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Endocrinology > Reproductive endocrinology > Flashcards

Reproductive endocrinology Flashcards

1
Q

Male Reproduction

A

Gametogenesis (spermatogenesis)
Delivery of sperm
Secretion of sex hormones (testosterone)

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2
Q

Female Reproductive System

A 
Gametogenesis (oogenesis)
Secretion of sex hormones ( progesterone and oestrogen)
Reception of sperm
Fertilisation
Maintenance of developing foetus
Parturition
Lactation
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3
Q

What are the key roles of the testis?

A

Sperm production

Hormone production

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4
Q

What are the 3 principle cell types in the testis?

A 
Leydig cells (outside tubules)
Sertoli Cells (within tubules)
Germ cells (at different stages within tubules and lumen)
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5
Q

Describe the hypothalamic pituitary regulation of LH and FSH in the male

A
  • LH and FSH are produced by gonadotroph cells in the anterior pituitary
  • LH and FSH circulate in the systemic system
  • Secretion of LH and FSH is stimulated by the hypothalamic peptide GONADOTROPHIN RELEASING HORMON (GnRH)
  • LH and FSH act on particular cell types in the testis:
    • LH > leydig cells > TESTOSTERONE
    • FSH > Sertoli cells > INHIBIN
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6
Q

Now describe the negative feedback control of the hypo and anterior pituitary

A

Testosterone > produced by leydig cells in response to LH.
this exerts a -ve feedback on both the
-hypothalamus > inhibit GnRH release
-Ant. Pit > inhibit LH and FSH released by sertoli cells in response to FSH, selectively inhibits FSH release from the pituitary

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7
Q

What hormones are required for Spermatogenesis?

A

LH
Testosterone
FSH

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8
Q

What role does LH play in spermatogenesis?

A

binds to surface receptors (G-proteins) on leydig cells, and activates a cAMP/protein kinase A pathway, this promotes testosterone synthesis from cholesterol

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9
Q

What role does Testosterone have in spermatogenesis?

A

Bind to AR, and promotes germ cell division

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10
Q

What role does FSH have in spermatogenesis?

A

Binds to G protein coupled receptors on SERTOLI cells, activating a cAMP/protein kinase A pathway

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11
Q

What does binding of FSH to G protein coupled receptors on sertoli cells cause?

A

Causes the production of:
androgen-binding protein (ABP) - concentrates testosterone in lumen
nutrients and other factors are required for spermatogenesis
inhibin - protein hormone that controls FSH secretion
Aromatase - enzyme that converts androgens to oestrogens

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12
Q

Male sex hormones

A

ANDROGEN
synthesised in leydig cells in response to LH in interstitial tissue. androgens are derived from cholesterol.
primary testicular androgen is TESTOSTERONE

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13
Q

Testosterone

A

Some is metabolised to DIHYDROTESTOSTERONE (DHT) very potent androgen (in the testes and certain peripheral tissue)
some testosterone is metabolised to oestrogen (In sertoli cells and adipose tissue)
Testosterone and other androgens circulate bound to ANDROGEN BINDING PROTEIN (ABP)

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14
Q

Androgen activation involves dissociation from ___ and diffusion into cells. binding to ____________ receptors in target cells.

Target cells bind ____ with higher affinity but can also bind __________.

A

Androgen activation involves dissociation from ABP and diffusion into cells. binding to Intracellular receptors in target cells.

Target cells bind DHT with higher affinity but can also bind Testosterone.

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15
Q

What are the effects of androgens before birth?

A

Testosterone is synthesised by foetal leydig cells in response to the mature hCG.
Testosterone masculinises the external genitalia (requires conversion of T to DHT by 5-alpha reductase enzyme)
T promotes descent of testes into scrotum

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16
Q

What are the effects of androgens after birth?

A

Testosterone production very low until puberty

Around puberty LH production by the pituitary is initiated and this stimulates T output by testis.

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17
Q

What are the effects of testosterone of Sex-Specific tissues?

A

Promote growth and maturation of reproductive system at puberty
Essential for spermatogenesis
Maintains reproductive tract throughout adulthood

18
Q

Effects of Testosterone

A

Development of the sex drive - libido - at puberty

Control Gonadotrophin secretion via -ve feedback

19
Q

What are the effects of androgens on secondary sex characteristics?

A

promotes muscle growth for male body conformation
-increases protein synthesis
-decreases protein degradation
-increases lean:fat ratio
promotes bone growth at puberty and closure of epiphyses
induces male pattern of hair growth
causes depending of voice
skin thickness and sebaceous glands thicken (acne)

20
Q

What does puberty require?

A

Maturation of the Hypothalamic - pituitary - Gonadal Axis

21
Q

What is the state before puberty?

A

very low GnRH/LH/FSH and very little gonadal activity

22
Q

What happens as puberty approaches?

A

increased GnRH secretion
increased sensitivity of Gonadotrophs to GnRH
Decreased sensitivity of hypo and ant. pit to -ve feedback action of gonadal steroids
Increased LH/FSH release
Testis development
Testosterone production
Spermatogenesis

23
Q

FEMALE REPRODUCTIVE ENDOCRINOLOGY

A

females show regular cyclic changes in gonadal activity
they are the only primates that have a menstrual cycle
rhythmic changes occur in hormone secretion and in size of ovaries and uterus

24
Q

What are the basic features of the female cycle?

A

single mature ovum released from ovaries each month (ovum=egg=oocyte)
endometrium (lining of uterus) is specially prepared for implantation of the ovum, should it be fertilised.
if fertilisation does NOT occur endometrium degenerates and maturation of a new ovum-containing follicle resumes and the cycle repeats.

25
Q

What does HPO axis stand for?

A

The hypothalamic - Pituitary - Ovarian Axis

26
Q

What are the principle hormones produced by the ovary?

A

ANDROGENS - testosterone
OESTOGENS - estrogen
PROGESTERONE - progestin
INHIBIN

27
Q

When does the ovarian cycle start?

A

at puberty

28
Q

When does the ovarian cycle end?

A

at the menopause

29
Q

Describe the 3 phases of the ovarian cycle

A

Follicular phase: follicle mature, oocyte prepared for release
Ovulation (mid cycle): rupture of follicle and release of oocyte
Luteal phase: luteinization of ruptured follicle, preparation of reproductive tract for pregnancy if fertilisation occurs (Progesterone is high and LH and FSH are low)

30
Q

Describe the regulation of the H-P-O axis

A

hypothalamic GnRH stimulates release of LH and/or FSH from the ant. pituitary.
LH and FSH cause increase in ovarian progesterone (P) and oestrogen (E) secretion.
(P mainly from corpus luteum)
P has a NEGATIVE FEEDBACK effect on the pituitary and HYPOTHALAMUS, inhibiting both LH and FSH secretion
Low to moderate levels of E have a NEGATIVE FEEDBACK effect on the pituitary and hypothalamus, inhibiting both LH and FSH secretion.
Providing P is low, high levels of E have a POSITIVE FEEDBACK action on hypo and pit to stimulate the pre-evolutionary surge of LH.
Inhibit acts on the pituitary to selectively decrease FSH secretion

31
Q

Describe the three phases in the UTERINE/ENDOMETRIAL cycle

A

PROLIFERATIVE PHASE:
E increase thickness of endometrium
E increase growth of endometrial glands and blood vessels
E promotes secretion of thin stringy mucus
SECRETORY PHASE:
P causes endometrial swelling and secretory development
P increases blood supply
P increases lipid glycogen deposition
MENSTURATION:
Caused by sudden decrease of P&E at end of luteal phase loss of hormonal stimulation initiates necrosis in the endometrium

32
Q

Describe the follicular phase of the menstrual cycle

A

FSH rises at the start of the cycle, stimulates growth of 6-12 small astral follicles (secondary follicles). by day 6 in the cycle one follicle has been selected = DOMINANT FOLLICLE.
this dominant follicle grows rapidly into a preovulatory (tertiary or Graffian) follicle.
Other follicles not selected to grow undergo atresia (degradation)
typically only one follicle grows large enough to ovulate.

33
Q

What triggers ovulation?

A

A surge of LH from the anterior pituitary

34
Q

Describe ovulation

A
  • occurs in response to th mid cycle surge in LH (&FSH) from the pituitary (~14days)
  • ovulation occurs within 24h of LH/FSH surge
  • increased LH causes swelling of follicle
  • oocyte with surrounding cumulus oophrus is released into the peritoneal cavity, where it is drawn into the fallopian tube.
  • remainder of follicle (theca and granulose cells) develops into corpus luteum -> lasts for 14 days of LUTEAL PHASE
35
Q

List the stages at mid cycle

A
  1. high levels of oestrogen’s from almost mature follicle stimulate release of more GnRH and LH
  2. GnRH promotes release of FSH and more LH
  3. LH surge brings about ovulation
36
Q

What occurs at oestrogen synthesis during follicular phase?

A

> LH stimulates the synthesis of ANDROGENS (from cholesterol in theca cells)
some Androgen (A) diffuses to nearby granulose cells of follicle
FSH stimulates the conversion of ANDROGENS in ESTROGEN’S into granulosa cells (P450 aromatase enzyme)
two hormone/two cell mechanism

37
Q

Discuss Fertility drugs

A

given to increase chances of pregnancy
FSH is widely used in IVF and can induce multiple follicle development
In animal experiments immunisation against INHIBIN also shown to induce multiple follicle development - works by blocking inhibin negative feedback on ant. pit

38
Q

Anti Fertility Drugs

A

> Oral contraceptive pills: synthetic oestrogen and or progesterone derivatives
inhibit follicle development and ovulation
exert negative feedback on hypo-pit
GnRH ANTAGONISTS
inhibit LH/FSH release
inhibit follicle development

39
Q

What are the effects of female sex hormones?

A

mediated by binding to specific intracellular receptors that are LIGAND-ACTIVATED TRANSCRIPTION FACTORS. alteration of gene transcription, mRNA, protein.

40
Q

What are the effects of oestrogens?

A

stimulates uterine endometrial cells to proliferative during first half of female ovarian cycle (follicular phase)
Makes cervical mucus more penetrable for sperm and less hostile
promotes breast development
Promotes bone formation
fat deposition (hips, buttocks)
Both negative and positive feedback regulation of LH/FSH

41
Q

What are the effects of progesterone?

A

promotes secretory changes in uterine endometrium during the second half of female sexual cycle to prepare uterus for potential implantation of fertilised ovum.
promotes development of lobules and alveoli of breast (DOES NOT ACTUALLY STIMULATE MILK SECRETION)
decreases frequency of uterine contractions
negative feedback effect on LH/ FSH secretion.

42
Q

Effects of Androgens?

A

spurt in adrenal androgen production at puberty (ovary & adrenal) causes pubertal growth spurt.
Growth of axillary and pubic hair
Development of libido

Endocrinology (12 decks)

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