the respiratory system

• Respiratory system

  The system responsible for gas exchange in the body
• Topics covered in this lecture

  • Respiratory system anatomy
  • Pulmonary ventilation
  • Gas exchange
  • Control of respiration
• Functions of the respiratory system

  Houses the lungs and facilitates gas exchange
• Respiratory system structural zones

  • Upper respiratory tract
  • Lower respiratory tract
• Upper respiratory tract structures

  • Nose
  • Pharynx
• Lower respiratory tract structures

  • Larynx
  • Trachea
  • Bronchi
  • Lungs
• Respiratory system functional zones


  • Conducting Zone
  • Respiratory Zone
• Conducting Zone

  Involved with bringing air to the site of external respiration, consisting of the nose, pharynx, larynx, trachea, bronchi, bronchioles and terminal bronchioles
• Respiratory Zone

  Main site of gas exchange, consisting of the respiratory bronchioles, alveolar ducts, alveolar sacs, and alveoli
• Structures air passes through in the respiratory tract

  • Nasal cavity
  • Pharynx
  • Larynx
  • Trachea
  • Primary bronchi
  • Secondary bronchi
  • Tertiary bronchi
  • Bronchioles
  • Alveoli
• Nasal cavities

  External nose - visible on the face

  Internal nose - large cavity beyond the nasal vestibule, divided by nasal septum into right and left nares
• Pharynx

  Hollow tube that starts posterior to the internal nares and descends to the opening of the larynx in the neck, formed by a complex arrangement of skeletal muscles that assist in deglutition, functions as a passageway and resonating chamber housing the tonsils
• Larynx

  Voice box, composed of 9 pieces of cartilage, forms a short passageway connecting the laryngopharynx with the trachea
• Trachea

  Semi-rigid pipe made of semi-circular cartilaginous rings, located anterior to the esophagus, ~12 cm long extending from the inferior portion of the larynx, divides into right and left primary bronchi, composed of 4 layers: mucosa, submucosa, hyaline cartilage, and adventitia
• Respiratory tract cilia

  Cilia in the upper respiratory tract move mucous and trapped particles down toward the pharynx, cilia in the lower respiratory tract move them up toward the larynx
• Bronchial Tree

  All the branches from the trachea to the terminal bronchioles are conducting airways and do not participate in gas exchange
• Pulmonary lobule

  Wrapped in elastic connective tissue, contains a lymphatic vessel, an arteriole, a venule, and a terminal bronchiole. Respiratory bronchioles give way to alveolar ducts, and the epithelium changes to simple squamous, which comprises the alveolar ducts, alveolar sacs, and alveoli. Respiratory bronchioles mark the start of the respiratory zone.
• Alveoli

  Cup-shaped outpouchings which participate in gas exchange, alveolar sac comprises two or more alveoli that share a common opening. Type I cells are simple squamous epithelial cells, the site of gas exchange. Type II cells are cuboidal epithelial cells with microvilli that secrete surfactant to reduce surface tension. Alveolar macrophages remove dust, and fibroblasts produce reticular/elastic fibers.
• Gas exchange takes place across the 0.5 μm thick respiratory membrane in the alveoli
• Pleura and pleural cavity

  Pneumothorax - air, Hemothorax - blood/pus
• Pulmonary Circulation

  The lungs receive blood via two sets of arteries: Pulmonary arteries carry deoxygenated blood from the right heart to the lungs for oxygenation, Bronchial arteries branch from the aorta and deliver oxygenated blood to the lungs primarily perfusing the muscular walls of the bronchi and bronchioles
• Ventilation-Perfusion Coupling


  Blood flow to each area of the lungs matches the extent of airflow to alveoli in that area. In the lungs, vasoconstriction in response to hypoxia diverts pulmonary blood from poorly ventilated areas of the lungs to well-ventilated regions. In all other body tissues, hypoxia causes dilation of blood vessels to increase blood flow.
• Steps of respiration


  • Pulmonary ventilation
  • External (pulmonary) respiration
  • Internal (tissue) respiration
• Pulmonary Ventilation - Breathing

  Movement of air between the atmosphere and the alveoli, consisting of inhalation and exhalation. Changes to intra-thoracic volume allow ventilation to take place. Rate of airflow and effort required depend on alveolar surface tension, compliance of the lungs, and airway resistance.
• Volume-pressure relationship - Boyle's Law

  The pressure of a gas in a closed container is inversely proportional to the volume of the container
• External respiration


  Gas exchange between the alveoli and the blood
• Internal respiration

  Gas exchange between the systemic capillaries and the tissues of the body
• Factors affecting respiration rate

  Partial pressure difference of the gases, surface area available for gas exchange, diffusion distance, molecular weight and solubility of gases
• Oxygen transport

  In the blood, some O2 is dissolved in the plasma as a gas (about 1.5%), but most O2 (about 98.5%) is carried attached to haemoglobin (Hb). Oxygenated Hb is called oxyhaemoglobin. The higher the PO2, the more O2 combines with Hb.
• Carbon dioxide transport

  CO2 is transported in the blood in three different forms: 1) 7% is dissolved in the plasma, as a gas, 2) 70% is converted into carbonic acid by carbonic anhydrase (CA) before dissociating into bicarbonate and protons, 3) 23% is attached to Hb forming carbaminohaemoglobin (Hb-CO2).
• Summary of topics covered

  • Respiratory system anatomy
  • Pulmonary ventilation
  • Gas exchange
  • Control of respiration