Sileälihassolu

Sileälihassolu, also known as a smooth muscle cell, is a type of muscle cell found in various organs and structures throughout the body, including the walls of internal organs like the stomach, intestines, bladder, uterus, and blood vessels. Unlike skeletal muscle cells, which are voluntary and striated, smooth muscle cells are involuntary and lack striations. This means their contractions are not under conscious control and their microscopic appearance is less organized.

Smooth muscle cells are typically spindle-shaped with a single, centrally located nucleus. Their cytoplasm contains actin and myosin filaments, the proteins responsible for muscle contraction, but these are arranged in a less regular pattern than in skeletal muscle. This arrangement allows for sustained, slow contractions, which are ideal for functions such as moving food through the digestive tract, regulating blood pressure by constricting or dilating blood vessels, and expelling urine from the bladder.

The contraction of smooth muscle is triggered by various stimuli, including nerve impulses from the autonomic nervous system, hormones, and local chemical signals. These cells can also contract spontaneously, as seen in the rhythmic contractions of the uterus during childbirth. The coordinated action of many smooth muscle cells allows for significant changes in the size and shape of the organs they compose, playing a crucial role in maintaining vital bodily functions.