Biol 216 2020 Topic 10 Respiratory System_Power Point 10.0 Lungs and Breathing

Biol 216 Topic 10: The Respiratory System

Overview

• Focuses on the lungs and breathing.

Learning Goals

1. Describe the interaction of the components of the mammalian respiratory system.

2. Explain the relationship between partial pressures and gas exchange, and pressure changes during breathing.

Breathing (Gas Exchange)

• Two primary operating features:

  • Respiratory medium: air or water.

  • Respiratory surface: wetted epithelium for gas exchange.

• Features of respiratory surfaces:

  • Thin structure.

  • Large surface area.

  • Moist environment is essential, as gases must dissolve in water to move in and out of epithelial cells.

  • Human lungs are designed as invaginated pockets to prevent drying out; moisture is added to air in the mouth and nasal passages.

Respiration

• Ventilation: flow of the respiratory medium (air, water) over the external side of the respiratory surface.

• Perfusion: flow of blood or other body fluids on the internal side of the respiratory surface.

Gas Exchange

• Driven by simple diffusion of molecules across the respiratory surface, moving from higher to lower concentration.

• The area of the respiratory surface determines the total quantity of gases exchanged by diffusion.

Lungs (Air Breathers)

• Allow air to saturate with water before reaching the respiratory surface, reducing water loss by evaporation.

• Increase surface area for gas exchange.

Lung Ventilation

• Positive pressure breathing (e.g., frogs): Air is forced into lungs through muscle contractions.

• Negative pressure breathing (mammals): Muscle contractions expand lungs, decreasing air pressure inside, allowing air to be pulled into the lungs.

Questions on Ventilation Systems

1. For infectious diseases like COVID-19, one should stay in a _______ pressure ventilation system: A. Positive B. Negative

2. If severely compromised, one should stay in a _______ pressure ventilation system: A. Positive B. Negative

Answers to Ventilation Questions

• COVID-19: Negative pressure is safer as air is pulled into the room, preventing spread.

• Severely compromised immune system: Positive pressure protects against outside pathogens by preventing air from leaking in.

Negative Pressure Room Features

• Designed to ensure contaminated air cannot escape; air flows from outside into the negative pressure room.

• Creates a ventilation balance with more exhausted air than supplied, maintaining negative pressure.

The Mammalian Respiratory System

• Airway functions: filter, moisten, and warm air entering the lungs.

• Ventilation Mechanism: Contractions of diaphragm and intercostal muscles facilitate breathing.

• Control Centers: Located in the brain stem.

• Negative Pressure Breathing: Muscular contractions cause air to be pulled inward.

Airway Structure

• When air enters, it goes through:

  • Nose and mouth ➔ pharynx ➔ larynx ➔ trachea ➔ bronchi ➔ bronchioles ➔ alveoli surrounded by capillaries.

• The lung is a lobed elastic organ for gas exchange.

• Bronchi and bronchioles: Airways have varying muscular control.

• Alveoli: 150 million present, providing a vast area for gas exchange.

Gas Exchange Overview

• Achieved through diffusion in alveoli surrounded by capillaries.

Lung Ventilation

Mechanics of Ventilation

• Air moves in/out through pressure changes during inhalation and exhalation.

• Inhalation: Diaphragm contracts, rib cage expands, increasing volume and decreasing pressure, drawing air in.

• Exhalation: Diaphragm relaxes, rib cage shrinks, decreasing volume and increasing pressure, expelling air.

Pleural Cavity and Lung Structure

• Pleura Layers:

  • Visceral: attached to lung surface.

  • Parietal: attached to chest cavity.

• The fluid-filled space between layers facilitates smooth lung movement.

• Lungs maintain elasticity to aid in expulsion.

Measuring Lung Ventilation

• Tidal Volume: ~500ml moved during rest inhalation/exhalation.

• Vital Capacity: Total air volume capable of inhalation/exhalation (max male: 4800ml, female: 3400ml).

• Residual Volume: Air remaining after max exhalation (males: 1200ml, females: 1000ml).

Gas Flow and The Ideal Gas Law

• Air flows from high to low pressure due to differences in pressure.

• Ideal Gas Law: PV=nRT, considering pressure (P), volume (V), number of molecules (n), universal gas constant (R), and temperature (T).

• Boyle's Law: Relationship between pressure and volume expressed as P1V1 = P2V2.

Factors in Breathing Mechanics

• Change in thorax size essential for breathing.

• Key Influences on Breathing:

  1. Negative intra-pleural pressure keeps lungs in contact with wall.

  2. Surface tension of pleural fluid aids lung adhesion to the chest wall.

  3. Lungs' compliance and elasticity ensure efficient airflow.

Ventilation: Alveolar Pressure Dynamics

• During breathing, air moves due to pressure differentials between alveolar pressure (Palv) and atmospheric pressure (Patm).

• Inspiration: Alveolar pressure must drop below atmospheric pressure for air to flow in.

• Expiration: Alveolar pressure must exceed atmospheric pressure for air to exit.

Pressure Changes During Breathing

• Inspiration Mechanics:

  • Chest expansion decreases Pip (intrapleural pressure).

  • Increased transpulmonary pressure (Ptp) expands lungs, lowering Palv and drawing air in.

• Expiration Mechanics:

  • Relaxation of muscles causes a decrease in lung volume, raising Palv, pushing air out.

Lung Compliance

• Measure of lung expansion ease, influenced by stretchability and alveolar surface tension.

• Surfactant: Reduces surface tension in alveoli, increasing compliance and preventing collapse.

Recap

• The lungs are structured to promote ventilation and perfusion through pressure changes.

• Questions encouraged to clarify understanding.