ch11. respiratory system

• Respiratory system


  Network of organs and tissues that help us breathe
• Functions of the respiratory system

  • Helps us absorb O2 from the air (needed for cellular respiration)
  • Removes waste gases, (mainly CO2) from the blood
• Respiration


  The process by which living organisms take O2 into their cells in the process of energy production and CO2 is a byproduct of this reaction
• Erythrocytes (red blood cells)


  Carry out the transport of gases (O2 and CO2)
• Composition of air


  • Nitrogen (~78%)
  • Oxygen (~21%)
  • Argon (~1%)
  • Very small amounts of xenon, neon, hydrogen, helium, krypton and carbon dioxide
• Why animals need oxygen

  • O2 fuels our cells and provides basic building blocks we need to survive
  • O2 is used to make carbohydrates that provide energy
  • O2 is crucial for cellular respiration – used by cells to generate energy (ATP)
• Oxygen concentrations are much higher in air (~21% oxygen), than in water (~0.4-0.7% oxygen)
• Warm water holds less O2 than cold water, and salt-water holds less O2 than fresh water
• Cold salt-water only contains 0.7% O2, and warm salt-water only contains 0.4% O2
• Gills of fish

  • Designed so that water can flow continually passed them
  • Water enters through the mouth and passes out through the single external gill opening
  • Gill rakers make sure that no unnecessary material clogs up the gill filaments
• Gill filaments


  • Contain a lot of lamellae (singular: lamella), extending out from both sides of the filament body
  • The lamellae greatly increase the surface area of the gills, so a large amount of water is available for gaseous exchange at any time
  • Uptake of O2 occurs at the lamellae, when it diffuses from the water to the fish's blood
  • Blood vessels are sandwiched between the lamellae, allowing the dissolved gases (O2 and CO2) to diffuse between the two
• Gases can only diffuse along a concentration (or partial pressure) gradient
• O2 only diffuses into the blood at the gills if the O2 level in the water > O2 level in the blood
• Whether living in water or in air, gas exchange ALWAYS happens across an air-water interface
• Main components of human respiratory tract

  • Nasal and oral cavities (nose and mouth)
  • Pharynx (throat) and larynx
  • Trachea
  • Bronchi and bronchioles
  • Alveolar ducts (or terminal bronchioles)
  • Alveoli – where gas exchange takes place
• Human lungs


  • Two pyramid-shaped organs, enclosed by double-layered membrane (pleurae)
  • Right lung - shorter and wider than the left lung
  • Left lung is a smaller volume than the right lung, and contains cardiac notch (space for the heart)
  • Each lung made up of smaller units called lobes, separated by fissures (deep grooves)
  • The right lung - three lobes: called superior, middle, and inferior
  • The left lung - two lobes: called superior and inferior
  • The lobes are divided into bronchopulmonary segments, which receives air from its own tertiary bronchus and is supplied with blood by its own artery
• Physiological respiration


  • Pulmonary ventilation (breathing)
  • External respiration (exchange of gases between the lungs and blood)
  • Internal respiration (exchange of gases between the blood and cells)
• Pulmonary ventilation


  1. Inhalation: Air is inhaled through the nasal and oral cavities (the nose and mouth), moves through the pharynx, larynx, and trachea into the lungs

  2. Exhalation: Air is exhaled, flowing back through the same pathway
• Breathing


  • Triggered by changes to the volume and air pressure in the lungs
  • During inhalation, the diaphragm and intercostal muscles contract and the ribcage elevates, causing the air pressure to drop and air to rush in
  • During exhalation, the diaphragm and intercostal muscles relax, the lungs become smaller, the air pressure rises, and air is expelled
• Passage of air in upper airways

  • Air breathed in through the nose (and mouth)
  • Nasal cavities have several folds, or shelves, called nasal conchae, which expose a large area of nasal membrane to the air
  • Sinuses produce nitric oxide (NO) – helps with uptake of O2
  • Cells of the nasal epithelium contain cilia, which act like a brush to catch dust particles, pathogens, and irritants
  • Goblet cells produce mucus, trapping dust, smoke, bacteria, etc.
  • Inhaled air takes up moisture from the mucus, and heat from underlying blood vessels, becoming almost completely saturated with water vapor and almost at body temperature by the larynx
  • On exhalation, the mucus in the cool and dry nose re-captures some of the warmth and moisture from that exhaled air by condensation
• Pharynx (throat)


  • Connects the nasal cavity and the back of the mouth to the larynx and oesophagus
  • Part of both the respiratory and digestive systems
  • Air passes from the nasal cavity through the pharynx to the larynx (and in the opposite direction)
  • Food passes from the mouth through the pharynx to the oesophagus
• Larynx (voice box)


  • Contains flap-like mechanical barrier (epiglottis), which stops ingested food and liquids from being sucked into the trachea
  • Vibrates vocal folds to produce sound, allows you to talk and make sounds when air moves in and out
  • Assists in the cough reflex – via special cough receptors
• Passage of air in lower airways

  • Often described as the respiratory or tracheobronchial tree
  • Larger airways give rise to narrower more numerous branches
  • The larger structures are the trachea and bronchi, which mainly transmit air to the lower airways
  • The trachea and the first portions of the main bronchi are outside the lungs
• Trachea


  • Widest of the tubes
  • Contain stiff cartilage and smooth muscle (trachealis muscle)
• Trachea and bronchi


  • Lined with cilia-bearing epithelial cells
  • Goblet cells secrete mucus and form a mucus sheet, which is continually transported away from the lungs (towards the mouth) by the coordinated movement of the cilia, serving as a dust-trap
• Bronchioles


  • Smaller branches of the bronchi
  • Contain SMOOTH MUSCLE, but NO cartilage, cilia or goblet cells
  • Any particles deposited in the bronchioles (and alveoli) are removed by alveolar macrophages
• Alveoli


  • Blind-ended terminals so air that enters them must exit the same way, via breathing
  • Microscopic sacs ~0.3 mm (~300 µm) in diameter, specialized for gas exchange
  • In a pair of human lungs, there are ~300 million (300,000,000) alveoli
• External respiration (exchange of gases between the lungs and blood)

  1. O2 from the inhaled air diffuses from the alveoli into pulmonary capillaries surrounding them

  2. CO2 from deoxygenated blood diffuses from the capillaries into the alveoli and is expelled through exhalation
• Alveolus


  • Has a VERY important film of water on the inner surface that allows gas exchange to take place
  • Surface tension can cause the alveoli to collapse
  • Alveolar cells produce surfactant, which forms a layer around the inside of the alveoli, creating a barrier between the air and water, decreasing the surface tension
• Components of surfactant


  • Phospholipids (phosphatidylcholine and phosphatidylglycerol)
  • Cholesterol
  • Some proteins (SP-A to SP-D)
• Type I and II pneumocytes

  • Type I - ONLY used for gas exchange
  • Type II - act as stem cells to replenish the type I and II pneumocytes and secrete surfactant
• In developing human embryos, surfactant production begins at ~28 weeks of gestation
• Premature babies (born before 28 weeks) have less surfactant, more surface tension and are more at risk of lung collapse, called infant respiratory distress syndrome (RDS)
• Premature babies can be treated with surfactant replacement therapy, provided to lungs by endotracheal tube
• Components of external respiration

  • Alveolar surface: high surface area to volume ratio and thin walls
  • Partial pressure gradients: Allow gases to flow from areas of high pressure to areas of lower pressure
  • Ventilation and perfusion in the alveoli must be balanced to maintain efficient gas exchange
• Alveolar surface area


  • Very high surface area to volume ratio - allows for efficient gas exchange
  • Alveolar and capillary walls are both made up of very thin cells
  • Alveoli covered with high density of capillaries providing many sites for gas exchange
• Partial pressure gradients


  • O2 is loaded into the blood stream and CO2 is unloaded from the bloodstream by diffusion due to partial pressure gradients (differences in partial pressure or concentration)
  • O2 has a partial pressure gradient of ~60 mmHg (100 mmHg in alveolar air and 40 mmHg in deoxygenated blood)
  • CO2 has a partial pressure gradient of only 6 mmHg (46 mmHg in deoxygenated blood and 40 mmHg in alveolar air), but has higher solubility in blood
• So-called deoxygenated blood isn't completely lacking in O2, it has a partial pressure of 40 mmHg, and not all CO2 is removed from the blood as oxygenated blood still contains 40 mmHg
• Ventilation (V) and Perfusion (Q) Matching

  • V and Q must be balanced to maintain efficient gas exchange in the alveoli
  • If V is slowed due to a blockage in the airways, CO2 levels in the alveoli increase but O2 levels decrease, causing the alveolar capillaries to constrict to reduce blood flow (Q)
  • If Q decreases due to a blood capillary blockage, the low level of CO2 stimulates the bronchioles to constrict, leading to a drop in ventilation (V)
• External Respiration: Exchange of gases between the lungs and blood

  1. The bloodstream delivers O2 to the cells and removes waste CO2 from the cells

  2. When oxygenated blood reaches the narrow capillaries that surround the tissues, the red blood cells release the O2 and it diffuses through the capillary walls into body tissues

  3. At the same time, CO2 diffuses from the tissues into the red blood cells and plasma

  4. The deoxygenated blood carries the CO2 back to the lungs for release by exhalation