Human Physiology: Respiratory Mechanics

Physiology of the Respiratory System

• The respiratory system's main function is gas exchange—getting oxygen into the body and removing carbon dioxide.
• Breathing involves the exchange of gases between the atmosphere and blood.
• Homeostatic regulation of body pH is a vital function of the respiratory system.
• Protection from inhaled pathogens and irritating substances is another protective function of the respiratory system.
• Vocalization is a function of the respiratory system.
• Cellular respiration is the intracellular process that uses oxygen to produce energy (ATP).
• External respiration is the interchange of gases between the environment and the body's cells.

Learning Outlines

• The respiratory system's importance is described.
• The gas laws are stated.
• The ventilation process is explained.
• Gas exchange in the lungs and tissues is described.
• Gas transport in the blood is described.
• The factors that regulate ventilation are identified.
• Pulmonary function tests are described.
• A proper correlation between the respiratory system and daily life is established.
• The magnificence of God's creation is acknowledged.

Breathing—Why Bother?

• Exchange of gases between the atmosphere and blood is essential.
• Homeostatic regulation of the body's pH is maintained.
• Protection from inhaled pathogens and harmful substances is provided.
• Vocalization is enabled through the respiratory system.

Two Types of Breathing

• Cellular respiration: intracellular process where oxygen and organic molecules convert to carbon dioxide, water, and ATP
• External respiration: interchange of gases between the environment and body's cells

External and Internal Respiration

• External respiration occurs between inhaled air and the bloodstream, while internal respiration occurs between the blood and body cells.
• Oxygen in the air diffuses into the blood.
• Carbon dioxide in the blood diffuses out into alveoli.
• Oxygen from the blood diffuses into the tissues.
• Carbon dioxide from the tissues diffuses into the blood.

The Lungs and Breathing

• The pleural space is the area between the lung surface and the thoracic wall.
• This area usually contains pleural fluid for lubrication.
• The pleural fluid creates a seal-like effect, holding the lungs against the thoracic wall.
• The force of the seal ensures that lung expansion and contraction follow thoracic activity.

Mechanics of Breathing

• Air movement in and out of the lungs is based on pressure differentials.
• Inspiration occurs when pressure within alveoli is lower than atmospheric pressure.
• Expiration occurs when alveoli pressure exceeds atmospheric pressure.

Muscle of Breathing

• The diaphragm, external intercostals, sternomastoids, and scalenes are inspiratory muscles.
• The internal intercostals and abdominals are expiratory muscles.

Mechanics of Breathing—Focus on Diaphragm

• At rest, the diaphragm is relaxed.
• When the diaphragm contracts, thoracic volume increases.
• When the diaphragm relaxes, thoracic volume decreases.

Mechanics of Breathing—Focus on Intercostals

• The intercostal muscles move the ribs.
• Inspiration—the "pump handle" action increases the anterior-posterior dimension, and the "bucket handle" action increases the lateral dimension of the rib cage.
• Expiration—the "pump handle" action decreases the anterior-posterior rib cage dimension, and the "bucket handle" action decreases the lateral rib cage dimension.

Volume and Pressure

• Muscle contraction and relaxation change thoracic cavity volume, affecting lung volume and pressure.
• Changes in lung volume cause pressure changes, enabling breathing.

Boyle's Law

• Boyle's law states that gas volume and pressure are inversely proportional (at constant temperature).
• An increasing volume leads to a decrease in pressure.
• A decreasing volume leads to an increase in pressure.

Gases Movement

• Gases move from areas of high pressure to low pressure.
• Solubility of a gas in a liquid is affected by its pressure.

Inspiration

• During inspiration, inspiratory muscles contract, increasing thoracic cavity volume and causing lung volume increase.
• Lung expansion follows thoracic cavity expansion, allowing air entry.
• The diaphragm and external intercostal muscles are critical during inspiration.

Expiration

• Expiration involves relaxation of inspiratory muscles, decreasing thoracic cavity volume and reducing lung volume.
• Elastic recoil in lung tissue and the abdominal muscles support expiration.

Process of Expiration

• During expiration, the diaphragm relaxes and the chest wall recoils—reducing the volume within the thoracic cavity.
• Lung volume decrease causes an increase in pressure inside the lungs, expelling air.
• Inspiration muscles are relaxed, which allows expiration to occur.

Determinants of Airway Resistance

• Upper airways are more involved than simple passageways for warmed and humidified air.
• Foreign materials are filtered.
• Cilia remove mucus from the airways.
• The secretion of watery mucus is functional for trapping harmful substances.
• Mucus removal is crucial.

Blood Flow Rate and Pressure in Lungs

• Blood flow rate in lungs is high—compared to other tissues.
• Pressure in the lung is low.
• The low pressure is due to low hydraulic pressure.
• Lymphatic system removes excess fluid.

Ohm's Law

• Ohm's law illustrates the relationship among airflow, pressure gradient, and resistance in lung function.
• Flow is the quotient of the pressure gradient and resistance.

Clinical Relevant: Asthma

• During asthma exacerbations, airways narrow due to smooth muscle constriction and inflammation.
• This increased resistance requires more effort from the patient to move air into the alveoli.
• Increased resistance leads to turbulent airflow, characteristic of asthma's wheezing.

Gas Exchange

• Gas exchange is the process of moving oxygen between the bloodstream and lungs.
• Gas movement is vital for maintaining a constant oxygen supply to the tissues and removing carbon dioxide.

What is It?

• The process of gas exchange involves oxygen uptake and carbon dioxide removal through the bloodstream and lungs.

Gas Exchange in Alveoli and Cells

• Gas exchange in the alveoli and cells is influenced by partial pressure differences.

Oxygen Transport in the Blood

• Oxygen circulates in the blood (mostly within red blood cells) and dissolves in plasma.
• Hemoglobin (Hb) is a vital component for carrying oxygen.

Carbon Dioxide Transport

• Carbon dioxide moves from tissues to the lungs through the bloodstream.
• Various processes enable carbon dioxide to be transported from tissues to lungs, such as dissolving in plasma, associating with hemoglobin and converting to bicarbonate (HCO3).

Ventilation-Perfusion Matching

• Ventilation-perfusion matching is crucial for optimal gas exchange.
• A match between ventilation and perfusion ensures an adequate supply and removal of oxygen and carbon dioxide.
• Ventilation and perfusion ratios aid in the identification of conditions causing ventilation and perfusion differences.

Local Control of Ventilation and Perfusion

• Ventilation and perfusion are controlled and coordinated locally to maintain adequate gas exchange.
• Partial pressure of gases (oxygen and carbon dioxide) in tissues regulates ventilation and perfusion.

Regulation of Respiration

• Breathing control centers, located in the medulla and pons of the brain.
• Nerve signals from chemical receptors and stretch receptors in the body tissues and aorta guide respiration.
• Respiration occurs in response to oxygen and carbon dioxide levels in the body.
• Control centers are responsible for coordination of respiratory activity.

Control of Breathing

• The medulla oblongata is the respiratory control center.
• The pons is involved in the smooth transition between inspiration and expiration.
• CO₂ levels in the cerebrospinal fluid (CSF) signal the brain for adjustments to breathing rate.
• Breathing rate is also adjusted to changes in oxygen (O₂) levels in the body's cells.
• Other factors, including emotions and psychological conditions, can impact breathing.

Phrenic Nerve Paralysis

• Phrenic nerve paralysis affects breathing by affecting the diaphragm's function.
• This condition is due to damage to the phrenic nerve.
• Common causes of phrenic nerve paralysis include injuries and surgical complications.

Pulmonary Function Test

• Spirometry is used to measure air volume during breathing cycles.
• Lung volumes (tidal volume, inspiratory reserve volume, expiratory reserve volume, and residual volume) are described and defined.
• Lung capacities (vital capacity and total lung capacity) are identified and their definitions are provided.

Variations in Lung Volume

• Variations in lung volumes and capacities are described.

Lung Capacities

• Lung capacities represent the sum of multiple lung volumes.
• Vital capacity is the maximum volume of air that can be breathed in and out during a respiratory cycle.
• Total lung capacity represents the overall volume of air within the respiratory system.
• Lung capacities are involved in assessing lung function.

Swimming & Lung Capacity

• Swimming increases lung capacity and delivers more oxygen to the body.

End of Lecture

• The lecture concludes with a thank-you acknowledgment.

Test your knowledge on the mechanics of breathing in human physiology. This quiz covers concepts such as lung pressure changes, muscle functions during inspiration and expiration, and the role of Boyle's Law. Challenge yourself with questions related to the respiratory system and gas movement.