REPRODUCTIVE SYSTEM HISTOLOGY
The male and female systems are anatomically and developmentally homologous: they have similar functions and develop from similar embryological tissues. Depending on the genetic makeup of the embryo (XY in a male, XX in a female), development proceeds along two different pathways. In the male, the embryonic gonads develop into testes. Cells associated with the testes secrete testosterone and a substance called anti-Mullerian factor, which direct the development of internal and external genitalia along the male model. In the female, the embryonic gonads develop into ovaries, testosterone and anti-Mullerian factor are not secreted, and the internal and external genitalia develop along the female model.
In the male, beginning at puberty, mitotic division of stem cells (spermatogonia) in testicular structures called seminiferous tubules produces cells called spermatocytes, which undergo meiotic cell division and differentiation to produce small haploid motile cells called spermatozoa. Spermatozoa are stored and undergo development in the epididymis, an organ that lies adjacent to the testes. Male gametes or sperm are produced continuously in large numbers. Production of the male androgen, testosterone, is accomplished by interstitial cells, which are located in the spaces between seminiferous tubules.
All of the gametes that a female will possess are present within the ovary at birth, contained in structures called follicles. The follicle, in addition to supporting gamete development, also produces hormones that direct follicle and uterine development. Gametogenesis begins before birth and is suspended until puberty, when cyclical gametogenesis resumes. During each ovarian cycle, several follicles are stimulated and undergo a process of growth, development and maturation. Usually only a single follicle completes development, resulting in the release of a single oocyte per follicle. The remnants of the follicle are transformed into the corpus luteum, which secretes hormones necessary for the maintenance of the uterus. As a result, female gametes are larger and non-motile and are produced discontinuously in much smaller numbers.
Slide 1: Testis, scanning power
The first slide shows a low-magnification view of a section through a testicular lobule. The letters (A-E) indicate sections through five seminiferous tubules. Carefully observe the shapes and orientation of the sections
This image demonstrates cross sections of the coiled seminiferous tubules. Parts of the tubules like E or B are cut transversely, while areas like A, C, and D include regions that are cut more longitudinally. As you will notice, the arrangement of the tubules is not very regular. The long, coiled tubules provide a large surface area for the production of large quantities of sperm.
Slide 2: Testis, low power
The second slide shows a higher-magnification view of the same lobule. The arrows (A and B) indicate two different populations of cells.
In this high-power view of the seminiferous tubules, the interstitial cells (labeled A) become apparent as you can see them located between the tubules. The interstitial cells, when stimulated by LH, release Androgens like Testosterone.
Slide 3: Testis, high power
The third slide shows a high-magnification view of a single seminiferous tubule.
This is a cross section of seminiferous tubule. Notice the layered, or stratified, epithelium. There are two types of cells inside the tubule. The cell labeled A spans the entire length of the cell layers. This is a Sustentacular cell(or Nurse cell). Sustentacular cells(or Nurse cells) provide nutritional support for the cells that produce sperm as well as the stimulation for those cells to divide. The rest of the labeled cells are the cells directly responsible for becoming sperm. The cell at D is the stem cell responsible for producing new sperm. This stem cell is called the spermatogonium; it is diploid and divides normally by mitosis. Cells at C and B are spermatocytes that are undergoing meiosis. These cells are haploid and the closer to the lumen they are, the more mature they are. Not pictured in this slide are spermatids. The immature sperm that are done with meiosis.
Slide 4: Epididymis, high power
Slide 4 is a high-magnification section through the epididymis, a highly coiled tube that wraps around the dorsal surface of the testis.
The epididymis is where the sperm undergoes maturation. During their storage, the sperm develop the capability for locomotion. The lining of the tubules in the epididymis are pseudostratified, so there is only a single layer of cells. During ejaculation, movement of cilia that line the epididymis and smooth muscle contractions sweep the sperm out of the epididymis and into the ductus deferens.