Mucus secretion stimulus

Effector organs are mainly the respiratory muscles, as described previously. Other effectors are muscles located in the airways and tissues for mucus secretion. Control of respiration appears to be based on two criteria (1) removal of excess CO2 and (2) minimization of energy expenditure. It is not the lack of oxygen that stimulates respiration but increased CO2 partial pressure that acts as a powerful respiratory stimulus. Because of the buffering action of blood bicarbonate, blood pH usually falls as more CO2 is produced in the working muscles. Lower blood pH also stimulates respiration. 

Three factors contribute to airway obstruction in asthma (1) contraction of the smooth muscle that surrounds the airways (2) excessive secretion of mucus and in some, secretion of thick, tenacious mucus that adheres to the walls of the airways and (3) edema of the respiratory mucosa. Spasm of the bronchial smooth muscle can occur rapidly in response to a provocative stimulus and likewise can be reversed rapidly by drug therapy. In contrast, respiratory mucus accumulation and edema formation are likely to require more time to develop and are only slowly reversible. 

When alarmed, earthworms secrete coelomic fluid through dorsal pores, located in the grooves between the segments. To trigger release of the alarm secretion, one can shock an earthworm electrically (obviously not exactly a natural stimulus) with current from two size D batteries while on a wax paper. The worm will secrete coelomic fluid. A 2-cm piece of this paper with secretion can be cut out and presented to another, naive earthworm. Observe the response rearing up and withdrawing. Compare this behavior with the response to control stimuli such as salt solution or the normal mucus from an undisturbed earthworm (Rosenkoetter and Boice 1975). 

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