2. Control of Reproductive Processes Flashcards
What are the hormones secreted from the anterior pituitary?
Follicle stimulating hormone (FSH), lueinising hormone (LH), thyroid stimulating hormone (TSH), ACTH, melanocyte stimulating hormone (MSH), growth hormone, prolactin.
Which hormones are secreted by gonadotroph cells of the anterior pituitary gland?
FSH, LH.
Which cell type secretes prolactin?
Lactotrophs of the anterior pituitary.
What do FSH and LH target?
Gonads.
Where does prolactin act?
Ovaries and mammary glands.
What is the principle action of FSH?
Growth of reproductive system.
What is the principle action of LH?
Sex hormone production.
What are the principle actions of prolactin?
Secretions of oestrogen, progesterone, milk production.
How does the hypothalamus have an effect on anterior pituitary hormone secretion?
Nerve cells produce hormones that pass into anterior pituitary in hypophyseal portal vessels.
What controls FSH and LH secretion from gonadotrophs?
Gonadotrophin releasing hormone (GnRH).
What is the pattern of GnRH release in hypothalamic neurones?
Pulsatile fashion, burst of secretion once an hour.
Which hormones affect GnRH release?
Testosterone (reduces), oestrogen at intermediate concentration (reduces by lowering amount secreted per pulse), progesterone (reduces by increasing effect of oestrogen and lowering frequency of pulses), oestrogen alone at high concentration (promotes release).
How is the amount of FSH released in response to GnRH reduced?
Inhibin selectively inhibits its release.
What produces inhibin?
Developing follicles in the ovary and seminiferous tubules in testis.
What is the action of LH in the testes?
Acts on Leydig cells -> promotes secretion of testosterone.
What enhances the effects of LH on Leydig cells?
Prolactin and inhibin.
What is the action of testosterone in the testes?
Acts on Sertoli cells -> promotes spermatogenesis.
What is the action of FSH in the testes?
Maintains Sertoli cells so they’re responsive to testosterone.
How do LH and FSH work in the antral phase in the ovaries?
LH binds to Theca Interna cells to produce androgens, androstenedione. FSH binds to granulosa cells to produce enzymes to make androgens -> oestrogen.
How is the amount of oestrogen produced affected as the follicle grows?
More produced for a given amount of LH and FSH as the follicle is bigger.
What happens hormone-wise in the pre-ovulatory phase?
Follicle has grown so produces lots of oestrogen. LH receptors develop in outer layers of granulosa cells. Positive feedback from high [oestrogen] causing LH surge to stimulate ovulation.
What is the effect of the LH surge?
Stimulates ovulation, follicle size increases and collagenase activity, FSH still inhibited by inhibin.
What happens hormone-wise in the luteal phase?
Follicle reorganises to corpus luteum. LH stimulates it. Corpus luteum produces oestrogen and progesterone.
What is the effect of progesterone from the corpus luteum?
It prevents positive feedback and enhances negative feedback of oestrogen.
What is meant by determinative effects of gonadal steroids?
Qualitative and only partly reversible, e.g. deepening of the voice and other mostly secondary sexual characteristics.
What is meant by regulatory effects of gonadal steroids?
Highly reversible, rely on continuous hormonal stimulation for maintenance.
What are the determinative actions of testosterone?
Increase size and mass of muscles, vocal cords, and bones; deepening of voice; facial and body hair; increased stature; growth of penis.
What are the regulatory actions of testosterone?
Maintain male internal genitalia; metabolic action; behavioural effects - aggression, sexual activity.
What are the actions of oestrogen?
Fallopian tube function, thickening of endometrium, growth and motility of myometrium, thin alkaline cervical mucus, vaginal changes, changes in skin + hair + metabolism, calcium metabolism.
What are the actions of progesterone on oestrogen primed cells?
Further thickened of endometrium into secretory form, thickening of myometrium but reduction of motility, thick acidic cervical mucus, changes in mammary tissues, increased body temperature, metabolic changes, electrolyte change.
What are the phases of the menstrual cycle?
Follicular phase, pre-ovulation, luteal phase.
Summarise the follicular phase of the menstrual cycle.
Stimulates development of the follicle in ovary. Uterus prepares for sperm transport and implantation of conceptus.
Summarise the pre-ovulation phase of the menstrual cycle.
LH surge causes ovulation, brief period of fertility, corpus luteum forms.
Summarise the luteal phase of the menstrual cycle.
LH maintains corpus luteum in ovary.
What are the changes in the ovary and endometrium during the follicular phase?
Rising oestrogen. Fallopian tube has increased secretion, motility, cilia. Myometrium increase growth, motility. Endometrium thickened and more glandular invaginations, secretes watery fluid conductive to sperm. Increases cervical mucus - thin, alkaline, conductive to sperm. Vaginal epithelium has more mitosis.
What are the changes in the ovary and endometrium during the luteal phase?
Progesterone acts on oestrogen primed cells. Fallopian tube has decreased motility, secretion, cilia. Myometrium thickens further but less motile. Endometrium thickens further and more secretions, spiral arteries develop. Cervical mucus thickens and acidifies to inhibit sperm transport.
How is menstrual bleeding triggered?
Sudden fall in progesterone and oestrogen levels so secretory epithelium of endometrium collapses and there is apoptotic cell death. Spiral arteries contract to reduce bleeding.
What are the gonadotrophins and gonadal steroids secreted during the start of the cycle?
Oestrogen, progesterone, and inhibin are low. GnRH secretion. LH and FSH rise, FSH more as low as inhibin levels mean less inhibition.
What are the gonadotrophins and gonadal steroids secreted during follicle growth?
Oestrogen and inhibin rises. FSH selectively inhibited by inhibin. Rising oestrogen stimulates GrnRH to release LH.
What are the gonadotrophins and gonadal steroids secreted 12-14 days into cycle?
Positive feedback of oestrogen so LH surge which triggers ovulation. Oestrogen levels fall and corpus luteum forms.
What are the gonadotrophins and gonadal steroids secreted after ovulation?
LH promotes oestrogen and progesterone secretion from corpus luteum, more released as it grows. No positive feedback from oestrogen on LH as progesterone blocks it.
What are the gonadotrophins and gonadal steroids secreted 14 days after ovulation?
Corpus luteum regresses so progesteron and oestrogen fall, menstrual bleed is triggered. Inhibition of GnRH, FSH, and LH are relieved so these start to rise in new cycle.
What are the gonadotrophins and gonadal steroids secreted if conception occurs?
Placenta secretes human chorionic gonadotrophin (hCG) which prevents regression of corpus luteum so it continues to secrete oestrogen and progesterone.
How are levels of testosterone regulated?
If levels rise, GnRH secretion is inhibited so LH and FSH reduce. Further reduced by testosterone reducing sensitivity of gonadotrophs to GnRH so testosterone levels fall.
What happens if spermatogenesis proceeds too rapidly?
Inhibin levels rise so reduced secretion of FSH acting on gonadotrophs.
