Development and Working of Lungs

Introduction

The lungs are the vital organs of the respiratory system. A pair of lungs are situated in the center of the chest on either side of the heart. The prime role of the lungs is gaseous exchange. It also helps maintain homeostasis, protects the body from harmful substances, and helps speech function.

What Are Lungs?

The lungs form the significant organs of the respiratory system. The lungs are spongy and pinkish-gray in color. The lungs are covered by thin membranous coverings called pleura. Two layers of pleura are present. The space between the parietal and visceral pleura is called the pleural space, in which a thin layer of pleural fluid is present to act as a lubricant during the expansion and contraction of the lungs. Two lungs are present on either side of the chest in the thoracic cavity. The right and left lungs are part of the lower respiratory tract.

How Do Lungs Develop?

Lung development starts in the third week of gestation. The lungs develop as an outpouching of the foregut. The foregut is a tube that later forms the upper part of the digestive tract. The fetal lungs are held in the amniotic sac and do not function for breathing. Instead, the blood from the lungs is diverted through the ductus arteriosus. This closes at birth, air enters the lungs, and respiration begins. Lung development is complete only during early childhood.

What Are the Parts of the Lungs?

The lungs are situated in the center of the chest. The lungs are conical with a narrowly rounded apex and a broad concave base. The right and left lungs have a central recession called the hilum. Hilum allows the blood vessels and airways to enter the lungs. The lungs form the lower respiratory tract and accommodate the bronchi that branch from the trachea. The bronchus terminates in the alveoli, forming the lungs' functional tissue. Both lungs are divided into sections called lobes. The lobes are divided into segments which are further divided into lobules.

• Right Lung - The right lung is divided into three lobes: one oblique fissure and one horizontal fissure. It is divided into the upper, middle, and lower lobes. The location of the heart creates an impression on the mediastinal surface of the lung called a cardiac impression.

• Left Lung - The left lung is divided into upper and lower lobes by the oblique fissure. It does not have a middle lobe but a projection from the upper lobe called a lingula. The left lung has a sizeable cardiac impression on the mediastinal surface.

• Bronchi - Bronchi are the tubes that branch from the trachea. The right and left bronchi direct air into the right and left lungs. They further divide into smaller branches called bronchioles. The bronchioles give rise to alveolar ducts that lead to the air sacs containing two or more alveoli.

What Are the Variations in the Lungs?

Anatomical variations are seen in the lobes of the lungs. A horizontal interlobar fissure can be incomplete or absent in some cases. An accessory fissure can be present sometimes. An incomplete oblique fissure may be present in the left lungs. In rare cases, the fissure is absent, or an extra fissure is present, which results in two lobes in the right lung or a left lung with three lobes. Other variations, like congenital missing of one or both lungs, are noted.

How Does the Respiratory System Function?

The trachea is the primary airway that receives air from the pharynx and travels through the bronchial tubes to enter the lungs. This branches into secondary and tertiary bronchi and further into smaller bronchioles. The bronchioles supply air to the alveoli through the alveolar ducts and aid in exchanging gasses. The oxygen breathed in diffuses into the enveloping capillaries and circulation through the alveolar walls. Likewise, carbon dioxide from the bloodstream diffuses into the lungs and is breathed out.

How Do the Lungs Function?

• Gas Exchange - The primary function of the lungs is gaseous exchange. The lungs help supply oxygen to the body and remove carbon dioxide. The pulmonary artery carries the oxygen-poor blood from the heart to the lungs for oxygenation. The oxygenated blood from the lungs is carried back to the heart by the pulmonary veins for systemic circulation. The muscles of respiration help in the contraction and relaxation of the lungs during inspiration and expiration.

• Protection - The respiratory epithelium that lines the respiratory tract has hair-like projections called cilia that prevent infections by mucociliary clearance. The bacteria and the dust particles are caught by the mucus and cleared by the cilia. The lining of the lungs produces immunoglobulin A and protects against infections. The mucus produced by the goblet cells also contains various antimicrobial compounds like defensins, antiproteases, and antioxidants. The lining of the lungs also contains immune cells that destroy pathogens and activate the immune system.

• Other Functions - The lungs play a role in maintaining acid-base homeostasis by removing carbon dioxide during breathing. It helps regulate blood pressure as a part of the renin-angiotensin system. The lungs play a role in the absorption, modification, or excretion of drugs and other substances. It helps prevent stroke by filtering small blood clots from veins and preventing their entry into the arteries. Finally, it plays a vital role in a speech by providing airflow to produce vocal sounds.

What Affects the Lung Function?

Lungs can be affected by various diseases and disorders. Infection, inflammation, changes in the blood supply, obstruction, cancers, tumors, congenital anomalies, pleural space changes, and injuries can affect lung function. Cardiac disorders and other organ system disorders can also affect lung function. Lung function tests, plethysmographs, spirometry, and diffusion capacity testing are some tests performed to examine lung functions.

Conclusion

The lungs are the significant organs of the respiratory system. They are self-cleaning organs. Oxygen is essential for every cell in the human body to function. Lungs play a significant role in human health by helping exchange gasses. They also play a significant role in defense mechanisms. Therefore, the healthy functioning of the lungs is essential for healthy living.