Respiratory System in Humans Grade 11

Respiratory System in Humans Grade 11 Biology: Breathing and Exchange of Gases Comprehensive Study Guide Human Physiology: Respiration 1 Table of Contents 1. Introduction to Respiration 2. Types of Respiration 3. Human Respiratory Organs 4. The Conducting & Respiratory Zones 5. Alveoli: Site of Exchange 6. Mechanism of Breathing 7. Inspiration & Expiration 8. Respiratory Volumes 9. Respiratory Capacities 10. Exchange of Gases 11. Partial Pressures 12. Transport of Oxygen 13. Oxygen-Hemoglobin Dissociation 14. Transport of Carbon Dioxide 15. Regulation of Respiration 16. Chemical Control of Breathing 17. Common Respiratory Disorders 18. Summary & Insights Human Physiology: Respiration 2 19. Practice Exercises 20. Glossary Human Physiology: Respiration 3 1. Introduction to Respiration Respiration is a vital metabolic process by which living cells of an organism obtain energy by taking in oxygen and releasing carbon dioxide from the oxidation of complex organic substances. In humans, this involves two distinct but linked processes: 1. Breathing (External Respiration): The physical process of inhaling oxygen-rich air and exhaling carbon dioxide-rich air. 2. Cellular Respiration (Internal Respiration): The biochemical process where glucose is broken down in the presence of oxygen to release energy (ATP) in the mitochondria. Human Physiology: Respiration 4 2. Types of Respiration Organisms exhibit different respiratory mechanisms depending on their environment and level of organization. - Aerobic Respiration: Occurs in the presence of oxygen. Most efficient, yielding 36-38 ATP per glucose molecule. - Anaerobic Respiration: Occurs in the absence of oxygen. Common in yeast (fermentation) and human muscle cells during strenuous exercise (producing lactic acid). This guide focuses on the complex aerobic system of humans, optimized for high oxygen demand and efficient waste removal. Human Physiology: Respiration 5 3. Human Respiratory Organs: The Upper Tract The human respiratory system starts with the nostrils and ends in the microscopic alveoli. - External Nostrils: Air enters here and is filtered by hair and mucus. - Nasal Chamber: Lines with ciliated epithelium and mucus-secreting cells. It warms and moistens the air. - Pharynx: A common passage for food and air. - Larynx (The Voice Box): A cartilaginous box which helps in sound production. During swallowing, the glottis is covered by the epiglottis to prevent food entry. Larynx Trachea Figure: Diagrammatic representation for academic study. Human Physiology: Respiration 6 4. The Lower Tract: Trachea & Bronchi - Trachea (Windpipe): A straight tube extending up to the mid-thoracic cavity. It is supported by 'C'-shaped hyaline cartilaginous rings which prevent collapse. - Bronchi: At the level of the 5th thoracic vertebra, the trachea divides into right and left primary bronchi. - Bronchial Tree: Bronchi divide repeatedly into secondary, tertiary bronchi, and then into very thin terminal bronchioles. Human Physiology: Respiration 7 5. Alveoli: The Functional Units Each terminal bronchiole gives rise to a number of very thin, irregular-walled and vascularized bag-like structures called alveoli. Key Features of Alveoli: - Enormous Surface Area: Roughly 70 to 100 square meters. - Extremely Thin Walls: Composed of single-layered squamous epithelium. - Rich Blood Supply: Closely surrounded by a network of pulmonary capillaries. This setup ensures rapid diffusion of gases between the air and the blood. Alveolus Capillary Figure: Diagrammatic representation for academic study. Human Physiology: Respiration 8 6. Mechanism of Breathing Breathing involves two stages: Inspiration (air moves into lungs) and Expiration (air moves out). Movement of air is driven by a pressure gradient between the lungs and the atmosphere. - Inspiration occurs if the pressure within the lungs (intra-pulmonary pressure) is less than atmospheric pressure. - Expiration occurs when intra-pulmonary pressure is higher than atmospheric pressure. This gradient is generated by the diaphragm and a specialized set of muscles called external and internal intercostal muscles. Human Physiology: Respiration 9 7. The Breathing Cycle 1. Diaphragm Contraction: Increases the volume of the thoracic chamber in the antero-posterior axis. 2. Intercostal Contraction: Lifts up the ribs and sternum, increasing volume in the dorso-ventral axis. 3. Result: Thoracic volume increases -> Pulmonary volume increases -> Pulmonary pressure decreases -> Air rushes in. Relaxation of these muscles decreases the thoracic volume, increases pressure, and forces air out (Expiration). Thoracic volume increases Diaphragm contracts Figure: Diagrammatic representation for academic study. Human Physiology: Respiration 10 8. Respiratory Volumes (I) Spirometry is used to measure the volume of air involved in respiratory movements. - Tidal Volume (TV): Volume of air inspired or expired during normal breathing. Approx. 500 mL. - Inspiratory Reserve Volume (IRV): Additional volume a person can inspire by a forcible inspiration. 2500 mL to 3000 mL. - Expiratory Reserve Volume (ERV): Additional volume a person can expire by a forcible expiration. 1000 mL to 1100 mL. Human Physiology: Respiration 11 9. Respiratory Volumes (II) & Capacities - Residual Volume (RV): Volume of air remaining in the lungs even after a forcible expiration. 1100 mL to 1200 mL. - Vital Capacity (VC): The maximum volume of air a person can breathe in after a forced expiration (TV + IRV + ERV). - Total Lung Capacity (TLC): Total volume of air accommodated in the lungs at the end of a forced inspiration (VC + RV). Human Physiology: Respiration 12 10. Exchange of Gases Gaseous exchange takes place in two locations: (i) Between Alveoli and Blood, and (ii) Between Blood and Tissues. Exchange occurs through Simple Diffusion based on: 1. Pressure/Concentration gradient. 2. Solubility of the gases. 3. Thickness of the membranes. Solubility of CO2 is 20-25 times higher than that of O2, making its diffusion rate much faster. Human Physiology: Respiration 13 11. Partial Pressures of Gases Partial pressure is the pressure contributed by an individual gas in a mixture of gases (denoted as pO2 and pCO2). Values (in mmHg): Atmospheric: O2 (159), CO2 (0.3) Alveoli: O2 (104), CO2 (40) Deoxygenated Blood: O2 (40), CO2 (45) Oxygenated Blood: O2 (95), CO2 (40) Tissues: O2 (40), CO2 (45) Human Physiology: Respiration 14 12. Transport of Oxygen Oxygen is transported in the blood in two ways: 1. Dissolved state in Plasma (3%). 2. Bound to Hemoglobin (97%) in RBCs. Hemoglobin (Hb) is a red-colored iron-containing pigment. Each Hb molecule can carry a maximum of four molecules of O2. Binding of oxygen depends on pO2, pCO2, H+ concentration, and temperature. Human Physiology: Respiration 15 13. Oxygen-Hemoglobin Dissociation Curve A sigmoid (S-shaped) curve is obtained when the percentage saturation of hemoglobin with O2 is plotted against pO2. Factors shifting curve to the Right (Low affinity): High pCO2, High H+, High Temperature. Factors shifting curve to the Left (High affinity): High pO2, Low pCO2, Low Temperature. In tissues, low pO2 and high pCO2 favor the dissociation of O2 from oxyhemoglobin. Larynx Trachea Figure: Diagrammatic representation for academic study. Human Physiology: Respiration 16 14. Transport of Carbon Dioxide CO2 is transported in three forms: 1. Dissolved in Plasma (7%). 2. As Carbamino-hemoglobin (20-25%). 3. As Bicarbonate ions (70%). Enzyme Carbonic Anhydrase (highly concentrated in RBCs) facilitates the reaction: CO2 + H2O <-> H2CO3 <-> HCO3- + H+. Every 100 mL of deoxygenated blood delivers approx. 4 mL of CO2 to the alveoli. Human Physiology: Respiration 17 15. Regulation of Respiration The human body has a significant ability to maintain and moderate the respiratory rhythm to suit the demands of the body. - Respiratory Rhythm Center: Located in the Medulla oblongata. Primarily responsible for regulation. - Pneumotaxic Center: Located in the Pons Varolii. It can moderate the functions of the rhythm center by reducing the duration of inspiration. Human Physiology: Respiration 18 16. Chemical Control of Breathing - Chemosensitive Area: Situated adjacent to the rhythm center. Highly sensitive to CO2 and hydrogen ions. - Aortic Arch and Carotid Artery Receptors: Can recognize changes in CO2 and H+ concentration and send signals to the rhythm center. Surprisingly, the role of Oxygen in the regulation of respiratory rhythm is quite insignificant compared to CO2. Human Physiology: Respiration 19 17. Common Respiratory Disorders - Asthma: Difficulty in breathing causing wheezing due to inflammation of bronchi and bronchioles. - Emphysema: Chronic disorder where alveolar walls are damaged, reducing respiratory surface area. Major cause is cigarette smoking. - Occupational Disorders: In industries like stone-grinding, long-term exposure to dust leading to lung fibrosis (e.g., Silicosis, Asbestosis). Human Physiology: Respiration 20 18. Summary & Key Concept Map Respiration involves: 1. Breathing -> 2. Diffusion across alveolar membrane -> 3. Transport by blood -> 4. Diffusion between blood and tissues -> 5. Utilization of O2 in cells. Key regulators: Medulla (Inspiration), Pons (Switch off), CO2 levels (Sensitivity). Efficient exchange relies on the massive surface area of alveoli and the thinness of the respiratory membrane. Human Physiology: Respiration 21 19. Practice Questions • 1. Define Vital Capacity. What is its significance? • 2. What is the role of Carbonic Anhydrase in CO2 transport? • 3. Explain the effect of high altitude on respiration. • 4. Why is the shape of the oxygen dissociation curve sigmoid? • 5. Differentiate between IRV and ERV. Human Physiology: Respiration 22 20. Glossary of Terms Oxyhemoglobin: Complex formed by the binding of oxygen with hemoglobin. Pneumotaxic center: Region in the pons that limits inspiration. Pulmonary: Relating to the lungs. Spirometer: Instrument for measuring volumes of air inspired and expired. Hypoxia: Deficiency in the amount of oxygen reaching the tissues. Human Physiology: Respiration 23