OIA1004 RESPIRATORY SYSTEM II

Overview of the Respiratory System

Learning Outcomes

Understand the mechanisms of inhalation and exhalation, including the roles of various muscles.

Identify factors affecting pulmonary ventilation, such as pressure changes and airway resistance.

Define lung volumes and capacities, and their significance in respiratory health.

Explain gas exchange processes in external and internal respiration.

Describe how oxygen and carbon dioxide are transported in the blood.

Discuss the regulation of respiration and its physiological importance.

Processes of Respiration

Pulmonary Ventilation: The process of air exchange between the atmosphere and the lungs, consisting of inhalation (active) and exhalation (passive).

External Respiration: Gas exchange between the lungs and blood, where oxygen is absorbed and carbon dioxide is released.

Internal Respiration: Gas exchange between blood and body cells, where carbon dioxide is absorbed and oxygen is released.

Mechanics of Breathing

Inhalation and Exhalation

Inhalation: An active process involving contraction of the diaphragm and external intercostal muscles, leading to increased thoracic volume and decreased intrapulmonary pressure.

Exhalation: Generally a passive process where the diaphragm relaxes, leading to decreased thoracic volume and increased intrapulmonary pressure, except during forced exhalation where abdominal muscles contract.

Boyle’s Law

Boyle’s Law states that at constant temperature, the pressure of a gas varies inversely with its volume, which is fundamental to understanding respiratory mechanics.

Factors Affecting Pulmonary Ventilation

Air Pressure Changes

Changes in air pressure are crucial for pulmonary ventilation, as they drive airflow into and out of the lungs.

Surface Tension of Alveolar Fluid

Surface tension in the alveoli, caused by the attraction of water molecules, can lead to alveolar collapse if not regulated by pulmonary surfactant, which reduces surface tension and prevents collapse.

Respiratory Distress Syndrome (RDS): A condition in premature infants due to insufficient surfactant, leading to increased surface tension and alveolar collapse.

Lung Compliance and Airway Resistance

Lung Compliance: Refers to the lungs' ability to stretch and expand; decreased compliance can occur in diseases like tuberculosis and pulmonary edema.

Airway Resistance: Resistance to airflow in the respiratory passages, influenced by airway diameter; conditions like asthma and COPD increase resistance.

Lung Volumes and Capacities

Definitions and Measurements

Tidal Volume (TV): The amount of air inhaled or exhaled in a normal breath (~500 mL).

Inspiratory Reserve Volume (IRV): The additional air that can be inhaled after a normal inhalation (1900 mL in females, 3100 mL in males).

Expiratory Reserve Volume (ERV): The additional air that can be exhaled after a normal exhalation (700 mL in females, 1200 mL in males).

Residual Volume (RV): The air remaining in the lungs after forced exhalation (1100 mL in females, 1200 mL in males).

Lung Capacities

Inspiratory Capacity (IC): Maximum air that can be inspired after normal expiration (IC = TV + IRV).

Functional Residual Capacity (FRC): Volume remaining in the lungs after normal expiration (FRC = ERV + RV).

Vital Capacity (VC): Maximum air that can be expired after maximum inhalation (VC = TV + IRV + ERV).

Total Lung Capacity (TLC): Maximum air contained in the lungs after maximum inhalation (TLC = TV + IRV + ERV + RV).

Gas Exchange Mechanisms

Dalton’s Law

Dalton’s Law states that the total pressure of a gas mixture is equal to the sum of the partial pressures of each individual gas, which is crucial for understanding gas exchange in the lungs.

Example: The partial pressure of oxygen (PO2) can be calculated as PO2 = 20.9% x 760 mmHg = 159 mmHg.

Gas Exchange Processes

External Respiration: Involves the exchange of gases between the alveoli and the blood in pulmonary capillaries, where oxygen enters the blood and carbon dioxide is expelled.

Internal Respiration: The exchange of gases between the blood in systemic capillaries and the body cells, where oxygen is delivered to cells and carbon dioxide is collected for removal.

Partial Pressure and Gas Diffusion

Gases diffuse from areas of higher partial pressure (↑P) to areas of lower partial pressure (↓P), which is fundamental to gas exchange in the lungs and tissues.

The greater the difference in partial pressure, the faster the rate of diffusion, facilitating efficient gas exchange.

Example: Oxygen (O2) diffuses from the alveoli (high partial pressure) into the blood (lower partial pressure) during inhalation.

Henry's Law and Gas Solubility

Henry's Law states that the amount of gas that dissolves in a liquid is proportional to its partial pressure and solubility in that liquid.

Increased partial pressure and solubility lead to a greater ability of the gas to remain in solution, which is crucial for oxygen and carbon dioxide transport in blood.

Example: Carbon dioxide (CO2) is approximately 24 times more soluble in blood than oxygen, leading to higher concentrations of CO2 in the blood compared to O2.

Factors Affecting Gas Exchange

Surface Area: The alveoli provide a large surface area for gas exchange, maximizing the diffusion of gases.

Diffusion Distance: The respiratory membrane is only 0.5 µm thick, allowing for rapid diffusion of gases; increased partial pressure differences enhance this process.

Efficient gas exchange relies on both external respiration (lungs) and internal respiration (tissues).

Transport of Respiratory Gases

Oxygen Transport

Oxygen is transported in two main ways: dissolved in plasma (1.5%) and bound to hemoglobin (98.5%).

Hemoglobin (Hb) can bind up to four oxygen molecules, forming oxyhemoglobin (HbO2), which is crucial for oxygen delivery to tissues.

Factors affecting oxygen binding include partial pressure of oxygen (PO2), carbon dioxide levels (PCO2), blood pH, temperature, and 2,3-bisphosphoglycerate (BPG).

Carbon Dioxide Transport

Carbon dioxide is transported in three forms: dissolved in plasma (~7%), bound to hemoglobin as carbaminohemoglobin (~23%), and as bicarbonate ions (HCO3-) (~70%).

The conversion of CO2 to bicarbonate is a reversible process that plays a key role in maintaining blood pH and facilitating CO2 transport from tissues to lungs.

Regulation of Breathing

Control Centers for Respiration

The respiratory center consists of clusters of neurons in the brain that regulate breathing, including the medullary rhythmicity area, pneumotaxic area, and apneustic area.

These centers coordinate the transition between inhalation and exhalation, controlling the rate and depth of breathing.

Factors Influencing Breathing Rate and Depth

Normal respiratory rate ranges from 12 to 15 breaths per minute, but can increase (hyperpnea) during exercise or other activities requiring more oxygen.

Various factors influence breathing, including physical activity, emotional state, and chemical signals from CO2 and O2 levels.

Homeostatic Imbalances and Respiratory Diseases

Common Respiratory Conditions

Upper respiratory tract infections (URTIs) include rhinitis, sinusitis, and laryngitis, while lower respiratory tract infections (LRTIs) include pneumonia and bronchitis.

Chronic obstructive pulmonary disease (COPD) encompasses conditions like emphysema and chronic bronchitis, characterized by airflow obstruction and difficulty breathing.

Asthma and COPD

Asthma is a chronic inflammatory disorder of the airways, leading to hypersensitivity and reversible airway obstruction, often triggered by allergens or stress.

COPD is characterized by irreversible airflow obstruction, primarily caused by smoking, leading to symptoms like dyspnea and chronic cough.

Discussion questions

1/6

What are the primary mechanisms involved in inhalation and exhalation, and how do they differ?

Difficulty: Easy

Show example answer

2/6

How do factors such as lung compliance and airway resistance affect pulmonary ventilation?

Difficulty: Medium

Show example answer

3/6

Discuss the significance of Boyle's Law in the mechanics of breathing.

Difficulty: Medium

Show example answer

4/6

What roles do Dalton's and Henry's Laws play in the process of gas exchange in the respiratory system?

Difficulty: Hard

Show example answer

5/6

Analyze the impact of respiratory diseases such as COPD and asthma on lung function and gas exchange.

Difficulty: Hard

Show example answer

6/6

How does the regulation of respiration involve both neural and chemical factors?

Difficulty: Medium

Show example answer