Sexual Development and Reproductive Hormones Flashcards
When is genetic (chromosomal) sex determined?
At fertilization
Gonadal sex is determined by what genes?
Testis determining (SRY and SOX9)
Ovary determining (RSPO1 and WNT)
Hormones involved in determination of phenotypic sex
Anti-Mullerian
Testosterone
Dihydrotestosterone
What happens in the presence of Testis Determining Factor (TDF) SRY?
Medullary cords differentiate into Sertoli cells, cortical sex cords degenerate
Sex cords differentiate into seminiferous tubules and give rise to rete testis
Pre-Sertoli cells produce Anti-Mullerian hormone
What happens in the absence of SRY?
cortical sex cords develop into follicles, medullary sex cords degenerate. Makes a female.
What occurs in bovines when fusion of placental circulation causes Anti Mullerian Hormone to transfer from a male to a female co-twin?
Free Martinism. Vestigial development of vagina, cervix, uterus and uterine tubes. Female can’t breed. Almost normal vulva and vestibulum.
What disorder is caused by a disagreement between chromosomal and gonadal sex?
Sex reversal.
XX genotype but some testicular development.
XX male if bilateral testes
XX true hermaphrodite if testis and ovary present
Why does sex reversal happen?
SRY translocation in most cases
20% have no SRY
Functional areas of the female hypothalamus (2)
*secrete GnRH
Tonic - arcuate ventromedial region; ARC
Surge - preoptic area; POA - causes ovulation
Role of testosterone in development of the hypothalamus
Inherently female. Testosterone crosses BBB and is converted to estradiol, which defeminizes brain and eliminates surge center.
*Estradiol from fetal ovaries is bound to alpha-fetoprotein and does not cross BBB
Examples of body functions hormones regulate
Metabolism Sleep Lactation Growth Mood Reproduction
3 main classes of hormones
Steroids
Peptides/proteins/glycoproteins
Eicosanoids
Endocrine hormones
Estradiol and FSH
Neuroendocrine hormones
Gonadotropin Releasing Hormone (GnRH)
Testosterone from Leydig cells influencing Sertoli cells in the testis is an example of what type of hormone delivery?
Paracrine
Estradiol from Sertoli cells hastening development of these same cells is what type of hormone delivery?
Autocrine
The “Ram Effect”, in which females all go into heat at the same time when a Ram is around, is an example of what kind of hormone delivery?
Pheromonal or “ectohormonal”
Besides the Ram Effect, what’s another example of Pheromonal hormone delivery?
Bruce Effect - female mice terminate pregnancies due to pheromones of an unfamiliar male in the area.
How does supraphysiological stimulation work?
Normally, hormone receptors are internalized as part of a negative feedback mechanism, which renders the hormone ineffective.
It is possible to overcome this mechanism with treatment. (Fertility treatments increase ovulation rates past what is physiologically normal)
*Supprelin = high dose GnRH analogue
The pineal gland produces _____, which regulates cycles of seasonal breeders
Melatonin
The pituitary gland produces which 4 hormones?
FSH
LH
Prolactin
Oxytocin
The ovaries produce which 5 hormones?
Estradiol Progesterone (by Corpus Luteum!) Inhibin Testosterone Relaxin
The testes produce which 3 hormones?
Testosterone
Inhibin
Estradiol
Prostglandin F2 alpha (PGF2a) is produced by which organ?
Uterus
*also produces some estradiol
Progesterone, estradiol, hCG, eCG, oxytocin, and PGF2a are produced by…
The placenta
Estradiol, Progesterone, and Testosterone are what kind of hormone?
Steroids.
*Can diffuse through skin/mucosa and cause prolonged effects.
What type of hormone can be converted from one form to another based on what the body needs?
Prostaglandins (PGF2a <> PGE2)
Steroid biosynthesis with treatment…
Can administer one form of a steroid and it changes to another.
Estradiol administered to cattle would convert to testosterone.
It’s bad.
Where is Estradiol produced and metabolized? What pathological effect can it have on males?
Produced mainly in follicular cells of ovaries
- some in placenta
- small amt in adrenals, testis, fat
Metabolized in the liver
Males with neoplastic conditions of the testes will have too much estradiol which will cause fertility issues
Functions of Estradiol
Sexual behavior Uterine development/function Cervical mucous (indicator of cycle) Vaginal proliferation Mammary development Mediated ovulatory surge of LH Bone health/anabolic
What enzyme is involved in the synthesis of endogenous estrogens from androgens?
aromatase
Which cells of the corpus luteum produce progesterone?
Both granulosa (large luteal) and theca interna (small luteal cells).
*Large luteal (granulosa) produce more
Functions of progesterone
Development/function of uterus QUIESCENCE of myometrium Closure of cervix MAINTENANCE OF PREGNANCY Mammary development EFFECTS ON BRAIN effects on immune function
5-a-Dihydroprogesterone, critical for equine pregnancy, is what type of hormone which binds to progesterone receptors?
progestagens
Where is testosterone produced and metabolized?
Produced mainly by Leydig cells of testes
Some in ovaries and adrenals
Metabolized by liver and minorly in prostate
How does prostate disease contribute to male infertility?
Prostate metabolizes more testosterone than it should
Functions of testosterone
Masculinization Maturation/function of male repro tract Spermatogenesis Male sexual behavior Muscle mass/bone density (anabolic) Increased metabolism
How does GnRH travel so that it is not metabolized by the liver and gets to the site of action in high concentrations?
Generated in the hypothalamus and then travels in the hypophyseal portal circulation to the pituitary gland.
Describe the hypothalamo-hypophyseal-gonadal axis
GnRH is produced in the hypothalamus and sent to the pituitary via the hypophyseal portal vessels. The pituitary then releases FSH and LH, which travel to either the ovaries or testes and causes them to produce estrogen, progesterone, or androgens (and inhibin). Production of these hormones feeds back to the pituitary and hypothalamus to inhibit production of GnRH.
If less testosterone is reaching the brain, the hypothalamus will be signaled to produce more GnRH.
