Respiratory

Respiratory System Anatomy & Physiology

Overview

  • The respiratory system facilitates gas exchange (O2 and CO2) between the atmosphere and body cells, being essential for aerobic ATP production and CO2 disposal.

  • Comprises respiratory passageways in the head, neck, trunk, and lungs.

General Functions of the Respiratory System

  1. Passageway for Air

    • Air moves between the atmosphere and alveoli during breathing.

  2. Site for Gas Exchange

    • Oxygen diffuses from alveoli into blood; carbon dioxide diffuses from blood into alveoli.

  3. Olfaction

    • Olfactory receptors located in the superior nasal cavity detect odor.

  4. Sound Production

    • Air movement across the vocal cords in the larynx vibrates to produce sound.

Organization of the Respiratory System

Structural Organization

  • Upper Respiratory Tract:

    • Nose, nasal cavity, pharynx, larynx.

  • Lower Respiratory Tract:

    • Trachea, bronchi, bronchioles, alveolar ducts, alveoli.

Functional Organization

  • Conducting Zone:

    • Structures transport air from the nose to terminal bronchioles.

  • Respiratory Zone:

    • Structures participating in gas exchange include respiratory bronchioles, alveolar ducts, and alveoli.

Anatomy of the Respiratory System

Respiratory Mucosa

  • The respiratory tract is lined by a mucosa (mucous membrane), termed the respiratory mucosa:

    • Epithelium with cilia

    • Lamina Propria: Areolar connective tissue with mucosa-associated lymphoid tissue (MALT)

    • Epithelium becomes progressively thinner from the nasal cavity to alveoli:

      • Starts as pseudostratified ciliated columnar

      • Transitions to simple ciliated columnar, simple cuboidal, and finally simple squamous.

    • Exceptions: Stratified squamous epithelium found in high abrasion areas (oropharynx, laryngopharynx, vocal cords).

Mucous Secretions

  • Produced from goblet cells and mucous & serous glands in the lamina propria.

  • Contains mucin protein to trap dust and microbes, and includes:

    • Lysozyme (antibacterial enzyme)

    • Defensins (antibacterial proteins)

    • Immunoglobulin A (antibody).

  • Mucus that is coughed up is termed sputum.

Clinical View: Cystic Fibrosis

  • Caused by defective chloride channels, leading to thick mucus that cilia cannot mobilize, resulting in blockages and increased pulmonary infections.

  • Also affects pancreatic ducts.

Nose and Nasal Cavity

Anatomy

  1. Nose:

    • Composed of bone, hyaline cartilage, and skin.

    • Bridge formed by paired nasal bones; nostrils (nares) made of dense irregular connective tissue.

  2. Nasal Cavity:

    • Extends from nostrils to choanae (openings to pharynx).

    • Floor is the palate; roof composed of bones and cartilage.

    • Nasal Septum: Divides left and right sides (made of septal nasal cartilage and the bony perpendicular plate of ethmoid and vomer).

  3. Nasal Conchae:

    • Three paired bony projections (superior, middle, inferior) that partition the cavity into passages (meatuses).

  4. Nasal Vestibule:

    • Lined with skin and hairs (vibrissae).

  5. Olfactory Region:

    • Contains olfactory epithelium for odor detection.

  6. Respiratory Region:

    • Lined by pseudostratified ciliated columnar epithelium with an extensive vascular network for warming air.

    • Nosebleeds are common due to the density of blood vessels.

Nasal Functionality

  • Nasolacrimal ducts drain lacrimal secretions into the nasal cavity; conditions air by warming, cleansing, and humidifying it.

  • Air turbulence caused by conchae enhances these processes.

Clinical View: Runny Nose

  • Rhinorrhea due to:

    • Increased mucus production (allergies, viruses)

    • Increased lacrimal secretions (crying)

    • Exposure to cold air.

Paranasal Sinuses

  • Spaces within skull bones connected to the nasal cavity:

    • Frontal sinuses, ethmoidal sinuses, sphenoidal sinuses, maxillary sinuses.

  • Lined by pseudostratified ciliated columnar epithelium; mucus swept into pharynx.

Clinical View: Sinus Infections

  • Inflammation of sinuses blocks drainage, causes mucus accumulation, potentially leading to infection and headaches.

Pharynx

  • Structure: Funnel-shaped passageway (throat) behind nasal cavity, oral cavity, and larynx, composed of skeletal muscles.

  • Divided into three regions:

    • Nasopharynx: Air passage above soft palate, lined with pseudostratified ciliated columnar epithelium, connects auditory tubes, contains tonsils.

    • Oropharynx: Extends from soft palate to hyoid bone, passage for air and food, lined with nonkeratinized stratified squamous epithelium containing palatine and lingual tonsils.

    • Laryngopharynx: Extends from hyoid bone to esophagus, also a passage for air and food, lined with nonkeratinized stratified squamous epithelium.

Larynx

  • Function: Voice production, air passage, and prevents ingested material entry (epiglottis action during swallowing).

  • Anatomy: Pyramid-shaped structure consisting of:

    • Cartilage: 9 pieces, including thyroid, cricoid, and epiglottis; paired arytenoid, corniculate, and cuneiform cartilages.

    • Vocal Folds: Vibrate during expiration, produce sound; tension affects pitch:

      • Increased tension raises pitch, force of air increases loudness.

Clinical View: Laryngitis

  • Inflammation leading to a sore throat and hoarseness due to infections or overuse.

Lower Respiratory Tract

  • Comprises conducting pathways (trachea to terminal bronchioles) and gas-exchange structures (respiratory bronchioles, alveolar ducts, alveoli).

Trachea

  • Connects larynx to main bronchi; approx. 13 cm long, 2.5 cm in diameter, supported by C-shaped hyaline cartilage rings.

  • Function and Structure:

    • Maintains open airway; trachealis muscle facilitates cough reflex.

    • Internal carina initiates cough reflex.

Clinical View: Tracheotomy and Cricothyrotomy

  • Tracheotomy: Incision to facilitate breathing when obstructed.

  • Cricothyrotomy: Incision between specific cartilages to place airway.

Bronchial Tree

  • A highly branched air passage system starting from main bronchi, subdividing into narrower tubes down to bronchioles.

  • Histology shows decreasing cartilage support and increasing smooth muscle.

Clinical View: Bronchitis

  • Inflammation leading to acute or chronic bronchitis with symptoms of cough and mucus production, potentially requiring treatment.

Respiratory Zone: Respiratory Bronchioles, Alveolar Ducts, and Alveoli

  • Respiratory Bronchioles: Mark the beginning of the respiratory zone, followed by alveolar ducts and leading to alveolar sacs (clusters of alveoli).

  • Alveoli:

    • Approximately 300 to 400 million in each lung; surrounded by pulmonary capillaries.

    • **Types of Cells:

      • Type I Cells:** Comprise 95% of alveolar surface area, facilitating gas exchange.

      • Type II Cells: Secrete surfactant, preventing alveolar collapse.

      • Alveolar Macrophages: Engulf microorganisms.

Respiratory Membrane

  • Composition: Consists of the plasma membranes of alveolar type I cells and pulmonary capillary endothelial cells, which allows for gas exchange.

Clinical View: Pneumonia

  • Infection leading to alveolar filling with fluids and pus with symptoms including cough, fever, and breathing difficulty.

Circulation to and from the Lungs

Pulmonary and Bronchial Circulation

  • Pulmonary Circulation: Replenishes O2 and eliminates CO2 via pulmonary arteries.

  • Bronchial Circulation: Supplies oxygenated blood to lung tissues from bronchial arteries.

Lymph Drainage

  • Located within lung connective tissue and around bronchi, important in removing excess fluid and filtering particles.

Pleural Membranes and Cavity

  • Pleura: Serous membrane lining lungs and thoracic wall, consisting of visceral (adhering to lungs) and parietal layers (lining thoracic cavity).

  • Pleural Cavity: Between layers, containing serous fluid for lubrication.

Clinical Views: Pleurisy and Pleural Effusion

  • Pleurisy: Inflammation causing severe chest pain upon breathing.

  • Pleural Effusion: Excess fluid leading to shortness of breath and chest pain.

How Lungs Remain Inflated

  • Inflated by:

    • Expanding chest wall, elastic recoil of lungs, and pleural cavity structure.

    • Intrapleural pressure is lower than intrapulmonary pressure, essential for lung inflation.

Clinical Views: Pneumothorax and Atelectasis

  • Pneumothorax: Air in pleural cavity that can lead to lung collapse.

  • Atelectasis: Resulting from pressure equalization causing lung collapse until air is removed.