Leydig cells (or testicular interstitial cells) are the primary producers of the male sex hormone, testosterone. They are found close to the seminiferous tubules of the testes, where they secrete testosterone in the presence of luteinizing hormone (LH). Testosterone is the driving force behind male sexual development and fertility and is vital for spermatogenesis, male embryonic development, and the development of primary and secondary sex characteristics.
What is a Leydig Cell?
A Leydig cell is a type of specialized cell found in the male testes. Leydig cells are located in the connective tissue of the seminiferous tubules, where they produce the androgen testosterone. Testosterone production by the Leydig cells is controlled by the presence or absence of luteinizing hormone (LH).
Functions of Leydig Cells
The key function of a Leydig cell is to produce the male sex hormone, testosterone. Testosterone is vital for spermatogenesis (i.e., sperm production), and for the development of primary and secondary male sex characteristics.
Leydig cells produce testosterone in the male testes. This process is controlled by luteinizing hormone (LH), which is secreted in pulses from the pituitary gland. In the presence of LH, the Leydig cells are stimulated to produce testosterone.
Testosterone production is controlled by a negative feedback loop between testosterone and LH. When testosterone levels are high, LH is suppressed and production stops. When testosterone levels are low, LH is released from the pituitary gland and production resumes. Therefore, testosterone and LH are produced and secreted in alternate pulses.
Male sex cells (i.e., sperm) develop from germ cells in the testes through a process called spermatogenesis. Sperm production is driven by testosterone so, as the primary producers of this hormone, Leydig cells play a crucial role in spermatogenesis.
Testosterone secreted by Leydig cells diffuses into the seminiferous tubules of the testes, which is where spermatogenesis takes place. The seminiferous tubules are composed of three major cell types; these are the peritubular myoid (PTM) cells, the Sertoli cells, and the germ cells.
Germ cells are a type of unipotent stem cell that divides to produce gametes in sexually reproducing organisms. In male organisms, they give rise to sperm cells. During spermatogenesis, germ cells divide by meiosis to produce four haploid daughter cells. Each daughter cell is a genetically unique sperm cell and can take part in fertilization.
Testosterone is a vital component in this process, as it supports the completion of meiosis, the maturation of sperm cells, and the release of sperm. In the absence of testosterone, germ cells can still divide by meiosis. However, the resultant sperm fail to mature or cannot be released, resulting in infertility.
Development of Male Embryos
The testosterone produced by Leydig cells is also crucial for male sexual development, as this hormone is responsible for driving sex differentiation and for producing male sex characteristics.
During the first 6 weeks of development, male and female embryos are indistinguishable from one another. When the testicles of male embryos begin to develop (which happens around the week 7 mark) fetal Leydig cells migrate into the developing gonads, and testosterone production begins. Testosterone is crucial for the formation of the male genitalia, and the descent of the testes in the final 2 months of fetal development.
Primary and Secondary Sexual Development
After birth, testosterone is the driving force behind primary sexual development, which typically takes place between the ages of 11 and 15 years. During this phase, testosterone induces spermatogenesis, enlargement of the genitals, descending of the testicles, and increased libido.
Testosterone is also responsible for the development of male secondary sex characteristics, which include the growth of facial and chest hair, and the deepening of the voice. Testosterone is also responsible for producing growth spurts during puberty of male organisms.
Structure of Leydig Cells
Leydig cells are typically found in groups of ten in the connective tissues of the seminiferous tubes. They are characterized by their large, round nuclei, their prominent nucleoli, and their high lipid content.