Final answer:
Mammary gland tenderness during the first trimester of pregnancy is due to increasing levels of hormones, especially estrogen, progesterone, and prolactin, which are key for preparing the breasts for lactation and feeding after childbirth.
Step-by-step explanation:
The tenderness of mammary glands during the first trimester of pregnancy is due to increasing levels of hormones such as estrogen and progesterone. These hormones are responsible for several changes in the body to prepare for the growth and development of the fetus, and one of their effects is the further development of the mammary tissue and enlargement of the breasts. Such hormonal changes can lead to swelling and tenderness of the breast tissue, a symptom commonly experienced by pregnant individuals.
As the pregnancy progresses, particularly near the fifth week, the anterior pituitary ramps up its hormone production, raising levels of prolactin, which is also crucial for mammary gland development and ultimately, milk production post-childbirth. Although prolactin levels rise significantly during pregnancy, the presence of estrogen, progesterone, and other placental hormones inhibits milk synthesis until after the delivery when the placenta is expelled, lifting the inhibition on prolactin-mediated milk synthesis.