Regulation of Respiration

Respiration is a vital physiological process that provides oxygen for cellular metabolism and removes carbon dioxide from the body. In higher animals, the rate and depth of breathing are not constant but are carefully regulated according to the body’s oxygen demand and carbon dioxide levels. The regulation of respiration ensures homeostasis, maintains blood gas levels, and supports proper cellular function during activities like exercise, rest, or stress.

1.0What Is Regulation of Respiration?

Regulation of respiration refers to the control of breathing rate, depth, and rhythm by the nervous and chemical mechanisms. This regulation ensures that the body maintains:

• Optimal oxygen levels for tissues
• Safe carbon dioxide levels in the blood
• Proper pH balance in body fluids

2.0Nervous Regulation of Respiration

The nervous system controls respiration through respiratory centres located in the brainstem.

1. Respiratory Centres in the Brain

Mechanism:

• The dorsal respiratory group (DRG) sends impulses to the diaphragm and external intercostal muscles, causing inspiration.
• The ventral respiratory group (VRG) is mainly active during forced breathing and controls accessory muscles.

2. Reflexes in Respiratory Regulation

Various reflexes influence respiration:

• Hering-Breuer Reflex: Prevents over-inflation of the lungs via stretch receptors.
• Cough Reflex: Clears the respiratory tract of irritants.
• Sneezing Reflex: Expels irritants from the nasal cavity.
• Sneeze and Gag Reflexes: Protect airways.

3.0Chemical Regulation of Respiration

The chemical composition of blood—particularly CO₂, O₂, and pH—plays a crucial role in regulating respiration.

1. Central Chemoreceptors

• Located in the medulla oblongata.
• Sensitive primarily to CO₂ levels in cerebrospinal fluid (CSF).
• High CO₂ → Low pH → Stimulation of medullary centres → Increased breathing rate and depth.

2. Peripheral Chemoreceptors

• Found in carotid bodies (near carotid arteries) and aortic bodies (near aortic arch).
• Sensitive to:
• • Low O₂ levels (hypoxia)
  • High CO₂ levels (hypercapnia)
  • Low pH (acidosis)
• Stimulate the respiratory centres to increase ventilation.

4.0Nervous Regulation of Respiration

The nervous system controls respiration through respiratory centres located in the brainstem.

1. Respiratory Centres in the Brain

• Medullary Respiratory Centre: Located in the medulla oblongata, it controls the basic rhythm of breathing. It contains two main groups of neurons:
• • Dorsal Respiratory Group (DRG): Responsible for the normal, quiet breathing rhythm. It sends impulses to the diaphragm and external intercostal muscles, causing inspiration.
  • Ventral Respiratory Group (VRG): Primarily active during forced breathing (e.g., exercise) and controls accessory muscles of respiration.
• Pontine Respiratory Group (PRG): Located in the pons, it modulates the rate and smoothness of breathing. It includes the apneustic center and the pneumotaxic center.
• • Apneustic Center: Stimulates inspiration, preventing the abrupt stopping of inhalation.
  • Pneumotaxic Center: Inhibits inspiration to regulate the rate and depth of breathing. It fine-tunes the activity of the medullary centers.

2. Reflexes in Respiratory Regulation

Various reflexes also influence breathing patterns:

• Hering-Breuer Reflex: This reflex is triggered by stretch receptors in the walls of the bronchi and bronchioles. It prevents over-inflation of the lungs by sending signals that inhibit the inspiratory centers.
• Cough Reflex: A protective reflex that clears the respiratory tract of irritants by forcefully expelling air.
• Sneezing Reflex: Similar to the cough reflex, it expels irritants from the nasal cavity.

5.0Factors Affecting the Regulation of Respiration

1. Partial Pressure of Gases
2. • Low O₂ or high CO₂ stimulates respiration.
2. Blood pH
3. • Decreased pH (acidosis) increases breathing to remove CO₂.
3. Exercise
4. • Increases O₂ demand and CO₂ production → Breathing rate increases.
4. Emotions and Pain
5. • Stress or anxiety can alter breathing patterns via the limbic system.
5. Temperature
6. • Higher body temperature may slightly increase respiration rate.

6.0Voluntary Control of Respiration

Although mostly automatic, respiration can also be voluntarily controlled by the cerebral cortex. Examples include:

• Holding breath
• Singing or speaking
• Deep breathing exercises

Limitation:

• CO₂ buildup eventually overrides voluntary control, restoring normal breathing.

7.0Comparison Between Nervous and Chemical Regulation