Discuss the physiological functions of placental hormones in pregnancy.

Placental Hormones and Their Physiological Functions

The placenta begins to function as an endocrine organ early in gestation, with hormone production increasing progressively. The major hormones and their functions are detailed below:

1. Human Chorionic Gonadotropin (hCG)

• Synthesis: Produced by syncytiotrophoblast cells.
• Maternal Effects: Maintains the corpus luteum in early pregnancy, ensuring continued progesterone and estrogen production until the placenta takes over. It also suppresses maternal immune response to fetal tissues.
• Fetal Effects: Stimulates fetal testes to produce testosterone, crucial for male fetal development.
• Clinical Significance: Basis for pregnancy tests. Levels peak around 8-11 weeks and then decline. Abnormal levels can indicate ectopic pregnancy or fetal abnormalities.

2. Estrogens (primarily Estriol)

• Synthesis: Initially from the corpus luteum, then primarily from the placenta, utilizing fetal precursors.
• Maternal Effects:
  • Stimulates uterine growth and increases uterine blood flow.
  • Increases breast size and prepares mammary glands for lactation.
  • Relaxes pelvic ligaments.
  • Increases plasma protein levels.
• Fetal Effects: Promotes fetal growth and maturation.

3. Progesterone

• Synthesis: Initially from the corpus luteum, then primarily from the placenta.
• Maternal Effects:
  • Maintains the endometrium, preventing uterine contractions.
  • Suppresses maternal immune response.
  • Increases maternal respiration and ventilation.
  • Relaxes smooth muscle, reducing gastrointestinal motility.
• Fetal Effects: Suppresses fetal immune response, preventing rejection of the fetus.

4. Human Placental Lactogen (hPL) / Human Chorionic Somatomammotropin (hCS)

• Synthesis: Syncytiotrophoblast cells.
• Maternal Effects:
  • Alters maternal glucose and protein metabolism, making glucose available to the fetus. This leads to maternal insulin resistance.
  • Promotes lipolysis, providing fatty acids for fetal energy.
  • Prepares mammary glands for lactation.
• Fetal Effects: Promotes fetal growth.

5. Human Placental Growth Hormone (hPGH)

• Synthesis: Syncytiotrophoblast cells.
• Effects: Similar to pituitary growth hormone, contributing to fetal growth. It has a longer half-life than pituitary GH.

6. Relaxin

• Synthesis: Corpus luteum and placenta.
• Maternal Effects: Relaxes pelvic ligaments and softens the cervix, preparing for labor.
• Fetal Effects: May contribute to fetal lung maturation.

7. Other Hormones

• Cortisol: Placental production increases maternal cortisol levels, influencing glucose metabolism.
• Prolactin: Placental prolactin contributes to mammary gland development.
• Thyroid Hormones: Placenta produces thyroid-binding globulin, affecting maternal thyroid hormone levels.

The interplay between these hormones is complex and tightly regulated. Changes in hormone levels throughout pregnancy are crucial for normal fetal development and maternal adaptation. For example, the shift from corpus luteum-derived hormones to placental hormone production is a critical transition in early pregnancy.

Hormone	Primary Source	Major Maternal Effects	Major Fetal Effects
hCG	Syncytiotrophoblast	Maintains corpus luteum, suppresses immunity	Stimulates fetal testosterone production
Estrogen	Placenta (after corpus luteum)	Uterine growth, breast development, pelvic relaxation	Fetal growth and maturation
Progesterone	Placenta (after corpus luteum)	Maintains endometrium, suppresses immunity	Suppresses fetal immunity
hPL	Syncytiotrophoblast	Alters glucose/protein metabolism, lipolysis	Promotes fetal growth