Reproductive endocriology Flashcards
what are the 3 main cases of hormones in the body?
proteins/polypeptides
steroids
derivatives of the amino acid tyrosine
what are some examples of protein hormones/polypeptides?
insulin
growth hormone
Thyroid stimulating hormone
what are some examples of steroid hormones?
cortisol
oestrogen
progesterone
what are some examples of dervivates of the amino acid tyrosine hormones?
thyroxine
adrenaline
which kinds of hormones are hydrophilic?
proteins/polypeptides (insulin)
derivatives of the amino acid tyrosine (adrenaline)
what kind of hormones are hydrophobic?
steroid hormones (oestrogen)
where are steroid hormones derived from?
cholesterol
enzymatic modification of cholesterol
what is the structure of polypeptide hormones?
chain of amino acids
where are derivatives of tyrosine hormones synthesised?
in the adrenal glands as well as the thyroid
where do receptors tend to be located?
present in serum and tissues at low concentrations so must have high affinity
where does the synthesis of steroid hormones generally occur?
mitochondria and the SER
why are steroid hormones not stored before secretion?
because they are lipid soluble and are therefor permeable to membranes
what is the mechanism of action of steroid hormones?
- steroid hormone enters target cell
- binds to a receptor present in target cell
- the hormone-receptor complex enters the nucleus
- binds to DNA in the nucleus and activates transcription
- new mRNA is made which moves to the cytoplasm
- translation produces new proteins
what are circulating oestrogen?
a mix of oestrone and oestradiol
where is oestrogen synthesised?
directly from the ovary or converted from androstenedione
how is oestrogen produced from androstenedione?
estradiol produced by the ovary, deduced by direct synthesis in the developing follicles or through conversion of oestrone
the enzyme aromatase is responsible for this conversion
what is oestrogen involved in?
development of female secondary sex characteristics
control of the menstrual cycle
pregnancy
bone strength
what are the 3 major endogenous oestrogens?
oestrone
oestradiol
oestriol
which type of oestrogen is the most prevalent and potent?
oestrodiol
what is the hormone that covers androgen to oestrogen?
aromatase
what are some examples of oestrogens?
testosterone, androstenedione and dihydrogen, dihydrotesterone
where are androgens synthesised?
testis
ovary
adrenal gland
what is the role of androgens?
regulate male primary sec organs and secondary sexual characteristics
important in libido and sexual arousal
where are progestins (progestogens) synthesised?
from cholesterol via pregenolone
-produced primarily in the Corpus luteum of ovary, the adrenal glands and in the placenta during pregnancy
what are the roles of progestones?
maintaining endometrium to support pregnancy
important for mammary gland development in pregnancy
where is the hypothalamus located?
located anterior and inferior to the thalamus
where is the hypothalamus located?
sits above the pituitary gland and. the pituitary gland is cradled within the cellar of the bone of the skull
what are the 2 lobes of the pituitary gland?
arise from distinct parts of the embryonic tissue and there is a posterior and anterior lobe
what is the posterior pituitary gland lobe made up of?
neural tissue
what is the anterior pituitary gland lobe made up of?
glandular tissue
roughly how large is the pituitary gland?
generally the size of a pea
what are the main roles of the hypothalamus?
-links the nervous system to the endocrine system
-located below the thalamus
-part of the limbic system
-controls body temp. hunger, thirst, sleep etc
what is the main roles of the pituitary gland?
-endocrine gland
-suspended from the underside of the brain by the pituitary stalk
-has an anterior and a posterior portion
what connects the hypothalamus to the pituitary gland?
a stem called the infundibulum
sometimes called the pituitary stalk
what is the unique vasculature between the hypothalamus and pituitary?
hypothalamo-hypophysial portal system which allows connection between them
what hormones are released by the posterior pituitary?
ADH
oxytocin
what hormones are released by the anterior pituitary?
FSH/LH
growth hormone
thyroid stimulating hormone
adrenocorticotrophic hormone
prolactin
what does oxytocin do?
promotes uterine contractions during labour
milk ejection during lacation
what does FSH/LH do?
regulation of gamete production and reproductive hormones
what does growth hormone do?
stimulates cell proliferation and regulates growth
what does thyroid stimulating hormone do?
stimulates synthesis and release of thyroid hormones
what does adrenocorticotrophic hormone do?
stimulates cortisol secretion from the adrenal gland
what does prolactin do?
stimulates milk production during lactation
what is the hypothalamic-pituitary axis?
command centre of the endocrine system
coordinates messages of the endocrine and nervous system together
stimulus is received by NS will pass through the hypothalamic pituitary complex to be translated into hormones that elicit a response
what regulates reproduction?
hypothalamic-pituitary-honadal axis
how does the hypothalamic-pituitary-honadal axis work?
-hypothalamus secretes gonadotrophin (GnRH) which stimulates anterior pituitary to release FSH and LH
-thr ovary or testis (and placenta) respond to the levels of gonadotrophin and secrete steroid sex hormones
where is GnRH secreted from?
neurosecretory cells within the hypothalamus
what Is GnRH?
a 10 amino acid peptide with a short half life
what is the hypothalamic control of GnRH?
It is secreted into the portal vessel
secreted in a pulsatile manner
activates its receptor (GnRHR) within the anterior pituitary which stimulates the release of gonadotrophin
what level of hormonal control of reproduction do we consider the pituitary gland?
2nd level
what does the anterior pituitary gland do?
secrete peptide hormones
-FSH
-LH
-acts on the ovary and testis
what does the posterior pituitary gland do?
secretes oxytocin
-involved In childbirth and lactation
what is the role of FSH in males?
-stimulates primary spermatocytes to undergo meiosis
-enhances production of androgen binding protein in Sertoli cells of the testis
what does FSH do in females?
-initiates recruitment and supports growth of ovarian follicles
(granulose cells)
what does LH do in males?
-acts on the leydig cells of the testis to regulate production of testosterone
what does LH do in females?
-supports ovarian theca cells
-LH surge triggers ovulation
-trigger for ovulation
what effect does LH have on theca cells?
produce androgens which get passed to the granulose cells t produce oestrogens
what effect does rising oestrogen or testosterone have?
negative feedback on the hypothalamus and inhibits the release go GnRH and FSH, LH
when do we get positive feedback for FSH and LH?
to allow ovulation
breast feeding
which pituitary hormone stimulates Sertoli cells in the testis?
FSH
