Week 29- The respiratory system

• Conducting system or airways consist of

  • Upper respiratory tract (Mouth basal cavity, pharynx, larynx)
  • Lower respiratory tract (Trachea, 2 primary bronchi, their branches, lungs)
• External respiration

  • Movement of gases between the environment and the body’s cells
• Airway Epithelium are Ciliated, and Alveoli are the Site of Gas Exchange
• Failure of CFTR in cystic fibrosis leads to thick, sticky mucus
• Pleural fluid is between pleural membranes, lowers friction between membranes, holds lungs tight against the thoracic wall
• Pleural effusion is when pleural fluid accumulates, e.g., in TB, also when body fluid volumes are disturbed
• Connective tissue in the respiratory system includes elastin and collagen, with a close association with capillaries
• The lower tract is also called the thoracic portion because it is enclosed in the thorax
• Dalton’s law states that the total pressure of a mixture of gases is the sum of the pressures of the individual gases
• Thoracic cage consists of bones and muscle of thorax and abdomen
• Gas laws overview: Gases move down pressure gradients, air is a mixture of gases
• The respiratory tract is divided into upper and lower regions
• Pleurisy is inflammation of the pleura, making breathing laboured, usually caused by another condition such as an infection
• Type I alveolar cells are for gas exchange, Type II alveolar cells produce surfactant
• Boyle’s law describes pressure-volume relationships
• Breathing (ventilation)

  When we breathe, we perform inspiration (inhalation) and expiration (exhalation). Quiet breathing requires very little muscle contraction, while forced breathing is deeper due to increased physical activity. Several muscles are involved in forced inspiration and expiration
• Alveoli (singular alveolus) are the site of gas exchange
• Partial pressure of a gas

  The pressure of an individual gas in a mixture
• How do we measure lung function?

  Using a portable spirometer
• Aspects impacting lung function/breathing

  • Anatomical aspects: Lungs (bronchi, bronchioles, alveoli), Chest cavity (ribs/intercostal muscles, diaphragm muscle), Pleural membranes (pleural fluids, pleural pressure)
  • Functional aspects: Passive (shallow) breathing - lung elasticity (recoil), pressure gradients, Active (deep) breathing – different muscles involved, larger tidal volumes up to vital capacity (maximum)
• Dalton’s law: The total pressure of a mixture of gases is the sum of the pressures of the individual gases
• How pressure changes during quiet breathing

  1. Inspiration occurs when alveolar pressure decreases

  2. Expiration occurs when alveolar pressure increases

  3. Passive vs. active expiration
• Important measures used to monitor lung function

  • Forced vital capacity (FVC) - total amount of air blown out in one deep breath, Forced expiratory volume in 1 sec (FEV1) - amount of air blown out within one second
• Alveolar ventilation is a better indication of how much fresh air reaches the alveoli. Fresh air remaining in the dead space does not get to the alveoli
• The pressure exerted by an individual gas is determined only by its relative abundance in the mixture and is independent of the molecular size or mass of the gas
• Total pulmonary ventilation is greater than alveolar ventilation because of dead space
• Pulmonary volumes and capacities

  • Tidal volume (TV) - ~500ml/0.5L, Expiratory reserve volume (ERV), Inspiratory reserve volume (IRV), Vital Capacity (VC) - TV + ERV + IRV
• Overview of gas exchange: The body needs oxygen and removes carbon dioxide. Hypoxia – too little oxygen. Hypercapnia – increased concentrations of carbon dioxide. To avoid hypoxia and hypercapnia, the body responds to three regulated variables: Oxygen, Carbon dioxide, pH
• Breathing is bulk flow of air into and out of lungs
• Alveolar ventilation rate influences gas pressures
• At equilibrium, P(O2) in air and water is equal. Low O2 solubility means concentrations are not equal
• Ventilation and alveolar blood flow are matched: Ensures efficiency of gas exchange between alveoli and capillaries
• Haemoglobin is an oxygen carrier protein
• Compared with other ways for this protein to work the cooperativity allows release of more oxygen at tissues and good binding in the lungs
• Gases such as oxygen are MORE soluble in cold water than hot water
• As [CO2] increases, Hb releases oxygen more readily
• Total pressure of mixed gas = sum of partial pressures of individual gases
• Haemoglobin transports most oxygen to the tissues
• The shape of this binding curve illustrates the ideally adapted properties of human Hb as an oxygen transporter under physiological conditions
• Fresh air into lungs ≈ 10% total lung volume at the end of inspiration