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Endocrinology > Gonads 1 > Flashcards

Gonads 1 Flashcards

1
Q

What are the gonads in males and females?

A

Males: Testes
Females: Ovaries

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2
Q

Both gonads originate from the same undifferentiated structure, what determines differentiation into testes?

A

Genes on Y chromosome

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3
Q

What are the 2 functions of the gonads?

A

Production of gametes for reproduction (gametogenesis)

Production of steroid hormones (steroidogenesis)

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4
Q

Gametogenesis in males and females

A

Males: Spermatogenesis (mature spermatozoa)
Females: Oogenesis (ripe ova)

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5
Q

Steroidogenesis in males and females

A

Males: Androgens (+ small amounts oestrogen and progestogens)
Females: Oestrogens and Progestogens (+ small amounts of androgens)

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6
Q

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

A 
Maximum (24 weeks gestation): ~7 million
Birth: 2 million 
Puberty: 500,000 
~300 mature eggs released 
Menopause: 0
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7
Q

Gametogenesis in men

A

Begins at puberty
High levels maintained through life
300-600 sperm/gm testis/ second

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8
Q

What is the process by which oogonia degenerate and die?

A

Atresia

Occurs rapidly before birth and continues slowly through life

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9
Q

Describe the steps in spermatogenesis.

A

Germ cells (44+XY) divide to produce spermatogonia. Spermatogonia remain dormant until puberty where there is division of spermatogonia to produce more spermatogonia and primary spermatocytes (still diploid).
Primary spermatocytes enter 1st meiotic division to form secondary spermatocytes (haploid).
Secondary spermatocytes enter 2nd meiotic division to form spermatids.
Spermatids mature into spermatozoa. (22X or 22Y)

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10
Q

Describe the steps in oogenesis.

A

Germ cells (44XX) divide to produce oogonia.
Oogonia divide mitotically to produce primary oocytes (diploid).
Primary oocytes enter the 1st meiotic division straight away but are halted in prophase of the 1st meiotic division = “miotic arrest”
The oocytes are inside primordial follicles, some enter process of atresia
Remain dormant for 12-50 years.
At puberty complete 1st meiotic division to form secondary oocytes (22X) and a polar body
Secondary oocytes complete 2nd meiotic division at fertilisation to produce ovum and 2nd polar body

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11
Q

What is meant by the formation of a secondary oocyte and a polar body?

A

1 daughter cell retains cytoplasm and all resources

Other cell is just membrane and chromosomes (polar body)

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12
Q

Where do the testes develop and where do they descend?

A

Develop in abdomen

Descend into scrotum just before birth

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13
Q

What happens at puberty in males?

A

Increased secretion of gonadotrophin and testosterone
Testosterone causes secondary sexual characteristics and causes testes and seminiferous tubules to mature
- spermatogenesis can occur

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14
Q

Where do sperm drain, stored and mature?

A

Epididymis

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15
Q

What are sperm expelled via?

A

Vas deferens

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16
Q

Describe the structure of seminiferous tubules.

A

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

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17
Q

Describe the layer of elongated sertoli cells

A

Connected at periphery by tight junctions
Creates blood:testes barrier so large molecules can’t enter seminiferous tubules
Spermatogonia can cross the barrier
Synthesise FSH and androgen receptors
Respond to FSH

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18
Q

Where does spermatogenesis occur?

A

In sertoli cells

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19
Q

What is outside seminiferous tubules?

A

Leydig cells
Synthesise LH receptors
In response to LH are the principal source of testicular androgens (mainly testosterone)

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20
Q

Why is close connection between cells in the testes vital?

A

Intra-testicular testosterone levels are 50-100X higher than circulating testosterone levels.
Spermatogenesis won’t take place without this raised level of androgen in the testes.

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21
Q

What is inhibin and what cells produce this?

A

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

22
Q

Ovaries contain follicles formed before birth. Describe follicles

A

Follicles contain oocyte and at least 1 layer of cells
Follicles at different stages of development (some undergoing atresia)
Follicles embedded in stroma

23
Q

What is a Graafian follicle?

A

The maximum size of a maturing follicle

Ready for ovulation

24
Q

What is the ovum surrounded by?

A

Layers of granulosa cells and thecal cells

Large fluid filled space

25
Q

What are all steroid hormones produced from? What does type of hormone depend on?

A

Cholesterol (27C)

Hormone produced depends on which enzymes are present

26
Q

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

A

The 1st 4 steps:
cholesterol –> pregnenolone –> progesterone
–> 17 hydroxyprogesterone –> androstenedione

27
Q

What enzyme in the testes converts androstenedione to testosterone?

A

17 hydroxysteroid dehydrogenase

28
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

29
Q

Potency of testosterone and dihydrotestosterone

A

Testosterone is a potent androgen

Dihydrotestosterone is even more potent

30
Q

Where does the 5 alpha reduction of testosterone occur and what does it produce?

A

Dihydrotestosterone

Mainly occurs in epididymis, prostate or peripheral tissue

31
Q

Describe 3 characteristics of the Menstrual cycle

A

Lasts ~28 days
Begins on 1st day of menstruation (loss of blood and cellular debris from necrotic uterine epithelium)
Reproductive event of OVULATION (release of ripe ovum) occurs ~day 14

32
Q

What are the 2 cycles within the menstrual cycle?

A 
OVARIAN CYCLE (ovary)
ENDOMETRIAL CYCLE (endometrium is the lining of the uterus)
33
Q

What are the phases of the ovarian cycle?

A

Follicular Phase –> Ovulation –> Luteal Phase

34
Q

What are the phases of the endometrial cycle?

A

Proliferative phase –> Secretory Phase

35
Q

Describe the broad stages of the menstrual cycle including the follicular phase, proliferative phase, ovulation, luteal phase and secretory phase

A
  1. In follicular phase, dominant influence= 17 Beta-oestradiol: stimulates proliferation of endometrium
  2. Ovulation occurs mid cycle
  3. Luteal phase:
    Progesterone and 17 Beta-oestradiol produced
    Progesterone has dominant effect:
    Reduces oestrogens proliferative effects
    Increases secretive activity of endometrium
36
Q

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

A

Oestrogen increases mitosis, increases progesterone receptors and increases oestrogen receptors.
It stimulates thickening of the endometrial lining.

37
Q

What are the effects of progesterone in the secretory phase?

A

Reduces the proliferation caused by oestrogen
Increases secretory activity of the endometrium (make endometrium suitable for implantation when blastocyst arrives in uterus)

38
Q

Describe the menstrual cycle.

A

Slightly elevated level of FSH at the start of the cycle:
Stimulates a cohort of follicles to start developing
Follicles start producing 17 Beta-oestradiol which inhibits gonadotrophins (FSH and LH- levels start to decline)
1 follicle selected to become dominant - others undergo atresia
Continues growing, produces lots of Oestrogen
When it has produced enough oestrogen, triggers positive feedback effect and stimulates a surge of gonadotrophins
Surge in LH stimulates ovulation, egg is released
Empty follicle becomes a corpus luteum and produces 17 beta-oestradiol and progesterone, which together have a negative feedback effect on gonadotrophins
If fertilisation doesn’t take place, oestrogen and progesterone levels fall, negative feedback on FSH and LH decreases, so levels rise again and another cohort of follicles is selected to start developing

39
Q

What happens to basal body temperature after ovulation?

A

Basal body temperature increases slightly due to secretion of progesterone in 2nd half of cycle.

40
Q

What stage do the follicles develop to in embryonic life?

A

Pre-antral stage

41
Q

What is the next step in embryonic life for pre-antral follicles and what is required to stimulate this step?

A

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

42
Q

What are the 2 cell types surround the ovum once the follicles start growing and developing? 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
43
Q

What happens to the mature Graafian follicle after ovulation?

A

After ovulation, follicle transforms into corpus luteum. Granulosa cells proliferate and are invaded by blood vessels, continue producing oestrogen and produce A LOT of progesterone for the next 14 days.

44
Q

Why can LH only stimulate steroidogenesis in thecal cells up to the androgen cells? What happens to the androgens?

A

As don’t have aromatase in them

Androgens diffuse into inner granulosa cells which have aromatase and FSH receptors.

45
Q

What is the only cell in the female to express FSH receptors?

A

Granulosa cells

46
Q

What happens when androgens enter granulose cells?

A

FSH receptor activates aromatase and causes androgens to be used to synthesise 17 Beta- Oestradiol

47
Q

What happens if fertilisation doesn’t occur?

A

Oestrogen and progesterone levels decline due to low levels of FSH and LH
Blood vessels constrict
Ischaemia in tissue and tissue becomes necrotic.
Endometrium releases prostaglandins: stimulates underlying muscle layer (Myometrium) to contract, helping to shed necrotic tissue in menstruation.

48
Q

Describe the state of the endometrium in:

  1. Proliferative phase
  2. Ovulation
  3. Secretory phase
  4. Menstruation
A
  1. Proliferative phase: Thin
  2. Ovulation: Thickens (mitosis)
  3. Secretory phase: Becomes secretory
  4. Menstruation: Becomes necrotic and is shed
49
Q

Describe the state of the glands in:

  1. Proliferative phase
  2. Ovulation
  3. Secretory phase
A
  1. Proliferative phase: Straight
  2. Ovulation: Enlarge, coil: increased blood supply
  3. Secretory phase: Secrete glycogen and mucopolysaccharides, mucosa engorged with blood
50
Q

Which hormone is dominant in the proliferative and secretory phases of the menstrual cycle?

A

Proliferative: Oestrogen
Secretory: Progesterone (and oestrogen)

Endocrinology (12 decks)

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