Clinical Note

Immune-mediated responses in many organs lead to altered smooth muscle function. The breathing in of an antigen by an individual who is sensitized will result in the release of various cytokines that induce contraction of airway smooth muscle, thus increasing airway resistance. On the other hand, antigen-induced responses taking place within or in proximity to blood vessels can lead to vascular smooth muscle relaxation and a decrease in arterial blood pressure.

development, myosin phosphorylation and crossbridge cycling are relatively high; however, during the tonic phases of the contraction, both myosin phosphorylation and crossbridge cycling fall, whereas force development remains high. Thus, force can be maintained with minimal expenditure of ATP. The exact basis for this economy is not known.

As in striated muscle, smooth muscles use both glycolysis and oxidative phosphorylation for ATP generation. The importance of each process varies from smooth muscle to smooth muscle, with some being more dependent on oxygen than others; however, there do not appear to be the clear-cut distinctions among smooth muscles that exist among striated muscles.

Suggested Readings

Bohr DF, Somlyo AP, Sparks HV, Eds. Handbook of physiology, Section 2: The cardiovascular system. Bethesda, MD: American Physiological Society, 1980 Bolton TB, Prestwich SA, Zholos AV, Gordienko DV. Excitation-contraction coupling in gastrointestinal and other smooth muscles. Annu Rev Physiol 1999; 61:85-115 Kamm KE, Stull JT. The function of myosin and myosin light chain kinase phosphorylation in smooth muscle. Annu Rev Pharmacol Toxicol 1985; 25:593-620

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