1) What is a sphincter muscle? 2)Name TWO places in the alimentary canal where sphincter muscles are found?

1-A ring-shaped muscle that relaxes or tightens to open or close a passage or opening in the body.

2-Sphincters are specialized muscles that are located at the upper esophagus (upper esophageal sphincter (UES) and the gastroesophageal junction

Explanation:

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explanation:

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the level of progesterone is low at the pre-ovulatory phase of the cycle but it gradually increases and the levels are high at the luteal phase. if pregnancy occurs, the level of progesterone will be high throughout the pregnancy.

if egg is fertilized and the mother gets pregnant, progesterone starts preparing the uterus for the implantation. it starts building up the lining of uterus and make it hostile of the period of pregnancy.