Lactiferous duct is present in

Signal for uterine contractions and parturition originates when . . . . . . .

$A$: Lactational amenorrhoea is due to high levels of prolactin.
$R$: Prolactin stimulates the release of gonadotropins.

Some hormones prevent the secretion of milk by the mammary glands until the birth of the young ones,even though the glands are fully prepared to do so. These hormones are:

The contraction of the uterus at the time of childbirth is stimulated by $........$.

Assertion $A :$ Colostrum provides passive immunity to the infant.
Reason $R :$ Colostrum secreted by the mother contains antibodies that protect the infant.