the second thoracic to the first lumbar spinal nerves.
3. Posteriorly: Posterior rami of spinal nerves through medial branches in the upper thoracic and lateral branches in the lower thoracic and lumbosacral parts.

The second intercostal nerve joins the medial cutaneous nerve of the arm via the intercostobrachial nerve, which supplies the skin of the armpit and the upper medial side of the arm. In cases of coronary artery disease, pain may be referred along this nerve to the medial side of the arm, illustrating the concept of referred pain.

The 7th to 11th intercostal nerves leave the thoracic wall and enter the anterior abdominal wall, supplying:

• Dermatomes on the anterior abdominal wall
• Muscles of the anterior abdominal wall
• Parietal peritoneum

Referred pain is abdominal pain that arises from conditions such as pulmonary thromboembolism or pneumonia with pleurisy involving the costal parietal pleura, leading to abdominal tenderness and rigidity.

The first six intercostal nerves supply the intercostal muscles, transversus thoracis, serratus posterior superior, and levator costarum. The seventh to eleventh nerves supply the skin, parietal peritoneum, and anterior abdominal muscles.

The main intercostal nerve and its collateral branches supply the parietal pleura and periosteum of the rib. The lower intercostal nerves also supply the parietal peritoneum.

Herpes Zoster, or Shingles, is caused by the reactivation of the latent varicella-zoster virus. Symptoms include a band of dermatomal pain in the distribution of the sensory neuron in a thoracic spinal nerve, followed by a skin eruption.

During a needle thoracostomy, the following structures are pierced: (a) skin, (b) superficial fascia, (c) pectoral muscles (in the anterior approach), (d) serratus anterior muscle, (e) external intercostal muscle, (f) internal intercostal muscle, (g) innermost intercostal muscle, (h) endothoracic fascia, and (i) parietal pleura.

With increasing age, the rib cage becomes more rigid due to calcium deposits in the costal cartilages, making the ribs brittle and more prone to breaking at their weakest part, which is their angles.

The right subclavian artery originates from the brachiocephalic trunk, which is the first branch off the aortic arch. It arises posterior to the right sternoclavicular joint.

The left subclavian artery arises directly from the aortic arch, to the left of the trachea, and its origin is slightly more distal and posterior compared to the right subclavian artery.

The costocervical trunk supplies the upper two costal spaces and the deep muscles of the neck.

In the first part, the subclavian artery is covered anteriorly by the sternocleidomastoid muscle and is crossed by the vagus nerve and phrenic nerve. It lies posterior to the subclavian vein and is separated from it by the anterior scalene muscle.

The subclavian artery is closely related to the brachial plexus, especially in the second and third parts. The middle scalene muscle lies posterior to the artery as it passes between the scalene muscles.

The Blalock-Taussig operation is a palliative procedure used in infants or children with tetralogy of Fallot who are too young for corrective surgery but exhibit significant symptoms. It involves creating an end-to-side shunt between the subclavian artery and the pulmonary artery, providing temporary relief and improving oxygenation until definitive surgical correction can be performed.

The internal thoracic artery originates from the lower surface of the 1st part of the subclavian artery, approximately 2 cm above the sternal end of the clavicle. It runs vertically down into the thorax, positioned behind the sternal end of the clavicle, and descends behind the upper 6 costal cartilages, maintaining a distance of 1 cm from the lateral margin of the sternum.

The anterior intercostal arteries are present only in the upper 9 intercostal spaces and are absent in the 10th and 11th spaces. Each of the first 6 spaces has 2 anterior intercostal arteries, with the 1st to 6th arising from the internal thoracic artery and the 7th, 8th, and 9th arising from the musculophrenic artery, which is a terminal branch of the internal thoracic artery.

The two terminal branches are the musculophrenic artery and the superior epigastric artery.

The internal mammary artery is preferred because it is long-lasting and less prone to develop atherosclerosis due to its histological peculiarity, which includes a wall containing elastic tissue only and endothelial cells that secrete chemicals preventing atherosclerosis.

The anterior and posterior intercostal arteries establish communication between the first part of the subclavian artery and the descending thoracic aorta through free anastomosis.

In the case of coarctation of the aorta, blood is supplied to the descending aorta via the intercostal anastomosis.

The 1st and 2nd posterior intercostal arteries arise from the superior intercostal branch of the costo-cervical trunk of the subclavian artery.

The 3rd to 11th posterior intercostal arteries are branches of the descending aorta.

The right posterior intercostal artery arises from the back of the aorta and passes downwards and laterally in front of the vertebral column, behind the oesophagus, thoracic duct, azygous vein, and sympathetic trunk. In contrast, the left posterior intercostal artery passes backwards and laterally by the side of the vertebrae, behind the hemi-azygous vein and sympathetic chain.

The posterior intercostal arteries run over the corresponding vertebra and lie between the costal pleura and the posterior intercostal membrane. Anteriorly, they lie between the internal and inner intercostal muscles in the costal groove, where they give a collateral branch that runs along the upper border of the lower rib.

In cases of aortic coarctation or narrowing, the posterior intercostal arteries enlarge greatly to provide collateral circulation. The pressure from these enlarged arteries can produce characteristic notching on the ribs, especially in their posterior parts.

The anterior intercostal veins from the 1st to 6th spaces drain into the internal thoracic vein, while those from the 7th to 9th spaces drain into the musculophrenic vein.

The drainage pattern of the left posterior intercostal veins is as follows:

• 1st posterior intercostal vein drains into the left brachiocephalic vein.
• 2nd, 3rd, and 4th veins join to form the left superior intercostal vein, which drains into the left brachiocephalic vein.
• 5th to 8th veins drain independently into the accessory hemi-azygous vein.
• 9th to 11th veins drain into the hemi-azygous vein.
• The subcostal vein drains into the hemi-azygous vein.

The drainage pattern of the right posterior intercostal veins is as follows:

• 1st posterior intercostal vein drains into the right brachiocephalic vein.
• 2nd, 3rd, and 4th veins join to form the right superior intercostal vein, which drains into the arch of the azygos vein.
• 5th to 11th veins drain into the azygos vein.

Intercostal nerves arise as the ventral ramus of the corresponding thoracic nerve.

The 3rd to 6th intercostal nerves are named typical intercostal nerves as they are confirmed to the thorax.

The 1st intercostal nerve contributes to the lower trunk of the brachial plexus.

The 2nd intercostal nerve forms the intercostobrachial nerve, which supplies the axilla.

The 7th to 11th intercostal nerves supply the skin over the abdominal region in the anterior part.

Each intercostal nerve arises from the corresponding inter-vertebral foramina, runs along with the vascular bundle in between the costal pleura and posterior intercostal membrane, and lies above the VAN in the costal groove.

The collateral branch arises from the posterior part of the intercostal nerve before it reaches the angle of the rib and follows the inferior margin of the space in the neurovascular plane, potentially re-joining the main trunk.

The intercostal nerve supplies muscular branches to the intercostal muscles and the serratus posterior superior muscle in the back.

The lateral cutaneous branch pierces the internal and external intercostal muscles at the mid axillary line, supplying the skin along with anterior and posterior cutaneous nerves. It divides into anterior and posterior branches, with the posterior branches supplying the skin of the back overlying the scapula and latissimus dorsi muscle, and the anterior branches supplying the skin overlying the pectoralis major muscle.

Right Side Superior:

1. Pulmonary ligament
2. Terminal part of azygos vein

Left Side Superior:

1. Arch of the aorta

The right primary bronchi is shorter, larger, and straighter, which increases the chances of infection. In contrast, the left primary bronchi is longer, narrower, and more oblique.

The right primary bronchi divides into 3 secondary bronchi (lobar bronchi) for each lobe, while the left primary bronchi divides into 2 secondary bronchi (lobar bronchi) for each lobe.

A pulmonary unit is aerated by a respiratory bronchiole and consists of:

1. Respiratory bronchiole
2. Alveolar ducts
3. Atria
4. Air saccules
5. Pulmonary alveoli

Gaseous exchange takes place in the alveoli.

Bronchopulmonary segments are well-defined sectors of the lung, each aerated by a tertiary or segmental bronchus. Each segment is pyramidal in shape with its apex directed towards the root of the lung.

The right side has one bronchial artery that arises either from the 3rd right posterior intercostals artery or the descending thoracic aorta.

There are two bronchial arteries on the left side, both of which arise from the descending thoracic aorta.

The right bronchial veins drain into the azygos vein.

The left bronchial veins drain either into the left superior intercostals vein or the hemiazygos vein.

The two sets of lymphatics drain into the bronchopulmonary nodes: 1. Superficial vessels drain the peripheral lung tissue beneath the pulmonary pleura. 2. Deep lymphatics accompany bronchial and pulmonary vessels towards the hilum.

Parasympathetic nerves are derived from the Vagus nerve, providing motor function to bronchial muscles and secretomotor function to mucus glands.

Sympathetic nerves, derived from T2-5, are inhibitory to the smooth muscle and glands of the lungs.

Hemoptysis is the coughing of blood, often associated with pulmonary tuberculosis.

Chronic bronchitis may develop into bronchiectasis.

Emphysema is the permanent distension of the alveoli resulting from chronic cough.

Pneumonia is more common in children.

Bronchogenic carcinoma is a type of lung cancer that originates in the bronchial tubes.

Pulmonary thromboembolism is a blockage in the pulmonary arteries, often due to blood clots.

Infections of a segment usually remain restricted to that segment, although tuberculosis can spread between segments.

Segments are not barriers to bronchogenic carcinoma, allowing it to spread across segments.

The knowledge of bronchopulmonary segments has advanced pulmonary surgery from lobectomy to segmental resection.

The exact topography of the bronchi aids in the postural drainage of lung abscesses and bronchiectasis.

With the knowledge of bronchial anatomy, bronchography has greatly advanced for diagnostic purposes.

The common sites of lung abscesses, such as the posterior segment of the right upper lobe and the apical segment of the right lower lobe, are better understood as postural phenomena.

The two layers of pleura are the visceral pleura, which is attached to the lung, and the parietal pleura, which covers the external surface of the lung.

The cervical pleura covers the apex of the lung, extending from the 1st rib to about 2.5 cm above the sternal end of the clavicle, and is protected by sibson's fascia externally.

The costal pleura covers a major part of the lung, lining the inner surface of the sternum, ribs, intercostal spaces, and lateral sides of the vertebral bodies.

The costal pleura is reflected over the diaphragm at the base of the lung along the line of costo-diaphragmatic reflection.

The mediastinal pleura is described in three parts:

1. Part above the hilum of lung: Runs from behind the sternum to the lateral side of the vertebral column in the anteroposterior direction.
2. Part at the hilum of lung: Encloses various structures at the root of the lung in a tubular fashion and reflects onto the lung as the visceral pleura. At the level of the heart, it is known as the pericardial pleura.
3. Part below the hilum of lung: Not explicitly described in the provided text, but typically includes the diaphragmatic pleura.

The structures enclosed by the pleura at the hilum of the lung, from anterior to posterior, are:

1. Pulmonary vein
2. Pulmonary artery

The pulmonary ligament extends from the center of the two lungs to the side of the esophagus. It consists of loose areolar tissue and few lymphatics, and it separates superiorly to enclose structures at the root of the lung, while the inferior fused layer lies free over the diaphragm.

The diaphragmatic pleura covers the base of the lung over the diaphragm and is reflected over the lateral surface of the lung along the costo-diaphragmatic reflection. Medially, it is reflected to the mediastinal pleura by the side of the fibrous pericardium over the central tendon.

1. Right costo-xiphoid junction
2. Right and left costo vertebral angles
3. Cervical pleura which extends into the root of neck (known as naked pleura)

On the right side, it extends from the Sternoclavicular joint downwards to the center of the sternal angle, then passes straight down to the xiphisternal joint, running laterally along the 7th costal cartilage. On the left side, it extends from the Sternoclavicular joint to the center of the sternal angle, then vertically down to the 4th costal cartilage, running laterally to the lateral border of the sternum and down to the 6th costal cartilage.

The line of costo-diaphragmatic reflection extends from the lateral border of the xiphisternal joint to the 8th costal cartilage in the midclavicular line, then to the 10th rib in the midaxillary line, and runs posteriorly to a point 2.5 cm lateral to the 12th thoracic vertebra. It provides a potential space for lung expansion during forceful respiration, being widest at the midaxillary line.

1. Costodiaphragmatic recess: A potential space between the lower limit of the pleural sac and the lower border of the lung, allowing for lung expansion during respiration.
2. Costomediastinal recess: Present along the anterior costomediastinal reflection of pleura, maximal in the region of the cardiac notch, also serving as a reserve space for lung expansion.

1. Parietal pleura:
   • Costal and peripheral part of diaphragmatic pleura: Supplied by corresponding intercostal nerves.
   • Mediastinal and central part of diaphragmatic pleura: Supplied by the phrenic nerve.
2. Visceral pleura: Supplied by autonomic nerves.

The sympathetic supply is provided by the 2 to 5 sympathetic ganglia, while the parasympathetic supply is provided by the Vagus Nerve.

The lymphatic drainage for the pleura is as follows:

The two pleural sacs are in close apposition at the following locations:

1. Behind the body of the sternum in the midline - from the level of the sternal angle to the 4th costal cartilage.
2. Mid thoracic region at the level of T8-T9 vertebra.

The clinical conditions associated with the pleura include:

• Pleuritis: Inflammation of the pleura
• Pleural effusion: Collection of fluid in the pleural cavity
• Pneumothorax: Air in the pleural cavity
• Hydrothorax: Fluid in the pleural cavity
• Paracentesis thoracis: Drainage of fluid at the 8th intercostal space in the midaxillary line

The pericardium is a fibro-serous sac that encloses the heart and the roots of the great vessels. It is derived from the splanchnic mesoderm lying cranial to the prochondral plate, constituting the cardiogenic area. The pericardial cavity is derived from the intra-embryonic coelom.

The pericardium is made up of two parts:

1. Fibrous pericardium
2. Serous pericardium

The pericardium is conical in shape with the apex upwards and the base downwards. It extends from the 2nd to 6th costal cartilage, corresponding to the T5 - T8 vertebral levels.

1. The apex blends with the serous coat of great vessels at their origin and the pretracheal, lying at the level of the sternal angle.

2. Its base fuses with the upper surface of the central tendon of the diaphragm.

3. Anteriorly, it is attached to the body of the sternum via superior and inferior sterno-pericardial ligaments.

• Anterior margin of pleura and lung
• Posterior surface of sternum

• The two principal bronchi
• Esophagus with the plexus of nerves
• Thoracic duct
• Azygos system of veins

The serous pericardium is a closed sac made up of mesothelium, consisting of parietal and visceral layers that envelope the heart.

• Phrenic nerve
• Mediastinal pleura
• Pericardiophrenic vessels

• Diaphragm
• Liver and stomach

The two layers of the pericardium are the parietal layer and the visceral layer. The parietal layer is adherent to the fibrous pericardium, while the visceral layer, also known as the epicardium, is adherent to the myocardium of the heart. The visceral layer continues with the parietal layer at the roots of the great vessels.

The boundaries of the transverse sinus are as follows:

• Anterior: Ascending aorta and pulmonary trunk
• Posterior: Upper margin of left atrium and intra-pericardial part of superior vena cava
• Superior: Bifurcation of pulmonary trunk
• Inferior: Upper surface of left atrium
• On the sides: Opens into pericardial cavity

The oblique sinus is a cul-de-sac located behind the left atrium, functioning as a parieto-visceral space. Its boundaries are:

• Anterior: Left atrium
• Posterior: Parietal layer covering the posterior part of fibrous pericardium
• Right side: Right pulmonary veins and inferior vena cava
• Left side: Left part of pulmonary veins
• Superior: Upper margin of left atrium
• Inferior: Open into pericardial cavity

The arterial supply to the fibrous pericardium and parietal layer of the serous pericardium comes from:

• Internal thoracic artery
• Descending aorta

The venous drainage of the fibrous pericardium and parietal layer is through:

• Azygos veins
• Internal thoracic veins

The fibrous pericardium and parietal layer are supplied by the phrenic nerve, which is sensitive to pain.

Pericarditis is the inflammation of the pericardium.

The two routes for draining pericardial effusion are:

1. Parasternal Route: A needle is inserted close to the sternal margin in the 4th or 5th intercostal space on the left side.
2. Subcostal Route: Aspiration is performed through the left costo-xiphoid angle with an upward inclination of the needle of 45°.

Intracardiac injection or adrenaline is given through the Parasternal route during cardiopulmonary resuscitation.

The transverse pericardial sinus is significant because a temporary ligature may be passed through it to block flow through the aorta and pulmonary trunk during cardiac surgery.

Cardiac tamponade is the collection of fluid in the pericardial cavity, which prevents proper ventricular systole and can lead to breathlessness.

The right atrium receives deoxygenated blood from the whole body and pumps it to the right ventricle through the tricuspid valve.

The right atrium extends from the orifice of the superior vena cava to the orifice of the inferior vena cava, and from the 3rd costal cartilage to the 6th cartilage on the right side.

The right auricle is a hollow conical muscular projection from the antero-superior aspect of the upper end of the right atrium, extending towards the left side in front of the aorta.

The musculi pectini in the right auricle are dense muscular structures that serve as a potential site for thrombi formation. If thrombi dislodge from the right atrium, they can enter the pulmonary circulation, potentially leading to pulmonary embolism.

The sulcus terminalis is a shallow vertical groove along the right border of the heart. Internally, it produces the crista terminalis, which contains the S A node in its upper part.

The main tributaries that open into the right atrium include:

1. Superior vena cava (SVC)
2. Inferior vena cava (IVC)
3. Coronary sinus
4. Venae cordis minimi (Thebesian vessels)

Additionally, the right marginal vein and anterior cardiac veins may also open into the right atrium.

The internal features of the right atrium include:

• Smooth posterior part (sinus venarum) derived from the right horn of the sinus venosus.
• Venae cordis minimae, small pits that ensure better blood supply to the myocardium on the right side.
• IVC opening at the lower end, guarded by the Eustachian valve.
• Intervenous tubercle, a small projection directing SVC blood to the right ventricle.
• Coronary sinus, guarded by the Thebesian valve, located between the IVC and tricuspid orifice.

The triangle of Koch is an identifiable landmark in the right atrium during surgery, defined by three boundaries:

1. Anteriorly: Septal cusp of the tricuspid valve.
2. Posteriorly: Valve of the coronary sinus.
3. Superiorly: Tendon of Todaro.

The tendon of Todaro is a subendocardial fibrous thickening that extends from the confluence of the valve of the inferior vena cava (IVC) and the limbus of the fossa ovalis to the anterior point of the septal cusp of the tricuspid valve. It plays a role in the conduction system of the heart.

The AV node is located at the apex of Koch's triangle, which is situated in the floor of the right atrium near the lower end of the interatrial septum. This area is significant for the conduction of electrical impulses in the heart.

The atrioventricular membranous septum is located antero-superior to the tendon of Todaro and serves as a barrier between the right atrium and the left ventricle, playing a crucial role in the heart's structure and function.

The torus aorticus is a bulge in the atrial wall located above the atrioventricular membranous septum. It is produced by the adjustment of the non-coronary aortic sinus at the base of the ascending aorta, contributing to the structural integrity of the heart.

The right ventricle has two parts:

1. Inflowing part: Rough surface due to muscular ridges called trabeculae carneae, which develop from primitive ventricular chambers.

2. Outflowing part (infundibulum): Smooth surface that leads to the pulmonary trunk, developing from the bulbus cordis. This distinction is important for understanding the flow of blood through the heart.

The thickness of the ventricular wall is proportionate to its workload. In the fetal stage, the right ventricle has a thicker wall because it pumps blood into the aorta through the ductus arteriosus. In the postnatal stage, the right ventricle pumps blood into pulmonary circulation, where the systolic arterial pressure is lower (25-35 mm Hg), resulting in a thinner wall compared to the left ventricle.

The papillary muscles are conical-shaped and include:

1. Anterior Papillary Muscle: Attached to the right antero-lateral wall, blending with the right end of the septo-marginal trabecula (moderator band).
2. Posterior Papillary Muscle: Attached to the inferior wall.
3. Septal Papillary Muscles: Several small muscles attached to the septal limb of the septo-marginal trabecula.

The tricuspid valve has the following key features:

• Accommodates the tips of three fingers.
• Composed of three cusps, each with two surfaces.
• Formed by the reduplication of endocardium containing lamina fibrosa, continuous with the valve annulus.
• The annulus is a ring of collagenous tissue for cusp attachment.
• Each cusp has three zones: rough (thick, for chordae tendinae attachment), clear (thin, no chordal attachment), and basal (thick, vascular, for basal chordae attachment).

During ventricular diastole, when the intra-ventricular pressure is low, the papillary muscles are relaxed and the chordae tendineae are slack. At this stage, the tricuspid and pulmonary valves open, allowing the apices of the cusps to project into the ventricle.

During ventricular systole, the intra-ventricular pressure increases, driving the cusps of the tricuspid valve upwards. The papillary muscles contract and tighten the chordae tendineae, leading to the closure of the valve.

The pulmonary valve is a semilunar valve with three half-moon shaped cusps: right anterior, left anterior, and posterior. It features a nodule of Arantius at the midpoint of the free margin and thin margins called linules on either side. The pulmonary sinus is the dilatation in the wall of the pulmonary trunk just above the cusps.

The skeleton of the heart consists of four fibrous rings at the bases of both ventricles around the right and left atrio-ventricular, pulmonary, and aortic orifices. The pulmonary ring is positioned above, in front of, and slightly left to the aortic ring, with both rings set at right angles to each other and connected by a fibrous septum known as the tendon of infundibulum. The right and left atrio-ventricular rings are united by a condensed mass of fibrous tissue known as the trigonum fibrosum dextrum.

The fibrous skeleton is capable of holding sutures under persistent tension during heart valve prosthesis operations.

The three types of trabeculae carneae are:

1. Ridges - Fixed elevations throughout the wall.
2. Bridges - Muscular elevations with two fixed ends and a free center.
3. Pillars (papillary muscles) - One end attached to the ventricular wall and the other connected to the cusps of the tricuspid valve by chordae tendinae.

Papillary muscles are conical projections that regulate the closure of atrio-ventricular valves by connecting to the chordae tendinae, which in turn attach to the valve cusps, ensuring proper blood flow across the orifices.

The supraventricular crest is a ridge present between the pulmonary and atrioventricular orifices in the right ventricle. It plays a role in the structural organization of the heart and aids in directing blood flow from the right ventricle to the pulmonary trunk.

The septomarginal trabeculae, also known as the Moderator band, is a specialized bridge that extends from the interventricular septum to the base of the anterior papillary muscle. It contains the right branch of the atrioventricular (A.V.) bundle, contributing to the conduction system of the heart.

The left atrium is cubical in shape and forms 2/3 of the base of the heart. Its anterior surface is concealed by the pulmonary trunk and the ascending aorta.

The interior of the left atrium consists of a relatively featureless cavity with a smooth part that has openings for the pulmonary veins, and a rough part that corresponds to the left auricle, which contains musculi pectini and develops from the primitive atrium.

The left auricle is a potential site for the formation of thrombi, which, if dislodged, can result in embolism in the systemic circulation.

The left ventricle has walls that are twice as thick as those of the right ventricle, a conical cavity that is longer, and a mesh of trabeculae carneae that is finer and more numerous, especially rich at the apex and inferior wall.

The mitral valve, also known as the bicuspid valve, has two cusps resembling a Bishop's miter. It opens during systole to allow blood flow and closes during diastole to prevent backflow, with the anterior cusp being longer and attached to the upper and right margin of the orifice.

Mitral stenosis is the narrowing of the mitral orifice, which can affect blood flow from the left atrium to the left ventricle.

Left atrial obstruction during ventricular filling leads to:

• Increased left atrial pressure
• Pulmonary venous hypertension
• Symptoms such as dyspnea, cough, and hemoptysis (blood in sputum)
• Enlargement of the left atrium, which can cause:
  • Dysphagia (difficulty swallowing) by pressing on the esophagus
  • Hoarseness of voice (Ortner's syndrome) by affecting the left recurrent laryngeal nerve

Mitral valvotomy is a surgical procedure that involves the dilatation of the mitral orifice. It can be performed in two ways:

1. Closed mitral valvotomy
2. Open mitral valvotomy

In mitral regurgitation:

• The mitral valve fails to close during systole, causing blood to regurgitate from the left ventricle into the left atrium.
• This leads to overfilling of the left ventricle during diastole.
• A portion of blood shuttles between the left atrium and left ventricle, increasing the workload of the left ventricle.
• Over time, this can result in gross dilatation and hypertrophy of the left ventricle, potentially culminating in left ventricular failure.

The azygos vein is significant because:

• It is unpaired and runs straight along the right side of the vertebral column.
• It drains blood from the posterior abdominal wall and posterior mediastinum.
• It communicates with the venacaval system anteriorly and the vertebral venous system posteriorly.
• It forms an important collateral channel connecting the superior vena cava (SVC) and inferior vena cava (IVC).

The azygos vein is formed by the union of the right ascending lumbar vein and the right subcostal vein at the level of T-12. It can also occasionally form from:

• A lumbar azygos vein from the back of the IVC at the level of the right renal vein.
• A continuation of the right subcostal vein.
• Rarely from the right renal vein or the right first lumbar vein.

The azygos vein ascends into the thorax via the aortic opening of the diaphragm, passing upwards in front of the vertebral column, anterior to the lower 8 thoracic vertebrae. It arches above the root of the right lung at the level of T-4 and ends in the superior vena cava (SVC).

Anteriorly, the azygos vein is related to the oesophagus. Posteriorly, it is related to the lower eight thoracic vertebrae and the right posterior intercostal arteries.

The tributaries of the azygos vein include:

• Right posterior intercostal veins (except the 1st)
• 2nd, 3rd, and 4th posterior intercostal veins that unite to form the right superior intercostal vein
• 5th to 11th posterior intercostal veins that end separately
• Union of the right subcostal vein and right ascending lumbar vein
• Hemiazygos vein at T-8 level
• Accessory hemiazygos vein at T-7 level
• Right bronchial vein
• Oesophageal, pericardial, and mediastinal veins

The bronchial veins drain into the azygos vein on the right side and into the accessory hemiazygos vein on the left side, contributing to the venous drainage of the thoracic structures.

Obstruction of the SVC serves as a channel to shunt blood from the upper part of the body to the inferior vena cava (IVC).

The thoracic duct originates from the upper end of the cisterna chyli at the lower border of the T12 vertebra and drains chyle and most of the lymph of the body into the bloodstream.

In the thorax, the thoracic duct passes upwards in the posterior mediastinum on the right side of the vertebral column behind the esophagus, and at the lower border of T4, it crosses to the left side.

Key features of the thoracic duct include:

1. Length: 45 cm
2. Breath: 0.5 cm
3. Appearance: Beaded due to the presence of numerous valves in its lumen.

The thoracic duct usually ends by opening into the junction of the left subclavian and internal jugular veins in the neck, guarded by a pair of valves.

The anterior relations of the thoracic duct at the aortic opening include the diaphragm (median arcuate ligament).

The structures located posterior to the thoracic duct in the posterior mediastinum include the vertebral column and the right posterior intercostal arteries.

On the left side in the posterior mediastinum, the thoracic duct is related to the descending thoracic aorta.

In the superior mediastinum, the structures found anterior to the thoracic duct include the arch of the aorta and the origin of the left subclavian artery.

The tributaries include:

1. A pair of ascending lymph trunks – drains the upper lumbar lymph nodes.
2. A pair of descending lymph trunks – drains the posterior intercostal lymph nodes of lower six spaces.
3. Vessels that drain posterior mediastinal lymph nodes.
4. Posterior intercostal lymph nodes of upper six spaces of the left side.
5. Left jugular trunk.
6. Left subclavian lymph trunk.
7. Left broncho-mediastinal lymph nodes.

The thoracic duct drains lymphatics from the entire body except for the right side of the head and neck, right upper limb, right lung, right thoracic wall, right half of the heart, and the convex surface of the liver.

Filariasis can cause obstruction of lymphatics, potentially blocking the thoracic duct and leading to edema of the limbs. It may also result in the bursting of the thoracic duct into pleural cavities, causing a chylous pleural effusion.

Chylothorax is the accumulation of lymph in the pleural cavities, which may occur due to the rupture of the thoracic duct.

A thoracic duct fistula is the leakage of lymphatic fluid from the thoracic duct following surgeries at the root of the neck. It should be treated surgically.

The esophagus extends from the lower end of the pharynx (at the level of the lower border of C6 vertebra) to the cardiac orifice of the stomach (at the level of T11 vertebra).

The esophagus measures approximately 25 cm in length and 2 cm in width.

The esophagus follows this course:

• It passes downwards in front of the vertebral column.
• It runs through the posterior part of the superior mediastinum behind the trachea and arch of aorta.
• It then passes through the posterior mediastinum, in front and to the right of the descending aorta.
• Finally, it pierces the diaphragm at the level of T10 vertebra and ends in the cardiac end of the stomach at the level of T11 vertebra, 2.5 cm to the left of the median plane.

The relations of the esophagus are as follows:

The esophagus has slight external curvatures and internal constrictions. The curvatures include:

1. Anteroposterior curvature corresponding to the cervical and thoracic spine.
2. Lateral curves on the left side at:
   • Upper end (C6 vertebra)
   • Near lower end (opposite T6-T7 vertebra)

The esophagus is supplied by the following arteries:

1. Inferior thyroid artery
2. Descending aorta
3. Bronchial artery
4. Left gastric artery
5. Left phrenic artery

The venous drainage of the esophagus is as follows:

1. Cervical part - Inferior thyroid vein
2. Thoracic part - Azygos vein and hemiazygos vein

The cervical part of the esophagus drains into the jugulo-omohyoid lymph nodes.

The sympathetic supply to the esophagus is derived from the T5-T6 segments and is vasomotor in function.

Hematemesis occurs in cirrhosis of the liver due to portal hypertension, which leads to the opening of anastomotic channels in the lower end of the esophagus, causing engorged veins that can burst.

Achalasia cardia is the congenital absence of ganglionic cells or myenteric plexus in the esophageal wall, leading to neuromuscular incoordination and food accumulation in the esophagus.

A barium swallow is a special radiological procedure used to visualize the esophagus for compression or constriction.

Dysphagia is defined as difficulty in swallowing.

The right coronary artery is smaller than the left coronary artery, and both arise from the aortic sinus of the ascending aorta.

The right coronary artery has several branches:

Large branches:

1. Right Marginal Artery - Longest ventricular ramus, supplies the adjoining surface of the right ventricle.
2. Posterior Interventricular Artery - Supplies the diaphragmatic surface of the right ventricle.

Small branches:

1. Nodal branches - Present in 65% of cases, supply the nodal tissues.
2. Right Atrial and Ventricular Rami - Supply the myocardium of the right atrium and ventricle.
3. Infundibular Branch - Supplies the infundibulum of the right ventricle.
4. Terminal Branches - Supply the terminal areas of the heart.

The right coronary artery is smaller than the left coronary artery. It arises from the anterior aortic sinus, positioned between the root of the pulmonary trunk and the right auricle.

The posterior interventricular artery arises from the right coronary artery near the crux of the heart in 70% of subjects. It passes along the posterior interventricular groove and anastomoses with the anterior interventricular branch of the left coronary artery near the apex.

The most significant branches of the posterior interventricular artery are the septal rami, which supply the postero-inferior one third of the ventricular septum. One of the septal rami also supplies the AV node. Additionally, the right posterior atrial rami supply the posterior surface of both the right and left atria.

The posterior interventricular artery supplies the following areas:

1. Right atrium
2. Ventricles
   • Greater part of the right ventricle (except the area adjoining the anterior interventricular groove)
   • A small part of the left ventricle adjoining the posterior interventricular groove
3. Postero-inferior one third of the interventricular septum
4. Whole of the conducting system of the heart (except a part of the left branch of the AV bundle).

The left coronary artery is usually wider than the right coronary artery. It arises from the left posterior aortic sinus and passes behind the pulmonary trunk, appearing in the interval between the pulmonary trunk and left auricle.

The left coronary artery divides into two main branches:

1. Anterior interventricular artery:

   • Descends in the anterior interventricular groove and anastomoses with the posterior interventricular branch of the RCA at the apex.
   • Branches include:
     • Anterior interventricular rami: supply both right and left ventricles.
     • Diagonal artery: a large left ventricular ramus.
     • Left conus artery: supplies the infundibulum of the right ventricle.
     • Septal rami: supply the antero-superior 2/3 of the ventricular septum.

2. Circumflex artery:

   • Passes along the left part of the atrio-ventricular groove, winds around the left border of the heart, and occupies the posterior part of the atrio-ventricular groove.

The branches of the left coronary artery include:

1. Atrial rami: Supply the adjoining left atrium.
2. Ventricular rami: Supply the adjoining left ventricle.
3. SA nodal artery: Supplies the SA node in 35% of individuals after encircling the superior vena cava.
4. Left marginal artery: Follows the left border of the heart towards the apex.
5. Posterior interventricular artery: Usually a branch of the RCA, but in 10-20% of cases, it is a continuation of the left circumflex artery (indicating left dominance).
6. Kugel's artery: An atrial branch that communicates with a similar branch of the RCA on the anterior atrial wall.

Coronary predominance refers to the origin of the posterior interventricular artery:

• Right coronary predominance: 90% of individuals have the posterior interventricular artery originating from the right coronary artery.
• Left coronary predominance: 10% have it as a continuation of the left circumflex artery.
• Balance dominance: Rarely, it can originate from both arteries, which is less likely to affect coronary disease.

Occlusion of the coronary arteries can lead to myocardial ischemia, which is a condition where the heart muscle does not receive enough blood. This lack of blood flow can result in angina pectoris, characterized by chest pain or discomfort due to insufficient oxygen supply to the heart muscle.

Common symptoms include:

• Pain in the left precordium or chest
• Referred pain to the left shoulder, left arm, forearm, right arm, epigastrium, or back
• Angina characterized by pressure or sinking sensation in the chest
• Tachycardia
• Perspiration
• Nausea and vomiting
• Shortness of breath

Myocardial ischemia, primarily caused by infarction, is a chief cause of sudden death.

The incidence of occlusion in major coronary arteries is as follows:

• Left Anterior Descending (LAD): 40-50%
• Right Coronary Artery: 30-40%
• Circumflex (LCX): 15-20%

Angiography can be performed using:

1. Femoral approach
2. Radial approach

Angioplasty is performed to open the blocked artery, restoring blood flow.

A coronary artery bypass graft is used to bypass the blocked segment of a coronary artery, improving blood flow to the heart muscle.

1. Coronary sinus
2. Anterior cardiac vein
3. Venae cordis minimi (thebesian vein)

60% of the venous drainage returns to the right atrium.

The coronary sinus collects deoxygenated blood from the heart muscle and drains it into the right atrium.

The coronary sinus is located in the posterior part of the atrioventricular (AV) groove.

The coronary sinus originates from the left part of the posterior AV groove and is a continuation of the great cardiac vein.

The coronary sinus terminates by opening into the right atrium, located between the inferior vena cava (IVC) opening and the tricuspid valve orifice, and is guarded by an incomplete semicircular valve known as the Thebesian valve.