sileälihassoluissa

Sileälihassoluissa, also known as smooth muscle cells, are a type of muscle cell found in the walls of internal organs and structures in the body. Unlike skeletal muscle, which is under voluntary control, smooth muscle operates involuntarily. These cells are spindle-shaped and have a single, centrally located nucleus. Their cytoplasm is filled with actin and myosin filaments, which are the contractile proteins responsible for muscle contraction. However, these filaments are arranged differently than in skeletal muscle, giving smooth muscle its characteristic "smooth" appearance under a microscope and enabling slower, sustained contractions.

The primary function of smooth muscle is to propel substances through internal passageways and to regulate the size of organs and blood vessels. They are found in the walls of the digestive tract, where they facilitate peristalsis to move food. In the urinary tract, they help expel urine. Smooth muscle also forms the muscular layer of blood vessels, where its contractions and relaxations control blood pressure and flow. In the respiratory system, smooth muscle in the airways can constrict or dilate to regulate airflow. The uterus also contains smooth muscle, crucial for childbirth.

Smooth muscle contraction is regulated by the autonomic nervous system, hormones, and local factors, allowing for fine-tuned control of bodily functions without conscious effort. This allows for slow, rhythmic contractions that can maintain tension for extended periods, which is essential for many of the body's continuous operations.