21.23: Gonadal and Placental Hormones

The gonads, namely the testes in males and the ovaries in females, are pivotal in producing gonadal hormones that orchestrate the intricate processes of sexual development and reproduction.

In males, testosterone is the primary gonadal androgen. It plays a central role in the maturation of male reproductive organs — the penis and testes. Additionally, testosterone is instrumental in the development of secondary sexual characteristics — a deep voice as well as facial and pubic hair growth — and the production of sperm.

On the female front, estrogen and progesterone are vital gonadal hormones. Estrogen is paramount for the development of female reproductive organs like the uterus and vagina. It also regulates secondary sexual characteristics, including breast development, and plays a crucial role in the menstrual cycle and the maintenance of pregnancy. Progesterone, on the other hand, prepares the uterus for the implantation of the zygote and ensures pregnancy by inhibiting uterine contractions.

The placenta takes center stage during pregnancy, secreting hormones vital for fetal growth and development. Human chorionic gonadotropin (hCG), a hormone that placental cells produce, supports pregnancy, particularly during the first trimester. Another placental hormone, human placental lactogen (hPL), regulates the mother's metabolism and stimulates the secretion of breast milk.

This interplay of gonadal and placental hormones is essential for the proper progression of reproductive processes and the sustained well-being of both mother and fetus during pregnancy.

The gonads, the testes in males, and the ovaries in females produce gonadal hormones.

Testosterone is the primary male gonadal androgen. It is responsible for the maturation of male reproductive organs, such as the penis and testis, and secondary sexual characteristics, such as facial hair growth and sperm production.

Estrogen and progesterone are two important female gonadal hormones.

Estrogen is responsible for the development of female reproductive organs, such as the uterus and vagina, and secondary sexual characteristics, such as breast development, regulation of the menstrual cycle, and pregnancy maintenance.

Progesterone prepares the uterus for fertilized egg implantation and preserves pregnancy by inhibiting uterine contractions.

During pregnancy, the placenta forms and secretes hormones to ensure the proper growth and development of the fetus.

Placental cells secrete human chorionic gonadotropin, or hCG, which supports the pregnancy during the first trimester.

Another placental hormone called human placental lactogen, or hPL, regulates the mother's metabolism and stimulates breast milk secretion.