lecture 21 physiology

BIO 1220

• Course Title: Human Physiology

• Lecture: 21 - Respiration

• Instructor: Dr. Suzanne Gray, UPEI - Winter 2025

Table of Contents

1. Introduction

2. Forces for Pulmonary Ventilation

3. Gas Exchange

4. Control of Respiration

5. Respiratory Acid-Base Balance

1. Introduction

• Respiration: Process of gas exchange

  • External Respiration: Exchange between atmosphere and body tissues

  • Internal Respiration: Use of oxygen to generate ATP in cells (cellular respiration)

2. External Respiration Processes

• Four processes involved:

  1. Breathing (inspiration and expiration)

  2. Exchange of gases between lungs and blood

  3. Transportation of gases between lungs and tissues

  4. Exchange of gases between blood and tissues

3. Functions of the Respiratory System

• Besides gas exchange, the respiratory system has several additional functions:

  1. Contributes to acid-base balance in blood

  2. Enables vocalization

  3. Defense against pathogens and foreign particles

  4. Provides route for water and heat loss

  5. Enhances venous return

  6. Activates certain plasma proteins

4. Overview of the Respiratory System

• Conducting Zone:

  • Upper respiratory tract and lower respiratory tract

• Respiratory Zone:

  • Alveoli where gas exchange occurs

  • Bronchial tree structure:

    • Bronchi divide, leading to terminal bronchioles which are the last component of the conducting zone and then to the respiratory bronchioles as the first part of the respiratory zone

5. The Alveoli

• Site of gas exchange

  • Blood in capillaries adjacent to alveoli

  • Alveoli found in clusters called alveolar sacs

  • Cell types within alveoli:

    • Type I Cells: Squamous epithelial cells, structural, 97% of alveolar surface area

    • Type II Cells: Secrete pulmonary surfactant to decrease surface tension of alveoli

    • Macrophages: Phagocytic cells that remove debris/pathogens from alveoli

6. Forces for Pulmonary Ventilation

a. Pulmonary Pressures

• Three primary pressures:

  1. Atmospheric Pressure (Patm): Pressure in surrounding air, generally around 760 mm Hg at sea level

  2. Intra-Alveolar Pressure (Palv): Pressure inside alveoli which varies during respiration

  3. Intra-Pleural Pressure (Pip): Slightly negative pressure in pleural cavity, lower than intra-alveolar pressure which helps keep lungs inflated

b. Pressure Relationships

• Transpulmonary Pressure: Difference between intra-alveolar pressure and intra-pleural pressure (Palv - Pip)

• Importance of maintaining lower pleural pressure: Equalization can cause lung collapse

• During relaxation, no air movement; breathing requires muscular movements to create pressure gradients

c. Mechanics of Breathing

Inspiration

• Diaphragm contracts and moves inferiorly, increasing thoracic cavity volume

• External intercostal muscles aid in this process, resulting in air rushing into the lungs

Expiration

• Primarily relies on elastance of lungs; diaphragm relaxes and rib cage descends

• Internal intercostal muscles can assist during forceful expiration

7. Lung Volumes and Capacities

• Spirometers: Assess lung functioning; critical in diagnosing pulmonary diseases

• Categories of Lung Volumes:

  • Tidal Volume (VT): Normal breath (~500 ml)

  • Inspiratory Reserve Volume (IRV): Max amount inhaled after a normal breath (~2000 ml)

  • Expiratory Reserve Volume (ERV): Max amount exhaled after a normal breath (~1000 ml)

  • Residual Volume (RV): Air that cannot be exhaled (~1200 ml)

8. Lecture Recap

• Focus of today's lecture: Respiratory system overview

• Next class: Continuation of respiration topics

• Instructor: Dr. Suzanne Gray, UPEI - Winter 2025