Endocrinology 10 - The Gonads I Flashcards

1
Q

What are the function of the gonads?

A
  1. Gametogenesis (production of gametes)
    - Males = Spermatogenesis.
    - Females = Oogenesis.
  2. Steroidogenesis (production of steroid hormones)
    - Males = Androgens (small amounts of oestrogen + progesterone).
    - Females = Oestrogen + progesterone (small amounts of androgen).
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2
Q

When are germ cells activated? Where do male and female germ cells derive from?

A
  1. They are activated during embryogenesis where germ cells proliferate reaching around 6-7 million.
  2. Male germ cells are called spermatogonia and female germ cells are called oogonia.
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3
Q

Describe spermatogonia levels in males throughout life.

A

During childhood, spermatogonia are dormant and are only activated during puberty. Spermatogonia levels remain high throughout life in males.

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4
Q

Describe oogonia levels in females throughout life.

A
  1. Oogonia levels reach a maximum at 24 weeks, after this no more oogonia are produced so there are only a finite number of eggs.
  2. The number of oogonia decrease (atresia) throughout life, rapidly at first.
  3. At menopause the ovary is depleted of oogonia.
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5
Q

What is Atresia?

A

When the cells start degenerating and dying off.

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6
Q

Explain the process of spermatogenesis.

A
  1. Germ cells in embryogenesis multiply and differentiate into spermatogonia (DIPLOID).
  2. During puberty = high levels of FSH + testosterone cause spermatogonia to divide by mitosis - either more spermatogonia or primary spermatocytes (DIPLOID).
  3. Primary spermatocytes enter 1st meiotic division = Secondary spermatocytes (HAPLOID).
  4. Secondary spermatocytes enter 2nd meiotic division = spermatids.
  5. Spermatids mature and differentiate into spermatozoa.
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7
Q

Explain the process of oogenesis.

A
  1. Germ cells multiply to produce oogonia (DIPLOID).
  2. Oogonia multiply to produce primary oocytes (DIPLOID).
  3. Primary oocytes enter 1st meiotic division, however halted at prophase = form primordial follicles.
  4. Primary oocytes are dormant for 12-50 years - atresia takes place as well.
  5. When puberty starts, some primary oocytes will be rescued by increased levels of FSH (ovulation) = secondary oocytes + polar body.
  6. Secondary oocyte enters 2nd meiotic division and will only complete it during fertilization = ovum + polar body.
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8
Q

What is a polar body?

A
  1. In female meiosis, there is an unequal distribution of cytoplasm.
  2. One cell retains all the cytoplasm and the cell resources and the other daughter cell only contains the chromosomes and will die off - this is the polar body.
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9
Q

Describe the journey of spermatozoa.

A
  1. Spermatogenesis takes place in the seminiferous tubules.
  2. Semiferous tubules are lined with layers of spermatogonia and sertoli cells.
  3. Spermatozoa travel down to Rete testis and they are concentrated and drained by the Vasa efferentia into the epididymis (highly coiled) where they are stored.
  4. In the epididymis, nutrients are secreted for them and they mature here.
  5. They are propelled by vas deferens (surrounded by smooth muscle) via the urethra.
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10
Q

Where do the testes develop?

A

They develop in the abdomen and descend into the scrotum just before birth.
The scrotum is 2-3 degrees cooler than core temperature = critical for spermatogenesis.

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11
Q

Describe the function of sertoli cells. (4)

A
  1. Sertoli cells line the seminiferous tubule and form tight junctions that prevent large proteins (e.g. antibodies) getting inside to the spermatozoa. This forms a blood-testis barrier.
  2. Sertoli cells also provide structural and metabolic support.
  3. Synthesize FSH and androgen receptors.
  4. Produce inhibin in response to FSH (negative feedback for FSH).
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12
Q

How do spermatogonia get through the sertoli cell layer?

A
  1. They are enclosed in the cytoplasm of the sertoli cells.
  2. Here they undergo spermatogenesis.
  3. As they develop, they move towards the lumen and are released into the lumen.
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13
Q

What are Leydig cells? (3)

A
  1. Leydig cells are located close to the seminiferous tubule.
  2. Produce LH receptors.
  3. They contain enzymes that allow them to synthesize and release testosterone in response to LH.
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14
Q

Where does oogenesis take place?

A

In the ovaries. The ovaries contain follicles at all stages of development (e.g. some will be undergoing atresia).

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15
Q

What is a graafian follicle?

A

A follicle which has reached its maximum size and is ready for ovulation.

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16
Q

Where are all the follicles embedded in?

A

In the ovarian stroma.

17
Q

What is corpus luteum?

A

What the follicle transforms into after ovulation.

18
Q

What are the steroids produced in the gonads? (3)

A
  1. Progesterone (C21).
  2. Androgens (C19).
  3. Oestrogens (C18).
19
Q

What are the similarities and differences between the production of steroids in the gonads and the adrenals?

A
  1. Similarities - the first 4 reactions in steroidogenesis are common in both adrenals and gonads.
  2. Differences - Only adrenals have 21-hydroxylase to produce deoxycorticosertone or 11-deoxycortisol.
    Gonads have 17-hydroxysteroid dehydrogenase that converts androsteronedione to testosterone.
20
Q

What is the process of dihydrotestosterone production?

A

Cholesterol => prognenolone => progesterone => 17-OH-progesterone => androstenedione => testosterone => dihydrotestosterone.

21
Q

What is the process of 17-beta-oestradiol production?

A

Cholesterol => prognenolone +> progesterone => 17-OH-progesterone => androstenedione => oestrone => 17-beta-oestradiol. (or testosterone => 17-beta-oestradiol).

22
Q

What are the 2 related events in the menstrual cycle?

A
  1. Ovarian cycle - follicular phase (first half) => ovulation (mid-cycle) => Luteal phase (second half).
  2. Endometrial cycle - proliferative => secretory.
23
Q

What does oestrogen do to the endometrium?

A
  1. It causes the proliferation of the endometrium.
  2. There is an increase in mitosis and increase in progesterone and oestrogen receptors.
  3. The endometrium gets thicker, blood vessels longer and glands get bigger.
24
Q

What is the main hormone of the luteal phase? And what are its effects? (3)

A

Progesterone is the main hormone of this stage although oestrogen is still produced as well.

  1. Decreases the proliferation that oestrogen caused.
  2. Increases secretory activity of the cells in the myometrium to make it more suitable for implantation.
  3. Reduces oestrogen receptors.
25
Q

Describe the variation hormones throughout the menstrual cycle.

A
  1. FSH slightly raised at beginning in order to rescue dormant follicles.
  2. Follicles grow and produce 17-beta-oestradiol.
  3. 17-beta-oestradiol has a negative feedback on gonadotrophins.
  4. One of the follicles are selected to be the dominant follicle = produces large amounts of oestrogen.
  5. High oestrogen levels (36hours) stimulates a surge of gonadotrophins (LH + FSH) = ovulation.
  6. After ovulation, empty follicle converts into corpus luteum = continues oestrogen and high progesterone production (Luteul phase)
  7. Oestrogen + progesterone give negative feedback for gonadotrophins - gonadotrophin level low.
  8. If fertilization does not occur, progesterone and oestrogen levels decrease = endometrium changes (vasospasm, necrosis and loss of tissue + blood = menstruation).
  9. Negative feedback on FSH reduced and hence FSH levels rise to the start of the cycle.
26
Q

What happens to the body temperature after ovulation?

A

Body temperature increases.

27
Q

Describe the development of the follicles in the ovaries.

A
  1. Follicle with oocyte stuck in early stage of meiosis.
  2. Follicle will develop over embryonic life into pre-antral stage (gonadotrophins not needed).
  3. FSH required for next step - develop into early-antral follicle.
  4. Under influence of FSH - selected follicle will grow into maximum size = graafian follicle (ready for ovulation).
  5. LH surge causes rupture of follicle and release of egg.
  6. After ovulation, follicle converted to corpus luteum.
  7. Surge of LH stimulates egg to complete first meiosis.
28
Q

How does the follicle produce oestrogen and progesterone?

A
  1. LH binds to Thecal cells.
  2. LH stimulates the synthesis of androgens by the thecal cells.
  3. Androgens diffuse into the inner cells called the granulosa cells.
  4. FSH binds to Granulosa cells and stimulate the aromatase enzyme = converts androgen to oestradiol.
  5. After ovulation, thecal and granulosa cells will continue to be stimulated by LH and FSH to produce oestrogen and high progesterone.
29
Q

How many oogonia are present at birth, puberty and at menopause? How many of these reach maturation and ovulation?

A
  1. Oogonia = 2 million, 400,000 and 0.

2. 300-400 reach maturation and ovulation.

30
Q

How long does the menstrual cycle last and when does ovulation occur?

A

Lasts 28 days roughly and ovulation takes place around day 14.

31
Q

What is the endometrium?

A

The lining of the uterus that contains a superficial epithelial layer and a deep stromal layer.

32
Q

What kind of receptors do thecal cells have?

A

LH receptors.

33
Q

What kind of receptors do granulosa cells have?

A

FSH receptors.

34
Q

What is the outer layer of the follicle made of?

A

Thecal cells.

35
Q

What is the inner layer of the follicle made of?

A

Granulosa cells.

36
Q

What is the dominant influence during the proliferative phase?

A

Oestradiol.

37
Q

What is the dominant influence during the secretory phase?

A

Progesterone.

38
Q

What happens during the secretory phase?

A
  1. Oestrogen and progesterone are secreted.
  2. Glands become secretory, dilate and produce large amounts of glycogen.
  3. Mucosa engorged with blood.
  4. Better environment for implantation to occur.
39
Q

What happens during the proliferative phase?

A
  1. Endometrium thickens.
  2. Mitosis of the glands become enlarged and coil.
  3. Blood vessels get longer.
  4. Increase in progesterone and oestrogen receptors.