Lungs - description, syntopy, borders and projection onto thoracic wall, vascular and nerve supply and lymphatics

Lungs Overview:

The lungs are the organs of respiration, located within the thorax on either side of the mediastinum. Their primary function is to oxygenate blood by bringing inspired air into close contact with oxygen-poor blood in the pulmonary capillaries.

### *Anatomical Position and Relations:*

The lungs lie within the thoracic cavity, encased in pleural cavities formed by the *visceral* and *parietal pleura. They are connected to the mediastinum via the **lung roots* (containing structures like bronchi, arteries, and veins).

Borders of the Lungs:

Anterior Border:

  - Formed where the *mediastinal* and *costal surfaces* meet.

  - The eft lung features the *cardiac notch*, created by the apex of the heart.

- Posterior Border

  - Smooth and rounded, it forms where the *costal* and *mediastinal surfaces* meet posteriorly.

- Inferior Border:

  - Separates the base of the lung from its *costal* and *mediastinal* surfaces. The inferior border sits above the diaphragm.

Projection of the Lungs onto the Thoracic Wall:

- *Anterior Border:*

  - Right lung runs close to the sternum from the clavicle down to the 6th rib.

  - Left lung deviates laterally at the *4th rib* to accommodate the *cardiac notch*.

- Inferior Border: Projects along the following landmarks:

  - *6th rib* at the *midclavicular line*.

  - *8th rib* at the *midaxillary line*.

  - *10th rib* posteriorly at the *scapular line*.

Lung Structure:

- Apex: The blunt superior end that projects above the 1st rib into the neck.

- Base: The concave inferior surface resting on the diaphragm, deeper on the right due to the liver.

- Lobes:

  - Right lung: has three lobes (superior, middle, inferior) separated by the *oblique* and *horizontal fissures*.

  - Left lung :has two lobes (superior, inferior) separated by the *oblique fissure*.

- Surfaces:

  - *Costal Surface:* Smooth and convex, faces the ribs.

  - *Mediastinal Surface:* Faces the mediastinum and contains the *hilum*.

  - *Diaphragmatic Surface:* Contacts the diaphragm and forms the lung's base.

- Hilum and Root:

  - The *hilum* is the wedge-shaped area where the *root of the lung* (bronchi, pulmonary vessels, lymphatics) enters.

Syntopy (Relations of Lung Surfaces to Surrounding Structures):

- Mediastinal Surface:

  - *Both lungs:* Groove for the *1st rib* and *subclavian artery*, cardiac impression.

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

  - *Left lung:* Grooves for the *aorta, **brachiocephalic vein*, and esophageal impression.

- Costal Surface: Related to the *ribs* and *intercostal muscles*.

- Diaphragmatic Surface:

  - Right lung: Contacts the *liver*

  - Left lung: Contacts the *stomach* and *spleen*.

Bronchopulmonary Segments:

Each lung lobe is further divided into bronchopulmonary segments, each supplied by a segmental bronchus. These segments are clinically significant as they are functionally independent units of the lung.

- *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, superior and inferior lingula.

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

Vasculature:

- *Pulmonary arteries* carry deoxygenated blood to the lungs for oxygenation.

- *Bronchial arteries* supply oxygenated blood to the lung tissue itself.

- *Bronchial veins* drain blood into the *azygos* and *accessory hemiazygos veins*.

Innervation:

- *Pulmonary plexus* supplies autonomic innervation.

  - *Parasympathetic (via Vagus Nerve):* Promotes bronchial constriction, mucus secretion, and vasodilation.

  - *Sympathetic (via Sympathetic Trunk):* Induces bronchial relaxation and vasoconstriction.

- *Visceral afferent fibers* conduct sensory information, including pain.

Lymphatic Drainage:

- *Superficial (subpleural) lymphatic plexus* drains the lung parenchyma.

- *Deep lymphatic plexus* drains structures at the lung root.

- Both plexuses drain into the *tracheobronchial nodes*.

summary:

The lungs are crucial for oxygenating blood and are organized into distinct anatomical units like lobes and bronchopulmonary segments. Their position and projection onto the thoracic wall are important in clinical settings for physical examination and imaging. The lungs' complex relationships with surrounding mediastinal structures, their vascular supply, innervation, and lymphatic drainage, contribute to their essential function in respiration.