Lungs - description, syntopy, bronchopulmonary segments

Lungs Overview:

- The lungs are the primary organs of respiration located within the thorax, on either side of the mediastinum.

- They oxygenate blood by bringing inspired air into contact with oxygen-poor blood in the pulmonary capillaries.

Anatomical Position and Relations:

- The lungs are housed in the thoracic cavity and surrounded by the pleural cavity formed by visceral and parietal pleura.

- The right lung and left lung each have a medial surface that lies close to various mediastinal structures:

  - Right lung: Close to the heart, esophagus, inferior vena cava, superior vena cava, and azygous vein.

  - Left lung: Close to the heart, arch of the aorta, thoracic aorta, and esophagus.

Lung Structure:

Each lung has an apex, base, three surfaces, and three borders, with the *left lung* being smaller due to the presence of the heart.

Key Features:

- Apex: The blunt superior part extending above the 1st rib.

- Base: The inferior surface resting on the diaphragm.

- Lobes: The right lung has three lobes (superior, middle, inferior), while the left lung has two lobes (superior, inferior).

- Surfaces:

  - *Mediastinal surface: Faces the mediastinum, where the hilum is located.

  - *Diaphragmatic surface: Concave, deeper in the right lung due to the liver.

  - *Costal surface: Smooth and convex, related to the chest wall and ribs.

- Borders:

  - Anterior border: Convergence of mediastinal and costal surfaces. The left lung has a cardiac notch.

  - Inferior border: Separates the base from the other surfaces.

  - Posterior border: Smooth and rounded, where the costal and mediastinal surfaces meet.

- Hilum and Root:

  - The hilum is the wedge-shaped area where the root enters the lung. The root contains bronchi, pulmonary arteries, veins, and other structures.

Lobes and Fissures:

- Right lung:

  - Three lobes: Superior, middle, inferior.

  - Two fissures:

    - Oblique fissure: Runs supero-posteriorly.

    - Horizontal fissure: Runs at the level of the 4th rib.

- Left lung:

  - Two lobes: Superior, inferior.

  - One fissure: *Oblique fissure* similar to the right lung.

Syntopy (Relations of the Lungs):

- Mediastinal surface:

  - Both lungs have grooves for the 1st rib and subclavian artery and a cardiac impression.

  - Right lung: Grooves for the esophagus, superior vena cava, and azygos vein.

  - Left lung: Grooves for the brachiocephalic vein, aorta, and esophagus.

- Costal surface: Impressions for the ribs.

- Diaphragmatic surface: Contacts the diaphragm.

  - Left lung: Contacts the stomach and spleen.

  -Right lung: Contacts the liver.

Bronchopulmonary Segments:

Each lobe of the lung is further divided into bronchopulmonary segments, which are supplied by a segmental bronchus.

- Right lung:

  - Superior lobe: Apical, posterior, anterior.

  - Middle lobe: Lateral, medial.

  - Inferior lobe: Superior, medial basal, anterior basal, lateral basal, posterior basal.

- Left lung:

  - Superior lobe: Apico -posterior, anterior, lingula (superior, inferior).

  - Inferior lobe: Superior, medial basal, anterior basal, lateral basal, posterior basal.

Vasculature:

- Pulmonary arteries supply deoxygenated blood to the lungs.

- Bronchial arteries supply oxygenated blood to lung tissue.

- Bronchial veins drain blood, with the right vein draining into the azygous vein and the left vein into the accessory hemiazygous vein.

Innervation:

- Pulmonary plexus provides both parasympathetic and sympathetic innervation:

  - Parasympathetic (Vagus Nerve): Stimulates secretion from club cells, contraction of bronchial smooth muscle, and vasodilation of pulmonary vessels.

  - Sympathetic (Sympathetic Trunk): Stimulates relaxation of bronchial smooth muscle and vasoconstriction of pulmonary vessels.

- Visceral afferents conduct pain sensations to the sensory ganglia of the vagus nerve.

Lymphatic Drainage:

- Subpleural lymphatic plexus drains the lung parenchyma.

- Deep lymphatic plexus drains the root of the lung.

- Both drain into the *tracheobronchial nodes.

Conclusion:

The lungs, complex organs responsible for respiration, exhibit unique structural and functional features. Their relationships with surrounding mediastinal structures, segmental organization, blood supply, nerve innervation, and lymphatic drainage all contribute to their essential role in oxygenating blood.