2. Control of Reproductive Processes

Question 1

What are the hormones secreted from the anterior pituitary?

Answer 1

Follicle stimulating hormone (FSH), lueinising hormone (LH), thyroid stimulating hormone (TSH), ACTH, melanocyte stimulating hormone (MSH), growth hormone, prolactin.

Question 2

Which hormones are secreted by gonadotroph cells of the anterior pituitary gland?

Answer 2

FSH, LH.

Question 3

Which cell type secretes prolactin?

Answer 3

Lactotrophs of the anterior pituitary.

Question 4

What do FSH and LH target?

Answer 4

Gonads.

Question 5

Where does prolactin act?

Answer 5

Ovaries and mammary glands.

Question 6

What is the principle action of FSH?

Answer 6

Growth of reproductive system.

Question 7

What is the principle action of LH?

Answer 7

Sex hormone production.

Question 8

What are the principle actions of prolactin?

Answer 8

Secretions of oestrogen, progesterone, milk production.

Question 9

How does the hypothalamus have an effect on anterior pituitary hormone secretion?

Answer 9

Nerve cells produce hormones that pass into anterior pituitary in hypophyseal portal vessels.

Question 10

What controls FSH and LH secretion from gonadotrophs?

Answer 10

Gonadotrophin releasing hormone (GnRH).

Question 11

What is the pattern of GnRH release in hypothalamic neurones?

Answer 11

Pulsatile fashion, burst of secretion once an hour.

Question 12

Which hormones affect GnRH release?

Answer 12

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).

Question 13

How is the amount of FSH released in response to GnRH reduced?

Answer 13

Inhibin selectively inhibits its release.

Question 14

What produces inhibin?

Answer 14

Developing follicles in the ovary and seminiferous tubules in testis.

Question 15

What is the action of LH in the testes?

Answer 15

Acts on Leydig cells -> promotes secretion of testosterone.

Question 16

What enhances the effects of LH on Leydig cells?

Answer 16

Prolactin and inhibin.

Question 17

What is the action of testosterone in the testes?

Answer 17

Acts on Sertoli cells -> promotes spermatogenesis.

Question 18

What is the action of FSH in the testes?

Answer 18

Maintains Sertoli cells so they’re responsive to testosterone.

Question 19

How do LH and FSH work in the antral phase in the ovaries?

Answer 19

LH binds to Theca Interna cells to produce androgens, androstenedione. FSH binds to granulosa cells to produce enzymes to make androgens -> oestrogen.

Question 20

How is the amount of oestrogen produced affected as the follicle grows?

Answer 20

More produced for a given amount of LH and FSH as the follicle is bigger.

Question 21

What happens hormone-wise in the pre-ovulatory phase?

Answer 21

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.

Question 22

What is the effect of the LH surge?

Answer 22

Stimulates ovulation, follicle size increases and collagenase activity, FSH still inhibited by inhibin.

Question 23

What happens hormone-wise in the luteal phase?

Answer 23

Follicle reorganises to corpus luteum. LH stimulates it. Corpus luteum produces oestrogen and progesterone.

Question 24

What is the effect of progesterone from the corpus luteum?

Answer 24

It prevents positive feedback and enhances negative feedback of oestrogen.

Question 25

What is meant by determinative effects of gonadal steroids?

Answer 25

Qualitative and only partly reversible, e.g. deepening of the voice and other mostly secondary sexual characteristics.

Question 26

What is meant by regulatory effects of gonadal steroids?

Answer 26

Highly reversible, rely on continuous hormonal stimulation for maintenance.

Question 27

What are the determinative actions of testosterone?

Answer 27

Increase size and mass of muscles, vocal cords, and bones; deepening of voice; facial and body hair; increased stature; growth of penis.

Question 28

What are the regulatory actions of testosterone?

Answer 28

Maintain male internal genitalia; metabolic action; behavioural effects - aggression, sexual activity.

Question 29

What are the actions of oestrogen?

Answer 29

Fallopian tube function, thickening of endometrium, growth and motility of myometrium, thin alkaline cervical mucus, vaginal changes, changes in skin + hair + metabolism, calcium metabolism.

Question 30

What are the actions of progesterone on oestrogen primed cells?

Answer 30

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.

Question 31

What are the phases of the menstrual cycle?

Answer 31

Follicular phase, pre-ovulation, luteal phase.

Question 32

Summarise the follicular phase of the menstrual cycle.

Answer 32

Stimulates development of the follicle in ovary. Uterus prepares for sperm transport and implantation of conceptus.

Question 33

Summarise the pre-ovulation phase of the menstrual cycle.

Answer 33

LH surge causes ovulation, brief period of fertility, corpus luteum forms.

Question 34

Summarise the luteal phase of the menstrual cycle.

Answer 34

LH maintains corpus luteum in ovary.

Question 35

What are the changes in the ovary and endometrium during the follicular phase?

Answer 35

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.

Question 36

What are the changes in the ovary and endometrium during the luteal phase?

Answer 36

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.

Question 37

How is menstrual bleeding triggered?

Answer 37

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.

Question 38

What are the gonadotrophins and gonadal steroids secreted during the start of the cycle?

Answer 38

Oestrogen, progesterone, and inhibin are low. GnRH secretion. LH and FSH rise, FSH more as low as inhibin levels mean less inhibition.

Question 39

What are the gonadotrophins and gonadal steroids secreted during follicle growth?

Answer 39

Oestrogen and inhibin rises. FSH selectively inhibited by inhibin. Rising oestrogen stimulates GrnRH to release LH.

Question 40

What are the gonadotrophins and gonadal steroids secreted 12-14 days into cycle?

Answer 40

Positive feedback of oestrogen so LH surge which triggers ovulation. Oestrogen levels fall and corpus luteum forms.

Question 41

What are the gonadotrophins and gonadal steroids secreted after ovulation?

Answer 41

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.

Question 42

What are the gonadotrophins and gonadal steroids secreted 14 days after ovulation?

Answer 42

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.

Question 43

What are the gonadotrophins and gonadal steroids secreted if conception occurs?

Answer 43

Placenta secretes human chorionic gonadotrophin (hCG) which prevents regression of corpus luteum so it continues to secrete oestrogen and progesterone.

Question 44

How are levels of testosterone regulated?

Answer 44

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.

Question 45

What happens if spermatogenesis proceeds too rapidly?

Answer 45

Inhibin levels rise so reduced secretion of FSH acting on gonadotrophs.