Hormonal control hierarchy
Spermatogenesis regulation is carried out top-down in a multi-level scheme. The highest center is the hypothalamus: its arcuate nuclei secrete gonadotropin-releasing hormone (gonadoliberin).
Under the action of liberins, the anterior pituitary begins to produce gonadotropic hormones, which selectively act on different targets within the testis:
- LH cells of the hypophysis secrete luteinizing hormone (LH). In the male body, it is often called ICSH — interstitial cell-stimulating hormone.
- Pituitary FSH cells secrete follicle-stimulating hormone (FSH), which acts on sustentocytes.
Leydig cells: the testosterone factory
Testicular endocrinocytes, or Leydig cells (Glandulocytus testis), are located in the connective tissue strictly between the seminiferous tubules. They have a rounded shape and characteristic oxyphilic cytoplasm.
The main task of Leydig cells is the synthesis of testosterone. This process directly depends on hydroxylation and microsomal oxidation reactions. That is why, at the ultrastructural level, the smooth (agranular) endoplasmic reticulum is heavily developed in glandulocytes.
An interesting feature of hormone transport is that a «cap» of lymphatic sinusoidal capillaries forms around each seminiferous tubule. A significant part of the freshly synthesized testosterone enters not directly into the bloodstream, but into an extensive network of lymphatic sinuses. From there, via efferent lymphatic vessels, the hormone collects into the thoracic duct and only then enters the systemic circulation of the greater circulation.
Mechanisms of testosterone action
Testosterone secreted by Leydig cells operates in two main directions:
- Systemic action: the hormone is carried to distant target organs and simultaneously exerts negative feedback — high levels of testosterone directly inhibit LH production by the pituitary gland.
- Local action: part of the hormone remains inside the testis. Testosterone penetrates the basement membrane of the convoluted seminiferous tubules and enters the Sertoli cells, stimulating the synthesis of specific proteins in them. Next, it enters the lumen of the tubule, where it critically influences the maturation of spermatocytes and spermatids.
Role of Sertoli cells (sustentocytes)
Sertoli cells act as the main intermediaries between hormonal signals and developing germ cells. Their activity is controlled simultaneously by FSH from the pituitary gland and local testosterone.
Sustentocytes possess rich secretory activity:
- ABP (Androgen-Binding Protein): binds testosterone in the tubule lumen, creating a locally high concentration of the hormone around spermatogenic cells necessary for their development.
- Activin and Interleukin-1: serve as growth factors stimulating the division of early cells — spermatogonia.
- Inhibin: a factor that, via a feedback mechanism, inhibits FSH production in the anterior pituitary gland.
In addition, local steroid metabolism occurs in Sertoli cells. Under the action of enzymes, a small fraction of testosterone is converted into the female sex hormone — estradiol. It diffuses back into the interstitium and exerts a paracrine (local) inhibitory effect, preventing Leydig cells from synthesizing too much testosterone.
Morphology of spermatogenesis in a micropreparation
The spermatogenic epithelium functions cyclically, forming the so-called «wave» of spermatogenesis. With standard hematoxylin-eosin staining on a cross-section of a seminiferous tubule, different stages of cell development can be identified depending on their position:
- In the basal part (near the membrane) lie spermatogonia and spermatocytes.
- Closer to the lumen of the tubule are early spermatids with rounded nuclei.
- At the very edge (in the lumen) are late spermatids: they are easily recognized by elongated dark nuclei and actively forming flagella. These cells are already preparing to enter the tubule lumen.
Briefly: answers to topical questions
What structures and contacts form the blood-testis barrier?
The blood-testis barrier is a multilayered structure separating the bloodstream from the spermatogenic epithelium. The components of the barrier include:
- Capillary endothelium — fenestrated endothelium of the testis and its basement membrane.
- Interstitial tissue — narrow connective tissue layers.
- Lymphatic vessel wall — sinusoidal capillaries forming the «cap».
- Proper sheath — the capsule of the seminiferous tubules.
- Basement membrane — the membrane of the spermatogenic epithelium.
- Tight junctions (zonula occludens) — specialized junctions between the lateral processes of neighboring Sertoli cells.
Tight junctions are a key link of the barrier, ensuring its high tightness.
What consecutive stages (phases) does the process of spermatogenesis include?
The process of spermatogenesis is subdivided into four consecutive phases.
- Phase of proliferation — division of the original spermatogenic tissue cells via mitosis with the formation of diploid spermatogonia.
- Phase of growth — interphase I of meiosis, during which DNA replication occurs, cells increase in size, and develop into primary spermatocytes.
- Phase of maturation — cell division by meiosis: after the first division, secondary spermatocytes are formed; after the second, haploid spermatids.
- Phase of formation — the process of cellular differentiation during which mature spermatozoa are formed from spermatids.
From which embryonic source do interstitial Leydig cells develop?
Interstitial Leydig cells develop from mesenchyme. During testicular histogenesis, mesenchyme acts as the primary source for the formation of the organ's interstitial tissue. Endocrinocytes (Leydig cells) and other interstitial cells differentiate precisely from it. At the same time, the remaining elements of the testis develop from other embryonic primordia: the spermatogenic epithelium is formed from gonocytes of the yolk sac, and sustentocytes (Sertoli cells) from the coelomic epithelium.
L-L, F-S: LH acts on Leydig cells, FSH stimulates Sertoli cells.
Class and exam questions
Where does the majority of testosterone go immediately after synthesis?
Unlike the hormones of many other glands, a significant portion of testosterone is secreted not into blood capillaries, but into lymphatic sinuses surrounding the seminiferous tubules. From there, the hormone travels via lymphatic vessels into the thoracic duct and systemic circulation.
How does testosterone reach the developing spermatozoa?
It penetrates through the basement membrane of the tubules into Sertoli cells and then enters the lumen. There, it binds to androgen-binding protein (ABP), which maintains a high concentration of the hormone right around the maturing cells.
Why is the female hormone estradiol produced in the testes?
Sertoli cells convert a small fraction of testosterone into estradiol for local (paracrine) regulation. Estradiol returns to the interstitium and inhibits the excessive activity of Leydig cells.
How does the pituitary gland "know" that it needs to reduce hormone production?
A dual negative feedback mechanism operates. Testosterone from Leydig cells inhibits LH production, while inhibin secreted by Sertoli cells suppresses FSH secretion.
What else to study on this topic
- Cytological features of smooth ER and microsomal oxidation
- Structure and functions of androgen-binding protein (ABP)
- Biological significance of the «wave» of spermatogenesis
- Role of activin and interleukin-1 in spermatogonial division
Master the entire topic in the "Histology" course
This is a summary. The course covers everything tested in classes and exams.
- Complete study guide on «Endocrine regulation of spermatogenesis» and 3,485 more subject pages
- Assignments and quizzes after every topic — just like in a colloquium
- AI tutor answers questions on the topic anytime
- 137 video lessons on the subject
Other topics in the "Male Reproductive System" section
Free video lessons: histologyShort lessons with study notes — no registration required.
Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.