Respiratory System Overview

Respiratory System Overview

• The respiratory system's function is to facilitate gas exchange between the atmosphere and the blood
• Objectives include: organization of the respiratory system, type of respiration, mechanism of breathing, transport of blood gases, and control of breathing.

Organization of the Respiratory System

• Upper Respiratory Tract:

  • Nose: Warms, humidifies, and filters inspired air
  • Pharynx (throat): Common passageway for air and food
  • Larynx (voice box): Contains vocal cords, directs air to the trachea. Food is directed towards the esophagus.

• Lower Respiratory Tract:

  • Trachea: Cartilaginous tube that connects the larynx to the bronchi. The walls contain cartilage which gives it its cylindrical shape and supports it
  • Bronchi: Two branches bifurcating from the trachea, one entering each lung
  • Bronchial tree: A branching network of bronchi within each lung
  • Alveoli: Tiny air sacs where gas exchange occurs, approximately 300 million in an adult. Lined with a moist layer, which permits gas exchange.

Steps Of Respiration

• Ventilation: Exchange of air between atmosphere and alveoli. Air moves by bulk flow from high pressure to low pressure
• Gas Exchange: Oxygen and Carbon dioxide exchange between alveolar air and blood in lung capillaries by diffusion
• Transport: Oxygen and carbon dioxide transport through pulmonary and systemic circulation by bulk flow
• Gas Exchange 2: Oxygen and carbon dioxide exchange between blood in tissue capillaries and cells in tissues by diffusion
• Cellular Utilization: Cellular utilization of oxygen and production of carbon dioxide

Phases Of Respiration

• Respiration occurs in two phases: inspiration (air enters the lungs) and expiration (air leaves the lungs).
• During normal quiet breathing, inspiration is an active process while expiration is passive.
• Exercise or hyperventilation can make expiration an active process

Expiration is Active During...

• During exercise or voluntary hyperventilation, expiration becomes active. A larger volume of air must be exhaled more rapidly.
• Muscles of the abdominal wall contract, pushing inward on abdominal contents and increasing abdominal pressure, which forces the diaphragm upward.

Mechanics of Respiration

• Air movement is driven by bulk flow, from high to low pressure.
• Air movement in and out of lungs is facilitated by pressure differences caused by changes in lung volume.

Pressures Affecting Respiration

• All respiratory pressures are measured relative to atmospheric pressure ( 760 mmHg at sea level).
• Alveolar pressure fluctuates but is normally about zero
• Intrapleural pressure is always negative to prevent lung collapse. This negative pressure is due to elastic recoil of both lungs and chest wall

Stretchability of the Lung (Compliance)

• Compliance is the ease with which the lungs expand.
• Two main determinants of lung compliance are:
  • Stretchability of lung tissues (particularly elastic connective tissues)
    • Lung tissue thickening reduces compliance
  • Surface tension at the air-water interface within the alveoli

Surface Tension

• Alveolar cells lining the alveoli are moist.
• Surface tension is created by attractive forces between water molecules at the air-water interface.
• Surface tension tends to shrink and resist stretching.
• Lung expansion requires overcoming surface tension.

Surfactant

• Surfactant reduces cohesive forces between water molecules at the alveolar surface.
• Increased lung compliance allows for easier expansion by lowering surface tension.
• Surfactant is secreted by Type II alveolar cells.
• Surfactant molecules reduce hydrogen bonds with water molecules at the air-water interface in the alveoli

Transport of Blood Gases

• OXYGEN TRANSPORT:

  • Dissolved form (3%)
  • Combination with Hemoglobin (97%)

• CARBON DIOXIDE TRANSPORT:

  • Dissolved form (7%)
  • Bicarbonate (63%)
  • Carbamino compounds (30%)

Control of Respiration

• Respiratory control is achieved by:
  • Neural control
  • Chemical regulation

Neural Generation of Rhythmical Breathing

• Inspiration begins through action potentials in nerves leading to the inspiratory muscles.
• Inspiration ends, and expiration occurs when these action potentials stop, and the inspiratory muscles relax due to elastic rebound.

Neural Control of Breathing

• Medullary inspiratory neurons are located in the medulla.
  • They discharge in synchrony with inspiration and stop discharging during expiration.
  • Provide rhythmic input to inspiratory muscles, resulting in rhythmic breathing.
  • The medullary centers contain inspiratory and expiratory centers

Chemical Regulation of Respiration

• Peripheral chemoreceptors are stimulated by:
  • Decreased arterial PO₂
  • Increased arterial H⁺ concentration
  • Increased arterial CO₂ concentration
• Peripheral chemoreceptors (carotid and aortic bodies) send signals to brainstem and provide excitatory input to medullary centers (insrpiratory neurons).
• Central chemoreceptors are located in the medulla.
  • Stimulated by increased H⁺ concentration in the brain's extracellular fluid (which, in turn, is a result of increased CO₂ in the blood).
  • Provide excitatory synaptic input to medullary inspiratory neurons.

Dive into the essentials of the respiratory system with this quiz. Explore the organization, function, and mechanisms of both the upper and lower respiratory tracts. Test your knowledge on how the body facilitates gas exchange and controls breathing.