Smooth muscle is one of the three types of muscle tissue in the human body, along with skeletal muscle and cardiac muscle. Smooth muscle is found in various organs of the body, such as the stomach, intestines, blood vessels, and bladder. Unlike skeletal muscle, which is under voluntary control, smooth muscle acts involuntarily.

Characteristics of Smooth Muscle:
- Smooth muscle is non-striated, meaning it lacks the striped appearance of skeletal muscle.
- It is composed of spindle-shaped cells with a single nucleus.
- Smooth muscle contracts slowly and rhythmically, allowing for sustained contractions.
- It is controlled by the autonomic nervous system and hormones, rather than conscious control.

Function of Smooth Muscle:
- Smooth muscle plays a crucial role in the involuntary movement of substances through various organs, such as peristalsis in the digestive tract.
- It regulates the diameter of blood vessels, helping to control blood pressure.
- Smooth muscle in the bladder contracts to expel urine, while in the uterus, it contracts during childbirth.

Comparison with Cardiac Muscle:
While both smooth muscle and cardiac muscle are involuntary, they have different functions and structures. Cardiac muscle is found only in the heart and is responsible for pumping blood throughout the body. It has a striated appearance like skeletal muscle but functions involuntarily like smooth muscle.
In conclusion, smooth muscle is a type of muscle tissue that acts involuntarily and is essential for the proper functioning of various organs in the body. Its unique characteristics and functions distinguish it from skeletal and cardiac muscle.

Smooth muscle and cardiac muscle