Male Reproductive System
Spermatogenesis and Spermiogenesis
- Spermatogenesis: division of spermatogonia to spermatid
- Spermiogenesis: differentiation of spermatid to sperm (spermatozoon)
-no cell division in this process, this process is transformational, not proliferative
- Steps are temperature sensitive! Optimal at 3 degrees below core temperature.
-testicles are outside main pelvic cavity (must be regulated, no constant temperature)
-Muscular Regulation: change distance of testicles from body (closer vs. further)
-cremaster muscle elevates (contracts = elevates, detracts = go down)
-dartos muscle wrinkles up
-Vascular Regulation: network, pampiniform venous plexus (cools arterial blood)
-blood vessels, veins returning to the body (colder temperature) spread out and
wrap themselves around arteries entering the network, which cools the blood by
absorbing heat out of arterial blood (warms up veins, cools down arteries) to
- It begins with a stem cell (spermatogonium). It’s not alone in its efforts, depends on other
help, which regulates processes.
- Sertoli Cells: direct regulators of the process
-secrete growth factors that stimulate proliferation and differentiation (in response to
testosterone and FSH)
-release androgen-binding protein (ABP) in response to FSH. Increases testosterone
-tight junctions form blood-testis barrier
-secrete inhibit (negative feedback)
- Gonadotropins: two primary ones in gametogenesis
-FSH: follicle-stimulating hormone
-LH: luteinizing hormone
-released from the anterior pituitary gland
-stimulates release by GnRH (gonadotropin releasing hormone)
- Luteinizing Hormone:
-stimulate Leydig/interstitial cells to secrete testosterone
*note the separation of androgen production (Leydig cells) and sperm development
(sertoli cells/seminiferous tubules)
- Follicle-Stimulating Hormone:
-exerts an indirect effect on spermatogenesis
-stimulates sertoli cells to express androgen-binding protein (ABP) which increases local
-stimulates settle cells to secrete inhibit (negative feedback)
1) Mitosis: Spermatogonium (2n)
-daughter cell 1: renewed spermatogonium (stays back in blood-testis barrier)
-daughter cell 2: primary spermatocyte (2n) —> undergoes other mitosis divisions
2) Meiosis I: secondary spermatocytes (n), haploid cells (2 sets of chromosomes are identical)
3) Meiosis II: spermatids (n), true haploid cell (one copy of each chromosome) Spermiogenesis
-from spermatid to spermatozoa
-complex structural reorganization and ﬂagella development
-occurs mostly in adluminal compartment of Sertoli cells
-motility and partial capacity to fertilize occurs in epididymis
Processes involved in sperm production:
-spermatogenesis and spermiogenesis
-sertoli calls highly regulate these processes
-testosterone comes from leydig cells (in response to LH)
1) Sperm travels for 20 days towards the epididymis, where it gains motility and capacity to
fertilize an egg.
2) Travels into the vas deferens where seminal vesicles add ~60% semen volume (alkaline,
fructose, prostaglandins, etc).
3) Sperm and semen travel through prostate gland, which adds activating enzymes that
comprise 13 of semen volume.
4) Travels into spongy urethra where bulbotrethral gland has secreted a mucous that lubricates
the way and neutralizes the semen.
Which of the following is not a function of Sertoli cells?
a) Form the blood-testis barrier
b) Secretes testosterone in response to LH (Leydig cells)
c) Secretes factors to stimulate spermatogenesis
d) Secretes inhibin
e) Nourish developing spermatozoa
Which of the following is/are false?
a) Leydig cells secrete testosterone
b) Inhibit exerts negative feedback on LH (FSH)
c) A matured sperm is called a spermatozoa
d) The process of a sperm undergoing structural rearrangement is spermatogenesis
e) b and d
Which of the following statements about gonadotropins is false?
a) are secreted by the pituitary gland
b) include LH and FSH
c) are hormones with important functions in both sexes
d) Are sex hormones secreted by the gonads
Spermatids: (ﬁnal step of spermatogenesis)
a) are haploid
b) are diploid
c) developed a ﬂagella
d) are in the basal compartment of sertoli cells (in luminal compartment)
e) a and c
f) a and d
seminal vesicles, prostate, ampulla** diagram of cross section of penis
-spongiosum Oogenesis: ovary is the site of action
- Stem cells have all formed into primordial follicles (primary oocytes) by birth. They are frozen
in prophase of meiosis I.
Unlike males, females have all the oocytes that they will ever have by shortly after birth.
When they run out, they lose ability to ovulate oocytes (menopause).
- The ﬁrst meiotic division only occurs in ovulated oocytes. Therefore only about 400 of the 3
million oocytes present at birth complete this division. The rest degenerate (atresia).
- Like spermatogenesis, oocyte development occurs in a complex niche (the follicle).
- Primordial follicle: primary oocyte surrounded by a single layer of granulosa cells. (start)
-stage at birth (stalled)
- Primary Follicle
-occurs without hormonal input
-enlargement of oocyte
-thickening of granulosa cell layer
-formation of theca cell layer
-formation of zona