来源：互联网
肛管被肛门括约肌复合体围绕，肛门括约肌复合体由互相重叠的两层肌肉构成。其外层为肛门外括约肌，它是肛管的最外层肌肉，是骨骼肌（横纹肌），受体神经支配，为随意肌。可分为三层，即皮下层、浅层和深层，其中皮下层环绕肛管下端。内层为肛门内括约肌，它是直肠环肌层的延续，属不随意的平滑肌部分，呈珠白色。
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