Gonads 1

Question 1

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

Answer 1

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

Question 2

What is the process by which oogonia degenerate and die?

Answer 2

Atresia

Question 3

Describe the steps in spermatogenesis.

Answer 3

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 oocytes (haploid). Secondary oocytes enter second meiotic division to form spermatids. Spermatids mature into spermatozoa.

Question 4

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

Answer 4

FSH release during puberty

Question 5

How long does the process of spermatogenesis take place?

Answer 5

70 days

Question 6

Describe the steps in oogenesis.

Answer 6

Begin with oogonia from division of germ cells. 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.

Question 7

What is produced after the first meiotic division is complete?

Answer 7

Secondary oocyte + first polar body

Question 8

What is required to complete the second meiotic division?

Answer 8

Fertilisation

Question 9

What is produced after the second meiotic division is complete?

Answer 9

Ovum + second polar body

Question 10

Describe the passage of sperm from production to release.

Answer 10

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.

Question 11

Describe the structure of seminiferous tubules.

Answer 11

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

Question 12

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

Answer 12

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

Question 13

How do spermatogonia pass through the Sertoli cell barrier?

Answer 13

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.

Question 14

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

Answer 14

Sertoli Cells - FSH receptor and Androgen receptor

Leydig Cells - LH receptor

Question 15

What is inhibin and what cells produce this?

Answer 15

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

Question 16

What is a Graffian follicle?

Answer 16

The maximum size of a maturing follicle

Question 17

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

Answer 17

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

Question 18

What enzyme in the testes converts androstenedione to testosterone?

Answer 18

17 hydroxysteroid dehydrogenase

Question 19

What do the ovaries do to androstenedione and testosterone?

Answer 19

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

Question 20

What are the phases of the ovarian and endometrial cycle?

Answer 20

Ovarian - Follicular –> (ovulation) –> Luteal

Endometrial –> Proliferative –> Secretory

Question 21

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

Answer 21

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

Question 22

What are the effects of progesterone in the secretory phase?

Answer 22

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

Question 23

Describe the menstrual cycle.

Answer 23

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.

Question 24

What other effect does progesterone have on the body?

Answer 24

Increases body temperature

Question 25

What stage do the follicles develop to in embryonic life?

Answer 25

Pre-antral stage

Question 26

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

Answer 26

They develop to early antral follicles - stimulation is FSH

If FSH isn’t high enough, they undergo atresia.

Question 27

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

Answer 27

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