An acute asthma attack is characterized by increased

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An acute asthma attack is characterized by increased contraction of smooth muscle in the bronchi and bronchioles, decreasing air flow to the lungs. In extreme cases, airflow may become so restricted that an attack may be life threatening. A more detailed explanation of asthma is included in the "Pathological Conditions of the Respiratory System" at the end of this module.
224 [CLICK HERE to return to beginning] 6.1.3 - Respiratory Membrane Respiratory Membrane in the Alveoli . Image drawn by BYU-Idaho student: Jared Cardinet
225 [CLICK HERE to return to beginning] The respiratory membrane is what separates the inside of the alveoli from the blood. It consists of six layers that gases must cross to enter the blood from the alveoli or vice versa. Imagine molecules of oxygen and carbon dioxide that must pass through the following six layers. 1) fluid covering the inside of the alveoli (surfactant) 2) squamous cells (alveolar epithelium) lining the alveoli 3) basement membrane of alveolar epithelium 4) small space between two basement membranes (interstitial space) 5) basement membrane of capillary endothelium 6) squamous cells that make up the wall of the capillaries (capillary endothelium)
226 [CLICK HERE to return to beginning] Respiratory Dead Space Within the respiratory system there is physiological dead space where a portion of the air inhaled does not participate in the exchange of oxygen and carbon dioxide. This portion of the air, roughly a third of each breath, is “wasted”. Why is it wasted? Some of the wasted air remains in the conducting airways or pathway leading to the lung (anatomical dead space) and includes air within the mouth, trachea and bronchioles. The rest of the air reaches the alveoli but may be poorly perfused within the alveoli due to reduced blood flow to the alveolar capillaries or to lung disease. This is known as alveolar dead space. The alveolar dead space combined with the anatomical dead space adds up to the total physiological dead air space of the respiratory system. Think of this dead space like breathing through a tube. With every breath you exhale, a certain portion of the air you inhale with next breath will be a mix of both new fresh air coming in combined with some of the air you have just expelled what is still trapped in the tube. Due to this mixing of air, air used inside our alveoli for gas exchange contains less oxygen and more carbon dioxide than atmospheric air. We will learn more about this as we study partial pressure later in this module. What are the benefits of having respiratory dead space? As a portion of the air sits in this dead space it helps to accomplish the following: warming the air to body temperature so hemoglobin will more readily bind to the oxygen in the air: retaining carbon dioxide at a level higher than the atmospheric levels so that this carbon dioxide may be used for maintaining the bicarbonate buffering system, and giving the body time to humidify and clean the air by trapping matter in the mucous lining before the air is used for gas exchange.

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