Regulation of Respiration PDF

Regulation of respiration D/Suzan Mustafa Hazzaa Professor of clinical physiology Physiology department Menoufia University  1) Neural regulation The respiratory system is under involuntary control by the brainstem (medulla oblongata and pons). But can be overridden by...

Regulation of respiration D/Suzan Mustafa Hazzaa Professor of clinical physiology Physiology department Menoufia University  1) Neural regulation The respiratory system is under involuntary control by the brainstem (medulla oblongata and pons). But can be overridden by voluntary control from the cerebral cortex during activities like speaking or holding your breath.  Medullary Respiratory Centers: The medulla oblongata contains two key groups of neurons: Dorsal Respiratory Group (DRG): This group controls the basic rhythm of breathing by generating impulses that cause the diaphragm and external intercostal muscles to contract, initiating inspiration. It primarily responds to feedback from chemoreceptors and mechanoreceptors. Ventral Respiratory Group (VRG): This group becomes active during forced breathing (e.g., exercise, or when you need to breathe more deeply). It controls both inhalation and exhalation by stimulating accessory respiratory muscles.  Pontine Respiratory Centers: Located in the pons, these centers regulate the rhythm of breathing by interacting with the medullary centers. Pneumotaxic Center: It helps limit inspiration and regulate the transition from inspiration to expiration, preventing overinflation of the lungs. Apneustic Center: Promotes deeper and prolonged inspiration by stimulating the DRG.  2) Chemical regulation The most important regulators of breathing are chemoreceptors that monitor the levels of carbon dioxide (CO₂), oxygen (O₂), and pH in the blood and cerebrospinal fluid (CSF). They ensure that breathing rate and depth adjust to maintain appropriate gas levels.  Central Chemoreceptors Located in the medulla oblongata, these receptors are sensitive to the pH of the cerebrospinal fluid, which is influenced by CO₂ levels in the blood. High CO₂ levels lead to an increase in H⁺ concentration (lower pH), which stimulates the central chemoreceptors to increase the rate and depth of breathing (hyperventilation), promoting CO₂ elimination. Low CO₂ levels lead to a decrease in ventilation (hypoventilation).  Peripheral Chemoreceptors Located in the carotid bodies and aortic bodies, these receptors primarily detect changes in blood oxygen levels (PaO₂) and to a lesser extent CO₂ and pH. When oxygen levels drop significantly (hypoxemia), these chemoreceptors send signals to the brainstem to increase breathing rate and depth. Peripheral chemoreceptors are particularly important in conditions where oxygen is low, such as high altitudes or lung diseases.  3) Mechanical Control (Stretch Receptors and Proprioceptors): Pulmonary Stretch Receptors (Hering-Breuer Reflex): Located in the smooth muscles of the airways, these receptors prevent overinflation of the lungs by detecting lung stretch. When the lungs are overstretched during deep inspiration, stretch receptors send inhibitory signals to the brainstem, preventing further inspiration (inhibiting the DRG) and stimulating expiration. Proprioceptors: Located in muscles and joints, proprioceptors detect body movement and can signal an increased need for oxygen during exercise, thus increasing the breathing rate.  4) Voluntary Control (Cerebral Cortex): The cerebral cortex allows voluntary control over breathing, which is important for activities like speaking, singing, or breath-holding. However, the brainstem will eventually override voluntary control when CO₂ levels rise too high, forcing the person to breathe (e.g., after holding your breath for too long).  5) Chemical Feedback from Blood (CO₂, O₂, pH): Carbon Dioxide (CO₂): CO₂ is the most important driver of respiration. Even slight increases in CO₂ levels (hypercapnia) will trigger an increase in breathing to expel excess CO₂. Oxygen (O₂): O₂ levels play a lesser role in regulating respiration, but when they fall below a critical threshold, peripheral chemoreceptors trigger an increase in ventilation. pH (Hydrogen Ion Concentration): Changes in blood pH (acidosis or alkalosis) also influence breathing. For example, increased H⁺ levels (low pH) in the blood due to conditions like metabolic acidosis will stimulate an increase in respiratory rate to "blow off" CO₂ and raise pH.  6) Other Factors Affecting Respiratory Control: Emotions: The limbic system and hypothalamus can influence breathing during emotional states (e.g., fear, anxiety, pain). Temperature: Increases in body temperature, such as during fever or exercise, can increase breathing rate. Medications: Drugs like opioids or sedatives can depress the respiratory centers, leading to slower breathing or respiratory failure. Exercise: During physical activity, respiratory rate and depth increase to meet the higher oxygen demand and eliminate excess CO₂ produced by working muscles.  Hypoxia Hypoxia is a condition in which there is an inadequate supply of oxygen to the tissues of the body. 1. Hypoxic hypoxia: It is a specific type of hypoxia in which the oxygen pressure in the blood is low because of insufficient oxygen levels in the environment or inadequate lung function. This condition results in reduced oxygen delivery to tissues and cells, even though the blood flow may be normal. Causes of Hypoxic Hypoxia: a. Low oxygen tension as in High Altitudes. b. Lung Diseases: Conditions like chronic obstructive pulmonary disease (COPD), pneumonia, or acute respiratory distress syndrome (ARDS) can impair oxygen absorption in the lungs. c. Airway Obstruction: Blockages in the airway, like choking or a severe allergic reaction, can limit oxygen intake. 2. Anemic hypoxia: It is a form of hypoxia in which the blood's ability to carry oxygen is reduced, despite normal oxygen levels in the lungs and air. This occurs when there is a deficiency of hemoglobin. Causes of Anemic Hypoxia: a. Anemia: Conditions that reduce red blood cell count or hemoglobin levels, such as iron deficiency anemia, vitamin B12 deficiency, or chronic diseases, can lead to this form of hypoxia. b. Hemorrhage: Severe blood loss from trauma, surgery, decreasing oxygen delivery to tissues. c. Carbon Monoxide Poisoning: Carbon monoxide binds tightly to hemoglobin, preventing oxygen from binding and being transported, leading to hypoxia. d. Hemoglobin Abnormalities: Conditions like sickle cell disease or thalassemia can cause abnormal hemoglobin, reducing its ability to carry oxygen. e. Chronic Kidney Disease: Reduced production of erythropoietin, a hormone that stimulates red blood cell production, can lead to anemia and subsequent hypoxia. 3. Stagnant hypoxia (ischemic hypoxia: It occurs when the flow of oxygenated blood to tissues is reduced or slowed, leading to inadequate oxygen delivery, even though the blood contains normal amounts of oxygen. This condition is primarily due to poor blood circulation rather than a problem with the oxygen content of the blood itself. Causes of Stagnant Hypoxia: a. Heart Failure: When the heart is unable to pump blood effectively, it leads to poor circulation and decreased oxygen delivery to tissues. b. Shock: Conditions like septic, hypovolemic, or cardiogenic shock can severely reduce blood flow and oxygen transport to tissues. c. Blood Clots or Embolism: Blockages in blood vessels, such as a deep vein thrombosis or pulmonary embolism, can restrict blood flow, causing localized hypoxia. d. Prolonged Bed Rest or Immobilization: Lack of movement can reduce circulation in certain areas of the body, leading to stagnation and inadequate oxygen supply. 4. Histotoxic hypoxia: It occurs when the cells and tissues of the body are unable to use the oxygen that is delivered to them, despite adequate oxygen supply in the blood and normal circulation. The cells cannot effectively utilize the oxygen because they have been poisoned or damaged, often by toxins that interfere with cellular respiration. Causes of Histotoxic Hypoxia: a. Cyanide Poisoning: Cyanide inhibits cellular enzymes, particularly cytochrome oxidase, which is crucial for the electron transport chain in mitochondria, preventing cells from using oxygen to produce energy (ATP). b. Alcohol Poisoning: High levels of alcohol can interfere with cellular metabolism and the ability of cells to use oxygen efficiently. c. Certain Drugs or Poisons: Some drugs and chemicals, like narcotics or anesthetics, can impair cellular respiration. d. Sepsis: Severe infections can cause toxins to be released into the bloodstream, impairing cellular oxygen utilization. e. Carbon Monoxide Poisoning: Although primarily a cause of anemic hypoxia, carbon monoxide also has a histotoxic effect by inhibiting cellular respiration in tissues. Symptoms of Hypoxia: 1. Shortness of breath (dyspnea) 2. Rapid breathing (tachypnea) 3. Dizziness or lightheadedness 4. Cyanosis (bluish discoloration of the skin or lips) 5. Confusion or impaired mental function 6. Fatigue and weakness 7. Loss of consciousness in severe cases  Cyanosis Cyanosis is a condition characterized by a bluish discoloration of the skin and mucous membranes. It occurs when reduced hemoglobin increase above 5%. Types of Cyanosis: 1. Central Cyanosis: This form affects the lips, tongue, and other central parts of the body. It indicates a systemic lack of oxygen in the blood. Causes: a. Respiratory diseases (e.g., chronic obstructive pulmonary disease, pneumonia) b. Congenital heart disease c. Severe hypoxia (e.g., high altitude, drowning) d. Pulmonary embolism or other lung conditions 2. Peripheral Cyanosis: This form affects the extremities, such as fingers, toes, hands, and feet, usually due to poor circulation or reduced oxygen delivery to these areas. Causes: a. Cold exposure (leading to vasoconstriction) b. Peripheral vascular disease c. Heart failure. Thank you 22