the anus is surrounded by a circular muscles true or false
Answers
Answer:
Sphincter muscle, any of the ringlike muscles surrounding and able to contract or close a bodily passage or opening. One of the most important human sphincter muscles is the sphincter pylori, a thickening of the middle layer of stomach muscle around the pylorus (opening into the small intestine) that holds food in the stomach until it is thoroughly mixed with gastric juices. Other sphincters are involved in excretion of waste: the sphincter ani externus keeps the anal opening closed by its normal contraction, and the sphincter urethrae is the most important voluntary control of urination. There is also a sphincter in the eye, the sphincter pupillae, a ring of fibres in the iris that contracts the pupil in the presence of bright light. Compare dilator muscle.
Explanation:
Answer:
Anal canal, the terminal portion of the digestive tract, distinguished from the rectum because of the transition of its internal surface from a mucous membrane layer (endodermal) to one of skinlike tissue (ectodermal). The anal canal is 2.5 to 4 cm (1 to 1.5 inches) in length; its diameter is narrower than that of the rectum to which it connects. The canal is divided into three areas: the upper part, with longitudinal folds called rectal columns; the lower portion, with internal and external constrictive muscles (sphincters) to control evacuation of feces; and the anal opening itself.