Endo 9 - The gonads 1

Question 1

What are the functions of the gonads?

Answer 1

1. gametogenesis
   - spermatogenesis in males
   - oogenesis in females
2. steroidogenesis
   - males: lots of androgens, few progestogens/oestrogens
   - females: lots of oestrogen/progestogen, few androgens

Question 2

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

Answer 2

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

Question 3

What is the process by which oogonia degenerate and die?

Answer 3

Atresia

Question 4

Describe the steps in spermatogenesis.

Answer 4

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

Question 5

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

Answer 5

FSH release during puberty

Question 6

How long does the process of spermatogenesis take place?

Answer 6

70 days

Question 7

Describe the steps in oogenesis.

Answer 7

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 and become secondary oocytes + first polar body. If fertilisation takes place, they will complete the second meiotic division to form an ovum + second polar body.

Question 8

When is first meosis of oogenesis completed? What is its result ?

Answer 8

Just before ovulation

Result = secondary oocyte + first polar body

Question 9

What is required to complete the second meiotic division of oogenesis?

Answer 9

Fertilisation to give ovum

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 - they compose the seminiferous tubules.
The lumen of the seminiferous tubule is on the inside
Leydig cells are in between seminiferous tubules

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 as they synthesise LH receptors.
In response to LH they are the principal source of testicular androgens, mainly testosterone.

Question 13

How do spermatogonia pass through the Sertoli cell barrier?

Answer 13

They move into the Sertoli cells and are engulfed/enclosed in the cytoplasm of the Sertoli cells.
The Sertoli cells provide structural and metabolic support for the spermatogonia and help them develop. (spermatogenesis takes place inside the sertoli cells) 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 - in response to FSH produce various molecules like inhibin
Leydig Cells - LH receptor. Testosterone

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

What does the ovarian stroma consist of?

Answer 17

1. Primordial Follicles undergoing Atresia.
2. Graffian Follicles: A follicle ready for ovulation. It contains a maturing oocyte that is surrounded by fluid. 2 layers of cells surround the follicle: inner granulosa cells and outer thecal cells.
3. Remnants of the last corpus luteum (after ovulation).

Question 18

The menstrual cycle is composed of:

Answer 18

• > the ovarian cycle: follicular phase - ovulation - luteal phase
• > the endometrial cycle: proliferative phase (oestrogen)- secretory phase (progesterone) - menstruation

Question 19

Describe a whole menstrual cycle

Answer 19

The pituitary gland produces FSH. The concentration of the FSH increases.
Many follicles will develop in response to FSH (=Follicle Stimulating Hormone).
The Follicles will secrete oestrogen as they develop. –> 17beta-oetradiol –> stimulates the proliferative phase of the endometrial cycle. endometrium thickens and moistens
The oestrogen has a negative feedback on FSH.
Since FSH is inhibited, the follicles will stop producing oestrogen. They will undergo atresia.
However, one follicle will be dominant. It will have become independent of FSH.
The dominant follicle will develop further, continuing to produce oestrogen.
The oestrogen levels continue to rise.
High levels of oestrogen cause a ‘switch’ in the pituitary. There is no longer a negative feedback on FSH/LH; rather, there is a positive feedback.
This causes an LH surge, together with some FSH.
LH (=Luteinising hormone) causes Ovulation.
Progesterone is produced by the Corpus Luteum –> progesterone stimulates the secretory phase of the endometrial cycle –> production of glycogen and mucopolysaccharides, mucosa blood
Progesterone continues to rise.
This causes a negative feedback on FSH and LH (so their levels fall).
Since levels of FSH/LH fall, the progesterone levels fall as well. –> menstruation happens
The corpus luteum breaks down.
The falling levels of progesterone mean that there is less inhibition of gonadotrophins.
The pituitary gland produces FSH. The concentration of the FSH increases. The cycle restarts.

Question 20

What composes a follicule?

Answer 20

On the outside –> layer of thecal cells, then layer of granulosa cells then antral space then follicule surrounded by cells contained in that space
Follicule influenced by LH and FSH
Thecal cells produce androgens
Androgens stimulate the granulosa cells (which contain AROMATASE) to produce 17β- OESTRADIOL
After ovulation, the corpus luteum converts androgens to 17β- Oestradiol