The role of biological anus in the second volume of the seventh grade

The anus is the end of the whole digestive tract. It has the function of controlling defecation.

The anus will naturally contract when defecating, and with the discharge of gas, it will not bring out fecal residue. This is because the anus has very good sensory control ability, and the closed anus can prevent bacteria and foreign bodies from entering the human body in vitro. The skin of anus contains a large number of lymphocytes, and its self-cleaning ability and contraction ability are incomparable with the skin of other parts of human body.