Anatomy of lungs

The lungs are essential respiratory organs located in the thoracic cavity, flanking the heart and mediastinum. They are primarily responsible for the exchange of oxygen and carbon dioxide between the air and the bloodstream. The anatomy of the lungs is both complex and designed to maximize efficiency in gas exchange.

Structure of lungs

External Anatomy

1) Number and Position

• Humans have two lungs, a right lung and a left lung, housed within the ribcage.

• The right lung is slightly larger and has three lobes, while the left lung has two lobes to accommodate the heart's position.

2) Lobes

• Right Lung: Divided into three lobes – superior, middle, and inferior – separated by the horizontal and oblique fissures.

• Left Lung: Divided into two lobes – superior and inferior – separated by the oblique fissure.

3) Pleura

• The lungs are encased in a double-layered membrane called the pleura:

  • Visceral Pleura: Directly covers the lung surface.

  • Parietal Pleura: Lines the inner chest wall and diaphragm.

• The pleural cavity (space between the layers) contains lubricating fluid for smooth lung movement during respiration.

4) Hilum

• The medial surface of each lung has an opening called the hilum, through which the bronchi, blood vessels, lymphatic vessels, and nerves enter and exit the lung.

Internal Anatomy

1) Bronchial Tree

• The trachea divides into:

  • Right and left main bronchi → branch into lobar bronchi → segmental bronchi → smaller bronchioles → terminal bronchioles.

2) Alveoli

• Terminal bronchioles connect to alveolar ducts, leading to alveolar sacs containing alveoli.

• Gas Exchange: Occurs in the alveoli, where oxygen diffuses into the blood and carbon dioxide diffuses out via a thin capillary network.

3) Blood Supply

• Bronchial Arteries: Provide oxygenated blood to lung tissues.

• Pulmonary Arteries: Deliver deoxygenated blood for oxygenation.

• Pulmonary Veins: Return oxygenated blood to the heart.

4) Lymphatics and Nerves

• Lungs have a lymphatic system for fluid removal and immune defense.

• The pulmonary plexus supplies nerves for bronchial regulation.

Function in Respiration

1) Ventilation

• The mechanical process of moving air into and out of the lungs, facilitated by the diaphragm and intercostal muscles.

2) Gas Exchange

• Takes place in the alveoli:

  • Oxygen diffuses into the blood.

  • Carbon dioxide diffuses out to be expelled.