A&P Ch. 27B (Finished)

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The male reproductive system.
updated 8 days ago by KC1999
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  • A haploid, specialized sex cell


  • Testes are located in this skin-covered, highly pigmented, muscular sack
  • Extends from body behind penis

Why is the scrotum behind the penis?

  • Important in sperm production, which occurs within testes → proceeds more efficiently when testes are kept 2-4°C below core body temperature.

What makes up the subcutaneous muscle layer of the scrotum?

  • Dartos muscle
  • Continues internally to make up scrotal septum

Scrotal septum:

  • Wall that divides scrotum into 2 compartments, each housing 1 testis.

What extends from the internal oblique muscle of the abdominal wall?

  • 2 cremaster muscles, which cover each testis like muscular net.
  • By contracting simultaneously → dartos & cremaster muscles can elevate testes in cold weather (or H2O) → moving testes closer to body & ↓ surface area of scrotum to retain heat.


  • Externally, scrotum has raised medial thickening on surface


(singular: testis)

  • Male gonads- produces sperm & androgens- like testosterone → active throughout reproductive lifespan of male
  • Paired ovals, each approximately 4-5cm in length & are housed within scrotum.
  • Surrounded by 2 distinct layers of protective CT → outer tunica vaginalis & tunica albuginea

Outer tunica vaginalis of testes:

  • Serous membrane that has both parietal & thin visceral layer

Inner tunica albuginea of testes:

  • Tough, white, dense- CT layer covering testis itself
  • Covers outside of testis, also invaginates to form septa that divide testis into 300-400 structures (lobules).
  • Within lobules, spermb develop in seminiferous tubules.

What is the “descent of the testis"?

  • During seventh month of developmental period of male fetus, each testis moves through abdominal musculature to descend into scrotal cavity.


  • When one or both of testes fail to descend into scrotum prior to birth

Seminiferous tubules

  • Forms bulk of each testis.
  • Composed of developing sperm cells surrounding lumen (hollow center of tubule), where formed sperm are released from lumens

Once sperm is released from the seminiferous tubules

  • Sperm move into straight tubules (tubuli recti) → fine meshwork of tubules (rete testes) → Sperm leave rete testes & testis itself, through 15-20 efferent ductules that cross tunica albuginea.

How many types of cells are in the seminiferous tubules?

  • 6

Sertoli cells:

(sustentacular cell or sustentocyte due to function)

  • Type of supporting cell, typically found in epithelial tissue.
  • Sertoli cells secrete signaling molecules that promote sperm production & control whether germ cells live or die.

How is the blood-testes barrier created?

  • Sertoli cells physically extend around germ cells from peripheral basement mb of seminiferous tubules to lumen.
  • Tight junctions between these sustentacular cells create this barrier

Blood-testis barrier:

  • Keeps bloodborne substances from reaching germ cells & keeps surface antigens on developing germ cells from escaping into bloodstream & prompting autoimmune response


(singular = spermatogonium)

  • Stem cells of testis, which means they can differentiate into many different cell types throughout adulthood
  • Line basement mb inside tubule

What do spermatogonia divide into?

  • Primary & secondary spermatocytes → spermatids, which finally produce formed sperm


  • Process that begins with spermatogonia & concludes with production of sperm

One production cycle, from spermatogonia to formed sperm takes how many days?

  • ~64 days

When does a new spermatogenesis cycle start?

  • Every 16 days, although timing is not synchronous across seminiferous tubules

How many cells result from spermatogonia mitosis?

  • 2 identical diploid cells result
  • 1 of cells remain a spermatogonium
  • Other becomes primary spermatocyte, next stage in the process of spermatogenesis.

What is the result of meiosis I in spermatogenesis?

  • Each of 23 pairs of chromosomes separates.
  • Results in 2 haploid secondary spermatocytes

What's the result of meiosis II in spermatogenesis?

  • Results in total of 4 haploid spermatids.


  • Process that transforms early spermatids → ↓ cytoplasm & beginning formation of parts of true sperm.
  • The 5th stage of germ cell formation- spermatozoa, or formed sperm- is end result → which occurs in portion of tubule nearest to lumen

Once sperm is released into the lumen, where does it go from there?

  • Moved along series of ducts in testis toward epididymis for next step of sperm maturation

What's the volume of a sperm cell compared to a female gamete?

  • 85,000x less!

How many sperm cells are produced each day?

  • 100-300 million

What composes the 5 μm long head of a sperm cell?

  • Extremely compact haploid nucleus with very little cytoplasm
  • Acrosome covers most of head of sperm cell as “cap” thats filled with lysosomal enzymes important for preparing sperm to participate in fertilization

What composes the mid-piece of a sperm cell?

  • Tightly packed mitochondria fill the mid-piece of sperm
  • ATP produced by these mitochondria will power flagellum, which extends from neck & mid-piece through tail of sperm, enabling it to move entire sperm cell.

What is the central strand of the flagellum (axial filament) formed from?

  • 1 centriole inside maturing sperm cell during final stages of spermatogenesis.


(plural: epididymides)

  • Coiled tube attached to testis where newly formed sperm continue to mature
  • Tightly coiled state, would be ~6m (20ft) long if straightened.

Spermatic cord:

  • Pair of tubular structures that support testes in scrotum.
  • Each cord is sheathed in CT & contains a network of arteries, veins, nerves & 1st section of ductus deferens, through which sperm pass in process of ejaculation.

Inguinal canal:

  • From each epididymis → Each ductus deferens extends superiorly into abdominal cavity through this

Where does the ductus deferens end?

  • Ends posterior to bladder where it dilates in ampulla (meaning “flask”)

What percent of semen is actually sperm?

  • Only 5%of final volume

How many glands is semen produced by?

  • 3
  • Seminal vesicles
  • Prostate
  • Bulbourethral glands

As sperm pass through the ampulla of the ductus deferens at ejaculation, they mix with fluid that's associated with what?

  • Seminal vesicles

Seminal vesicles:

  • Paired glands that contribute ~60% of semen volume.
  • This fluid contains ↑ amounts of fructose → used by sperm mitochondria to generate ATP to allow movement through female reproductive tract

Ejaculatory duct:

  • *After being mixed with seminal vesicle fluid*
  • Short structure formed from ampulla of ductus deferens & duct of seminal vesicle.
  • The paired ejaculatory ducts transport seminal fluid into prostate gland

Where is the prostate gland located?

  • Sits anterior to rectum, at base of bladder surrounding prostatic urethra (portion of urethra that runs within prostate)

How big is the prostate gland?

  • ~ size of walnut, prostate is formed of both muscular & glandular tissues

What does the prostate gland secrete and is its main function?

  • An alkaline, milky fluid → passing seminal fluid, now semen.
  • Critical to first coagulate → then decoagulate semen following ejaculation

Why does semen temporarily thicken?

  • Helps retain it within female reproductive tract, providing time for sperm to utilize fructose provided by seminal vesicle secretions.
  • When the semen regains its fluid state, sperm can then pass farther into female reproductive tract.

At ~25, what does the prostate do?

  • Gradually begins to enlarge.
  • This enlargement does not usually cause problems

What are a couple conditions that can arise with the enlargement of the prostate and what are the symptoms?

  • Abnormal growth of prostate, or benign prostatic hyperplasia (BPH)
  • Causes constriction of urethra as it passes through middle of prostate gland, leading to number of lower urinary tract symptoms like frequent & intense urges to urinate, weak stream & sensation that bladder has not emptied completely

By ~60, what percentage of men have some degree of BPH?

  • ~40%

By ~80, how many men have BPH?

  • ~80%

Bulbourethral glands:

(Cowper’s glands)

  • Makes final addition to semen → releases thick, salty fluid that lubricates end of urethra & vagina → Helps to clean urine residues from penile urethra
  • Released after male becomes sexually aroused & shortly before release of semen (pre-ejaculation)

Can bulbourethral fluid (pre-ejaculation) cause pregnancy?

  • Yes, it can pick up sperm already present in urethra


  • Organ of copulation (sexual intercourse)
  • Flaccid for non-sexual actions, like urination
  • Turgid & rod-like with sexual arousal

What surrounds the urethra of the penis?

  • Shaft → composed of 3 column-like chambers of erectile tissue that span the length of shaft.

Corpus cavernosum:

(Plural: Corpora cavernosa)

  • The 2 larger lateral chambers of shaft
  • Together, these make up bulk of penis

Corpus spongiosum:

  • Smaller chamber that surrounds spongy, penile, urethra
  • Can be felt as raised ridge on erect penis

Glans penis:

  • End of penis
  • ↑ concentration of nerve endings → ↑ sensitive skin → influences likelihood of ejaculation



  • Skin from shaft extends down over glans → forms collar → forming this
  • Dense concentration of nerve endings → lubricates & protects sensitive skin of glans penis.


  • Often performed for religious or social reasons → removes prepuce, typically within days of birth.

During sexual arousal, where is nitric oxide (NO) released from?

  • Nerve endings near blood vessels within corpora cavernosa & spongiosum.

What is the 1st step to an erection?

  • ↑ arterial blood flowing into penis than leaving in veins → vasocongestion or engorgement of corpora cavernosa & spongiosum

What is the 2nd step to an erection?

  • NO (nitric oxide) released → activates signaling pathway → results in relaxation of smooth muscles that surround penile arteries → dilation .

Increased vasodilation of penile arteries result in what?

(This would be considered the 3rd step)

  • ↑ Dilation → ↑ amount of blood that can enter penis → induces endothelial cells in penile arterial walls to also secrete NO → perpetuating vasodilation.

Filling of the erectile chambers rapidly results in what?

(This would be the 4th step)

  • Compression of thin-walled penile venules, ↓ venous drainage of penis → ↑ pressure of said chambers →
  • An erection is ↑ blood flow to penis & ↓ blood return from penis is erection.

How is vasodilation of the penis reversed?

  • Enzyme {phosphodiesterase (PDE)} → degrades cGMP → key component of NO signaling pathway → inhibition of PDE results in vasodilation & vice versa
  • PDE Type-5 is type of PDE found in tissues of the penis → several different forms of this enzyme


  • Androgen & steroid hormone produced by Leydig cells

How many milligrams of testosterone do leydig cells produce a day?

  • ~6-7 mg

Testicular steroidogenesis results in what?

  • Testosterone concentrations that are 100x higher in testes than in circulation
  • Normal concentrations → promotes spermatogenesis
  • ↓ concentrations → can lead to infertility.

When testosterone is secreted into systemic circulation, what are its effects?

  • Plays important role in muscle development
  • Bone growth
  • Development of secondary sex characteristics
  • Maintaining libido

Do biological females produce any testosterone?

  • Yes, ovaries secrete small amounts but it's mostly converted to estradiol
  • A small amount of testosterone is also produced by adrenal glands regardless of gender

Where does the "internal" regulation of testosterone begin?

  • Begins with pulsatile release of gonadotropin-releasing hormone (GnRH) from hypothalamus → stimulating endocrine release of hormones from pituitary gland.

Where does the "external" regulation of Leydig cell production of testosterone begin?

  • Outside of testes.
  • The hypothalamus & pituitary gland in brain integrate external AND internal signals to control testosterone synthesis & secretion

Binding of GnRH to its receptors on the anterior pituitary gland stimulates release of which 2 gonadotropins?

  • Luteinizing hormone (LH) & follicle-stimulating hormone (FSH)
  • Both critical for reproductive function regardless of gender.

In males, what does follicle stimulating hormone (FSH) bind to most predominately?

  • Sertoli cells within the seminiferous tubules → promoting spermatogenesis.

What hormones does follicle stimulating hormone (FSH) stimulate the Sertoli cells to produce?

  • Inhibins → inhibits FSH release from pituitary → ↓ testosterone secretion.
  • These polypeptide hormones correlate directly with Sertoli cell function & sperm number

What can inhibin B be used for?

  • Marker of spermatogenic activity

What does luteinizing hormone bind to and do?

  • Binds to receptors on Leydig cells in testes
  • Upregulates production of testosterone

What controls the synthesis and secretion of both FSH & LH?

  • A negative feedback loop

What is the 1st step of the negative feedback loop?

  • ↓ blood concentrations of testosterone → stimulate hypothalamic release of GnRH → GnRH stimulates anterior pituitary to secrete LH into bloodstream.

What is the 2nd step of the negative feedback loop?

  • In testis LH → LH receptors on Leydig cells → stimulates release of testosterone → Blood testosterone levels reach critical threshold

When testosterone itself binds to the androgen receptors on both the hypothalamus and the anterior pituitary, what happens?

(Would be 3rd step of the negative feedback loop)

  • Inhibits synthesis & secretion of GnRH & LH

Once the synthesis & secretion of GnRH & LH have been inhibited, what happens from there?

( Would be 4th step of the negative feedback loop)

  • Blood concentrations of testosterone once again ↓ → testosterone no longer interacts with receptors to same degree

Once blood concentrations of testosterone fall again, what happens?

(Would be 5th step of negative feedback loop)

  • GnRH & LH are once again secreted → stimulating ↑ testosterone production.
  • This same process occurs with FSH & inhibin to control spermatogenesis.