lecture 22 physiology

Lecture Overview

• Course: BIO 1220 Human Physiology

• Lecture Title: Respiration, cont'd

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

1. Control of Respiration

A. Introduction

• Essential for maintaining breathing.

• Automatic, adaptable, and subject to voluntary control.

2. Forces for Pulmonary Ventilation

• Forces that facilitate inflation and deflation of the lungs.

3. Gas Exchange

• During external respiration:

  • Oxygen diffuses into blood.

  • Carbon dioxide diffuses out.

• Characteristics:

  • Passive process requiring no energy.

  • Relies on pressure relationships.

A. Mechanism

• Partial pressure differences drive gas exchange.

  • O2 moves from alveoli to blood; CO2 moves from blood to alveoli.

  • Equilibrium stops further gas exchange.

B. Factors Aiding Gas Exchange

• Surface Area: High due to numerous alveoli (~90 m2).

• Membrane Thickness: Extremely thin membranes facilitate diffusion.

4. Control of Respiration

A. Neural Control

• Breathing involves:

  • Motor neurons activating inspiratory muscles.

  • Expiration is a passive process.

• Key components:

  • Phrenic Nerve: stimulates the diaphragm.

  • Intercostal Nerves: stimulate intercostal muscles.

B. Breathing Rhythm Generation

• Breathing controlled both voluntarily and involuntarily.

• Respiratory Control Regions:

  • Located in pons and medulla; regulate inspiratory and expiratory centers.

  • Quiet breathing primarily regulated by the medulla.

C. Peripheral Input

• Sensory Inputs affecting respiration:

  • Central and peripheral chemoreceptors monitor CSF and arterial blood.

  • Primary sensors: located in carotid and aortic bodies.

  • Pulmonary Stretch Receptors: located in smooth muscle of pulmonary airways.

  • Irritant Receptors: respond to environmental irritants.

D. Chemical Composition Changes

• Slow breathing alters blood's chemical composition; detected by chemoreceptors.

5. Hyperventilation

• Involves excessive CO2 removal, leading to:

  • Low CO2 levels causing cerebral blood vessel constriction.

  • Increased breathing rate and depth may lead to fainting.

A. Breathing into a Paper Bag

• Helps alleviate symptoms:

  • Bag fills with CO2; inhaling CO2 can replenish levels in over-oxygenated blood.

6. Other Controls of Breathing

A. Hypothalamus

• Influences breathing rate during emotions or pain.

B. Cerebral Cortex

• Allows conscious control over breathing; can bypass medulla.

  • Examples: Holding breath when angry.

C. Respiratory Adjustments

• During exercise:

  • Proprioceptors in joints and muscles stimulate respiratory centers.

D. High Altitude Adjustments

• Increased breathing rates; may cause dizziness, nausea, headaches.

• Acclimatization: physiological adaptation over time.

7. Respiratory Acid-Base Balance

A. Importance of pH Regulation

• pH influences nearly all biochemical reactions.

  • Arterial blood: ~7.4, Venous blood: ~7.35, Intracellular fluid: ~7.0.

B. Acid-Base Balance Regulation

• Regulatory Mechanisms:

  • Chemical buffers respond in seconds.

  • Respiratory rate adjusts within minutes.

  • Kidneys modify acid-base balance over hours/days.

C. Respiratory pH Imbalances

1. Respiratory Acidosis

   • Occurs when breathing is insufficient, CO2 builds up, blood becomes acidic.

   • Common in lung ailments (e.g. pneumonia).

2. Respiratory Alkalosis

   • Occurs with hyperventilation due to stress or pain.

D. Metabolic pH Imbalances

1. Metabolic Acidosis

   • Caused by high blood acidity due to factors such as alcohol consumption or kidney failure.

2. Metabolic Alkalosis

   • Less common may result from prolonged vomiting or excessive antacid consumption.

E. Impact and Differences

• Respiratory imbalances affect CO2 levels; metabolic imbalances affect HCO3 (bicarbonate).

8. Key Topics to Understand

1. Pulmonary pressures and lung capacity.

2. Mechanisms of gas exchange in alveoli (diffusion).

3. Regulation of breathing (neural control and receptors).

4. Acid-base balance: acidosis and alkalosis.

9. Recap and Next Class

• Today's Learning: Respiratory system insights.

• Upcoming Class Topic: Urinary System.