The esophagus contains two types of muscle: skeletal muscle and smooth muscle.
Skeletal Muscle in the Esophagus
The upper portion of the esophagus (approximately 2-4 cm) is composed entirely of skeletal muscle. This type of muscle is under voluntary control, meaning you can consciously influence its actions (although swallowing is largely a reflex). Its striated appearance under a microscope distinguishes it from smooth muscle.
Smooth Muscle in the Esophagus
The lower portion of the esophagus is primarily composed of smooth muscle. This involuntary muscle type is responsible for the peristaltic waves that propel food towards the stomach. Unlike skeletal muscle, you cannot consciously control its contractions. A transitional zone exists where both skeletal and smooth muscle fibers mix.
Muscle Distribution in the Esophagus
The transition between these muscle types isn't abrupt. The upper esophagus is purely skeletal, the middle portion is a mixture of skeletal and smooth muscle, and the lower part is entirely smooth muscle. This arrangement allows for both voluntary control at the beginning of the swallowing process and involuntary, rhythmic contractions to move food throughout the rest of its journey.
Reference Integration: The provided text explicitly states, "Esophagus is unique, unlike any other organ in the body, it is made up of partly skeletal and partly smooth muscles. Upper part is entirely skeletal (2–4 cm), the middle, a mixture of skeletal and smooth muscle (Figure 9), and the lower part, 11 cm or so in length is entirely smooth." This perfectly describes the distribution and types of muscle found within the esophagus.
