Hormonal Regulation of Testes Flashcards
GnRH is a ___ hormone synthesized by neuroendocrine cells whos cell bodies reside in the ____ and ___ nuclei.
Released into the ____ in the median eminance to go bind gonadotrophs and stimulate synthesis & release of FSH & LH
GnRH is a peptide hormone synthesized by neuroendocrine cells whos cell bodies reside in the arcuate and preoptic nuclei.
Released into the primary capillary plexus in the median eminance to go bind gonadotrophs and stimulate synthesis & release of FSH & LH
Describe testosterone regulation
Hypothalamus GnRH > Ant pituitary LH > Leydig cell testosterone
-
Testosterone neg feedbacks itself:
- inhibits hypothalamic GnRH
- inhibits anterior pituitary’s LH
- Estrogen from sertoli cells inhibits testosterone production from Leydig cells
LH activates ___ cells to secrete ___
FSH activates ___ cells to secrete ___
LH activates Leydig cells to secrete testosterone
FSH activates Sertoli cells to secrete estrogen, ABP, growth factors, and inhibin B to induce & regulate spermatogenesis
Inhibin B from ___ does what?
Inhibin B from Sertoli cells neg feedbacks anterior pituitary to inhibit FSH production
Activin from __ does what?
Activin from anterior pituitary antagonizes inhibin B to increase FSH synthesis
What hormone is responsible for the size of the testis?
FSH
Because it controls sertoli cell proliferation and seminiferous tubule growth
What hormone is most important in the initiation of spermatogenesis during puberty?
FSH because it controls Sertoli cell proliferation, seminiferous tubule growth, production of ABP, and development of blood-testis barrier
___ levels correlate with total sperm count and testicular volume, and can be used as an index of spermatogenseis
Inhibin B
Androgens are produced by the ___, then they diffuse intot he ___ where it’s converted to ___
Produced by leydig cells, diffuses across basement membrane into the seminiferous tubule where Sertoli cells turn it into estrogen
Describe how testosterone circulates
~50% is bound to albumin
~44% is tightly bound to sex hormone-binding globulin (SHBG) - not bioavailable
2-3% are free
When T is transferred to target tissues, what can happen to it?
What happens if it does not get fixed to tissues?
In the tissues, it can remain as T, or converted to DHT or estrogen
T that doesn’t get fixed to tissues is rapidly converted by the liver into inactive products for excretion in gut or urine
Testosterone is the pinrcipal circulating androgen and nearly all is produced by the testis.
Binds to its receptor, ____
androgen receptor
T, DHT, or weak androgens all bind to this receptor that regulates gene expression. PSA tumor markers (PSA is a gene) are really markers for androgen receptor activity
Functions of testosterone
High local levels of T in the testes -> spermatogenesis
Peripheral testosterone in th ebody -> masculine characteristics (either as T, DHT, or estrogen)
How do testosterone levels change from fetal life to childhood to puberty?
- Fetal: hCG from placenta stimulates testes to produce T
- Childhood: no T
- Puberty: Pulsatile GnRH secretion -> FSH & LH -> T
In puberty, plasma levels of FSH & LH increase primarily during ___.
___ and ___ are responsible for normal pubertal growth.
sleep -> GH & T, but this diurnal rhythm of FSH & LH is lost after puberty (~16-18yo)
growth hormone & testosterone are responsible for normal puberty growth
Aging & testosterone
- After age 40, T declines every year with increased SHBG (less bioavailable T)
- Decreased T:E
- Decreased LH pulse frq
- Decreased DHT in reproductive tissues
Hypergonadism - how does it present before or after puberty?
Before puberty - precocious puberty
After puberty - early hair loss
Causes of hypergonadism
- Hypothalamic, adrenal, or Leydig cell tumors
- LH receptor mutations
- Congenital adrenal hyperplasia
- Pinealoma - tumor that destroys pinealocytes so melatonin cant inhibit GnRH release
Melatonin regulation of GnRH
Melatonin inhibits the GNRH pulse generator (functioning since birth) throughout childhood
At puberty, body mass increases -> decreased [melatonin] -> GnRH pulse generator re-activated
Hypogonadism types
-
Primary hypogonadism - testes is messed up
- low T, high LH
- Also called hypergonadotropic
- Damage, cryptorchidism, gonadal dysgenesis, enzyme defects, LH receptor defects, etc
-
Secondary hypogonadism - hypothalamic/pituitary messed up
- low FSH, LH, and T
- Also called hypogonadotropic
- genetic defects; adrenal hypoplasia; mutations of GnRH receptor; etc
To differentiate between primary and secondary hypogonadism, you look at levels of
LH
- Primary* - low T / high LH / normal FSH
- Secondary* - low T, LH, and FSH
How can you differentiate between hypothalamic or pituitary dysfunction in secondary hypogonadism (hypogonadotropic)?
Give low-dose GnRH stimulation/priming, then a high dose GnRH injection
If the hypothalamus is the problem, you see increased LH
If pituitary is the problem, this has no effect on LH
Intratesticular vs excurrent ducts
- Intratesticular:
- straight tubules
- rete testis
- Excurrent:
- efferent ductules
- ductus epididymis
- vas deferens
Straight tubules / tubuli recti
very short terminal section of the seminiferous tubules
Initial segments lined with sertoli cells
Near their termination, they narrow and become lined with simple cuboidal epithelium
How an you dfiferentiate between the rete testis and the veins in the media stinum testis?
Rete testis is has more basophilic, cuboidal lining
Veins have acidophilic, squamous lining
Function of efferent ductules
- transport of sperm toward the epididmis
- reabsorption of most of the fluid secreted in tehs eminiferous tubules
Efferent ductules structure
-
Pseudostratified columnar epithelium lining of tall & short cells –> wavy outline
- Tall cells w cilia
- Short cells w microvilli - reabsorption of fluid from seminiferous tubules
- Basal cells
- Single layer of smooth muscle w/ elastic fibers
Sperm transport is effected by
ciliary action of tall pseudostratified columnar epithelium
contraction of fibromuscular layer
What are the asterisks?
Wavy lumen -> efferent ductules
the asterisks must be sperm
What is this a picture of? Where is the smooth muscle?
Functions of the epididymis
- Sperm transport
- Re-absorption of most of the fluid that is not reabsorbed by the efferent ductules
- Place of sperm maturation (recall this is when they become motile)
- Storage reservoir for matured sperm
Which part of the epididymis has a single layer of circular smooth muscle?
Head (efferent ductule) & body
contracts spontaneously
In which part of the epdidymis do spermatozoa mature?
Mature in the body
They acquire the ability to move, but several inhibitory protein shere prevent actual motility until after ejaculation
Can fertilize if placed in the oviduct
Which part of the epididymis is the principal reservoir for mature spermatozoa?
tail
Which part of the epididymis has 3 layers of smooth muscle?
Tail - inner and outer longitudinal layers in addition to the circular layer
Only contracts after appropriate neural stimulation from ejaculation (not spontaneous)
Compare and onctrast efferent ductules’ appearance vs ductus epididymis
What is the function of stereocilia on the tall principal cells of the ductus epididymis?
Reabsorption of fluid!
Where is this slide from?
Body of the epididymis because there’s only one single layer of smooth muscle
What are we looking at?
Lumen is bigger in the epididymis
Vas deferens function
Ejaculation via strong, peristaltic contractions (along w the epididymis tail) after appropriate neural stimulation
Vas deferens appearance
- Deep longitudinal folds (caused by muscle contraction) in the lumen
- Stereociliated pseudostratified columnar epithelium (columnar and basal cells)
- Lamina propria is thick, loose ct w elastic fibers
- 3 layers of smooth muscle: thick circular layer between thinner inner & thick outer longitudinal layers
- Denser adventitia that blends with fibrous connective tissue of the spermatic cord, containing nerves and some bv
When do you start to see stereocilia?
you start seeing stereocilia at the body of the epididymis
But it’s also in the tail and vas deferens
What is this
vas deferens
What is this?
spermatic cord
What is this?
vas deferens
What is this?
Isthmus of the oviduct
- Mucosa folds
- Unlike the vas deferens, these wont go away when the muscle relaxes
- Inner circular & outer longitudinal layer of smooth muscle
- simple columnar epithelium w ciliated cells and peg cells,
- *Peg cells that protrude is how you can differentiate betewen isthmus and vas deferens*
- Very narrow so it’s the isthmus
What is this?
Ureter
Muscularis is not as dense as the vas deferens
Transitional epithelium
Ejaculatory duct
what does it connect?
structure?
Connects the end of the vas deferens to the urethra through the prostate
- Mucosa like vas deferens, but no muscularis layer
recap on ducts
True or false? Why?
True or false? Why?
False - testosterone and other male hormones will still be produced and secreted into the bloodstream from the testis.
True because the immune system could be exposed to spermatozoa that may leak from the severed vas deferens
Anti-sperm antibodies in the blood would make infertility from vasectomy irreversible
False, only anti-sperm antibodies present on the sperm would hinder fertility; remember the blood testis barrier
True or false: there would be no ejaculate or significant reduction in ejaculate volume from vasectomy
False.
Low sperm count
FSH works on Sertoli cells/supporting cells, which support spermatogenesis
D. Ejaculation results from smooth muscle contractions around the vas deferens and ductus epididymis
B is incorrect
in the first meiotic division, primary spermatocytes would give secondary spermatocytes
Epididymis
Efferent duct
epididymis
vas deferens
