Lecture 9 - The Gonads 2

Question 1

List three androgens

Answer 1

Androstenedione - weak Testosterone Dihydrotestosterone (DHT)

Question 2

What can testosterone be synthesised to?

Answer 2

Via Reduction (5 alpha reductase) - DHT Via Aromatisation (Aromatase) - 17BO

Question 3

Where does the synthesis of DHT occur?

Answer 3

Prostate, testes, seminiferous tubules, seminal vesicles, skin, brain, adenohypophysis

Question 4

Where does the synthesis of 17BO occur?

Answer 4

Adrenals, testes, Sertoli cells, liver, skin, brain

Question 5

What is the main method of DHT transport in the BLOOD?

Answer 5

Sex hormone binding globulin - 60% (Albumin - 38% and FREE - 2%)

Question 6

What is the main method of DHT transport in the SEMINIFEROUS FLUID?

Answer 6

Androgen binding globulin - bioactive

Question 7

What actions do androgens have on a fetus?

Answer 7

Develop internal and external genitalia

General growth - males believed to be bigger at birth as androgens ^ growth

Behavioural characteristics

Question 8

What actions do androgens have on adults?

Answer 8

Spermatogenesis

Growth and development of male genitalia, 2ry sex glands (prostate), 2ry sex characteristics

Protein anabolism

Pubertal growth spurt with GH

Behavioural effects

Feedback regulation

NB: some androgenic effects mediated by turning into oestrogen

Question 9

Define oestrogens

Answer 9

Any substance that induces mitosis in the endometrium

Question 10

Give examples of oestrogens

Answer 10

17BO (MAIN ONE in menstrual cycle) - POTENT Oestrone (precursor) - WEAK Oestriol (MAIN ONE in pregnancy) - WEAK

Question 11

What are the principal actions of oestrogens, to do with reproductive characteristics?

Answer 11

Stimulate proliferation of endometrium Maturation of follicle during follicular phase Induction of LH surge -> ovulation Effects on vagina/cervix Stimulates growth of ductile system in breast Decreases sebaceous gland secretion

Question 12

What are the principal actions of oestrogens to do with whole body?

Answer 12

^ salt (and water) reabsorption ^ plasma protein synthesis - influences enzymes Metabolic actions - ^ HDL levels Stimulates osteobalsts Influences release of other hormones - prolactin, thyrotrophin Behavioral effects Feedback regulation - +VE and -VE

Question 13

Define progestogens

Answer 13

Any substance that induces secretory changes in the endometrium

Question 14

Give examples of progestogens

Answer 14

Progesterone - precursor in steroidal synthesis pathway 17 alpha-hydroxyprogesterone - small amounts released at points during menstrual cycle

Question 15

What are the principal actions of progestogens?

Answer 15

Stimulate secretory activity in endometrium/cervix/vagina Stimulates growth of alveolar system in breast Decreased renal NaCl reabsorption (competitive inhibition of aldosterone) Increase in basal body temperature Negative feedback regulation

Question 16

How do steroids cause a effect in the cell?

Answer 16

They have important genomic effects Enter the cell easily through the lipid membrane Bind to intracellular receptors in nucleus R-H complex acts as transcription factor and regulates production of new proteins

Question 17

What cell does FSH act on in males?

Answer 17

Sertoli cells

Question 18

What cell does LH act on in males?

Answer 18

Leydig cells

Question 19

What occurs when there is an increase in GnRH?

Answer 19

^ LH and FSH release FSH causes Leydig cells to release testosterone (which has virilisation effects) and stimulates Sertoli cells LH stimulates Sertoli cells to release Inhibin Both inhibin and testosterone cause an indirect and direct -ve effect, reducing GnRH levels Also Spermatogenesis ^ (Sertoli cells)

Question 20

How is GnRH secreted?

Answer 20

PULSATILE - In pulses (generated in hypothalamus) to get correct stimulation from GnRH

Question 21

What do Leydig cells do?

Answer 21

Production of androgen Stimulated by GnRH - LH*** Reduced by -ve feedback from testosterone Direct from adenohypophysis reducing LH and indirect to hypothalamus, reducing GnRH pulse generator

Question 22

What do Sertoli cells do?

Answer 22

Spermatogenesis Stimulated by GnRH - FSH*** Requires GnRH/LH/Testosterone for complete spermatogenesis Limited by inhibin (-ve feedback)

Question 23

What are the different phases in the menstrual cycle?

Answer 23

Early follicular phase Early mid-follicuar phase Mid-follicular phase Late follicular phase Luteal phase

Question 24

Describe the hormonal levels in the early follicular phase

Answer 24

Oestrogen and progesterone levels are low - LOW -ve feedback ^ in LH, FSH and GnRH LH and FSH stimulate development in some follicles in ovaries

Question 25

What occurs in the early-mid follicular phase?

Answer 25

No further increase in LH/FSH Oestrogen levels rise dramatically Progesterone stays the same

Question 26

What is the positive feedback loop that is formed during the EMFP?

Answer 26

LH enters the Thecal cell, androgens synthesised -> passed onto granulosa cell Granulosa converts androgen into 17BO which enters a +VE feedback loop, having an effect on oestrogen receptor - AUTOCRINE The more Oestrogen produced, the more the granulosa cells will produce oestrogen

Question 27

What is the local +ve feedback loop in the ovaries?

Answer 27

Granulosa cells multiply and increase in size

Means more oestrogen produced

So increase proliferation of granulosa so ^ oestrogen

Question 28

What happens in the mid follicular phase?

Answer 28

^ oestrogen levels have -ve feedback effect on FSH, so only Graffian follicle can grow on its own (using local oestrogens) All other follicles undergo atresia

Question 29

How does the -ve feedback loop in the MFP work?

Answer 29

Inhibin is released by Graffian, leading to inhibition of FSH - oestradiol also directly inhibits SPECIFICALLY FSH

Question 30

What is the Graffian follicle?

Answer 30

Largest follicle Doesn’t need FSH to develop/proliferate Continues to grow + produces large amount of 17BO - which after 36hrs results in -ve feedback switching to +ve feedback LH SURGE caused

Question 31

Describe events of late follicular phase

Answer 31

High oestrogen levels WITHOUT progesterone for min of 36hrs LH SURGE induced LH surge sufficiently high to overcome FSH -ve feedback so lesser FSH surge Small surge of 17 alpha hydroxyprogesterone- enhances oestrogen to cause LH surge

Question 32

What happens at the luteal phase? NFL-negative feedback loop

Answer 32

After ovulation cells of follicle collapse forming corpus luteum Oestrogen + Prog levels fall after ovulation, so still some LH and FSH released Stimulates corpus luteum to produce more oest + prog - NFL LH and FSH decrease (mainly NFL from prog) so oest and prog also falls - NFL again, ^LH and FSH again etc

Question 33

What happens if egg is fertilised?

Answer 33

Human chorionic gonadotrophin s released, which mimics effects of LH

Question 34

What is amenorrhea?

Answer 34

Absence of menstrual cycles Primary - if never happened Secondary if happened but have been stopped

Question 35

What is oligomenorrhea?

Answer 35

Infrequent menstrual cycles Various causes - due to absence of LH surge

Question 36

What is another function of prolactin?

Answer 36

Inhibits GnRH pulsatility This is to prevent female from getting pregnant straight away after having given birth

Question 37

What is infertility?

Answer 37

Inability to impregnate/to get pregnant Various causes - physical, psychological, emotional, endocrine Excess prolactin (prolactinoma)

Question 38

What can cause increased prolactin?

Answer 38

Pregnancy/lactation Prolactinoma Disconnection hyperprolactin - tumour pressing on stalk of dopamine

Question 39

What are the presenting symptoms of increased prolactin levels?

Answer 39

Galactorrhea Oligomenorrhea If tumour that presses against occipital nerve, then visual defects