Fetal Endocrine Development

On this page

Fetal Endocrine Timeline - Early Hormone Sparks

  • Weeks 6-8: Gonadal differentiation; Testes: Leydig cells appear.
    • Testosterone synthesis from ~8 weeks (placental hCG driven), vital for male differentiation.
  • Weeks 8-10: Adrenal cortex: Initial cortisol production.
    • Levels are low, ↑ later in gestation.
  • Weeks 10-12: Pituitary gland: Anterior lobe cells differentiate, preparing for hormone production (see ⭐ fact).
  • Weeks 10-12: Thyroid gland: Follicles become active.
    • Iodine trapping & T4 synthesis begin; fetal TSH detectable.
  • Weeks 10-12: Pancreas: Islets of Langerhans form.
    • Insulin & glucagon secretion initiated.

⭐ Fetal pituitary begins hormone synthesis by 10-12 weeks.

Fetal Hypothalamic-Pituitary Axis - Brain's Tiny Command

  • Initiation: Hypothalamus (5-6 wks), Pituitary (4-5 wks). Portal system functional by 12 wks.
  • Key Hormones:
    • Hypothalamus: GnRH, CRH, TRH, GHRH.
    • Anterior Pituitary: ACTH, TSH, GH, LH, FSH, Prolactin.
    • Posterior Pituitary: ADH, Oxytocin.
  • Function: Regulates fetal adrenal, thyroid, gonadal development & stress response.
    • ACTH crucial for adrenal cortisol.
    • TSH for thyroid hormone synthesis.

Fetal and Maternal Hypothalamic-Pituitary-Adrenal Axis

⭐ Fetal CRH surge in late gestation is implicated in the timing of parturition.

Fetal Thyroid & Adrenal Glands - Growth & Stress Duo

  • Fetal Thyroid Gland:
    • Develops from 4th week; iodine trapping by 10-12 weeks.
    • Produces T4 by 12 weeks; essential for CNS development.
    • Maternal T4 crosses placenta, crucial in 1st trimester.
  • Fetal Adrenal Glands:
    • Distinct fetal zone (produces DHEAS) & definitive zone.
    • Cortisol production ↑ significantly in late gestation (>34 weeks), vital for:
      • Lung maturation (surfactant synthesis).
      • Gut maturation, glycogen storage.
    • Responds to stress via ACTH. 📌 Thyroid for Thinking (brain), Adrenal for Air (lungs) & Adaptation (stress).

⭐ The fetal adrenal cortex's fetal zone is exceptionally large and produces DHEAS, a key precursor for placental estrogen synthesis.

Fetal Adrenal Gland Development

Fetal Gonads & Pancreas - Sex & Sugar Setup

  • Gonadal Differentiation:
    • Bipotential gonads until ~6 weeks.
    • SRY gene on Y chromosome dictates testicular differentiation around 6-7 weeks gestation.

    • Testes: Sertoli cells (AMH → Müllerian regression), Leydig cells (Testosterone → Wolffian development, virilization).
    • Ovaries: Develop by ~8 weeks if no SRY; Müllerian ducts persist, Wolffian regress.
  • Sexual Differentiation Pathway:
  • Fetal Pancreas:
    • Develops 4-5 weeks; Islets of Langerhans 10-12 weeks.
    • Insulin secretion from 10-12 weeks; key anabolic hormone for fetal growth (macrosomia if ↑). 📌 Mnemonic: "Sugar baby needs sweet setup early."
    • Maternal insulin does not cross placenta. Fetal Gonadal and Reproductive Tract Development

Placental-Fetal Endocrine Unit - The Vital Interface

  • Essential for pregnancy: coordinates maternal, placental, fetal endocrine functions.
  • Placenta: produces hCG, hPL, progesterone. Lacks key enzymes for de novo estrogen synthesis.
  • Fetal adrenal glands: provide DHEAS, crucial precursor for placental estriol.
  • Forms a vital interface for hormone exchange and fetal support. Feto-Placental Unit Estrogen Synthesis Pathway

⭐ The placenta lacks 17α-hydroxylase and 17,20-desmolase, thus relying on fetal adrenal DHEAS for estrogen production, forming the feto-placental unit.

High‑Yield Points - ⚡ Biggest Takeaways

  • Fetal HPA axis maturation (late gestation) releases cortisol, crucial for lung development.
  • Fetal thyroid functions from 10-12 weeks; maternal T4 is vital for early fetal brain development.
  • Fetal pancreas secretes insulin (major fetal growth factor) from 10-12 weeks.
  • Gonadal differentiation is genetically controlled (SRY gene for testes); fetal testes produce testosterone and AMH.
  • The large fetal adrenal gland produces DHEA-S, a key precursor for placental estrogen synthesis.
  • Fetal endocrine system develops largely autonomously despite significant placental hormone influence (e.g., hCG, hPL).
Rezzy AI Tutor

Have doubts about this lesson?

Ask Rezzy, our AI tutor, to explain anything you didn't understand

Practice Questions: Fetal Endocrine Development

Test your understanding with these related questions

If a baby has a XX or XY genotype, normal internal gonads, but ambiguous external genitalia, it is called?

1 of 5

Flashcards: Fetal Endocrine Development

1/7

During the second and third trimesters, 16-OH DHEA-sulfate is converted to _____ via the enzymes aromatase and sulfatase

TAP TO REVEAL ANSWER

During the second and third trimesters, 16-OH DHEA-sulfate is converted to _____ via the enzymes aromatase and sulfatase

estriol

browseSpaceflip

Enjoying this lesson?

Get full access to all lessons, practice questions, and more.

Start For Free