UNDERSTANDING THE ANATOMY OF MEDIASTINUM AND PERICARDIUM

The mediastinum is a central compartment within the thoracic cavity, bordered by the sternum in front, the vertebral column in back, and the lungs on each side. It is divided into three major subdivisions: anterior, middle, and posterior mediastinum, based on their anatomical location and the structures they contain.

1. Anterior Mediastinum: This region is located between the sternum and the pericardium (the sac that surrounds the heart). It contains mostly fat, lymph nodes, and some thymic tissue. The thymus gland, which plays a crucial role in the development of the immune system during childhood, is also located in this region.
2. Middle Mediastinum: This region contains the heart and the roots of the great vessels, including the superior and inferior vena cava, the pulmonary trunk, and the pulmonary veins. The pericardium encloses the heart and is part of this region.
3. Posterior Mediastinum: This region is located behind the pericardium and extends from the posterior border of the heart to the vertebral column. The posterior mediastinum contains the esophagus, thoracic duct, azygos vein, and sympathetic trunk. It also houses the spinal cord and nerve roots of the thoracic region.

Overall, the divisions of the mediastinum help to categorize and locate the structures within this important region of the thorax, aiding in the diagnosis and management of various conditions affecting the heart, lungs, and surrounding structures.

 

The heart is a muscular organ that pumps blood throughout the body. It is located in the chest cavity between the lungs, slightly to the left of the midline of the body.

The outline of the heart can be divided into four chambers: the right atrium, right ventricle, left atrium, and left ventricle. The right atrium and right ventricle are located on the right side of the heart, while the left atrium and left ventricle are located on the left side of the heart.

The normal position of the heart is tilted slightly to the left and sits in the middle of the chest, with the base of the heart located at the level of the second rib and the apex of the heart pointing towards the left hip. The heart is surrounded by a protective sac called the pericardium, which helps to cushion and protect the heart from injury.

 

The heart is located in the middle mediastinum, which is the central compartment of the thoracic cavity. It is surrounded by other structures that help support and protect it.

The heart is composed of four chambers: the right and left atria and the right and left ventricles. The atria are located superiorly, while the ventricles are located inferiorly. The right atrium receives deoxygenated blood from the body through the superior and inferior vena cava, while the left atrium receives oxygenated blood from the lungs through the pulmonary veins.

The right ventricle pumps deoxygenated blood to the lungs via the pulmonary artery, while the left ventricle pumps oxygenated blood to the rest of the body via the aorta.

The heart is also surrounded by several other structures that help support and protect it. The pericardium is a double-layered sac that encases the heart and helps reduce friction as the heart beats. The great vessels, including the aorta and pulmonary artery, are located superior to the heart, while the pulmonary veins and the inferior vena cava are located inferior to the heart.

In summary, the heart is composed of four chambers and is surrounded by several other structures, including the pericardium and great vessels. Understanding the location and function of these structures is important in the diagnosis and treatment of cardiovascular diseases.

 

The mediastinum is the central compartment of the thoracic cavity located between the lungs. It contains a variety of structures including:

• Heart: The heart is the main organ located in the mediastinum, which pumps blood throughout the body.
• Great vessels: These include the superior and inferior vena cava, aorta, pulmonary trunk, and their branches, which transport blood to and from the heart.
• Thymus: The thymus is a gland located in the superior mediastinum that is involved in the development of the immune system.
• Trachea: The trachea, also known as the windpipe, is a tube that connects the larynx to the lungs and passes through the mediastinum.
• Esophagus: The esophagus is a muscular tube that connects the pharynx to the stomach and passes through the posterior mediastinum.
• Nerves: The mediastinum contains several important nerves, including the vagus nerve, phrenic nerve, and sympathetic trunk.
• Lymph nodes: The mediastinum contains lymph nodes, which are part of the lymphatic system and help to fight infections and diseases.
• Connective tissue: The mediastinum contains various connective tissues that provide support and structure to the organs and vessels in the region.
• Fat: Adipose tissue is present in the mediastinum, which helps to protect and cushion the organs and vessels in the region.
• Other structures: Other structures present in the mediastinum include the thoracic duct, pericardium, and various blood vessels and nerves that supply the chest wall and diaphragm.

 

The pericardium is a double-layered, fibrous sac that surrounds and protects the heart. It consists of two layers: the outer fibrous pericardium and the inner serous pericardium.

The fibrous pericardium is the tough, outer layer of the pericardium. It is composed of dense connective tissue and provides a protective layer around the heart. The fibrous pericardium is attached to the central tendon of the diaphragm inferiorly and blends with the adventitia of the great vessels entering and leaving the heart.

The serous pericardium is the inner layer of the pericardium, and it consists of two layers: the parietal and visceral layers. The parietal layer lines the fibrous pericardium, while the visceral layer (also known as the epicardium) covers the surface of the heart. The space between the parietal and visceral layers is called the pericardial cavity, which contains a small amount of fluid that lubricates the heart as it beats.

Together, the fibrous and serous pericardium create a tough, protective sac around the heart that helps prevent injury and keeps the heart in place within the chest cavity.

 

The pericardium is a double-layered sac that surrounds the heart and is attached to the diaphragm and the root of the great vessels. The outer layer of the pericardium, called the fibrous pericardium, is a tough, fibrous membrane that attaches to the diaphragm inferiorly and blends with the adventitia of the great vessels superiorly.

The inner layer of the pericardium, called the serous pericardium, consists of two layers: the parietal layer, which lines the fibrous pericardium, and the visceral layer, which covers the surface of the heart. The space between the parietal and visceral layers is called the pericardial cavity and is filled with a small amount of fluid that lubricates the heart as it beats.

The pericardium is attached to the diaphragm by the phrenicopericardial ligament, which runs from the central tendon of the diaphragm to the fibrous pericardium. The pericardium is also attached to the root of the great vessels by the transverse pericardial sinus, a space between the ascending aorta and pulmonary trunk and the superior vena cava that allows blood to flow freely between them. Additionally, the pericardium is anchored to the posterior mediastinum by the posterior pericardiacophrenic ligament, which runs from the fibrous pericardium to the thoracic vertebrae.

 

The pericardial space is a fluid-filled sac that surrounds the heart and contains the heart, the roots of the great vessels, and the proximal portions of the aorta, pulmonary artery, and superior vena cava. The pericardial space is composed of two layers: the outer fibrous pericardium and the inner serous pericardium. The serous pericardium is further divided into two layers, the parietal layer and the visceral layer. The space between the parietal and visceral layers is the pericardial cavity, which contains pericardial fluid.

The pericardial fluid is a thin, serous fluid that is produced by the pericardial membranes. The fluid serves as a lubricant to reduce friction between the heart and the surrounding structures as they move during cardiac contractions. In normal conditions, the volume of pericardial fluid is about 20 to 50 mL.

The pericardial space has four recesses: the transverse sinus, the oblique sinus, the left atrial appendage recess, and the pulmonary vein recess. The transverse sinus is a space located posterior to the ascending aorta and anterior to the superior vena cava. The oblique sinus is located posterior to the left atrium and anterior to the esophagus. The left atrial appendage recess is a space between the pericardium and the left atrial appendage. The pulmonary vein recess is located between the pericardium and the pulmonary veins.

The pericardial space and its recesses play an important role in cardiac function, as they allow for the expansion and contraction of the heart during each cardiac cycle. The pericardial fluid also provides a cushion for the heart, protecting it from trauma or injury. In pathological conditions, such as pericarditis, the accumulation of excess fluid or inflammation can cause compression of the heart and compromise its function.

 

The fibrous pericardium is innervated by branches of the phrenic nerve, which is formed by the cervical nerve roots C3, C4, and C5. The phrenic nerve descends through the thorax along with the internal thoracic vessels, and it gives off branches that supply the fibrous pericardium.

The sensory fibers of the phrenic nerve provide pain and touch sensation to the fibrous pericardium. These fibers transmit information about the pericardium to the brain, allowing the body to detect and respond to any damage or inflammation in the pericardial sac.

In addition to innervation by the phrenic nerve, the fibrous pericardium may also receive sympathetic innervation from the sympathetic trunk and parasympathetic innervation from the vagus nerve. However, the functional significance of these innervations is less clear.