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Questions and Answers
What is the term for the cul-de-sac formed by the zone of reflections around the veins?
Which artery lies posterior to the ascending aorta and pulmonary trunk?
Which structure encircles the heart and separates the atria from the ventricles?
What does the posterior interventricular sulcus contain?
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Which nerve is NOT associated with the nervous supply to the pericardium?
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What type of fibres are present in Type 1 sympathetic trunks?
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Which ganglia does the Greater Splanchnic Nerve originate from?
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Where does the Left Vagus Nerve give off branches?
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What is the function of the Left Recurrent Laryngeal Nerve?
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Which structure does NOT have a direct attachment to the fibrous pericardium?
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What is the role of the pericardial cavity?
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Which phrenic nerve descends along the left side of the pericardial sac?
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What type of pericardium consists of a thin double-layered sac?
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Which of the following best describes the inner layer of the serous pericardium?
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Which nerve lies posterior to the left brachiocephalic vein?
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What condition may result from compression of the left recurrent laryngeal nerve due to a mass in the aortopulmonary window?
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What is a likely consequence when excess fluid accumulates in the pericardial cavity?
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Which anatomical anomaly is characterized by the aortic arch coursing to the right of the trachea?
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What condition is described when there is an abnormally large amount of fluid in the pericardial cavity?
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Which condition involves the left-to-right inversion of the body's organs?
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Where does the ascending aorta originate?
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What divides the inferior mediastinum into anterior, middle, and posterior sections?
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Which of the following arteries is the first branch of the arch of aorta?
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Which structure is found posterior to the trachea in the superior mediastinum?
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What structure does the ductus arteriosus connect during embryonic circulation?
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What is the major lymphatic vessel in the body that enters the superior mediastinum?
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What is the relationship of the right pulmonary artery to the ascending aorta?
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Which of the following vessels passes over the left side of the aortic arch?
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At what level does the arch of aorta end?
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What is the anterior boundary of the superior mediastinum?
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Which vein drains into the right atrium after passing through the pericardial sac?
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Which contents are located within the superior mediastinum?
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What is the position of the left pulmonary artery in relation to the descending aorta?
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The right and left brachiocephalic veins are located immediately posterior to which structure?
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How is the inferior vena cava formed?
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How is the superior mediastinum defined superiorly?
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What is the primary function of the thymus gland located in the superior mediastinum?
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The transverse plane between which two landmarks separates the superior mediastinum from the inferior mediastinum?
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Study Notes
Mediastinum
- The mediastinum is a broad central partition separating the two pleural cavities.
- Boundaries: Anteriorly - Body of sternum, Posteriorly - Vertebral bodies of thoracic vertebrae, Inferiorly - Diaphragm, Superiorly - Thoracic aperture
- The superior and inferior mediastinum are separated by a transverse plane between the sternal angle and the intervertebral disc at T4/T5.
- The inferior mediastinum is further subdivided into anterior, middle, and posterior regions.
Superior Mediastinum
- Centrally located in the thoracic cavity and contains the pericardium, heart, great vessels, and nerves.
- Superior boundary: Oblique plane passing from jugular notch to superior border of T1; Inferior boundary: Transverse plane between sternal angle and intervertebral disc at T4/T5
- Lateral boundary: Pleural cavities on either side
- Anterior boundary: Posterior surface of the manubrium; Posterior boundary: Body of the first four thoracic vertebrae
Superior Mediastinum Contents
- Thymus: Most anterior component, immediately posterior to the manubrium, asymmetrical, bilobed structure involved in early immune system development
- Left and Right Brachiocephalic Veins: Immediately posterior to the thymus
- Left Superior Intercostal Vein: Passes over the left side of the aortic arch, situated lateral to the vagus nerve and medial to the phrenic nerve
- Trachea and Oesophagus: Trachea is midline and palpable in the jugular notch, Oesophagus posterior to the trachea, immediately anterior to the vertebral bodies
- Thoracic Duct: Major lymphatic vessel in the body that enters the superior mediastinum inferiorly and continues upwards
Anterior Mediastinum
- Superior boundary: Transverse plane between the sternal angle and intervertebral disc at T4/T5; Inferior boundary: Diaphragm
- Lateral boundary: Pleural cavities on either side; Anterior boundary: Body of the sternum; Posterior boundary: Pericardial sac
- Type 1 Sympathetic Trunk: Branches from upper 5 ganglia, has postganglionic sympathetic fibers, contains visceral afferent fibers, supply thoracic viscera.
- Type 2 Sympathetic Trunk: Branches from lower 7 ganglia, has preganglionic sympathetic fibers, contains visceral afferent fibers, supply abdominal and pelvic viscera.
Sympathetic Trunks
- Greater Splanchnic Nerve: Descends across vertebral bodies medially, ends in the coeliac ganglion, some fibers go straight to the medulla of the adrenal gland
- Lesser Splanchnic Nerve: Ends in the aorticorenal ganglion
- Least Splanchnic Nerve: Ends in the renal plexus
Vagus and Phrenic Nerves in the Mediastinum
Right Vagus Nerve
- Lies between the brachiocephalic trunk and right brachiocephalic vein
- Descends posteriorly towards the trachea and crosses the lateral surface of the trachea, passing posterior to the oesophagus
- Gives branches to the cardiac plexus, pulmonary plexus, and oesophageal plexus
Left Vagus Nerve
- Lies posterior to the left brachiocephalic vein, between the left common carotid and left subclavian arteries
- Lies deep to the parietal pleura, crosses the left side of the arch of the aorta, passing posterior to the root of the left lung
- Gives branches to the cardiac plexus, pulmonary plexus, and oesophageal plexus
Left Recurrent Laryngeal Nerve
- Branch of the left vagus nerve
- Arises at the inferior margin of the arch of the aorta and lies lateral to the ligamentum arteriosum
- Passes inferior to the arch of the aorta, entering the groove between the trachea and oesophagus
Right Phrenic Nerve
- Enters the mediastinum lateral to the vagus nerve
- Lies posterolateral to the right brachiocephalic vein and continues along the right side of the SVC
- Descends along the right side of the pericardial sac within the fibrous pericardium, anterior to the root of the right lung
- Passes through the diaphragm at the caval opening
Left Phrenic Nerve
- Enters the mediastinum lateral to the left vagus nerve
- Lies posterolateral to the left brachiocephalic vein
- Passes superficially to the left vagus nerve and left superior intercostal vein
- Follows the left side of the pericardial sac and lies anterior to the root of the left lung
- Pierces the diaphragm near the apex of the heart
Superficial Anatomy of the Heart
Pericardium
- Fibro-serous sac surrounding the heart and root of great vessels
- Fibrous Pericardium: Tough connective tissue outer layer, cone-shaped bag, apex is continuous with the adventitia of great vessels, base is attached to the central tendon of the diaphragm, anterior attachment to the sternum via sternopericardial ligaments
- Serous Pericardium: Thin, consists of two parts: Parietal and Visceral layers, between the two layers is the pericardial cavity filled with fluid, allows for relatively uninhibited movement of the heart, Parietal layer lines the fibrous pericardium, Visceral layer is adherent to the heart
- Reflections of Serous Pericardium: Superiorly - Surrounds the aorta and pulmonary trunk, Posteriorly - Surrounding veins
- Oblique Pericardial Sinus: J-shaped cul-de-sac formed by reflections around the veins
- Transverse Pericardial Sinus: Passage between the two sites of reflections, lies posterior to the ascending aorta and pulmonary trunk, anterior to the superior vena cava, superior to the left atrium
Vessels and Nerves
- Arterial: Internal thoracic artery, pericardiophrenic, musculophrenic, and inferior phrenic arteries, thoracic aorta.
- Venous: Azygos system of veins, superior phrenic vein, internal thoracic vein.
- Nervous: Vagus and Phrenic nerves, Sympathetic trunks.
External Sulci
Coronary Sulcus
- Encircles the heart and separates the atria from the ventricles.
- Contains the right coronary artery, small cardiac vein, coronary sinus, and circumflex branch of the left coronary artery.
Interventricular Sulci
- Anterior Interventricular Sulcus: On the anterior surface of the heart, contains the anterior interventricular artery and great cardiac vein
- Posterior Interventricular Sulcus: On the diaphragmatic surface of the heart, contains the posterior interventricular artery and middle cardiac vein
Great Vessels
Pulmonary Trunk
- Contained within the pericardial sac, covered by the visceral layer of the serous pericardium, associated with the ascending aorta in the same sheath.
- Arises from the conus arteriosus of the right ventricle at the opening of the pulmonary trunk and ascends moving posteriorly.
- Initially anterior and then to the left of the aorta.
- At the intervertebral disc between T5/T6 the pulmonary trunk divides into the right pulmonary artery and left pulmonary artery.
Aorta
- Ascending Aorta: Originates at the aortic orifice at the base of the left ventricle, level of the lower edge of the 3rd costal cartilage, continues to the level of the 2nd costal cartilage where it enters the superior mediastinum to become the arch of the aorta.
- Arch of Aorta: Begins as the ascending aorta emerges from the pericardial sac, courses superiorly, posteriorly, and to the left, ends at the T4/T5 vertebral level, and extends as high as the manubrium of the sternum.
Branches of the Arch of the Aorta
- Brachiocephalic Trunk: The most anterior branch, divides into the right common carotid artery and right subclavian artery at the level of the sternoclavicular joint.
- Left Common Carotid Artery: Ascends on the left of the trachea and supplies the left side of the head and neck.
- Left Subclavian Artery: Ascends on the left of the trachea and supplies the left upper limb.
Ligamentum Arteriosum
- Important in embryonic circulation, connecting the pulmonary trunk and arch of the aorta, allowing blood to bypass the lungs during development.
- Closes soon after birth and forms the ligamentum arteriosum.
Superior Vena Cava
- The lower half is encased in the pericardial sac.
- Passes through the fibrous pericardium at the 2nd costal cartilage.
- Begins by the union of the right and left brachiocephalic veins and drains into the right atrium.
- Receives the azygos vein immediately before entering the pericardial sac.
Inferior Vena Cava
- Enters the fibrous pericardium at T8.
- Formed at L5 by the union of the right and left common iliac veins.
- Ascends anterior to the vertebral column, on the right side of the abdominal aorta.
Aortopulmonary Window
- The left recurrent laryngeal nerve passes between the pulmonary artery and aorta.
- Any mass in this region may compress the nerve which leads to left vocal cord paralysis and hoarseness of voice.
Pericardial Effusion
- Normally, only a tiny amount of fluid exists in the pericardial cavity.
- Excess fluid within the pericardial sac compresses the heart, resulting in cardiac tamponade.
- This leads to biventricular failure.
- Fluid is removed with a needle to relieve symptoms.
Aortic Arch Anomalies
- A right-sided aortic arch occurs when the vessel courses to the right of the trachea and passes over the right main bronchus.
- This is sometimes associated with dextocardia (right-sided heart) and situs inversus (left-to-right inversion of the body's organs).
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Test your knowledge on the anatomy of the cardiovascular system with this quiz. Answer questions related to the structure and function of the heart, its surrounding components, and key arteries. Challenge yourself and enhance your understanding of cardiovascular anatomy!
