Ovary — Hormones

NCERT grounding

NCERT Class XI Biology, Chapter 19, Section 19.2.10 anchors this subtopic. The text states that females have a pair of ovaries located in the abdomen, that the ovary is the primary female sex organ producing one ovum per menstrual cycle, and that it secretes two groups of steroid hormones — estrogen and progesterone. The ovary is described as being composed of ovarian follicles and stromal tissues. Estrogen is synthesised mainly by the growing ovarian follicles; after ovulation, the ruptured follicle becomes the corpus luteum, which secretes mainly progesterone. The chapter summary repeats these assignments and adds that estrogen stimulates female secondary sex characters while progesterone is essential for the maintenance of pregnancy.

"The estrogen is synthesised and secreted mainly by the growing ovarian follicles. After ovulation, the ruptured follicle is converted to a structure called corpus luteum, which secretes mainly progesterone."

NCERT Class XI Biology · 19.2.10 Ovary

The NIOS Senior Secondary Biology Lesson 17 supplement (Section 17.7, "Gonads") reinforces the same scheme and adds the practical observations: estrogen is secreted from the follicles and stimulates breast development and fat deposition on the hip in a mature woman; progesterone is secreted by the corpus luteum (the follicle left after release of the ovum) and prepares the uterus for pregnancy. NIOS also notes that human chorionic gonadotropin (hCG) sustains the corpus luteum's progesterone output when a woman becomes pregnant, a hand-off later transferred to the placenta. NEET draws every direct ovary question from this combined source set, which is why this subtopic sits within the small, finite syllabus of Chapter 19 rather than the broader cycle physiology of Chapter 3 reproduction.

Ovary as a dual gonad

The ovary is simultaneously a gametogenic and an endocrine organ. The gametogenic function — oogenesis — produces one secondary oocyte per cycle from a cohort of primordial follicles. The endocrine function is structurally inseparable from this: the same follicle that nurtures the developing oocyte also synthesises the steroid hormones that drive the cycle. NCERT explicitly lists the ovary among the "organised endocrine bodies" alongside the pituitary, pineal, thyroid, parathyroid, thymus, adrenal, pancreas and testis. In NEET terminology, the ovary is therefore both a primary sex organ and an endocrine gland, and questions exploiting this dual role are common.

Anatomically the cortex of the ovary contains the follicles at every stage from primordial through primary, secondary, tertiary and finally the mature Graafian follicle. The Graafian follicle is the immediate source of estrogen during the late follicular phase; after ovulation its remnants — the theca interna cells and the surviving granulosa cells — luteinise, fill with yellow lipid droplets (giving the corpus luteum its yellow body name) and switch their dominant output to progesterone. This anatomical switch is the single fact most heavily exploited by NEET stem-writers, because it explains why the same anatomical region of the ovary can be a source of estrogen on day 12 and a source of progesterone on day 16.

Estrogen — granulosa follicle hormone

Estrogen is the umbrella name NCERT uses for the family of C18 steroid hormones secreted by the ovary; estradiol-17β is the dominant species in non-pregnant adult women. The hormone is synthesised in two cell layers of the growing follicle: the theca interna cells, responding to LH, produce androgens (testosterone, androstenedione); these androgens diffuse across the basement membrane into the granulosa cells, where the FSH-driven enzyme aromatase converts them to estradiol. NEET 2024 (Assertion-Reason on FSH) tests precisely this: FSH acts upon ovarian follicles in females and Leydig cells in males, and growing ovarian follicles secrete estrogen.

The NCERT chapter summary defines the spectrum of estrogen actions explicitly. Estrogen produces "wide-ranging actions such as stimulation of growth and activities of female secondary sex organs, development of growing ovarian follicles, appearance of female secondary sex characters (e.g., high pitch of voice etc.) and mammary gland development. Estrogens also regulate female sexual behaviour." Behind each of these phrases lies a target organ.

The bone-protective effect deserves its own box because NEET 2018 used it directly. Estrogen suppresses osteoclast activity and promotes calcium retention; falling estrogen after menopause therefore accelerates bone resorption. The question asked which pair of hormones could play a significant role in osteoporosis, and the official answer was estrogen and parathyroid hormone — both modulators of bone calcium turnover. Students who only memorised "estrogen = secondary sex characters" missed this entirely. The same NEET 2018 paper also asked which of the listed hormones was an amino-acid derivative (answer: epinephrine), explicitly contrasting it with estradiol and estriol as steroid hormones — confirming once more the chemical class of ovarian estrogen.

Progesterone — corpus luteum hormone

Progesterone is a C21 steroid synthesised mainly by the corpus luteum. After the LH surge ruptures the Graafian follicle, the cellular debris reorganises into a yellow, lipid-rich body in which the luteinised granulosa cells produce progesterone and a smaller amount of estrogen. NCERT 19.2.10 distils its functions into a single sentence: "Progesterone supports pregnancy. Progesterone also acts on the mammary glands and stimulates the formation of alveoli (sac-like structures which store milk) and milk secretion." Behind this terse statement lie four target tissues.

Two of these four effects are tested almost every cycle. The pregnancy-maintenance role explains NEET 2017's classification of the corpus luteum as the body's only temporary endocrine gland — it is formed from the Graafian follicle after ovulation and produces progesterone (and some estrogen). The contraceptive logic — progesterone inhibits gonadotropins — explains why combined oral contraceptive pills are dominated by a synthetic progestin: continuous progestin exposure mimics the high-progesterone state of pregnancy and prevents the LH surge, so no ovulation occurs. NEET 2024 included progesterone in a list of steroid hormones (cortisol, testosterone, progesterone all steroid; glucagon the odd peptide), making chemical class identification a routine ask.

Relaxin and late-pregnancy support

Relaxin is the third ovarian hormone NEET expects students to know, even though NCERT mentions it only in the chapter summary and in passing. It is a peptide hormone — note the chemical class difference from estrogen and progesterone — secreted by the corpus luteum during the later phase of pregnancy. Its targets are the connective tissues of the pelvis: relaxin softens the pelvic ligaments and the pubic symphysis, and helps dilate the uterine cervix near term, widening the birth canal so that parturition can proceed. The placenta also contributes some relaxin in human pregnancy, but NEET 2021 explicitly tested the corpus luteum as the source and rejected uterus, Graafian follicle and foetus as distractors.

Cycle control — feedback loops

Ovarian hormones do not work in isolation; they participate in a closed loop with the hypothalamic GnRH, the anterior pituitary gonadotropins FSH and LH and the ovary itself. In the early follicular phase, low estrogen exerts negative feedback at the pituitary, holding FSH and LH low. As the dominant follicle matures and estrogen rises sharply, the feedback flips: very high, sustained estrogen exerts positive feedback at the hypothalamus and anterior pituitary, triggering the mid-cycle LH surge that causes ovulation. After ovulation, the corpus luteum produces progesterone and estrogen, both of which re-impose negative feedback on FSH and LH, preventing fresh follicular development. If pregnancy occurs, hCG from the trophoblast rescues the corpus luteum so its progesterone output continues. If not, the corpus luteum regresses on day 24–26, progesterone falls, the endometrium is shed and a new cycle begins.

The feedback architecture explains the seemingly contradictory roles of estrogen — it both triggers and inhibits LH, depending on dose and duration. It also explains why oral contraceptive pills work: a steady exogenous progestin (sometimes with low-dose estrogen) maintains negative feedback for the whole cycle, so the LH surge never happens and ovulation is suppressed. NEET 2024 tested precisely this idea by asking about the chemical class of these hormones — recognising progesterone as a steroid is the first step in understanding why the pill is taken orally despite being a steroid (steroids are lipid-soluble, so they are absorbed across the gut wall and act on intracellular receptors regulating gene transcription, as NEET 2019 reminds us).

Worked examples

Common confusion & NEET traps