Regulation of Respiration

Regulation of Respiration

Overview of the Respiratory System

  • Components:
    • Nasal cavity
    • Voice box (larynx)
    • Windpipe (trachea)
    • Bronchi
    • Lungs (right & left)
    • Alveoli
    • Capillaries
    • Diaphragm

Brain Stem Centers Regulating Respiration

  • Key centers:
    1. Medullary Rhythmicity Area (medulla oblongata)
    2. Pneumotaxic Center (upper pons)
    3. Apneustic Center (lower pons)

Medullary Rhythmicity Area

  • Divisions:
    • Inspiratory Area (Dorsal Respiratory Group, DRG):
    • Stimulates inhalation
    • Establishes basic rhythm of breathing
    • Mechanism: Impulses for 2 sec to intercostal muscles and diaphragm, followed by 3 sec of relaxation for expiration
    • Expiratory Area (Ventral Respiratory Group, VRG):
    • Involved in forceful expiration, becomes active during high demand (e.g., exercise)

Pneumotaxic Center

  • Function:
    • Located in upper pons, transmits inhibitory impulses to inspiratory area
    • Prevents over-inflation, encourages shorter inhalation
    • Coordinates transition between inspiration and expiration

Apneustic Center

  • Function:
    • Located in lower pons, stimulates and prolongs inspiration
    • Inhibits expiration, but can be overridden by signals from the pneumotaxic center

Regulation Influences

Chemical Influences

  • Central Chemoreceptors:
    • Located in the medulla, respond primarily to [H+] and indirectly PCO2 levels in CSF and blood
  • Peripheral Chemoreceptors:
    • Located in aortic and carotid bodies, respond to changes in blood PO2, PCO2, and [H+]

Other Influences on Respiration

  1. Cerebral Cortical Influences:
    • Voluntary control over breathing
    • Can override chemical stimuli but is limited by high CO2 and H+ levels
  2. Proprioceptors:
    • Located in muscles and joints, increase breathing rate during exercise
  3. Limbic System:
    • Anticipation of activity or emotional stress increases respiratory rate
  4. Body Temperature:
    • Increased temperature raises respiratory rate, while decreased temperature lowers it
  5. Pain:
    • Severe pain can cause brief apnea, while prolonged pain may increase rate
  6. Irritation of Airways:
    • Leads to cessation of breathing followed by coughing/sneezing
  7. Blood Pressure:
    • Baroreceptors react to pressure changes, sudden increases can temporarily decrease respiratory rate

Factors Affecting Ventilation

  • Stimuli That Increase Ventilation:

    1. Hyperventilation due to activity anticipation
    2. Increased arterial blood PCO2
    3. Decreased arterial blood PO2
    4. Increased activity by proprioceptors
    5. Elevated body temperature
    6. Prolonged pain
    7. Stretching of anal sphincter

  • Stimuli That Decrease Ventilation:

    1. Hypoventilation
    2. Decreased arterial blood PCO2
    3. Very low arterial blood PO2
    4. No or decreased activity of proprioceptors
    5. Low body temperature
    6. Severe pain
    7. Irritation from chemicals in the pharynx or larynx

Mechanisms of Respiratory Control

  • Negative Feedback Mechanism:
    • Reduces output when blood gases reach normal functioning levels (PCO2, PO2, [H+])
    • Chemoreceptors play key roles in this feedback to adjust breathing rate accordingly.

Importance of Carotid Body in Oxygen Sensing

  • Function:

    • Glomus cells in carotid bodies act as chemoreceptors, detecting low blood oxygen levels and signaling the respiratory control centers to increase ventilation.

  • Response Mechanism:

    1. Low PO2 closes K+ channels
    2. Cells depolarize and release dopamine, generating action potentials that signal for increased ventilation.