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.

A

Germ cells divide to produce spermatogonia. Spermatogonia remain dormant until puberty where a rise in FSH triggers division of spermatogonia to produce more spermatogonia and primary spermatocytes (still diploid). Primary spermatocytes enter first meiotic division to form secondary spermatocytes(haploid). Secondary spermatocytes 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

Germ cells divide to produce oogonia. Oogonia divide mitotically to produce primary oocytes (diploid). Primary oocytes enter the first meiotic division straight away but are halted in prophase of the first meiotic division. 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. 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. 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 (nutrients are secreted here and they attain their motility). 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 LH receptors and in response to this it produces 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. The Sertoli cells provide structural and metabolic support for the spermatogonia and help them develop. They then enter the lumen.

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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

17
Q

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

A

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

18
Q

What enzyme in the testes converts androstenedione to testosterone?

A

17 hydroxysteroid dehydrogenase

19
Q

which reactions happen in the adrenals ONLY?

A

Adrenals only contain 21-hydroxylase enzyme that can convert progesterone to deoxycorticosterone and then to aldosterone.
-same enzyme can convert 17-hydroxyprogesterone to 11-deoxycortisol and down to cortisol

Adrenals make aldosterone and cortisol

20
Q

What do the ovaries do to androstenedione and testosterone?

A

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

21
Q

What are the phases of the ovarian and endometrial cycle?

A

Ovarian - Follicular –> (ovulation) –> Luteal Endometrial: Proliferative –> Secretory

22
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.

23
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.

24
Q

Describe the menstrual cycle.

A

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. The follicles start producing 17 beta oestradiol which inhibits gonadotrophins (FSH and LH) One follicle becomes dominant - others undergo atresia 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 Empty follicle becomes a corpus luteum and produces 17 beta oestradiol and progesterone, which has a negative feedback effect on gonadotrophins If fertilisation doesn’t take place, oestrogen and progesterone levels fall and negative feedback on FSH and LH decreases so levels rise again.

25
Q

What other effect does progesterone have on the body?

A

Increases body temperature

26
Q

What stage do the follicles develop to in embryonic life?

A

Pre-antral stage

27
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.

28
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 (oestradiol) from progesterone using aromatase enzyme