Respiratory System Overview

Functions of the Respiratory System

• Brings air into lungs (breathing)
• Exchange of gases between air and blood, and between blood and systemic tissues
• Utilizes oxygen in cellular metabolism; maximum ATP synthesis requires oxygen (O₂) and produces carbon dioxide (CO₂)
• Requires breathing to take in oxygen and eliminate carbon dioxide

Respiration Definition

• Respiration involves:
  • Bringing air into the lungs (breathing)
  • Gas exchange between air and blood AND between blood and systemic tissues
  • Utilizing oxygen in cellular metabolism
  • Maximum ATP synthesis requiring oxygen (O₂) and producing carbon dioxide (CO₂)

Structure of the Respiratory System

• Series of passageways bring air into the body, permit gas exchange, and expel air.
• Major structures include:
  • Upper respiratory tract: Nose, nasal cavity, pharynx, larynx
  • Lower respiratory tract: Trachea, bronchial tree, lungs

Structural Organization

• Upper Respiratory Tract
  • Nose, nasal cavity, pharynx, larynx
• Lower Respiratory Tract
  • Trachea, bronchus, bronchioles, lungs
  • Divided into conducting zone (air passage) and respiratory zone (gas exchange)

Respiratory Epithelium

• Lined with mucosa:
  • Consists of epithelium, basement membrane, and lamina propria
  • Contains goblet cells and glands secreting mucus
  • Epithelium changes from nasal cavity to lungs, from pseudostratified ciliated columnar to simple squamous in alveoli

Functions of Upper Respiratory Tract

• Warms, cleanses, and moistens inhaled air
• Detects odors
• Amplifies voice

Pharynx

• Connects the nasal cavity to the larynx
• Divided into three regions:
  • Nasopharynx: Contains adenoids and auditory tube openings
  • Oropharynx: Contains palatine and lingual tonsils
  • Laryngopharynx: Connects to the larynx

Larynx

• Cartilaginous structure connecting pharynx and trachea
• Functions:
  • Air passageway, produces sound, aids in swallowing reflexes
• Framework composed of nine cartilages including
  • Thyroid cartilage (Adam's apple)
  • Epiglottis (covers larynx during swallowing)

Trachea

• Flexible tube located anterior to the esophagus, composed of C-shaped cartilaginous rings
• Contains mucosa lined with ciliated cells that expel debris

Bronchial Tree and Lungs

• Trachea splits into left and right main bronchi, leading to lobar and segmental bronchi
• Bronchioles have no cartilage and lead to respiratory bronchioles and alveolar sacs
• Alveoli:
  • Type I cells facilitate gas exchange
  • Type II cells secrete surfactant
  • Gas exchange occurs across the respiratory membrane

Respiratory Processes

• Processes of respiration include:
  • Pulmonary ventilation: Air movement in and out of lungs
  • Pulmonary gas exchange: Gas exchange between alveoli and blood
  • Gas transport: Transport of gases in blood
  • Tissue gas exchange: Gas exchange between blood and systemic cells

Physics of Respiration

• Boyle's Law: Inverse relationship between volume and pressure
• Airflow is dependent on pressure gradients and resistance of respiratory tract

Control of Breathing

• Regulated by the respiratory center located in the medulla oblongata and pons
• Stimulation of muscles occurs via phrenic and intercostal nerves

Breathing Mechanics

• Inspiration: Diaphragm and external intercostals contract, expanding thoracic cavity, lowering intrapulmonary pressure
• Expiration: Muscles relax, causing a decrease in thoracic cavity volume and an increase in intrapulmonary pressure

Gas Transport

• Oxygen transport:
  • 2% dissolved in plasma, 98% bound to hemoglobin
• Carbon dioxide transport:
  • 7% dissolved in plasma
  • 23% bound to hemoglobin
  • 70% converted to bicarbonate (HCO₃⁻) via carbonic anhydrase

Clinical Views

• Important related clinical issues such as asthma, pneumonia, and effects of smoking on lung health are discussed

Summary

• The respiratory system is vital for multiple functions including gas exchange, production of sound, and regulation of blood pH. Its complex structure supports these functions through diligent coordination of various components and muscles involved in respiration.