Elastic Fibers and Gas Exchange in the Respiratory System

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Elastic Fibers

Elastic fibers maintain the position of alveoli and bronchioles. When fibers recoil during exhalation, they reduce the size of alveoli and push air out.

Pneumocyte Type I

Pneumocyte type I cells are squamous epithelial cells that are unusually thin, providing an ideal site for gas diffusion.

Pneumocyte Type II

Pneumocyte type II cells are scattered among the squamous cells and produce surfactant.


Deep breathing, also known as diaphragmatic breathing, involves the contraction of the diaphragm to change the volume of the lungs, allowing air to be exhaled passively. Shallow breathing, or costal breathing, occurs when the rib cage alters its shape, changing the thoracic volume.

Dalton's Law

Dalton's Law states that the partial pressure (PP) of a gas is the pressure contributed by that gas in a mixture of gases. The PO2 in air is 159.

Henry's Law

Henry's Law states that the amount of gas in a solution is proportional to its pressure.

Partial Pressure of Alveolar Air

The partial pressure of oxygen (PO2) in alveolar air is 100, and the partial pressure of carbon dioxide (PCO2) is 40.


The partial pressure of oxygen (PO2) in tissues is 40, and the partial pressure of carbon dioxide (PCO2) is 45.

Efficient Gas Exchange

Efficient gas exchange requires a substantial difference in partial pressure across the membrane, short distances for diffusion, gases that are lipid soluble, a large total surface area, and coordinated blood flow and airflow.

Role of Red Blood Cells (RBC)

Red blood cells transport gases, including oxygen to tissues and carbon dioxide from tissues. They remove gases from plasma, allowing for continued diffusion of gases in the blood.

Hemoglobin Saturation

Hemoglobin saturation refers to the percentage of heme bound to oxygen.

CO2 Transport

CO2 is converted to carbonic acid, binds to hemoglobin (HbCO2), or dissolves in plasma for transport.

Respiratory Rhythm Center

The respiratory rhythm center includes the dorsal respiratory group (DRG) for quiet or forced breathing, which innervates the external intercostal muscles, and the ventral respiratory group (VRG) for forced breathing, which serves as the expiratory center.

Apneustic and Pneumotaxic Centers

The apneustic center adjusts inhalation, while the pneumotaxic center adjusts exhalation.

Respiratory Reflexes

Respiratory reflexes include chemoreceptors that are sensitive to PCO2, PO2, and blood pH; baroreceptors that are sensitive to changes in blood pressure; and stretch receptors that regulate the inflation reflex to prevent overexpansion and the exhalation reflex to inhibit exhalation. These reflexes help protect the respiratory system.


Aging can lead to reduced compliance, decreased vital capacity, arthritic changes in the ribs, decreased flexibility, and some degree of emphysema.

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