Biology · Chemical Coordination and Integration · NEET
Inhibin is made by the granulosa cells of the ovary (and Sertoli cells in the testis) and it inhibits FSH secretion from the anterior pituitary. Relaxin is secreted mainly by the corpus luteum (ovary) in the later phase of pregnancy and relaxes the pelvic ligaments to help childbirth. Memory hook: "in-HIBIN" = inhibits FSH; "RELAX-in" = relaxes pelvic bones.
Inhibin (granulosa/Sertoli cells) inhibits only FSH via negative feedback on the anterior pituitary, while relaxin (corpus luteum) relaxes the pelvic ligaments in late pregnancy - two peptide hormones with unrelated targets, so they are not antagonistic.
Your doubts, answered
Does inhibin inhibit FSH or LH?
Inhibin inhibits only FSH, not LH. This is the most tested trap in this topic. Inhibin gives negative feedback to the anterior pituitary so that FSH secretion goes down when it is not needed. LH is controlled separately (mainly by estrogen and progesterone feedback). So the correct NEET statement is: inhibin is produced by granulosa cells and inhibits the secretion of FSH.
Who secretes inhibin - granulosa cells or Sertoli cells?
Both. In females, inhibin is secreted by the granulosa cells of the ovarian follicle. In males, it is secreted by the Sertoli cells (nurse cells) of the testis. In NEET options, the female version (granulosa cells inhibiting FSH) is usually the correct answer, but remember the male source too because Sertoli-cell options appear as distractors.
Is relaxin secreted by the placenta or the ovary?
NCERT says relaxin is secreted by the ovary (corpus luteum) during the later phase of pregnancy, NOT by the placenta. The placenta secretes hCG, hPL, estrogens and progestogens - relaxin is a common wrong option added to placenta lists. Remember: hCG, hPL and relaxin appear in a woman ONLY during pregnancy, but relaxin's source is the ovary.
Are relaxin and inhibin antagonistic hormones?
No. Antagonistic hormones act on the SAME target with opposite effects (like insulin-glucagon or PTH-calcitonin). Relaxin relaxes pelvic ligaments at childbirth, while inhibin inhibits FSH secretion - they act on completely unrelated targets, so they are NOT antagonistic. NEET 2016 tested exactly this.
What is the function of relaxin during childbirth?
Relaxin relaxes the pelvic ligaments and softens the cervix and pubic symphysis in the later phase of pregnancy. This loosening of the pelvic bones makes the birth canal wider so that the baby can pass through during parturition. It works alongside oxytocin, which drives the actual uterine contractions.
⚠️ The NEET trap ✗ Inhibin inhibits both FSH and LH secretion. ✓ Inhibin inhibits only FSH secretion, not LH. 🧠 The word looks like it should stop everything, but NEET wants the exact target: FSH only. LH is controlled by estrogen/progesterone feedback, not inhibin.
Real NEET questions
NEET 2016
Identify the correct statement on 'inhibin':
A · Inhibits the secretion of LH, FSH and Prolactin
B · Is produced by granulosa cells in ovary and inhibits the secretion of FSH ✓
C · Is produced by granulosa cells in ovary and inhibits the secretion of LH
D · Is produced by nurse cells in testes and inhibits the secretion of LH
Solution: Inhibin is secreted by the granulosa cells of the ovarian follicle (and by Sertoli/nurse cells in the testis) and it selectively suppresses FSH secretion from the anterior pituitary, not LH. So option B correctly pairs the source (granulosa cells) with the target hormone (FSH).
NEET 2021
Which of the following secretes the hormone, relaxin, during the later phase of pregnancy?
A · Foetus
B · Uterus
C · Graafian follicle
D · Corpus luteum ✓
Solution: After ovulation the ruptured follicle becomes the corpus luteum. In the later phase of pregnancy the corpus luteum (ovary) secretes relaxin, which relaxes the pelvic ligaments. The foetus, uterus and Graafian follicle do not secrete relaxin.
NEET 2025
Match List-I with List-II. List-I: A. Progesterone B. Relaxin C. Melanocyte stimulating hormone D. Catecholamines. List-II: I. Pars intermedia II. Ovary III. Adrenal Medulla IV. Corpus luteum. Choose the correct answer:
A · A-II, B-IV, C-I, D-III ✓
B · A-III, B-II, C-IV, D-I
C · A-IV, B-II, C-I, D-II
D · A-IV, B-II, C-III, D-I
Solution: Progesterone - Corpus luteum (IV); Relaxin - Ovary (II); MSH - Pars intermedia (I); Catecholamines (adrenaline/noradrenaline) - Adrenal Medulla (III). This gives A-IV, B-II, C-I, D-III, which is option A. Note relaxin's source here is written as the ovary.
Solved Chemical Coordination and Integration NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Inhibin provides negative feedback to the anterior pituitary and inhibits FSH secretion. This controls the growth of ovarian follicles in females and sperm production in males, keeping FSH levels balanced.
Where is inhibin produced in males and females?
In females it is produced by the granulosa cells of the ovarian follicle. In males it is produced by the Sertoli cells (nurse cells) of the seminiferous tubules of the testis.
What does relaxin do during pregnancy?
Relaxin relaxes the pelvic ligaments and softens the cervix during the later phase of pregnancy, widening the birth canal to ease childbirth (parturition).
Which hormone secretes relaxin - ovary or placenta?
The ovary (corpus luteum) secretes relaxin in the later phase of pregnancy. The placenta does NOT secrete relaxin; the placenta secretes hCG, hPL, estrogens and progestogens.
Are inhibin and relaxin peptide or steroid hormones?
Both inhibin and relaxin are peptide (protein) hormones, so they act through membrane receptors, unlike the steroid sex hormones estrogen and progesterone.
