Respiratory System and Mechanics of Breathing

Function of the Respiratory System

• The main function is to bring oxygen into the body and remove carbon dioxide.
• Cells and tissues use oxygen to create energy (ATP) and generate carbon dioxide as a result.
• The respiratory system replenishes oxygen and eliminates carbon dioxide.

Anatomy of the Respiratory System

• Major structures include:
  • Nose
  • Oral cavity (mouth)
  • Pharynx
  • Larynx
  • Trachea (windpipe)
• The trachea is the first structure specifically devoted to the respiratory system.
• The trachea splits into the primary bronchi, which further branch out.
• The branching continues, leading to the alveoli, which are the functional parts of the lungs.

Bronchial Branching

• Trachea splits into primary bronchi.
• Primary bronchi split into secondary bronchi.
• Secondary bronchi split into tertiary bronchi.
• Bronchi continue to split, becoming smaller bronchioles.
• Bronchioles become terminal bronchioles.
• Terminal bronchioles end in alveoli (singular: alveolus).
• Alveoli are air-filled sacs where gas exchange occurs.

Functional Zones of the Lung

• Two functional zones:
  • Conducting Zone: Air passes through but no gas exchange occurs; essentially the pipes of the system.
  • Respiratory Zone: Gas exchange occurs; the most important part of the lung.

Conducting Zone

• The conducting zone includes the pipes that link the mouth and nose to the respiratory zone.
• The conducting zone warms and humidifies the air.
• Mucus in the conducting zone catches dust particles and bacteria.
• Air in the conducting zone is referred to as anatomical dead space because it doesn't participate in gas exchange.

Respiratory Zone

• The respiratory zone includes the last bronchioles and alveoli.
• Gas exchange takes place in the respiratory zone.

Alveoli

• Small sacs filled with air.
• Estimated 300-700 million alveoli in adult lungs.
• Alveoli are thin-walled and have a good blood supply, surrounded by capillaries.
• Perfectly adapted for gas exchange.

Alveolar Cells

• Type one cells:
  • Majority of cells, responsible for gas exchange.
• Type two cells:
  • Secrete surfactant, which reduces surface tension.
  • Surfactant makes it easier for alveoli to inflate, facilitating breathing.

Mechanics of Breathing

• How air moves in and out of the lungs.
• Air (like any fluid) moves from an area of high pressure to an area of low pressure.
• During inhalation, a low-pressure environment is created in the lungs, causing air to move in from the atmosphere.
• During exhalation, a high-pressure environment is created in the lungs, causing air to move out into the atmosphere.

Boyle's Law

• Boyle's Law: If you decrease the volume of a container filled with gas, you increase the pressure.
• P1V1 = P2V2 (but not explicitly stated in the transcript)
• Conversely, if you increase the volume of a sealed container, you reduce the pressure inside it.
• The lungs change pressure by altering volume.

Changing Lung Volume

• The volume of the lungs is altered through muscle contraction, particularly the diaphragm.
• During quiet breathing (normal, unconscious breathing), inhalation is active.
• The diaphragm contracts, which expands the lungs, sucking air in.
• It's important to get the cause and effect correct: Muscle contraction/relaxation changes volume, which changes pressure, which changes air movement.

Oxygen-Hemoglobin Dissociation Curve

• The curve illustrates the relationship between the partial pressure of oxygen (pO_2) and the saturation of hemoglobin.
• The curve is relatively flat at the top. The normal pO_2 in the lungs (alveoli) is about 100 mm Hg, resulting in almost 100% saturation of hemoglobin.