Overview of Control of Breathing: Respiratory Centre Physiology and Functions

The control of breathing is a complex process that involves the coordination of neuronal centers and respiratory receptors. Here's a brief overview for first-year medical students:

Respiratory Centers

1. Medullary Respiratory Center:

   • Dorsal Respiratory Group (DRG): Located in the medulla oblongata, it primarily controls the rhythm of inspiration.

   • Ventral Respiratory Group (VRG):

     Also in the medulla, it is responsible for both inspiration and expiration, especially during active breathing.

2. Pontine Respiratory Group:

   • Pneumotaxic Center: Found in the upper pons, it regulates the rate and pattern of breathing by inhibiting the DRG to shorten inspiration.

   • Apneustic Center: Located in the lower pons, it promotes deep and prolonged inspiration by stimulating the DRG.

Respiratory Receptors

1. Central Chemoreceptors: Located in the medulla, these receptors respond to changes in the pH of cerebrospinal fluid, which reflects CO2 levels. High CO2 levels (low pH) stimulate increased breathing to expel CO2.

2. Peripheral Chemoreceptors:

   • Carotid Bodies: Found at the bifurcation of the carotid arteries, they respond primarily to low oxygen levels (hypoxia) but also to CO2 and pH changes.

   • Aortic Bodies: Located along the aortic arch, they function similarly to carotid bodies, detecting changes in oxygen, CO2, and pH.

3. Pulmonary Stretch Receptors: These receptors, located in the smooth muscles of the airways, respond to the stretch of the lungs and help prevent over-inflation by initiating the Hering-Breuer reflex, which inhibits inspiration.

4. Irritant Receptors: Located in the airway epithelium, they respond to noxious stimuli such as smoke, dust, and cold air, leading to protective reflexes like coughing and bronchoconstriction.

Integration and Function

• The respiratory centers in the brainstem receive input from various receptors and higher brain centers to maintain homeostasis.

• This coordinated control ensures adequate ventilation to meet the metabolic demands of the body, maintaining appropriate levels of oxygen and carbon dioxide in the blood.