Respiratory System

• Functions of the Respiratory System

  • Gas exchange
  • Regulation of blood pH
  • Voice production
  • Olfaction
  • Protection
• Upper respiratory tract


  External nose, nasal cavity, pharynx, and associated structures
• Lower respiratory tract


  Larynx, trachea, the bronchi, and lungs
• Zones of the respiratory system

  • Conducting zone
  • Respiratory zone
• Otorhinolaryngology


  Medical specialty dealing with the ear, nose, and throat
• Pulmonologist


  Medical specialist in diseases of the respiratory system
• Bones of the nose

  • Frontal
  • Nasal
  • Maxillae
• Cartilage of the nose

  • Septal nasal
  • Lateral
  • Alar
• The nasal cavity connects to the pharynx
• The larynx is part of the lower respiratory system
• Vocal cords


  Located in the larynx
• Trachea


  1. Descends from the larynx through the neck to the fifth thoracic vertebra

  2. Composed of dense regular connective tissue, smooth muscle, and 15-20 C-shaped rings of hyaline cartilage

  3. The mucous membrane lining is made up of goblet cells and pseudostratified ciliated columnar epithelium

  4. Goblet cells produce mucus

  5. Ends by dividing into the two primary bronchi
• Right primary bronchus


  Wider, shorter and more vertical than the left
• The right primary bronchus is a common site for an inhaled object to become lodged
• By the time air reaches the bronchi, it is warmed, cleansed and saturated with water vapor
• Epithelial types in the respiratory system

  • Goblet cells and pseudostratified ciliated columnar epithelium
  • Ciliated simple cuboidal epithelium
  • Nonciliated simple cuboidal epithelium
  • Simple squamous epithelium
• Terminal bronchioles


  End of the conducting zone
• Structures in the respiratory zone

  • Respiratory bronchioles
  • Alveolar ducts
  • Alveolar sacs
  • Alveoli
• Emphysema affects the alveoli
• Respiratory membrane


  Where gas exchange occurs
• Lungs


  • Principal organs of respiration
  • Base rests on the diaphragm, apex extends superiorly to ~2.5 cm above the clavicle
  • Right lung has 3 lobes, left lung has 2 lobes
  • Each lobe is like a balloon filled with sponge-like tissue
• Postural drainage


  Technique to clear mucus from the lungs
• Pleural cavities and membrane


  Space between the parietal and visceral pleura, contains lubricating fluid
• Epithelial walls in the respiratory system

  • Conducting zones
  • Gas exchange zone
• Pulmonary ventilation


  1. Movement of air into and out of the lungs (breathing)

  2. Air flows between the atmosphere and the alveoli due to alternating pressure differences created by contraction and relaxation of respiratory muscles

  3. Rate of airflow and effort for breathing are influenced by alveolar surface tension, lung compliance, and airway resistance
• Inhalation


  1. Air pressure inside the lungs equals atmospheric pressure at sea level (760 mmHg or 1 atm)

  2. For air to flow in, alveolar pressure must become lower than atmospheric pressure

  3. This is achieved by increasing the size of the lungs
• Boyle's law


  Pressure of a gas in a closed container is inversely proportional to the volume of the container
• Diaphragm


  1. Most important muscle of inhalation

  2. Dome-shaped skeletal muscle that forms the floor of the thoracic cavity

  3. Innervated by the phrenic nerves

  4. Contraction causes it to flatten, increasing the vertical diameter of the thoracic cavity

  5. Responsible for 75% of air entering the lungs during quiet breathing
• External intercostals


  1. Contract to elevate the ribs, increasing the anteroposterior and lateral diameters of the chest cavity

  2. Responsible for 25% of air entering the lungs during quiet breathing
• Intrapleural pressure


  • Pressure within the pleural cavity, always negative (lower than atmospheric pressure)
  • Allows the visceral pleura to be attached to the chest wall
• Changes in intrapleural pressure during inhalation

  1. Before inhalation, intrapleural pressure is about 4 mmHg less than atmospheric pressure (756 mmHg)

  2. As the thoracic cavity expands, intrapleural pressure decreases to about 754 mmHg

  3. This causes alveolar (intrapulmonic) pressure to drop from 760 to 758 mmHg, creating a pressure difference that allows air to flow in
• Most of the increase in lung volume during inhalation is due to lengthening and expansion of the alveolar ducts and increase in size of the alveolar openings
• Accessory muscles of inspiration participate in increasing the size of the thoracic cavity during deep, forceful inhalations
• Inhalation


  1. Alveolar pressure drops from 760 to 758 mmHg

  2. Pressure difference established between atmosphere and alveoli

  3. Air flows from higher to lower pressure

  4. Air continues to flow into lungs as long as pressure difference exists

  5. Lungs enlarge in all directions, mainly due to lengthening and expansion of alveolar ducts and increase in size of alveolar openings

  6. Accessory muscles of inspiration contract during deep, forceful inhalations to increase size of thoracic cavity
• Exhalation


  1. Pressure in lungs greater than atmospheric pressure

  2. Exhalation is a passive process during normal quiet breathing, due to elastic recoil of chest wall and lungs

  3. Exhalation starts when inspiratory muscles relax, decreasing thoracic cavity size

  4. Alveolar pressure increases to about 762 mmHg, causing air to flow from alveoli to atmosphere

  5. Exhalation becomes active during forceful breathing, with abdominal and internal intercostal muscles contracting to increase pressure in abdomen and thorax
• Surface tension


  Force formed from thin layer of alveolar fluid, causes inwardly directed force on alveoli, must be overcome during inhalation, accounts for two-thirds of lung elastic recoil
• Surfactant


  Mixture of phospholipids and lipoproteins that reduces surface tension of alveolar fluid below that of pure water
• Deficiency of surfactant in premature infants causes respiratory distress syndrome, with increased alveolar surface tension and alveolar collapse
• Compliance


  How much effort is required to stretch the lungs and chest wall, related to elasticity and surface tension
• Decreased compliance is common in lung conditions that scar tissue, fill with fluid, or impede expansion