Reproductive endocrinology and menstrual Flashcards
what is the central core molecule of all steroids? (e.g. oestrogens (oestradiol, oestriol and oestrone), progesterone and testosterone)
Cholesterol is the central core molecule. This structure is shared by all steroids including the oestrogens (oestradiol, oestriol and oestrone), progesterone and testosterone.
what is an androgen? [1]
what are the roles of androgens?
what is an oestrogen? [1]
what are the roles of oestrogens?
An androgen is any natural or synthetic steroid hormone that regulates the development and maintenance of male characteristics in vertebrates by binding to androgen receptors.
- Maintain male somatic tissue differentiation
- Induce male secondary sexual characteristics
- Support spermatogenesis
- Influence sexual and aggressive behaviour (male & female)
- Promote protein anabolism, somatic growth & ossification
- Regulate gonadotrophin secretion (testosterone)
- Induce body hair (in females – pubic & axillary)
- 5-alpha reductase deficiency in males mean they can be born looking female as testosterone cannot be converted, so do not show male characteristics as you would normally.
An oestrogen is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogenous estrogens that have estrogenic hormonal activity: estrone, estradiol, and estriol
- Stimulate growth of mammary gland & endometrium
- Induce female secondary sexual characteristics
- Prepare uterus for spermatozoa transport
- Increase vascular permeability
- Mildly anabolic
- Regulate gonadotrophin secretion
- Also involved in calcium homeostasis
- Part of the menopause that reduction in oestrogen causes loss of bone mass
difference between oestrone, oestradoil and oestriol?
- Oestrone is biologically insignificant
- Oestradiol, and this is the main version of oestrogen, as it is the most involved in reproductive processes and the oestrogen intermediate that has the most effect
- Oestriol is only present in pregnancy
Steroid synthesis requires oxidative enzymes located in the mitochondria and endoplasmic reticulum.
First step in steroid synthesis is the conversion of WHAT to WHAT? [2]
From there it can either be converted to WHAT or WHAT dependent on the enzymes? [2]
Steroid synthesis requires oxidative enzymes located in the mitochondria and endoplasmic reticulum.
First step in steroid synthesis is the conversion of cholesetrol to pregnenolone [2]
From there it can either be converted to progesterone or 17-hydroxypregenelone dependent on the enzymes [2]
which horomone stimulates testosterone production? [1] in men
in which cells? [1]
which cell is the main targer of testosterone in males? [1] what occurs when testosterone goes to that cell? [2]
LH stimulates testosterone production by Leydig cells
Main target of testosterone and pituitary FSH are Sertoli cells (5-alpha reductase found in here to convert testosterone and DHT)
- In the Sertoli cells, the enzyme 5α reductase converts testosterone to DHT
- Sertoli cells then secrete androgen binding protein (ABP)
spermatogenesis is stimulated by the binding of which two molecules?
- ABP binds to testosterone & carries it to the seminiferous tubule where it stimulates spermatogenesis
which horomone stimulates testosterone production? [1] in women
in which cells? [1]
which cell is the main targer of testosterone in females? [1] what occurs when testosterone goes to that cell? [2]
LH stimulates testosterone production by theca cells in the ovarian follicle
Testosterone enters granulosa cells (which surround the oocyte) where it is converted by aromatase into oestrogen (mainly 17β oestradiol)
Oestradiol stimulates formation of LH receptors on granulosa cells
This will enable follicle to respond to LH surge thus giving rise to ovulation
what is the role of progesterone:
a) during menstrual cycle [1]
b) during pregnancy [1]
progesterone prepares the endometrium for implantation during the secretory phase of the menstrual cycle. Effects cervix, vagina and breast.
Placental progesterone maintains the endometrium (decidua) in pregnancy (after approximately 10-12 weeks)
what is the difference in structure between the gonadotrophins: LH, FSH and hCG
The α subunit is identical in FSH, LH and hCG (and TSH) and is composed of 92 amino acids
The β subunit is different in FSH, LH, hCG (and TSH) and confers specific biological action
GnRH (hypothalamic hormone) causes the secretion of [2]
LH and FSH
why does hCG need to replace the function of LH?
- The β subunit of LH and hCG contain the same sequence of amino acids and both stimulate the same receptor and the reason is hCG needs to replace the function of LH so needs to be able to bind to their receptors
what is the role of FSH is men [1] and women [1]
- Stimulates the growth of immature Graafian follicles (ovary) to maturity (female)
- Enhances the production of androgen-binding protein by the Sertoli cells of the testes and is needed for spermatogenesis.
what is the role of LH in women [3] & men [1]
Women
- Surge triggers ovulation and converts the residual follicle into a corpus luteum (female)
- Necessary to maintain luteal function (female)
- Stimulates thecal cells in the ovary to produce testosterone for oestradiol production (female)
Men
- Acts upon the Leydig cells of the testis and is responsible for the production of testosterone (male)
role of hCG? [1]
- Maintains corpus luteum in pregnancy
glycoproteins:
i) inhibin:
- produced where in males? [1] females? [1]
- function in males? [1] females? [1]
ii) activin: role in men and women? [1]
iii) relaxin: role in women? and men? [2]
- Inhibin: a glycoprotein produced by:
- In males by Sertoli cells. When sperm count high inhibin secretion increases and inhibits pituitary release of FSH and hypothalamic release of GnRH. When sperm count <20 million/ml inhibin secretion decreases.
- In females by granulosa cells. Helps to exert negative control on FSH production during the menstrual cycle.
- Activin – a glycoprotein belonging to the transforming growth factor β family. Increases FSH activity and enhances the actions of LH in both males and females.
- Relaxin – Now known to be several members of this peptide family with different roles:
In females produced during menstrual cycle (follicular development & oocyte maturation) and pregnancy (relaxation of ligaments and parturition).
In males found in seminal fluid to enhance sperm motility.
label A-D
A: FSH
B: LH
C: Oestrogen
D: Progesterone
