Lecture 9 - The Gonads 2 Flashcards

1
Q

List three androgens

A

Androstenedione - weak Testosterone Dihydrotestosterone (DHT)

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2
Q

What can testosterone be synthesised to?

A

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

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3
Q

Where does the synthesis of DHT occur?

A

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

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4
Q

Where does the synthesis of 17BO occur?

A

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

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5
Q

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

A

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

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6
Q

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

A

Androgen binding globulin - bioactive

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7
Q

What actions do androgens have on a fetus?

A

Develop internal and external genitalia

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

Behavioural characteristics

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8
Q

What actions do androgens have on adults?

A

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

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9
Q

Define oestrogens

A

Any substance that induces mitosis in the endometrium

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10
Q

Give examples of oestrogens

A

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

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11
Q

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

A

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

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12
Q

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

A

^ 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

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13
Q

Define progestogens

A

Any substance that induces secretory changes in the endometrium

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14
Q

Give examples of progestogens

A

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

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15
Q

What are the principal actions of progestogens?

A

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

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16
Q

How do steroids cause a effect in the cell?

A

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

17
Q

What cell does FSH act on in males?

A

Sertoli cells

18
Q

What cell does LH act on in males?

A

Leydig cells

19
Q

What occurs when there is an increase in GnRH?

A

^ 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)

20
Q

How is GnRH secreted?

A

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

21
Q

What do Leydig cells do?

A

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

22
Q

What do Sertoli cells do?

A

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

23
Q

What are the different phases in the menstrual cycle?

A

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

24
Q

Describe the hormonal levels in the early follicular phase

A

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

25
Q

What occurs in the early-mid follicular phase?

A

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

26
Q

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

A

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

27
Q

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

A

Granulosa cells multiply and increase in size

Means more oestrogen produced

So increase proliferation of granulosa so ^ oestrogen

28
Q

What happens in the mid follicular phase?

A

^ 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

29
Q

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

A

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

30
Q

What is the Graffian follicle?

A

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

31
Q

Describe events of late follicular phase

A

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

32
Q

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

A

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

33
Q

What happens if egg is fertilised?

A

Human chorionic gonadotrophin s released, which mimics effects of LH

34
Q

What is amenorrhea?

A

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

35
Q

What is oligomenorrhea?

A

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

36
Q

What is another function of prolactin?

A

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

37
Q

What is infertility?

A

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

38
Q

What can cause increased prolactin?

A

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

39
Q

What are the presenting symptoms of increased prolactin levels?

A

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