May 30, 2024

Mechanism/Physiology of respiration and regulation of respiration

Mechanism/Physiology of respiration and regulation of respiration

The mechanism of respiration involves a series of coordinated processes that facilitate the exchange of respiratory gases, specifically oxygen (O2) and carbon dioxide (CO2), between the body and the external environment. It can be divided into two main phases: inspiration (inhalation) and expiration (exhalation).


  1. Contraction of Diaphragm: The process begins with the contraction of the diaphragm, a dome-shaped muscle located at the base of the lungs. When the diaphragm contracts, it moves downward, expanding the volume of the thoracic cavity.
  2. Expansion of Thoracic Cavity: The contraction of the diaphragm is accompanied by the contraction of the external intercostal muscles located between the ribs. These muscles lift the ribcage upward and outward, further expanding the thoracic cavity.
  3. Increase in Lung Volume: The expansion of the thoracic cavity lowers the air pressure within the lungs, creating a pressure gradient between the lungs and the external environment. As a result, air flows from an area of higher pressure (outside the body) to an area of lower pressure (inside the lungs).
  4. Inhalation of Air: The increase in lung volume and the resulting decrease in pressure causes air to enter the respiratory tract through the nose or mouth. The air passes through the pharynx, larynx, and trachea, and finally reaches the bronchial tubes and alveoli in the lungs.


  1. Relaxation of Diaphragm and Intercostal Muscles: Expiration is typically a passive process that does not require muscular effort during normal breathing at rest. As the inspiratory muscles (diaphragm and external intercostals) relax, the elastic recoil of the lung tissue and the chest wall recoils inward, reducing the volume of the thoracic cavity.
  2. Decrease in Lung Volume: The decrease in thoracic cavity volume leads to an increase in air pressure within the lungs, creating a pressure gradient that favors the movement of air from the lungs to the external environment.
  3. Exhalation of Air: Air is forced out of the respiratory tract through the same pathway it entered during inspiration, following the pressure gradient from the higher pressure inside the lungs to the lower pressure outside the body.

Regulation of Respiration:
The process of respiration is regulated by the respiratory centers located in the brainstem, primarily the medulla oblongata and the pons. These centers receive sensory information from various sources, including chemoreceptors that monitor blood gas levels (primarily CO2 and O2), and adjust the rate and depth of breathing accordingly to maintain a balance.

The medulla oblongata plays a crucial role in setting the basic rhythm of breathing. It sends nerve impulses to stimulate the diaphragm and intercostal muscles for inspiration. The pons acts as a coordinating center, regulating the transition between inspiration and expiration by inhibiting or stimulating the respiratory centers in the medulla.

The regulation of respiration also involves feedback loops that respond to changes in blood gas levels and other factors, ensuring an appropriate supply of oxygen and removal of carbon dioxide to meet the body’s metabolic demands.

Overall, the mechanism of respiration relies on the coordinated contraction and relaxation of respiratory muscles, changes in thoracic cavity volume, and the resulting pressure gradients to facilitate the exchange of respiratory gases in the lungs.

Regulation of respiration

The regulation of respiration is a complex process that involves several mechanisms to ensure the proper exchange of oxygen and carbon dioxide in the body. It is primarily controlled by the respiratory centers in the brainstem, which receive input from various sensors and adjust the rate and depth of breathing accordingly. Here are the key components involved in the regulation of respiration:

  1. Medullary Respiratory Centers: The medulla oblongata, specifically the dorsal respiratory group (DRG) and the ventral respiratory group (VRG), contains the primary respiratory centers. The DRG controls the basic rhythm of breathing, while the VRG is responsible for coordinating respiratory muscles during forced or active breathing.
  2. Pontine Respiratory Centers: The pons, specifically the pneumotaxic center and the apneustic center, fine-tune the control of respiration. The pneumotaxic center helps regulate the rate and pattern of breathing by modifying the duration and intensity of inspiratory signals from the medullary centers. The apneustic center assists in the control of deep inspiration.
  3. Chemoreceptors: Chemoreceptors are specialized sensors that detect changes in the levels of oxygen, carbon dioxide, and pH (acidity) in the blood and cerebrospinal fluid. The central chemoreceptors, located in the medulla, respond primarily to changes in carbon dioxide levels and indirectly to pH. Peripheral chemoreceptors, located in the carotid and aortic bodies, respond to changes in oxygen, carbon dioxide, and pH levels.
  4. Baroreceptors: Baroreceptors are sensors located in the walls of certain blood vessels, such as the carotid sinus and aortic arch. They detect changes in blood pressure and provide feedback to the respiratory centers to adjust the respiratory rate accordingly.
  5. Stretch Receptors: Stretch receptors in the lungs and airways detect lung inflation and send signals to the respiratory centers, influencing the duration and intensity of expiration.
  6. Higher Brain Centers: The cerebral cortex, hypothalamus, and limbic system can influence respiration voluntarily or in response to emotional states, exercise, or other factors.

The regulation of respiration involves a delicate balance between oxygen demand, carbon dioxide removal, and maintaining acid-base homeostasis. The respiratory centers integrate input from various receptors and adjust the rate, depth, and pattern of breathing to meet the body’s metabolic needs and maintain blood gas levels within narrow limits.

Note that certain medical conditions, such as respiratory disorders, neurological diseases, or disturbances in the chemical or mechanical control systems, can lead to respiratory abnormalities and require medical intervention.

Suggested readings:

First Year Pharm D Subjects Syllabus, Notes, PDF Books, MCQ

1.1Human Anatomy and Physiology
1.3Medicinal  Biochemistry
1.4Pharmaceutical Organic Chemistry
1.5Pharmaceutical Inorganic Chemistry
1.6Remedial Mathematics/ Biology