Explain the processes of bronchoconstriction and bronchodilation and relate to h

Question

Explain the processes of bronchoconstriction and bronchodilation and relate to how asthma affects the respiratory system (See Clinical View on asthma).  Describe role of parasympathetic and sympathetic effects on the lungs related to bronchoconstriction and bronchodilation.  

Describe the role of alveolar type I vs type II cells and discuss how these cells function to keep alveoli open and prevent collapse.

Explain how Boyle’s gas law describes relationship between volume and pressure and describe functional changes that occur during pulmonary ventilation.  

Explanation / Answer

Bronchoconstriction is the constriction (narrowing) of bronchi and bronchioles. This causes restrictions of air flow which leads to shortness of breath, coughing and wheezing. This is the condition which happens in Asthma. Air flow gets restricted because of spasm of bronchi and bronchioles, Inflammation of middle layer of bronchi and bronchioles and because of over production of mucus. Activation of parasympathetic nervous system causes spasm of bronchi and bronchioles by releasing Acetylcholine. The Acetylcholine activates muscuranic receptors present on the smooth muscles of bronchi and bronchioles which activates intracellular G protein which further activates phospholipase C pathway due to which intracellular calcium levels increases leading to contraction/constriction of smooth muscles of bronchi and bronchioles which causes it's narrowing leading to bronchconstriction or Asthma.

Bronchodilation is the opposite of bronchconstriction. In bronchodilation there is dilation (relaxation) of smooth muscles of bronchi and bronchioles. Activation of sympathetic nervous system causes bronchodilation by release of adrenaline and noradrenaline.

Type 1 alveolar cells cover 95% of alveolar surface, it is thin and involved in gaseous exchange between alveoli and blood. Type 2 alveolar cells cover remaining 5% alveolar surface and are involved in secretion of pulmonary surfactant which decreases the surface tension in alveoli. The decrease surface tension prevents alveoli from collapsing and tends to keep it open. They also regenerate type 1 alveolar cells.

Boyel's law states that at constant temperature, when volume of gas increases the pressure of gas decreases in proportion or vice versa. Due to changes in Volume and pressure of air in lungs, pulmonary ventilation happens. During inspiration diaphragm contracts, intercoastal muscles contracts, ribcage elevates, this causes increase in volume of lung, due to this pressure inside the lung decreases and because of which air from outside gushes inside the lungs. During expiration, diaphragm relaxes, intercoastal muscles relaxes, ribcage subsides and due to which volume of lung decreases, pressure inside the lung increases and the air is expelled out.

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