Respiration is a vital physiological process that provides oxygen to body tissues and removes carbon dioxide produced during cellular metabolism. The body must continuously regulate the rate and depth of breathing to meet changing energy and oxygen demands. This control, known as the regulation of respiration, helps maintain proper gas exchange and ensures the normal functioning of cells, tissues, and organs. It is essential for maintaining the body's internal balance and supporting life.
Respiratory Centres in the Medulla Oblongata
1. Respiratory Rhythm Centre
- The respiratory rhythm centre is situated in the medulla oblongata and is primarily responsible for generating the basic rhythm of breathing. This centre controls the regular cycle of inspiration and expiration that occurs throughout life.
- Within the medulla, groups of neurons known as the dorsal respiratory group and ventral respiratory group coordinate respiratory movements.
- The dorsal respiratory group is mainly involved in normal inspiration, while the ventral respiratory group becomes more active during forceful breathing, such as during exercise or respiratory distress.
- The respiratory rhythm centre continuously generates nerve impulses that stimulate the respiratory muscles and maintain the normal breathing pattern.
2. Chemosensitive Area
- The medulla also contains a highly sensitive chemosensitive region that responds to changes in the concentration of carbon dioxide and hydrogen ions in body fluids.
- An increase in carbon dioxide concentration causes an increase in hydrogen ion concentration, which stimulates this area.
- When activated, the chemosensitive area sends signals to the respiratory rhythm centre, increasing the rate and depth of breathing. This helps remove excess carbon dioxide from the body and restore normal blood chemistry.
Respiratory Centres in the Pons
1. Pneumotaxic Centre
- The pneumotaxic centre is located in the upper region of the pons. This centre plays an important role in regulating the duration of inspiration.
- It sends inhibitory signals to the inspiratory centre in the medulla, thereby limiting the duration of inspiration and preventing excessive inflation of the lungs.
- The pneumotaxic centre helps regulate both respiratory rate and respiratory depth. Strong stimulation of this centre shortens inspiration and increases the breathing rate, whereas weaker stimulation allows longer inspiration and deeper breathing.
2. Apneustic Centre
- The apneustic centre is located in the lower region of the pons.
- This centre promotes inspiration by stimulating the inspiratory neurons present in the medulla.
- The apneustic centre prolongs inspiratory movements and contributes to the regulation of breathing depth.
- The balance between the stimulatory effects of the apneustic centre and the inhibitory effects of the pneumotaxic centre helps maintain a normal and coordinated breathing pattern.
Sensory Receptors Involved in Regulation of Respiration
The respiratory centres receive information from various sensory receptors located throughout the body. These receptors continuously monitor changes in oxygen concentration, carbon dioxide concentration, blood pH, and lung expansion.
Chemoreceptors
Chemoreceptors are specialised sensory receptors that detect chemical changes in blood and body fluids.
- Central Chemoreceptors: Central chemoreceptors are located on the ventral surface of the medulla oblongata. These receptors are highly sensitive to changes in hydrogen ion concentration within the cerebrospinal fluid, which is influenced by carbon dioxide levels in the blood.
- Peripheral Chemoreceptors: Peripheral chemoreceptors are present in the carotid bodies located near the carotid arteries and the aortic bodies situated near the aortic arch.
Pulmonary Receptors
The lungs contain stretch receptors within their walls. These receptors monitor the degree of lung expansion during inspiration. Excessive stretching of the lungs activates these receptors, which send inhibitory signals to the respiratory centres to terminate inspiration and prevent overinflation of the lungs.
Effector Organs of Respiration
The respiratory centres exert their effects through the respiratory muscles, which serve as the effector organs.
- Diaphragm: The diaphragm is the principal muscle of respiration. Contraction of the diaphragm increases the volume of the thoracic cavity, allowing air to enter the lungs during inspiration.
- Intercostal Muscles: The external and internal intercostal muscles are situated between the ribs. These muscles assist in expanding and contracting the chest cavity during breathing.
- Abdominal Muscles: During forceful expiration, such as during vigorous exercise or coughing, the abdominal muscles contract and help expel air from the lungs.
Factors Affecting the Rate of Respiration
- During exercise, muscles require greater amounts of oxygen and produce more carbon dioxide. Consequently, both the rate and depth of respiration increase significantly.
- An increase in body temperature stimulates metabolic activity and increases respiratory rate. Fever is therefore often associated with faster breathing.
- Emotions such as fear, anxiety, excitement, anger, and stress can influence respiratory centres through higher brain centres and alter the breathing pattern.
- An increase in carbon dioxide concentration is one of the strongest stimuli for increased respiration.
- Low oxygen levels, particularly at high altitudes, stimulate peripheral chemoreceptors and increase respiratory activity.
- Some drugs depress respiratory centres, while others stimulate respiratory activity. Toxic substances can also affect the regulation of breathing.