Study Notes for Kinesiology 260 - Respiratory

KNES 260: Respiratory

Class Outline

• ALVEOLI
  1. Introduction
  2. Key Respiratory Structures
  3. The Lungs
  4. Blood Supply
  5. Breathing Mechanisms

Introduction

• Respiration is defined as the exchange of gases between the atmosphere, blood, and cells, which occurs through three processes:
  • Ventilation (breathing)
  • External (pulmonary) respiration
  • Internal (tissue) respiration
• The cardiovascular system assists the respiratory system during internal respiration by transporting gases to the tissues for gas exchange.

Major Functions of the Respiratory System

• The primary functions of the major organs of the respiratory system include:
  • Providing oxygen to body tissues for cellular respiration.
  • Removing carbon dioxide, which is one of the main waste products of cellular respiration.
  • Aiding in the maintenance of acid-base balance.

Key Respiratory Structures

• The respiratory system can be organized by the functions of the areas into two zones: the conducting zone and the respiratory zone.
• The conducting zone includes the organs and structures not directly involved in gas exchange, whereas the respiratory zone is where gas exchange occurs, specifically occurring in the alveoli.

Conducting Zone

• The conducting zone has several main functions:
  • Provide a route for incoming and outgoing air.
  • Remove debris and pathogens from the incoming air.
  • Warm and humidify the incoming air.
• The major entrance and exit for the respiratory system is the nose, divided into:
  • External nose
  • Internal nose (nasal cavity)

Nasal Cavity

• The nares open into the nasal cavity, separated into left and right sections by the nasal septum.
• Each lateral wall of the nasal cavity has three bony projections called nasal conchae.
• Functions of this portion of the conducting zone include:
  • Cleaning and warming the air
  • Trapping water to prevent dehydration
  • Filtering air via hairs and mucus
  • Detecting odors

Trachea

• The trachea (windpipe) extends from the larynx towards the lungs, formed by 16 to 20 stacked, C-shaped pieces of hyaline cartilage connected by dense connective tissue, and open posteriorly.
• This design allows the trachea to stretch and expand slightly during inhalation and exhalation, while also providing structural support to prevent collapsing, especially during inhalation.

Bronchi

• The primary function of the bronchi, like other conducting zone structures, is to provide a passageway for air to move into and out of each lung.
• The mucous membrane along this pathway traps debris and pathogens, preventing them from entering the respiratory zone.

Bronchial Tree

• As the airways branch further, they form the bronchial tree (respiratory tree), known as generations:
  • Trachea starting as generation 0
  • Primary bronchi as the 1st generation
  • Generations 2-10 consist of the lobar and segmental bronchi
  • Bronchioles and terminal bronchioles make up generations 11-16
• The conducting zone ends at the 16th generation.

Respiratory Zone

• In contrast to the conducting zone, the respiratory zone consists of structures directly involved in gas exchange, beginning where the terminal bronchioles join the smallest bronchiole:
  • Respiratory bronchiole (generations 17-19)
  • Alveolar duct (generations 20-22)
  • Alveolar sac (23rd generation)

Alveolar Sac and Alveoli

• An alveolar sac is a cluster of many individual alveoli where gas exchange occurs with the external environment.
• Each alveolus is a tiny sac with elastic walls which stretch during air intake, greatly increasing the surface area available for gas exchange.
• Alveoli are interconnected by alveolar pores, helping to maintain equal air pressure throughout the alveoli and lungs.
• The simple squamous epithelium formed by type I alveolar cells is attached to a thin, elastic basement membrane that borders the endothelial membrane of capillaries.
• This thin respiratory membrane allows gases to readily cross by simple diffusion, enabling O2 to be picked up by the blood for transport and CO2 to be released into the air of the alveoli.

The Lungs

• When discussing the respiratory system, the first organ often considered is the lungs.
• Each lung comprises both the conducting and respiratory zones.
• The main function of the lungs is to take in O2 from the atmosphere and release CO2 produced in the body.
• Lungs perform gas exchange across a very large surface area, approximately 70-75 square meters.

Lung Membranes

• Each lung is covered with a connective tissue membrane, while another membrane lines the inside of the chest or thoracic cavity.
• There is a small space, called the pleural cavity, between the chest wall and the lungs, containing lubricating fluid (pleural fluid) which prevents sticking or rubbing between the membranes.

Blood Supply

• The blood supply to the lungs plays an important role in gas exchange and serves as a transport system for gases throughout the body.

Pulmonary Artery

• The pulmonary artery arises from the pulmonary trunk, carrying deoxygenated arterial blood to the alveoli.
• The pulmonary artery branches multiple times following the bronchi, with each branch becoming progressively smaller in diameter.
• One arteriole and the accompanying venule supply and drain each pulmonary lobule.

Pulmonary Capillaries

• Near the alveoli, the pulmonary arteries form a capillary network that branches and follows the bronchioles and structure of the alveoli.
• At this point, the capillary wall meets the alveolar wall, creating the respiratory membrane.
• Once blood is oxygenated, it drains from the alveoli via multiple pulmonary venules and veins, eventually exiting the lungs through the hilum.

Breathing Mechanisms

• The alveolar and intrapleural pressures depend on specific physical features of the lung.
• The ability to breathe (air entering the lungs during inspiration and exiting during expiration) relies on the atmospheric pressure and the air pressure within the lungs.

Boyle's Law

• At a constant temperature (homeostasis maintaining body temperature), changing the volume occupied by gas alters pressure.
• Boyle's Law describes this relationship between gas volume and pressure at constant temperature:
  • If volume increases, pressure decreases, and vice versa.
• Boyle's Law is expressed mathematically by the formula:
  $P<em>1V</em>1 = P<em>2V</em>2$

Pulmonary Ventilation

• Pulmonary ventilation refers to the act of breathing, which is the movement of air into and out of the lungs.
• Major mechanisms driving pulmonary ventilation include:
  • Atmospheric pressure
  • Alveolar pressure (pressure within the alveoli)
  • Intrapleural pressure (pressure within the pleural cavity)

Atmospheric Pressure

• Atmospheric pressure is defined as the force exerted by gases in the surrounding air on any surface, typically expressed in millimeters of mercury (mmHg).
• The standard sea-level pressure is 760 mmHg.
• Negative pressure (

Intra-alveolar Pressure

• Intra-alveolar pressure is the pressure of air within the alveoli, which changes during various phases of breathing.
• Due to the alveoli's connection to the external atmosphere through air passageways, they can ventilate: exchanging the body's gases with the environment.

Intrapleural Pressure

• Intrapleural pressure is the pressure within the pleural cavity between the visceral and parietal pleurae.
• Like intra-alveolar pressure, it fluctuates during the breathing phases and contributes to positive airflow driving changes in intra-alveolar pressure.

Competing Forces in Thorax

• In the thorax, competing forces lead to the development of negative intrapleural pressure:
  • Elasticity of the lungs pulls the lungs inward and away from the thoracic wall.
  • Surface tension of alveolar fluid (mostly water) creates an inward pull on lung tissue.
• The lung's inward tension is countered by opposing forces from pleural fluid and the thoracic wall.
• The chest wall naturally expands outward (compliance), opposing the inward pull of the lungs, thus creating pleural cavity surface tension which pulls the lungs outward.
• The net effect is that the outward pull (from the chest wall) is slightly greater than the inward pull (from the lungs), resulting in a negative pressure between pleural membranes, defined as intrapleural pressure, which is always negative compared to intra-alveolar pressure.

Pressure Differences

• Intrapleural pressure is always lower (negative) compared to intra-alveolar pressure and atmospheric pressure, fluctuating between approximately -3 to -6 mmHg throughout the breathing cycle, assisting in lung expansion.
• The lungs themselves are passive during the breathing process, with muscle contractions of both the diaphragm and thoracic muscles responsible for altering the thoracic cavity volume, facilitating inspiration and expiration.

Factors Affecting Airflow

• Flow Rate Formula:
  $Flow = \frac{DP \cdot \pi r^4}{8h l}$
• Factors influencing airflow rates of gas in airways:
  • Viscosity
  • Length
  • Radius (most significant factor affecting resistance)
• Greater pressure differentials (increased alveolar pressure) leads to greater airflow, as seen in responses such as sneezing, coughing, or speaking.

Airway Resistance

• Characteristics of the lungs impact the effort needed for ventilation, much like blood vessels, where airway size is a primary factor affecting resistance, impacting airflow, and can be expressed through the formula: $F = \Delta P \cdot R$
  • Airway divisions include:
    • One trachea
    • Two primary bronchi
    • Four secondary (lobar) bronchi
    • Segmental bronchioles
    • Terminal bronchioles
    • Respiratory bronchioles
• Although each individual airway is small, the total cross-sectional area is immense, leading to low overall resistance.