The Mediastinum and Heart: Anatomy, Vessels, and Innervation

What is the mediastinum?

The central compartment of the thoracic cavity that contains all thoracic viscera except the lungs.

What are the two portions of the mediastinum?

Superior Mediastinum and Inferior Mediastinum.

What structures are found in the superior mediastinum?

Thymus, left and right brachiocephalic veins, superior vena cava, arch of the aorta, vagus nerves, phrenic nerves, recurrent laryngeal nerve, trachea, esophagus, and thoracic duct.

What is the most anterior structure in the superior mediastinum?

The thymus.

What is the function of the thymus?

It is a primary lymphoid organ that is gradually replaced by fat post-puberty.

Where do the left and right brachiocephalic veins form?

At the junction between the internal jugular vein and subclavian veins.

What does the superior vena cava join?

The right atrium at the level of the right 3rd costal cartilage.

What are the major branches of the arch of the aorta?

Brachiocephalic trunk, left common carotid artery, and left subclavian artery.

What is the role of the vagus nerve in the mediastinum?

It provides parasympathetic innervation to the thoracic viscera and supplies the esophagus, cardiac plexus, and pulmonary plexus.

What is the function of the phrenic nerves?

They provide motor and sensory innervation to the diaphragm.

What does the left recurrent laryngeal nerve arise from?

It arises from the left vagus nerve near the arch of the aorta.

What is the trachea's anatomical position?

It is a midline structure that divides into the right and left bronchi between the sternal angle and vertebral level T4/5.

What is the esophagus?

A fibromuscular tube that extends from the pharynx to the stomach, located posterior to the trachea.

What is the thoracic duct?

The major lymphatic vessel in the body that drains into the venous angle between the left subclavian vein and left internal jugular vein.

What are the subdivisions of the inferior mediastinum?

Anterior mediastinum, middle mediastinum, and posterior mediastinum.

What contents are found in the anterior mediastinum?

Remnants of the thymus, lymph nodes, connective tissue, and fat.

What does the middle mediastinum contain?

The pericardium, heart, origins of the great vessels, arch of the azygos, and main bronchi.

What is the pericardium?

A double-walled fibrous sac that covers the heart and great vessels.

What are the two layers of the serous pericardium?

Parietal layer and visceral layer.

What is the function of the fibrous pericardium?

It helps to retain the heart in its position and limits cardiac distension.

What is the relationship of the trachea and esophagus in the mediastinum?

The trachea is anterior to the esophagus.

What is the significance of the azygos vein in relation to the superior vena cava?

The azygos vein drains into the superior vena cava before it enters the pericardial sac.

What anatomical structures run parallel through the superior thoracic aperture?

The trachea, esophagus, left recurrent laryngeal nerve, and thoracic duct.

What is the visceral layer of the serous pericardium?

It adheres to the heart and forms an outer covering.

What is the pericardial cavity?

A narrow space between the two layers of serous pericardium that contains a small amount of fluid.

What is the function of the pericardial fluid?

It allows for uninhibited movement of the heart.

What artery supplies the pericardium?

Pericardiophrenic artery, a branch off the internal thoracic artery.

Which nerve supplies sensory innervation to the pericardium?

Phrenic nerve (C3, 4, 5).

What is the shape of the heart?

Pyramid-shaped.

What are the three surfaces of the heart?

Anterior (sternocostal), inferior (diaphragmatic), and left (pulmonary).

What are the four borders of the heart?

Right, inferior, left, and superior.

How many chambers does the heart have?

The heart has two sides and four chambers: right atrium, right ventricle, left atrium, and left ventricle.

What separates the atria and ventricles in the heart?

Atrioventricular (AV) valves.

What is the right AV valve also known as?

Tricuspid valve.

What is the left AV valve also known as?

Mitral valve or bicuspid valve.

What is the fibrous skeleton of the heart?

Fibrous rings that provide attachment for the leaflets of the valves and act as an electrical insulator.

What is the fossa ovalis?

A remnant of the embryonic foramen ovale located in the right atrium.

What is the function of the foramen ovale?

It allows oxygenated blood to bypass the nonfunctional lungs in the fetus.

What are pectinate muscles?

Ridges found in the wall of the right atrium that extend into the right auricle.

What are trabeculae carneae?

Ridges in the walls of the ventricles.

What is the role of chordae tendineae?

They connect papillary muscles to the cusps of the valves to prevent prolapse.

What is the conus arteriosus?

The outflow tract of the right ventricle leading to the pulmonary trunk.

What is the function of the pulmonic valve?

It is the valve between the right ventricle and the pulmonary artery.

What does the left atrium primarily receive?

Oxygenated blood from the pulmonary veins.

What is the aortic semilunar valve?

The valve located between the left ventricle and the aorta.

What is the typical blood flow through the heart?

Deoxygenated blood enters the right atrium, flows to the right ventricle, is pumped to the lungs, returns oxygenated to the left atrium, flows to the left ventricle, and is pumped to the body.

What are coronary arteries?

Arteries that supply blood to the myocardium of the heart.

What is the right coronary artery's primary function?

It supplies the right atrium, most of the right ventricle, and the diaphragmatic surface of the left ventricle.

What is heart dominance?

It is defined by which coronary artery gives rise to the majority of the posterior interventricular artery.

What is the coronary sinus?

The confluence of cardiac veins that drains into the right atrium.

What is the function of the SA node?

It initiates and regulates the cardiac impulse, acting as the heart's pacemaker.

What is the AV node's role?

It receives impulses from the SA node and distributes them through the AV bundle.

What are thoracic splanchnic nerves?

Nerves that arise from the lower thoracic ganglia and supply abdominal and pelvic viscera.

What are the four locations where the esophagus can be compressed?

1. Junction with pharynx, 2. Superior mediastinum (crossed by aorta), 3. Posterior mediastinum (crossed by left main bronchus), 4. Esophageal hiatus in diaphragm.