After gastrulation,the roof of the archenteron is formed by:

During pregnancy,the levels of which hormones are increased?

$A$: If fertilization occurs,the corpus luteum is rescued from regression by human chorionic gonadotropin $(hCG)$,which is produced by the placenta.
$R$: In the first trimester,the corpus luteum,stimulated by $hCG$,is responsible for the production of progesterone.

If after ovulation no pregnancy results,the corpus luteum

Which is not the function of placenta?

Which of the following hormones is secreted by the human placenta?