Testis, ductus deferens, and seminal vesicle histology

Testes, or testis when singular, is responsible for the production of sperm, which is called spermatogenesis.The testes also produce sex hormones, mainly testosterone.The male genital ducts carry spermatozoa and liquid from the seminiferous tubules in the testes all the way to the penis.The genital ducts can be split into two groups, the excretory genital ducts and intratesticular ducts.The intratesticular ducts include the straight tubules (or tubuli recti), rete testis, and efferent ductules.And the excretory gential ducts include the epididymis, ductus (or vas) deferens, and urethra.This very low power image is a sagittal section of a testis, which also includes the head of the epididymis located posterior and partially superior to the testis.The epididymis is a single, long convoluted duct where spermatozoa accumulate and continue to mature even further, including the development of motility.Accessory glands, such as the seminal vesicles and prostate gland, secrete seminal fluid that provides lubrication and nutrients for the spermatozoa.The seminal fluid is also slightly alkaline, or basic.This alkalinity helps protect sperm and prolong their life after they’ve been deposited in the acidic environment of the vagina.Surrounding each testis is a thick capsule of connective tissue, called the tunica albuginea.The connective tissue extends inward from the posterior side of the testes and separates the seminiferous tubules into about 250 incomplete pyramid-shaped lobes.Each lobe contains one to four highly-coiled seminiferous tubules.Now, if we zoom in all the way to 40x magnification, we can see the individual seminiferous tubules, which have a germinal epithelium that’s responsible for spermatogenesis.In this one image, we can see the various stages of spermatogenesis.The spermatogonia are the undifferentiated germ cells that are mainly found along the periphery of the germinal epithelium, against the basement membrane.These cells are round with a large round nuclei and a pale cytoplasm.As the cell differentiates, it moves towards the central lumen of the tubule.The stages of differentiation can be identified based on subtle differences in the shape and staining of the nuclei.The next stage or cell type is the primary spermatocyte.These cells can be found at various levels between the basement membrane and the lumen, but they can be identified by their bigger cytoplasm and large nuclei that have thin threads or clumps of chromatin around them.The secondary spermatocytes arise from the primary spermatocytes, but they’re rarely seen in images because of how quickly they divide into two haploid spermatids.The early spermatids can be identified by their smaller size compared to spermatocytes and their very round nuclei.They continue to get smaller as they become late spermatids with small pointed nuclei, which is the last stage seen before finally becoming mature spermatozoa.Throughout the germinal epithelium, sertoli cells are also present, which are large columnar cells with pale, euchromatic nuclei and prominent nucleoliThese cells provide nutrition and mechanical support for the spermatogenic cells.The sertoli cells also secrete two hormones - inhibin and activin - which provide positive and negative feedback to the pituitary for FSH secretion.In this image, portions of the seminiferous tubules can be seen, but there are also Leydig cells, which are typically found between the tubules in the interstitial space.Leydig cells are large, round or polygonal cells with round nuclei and often have an eosinophilic cytoplasm because of the lipid droplets that they typically contain.Also, in this image, we can see the spindle-shaped nuclei of myoid cells surrounding the seminiferous tubules.The contractions of these cells help move the spermatozoa forward within the seminiferous tubules to eventually reach the next set of ducts, called the straight tubules.The spermatozoa will continue to travel through the rete testis and efferent ductules to reach the epididymis.If we take a look at a cross-section of just one duct of the epididymis, we can see that the epithelium consists mostly of pseudostratified columnar cells, called principal cells.These cells also have long microvilli that extend into the lumen, called stereocilia.The epithelium also includes basal cells, which are the round stem cells found along the basement membrane.Surrounding the epithelium is a layer of smooth muscle.This muscular wall gradually increases in thickness towards the tail or distal portion of the epididymis.Spermatozoa can also be seen in this image within the lumen of the duct.The peristaltic contractions of smooth muscle and stereocilia movement both help the spermatozoa move forward within the epididymis.The distal end of the epididymis leads to the ductus or vas deferens, which is a thick-walled muscular tube that connects the epididymis to the prostatic urethra.Similar to the epididymis, the smooth muscle surrounding the lumen produces peristaltic contractions.This lower power image shows just how thick the surrounding smooth muscle is in comparison to its lumen.Strong contractions are needed to expel its contents quickly into the urethra during ejaculation.Surrounding the ductus deferens, we can also see some connective tissue, adipose tissue, arteries, and veins.Together, they comprise the spermatic cord.If we zoom in closer to the smooth muscle at 20x magnification, we can see three distinct layers of smooth muscle.The inner layer and outer layer are arranged longitudinally, which is why they both have muscle fibers that look round in this cross-section.The middle layer is the thickest layer and has muscle fibers that are arranged circularly, or circumferentially, around the ductus deferens.These muscle fibers look long in comparison because they’re arranged along the same plane as the cross-section.Now, let’s take a closer look at the epithelium of the ductus deferens.Similar to the epididymis, the epithelium consists of principal cells, which are pseudostratified columnar cells with stereocilia, and there are also basal cells along the basement membrane.The most noticeable difference seen in the ductus deferens are longitudinal folds that allow the duct to expand during ejaculation.The distal end of the ductus deferens on both sides dilate right before reaching the prostate.This portion is called the ampulla of the ductus deferens and is also where it’s joined by a duct from the seminal vesicles, and together they form the ejaculatory ducts.The ejaculatory ducts from each side then combine and drain into the urethra within the prostate.The seminal vesicles are a pair of highly-coiled exocrine glands that secrete the majority of the seminal fluid and nutrients for the sperm.If we increase the magnification to 14x magnification, we can see that they’re surrounded by two layers of smooth muscle.The seminal vesicles’ mucosa has many convoluted cross bridges, as well as folds that project into the lumen.Though seminal vesicles are not meant to store sperm, spermatozoa are often found within the lumen due to reflux from the ampulla.Zooming all the way to 40x magnification, we can see that the epithelium consists of pseudostratified columnar cells, as well as some regions of simple columnar cells.The lamina propria seen mostly on the right consists of collagen, elastic fibers, and smooth muscle.