Chemical Coordination and Integration · Lesson 8 of 11
Testis and Ovary: Sex Steroids, Gamete Formation and Pregnancy
“Explain testicular testosterone, ovarian oestrogens and progesterone, and their control by LH and FSH.”
• Identify Leydig cells, testicular androgens and their functions. • Explain ovarian follicular oestrogen, corpus-luteum progesterone and their roles. • Trace LH and FSH action in male and female gonads. • Distinguish hormone-driven reproductive tissue development from direct gamete production.
The gonads have reproductive and endocrine roles
Testes and ovaries produce gametes and also act as endocrine organs. Their hormones influence reproductive anatomy, secondary sexual characteristics, reproductive cycles and aspects of metabolism. Their activities depend strongly on hypothalamic GnRH and the anterior pituitary gonadotrophins LH and FSH. These signals link neural and endocrine coordination to reproductive development. The gonads are not simply hormone reservoirs; specialised steroid-producing cells make hormones while other cells support developing gametes.
Testes contain tubules and interstitial endocrine cells
Human testes are usually located in the scrotum. Seminiferous tubules are the principal sites where sperm-forming germ cells develop with support from Sertoli cells. Between the tubules lie interstitial Leydig cells, which synthesise and secrete androgens, especially testosterone. LH stimulates Leydig cells, while FSH chiefly acts through Sertoli cells; testosterone and Sertoli-cell factors together support spermatogenesis. Having LH does not make a sperm cell directly, nor does FSH alone replace testosterone's contribution.
A class of steroid hormones, with testosterone as a major example, that influence male reproductive development, sexual characteristics and some metabolic functions.
Androgens support development and maintenance of male reproductive ducts and accessory organs such as the epididymis, vas deferens, seminal vesicles and prostate. At puberty they contribute to deeper voice, facial and body hair growth, muscle development and other secondary sexual traits. They also influence reproductive behaviour and can support anabolic protein-related processes. These effects are influenced by genetics, hormone exposure and other biological factors; hormones are not deterministic explanations of an individual's personality or social behaviour.
Ovarian follicles and corpus luteum produce different steroids
Ovaries contain developing follicles, each with an oocyte surrounded by specialised somatic cells. Developing follicles, especially their granulosa and theca cells working together, synthesise oestrogens such as estradiol. The source associates oestrogen secretion primarily with growing ovarian follicles. After ovulation, the ruptured follicular structure differentiates into the corpus luteum, which secretes progesterone and some oestrogen during the luteal phase.
A family of ovarian and other steroid hormones, especially estradiol, involved in development and maintenance of reproductive tissues, secondary sexual traits and menstrual-cycle regulation.
A steroid hormone produced prominently by corpus luteum after ovulation and, in pregnancy, increasingly by placenta; it supports the uterine environment and reproductive development.
Oestrogens support growth and activity of female accessory reproductive organs, development of secondary sexual characteristics, and endometrial growth during part of the menstrual cycle. They also influence many tissues beyond reproduction, including bone. Progesterone supports secretory transformation and maintenance of the uterine lining, preparing it for possible implantation and helping maintain pregnancy. Reproductive steroid secretion changes through the cycle, rather than remaining at one fixed high concentration.
The LH surge and corpus luteum sequence
FSH supports the growth of ovarian follicles. As a dominant follicle develops, circulating oestrogen rises in a pattern that, at a particular sustained stage of the cycle, helps trigger positive feedback and a surge of LH. The LH surge induces ovulation and luteinisation of the follicular remnants. The newly formed corpus luteum produces progesterone, which acts on the endometrium. Without continuing pregnancy-related support, corpus luteum activity later declines; in pregnancy it can be supported by human chorionic gonadotrophin before placental hormone production becomes dominant.
Hormones prepare the mammary gland for function
Oestrogens contribute to growth and development of mammary ducts, while progesterone supports lobuloalveolar maturation. The source states that progesterone influences alveolar formation and milk secretion. An important mechanistic qualification is that high progesterone during pregnancy generally restrains copious milk secretion; the drop in placental progesterone after birth permits prolactin-supported milk production. Milk ejection is then triggered by oxytocin. Mammary development, milk synthesis and milk ejection are separate but coordinated hormonal events.
| Structure or hormone | Source and regulator | Major function |
|---|---|---|
| Leydig cells | Testis; LH | Testosterone secretion |
| Sertoli cells | Testis; FSH and androgen environment | Support of spermatogenesis |
| Developing ovarian follicle | Ovary; FSH/LH-linked pathways | Oestrogen production and oocyte development |
| Corpus luteum | Post-ovulation follicle | Progesterone synthesis and luteal support |
| Oestrogen | Ovarian follicles and other tissues | Reproductive tissue development and cycle functions |
| Progesterone | Corpus luteum/placenta | Endometrial support and pregnancy maintenance |
A familiar feedback loop
The hypothalamus and pituitary respond to circulating reproductive steroids, including negative and—in a specific ovarian context—positive feedback. Testosterone often reduces drive for further LH production, while ovarian oestrogen and progesterone regulate gonadotrophin release in a stage-dependent manner. Such control prevents uncontrolled hormone output and helps produce timed reproductive patterns. Reproductive endocrine processes involve multiple interacting signals, not just one permanent stimulus from the pituitary.
LH, FSH and steroid hormones regulate reproductive cells and support gamete formation but are not themselves sperm or ova. Progesterone supports pregnancy yet does not directly produce milk ejection.
Quick Quiz
Quiz
Which testicular cell produces most circulating testosterone?
Which pituitary hormone stimulates Leydig cells?
Which pituitary hormone prominently acts on Sertoli cells?
Which structure makes progesterone after ovulation?
Which hormone surge triggers ovulation?
Oestrogens are especially associated with:
What is a central role of progesterone?
Which hormone triggers milk ejection after birth?
Why is it incorrect to say that gonadotrophins are themselves reproductive cells?
Practice Problems
- Draw and label the principal hormone pathways from pituitary to testes and ovaries.
- Explain how testosterone supports male reproductive development and function.
- Differentiate ovarian follicle and corpus luteum endocrine activities.
- Explain why a LH surge is needed near ovulation.
- Distinguish progesterone's effects on mammary development from prolactin and oxytocin roles after birth.
In testes show LH → Leydig → testosterone and FSH → Sertoli → support of spermatogenesis. In ovaries show FSH → follicle growth/oestrogen; LH surge → ovulation/corpus luteum → progesterone.
Key Takeaways
• Leydig cells secrete testosterone under LH stimulation; FSH supports Sertoli cell function. • Androgens support reproductive organ maturation and aspects of male secondary sexual development. • Ovarian follicles synthesise oestrogens; corpus luteum produces progesterone after ovulation. • An LH surge triggers ovulation and luteal transformation. • Progesterone supports endometrium and pregnancy; prolactin and oxytocin have distinct lactation roles.