seminiferous tubules and male reproductive physiology Flashcards
what are the important cells of the seminiferous tubules?
spermatogonia (germ cells), sertoli cells (non-germ cells), and leydig cells (endocrine cells)
what are spermatogonia? function and location
maintain the germ pool and produce primary spermatocytes. they line the seminiferous tubules
sertoli cell functions
support sperm synthesis
secrete inhibin: inhibits FSH
secrete androgen binding hormone to maintain local levels of testosterone
tight junctions btw adjacent sertoli cells form the blood testes barrier. the blood testes barrier is important for isolating the sperm from immune attack.
support and nourish developing spermatozoa; regulate spermatogenesis
produce MIF (mullerian inhibitory factor)
convert testosterone and androstenedione to estrogen via aromatase
sertoli cells: location, temperature effects; conditions that change temperature
sertoli cells are temperature sensitive. they decrease sperm production and decrease inhibit (which inhibits FSH) when temperatures are high. high temperatures are seen in cryptorchidism and varicoceles.
leydig cells: function and location, temperature effects, regulation
secrete testosterone in the presence of LH. testosterone production is unaffected by temperature. found in the interstitium of the seminiferous tubules.
leydig cells also contain aromatase and can therefore convert testosterone to estrogen
what is the progression of cells in sperm development? location?
spermatogonia are on the outer most part of the seminiferous tubules and are the germ cells. they are 46XY.
then, there is a blood-testes barrier formed by the sertoli cell tight junctions
primary spermatocyte is also diploid (46 chromosomes), but has replicated the DNA
it divides to form the secondary spermatocytes. these are haploid (23 chromosomes), but each of the chromosomes has 2 sister chromatids.
these divided to form the spermatids. spermatids mature to become mature spermatozoons
How long does it take for full sperm development to occur? where does it occur? what is the required for the maturation of the spermatids?
takes 2 months for the production of a new, mature sperm.
occurs in the seminiferous tubules
spermatids become mature spermatozoons when they loose their cytoplasmic contents and gain an acrosomal cap.
what are the androngens? Where are they produced? rate them in terms of potency
testosterone and DHT (dihydrotestosterone) are produced in the testes. androstenedione is made in the adrenal glands
in terms of potency, DHT > testosterone > androstenedione.
what does testosterone do in the body?
- differentiation of the vas deferens, epididymus, and seminal vesicles, ejaculatory duct (male internal genitalia
- growth spurt: penis, seminal vesicles, sperm, muscles, and RBCs
- deepening of voice
- closing the epiphyseal plates at the end of long bones (via conversion to estrogen)
- libido
What are the functions of DHT?
early: differentiation of the penis, scrotum, and prostate
late: prostate growth, balding, and sebaceous gland activity
how are the androgens and estrogens related to each other, biochemically? what enzymes are involved? drug tie-ins?
testosterone is converted to DHT by 5-alpha reductase (inhibited by finasteride)
in men, androgens are converted to estrogen by P-450 aromatase
exogenous testosterone inhibits the hypothalamic pituitary gonadal axis and causes decreased intratesticular testosterone, decreased testicular size, and azoospermia
tanner stages
I-V
I: prepubertal
II: pubic hair appears (pubarche) and breast buds form (thelarche)
III: pubic hair darkens and becomes curly. penis gets longer. breasts enlarge. peak height velocity.
IV: penis gets wider. scrotal skin darkens. glans develops. areolae are raised
V: adult: areolae no longer raised.
