Physiology of Respiration Quiz

Regulation of Respiration Lecture Notes

• Writer: Fatimah Adnan, Al-khamis
• Reviewer: Al-Zahraa Marai, Al-Shakhs
• Date: 2024-2025

Learning Objectives

• Chemoreceptors Location: Anatomical location of chemoreceptors sensitive to changes in arterial PO2, PCO2, and pH involved in ventilation control. Identify the most important chemoreceptors for acute and chronic blood gas alterations.
• Alveolar Ventilation Changes at Altitude: Describe changes in alveolar ventilation upon ascent to high altitude, after two weeks at high altitude, and upon return to sea level.
• Feed-forward Ventilation Control in Exercise: Explain the relevance of feed-forward control of ventilation during exercise.
• Exercise Effects on Blood Gases: Describe the effects of exercise on arterial and mixed venous PCO2, PO2, and pH.
• Hypoxia &Hypercapnia Interaction: Describe the interaction between hypoxia and hypercapnia in the control of alveolar ventilation.
• Causes of Hypoxemia: Define and list the four main causes of hypoxemia.

General Definitions

• Hypoxia: Insufficient oxygen at the cellular level
• Anemic hypoxia: Reduced blood oxygen-carrying capacity (low hemoglobin concentration).
• Circulatory hypoxia: Insufficient oxygenated blood delivery to tissues (stagnant hypoxia).
• Histotoxic hypoxia: Cells' inability to use available oxygen.
• Hypoxic hypoxia: Low arterial blood oxygen partial pressure (PaO2) accompanied by inadequate hemoglobin saturation.
• Respiratory arrest: Permanent cessation of breathing (unless corrected).
• Suffocation: Oxygen deprivation due to inability to breathe oxygenated air.
• Hypercapnia: Elevated partial pressure of carbon dioxide (PaCO2) above 45 mm Hg.

Ventilation

• Mechanism: Mechanical process moving air into and out of the lungs.
• Gas Exchange: Oxygen diffuses from the air to the blood, and carbon dioxide diffuses from the blood to the air (down a concentration gradient).
• Gas Exchange via Diffusion: Occurs entirely by diffusion.

Hyper- and Hypoventilation

• Hyperventilation: Greater than normal ventilation, resulting in PaCO2 below 40mmHg
• Hypoventilation: Lesser than normal ventilation, resulting in PaCO2 above 40mmHg

Components of Respiratory Regulation

• Stimulus: Triggers changes in breathing (e.g., increased CO2, decreased O2, pH changes).
• Sensors: Detect changes, including central and peripheral chemoreceptors and mechanoreceptors.
• Effectors: Respond to stimulus (e.g., respiratory muscles).
• Control Centers: Coordinate responses, including medulla oblongata and pons.

Respiratory Center

• Structure: Composed of neuronal groups in the medulla oblongata and pons (divided into collections of neurons).
• Inspiration: Active process requiring energy for muscle contraction (diaphragm and intercostal muscles)
• Expiration: Passive process involving the elastic recoil of the lungs.

Respiratory Center Components

• Dorsal Respiratory Group (DRG) & Ventral Respiratory Group (VRG): Groups of neurons in the medulla oblongata. DRG primarily responsible for basic rhythm and contraction of external intercostal muscles. VRG involved in forceful and active breathing, mostly contraction of internal intercostals and other muscles too.
• Pneumotaxic Center (PRG): In the pons. Regulates the rate and depth of breathing by controlling transitions between inspiration and expiration.

Chemoreceptors

• Peripheral Chemoreceptors: Located in major blood vessels (aortic bodies and carotid bodies). Detect changes in arterial PO2, PCO2, and pH and send signals to central control centers.
• Central Chemoreceptors: Located in the medulla. Detect changes in CO2 and H+ concentration in cerebrospinal fluid (CSF) and influence ventilation.

Central Chemoreceptors

• Stimulus: Increased PCO2, leading to increased H+ in the cerebrospinal fluid (CSF).
• Response: Increased ventilation to eliminate excess CO2.

Interaction between Hypoxia and Hypercapnia

• Hypoxia: Low oxygen levels.
• Hypercapnia: High carbon dioxide levels.
• Both hypoxia and hypercapnia affect respiration by stimulating chemoreceptors resulting in the regulation of breathing rate and depth.

Effect of High Altitude on Alveolar PO2

• Barometric Pressure Decrease: As altitude rises, barometric pressure decreases, resulting in lower PO2 in both inspired air and alveoli; reduces pulmonary diffusion capacity, reducing arterial PO2.
• Alveolar vs. Arterial PO2: Significant difference between inspired and arterial PO2 at high altitude
• Acute Ventilation Response: Initially, ventilation increases to compensate for reduced PO2.

Ventilation During Exercise

• Blood Gas Changes during Exercise: Arterial PO2, PCO2, and pH remain relatively normal—even during increased oxygen consumption and CO2 production.
• Anticipatory Ventilation: Brain anticipates the increased demand for oxygen and CO2 removal, and ramps up ventilation before the muscles actually need it.

Acclimatization to Low PO2 (High Altitude)

• Increased Pulmonary Ventilation: Increased respiratory rate and depth to enhance oxygen uptake.
• Increased RBC Production: Higher production of red blood cells (RBCs) through erythropoietin (EPO) to carry more oxygen.
• Increased Lung Diffusing Capacity: Increased lung surface area available for gas exchange.
• Increased Tissue Vascularity: Increased blood supply to tissues to facilitate oxygen delivery.
• Increased Oxidative Enzymes: Increased numbers of mitochondria and oxidative enzymes improve oxygen utilization by cells.

Main Causes of Hypoxemia

• Hypoventilation: Reduced breathing rate and depth, leading to insufficient oxygen intake.
• Ventilation-Perfusion Mismatch: Imbalance between airflow (ventilation) and blood flow (perfusion) in the lungs.
• Diffusion Limited: Obstruction of oxygen diffusion in the lungs.
• Low Oxygen in Inspired Air: Low oxygen in the air breathed as is the case in high altitude.

Quiz Questions

• Question 1: CO2 and H+ ions
• Question 2: Inside the medulla
• Question 3: Sensors

Additional Information

• References: Detailed references for further study are available.
• Next Lecture: Transcapillary transport.