What Are the Main Divisions and Functions of the Mediastinum?
Mediastinum, the anatomic region located between the lungs contains all the principal tissues and organs of the chest except the lungs. It extends from the sternum, or breastbone, back to the spinal column and is bounded laterally by the pericardium, the membrane enclosing the guts, and therefore the mediastinal pleura, membranes that are continuous with those lining the thoracic cage. The mediastinum may be a division of the thoracic cavity; it contains the guts, thymus, portions of the oesophagus and trachea, and other structures. For clinical purposes, it's traditionally divided into the anterior, middle, posterior, and superior regions.
One of the very first structures which may be observed when the external structure of the guts is viewed is that the pericardium.
Pericardium
The human heart is placed to the left of the chest and is filled within a fluid-filled cavity described as the pericardial cavity. The walls and lining of the pericardial space are made from a membrane referred to as the pericardium.
The pericardium may be a fibre membrane found as an external covering around the heart. It protects the heart by producing a serous fluid, which serves to lubricate the heart and stop the friction between the encompassing organs. The pericardium also helps by holding the heart in its position and by maintaining a cavity for the heart to expand itself when it's full. The pericardium has two exclusive layers-
Visceral Layer: It directly covers the surface of the heart.
Parietal Layer: It forms a sac around the outer region of the heart that contains the fluid within the pericardial space.
Structure of the Heart Wall
The heart wall is formed from 3 layers, namely:
Epicardium – Epicardium is that the outermost layer of the guts. It is composed of a thin-layered membrane that serves to lubricate and protect the outer section.
Myocardium – this is often a layer of muscle tissue, and it constitutes the centre layer wall of the heart. It contributes to the thickness and is liable for the pumping action.
Endocardium – it's the innermost layer that lines the inner heart chambers and covers the guts valves.
Function of Heart
The function of the heart in any organism is to take care of a continuing flow of blood throughout the body. This replenishes oxygen and circulates nutrients among the cells and tissues. Also, because the human heart may be a homologous organ, it functions no differently from the other vertebrates that possess a heart. Following are the main functions of the heart:
One of the first functions of the human heart is to pump blood throughout the body.
Blood delivers oxygen, hormones, glucose and other components to varied parts of the body, including the human heart.
The heart also ensures that adequate vital sign is maintained within the body
There are two sorts of circulation within the body, namely circulation and circulation.
Human Respiratory System
The different human respiratory system parts that play different roles. The different parts of the respiratory system anatomy are explained below along with their functions.
1. Nose
It is one of the important respiratory system organs that possess two exterior nostrils divided by septum. The Septum is a cartilaginous structure that divides the left nostril from the right nostril. Numerous tiny hair follicles are present that cover the interior nostril’s lining and thus act as the body’s first line of defence against foreign bodies (pathogens). The hair also provides humidity for inhaled air.
2. Larynx
Also known as the voice box or Adam’s apple, it is situated in the top of the neck facilitating the action of breathing. It is in the form of two cartilaginous chords and is located at the point of conjuction between the pharynx and trachea. It acts by rising or falling during the swallowing process and generates sound when air passes through the hollow portion in the middle. It also protects the trachea against food aspiration.
3. Pharynx
It is the part of the throat present behind the nasal cavity and the mouth, and above the larynx and oesophagus. It is a wide hollow space and a common path for air and food. It doesn’t allow the food particles entry into the windpipe. There is elastic cartilage between the oesophagus and the larynx that acts as a switch to allow the passage of air into the airway to the lungs and food into the gastrointestinal tract.
4. Trachea
It is the windpipe which is a tubular structure of about 4 inches long and half an inch in diameter. This airway system carries oxygen-rich air to the lungs. It begins under the larynx and runs down the neck through the breastbone or sternum. Its outer walls consist of C-shaped rings which are cartilaginous and provide hardness to it and can also expand completely. The trachea divides into smaller tubes called bronchi.
5. Bronchi
The trachea splits into smaller tubes called bronchi which is the main passageway into the lungs. It is further divided into secondary and tertiary bronchioles and then again into small air-sacs known as alveoli. Alveoli are minute air sacs with thin walls that enable the exchange of gases into or away from the bloodstream.
6. Lungs
It is the spongy air-filled chief organ of the respiratory system anatomy in humans and other vertebrates. Located in the thoracic cavity of the chest on either side of the heart, they are present as a pair and help in exchanging gases between the bloodstream and the air. The right lung appears to be heavier and bigger than the left lung.
FAQs on Mediastinum: Structure, Function, and Importance
1. What is the mediastinum and where is it located in the human body?
The mediastinum is the central compartment of the thoracic cavity, situated between the two pleural sacs that enclose the lungs. It extends from the sternum (breastbone) in the front to the thoracic vertebrae in the back, and from the superior thoracic aperture (top opening of the rib cage) down to the diaphragm.
2. What is the primary function of the mediastinum?
The mediastinum does not have a single physiological function like an organ does. Instead, its primary role is to serve as a protected passageway and housing unit for several vital structures. It acts as a conduit for the oesophagus, trachea, and major blood vessels, while also containing and protecting the heart within the pericardial sac.
3. What are the major structures contained within the mediastinum?
The mediastinum houses a collection of vital organs and structures. Key contents include:
- Heart and Pericardium: The heart and its protective sac.
- Great Vessels: The aorta, superior and inferior vena cava, and pulmonary arteries and veins.
- Trachea: The windpipe, before it bifurcates into the bronchi.
- Oesophagus: The tube connecting the pharynx to the stomach.
- Thymus Gland: A key organ of the immune system, prominent in children.
- Nerves: The phrenic nerves, vagus nerves, and sympathetic trunk.
- Lymphatics: The thoracic duct and numerous lymph nodes.
4. What are the anatomical borders and major divisions of the mediastinum?
Anatomically, the mediastinum is divided for descriptive purposes. A transverse plane running from the sternal angle (angle of Louis) to the intervertebral disc between the T4 and T5 vertebrae divides it into two main parts:
- Superior Mediastinum: The upper compartment, located above the heart.
- Inferior Mediastinum: The lower compartment, which is much larger and contains the heart.
The entire mediastinum is bordered by the sternum anteriorly, thoracic spine posteriorly, thoracic inlet superiorly, diaphragm inferiorly, and the mediastinal pleura laterally.
5. How is the inferior mediastinum further subdivided, and why is this important?
The inferior mediastinum is further divided into three parts based on its relationship to the pericardium (the sac containing the heart):
- Anterior Mediastinum: A small space located between the sternum and the pericardium.
- Middle Mediastinum: The most important section, containing the heart, pericardium, and the roots of the great vessels.
- Posterior Mediastinum: The area behind the pericardium and in front of the vertebrae, containing the oesophagus and thoracic aorta.
This subdivision is clinically significant as it helps surgeons and radiologists precisely locate pathologies like tumours, cysts, or inflammation.
6. What is the difference between the mediastinum and the pericardium?
The key difference lies in their definition and scope. The mediastinum is a large anatomical region or compartment within the chest that contains multiple organs. In contrast, the pericardium is a specific fibroserous sac that encloses only one organ—the heart—and the roots of the great vessels. Therefore, the pericardium is a structure located *within* the middle part of the inferior mediastinum.
7. Is the mediastinum considered a true body cavity? Why or why not?
No, the mediastinum is not considered a true body cavity. True serous cavities, like the pleural or pericardial cavities, are lined with a serous membrane and contain a thin layer of fluid to reduce friction. The mediastinum, however, is a space filled with loose connective tissue, organs, vessels, and nerves. It is a region that separates the two pleural cavities rather than being a cavity itself.
8. Which important gland is located in the mediastinum, and what is its role?
The thymus gland is a crucial lymphoid organ located in the superior and anterior parts of the mediastinum. Its primary role is essential for the immune system, as it is the site where T-lymphocytes (T-cells) mature. The thymus is largest and most active during childhood and adolescence, after which it begins to shrink and is replaced by fatty tissue in a process called involution.
9. Why is understanding the mediastinum's anatomy clinically important in medicine?
Understanding the mediastinum is critical for diagnosing and treating various medical conditions. For instance, a mediastinal shift, where the entire compartment is pushed to one side due to pressure from a collapsed lung (pneumothorax), is a medical emergency. Furthermore, it is a common site for tumours (like thymomas and lymphomas) and inflammation (mediastinitis), which can be life-threatening. Its complex anatomy is also central to cardiothoracic surgery.
