WEEK 3 RESPIRATORY SYSTEM

Why the Respiratory System?

• Oxygen (O_2) is essential for biological energy production via cellular respiration, powering bodily functions and sustaining life.

• The respiratory system enables the acquisition of O_2 from the environment, ensuring a continuous supply for ATP production from glucose, which fuels cellular activities.

As an Exercise Scientist

• **VO_2 max test**: Measures cardiorespiratory fitness/aerobic capacity, indicating the maximum rate of oxygen consumption during exercise.

  • This test involves incremental exercise to exhaustion while measuring ventilation (air in/out), and levels of expired O2 and CO2.

  • The plateau of oxygen consumption despite increasing workload signifies VO_2 max, crucial for assessing aerobic endurance.

• Information like ventilation and levels of expired O2 and CO2 is crucial to calculate internal oxygen consumption, reflecting the body's efficiency in utilizing oxygen.

  • The respiratory exchange ratio can offer information about fuel utilization during exercise (e.g. carbs vs fats)

• Analysis of O2 usage and CO2 production helps understand what macronutrients are being metabolized, providing insights into energy source utilization during physical activity.

• Uses:

  • Baseline measures pre-training, assessing initial fitness levels.

  • Post-training to assess training effectiveness, evaluating improvements in aerobic capacity.

  • Energy requirements for exercise, guiding training intensity and duration.

  • Resting metabolic rate for weight loss prescriptions, aiding in personalized dietary plans.

  • Estimation of lactate threshold to enhance performance, optimizing training strategies.

• **Scope of Practice**:

  • Assess functional capacity, determining the ability to perform physical tasks.

  • Utilize spirometry to measure lung function to interpret fitness levels, identifying potential respiratory limitations.

Primary Functions of the Respiratory System

• **Respiration (Breathing)**: Exchange of O2 and CO2 across lung membranes.

• **Respiration**: Act of breathing; gas exchange at the lungs, facilitating oxygen uptake and carbon dioxide removal.

• **Cellular Respiration**: Metabolic processes converting biochemical energy into ATP and producing waste (CO_2), essential for energy production at the cellular level.

Steps of Respiration

1. **Pulmonary Ventilation**: Movement of air in/out of the lungs.

   • **Inspiration**: Air enters the respiratory system, filling the lungs with oxygen-rich air.

     • Involves contraction of the diaphragm and external intercostal muscles, increasing thoracic volume.

   • **Expiration**: Air exits the respiratory system, expelling carbon dioxide-laden air.

     • Usually a passive process resulting from the relaxation of inspiratory muscles, decreasing thoracic volume.

2. **External Respiration**: Gas exchange between the alveoli and bloodstream.

   • O2 enters blood, CO2 exits, enriching the blood with oxygen and removing carbon dioxide.

   • Occurs due to differences in partial pressures of gases, with oxygen moving from alveoli to blood, and carbon dioxide from blood to alveoli.

3. **Transport of Gases**: Blood circulates O2 and CO2 to/from tissues, ensuring delivery of oxygen and removal of carbon dioxide.

   • Oxygen is primarily transported bound to hemoglobin in red blood cells, while carbon dioxide is transported as bicarbonate ions, dissolved in plasma, or bound to hemoglobin.

4. **Internal Respiration**: Gas exchange between blood and tissues.

   • O2 leaves blood for tissue, CO2 enters blood, delivering oxygen to cells and removing carbon dioxide waste.

   • Oxygen diffuses from blood to cells due to lower partial pressure of oxygen in tissues, while carbon dioxide diffuses from cells to blood due to higher partial pressure in tissues.

Additional Functions of Respiration

• Regulation of blood pH via CO_2 levels affecting acidity/alkalinity, maintaining acid-base balance.

  • Respiratory rate and depth can be adjusted to alter CO_2 levels in the blood, influencing pH.

• Production of chemical mediators, e.g., enzymes to regulate blood pressure, contributing to cardiovascular homeostasis.

  • The lungs produce angiotensin-converting enzyme (ACE), which plays a role in the renin-angiotensin-aldosterone system to regulate blood pressure.

• Voice production through air movement over vocal folds, enabling speech and vocalization.

• Olfaction (sense of smell), detecting airborne molecules for environmental awareness.

• Protection from microorganisms entering the body, filtering and trapping pathogens to prevent infections.

  • Structures like the mucociliary escalator in the respiratory tract help trap and remove pathogens and debris.

Respiratory Anatomy

• **Thoracic Cavity**: Space within the thoracic wall and diaphragm, housing the lungs and other respiratory structures.

• **Diaphragm**: Skeletal muscle separating thoracic and abdominal cavities, playing a key role in breathing.

  • Contraction of the diaphragm increases thoracic volume, leading to inhalation, while relaxation decreases thoracic volume, leading to exhalation.

• **Thoracic Wall**: Composed of vertebrae, ribs, costal cartilage, sternum, and associated muscles, providing structural support and protection.

• **Respiratory Musculature**:

  • **Inspiration**: Diaphragm, external intercostals, pectoralis minor, scalenes, sternocleidomastoid, facilitating lung expansion.

  • These muscles work together to increase the volume of the thoracic cavity, allowing air to flow into the lungs.

  • **Expiration**: Internal intercostals, abdominal muscles, aiding in lung compression.

  • These muscles contract to decrease the volume of the thoracic cavity, forcing air out of the lungs.

• Lungs: 50-100 m^2 surface area for gas exchange, 4-6 L volume, 2400 km of airway, 960 km of capillaries, maximizing gas exchange efficiency.

  • The large surface area and extensive network of capillaries facilitate efficient gas exchange between air and blood

• **Pleura**: Produces lubricating fluid to facilitate lung movement, reducing friction during breathing.

  • The pleura consists of two layers, the visceral pleura covering the lungs and the parietal pleura lining the thoracic cavity, with a pleural space in between filled with fluid.

Respiratory Tract Anatomy

• **Upper Respiratory Tract**:

  • External Nose, Nasal Cavity, Pharynx, Larynx.

  • The structures warm, humidify and filter air before it enters the lower respiratory tract

• **Lower Respiratory Tract**:

  • Trachea, Bronchi and Bronchioles, Lungs.

Conducting vs Respiratory Zones

• **Conducting Zone**: Air movement, includes trachea, bronchi, bronchioles, transporting air to the respiratory zone.

  • The conducting zone does not participate in gas exchange but serves to conduct air to the respiratory zone.

• **Respiratory Zone**: Site of gas exchange in respiratory bronchioles and alveoli, facilitating oxygen and carbon dioxide exchange.

  • The respiratory zone contains structures where gas exchange occurs, such as respiratory bronchioles, alveolar ducts, and alveoli.

Gas Laws in Respiration

1. **Boyle's Law**: Inversely related pressure and volume in gas systems, explaining air movement during breathing.

   • As the volume of the thoracic cavity increases during inspiration, the pressure decreases, causing air to flow into the lungs.

2. **Dalton's Law**: Total pressure equals sum of individual gas pressures, determining gas concentrations in mixtures.

   • The partial pressure of oxygen in the air determines the amount of oxygen that diffuses into the blood in the lungs.

3. **Henry's Law**: Gas dissolves in a liquid proportional to its partial pressure and solubility, affecting gas exchange in the lungs.

   • The amount of oxygen that dissolves in the blood is proportional to its partial pressure in the alveolar air and its solubility in blood.

Gas Exchange Mechanisms

• **Internal**: Gas exchange between systemic capillaries and tissue cells, delivering oxygen to tissues and removing carbon dioxide.

  • Oxygen diffuses from blood to cells, while carbon dioxide diffuses from cells to blood along partial pressure gradients.

• **External**: Gas exchange at alveolar membranes driven by partial pressure gradients, enabling oxygen uptake and carbon dioxide removal.

  • Oxygen diffuses from alveolar air to blood, while carbon dioxide diffuses from blood to alveolar air along partial pressure gradients.

• Factors affecting gas exchange rates include:

  • Partial pressure gradients for O_2