Smooth muscle

Smooth muscle is a type of muscle tissue that is found in various parts of the body, including the digestive system, respiratory system, and blood vessels. Unlike skeletal muscle, which is under voluntary control, smooth muscle is not under conscious control and is therefore referred to as involuntary.

Structure

Smooth muscle cells are spindle-shaped and have a single, centrally located nucleus. The cells are arranged in sheets or layers, with the long axes of the cells running parallel to each other. This arrangement allows for coordinated contractions and relaxations of the muscle tissue.

Function

The primary function of smooth muscle is to contract and relax in order to facilitate bodily functions. For example, in the digestive system, smooth muscle contractions help to move food along the gastrointestinal tract. In the blood vessels, smooth muscle contractions and relaxations help to regulate blood flow and pressure.

Types

There are two types of smooth muscle: single-unit (or unitary) and multi-unit. Single-unit smooth muscle cells are connected by gap junctions and contract as a single unit. This type of smooth muscle is found in the walls of hollow organs like the stomach and intestines. Multi-unit smooth muscle cells are not electrically linked and each cell can contract independently. This type of smooth muscle is found in the iris of the eye and the walls of blood vessels.

Clinical significance

Abnormalities in smooth muscle function can lead to a variety of medical conditions. For example, hypertension can result from excessive contraction of smooth muscle in the walls of blood vessels. Similarly, asthma can result from contraction of smooth muscle in the bronchial tubes.

See also

• Muscle contraction
• Muscle tissue
• Skeletal muscle
• Cardiac muscle

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