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Gonads Testes and Ovaries: Structure and Functions

BiologyTry the interactive 3D model →

The gonads are the reproductive glands — testes in males and ovaries in females. They have a dual role: producing gametes (sperm or eggs) and secreting sex hormones that control reproduction and secondary sexual characters.

They matter because they drive puberty, fertility, menstrual cycle, pregnancy support and many body changes such as voice deepening, breast development, and bone growth.

Key Concepts

  • Testes: located in scrotum; seminiferous tubules make sperm.
  • Testosterone: main male hormone from Leydig (interstitial) cells.
  • Ovaries: pelvic glands producing ova in follicles.
  • Oestrogen and progesterone: main female hormones from follicles/corpus luteum.
  • LH and FSH: pituitary gonadotropins controlling both gonads.
  • Secondary sexual characters: features developing at puberty under sex hormones.

How It Works

  1. Hypothalamus releases GnRH in pulses.
  2. Anterior pituitary releases LH and FSH.
  3. In testes: LH stimulates testosterone; FSH supports sperm production in seminiferous tubules (optimal ~2–3°C below core body temperature in scrotum).
  4. In ovaries: FSH grows follicles (oestrogen rises); LH surge triggers ovulation; corpus luteum then secretes progesterone preparing uterus.
  5. Sex hormones feed back to brain/pituitary regulating cycle and production.

Worked Example

Problem: Outline a 28-day ovarian cycle hormonally.

Step 1 (days 1–13): FSH grows a follicle; oestrogen rises and rebuilds uterine lining.

Step 2 (day ~14): High oestrogen triggers LH surge; ovulation releases egg.

Step 3 (days 15–28): Corpus luteum secretes progesterone maintaining lining for possible implantation.

Step 4: If no fertilisation, corpus luteum degenerates, hormones fall, lining sheds as menstruation and cycle restarts.

Common Misconceptions

  • Myth: Testosterone exists only in males and oestrogen only in females. Correction: Both sexes produce both hormone types, in different amounts and roles.
  • Myth: Ovaries produce new eggs throughout life continuously. Correction: Females are born with a finite pool of primary oocytes; ovulation releases from this pool.
  • Myth: Gonads work without brain control. Correction: The hypothalamic-pituitary-gonadal axis tightly regulates them.

Real-World Applications

Hormonal contraceptives use oestrogen/progesterone feedback to suppress ovulation. Fertility treatments use FSH/LH analogues to stimulate ovaries or sperm production. Delayed or absent puberty investigations check the HPG axis hormones.

Gonads unite reproduction and endocrinology: gametes for the next generation and hormones that shape the body producing them. Sex hormones also influence bone density, muscle mass, fat distribution, red blood cell production and mood in both sexes, which is why declining gonadal function with age or after gonad removal can increase osteoporosis and anaemia risk, and why hormone levels must be interpreted together with LH and FSH to locate whether a problem lies in the gonad or in pituitary control.

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