Respiratory System Physiology Review Sheet

Respiratory System Physiology: A Comprehensive Review Sheet

Understanding the respiratory system is crucial for anyone studying biology, medicine, or related fields. This comprehensive review sheet delves into the intricate processes involved in breathing, gas exchange, and the regulation of respiratory function. We'll cover everything from the basic anatomy to the complex interplay of neural and chemical controls. This in-depth review will equip you with a solid foundation in respiratory physiology.

I. Introduction: An Overview of Respiratory Function

The primary function of the respiratory system is gas exchange: taking in oxygen (O2) from the atmosphere and releasing carbon dioxide (CO2) produced by cellular metabolism. This vital process is essential for maintaining homeostasis and supporting life. The respiratory system achieves this through several key steps:

• Pulmonary Ventilation: The process of moving air into and out of the lungs (breathing).
• External Respiration: The exchange of gases between the lungs and the blood.
• Gas Transport: The movement of oxygen and carbon dioxide in the blood.
• Internal Respiration: The exchange of gases between the blood and the body tissues.
• Cellular Respiration: The use of oxygen by cells to produce energy (ATP) and the production of carbon dioxide as a byproduct.

II. Anatomy of the Respiratory System: A Structural Foundation

Effective gas exchange relies on a precisely structured system. Let's review the key anatomical components:

• Upper Respiratory Tract:

  • Nose and Nasal Cavity: Filters, warms, and humidifies incoming air. Contains olfactory receptors for smell.
  • Pharynx (Throat): Passageway for both air and food.
  • Larynx (Voice Box): Contains vocal cords responsible for sound production. Protects the airway during swallowing via the epiglottis.

• Lower Respiratory Tract:

  • Trachea (Windpipe): A rigid tube supported by cartilage rings, conducting air to the lungs.
  • Bronchi: The trachea branches into two main bronchi, which further subdivide into smaller bronchioles. These tubes are lined with cilia and mucus-producing cells to trap and remove foreign particles.
  • Bronchioles: The smallest airways, leading to the alveoli. Smooth muscle in their walls allows for regulation of airflow.
  • Alveoli: Tiny air sacs where gas exchange takes place. Their large surface area and thin walls facilitate efficient diffusion of oxygen and carbon dioxide.
  • Lungs: Paired organs housed in the thoracic cavity, containing millions of alveoli. Surrounded by the pleural membranes, which create a lubricating fluid-filled space reducing friction during breathing.

III. Pulmonary Ventilation: The Mechanics of Breathing

Breathing is a rhythmic process driven by changes in pressure within the thoracic cavity. Understanding the mechanics requires understanding the role of muscles and pressure gradients:

• Inspiration (Inhalation):

  • Diaphragm Contraction: The diaphragm, the primary muscle of breathing, contracts and flattens, increasing the volume of the thoracic cavity.
  • External Intercostal Muscle Contraction: These muscles between the ribs contract, lifting the rib cage and further expanding the thoracic cavity.
  • Decreased Intrapleural Pressure: The expansion of the thoracic cavity decreases the pressure within the pleural space (intrapleural pressure), causing the lungs to expand.
  • Decreased Intrapulmonary Pressure: The expansion of the lungs decreases the pressure within the lungs (intrapulmonary pressure), creating a pressure gradient that draws air into the lungs.

• Expiration (Exhalation):

  • Diaphragm Relaxation: The diaphragm relaxes and moves upwards, decreasing the volume of the thoracic cavity.
  • External Intercostal Muscle Relaxation: These muscles relax, allowing the rib cage to move downwards and inwards.
  • Increased Intrapleural Pressure: The decrease in thoracic volume increases intrapleural pressure.
  • Increased Intrapulmonary Pressure: The decrease in lung volume increases intrapulmonary pressure, exceeding atmospheric pressure and forcing air out of the lungs.

• Forced Breathing: During strenuous activity or respiratory distress, accessory muscles like the sternocleidomastoid and scalenes assist in inspiration, while abdominal muscles aid in expiration.

IV. Gas Exchange: Diffusion Across Membranes

The efficient exchange of oxygen and carbon dioxide relies on simple diffusion, driven by partial pressure gradients:

• Partial Pressure: The pressure exerted by a specific gas in a mixture of gases. The total pressure is the sum of the partial pressures of all gases.

• External Respiration (Alveoli to Blood): Oxygen diffuses from the alveoli (high partial pressure of O2) into the pulmonary capillaries (low partial pressure of O2). Simultaneously, carbon dioxide diffuses from the pulmonary capillaries (high partial pressure of CO2) into the alveoli (low partial pressure of CO2).

• Internal Respiration (Blood to Tissues): Oxygen diffuses from the systemic capillaries (high partial pressure of O2) into the body tissues (low partial pressure of O2). Carbon dioxide diffuses from the tissues (high partial pressure of CO2) into the systemic capillaries (low partial pressure of CO2).

• Factors Affecting Diffusion: Surface area of alveoli, thickness of respiratory membrane, partial pressure gradients, and solubility of gases all influence the rate of gas exchange.

V. Gas Transport: Oxygen and Carbon Dioxide in the Blood

Once gases have crossed the respiratory membrane, they are transported in the blood:

• Oxygen Transport:

  • Hemoglobin: The majority of oxygen is bound to hemoglobin, a protein in red blood cells. Hemoglobin's affinity for oxygen is influenced by factors like pH, temperature, and the partial pressure of carbon dioxide (Bohr effect).
  • Dissolved Oxygen: A small amount of oxygen is dissolved directly in the plasma.

• Carbon Dioxide Transport:

  • Bicarbonate Ions: Most carbon dioxide is transported as bicarbonate ions (HCO3-) in the plasma. This conversion occurs in red blood cells with the help of carbonic anhydrase.
  • Carbaminohemoglobin: Some carbon dioxide binds to hemoglobin, forming carbaminohemoglobin.
  • Dissolved Carbon Dioxide: A small amount of carbon dioxide is dissolved directly in the plasma.

VI. Neural Control of Respiration: Rhythmic Breathing

Breathing is controlled by a complex interplay of neural pathways:

• Respiratory Center: Located in the brainstem (medulla oblongata and pons), this center generates the rhythmic pattern of breathing. It receives input from chemoreceptors and other sensory receptors.

• Chemoreceptors: These sensory receptors detect changes in blood pH, partial pressure of carbon dioxide, and partial pressure of oxygen. They send signals to the respiratory center to adjust breathing rate and depth.

• Peripheral Chemoreceptors: Located in the carotid and aortic bodies, they primarily monitor blood oxygen levels.

• Central Chemoreceptors: Located in the medulla oblongata, they primarily monitor cerebrospinal fluid carbon dioxide levels. Increased CO2 leads to increased H+ ions (lower pH), stimulating the respiratory center.

• Other Sensory Input: Stretch receptors in the lungs (Hering-Breuer reflex) prevent overinflation, and irritant receptors trigger coughing or sneezing in response to foreign substances.

VII. Chemical Control of Respiration: Maintaining Blood Gases

The chemical environment of the blood plays a critical role in regulating breathing:

• Carbon Dioxide (CO2): The most potent stimulus affecting breathing rate and depth. Increased CO2 levels lead to increased H+ ions (lower pH), stimulating the respiratory center.

• Oxygen (O2): Oxygen levels exert a significant effect only when they are significantly low (hypoxia).

• pH: Changes in blood pH (acidosis or alkalosis) influence breathing. Acidosis (low pH) stimulates ventilation, while alkalosis (high pH) depresses ventilation.

VIII. Lung Volumes and Capacities: Measuring Respiratory Function

Several parameters quantify lung function:

• Tidal Volume (TV): The volume of air moved in and out of the lungs during a single breath.

• Inspiratory Reserve Volume (IRV): The extra volume of air that can be forcibly inhaled after a normal breath.

• Expiratory Reserve Volume (ERV): The extra volume of air that can be forcibly exhaled after a normal breath.

• Residual Volume (RV): The air remaining in the lungs after a maximal exhalation.

• Inspiratory Capacity (IC): TV + IRV

• Functional Residual Capacity (FRC): ERV + RV

• Vital Capacity (VC): TV + IRV + ERV

• Total Lung Capacity (TLC): TV + IRV + ERV + RV

IX. Respiratory Disorders: Common Conditions Affecting the System

Many conditions can impair respiratory function:

• Asthma: Characterized by bronchospasm, inflammation, and mucus production, leading to airway obstruction.

• Chronic Obstructive Pulmonary Disease (COPD): Includes emphysema and chronic bronchitis, causing airflow limitations.

• Pneumonia: Infection of the lungs causing inflammation and fluid accumulation in the alveoli.

• Cystic Fibrosis: A genetic disorder affecting mucus production, leading to airway obstruction and frequent lung infections.

• Pulmonary Embolism: A blood clot blocking blood flow to part of the lung.

• Lung Cancer: Uncontrolled growth of cells in the lungs.

X. Frequently Asked Questions (FAQ)

Q: What is the difference between internal and external respiration?

A: External respiration is the gas exchange between the lungs and the blood, while internal respiration is the gas exchange between the blood and body tissues.

Q: How is oxygen transported in the blood?

A: Most oxygen is transported bound to hemoglobin in red blood cells. A small amount is dissolved in the plasma.

Q: What is the role of the diaphragm in breathing?

A: The diaphragm is the primary muscle of breathing. Its contraction increases the volume of the thoracic cavity, leading to inhalation.

Q: How does the respiratory system regulate blood pH?

A: The respiratory system regulates blood pH by controlling the level of carbon dioxide in the blood. Increased CO2 leads to decreased pH (acidosis), and the respiratory system increases ventilation to remove CO2 and restore pH.

Q: What is the difference between tidal volume and vital capacity?

A: Tidal volume is the volume of air inhaled and exhaled in a single breath. Vital capacity is the maximum volume of air that can be exhaled after a maximal inhalation.

Q: What is the Hering-Breuer reflex?

A: The Hering-Breuer reflex is a protective mechanism that prevents overinflation of the lungs. Stretch receptors in the lungs send signals to the respiratory center to inhibit inspiration when lung volume reaches a certain point.

Q: What are some common signs and symptoms of respiratory problems?

A: Common signs and symptoms of respiratory problems include shortness of breath (dyspnea), cough, wheezing, chest pain, and increased sputum production.

XI. Conclusion: A Deeper Understanding of Respiration

This review sheet provides a comprehensive overview of respiratory system physiology. From the basic anatomy and mechanics of breathing to the complex regulatory mechanisms involved, understanding these processes is essential for appreciating the vital role respiration plays in maintaining life. Remember that continuous learning and further exploration of specific areas will solidify your understanding of this fascinating and critical physiological system. This detailed overview serves as a valuable resource for students and professionals alike, offering a solid foundation for further study and application. By understanding the intricacies of respiratory function, we can better appreciate its importance and address any challenges that may arise.