Functions of the Respiratory System

• Gas Exchange: Oxygen (O2) and carbon dioxide (CO2) exchanged between the blood and air.

• Communication: Involves speech and other vocalizations.

• Olfaction: The sense of smell.

• Acid-Base Balance: Influences body fluids' pH by eliminating CO2.

• Blood and Lymph Flow: Breathing creates pressure gradients that promote blood and lymph flow.

• Platelet Production: More than half of platelets are produced by megakaryocytes located in the lungs.

Anatomy of the Respiratory System

Upper Respiratory Tract

• Location: Head and neck; includes nose through larynx.

Lower Respiratory Tract

• Location: Thorax; includes trachea through lungs.

Conducting Zone

• Function: Conditions inhaled air (humidified, warmed, and filtered); no gas exchange occurs.

• Components: Nasal cavities, nasopharynx, larynx, trachea, bronchi, bronchioles.

Respiratory Zone

• Function: Passive gas exchange between atmosphere and blood.

• Components: Respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli.

Nose

• Functions:

  • Warms, cleanses, and humidifies inhaled air.

  • Detects odors.

  • Acts as a resonating chamber, amplifying the voice.

Nasal Mucosa

• Structure: Respiratory epithelium includes ciliated pseudostratified columnar epithelium.

  • Goblet Cells: Produce mucus.

  • Cilia: Motile and propel mucus towards the pharynx.

• Olfactory Epithelium: Sensory structure that detects odors.

Pharynx

• Structure: Muscular funnel with three regions:

  • Nasopharynx: Pseudostratified columnar epithelium, receives auditory tubes, contains the pharyngeal tonsil.

  • Oropharynx: Stratified squamous epithelium, space between soft palate and epiglottis, contains palatine tonsils.

  • Laryngopharynx: Stratified squamous epithelium, extends from epiglottis to cricoid cartilage.

Larynx

• Structure: Cartilaginous chamber regulates food and air passage, sound production (voice box).

• Cartilages: Nine cartilages make up larynx, with three larger ones:

  • Epiglottic Cartilage.

  • Thyroid Cartilage: Contains laryngeal prominence (Adam's apple).

  • Cricoid Cartilage: Connects larynx to trachea.

• Vocal Cords: Inferior vocal cords produce sound; superior vestibular folds play no role in speech.

Trachea

• Dimensions: About 12 cm long and 2.5 cm in diameter, reinforced with C-shaped rings of hyaline cartilage.

• Mucosa: Lined with ciliated pseudostratified columnar epithelium, containing goblet cells for mucus secretion.

• Trachealis Muscle: Adjusts airflow; spans the openings of cartilage rings.

Bronchial Tree

• Structure: Branching system extending from the trachea to terminal bronchioles (65,000 terminal bronchioles).

• Function: Conducts air to and from the lungs.

Lungs

Right Lung

• Septation: Shorter than left lung (accommodates liver), consists of three lobes (superior, middle, inferior).

Left Lung

• Septation: Tall and narrow (heart tilts left), consists of two lobes (superior and inferior).

Alveoli

• Cell Types:

  • Type I Alveolar Cells: Squamous, allow gas diffusion (95%).

  • Type II Alveolar Cells: Round/cuboidal, secrete surfactant (5%).

  • Alveolar Macrophages: Phagocytize dust particles.

• Respiratory Membrane: Composed of squamous alveolar cells, endothelial cells of blood capillary, and a shared basement membrane.

Pleura

• Function: Reduces friction, creates a pressure gradient to assist lung inflation, compartmentalization.

• Layers: Visceral pleura covers lungs; parietal pleura lines thoracic cavity.

Pulmonary Ventilation

• Breathing Cycle: Involves inspiration (inhaling) and expiration (exhaling).

• Types: Quiet respiration (at rest) and forced respiration (during exercise).

Respiratory Muscles

• Diaphragm: Primary muscle, contracts to enlarge thoracic cavity for inhalation, relaxes for exhalation.

• Other Muscles: Internal and external intercostals, sternocleidomastoid, scalenes, and pectoralis minor aid in ventilation.

Neural Control of Breathing

• Centers: Medulla oblongata (VRG and DRG) and pons (Pontine respiratory group).

• Regulations: Rate and depth of breathing adapted to physiological needs (sleep, exercise, etc.).

Gas Exchange

Dalton’s Law: The partial pressure of a gas represents its proportion within a mixture. Henry’s Law: A gas dissolves in liquid at a rate proportional to its partial pressure.

Alveolar Gas Exchange

• External Respiration: O2 diffuses into blood, CO2 diffuses into alveolar air.

Gas Transport

• Oxygen Transport: (98.5% bound to hemoglobin, 1.5% dissolved in plasma).

• Carbon Dioxide Transport: (7% dissolved, 70% in carbonic acid, 23% as carbamino compounds).

Respiratory Volumes and Capacities

• Tidal Volume: Volume of air exchanged in one cycle (500 mL).

• Inspiratory Reserve Volume: Air in excess after normal inhalation (3,000 mL).

• Experatory Reserve Volume: Air exhaled beyond tidal volume (1,200 mL).

• Residual Volume: Air remaining post expiration (1,300 mL).

• Vital Capacity: Total usable air capacity (4,700 mL).

Respiratory Disorders

• Restrictive Disorders: Reduced pulmonary compliance (e.g., pulmonary fibrosis).

• Obstructive Disorders: Limited airflow (e.g., asthma, chronic bronchitis).

• COPD: Chronic obstructive pulmonary disease affecting airflow balance.

Smoking and Lung Cancer

• Impact: Major cause of lung cancer; most carcinogens found in tobacco.

• Common Types: Squamous-cell carcinoma and adenocarcinoma affecting mucus glands.