Control of Respiration in Human Physiology

Control of Respiration

• Breathing is automatic, unlike the heart, which lacks a built-in pacemaker.
• Lung ventilation relies on coordinating complex skeletal muscle actions.
• Unconscious breathing is regulated by respiratory centers in the medulla oblongata and pons.
• Thoracic size changes due to breathing muscle contractions and relaxation, controlled by nerve impulses from the brain.
• Respiratory center is divided into two areas based on location and function: the medullary respiratory center (controls basic rhythm).
  • Two neuron collections: dorsal respiratory group (DRG) (formerly inspiratory area).
    • Normal breathing: DRG neurons trigger diaphragm and external intercostal muscle contractions, causing inhalation.
  • Ventral respiratory group (VRG) (formerly expiratory area).
    • Activated with forceful breathing.
    • Pre-Bötzinger complex is crucial in breathing rhythm generation.
• Pontine respiratory group (PRG) (pneumotaxic area):
  • Active during inhalation and exhalation.
  • Modulates the basic breathing rhythm by influencing the DRG.

Chemoreceptors and Respiration

• Respiratory center activity can be modified by inputs from other brain areas, peripheral nervous system receptors, and factors related to homeostasis.
• Cortical influences allow for conscious control of breathing.
• Chemical stimuli influence how quickly and deeply we breathe (e.g., noxious gases, water).
• Central chemoreceptors are in or near the medulla oblongata in the CNS.
  • Respond to changes in H+ concentration and/or PCO2 in cerebrospinal fluid.
• Peripheral chemoreceptors are located in:
  • Aortic bodies within the arch of the aorta.
  • Carotid bodies in the common carotid arteries' branching points.
  • They respond to changes in H+, PCO2, and PO2 in blood.

Stretch Receptors and Inflation Reflex

• Stretch receptors in bronchi/bronchioles send signals to the DRG (medullary respiratory center) upon lung over-inflation.
• This inhibits the DRG, causing diaphragm and external intercostal muscle relaxation and initiating exhalation.
• Stretch receptors stop sending signals when lungs deflate. DRG inhibition stops, and inhalation resumes—the inflation reflex (or Hering-Breuer).
• In adults, this reflex protects against lung over-expansion.

Other Influences on Respiration

• Other factors influencing respiration include blood pressure, limbic system activity, temperature, pain, anal sphincter stretching, and irritation to respiratory mucosa.

Bronchial Asthma and Emphysema

• Bronchial asthma involves an allergic reaction to inhaled substances (e.g., pollen, dust mites).
• Excessive mucus and edema in smaller airways impede airflow (bronchoconstriction).
• Wheezing sound accompanies air movement through narrowed airways.
• Expiration is more difficult than inspiration in asthma.
• Emphysema is a degenerative lung condition (destroys alveolar walls and air sacs).
• Alveolar surface area declines, reducing gas exchange efficiency.
• Loss of elasticity prevents sufficient exhalation.

Chronic Bronchitis

• Persistent cough producing mucus for at least three months in two consecutive years.
• Symptoms include overweight, cyanosis, peripheral edema, rhonchi, and wheezing.

This quiz explores the automatic and complex nature of breathing regulation in humans. It covers the roles of various brain structures, including the medulla oblongata and pons, in maintaining respiratory rhythm and the mechanics of lung ventilation. Test your understanding of the respiratory centers and their functions.