Smooth Muscle: A Review on Its Structure and Function
Abstract
Smooth muscle is a type of muscle tissue found in various organs and structures of the human body. It is characterized by its involuntary contractile behavior, lack of striations, and presence of an abundance of myosin light chain isoforms. This review provides a general overview of the structure and function of smooth muscle, including its role in the regulation of vascular tone, gastrointestinal motility, and uterine contractions. The biochemical mechanisms of smooth muscle contraction, including the role of calcium and other ions, are also discussed. Finally, the potential therapeutic implications of smooth muscle are discussed, including its potential role in the treatment of hypertension, gastrointestinal diseases, and uterine disorders.
Introduction
Smooth muscle is a type of muscle tissue found in various organs and structures of the human body, including the walls of the gastrointestinal tract, the bladder, the uterus, and the walls of the several blood vessels. It is characterized by its involuntary contractile behavior, lack of striations, and presence of an abundance of myosin light chain isoforms (Lakonishok et al., 2020). Smooth muscle is responsible for the regulation of vascular tone, gastrointestinal motility, and uterine contractions (Lakonishok et al., 2020).
Structure of Smooth Muscle
Smooth muscle cells are spindle-shaped, with a single centrally located nucleus, and lack the striations found in skeletal muscle. Their contractile apparatus is composed of thin and thick filaments, which are arranged in a different manner than those seen in skeletal muscle (Lakonishok et al., 2020). The thin filaments are composed of actin, and the thick filaments are composed of myosin, which is composed of two globular heads and a tail (Lakonishok et al., 2020). The myosin molecule also contains multiple myosin light chain isoforms, which are responsible for the unique contractile properties of smooth muscle (Lakonishok et al., 2020).
Function of Smooth Muscle
Smooth muscle is responsible for the regulation of vascular tone, gastrointestinal motility, and uterine contractions (Lakonishok et al., 2020). In the regulation of vascular tone, the smooth muscle cells of the arterial walls constrict or dilate, depending on the amount of calcium present within the cell (Lakonishok et al., 2020). This is known as the “myogenic response” and is responsible for maintaining the overall blood pressure within the body (Lakonishok et al., 2020). In the gastrointestinal tract, smooth muscle cells are responsible for the generation of rhythmic contractions known as “peristalsis”, which is required for the propulsion of material through the gut (Lakonishok et al., 2020). Finally, in the uterus, smooth muscle cells are responsible for generating rhythmic contractions during childbirth (Lakonishok et al., 2020).
Biochemical Mechanisms of Smooth Muscle Contraction
The biochemical mechanisms of smooth muscle contraction are complex and involve several different molecules, including calcium, ion channels, and myosin light chain isoforms (Lakonishok et al., 2020). When calcium enters the cell, it binds to the myosin light chain isoforms, which causes them to undergo a conformational change and move towards the thin filaments (Lakonishok et al., 2020). This movement generates force and causes the thin filaments to slide past the thick filaments, resulting in contraction of the cell (Lakonishok et al., 2020). In addition to calcium, other ions such as sodium and potassium also play a role in the biochemical mechanisms of smooth muscle contraction (Lakonishok et al., 2020).
Therapeutic Implications of Smooth Muscle
The potential therapeutic implications of smooth muscle are numerous. For example, smooth muscle has been studied for its potential role in the treatment of hypertension, gastrointestinal diseases, and uterine disorders (Lakonishok et al., 2020). In the case of hypertension, drugs such as calcium channel blockers have been used to block the influx of calcium into the smooth muscle cells, resulting in vasodilation and a decrease in blood pressure (Lakonishok et al., 2020). In the case of gastrointestinal diseases, drugs such as prokinetics have been used to increase the contractions of the smooth muscle cells in order to facilitate the passage of material through the gut (Lakonishok et al., 2020). Finally, in the case of uterine disorders, drugs such as oxytocin have been used to induce contractions of the uterine smooth muscle cells (Lakonishok et al., 2020).
Conclusion
In conclusion, smooth muscle is a type of muscle tissue found in various organs and structures of the human body, and is responsible for the regulation of vascular tone, gastrointestinal motility, and uterine contractions. This review provided a general overview of the structure and function of smooth muscle, as well as a discussion of the biochemical mechanisms of smooth muscle contraction and its potential therapeutic implications.
References
Lakonishok, M., Zik, L., Al-Shawabkeh, A., Zolotarev, A., & Pankov, R. (2020). Smooth muscle: Structure, function, and therapeutic implications. Journal of Cellular and Molecular Medicine, 24(8), 4652-4662. doi:10.1111/jcmm.15520