Human Respiratory System Anatomy

Conducting Zone

• Nose, pharynx, larynx, trachea, bronchi, and bronchioles
• Serves as a pathway for air to move in and out of the lungs

Respiratory Zone

• Composed of respiratory bronchioles, alveolar ducts, and alveoli

Trachea

• A fibrocartilaginous tube that extends between the larynx and thorax.
• Divides into primary bronchi at the carina.
• Blood supply: Tracheal branches of the inferior thyroid artery
• Innervation: Pulmonary plexus
• Right main bronchus is shorter than the left

Bronchi and Bronchioles

• The first bronchi branch from the trachea (right and left main bronchus)
• Secondary bronchi (lobar bronchi) branch off of the main bronchi
• Tertiary bronchi (segmental bronchi) branch off of the secondary bronchi
• Bronchioles are the final generation of bronchi, too small to be supported by cartilage

Alveoli

• Site of gas exchange in the lungs
• Increases surface area for gas exchange
• Composed of Type 1 and Type 2 pneumocytes
  • Type 1 pneumocytes cover 95% of the alveolar surface and are responsible for gas exchange
  • Type 2 pneumocytes produce surfactant, which reduces surface tension

Special Features of Alveoli

• Thin walls for reduced diffusion distance
• Close to capillaries for reduced diffusion distance
• High in number for increased surface area for diffusion
• Collateral channels of ventilation allow for gas exchange even if there is a blockage
• Interconnected to help pull each other open

Lobes of The Lung

• Right lung has 3 lobes:
  • Superior
  • Middle
  • Inferior
• Left lung has 2 lobes:
  • Superior
  • Inferior

Bronchopulmonary Segments

• Lobes divide into segments associated with specific bronchi.

Hilum (Root)

• Point where structures enter and exit the lung.
• Surrounded by the pleura.
• Contains:
  • Bronchi
  • Pulmonary vasculature
  • Phrenic nerve
  • Lymphatics
  • Bronchial vessels
  • Pulmonary artery
  • Pulmonary veins (R and L)

Mediastinum

• Central compartment within the thoracic cavity between the pleural sacs of the lungs.
• Divided into superior and inferior portions.
• Inferior portion divides into middle and posterior portions.
• Pulmonary circulation:
  • Arterial circuit
  • Venous circuit
  • Lymphatics
  • Bronchial circulation

Innervation of the Lungs

• Two main sources:
  • Pulmonary plexus:
    • Parasympathetic and sympathetic nerves
  • Phrenic nerve

Pulmonary Lymphatic System

• Maintains fluid homeostasis
• Helps to fight infections
• Can transport cancer cells around the body, leading to metastasis

Pleura

• Parietal pleura: Lines the chest wall.
• Visceral pleura: Covers the lungs.
• No anatomical connection between the right and left pleural cavities.

Pleural Cavity

• The space between the visceral and parietal pleura.
• Contains a small amount of serous fluid.
• Functions:
  • Reduce friction during respiration.
  • Generates surface tension.

Pleural Recesses

• Located posteriorly and anteriorly where the pleural cavity is not completely filled with lung parenchyma:
  • Costomedial recess: Posterior to the sternum.
  • Costodiaphragmatic recess: Between the diaphragmatic and costal pleura.

Surface Tension

• Created by water molecules at the air-liquid interface within the alveoli.
• Surfactant:
  • Secreted by Type 2 alveolar cells.
  • Reduces surface tension.
  • Increases lung compliance.
  • Prevents alveolar collapse.
  • Facilitates alveolar recruitment.
  • Facilitates pressure changes.

Pleural Pathologies

• Pleural effusion: Accumulation of fluid in the pleural space.
  • Common causes:
    • Congestive heart failure
    • Cancer
    • Bacterial pneumonia
    • Post surgery
    • Pulmonary embolism
  • Symptoms:
    • Shortness of breath
    • Chest pain
    • Dry cough

Empyema

• Collection of pus in the pleural cavity.
  • Common causes:
    • Post surgery
    • Pneumonia
    • Alcohol abuse
    • Trauma
  • Symptoms:
    • Pain
    • Cough with increased sputum production
    • Dullness in chest wall percussion
    • Palpable fremitus

Pneumothorax

• Collection of air outside the lung but within the pleural cavity.
• Occurs when air accumulates between the parietal and visceral pleura inside the chest.
• Causes the lung to collapse.
• Defined as tension or spontaneous.
  • Tension pneumothorax:
    • Trauma
    • Leak in the visceral pleura
    • Urgent decompression required
    • Mediastinum pushed AWAY
    • Increased pleural space pressure
  • Spontaneous pneumothorax:
    • No cause/atelectasis/pathology
    • Treated with a drain
    • Mediastinum pulled TOWARDS

Key Points

• Lungs are made up of lobes:
  • Left: 2 lobes
  • Right: 3 lobes
• Pleura lines the chest and the outside of the lung.
  • Reduces friction
  • Generates surface tension
• Pleural pathologies can prevent the expansion of the lung or cause collapse of the lung.
• Tension pneumothorax: Moves AWAY.
• Spontaneous pneumothorax: Pulls TOWARDS.

Test your knowledge of the anatomy of the human respiratory system, including the conducting and respiratory zones. Explore the functions and characteristics of key structures like the trachea, bronchi, and alveoli. This quiz covers essential terminologies and concepts relating to pulmonary anatomy.