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Endocrinology > Gonads 1 > Flashcards

Gonads 1 Flashcards

1
Q

Describe the change in number of oogonia in women throughout life.

A

Maximum (24 weeks gestation) - 6-7 million Birth - 2 million Puberty - 400,000 300-400 mature eggs released Menopause - 0

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2
Q

What is the process by which oogonia degenerate and die?

A

Atresia

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3
Q

Describe the steps in spermatogenesis. [4]

A
  1. Germ cells divide to produce spermatogonia.
  2. Spermatogonia remain dormant until puberty where a rise in FSH triggers division of spermatogonia to produce more spermatogonia and primary spermatocytes (still diploid).
  3. Primary spermatocytes enter first meiotic division to form secondary spermatocytes (haploid).
  4. Secondary oocytes enter second meiotic division to form spermatids. Spermatids mature into spermatozoa.
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4
Q

What stimulates the spermatogonia to proceed to the next stage and when does this happen?

A

FSH release during puberty

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5
Q

How long does the process of spermatogenesis take place?

A

70 days

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6
Q

Describe the steps in oogenesis.

A
  1. Germ cells produce oogonia via division.
  2. Oogonia divide mitotically to produce primary oocytes (diploid).
  3. Primary oocytes enter the first meiotic division straight away but are halted in prophase of the first meiotic division.
  4. The oocytes form a layer of cells around them, forming primordial follicles. These cells remain dormant for 12-50 years. More cells die of atresia.
  5. Puberty - release of FSH rescues a group of the dormant cells and they continue development. They complete the first meiotic division around the time of ovulation.
  6. If fertilisation takes place, they will complete the second meiotic division to form an ovum
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7
Q

What is produced after the first meiotic division is complete?

A

Secondary oocyte + first polar body

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8
Q

What is required to complete the second meiotic division?

A

Fertilisation

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9
Q

What is produced after the second meiotic division is complete?

A

Ovum + second polar body

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10
Q

Describe the passage of sperm from production to release.

A

Sperm is produced in seminiferous tubules. It moves to the rete testis where it is concentrated. It then moves via the vasa efferentia to the epididymis for storage. It is ejected via the vas deferens (which has smooth muscle around it) and then via the urethra.

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11
Q

Describe the structure of seminiferous tubules.

A

Spermatogonia around the outside Underlying this is a layer of Sertoli cells The lumen of the seminiferous tubule is on the inside

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12
Q

What important cell type lies outside the seminiferous tubules? What do they produce?

A

Leydig cells: they produce testosterone which is needed for spermatogenesis to take place

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13
Q

How do spermatogonia pass through the Sertoli cell barrier?

A

They move into the Sertoli cells and are enclosed in the cytoplasm of the Sertoli cells.

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14
Q

Describe which receptors are expressed by Sertoli cells and Leydig cells.

A

Sertoli Cells - FSH receptor and Androgen receptor

Leydig Cells - LH receptor

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15
Q

What is inhibin and what cells produce this?

A

Inhibin inhibits the release of FSH and is produced by Sertoli cells

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16
Q

What is a Graffian follicle?

A

The maximum size of a maturing follicle

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17
Q

Which steps in steroidogenesis are common to both adrenals and gonads?

A

The first four steps - pregnenolone –> progesterone –> 17 hydroxyprogesterone –> androstenedione

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18
Q

What enzyme in the testes converts androstenedione to testosterone?

A

17 hydroxysteroid dehydrogenase

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19
Q

What do the ovaries do to androstenedione and testosterone?

A

Aromatises androstenedione and testosterone to oestrone, which can then be converted to 17 beta-oestradiol

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20
Q

What are the phases of the ovarian and endometrial cycle?

A

Ovarian - Follicular –> (ovulation) –> Luteal

Endometrial –> Proliferative –> Secretory

21
Q

What are the effects of oestrogen on the endometrium in the proliferative phase?

A
  • increases mitosis
  • increases progesterone receptors
  • increases oestrogen receptors
  • stimulates thickening of the endometrial lining.
22
Q

What are the effects of progesterone in the secretory phase?

A

Progesterone - reduces the proliferation caused by oestrogen and stimulates secretory activity of the uterus to make it a better environment for implantation.

23
Q

Describe the menstrual cycle.

A
  1. There is a slightly elevated level of FSH at the start of the cycle. This rescues some of the follicles from dormancy so they continue development.
  2. The follicles start producing 17 beta oestradiol which inhibits gonadotrophins (FSH and LH). One follicle becomes dominant - others undergo atresia.
  3. Eventually oestrogen levels remain high enough for long enough that they switch to a positive feedback effect and stimulate a surge in LH and FSH. Surge in LH stimulates ovulation.
  4. Empty follicle becomes a corpus luteum and produces 17 beta oestradiol and progesterone, which has a negative feedback effect on gonadotrophins.
  5. If fertilisation doesn’t take place, oestrogen and progesterone levels fall and negative feedback on FSH and LH decreases so levels rise again.
24
Q

What other effect does progesterone have on the body?

A

Increases body temperature

25
Q

What stage do the follicles develop to in embryonic life?

A

Pre-antral stage

26
Q

What is the next step in embryonic life and what is required to stimulate this step?

A

They develop to early antral follicles - stimulation is FSH If FSH isn’t high enough, they undergo atresia.

27
Q

What are the two cell types in this follicle? What receptors do they have and what do they do?

A

Thecal cells (outside of follicle) - LH receptors - produce androgens Granulosa cells (inside of follicle) - FSH receptors - produces oestrogens from progesterone using aromatase enzyme

28
Q

What are oogonia?

A

immature female sex reproductive cell that upon maturation give rise to oocytes.

29
Q

Draw a diagram to show how the number of germ cells changes over time?

A
30
Q

Do men produce sperm throughout their whole life?

Explain your answer

A

Men retain spermatogenic capability throughout life producing 300-600 sperm/gm testis/second

Spermatogonia undergo differentiation and self-renewal therefor pool of spermatogonia remains available for subsequent spermatogenic cycles throughout life

31
Q

Draw a diagram of the testes

A
32
Q

Draw a diagram to show the hormone levels throughout the menstrual cycle

A
33
Q

Draw the cross section of the seminiferous tubule

A
34
Q

What are the roles of sertoli cells?

A
  • form seminiferous tubules
  • Response to FSH = production of inhibin
  • associated with developing spermatocytes
  • provide structural and metabolic support for the spermatogonia and help them develop which then enter the lumen.
35
Q

Draw the structure of an ovary

A
36
Q

Proliferative - oestradiol is dominant influence (on endometrium, therefore causing it to thicken)

Secretory - progesterone is dominant influence (works alongside with oestrogen in secretory phase)

A

What is the dominant influence for proliferation and secretion?

37
Q

What happens during the proliferation and secretory phase?

A

Proliferation:

endometrium thickens ( mitosis)

glands enlarge and coil - increased blood supply

Secretory:

endometrium becomes secretory

glands secrete glycogen, mucopolysaccharides etc + mucosa engorged with blood

ENDING : necrotic tissue shed

38
Q

How does progesterone reverse effects of oestrogen?

A

Reduces proliferation by reducing oestrogen receptors

39
Q

Draw a diagram to represent the hormones released during the different parts of ovarian and endometrial cycle

A
40
Q

How does progesterone increase the secretory activity of myometrial cells?

A

Glands become wider and produce substances which prepare environment for implantation

41
Q

Describe the sequence of events that lead to the changes in ovaries

A
  1. Follicles with the oocyte are stuck in early meiosis, develops into pre-antral stage
  2. FSH need development, if FSH not high enough, follicle –> atresia
  3. FSH cause follicles to get bigger until they mature into Graffin follicle ( r ovulation)
  4. LH surge –> follicle rupture –> ovum release( + 2nd meiosis occurs)
  5. Follicle –> corpus luteum in luteal phase
42
Q

What happens during the early follicular phase?

A
  • Menstruation
  • OESTROGEN and PROGESTERONE levels are LOW
  • LH and FSH start to stomulate follicle production
43
Q

What happens during the early-mid follicular phase?

A
  • Increase in follicles so increase in oestrogen
  • Increase leads to growth of granulosa cells
  • Increase levels

+VE FEEDBACK

44
Q

What happens during the mid follicular phase?

A
  • Rising oestrogen and inhibin –> -ve feedback –> low FSH
  • All FSH-dependent follicles undergo atresia
  • Graafin follicle emerges - it is able to grow under its own production of local oestrogens
45
Q

What happens om the late follicular phase?

A
  • Extremely high oestradiol (E2) from graafian follicle causes +ve feedback on GnRH/LH secretion
  • Leads to LH surge amd lesser FSH Surge
46
Q

What happens during the luteal phase?

A
  • Corpus luteum stimulated (has LH and FSH receptors) to produce oestrogen and progesterone
  • If there is no fertilisation, progesterone, E2 and inhibin exert a negative feedback on LH / FSH >>>> luteolysis and menstruation
47
Q

What is luteolysis?

A

Luteolysis is the structural and functional degradation of the corpus luteum

48
Q

What happens during the endometrial phase?

A

Endocrinology (15 decks)

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