(2.1) The Hormonal Control of the Reproductive System Flashcards
Where is the Gonadotrophin Releasing Hormone (GnRH) produced? What is its action?
- Exon of Hypothalamus
- Stimulates Gonadotophs of the Anterior Pituitary Gland to release Luteinising Hormone (LH) and Follicle Stimulating Hormone (FSH)
Where is Luteinising Hormone (LH) produced? What type of chemical is it and what is its action in male and in female before and after ovulation?
- Gonadotrophin of Anterior Pituitary Gland
- Glycoproteins
- Stimulates Leydig cells (male) to produce Testosterone
- Stimulates Thecal cells (female) to produce Androgen
- Stimulates Corpus Luteum (female) to produce Progesterone
Where is Follicle Stimulating Hormone (FSH) produced? What type of chemical is it and what is its action in male and female?
- Gonadotrophin of Anterior Pituitary Gland
- Glycoproteins
- Stimulates Sertoli cells (male) to perform Spermatogenesis
- Stimulates Granulosa cells (female) to convert Androgen to Oestrogen
- Stimulate Sertoli & Granulosa cells to produce Inhibin
Where is Inhibin produced in both sexes? What is its action?
- Sertoli cells of the Semiferous Tubules in male
- Granulosa cells in female developing FOLLICLE
- Inhibits FSH production from Anterior Pituitary Gland alone
What type of chemical is Prolactin and what is its action?
- Polypeptide
- Enhances effects of LH e.g. stimulates Corpus Luteum to produce more Oestrogen & Progesterone
- Milk production
Where is Testosterone produced in both sexes? What is its action?
- Leydig cells in male
- Granulosa cells in female
- Inhibits production of GnRH from Hypothalamus and productions of LH and FSH from Anterior Pituitary Gland
- Male characteristics & Anabolic effects & Emotional changes
How is Oestrogen produced and how is its concentration controlled BEFORE ovulation? What is its action on the developing follicle?
- Granulosa cells convert Androgen from Thecal cells into Oestrogen
- [Intermediate] gives positive feedback to Hypothalamus and Anterior Pituitary Gland
- Adds LH receptors on to Granulosa cells -> LH surge -> Ovulation
How do Releasing Hormones get from the Hypothalamus to the Anterior Pituitary Gland?
Hypophyseal Portal Circulation
What two hormones are released from Corticotrophs?
ACTH
MSH
What type of cell releases Growth Hormone? What type of chemical is it and what is its action?
- Somatotrophs of Anterior PItuitary Gland
- Polypeptides
- Promotes growth, lipid & carbohydrate metabolism
How is the concentration of Oestrogen controlled before ovulation? What physical changes does it make on the reproductive tract?
- [Intermediate] Oestrogen +ve feedbacks on Hypothalamus and Anterior Pituitary Glands
- Fallopian Tube: + secretion, cilia, motility
- Uterine Myometrium: + thickness, motility
- Cervical Mucus: thins & alkaline (sperm likes)
- Vaginal Epithelium: + mitotic activity
Suggest two places that Progesterone is released from.
- Corpus Luteum of the follicle
- Plancenta
Other than Inhibin, which other molecule enhances the effect of LH?
Prolactin
Why do you get a “surge” of LH, but not FSH?
As the follicle becomes more developed:
- More GnRH is released to stimulate Gonadotrophs
- More Inhibin is released from Granulosa cells
- Inhibin only inhibits positive feedback from FSH on to GnRH
Describe the Luteal phase of development.
- The remnant of follicle -> Corpus Luteum
- Corpus Luteum produce Progesterone (Thecal cells) and Oestrogen (Granulosa cells)
Suggest the non-reversible effects of Testosterone.
- Deepens voice, + vocal cords
- Facial & body hair
- Stature
- muscles & bones
Suggest the reversible effects of Testosterone.
- Maintenance of the male internal genitalia (Prostate, Seminal Vesicles, Vas deferens, Epididymis)
- Anabolic effects
- Aggressiveness, sexual activity
At what point in the day are the Testosterone levels the highest?
Early morning
How do you know which day Ovulation occurs, knowing the date of mensural bleed starts?
Counts 14 days backward, because Corpus Luteum has a time span of 14 days e.g. Luteal phase
Describe the changes in Gonadotrophin and Steroid levels in the first 12-14 days of the menstrual cycle (the Follicular/Proliferative phase)
- LH & FSH start high due to the small amount of Inhibin & Oestrogen
- Oestrogen slowly rising, Progesterone still low
- As follicle grows, Granulosa cells produce more Oestrogen, stimulating GnRH
- Granulosa cells produce more Inhibin, reducing amount of FSH
- GnRH acts to produce more LH
- As Oestrogen reaches its highest level, GnRH and LH surges occur
- Oestrogen [high] cause -ve feedback, level decreases largely
Describe the changes in Gonadotrophin and Steroid levels in the remaining 14 days of the menstrual cycle (the Luteal phase), assuming NO pregnancy takes place.
- The Corpus Luteum is formed and begins to increase levels of Progesterone and Oestrogen
- Progesterone -> -ve feedback on the release of GnRH, LH and FSH
- Without pregnancy, Corpus Luteum regresses -> Corpus Albican -> Steroid levels fall -> removing -ve feedback
- Myometerium regresses and menstruates away
Describe the changes in Gonadotrophin and Steroid levels in the remaining 14 days of the menstrual cycle (the Luteal phase), assuming pregnancy TAKES place.
- The Corpus Luteum is formed and begins to increase levels of Progesterone and Oestrogen
- Progesterone -> -ve feedback on the release of GnRH, LH and FSH
- Pregnancy, Placenta develops and secretes Human Chorionic Gonadotrophin
- hCG prevents regression of the Corpus Luteum -> continuous secretions of steroids
Why does LH only stimulate follicles that are partly grown and those in pre-antral phase?
The young follicles don’t yet have a Theca for the LH to bind to, so FSH needs to bind to the Granulosa to result in the follicle growing enough to have a Theca.
What is the significance of the growing follicle releasing increasing amounts of Inhibin as it grows?
Inhibin -> inhibits FSH -> prevents further development of new follicles
During the Follicular phase, what changes are there to the Uterus?
Increased Oestrogen -> thickens Endometrium & increased motility of Myometrium also Endometrial glands secrete alkaline and watery secretions to conduct sperms
Suggest some wider (not the reproductive tract) effects of the Follicular Phase on the body.
- Mild Anabolic activity
- Depresses appetite
- CVS effects
- Maintenance of bone structure
During the Luteal phase, what changes are there to the Uterus?
Increased Progesterone -> reduces Oestrogen -> develops Spiral arteries -> Endometrium & Myometrium thicken & reduced Myometrial motility
During the Luteal phase, what changes are there to the Cervical Mucus?
Increased Progesterone -> reduces Oestrogen -> thickens & acidic -> reduce Sperm transport
Suggest some wider (not the reproductive tract) effects of the Luteal Phase on the body.
Increased Progesterone -> reduces Oestrogen:
- Mild catabolic activity
- Increased body temperature
- Increased Na+ and H2) excretion
Describe the changes that occur to the reproductive tract when there is a sudden drop in Progesterone and Oestrogen.
- Myometrium regresses & Endometrium also thins -> Menses
- Constricted Spiral arteries reduce bleeding
What keeps the existence of a Corpus Luteum?
Human Chorionic Gonadotrophin produces by Syncytiotrophoblast of Placenta
Why are the changes in LH and FSH secretion at the Menopause different?
- Inhibin is only released if follicle/gametes develops -> BEFORE menopause -> inhibits FSH alone without affecting LH
- AFTER menopause -> no follicles/gametes -> no Inhibin
- AFTER menopause -> Oestrogen is always low -> +ve feedback on both FSH & LH
Therefore after menopause, the increase in [FSH] > [LH]
