Hypothalamopituitary axis becomes active and functional at:

Ans. a (20th week of gestation). (Ref. Nelson's textbook of Paediatrics 17th ed. 1870)# Hypothalamic neurons synthesize TRH by 6-8 weeks (of gestation) and TSH secretion is evident by 12th week of gestation.# Maturation of HP-thyroid axis occurs by 2nd half of gestation.# Feedback relationships by 3 months postnatally.- Fetal thyroid bilobed shape is recognised by 7th week of gestation- Thyroid folicle cell and colloid formation seen by 10th week- Thyroglobulin synthesis occurs from 4th week- T4, T3 synthesis and secretion from 12th week of gestationThe CNS-hypothalamic-pituitary-gonadal-target organ axisOvarian hormones have direct and indirect effects on other tissues (e.g., bone, skin, muscle). FSH = follicle-stimulating hormone; GnRH = gonadotropin-releasing hormone; LH = luteinizing hormone.