Not testable: The testes are named from the Latin "to swear on" (testify), i.e., a man's most precious possession, i.e., what a Roman put his hand on in court instead of the Bible (and lost if he proved to be lying.) Other colorful facts from the ancient world are numerous, as are double-entendre's in the modern ("Einstein", etc.)

The testis produces sperms and testosterone. It develops retroperitoneally, and descends (usually) into the scrotum.

Not testable: You'll be told that the testes are in the scrotum "because" they require a lower-than-core-body temperature for sperm production (body temperature's fine for testosterone production); the real reason probably began with "male display", probably in the late mesozoic, the better performance at low temperature being the result. Junqueira's discussion of thermoregulation in the scrotum ("pampiniform plexus", "cremaster muscle", "sweat on the scrotum") might also have included the countercurrent heat-exchanger (testicular artery and pampiniform plexus) and the famous dartos smooth muscle of the scrotum.

Usually the testicular pole (where everything comes together) is at the far-posterior-and-slightly-superior aspect, but testes can be backwards and/or upside-down. The tunica vaginalis ("jacket-sheath"), which is peritoneum, surrounds the testis and its cord; it has a pareital layer inside the skin of the scrotum, and a visceral layer which is the mesothelium around the tunica albuginea. The tunica albuginea is thick, very tough fibrous tissue, the thickest capsule in human biology, and as pain-and-pressure sensitive as any. There are many nerve endings in it, including a lot of apparent Meissner's corpuscles, and a bit of smooth muscle around the mediastinum which supposedly undergoes rhythmic contractions. The testicular artery and its branches are narrow and coil around considerably prior to entering the testis proper, making the pulse pressure low (compare the carotid siphon; for comfort I guess). Upon entering the testis, the testicular artery breaks up into a meshwork of little arteries under the tunica albuginea, called the tunica vascularis, which you can see if you look hard. The tunica albuginea thickens at the pole to form the mediastinum of the testis, where it then gives rise to the septa which divide the testis into around 250 lobules, tall pyramids each with 1-4 seminiferous tubules.

Each seminiferous tubule is maybe 50 cm long (branching does happen but is probably uncommon), and maybe 200 microns across. The total length for each testis is supposed to be 250 meters, or about 1/7 mile. Each is a thin tube of fibrous tissue ("tunica propria", i.e., "my own jacket") with an inner basement membrane and a distinctive germinal ("seminiferous") epithelium, which accounts for most of the size of the testis. The bottom layer is modified smooth muscle ("myoid cells") to milk the sperms in the correct direction. The pyramid-shaped Sertoli cells ("supporting cells") support the cells of spermatogenic lineage, i.e., that are going to give rise to sperms. Sertoli cells have indistinct borders which are indented by the various sperm precursors; they're the only cells in the tubules with prominent nucleoli. Their cytoplasm contains the usual stuff, including a good deal of smooth endoplasmic reticulum; they provide the blood-testis barrier (a seal composed of tight junctions between the bases of adjacent Sertoli cells, which form at puberty, i.e., they presumably keep bad things away from the developing sperm, and stuff injected into the bloodstream generally ends up inside the Sertoli cells but not in the spermatogenic cells). Under the influence of FSH and testosterone, the Sertoli cells concentrate testosterone in the testis and carry it (on "androgen binding protein") to the cells that will become sperms. They also secrete sperm transport fluid (fills the seminiferous tubules, called "testicular fluid"), which the sperm ride up to the prostate and seminal vesicles, inhibin to provide negative feedback on FSH production in grown men, and produce Muellerian regression factor ("anti-Muellerian hormone") in embryos destined to become male (if this is genetically deficient, you get a curious intersex). Sertoli cells are tough, and almost impossible to kill; an azoospermic-infertile man's seminiferous tubule generally presents a pizza-like cross-section, each slide being a sertoli cell. (There are other several other possible patterns in male infertility; for example, cyclists and guys with varicoceles tend to lose their spermatids into the lumen.)

Junqueira divides spermatogenesis into:

spermatocytogenesis: up to and including spermatocytes

meiosis: spermatocytes become haploid spermatids

spermiogenesis: spermatids get their tails and so forth

The spermatogonium, the stem cell of the prepubertal child, becomes at puberty the type A spermatogonium which, at each division, gives rise to one type A spermatogonium (stays at the bottom, of course) and one type B spermatogonium which will become a bunch of primary spermatocytes. These curious cells almost immediately go through S phase and then into prophase, and stay in prophase for 22 days; you can see their 92 chromosomes forming wiggly-squiggles in the nucleus. (Ignore the old-time cytologists' distinctions of "leptotene, zygotene, pachytene, and diplotene stages" as the wiggly-squiggles get thicker and thicker). They end up producing, by the first meiosis, four diploid cells called secondary spermatocytes. Don't try to pick them out in sections; their nuclei are also wiggly-squiggly but smaller than those of primary spermatocytes (why?) They divide in turn, again by meiosis, but with no S-phase, to produce spermatids, easily recognizable by their location near the lumen and their small size. All the progeny of one spermatogonium are supposedly connected by intercytoplasmic bridges until they become real sperms; this keeps them from sloughing off early.

Spermiogenesis begins with the formation of an acrosomal granules in an acrosomal vacuole, and the migration of the centrioles (first) and mitochondria (soon after) to the opposite side of the cell. The acrosomal vesicle then turns into a cap on one side of the nucleus, and the flagellar axoneme starts to form. The acrosomal cap, of course, contains enzymes to enable to sperm to pierce the egg. One of the centrioles sprouts a flagellum,the mitochondria organize around its base, the nucleus gets very compact, and bits of cytoplasm that are no longer needed fall off as "residual bodies" to be eaten by Sertoli cells or in the epididymis. A mature sperm's head ("acrosome") is 5 microns long, its "middle piece" (where the mitochondria are) is another 5 microns long, and its tail ("principal piece" plus "end piece") is maybe another 50 microns.

From spermatogonium to mature sperm takes about 64 days. The process proceeds through various stages at various places in the tubules, as waves. Men taking gym steroids get testicular atrophy due to inhibition of FSH production by the pituitary gland; don't expect to become a dad while on 'roids, and don't get upset if your testes shrink comically while your 'pecs become magnificent. Average sperm count is 100,000,000 little swimmers per mL of seminal fluid, and seminal fluid is produced at an average of about 2 mL per day. Counts rise with a few days of abstinence (as fluid is resorbed in the prostate and seminal vesicles), and drop spectacularly on the second ejaculation of the evening (i.e., the storage pool in the tail of the epididymis is depleted). A sperm that knows where it's going (i.e., under the influence of the chemical gradients in the female genital tract) proceeds at an incredible 3 mm / minute.

Between the tubules is a loose connective tissue interstitium richly supplied with vessels, lymphatics, and nerves, and with little clusters of Leydig cells ("interstitial cells"). You'll be surrised how few Leydig cells there are; you'll need to search to find the "5 per seminiferous tubule" in a cross-section. These are typical endocrine cells with abundant eosinophilic cytoplasm. They produce testosterone, the rocket fuel that makes male embryos differentiate as male, and turns boys into men and men into animals. (Production of testosterone is stimulated by placental gonadotropin in the unborn child, by LH at puberty and after.) Like other steroid-secreters, they contain abundant smooth endoplasmic reticulum. You might see a Reinke crystalloid in one of them; it looks like a pink bubblegum cigar.

The tubules cross-link with themselves and have no blind pouches, follow a convoluted course in the testis, and straighten out (tubuli recti, simple cuboidal / low-columnar epithelium) just before reaching the pole, where they then join an anastomosing mass of tubules called the rete testis (cuboidal epithelium). The rete drains, in turn, via 10-20 efferent ductules (cuboidal epithelium, many groups with cilia) into the duct of the epididymis, the structure at the back (usually) of each testis and whose name means "next to the twin" (go figure).

Each epididymis is a single coiled tube, its length variously given from 6 feet to 6 meters. The sperms, in their by-now-pasty fluid, spend about twelve days here, during which they develop more and start wiggling their tails. The epithelium is pseudostratified columnar with very long, spaghetti-like branching (sometimes) microvilli ("stereocilia", i.e., fool's cilia). The basement membrane is surrounded by smooth muscle which milks the sperm and testicular fluid along. Epididymis fluid in a grown man is thick and pasty, since much of the testicular fluid is reabsorbed here. From the other end of the epididymis, the tube becomes the vas deferens ("ductus deferens"), an extremely muscular (for peristalsis) tube with a very thin lumen lined by pseudostratified-columnar-with-stereocilia epithelium. Both the vas and the epididymis are easy to find on a guy if he holds still. The vas follows the spermatic cord up-around-and-in. "What's the difference between a man and a woman? A vas(t) deferens (difference)." Also in the spermatic cord: the nerve, the testicular artery, the cremaster muscle (around the cord), and the pampiniform plexus. As it approaches the prostate, the vas briefly dilates and acquires an infolded epithelium, this region being the "ampulla". The mucosa, but not the muscle, passes straight through the prostate as the ejaculatory duct. There is a howler in Junqueira: there is no "mucous" (slimy) layer of vas to continue through the prostate, it's the mucosa.

The seminal vesicles poke up like rabbit ears above the prostate and behind the bladder. Each is a single, coiled tube about 15 cm long. You might see a few sperms here, but they're named because they produce about 70% of the fluid part of semen (fructose, citric acid, sperm-activating proteins, prostaglandins, lots more). The epithelium is pseudostratified and protein-producing (lots of granules); the cells tend to contain lipofuscin and to be polyploid. Around the tubules is a layer of smooth muscle which contracts during emission (i.e., the phase in which semen enters the urethra, just before ejaculation). The fluid is produced at a more-or-less constant rate, but the volume (don't know about the concentration) increases during prolonged sexual stimulation.

The prostate is a radial array of branched tubuloalveolar glands in a dense fibromuscular stroma. It produces the rest of the seminal fluid, which it stores. The sensory nerves of the pelvic region sense the quantity of fluid on board, and high physical pressure here translates into heightened libido. The epithelium has a layer of cuboidal-to-columnar epithelium, and a second layer of myoepithelium, but the main contractile force comes from the smooth muscle in the stroma. Believe the story about "zones" of the prostate if you like; I suspect that "most cancers arise in the periphery of the prostate and in its posterior aspect" because this is the part that a doctor can feel with his gloved finger. Junqueira is as guilty as most other writers in using the term "benign prostatic hypertrophy"; older dudes' big benign prostates are hyperplastic, not hypertrophic, and all hypertrophies and all hyperplasias-proper are benign.

Cowper's bulbourethral glands are little mucus-producers with abundant smooth and skeletal muscle, just distal to the prostate. They produce most of the drop of mucus that acts as lubricant.

The penis is three cylinders of erectile tissue (masses of tough-walled veins with little else), plus their support structures. On each side is a corpus cavernosum; these are together surrounded by a super-tough-but-stretchable fibrous fascia, the other tunica albuginea, which holds them tight and enables them to get very hard. A big artery passes up the middle of each ("the deep artery"). The corpus spongiosum (ignore Junqueira's confusing term "corpus cavernosum of the urethra") contains the urethra and expands distally to form the glans. It's not encased, since if it got as hard as the cavernosa, ejaculation would be impossible (think about it). There's a little bundle of skeletal muscle around the most proximal portion of the urethra, which must relax or ejaculation will take place into the bladder (a side-effect of some drugs), and of course abundant skeletal muscle around the membranous urethra for coordinated contractions during ejaculation. You already know the little gland of Littre, mucus-producers along the urethra. The skin along the shaft acquires extra melanin at puberty, and the tiniest hairs in histology occur here, though only along the proximal portion. There's also a dartos, which makes the penis shrivel even more in the cold for some reason. Beneath the skin, and surrounding the three corpora, is Buck's fascia, which is very tough, flexible, and full of elastic, and there is a thin layer of ultra-loose connective tissue to allow the skin to slip way-up-and-down along the shaft. The squamous epithelium that covers the glans is keratinized if, and only if, circumcision has been performed. The prepuce is a fold of skin with considerable smooth muscle, which makes it wrinkly, and sebaceous glands on its undersurface which produce smegma.

Not testable: "Tyson's glands", on the corona, said to be a modified sebaceous gland which produces most smegma, do not exist. "Should I have my baby boy circumcised?" The answer isn't clear-cut, but as usual, reason takes the back seat to politics in the ongoing "discussion".

Not testable, but you'd ask if I didn't... Even in the 1990's, it is unusual for a man to try to make political capital by pretending to be "offended" by reasonable talk about male bodyparts or gender behavior. So I hope nobody's "upset". Our species is unusual in that our grownups are ready-and-willing to have intercourse most anytime, and this humans-are-special fact alone suggests to me that sexual behaviors (or thoughts or whatever) that aren't directly intended for reproduction can't all really be "against the will of the Creator" or whatever. 1960's graffiti: "All you need is love, all you get is sex." As a sixties survivor, I'd say that's the best single epitaph for those interesting times. But I think any impartial observer would decide that sexuality in its broadest sense (the entire physical-touchy-feely-with-each-other side of ourselves) helps promote affection among people (there's too little of that anyway), and that the key is "loving responsibly". Regardless of what decisions you make, somebody's going to call you bad names because of it. You don't want or need to know about the four worthless structures in the scrotum (i.e., the appendix tesits, eppendix epididymis, vas aberrans of Haller, or paradidymis of Giraldes). The gorilla's penis is only an inch long, the chimp's not much more, and the far larger human penis is, again, almost certainly "male display", with selective pressure for larger size balanced by the functional problems of the largest specimens. There's no question that in some local ecosystems, the males of some species are being un-masculinized from pollutants, but the evidence that this is happening to us human males, despite the media hoopla, is utterly unimpressive. Just for starters, despite claims (see below) that today's pollution-damaged young man produces only half as many sperms as his great-grandfather, today's "normal young man's testis" at autopsy looks no different from the classic descriptions. And there's no reason to believe the percentage of infertile men (which is easy to determine) is increasing, or that testicular size is decreasing. Reinke crystalloids exist only in humans and a cute furry creature called the "wild bush rat"; nobody knows what Reinke crystalloids are made of, and on ultrastructure, they're honeycomb-like hexagonal crystals. During the few moments proceeding emission, sperms stored in the caudal epididymis are pumped along the vas to the ejaculatory ducts, but this contributes only a small volume. A surprising number of grown men, who should know better, think sperms and even seminal fluid move en-masse up-and-out from storage in the testis during sex.

11762 PROSTATE, NORMAL

11763 PROSTATE, NORMAL

11871 BLADDER, PROSTATE AND PENIS, MODEL

15000 TESTIS (TUNICA ALBUGINEA), NORMAL

15001 TESTIS, NORMAL

15002 SEMINIFEROUS TUBULE, NORMAL

15003 SEMINIFEROUS TUBULE, NORMAL

15004 SEMINIFEROUS TUBULE, NORMAL

15005 SEMINIFEROUS TUBULE, NORMAL

15006 SEMINIFEROUS TUBULE, NORMAL

15011 RETE TESTIS, NORMAL

15012 RETE TESTIS, NORMAL

15013 RETE TESTIS, NORMAL

15015 EPIDIDYMIS, NORMAL

15016 EPIDIDYMIS WITH SPERMATOZOA, NORMAL

15017 EPIDIDYMIS WITH SPERMATOZOA, NORMAL

15018 EPIDIDYMIS WITH STEREOCILIA, NORMAL

15019 EPIDIDYMIS WITH STEREOCILIA, NORMAL

15020 DUCTUS DEFERENS, NORMAL

15021 DUCTUS DEFERENS, NORMAL

15022 DUCTUS DEFERENS, NORMAL

15023 DUCTUS DEFERENS, NORMAL

15024 SEMINAL VESICLE, NORMAL

15025 SEMINAL VESICLE, NORMAL

15026 SEMINAL VESICLE (SECRETORY EPITHELIUM)

15027 PROSTATE WITH CONCRETION, NORMAL

15028 PROSTATE WITH CONCRETION, NORMAL

15029 PROSTATE EPITHELIUM, NORMAL

15030 PROSTATE EPITHELIUM, NORMAL

15031 PROSTATE EPITHELIUM AND CONCRETIONS, NOR

15125 PROSTATE, NORMAL

15127 PROSTATE, NORMAL

15128 PROSTATE, NORMAL

15129 PROSTATE, NORMAL

15304 PROSTATE, NORMAL

15330 SEMINAL VESICLE, NORMAL, NORMAL

15331 SEMINAL VESICLE, NORMAL, NORMAL

17008 PROSTATE, NORMAL

20213 PROSTATE, NORMAL

20653 RETE TESTIS, NORMAL

20654 RETE TESTIS, NORMAL

20655 TESTIS, NORMAL

20656 SERTOLI CELL NUCLEUS, TESTIS, NORMAL

20657 SPERMATOGONIA, TESTIS, NORMAL

20658 TESTIS, NORMAL

20659 EPIDIDYMIS, NORMAL

20660 DUCTUS DEFERENS, NORMAL

20661 SPERMATIC CORD, NORMAL

20686 SEMINAL VESICLE

20688 SEMINAL VESICLE

20692 RETE TESTIS

20710 RETE TESTIS

20756 RETE TESTIS

20757 RETE TESTIS

20758 TESTIS

20759 TESTIS

20760 EPIDIDYMIS

20761 EPIDIDYMIS

20762 EPIDIDYMIS

20763 EPIDIDYMIS

20764 DUCTUS DEFERENS, NORMAL VAS DEFERENS

20765 DUCTUS DEFERENS, NORMAL VAS DEFERENS

20766 DUCTUS DEFERENS, NORMAL VAS DEFERENS

20786 DUCTUS DEFERENS, NORMAL, VAS DEFERENS

20787 DUCTUS DEFERENS, NORMAL

20939 PROSTATE

20940 SEMINAL VESICLE

20943 SPERMATOGONIUM, TESTES

20944 RETE TESTIS

20947 SPERMATOCYTE, PRIMARY, TESTIS

20949 EPIDIDYMIS

20950 DUCTUS DEFERENS, VAS DEFERENS

20951 SPERMATIC CORD

23971 PROSTATE, FETAL

23976 SEMINAL VESICLE, NORMAL

24693 PROSTATE, NORMAL

25123 TESTIS, NORMAL

25176 TESTIS, NORMAL

25225 PROSTATE, NORMAL

25226 PROSTATE, NORMAL

25227 PROSTATE, NORMAL

25236 EPIDIDYMIS, NORMAL

25240 SEMINAL VESICLE, NORMAL

25289 TESTIS, NORMAL

26696 SPERMATIC CORD

26723 SPERMATIC CORD

26735 SPERMATIC CORD

44447 TESTES, SEMINIFEROUS TUBULE

44448 TESTES, SEMINIFEROUS TUBULE

44449 TESTES, SEMINIFEROUS TUBULE

45131 SEMINAL VESICLE

45133 SEMINAL VESICLE

45135 SEMINAL VESICLE

45137 SEMINAL VESICLE

45139 SEMINAL VESICLE

45141 SEMINAL VESICLE

48674 TESTES, SEMINIFEROUS TUBULE

48675 TESTES, SEMINIFEROUS TUBULE

48676 TESTES, SEMINIFEROUS TUBULE

48677 TESTES, SEMINIFEROUS TUBULE

48678 TESTES, SEMINIFEROUS TUBULE

48679 TESTES, SEMINIFEROUS TUBULE

48692 EPIDIDYMIS

48693 EPIDIDYMIS

48694 EPIDIDYMIS

48695 EPIDIDYMIS

50492 SEMINIFEROUS TUBULES

50493 SEMINIFEROUS TUBULES

50494 SEMINIFEROUS TUBULES

50495 SEMINIFEROUS TUBULES

50496 SEMINIFEROUS TUBULES

50497 SEMINIFEROUS TUBULES

50498 SEMINIFEROUS TUBULES, MITOSIS

50499 SEMINIFEROUS TUBULES

50500 SEMINIFEROUS TUBULES

50501 SEMINIFEROUS TUBULES, CHROMOSOMES, MITOSES

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