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    Lungs

    Reviewed by our medical team

    Main organs of respiration.

    1. Overview

    The lungs are paired, spongy, air-filled organs that are the central components of the human respiratory system. They are responsible for facilitating the exchange of oxygen and carbon dioxide between the atmosphere and the bloodstream. Housed in the thoracic cavity, the lungs are divided into lobes and further into bronchopulmonary segments, allowing for compartmentalized function and efficient gas exchange. Their structure and function are optimized for continuous respiration, even under varying physiological demands.

    2. Location

    The lungs are located in the thoracic cavity, one on each side of the mediastinum. They are surrounded by the pleural cavities and protected by the rib cage. Specifically:

    • Right lung: Lies to the right of the heart and mediastinum

    • Left lung: Lies to the left of the heart and mediastinum, with a cardiac notch to accommodate the heart

    The lungs rest on the diaphragm inferiorly and extend superiorly above the first rib into the root of the neck (apex of the lung).

    3. Structure

    Gross Anatomy

    • Right lung: Has 3 lobes (superior, middle, inferior) separated by the horizontal and oblique fissures

    • Left lung: Has 2 lobes (superior, inferior) separated by the oblique fissure, and includes the lingula

    Hilum

    The medial surface of each lung contains the hilum, through which the following structures enter and exit:

    • Primary bronchi

    • Pulmonary arteries and veins

    • Lymphatic vessels

    • Nerves (pulmonary plexus)

    Internal Architecture

    • Bronchial tree: Begins with the trachea, branching into bronchi, bronchioles, terminal bronchioles, and respiratory bronchioles

    • Alveoli: Tiny sac-like structures where gas exchange occurs

    • Pleura: Each lung is enclosed in a double-layered pleural membrane (visceral and parietal pleura)

    Blood Supply

    • Pulmonary circulation: Pulmonary arteries bring deoxygenated blood from the right heart; pulmonary veins return oxygenated blood to the left heart

    • Bronchial circulation: Supplies oxygenated blood to lung tissue itself

    4. Function

    The lungs perform several essential functions:

    • Gas exchange: Exchange of oxygen and carbon dioxide occurs in the alveoli across the respiratory membrane

    • Air conduction: Passage of air from the external environment to the alveoli via the bronchial tree

    • Protective filtering: Mucociliary escalator traps and removes particles and pathogens

    • Vocalization: Airflow through the larynx enables speech

    5. Physiological Role(s)

    The lungs contribute to several broader physiological processes:

    • Acid-base regulation: By controlling CO₂ exhalation, they help maintain blood pH

    • Blood pressure regulation: Via conversion of angiotensin I to angiotensin II in the pulmonary endothelium (RAAS pathway)

    • Defense: Immune cells in the alveoli and airways protect against pathogens

    • Temperature and water balance: Humidify and warm incoming air; participate in water loss through exhalation

    6. Clinical Significance

    Respiratory Infections

    • Pneumonia: Inflammation of lung parenchyma due to infection, seen as lobar or patchy opacities on imaging

    • Tuberculosis: Commonly affects the upper lobes; may cause cavitation and fibrosis

    Chronic Obstructive Pulmonary Disease (COPD)

    A group of progressive lung diseases including emphysema and chronic bronchitis, often due to smoking, causing airflow limitation and alveolar destruction.

    Asthma

    A reversible airway disease marked by bronchospasm, inflammation, and mucous production, resulting in wheezing and dyspnea.

    Lung Cancer

    Primary malignancies may arise in any lobe. Staging and treatment (surgery, chemotherapy, radiotherapy) depend on the lobe involved and spread.

    Pleural Disorders

    • Pneumothorax: Air in the pleural cavity causing lung collapse

    • Pleural effusion: Fluid accumulation in the pleural space

    Pulmonary Embolism

    Obstruction of pulmonary arteries by thrombus, usually from deep veins in the leg. Can be life-threatening if large or untreated.

    Atelectasis

    Collapse of part or all of a lung due to blockage, compression, or surfactant deficiency. Common postoperatively or in immobile patients.

    Lung Transplantation

    In end-stage lung disease, one or both lungs may be replaced surgically. Donor-recipient size and lobe matching is critical.

    Did you know? The average adult breathes in about 10,000 liters of air every day.