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y1 lcrs endocrinology > 11 The Gonads I > Flashcards

11 The Gonads I Flashcards

1
Q

Q: What do the gonads develop from? How do they differ in males and females? Why?

A

A: undifferentiated structure

males-testes
females-ovaries

SRY gene on the Y chromosome triggers the differentiation into testes and in the absence of the gene, ovaries develop

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2
Q

Q: What are the function of gonads? (2) How do these 2 functions differ in males and females?

A

A: GAMETOGENSIS - Production of Gametes

  • Males = SPERMATOGENESIS (production of mature spermatazoa)
  • Females = OOGENESIS (production of ripe ova)

STEROIDOGENESIS - Production of Steroid Hormones

  • Males = ANDROGENS (and small amounts of oestrogen and progesterone)
  • Females = OESTROGENS and PROGESTERONES (and small amounts of androgens)
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3
Q

Q: Draw a graph showing how the number of germ cells in males changes over time. Describe. (5)

A

A: primordial germ cells proliferate, reaching large numbers around 6-7 million

males germ cells are spermatogonia

high number of spermatogonia remains throughout life (always produce)

spermatogonia have a dormant/quiescent period

they don’t become activated until puberty when spermatogenesis takes place

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4
Q

Q: Draw a graph showing how the number of germ cells in females changes over time. Describe. (6) What happens over a females reproductive life?

A

A: (females germ cells are called oogonia)

reach maximum levels of oogonia at 24 weeks - around 6-7 milion

don’t make any more after this-finite amount

process of ATRESIA commences = cells start degenerating and dying off

Atresia is rapid at first - by birth there are only about 2 million oogonia left

By puberty there are only about 400,000 oogonia left

By menopause the ovary has been depleted of these cells

only about 300-400 of these cells reach maturation and ovulation - very few are fertilised

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5
Q

Q: Outline spermatogenesis. (7) How long does it take? When does it start? why?

A

A: 1. start off with the germ cells in embryogenesis and they multiply and differentiate to produce spermatogonia which are DIPLOID = mitotic division

  1. spermatogonia divide by mitosis to produce either more spermatogonia or to produce primary spermatocytes (are also DIPLOID)
  2. Primary spermatocytes enter the first meiotic division to give secondary spermatoctyes which are HAPLOID
  3. Secondary spermatocytes enter second meiotic division to give spermatids (haploid)
  4. Spermatids then mature and differentiate into spermatozoa

This whole process takes around 70 DAYS
-puberty when gonadotrophins eg FSH and testosterone are released

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6
Q

Q: How does spermatogenesis change throughout life? (2)

A

A: Spermatogonia undergo differentiation and self-renewal; consequently, a pool of spermatogonia remains available for subsequent spermatogenic cycles
throughout life

Thus males normally retain some spermatogenic capability throughout life, producing 300-600 sperm/gm testis/second

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7
Q

Q: Outline oogenesis. (8)

A

A: 1. oogonia (diploid) then multiply to produce Primary Oocytes (mitotic division)

  1. As soon as the Primary Oocytes are formed they enter the first meiotic division -> BUT DOESN’T COMPLETE- STOPS AT PROPHASE and stays in that stage of development
  2. At this time, the oocytes form a layer of cells around them (primordial follicles - the oocytes are in a follicle)

This all occurs before birth - you have your primordial follicles with your oocytes in it before birth

  1. primary oocytes are dormant (stuck in that phase of meiosis) for the next 12-50 years (12= ~time taken to reach puberty, 50=~just before menopause)
  2. After 12 years (at puberty) some of the oocytes will be rescued (under the influence of FSH)=continue development - the last lot won’t be rescued until around menopause

// there is also a process of ATRESIA occuring-some of the cells are degenerating and start to die

  1. It isn’t until around the time of ovulation that they complete the first meiotic division to produce the Secondary Oocyte and a Polar Body

unequal distribution of the cytoplasm - one cell retains all the cytoplasm and the cells resources and the other daughter cells (the polar body) contains just the chromosomes and these cells will eventually die off

  1. The secondary oocyte enters the second meiotic division and it won’t complete that division until FERTILISATION
  2. If fertilised, it will produce the Ovum and the Second Polar Body

Ovum and Second Polar Body - again there is unequal distribution of cytoplasm - the ovum retains all the cells resources (and so becomes one of the largest cells in the body) - the Second Polar Body will eventually disintegrate

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8
Q

Q: Where do the testes develop from? When? What happens if this does not occur? Describe their environment. What occurs in the testes and specifically where? How does puberty change the testes and males? (3) as a result of?

A

A: The testes develop in the abdomen but descend into the scrotum just before birth

If testes don’t descend it could lead to infertility

The scrotum is 2-3 degrees cooler than core temperature - which is critical for spermatogenesis

Spermatogenesis takes place in the SEMINIFEROUS TUBULES of the testes

increased testosterone=

  • lead to development of secondary sexual characteristics
  • testes will grow
  • spermatotubules and seminiferous tubules will mature= spermatogenesis can take place
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9
Q

Q: Draw and label a diagram of the testes in terms of spermatogenesis. (5)

A

A: coiled seminiferous tubules are lined by layers of spermatogonia and layers of Sertoli cells

spermatozoa produced travel down to the collection in the Rete Testis

where they are concentrated and drained by the Vasa efferentia into the epididymis where they are stored

In the epididymis, nutrients are secreted for them - they mature in here and attain their motility

Then they are propelled via the vas deferens (surrounded by smooth muscle) via the urethra

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10
Q

Q: Draw a cross section of the seminiferous tubules and label. (4) How are the spermatozoa protected? Problem (1) and solution (4)? What else is needed for a vital event to occur? Where are they?

A

A: -lumen containing spermatozoa= maintains environment where they won’t be attacked by immune system

  • surrounded by elongated sertoli cells = connected at the periphery by tight junctions
  • layer of spermatogonia
  • sheath of connective tissue around outside

tight junctions between sertoli cells forms a blood-testis barrier which keeps out large proteins such as antibodies = Therefore, it protects spermatozoa from immune reactions

BUT spermatogonia also need a way to enter from the layer outside the sertoli cells

  • spermatogonia have a special mechanism by which they can get through the barrier
  • they move into the Sertoli cells and they are enclosed in the cytoplasm of the Sertoli cells where spermatogenesis actually takes place
  • Sertoli cells provide structural support for spermatogonia and provide metabolic support as well
  • As these cells develop they towards the lumen and are released into the lumen

Leydig cells contain enzymes so that they can make and secrete testosterone
-It is important that the Leydig cells are nearby because testosterone is needed for spermatogenesis to take place

leydig cells are found in clusters between tubules

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11
Q

Q: What are the 2 main types of testicular cells? (4,3)

A

A: SERTOLI CELLS

  • form the seminiferous tubules
  • synthesise FSH and androgen receptors and therefore respond to FSH + Androgen
  • in response to FSH produce various molecules including INHIBIN
  • are intimately associated with developing spermatocytes = provide metabolic support and protection

LEYDIG CELLS
- lie outside seminiferous tubules (have close important connection to sertoli cells)
- synthesise LH receptorsa and therefore respond to LH
- In response to LH are the principal source of testicular
androgens (mainly testosterone)= diffuse into sertoli cells = vital for spermatogenesis

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12
Q

Q: What produces inhibin? In response to? What are the effects on inhibin? (2)

A

A: sertoli cells, FSH production

feeds back on the axis and inhibits FSH secretion and cause production of androgen binding proteins]

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13
Q

Q: In females, where does gametogenesis start? What does this structure contain? (4)

A

A: Gametogenesis starts off in the ovaries

he ovaries will contain

  • follicles embedded in the ovarian stroma = follicles at all different stages of development but all contain oocyte and at least one layer of cells around
  • some follicles will be undergoing atresia
  • graffian Follicle - this follicle has reached its maximum size and is ready for ovulation
  • remnant of corpus luteum (from previous cycle- following ovulation, the remaining follicle is transformed into this)
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14
Q

Q: What’s the structure of a graffian follicle?

A

A: -ovum inside= surrounded by granulosa cells which are attached to inner wall

  • around= follicular fluid
  • granulosa cells
  • thecal cell (outside)
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15
Q

Q: What does steroidogenesis start from? What determines the hormone produced? How do adrenals and gonads differ in terms of the steroid produced? (3,3)

A

A: Steroid are all synthesised from CHOLESTEROL

The enzymes present in the tissue determines the hormones produced

ADRENALS = mineralocorticoids + glucocorticoids + (small amounts of) androgens

GONADS = progestogens (C21) + androgens (C19) + oestrogens (C18)

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16
Q

Q: What are the common steps of steroidogenesis in the adrenals and gonads? (4)

A 
A: CHOLESTEROL -> side chain cleaved ->
PREGNENOLONE ->
PROGESTERONE ->
17-OH PROGESTERONE ->
ANDROSTENEDIONE
17
Q

Q: In terms of steroidogenesis, what do the adrenals specifically contain? what does this allow? (2)

A

A: - ONLY the adrenals contain 21-hydroxylase enzyme that can convert progesterone to deoxycorticosterone and eventually to aldosterone
- Or the same enzyme can convert 17-hydroxyprogesterone to 11-deoxycortisol and down to cortisol

18
Q

Q: In terms of steroidogenesis, what do the testes specifically contain? (2) what do they allow? What do ovaries do?

A

A: - primarily the testes that contain the 17-hydroxysteroid dehydrogenase enzyme which converts androstenedione to testosterone
- dihydrotestosterone also made by 5 alpha reductase

  • ovaries aromatise androstenedione and testosterone in to oestrone which can then be converted to 17b-oestradiol
19
Q

Q: What does the control of reproduction involve? (3) What does it cause in females? Describe. (4)

A

A: hypothalamus, the pituitary and the gonads

This is so controlled in the female that one egg is released every month- reproductive cycle in females is cyclic

everytime ovulation takes place, the endometrium is prepped for pregnancy but if fertilisation doesn’t occur then menstruation occurs

20
Q

Q: How long is the menstrual cycle? When does is it historically taken to begin? What is the important reproductive event and when does it occur?

A

A: Usually taken as lasting approximately 28 days (but can last from 20 to 35+ days)

first day of menstruation (loss of blood and cellular debris from necrotic uterine epithelium)

OVULATION (release of the ripe ovum) which occurs around day 14

21
Q

Q: What are the 2 cycles of the menstrual cycle? Outline the sequence of each (3,2).

A

A: TWO related events:

Ovarian Cycle

  1. Follicular Phase (first half) = follicles grow and mature
  2. Ovulation (mid-cycle)
  3. Luteal Phase (second half)

Endometrial Cycle (uterus- lining contains epithelial layer of cells)

  1. Proliferative = E gets thicker
  2. Secretory = E becomes secretory
22
Q

Q: How are the 2 cycles of the menstrual cycle linked?

What is the main hormone produced by phase 1 of the ovarian cycle? What does it act on? Effects? (4) Result? (3)

A

A: (1ovarian) Follicular Phase
= main hormone produced=oestrogen (17beta-oestrodiol)

oestrogen acts on endometrium and causes the effects that we see in

(1endometrial) proliferative phase

  • proliferation of the endometrium
  • increase in mitosis
  • increase in the progesterone receptors (which acts later in the cycle)
  • an increase in oestrogen receptors

The endometrium gets thicker, the glands get bigger and the blood vessels get longer

(2ovarian) Ovulation (mid-cycle)

23
Q

Q: What is the endometrium?

A

A: lining of the uterus and contains a superficial epithelial layer and a deeper stromal layer

24
Q

Q: How are the 2 cycles of the menstrual cycle linked?

What are the main hormones produced by phase 3 of the ovarian cycle? What do they induce/cause? (2) Describe the actions of one of the hormones. (2) Result?

A

A: (2ovarian) Ovulation (mid-cycle)

(3ovarian) Luteal Phase (second half)

In the luteal phase, the hormones produced are progesterone and 17b-oestradiol

  • The effect that these have is to induce (2endometrial) Secretory phase = E becomes secretory
  • reduce gonadotrophin release

Progesterone reverses the effects of oestrogen - it reduces the proliferation that oestrogen causes by reducing oestrogen receptors

Progesterone also increases the secretory activity of the cells in the myometrium (middle layer of the uterus lining)

-glands become wider and produce various substances which make the environment suitable for implantation to occur

25
Q

Q: Draw a graph showing how hormone concentrations of 4 hormones varies during the menstrual cycle. Divided into? Days? What occurs mid cycle? When does menstruation occur?

A

A: REFER

LH
FSH
17beta-oestrodiol (main oestrogen)
progesterone

REPRESENTS ENDOMETRIAL CYCLE:
The cycle can be divided into the follicular phase (1st half) and the luteal phase (2nd half) - it lasts about 28 days and ovulation occurs mid-cycle

Menstruation occurs in the first 5 days of the cycle

26
Q

Q: Describe what happens during the menstrual cycle in terms of hormone levels and structural changes:

0-5days (3), 
6-13days (3),
day13 (3),
day14 (1),
15-22days (4),
23-28days (2)
28 continued (5).
A

A: 0-5 days:

  • FSH levels are slightly raised at the beginning
  • this small increase in enough to rescue the dormant follicles so they continue their development
  • follicles start growing and as they grow they start producing 17b-oestradiol

6-12 days:

  • The 17b-oestradiol has a negative feedback effect on gonadotrophin secretion
  • As these follicles grow, one of them is selected as the DOMINANT follicle and the others will undergo atresia
  • The dominant follicle will produce large amounts of oestrogen

day 13:

  • If oestrogen levels are high enough for long enough (36 hours)
  • instead of producing negative feedback effect it will switch to a positive feedback effect which stimulates a SURGE OF GONADOTROPHINS (LH and FSH)
  • At the time of the gonadotrophin surge, there might be a small surge of 17-hydroxyprogesterone which adds to the positive feedback effect that oestrogen has

day 14:
-This surge of gonadotrophins stimulates ovulation

15-22 days:

  • After ovulation, the empty follicle is transformed into the corpus luteum
  • which continues to produce 17b-oestradiol and produces large amounts of progesterone
  • LUTEAL PHASE - PROGESTERONE is the dominant hormone
  • Effect of oestrogen and progesterone together is a negative feedback effect on the gonadotrophins - the gonadotrophin levels become low

23-28 days:

  • If fertilisation does NOT take place - oestrogen and progesterone levels begin to FALL = no longer supporting the endometrium any more
  • As a result of the decrease in progesterone and oestrogen, the negative feedback is reduced so FSH levels start to rise again so you get back to the start of the cycle

28 continued: MENSTRUATION

  • get changes the endometrium
  • vasospasm in some blood vessels
  • necrosis of the tissue
  • contraction of the muscle
  • loss of the tissue with the blood
27
Q

Q: What can be noticed after ovulation? Why?

A

A: You can measure an increase in body temperature after ovulation

One of the effects of progesterone is that it has an effect on body temperature

28
Q

Q: What do our ovaries contain? When do they develop? stage? What is required for further development? What happens without? What happens with? (2)

A

A: -We have follicles with the oocyte that is stuck in the early stage of meiosis

  • The follicle will develop over embryonic life and will develop to this pre-antral stage
  • Up until the pre-antral stage, gonadotrophins are NOT needed
  • To develop any further requires FSH (to get to early-antral stage)
  • If FSH isn’t at a high enough level to continue the development they will undergo atresia
  • They will develop into Early-Antral Follicle (when exposed to sufficient FSH)
  • Under the influence of FSH, the follicles will get bigger until they eventually get to their maximum size which is the Graffian Follicle which is ready for ovulation

At this time, the LH surge occurs and causes rupture of the follicle and release of the egg

After ovulation, the follicle is transformed into a corpus luteum which continues to secrete oestrogen and progesterone in the Luteal phase of the cycle

The surge of LH will stimulate the egg to complete the first meiosis

29
Q

Q: Describe the ovarian cycle (5- 2,3,2,2,3).

A

A: 1. We have follicles with the oocyte that is stuck in the early stage of meiosis
- follicle developed over embryonic life and will develop to this pre-antral stage

Up until the pre-antral stage, gonadotrophins are NOT needed

  1. To develop any further requires FSH (to get to early-antral stage) - released post puberty
    - If FSH isn’t at a high enough level to continue the development they will undergo atresia
    - When exposed to sufficient FSH= develop into Early-Antral Follicle (when exposed to sufficient FSH)

((The outer layers of the follicle are the Thecal cells and the inner layer are the Granulosa cells))

  1. Under the influence of FSH, the follicles will get bigger
    - until they eventually get to their maximum size which is the Graffian Follicle = ready for ovulation
  2. at this time, the LH surge occurs and causes rupture of the follicle and release of the egg
    - The surge of LH will stimulate the egg to complete the first meiosis => secondary oocyte
  3. After ovulation, the follicle is transformed into a corpus luteum
    - granulosa cells in particular will proliferate and enlarge and become invaded by blood vessels
    - > now have capacity to secrete lots of progesterone and oestrodiol (luteul phase)
30
Q

Q: When does the ovarian cycle occur? Describe.

A

A: spontaneously through reproductive life

follicles are selectively stimulated to develop (one group at a time)

31
Q

Q: Hormone production during the ovarian cycle.

What receptors do you have in the follicle? (2) Which hormones bind and what are the effects?

How does this change after ovulation?

A

A: Thecal Cells - outer - LH Receptors

Granulosa Cells - inner - FSH Receptors

In response to LH stimulation, the Thecal Cells will start steroid hormone synthesis and produce the Androgens
- Thecal cells do NOT have the aromatase enzymes to convert androgens to oestrogen

The Granulosa cells have FSH Receptors and stimulation of these cells will stimulate the aromatase enzyme which convert these androgens into oestradiol

After ovulation, the corpus luteum is formed

The Thecal cells and Granulosa cells will still be stimulated by LH and FSH and they will continue to produce large amounts of 17b-oestradiol and Progesterone

32
Q

Q: What’s the dominant influence of endometrium proliferation? secretion?

A

A: oestrodiol

progesterone (corpus luteum makes a lot)

33
Q

Q: How do glands and the endometrium change during the menstrual cycle? (4,4)

A

A: glands:
1. straight ->
2. enlarge/coil with increased blood supply ->
OVULATION
3. secretes glycoproteins, mucopolysaccharides, mucosa engorged with blood ->
4. shed

endometrium:
1. thin
2. thickens (mitosis)
OVULATION
3. becomes secretory
4. becomes necrotic and is shed

y1 lcrs endocrinology (19 decks)

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