Endocrinology 10 - The Gonads 1 & 2

Question 1

What are the functions of the gonads?

Answer 1

• In males, undergo spermatogenesis and produce androgens (as well as oestrogens and progestogens)
• In females, oogenesis as well as produce oestrogen, progestogen (and androgens)

Question 2

Describe the production of spermatogonia throughout life.

Answer 2

• Sperm is produced to 6 million before birth

- This number remains relatively constant throughout life

Question 3

Describe the production of oogonia throughout life

Answer 3

• All of the eggs are produced in the foetus

- They then rapidly decrease in number until menopause

Question 4

Describe the stages of spermatogenesis

Answer 4

• Germ cell to spermatogonia
• Mitotic division to primary spermatocytes. Some are recycled to reform spermatogonia.
• First meiotic division to seconday spermatocytes
• Second meiotic division to spermatids
• Mature to spermatozoa (22x or 22y)

Question 5

When does gametogenesis begin in males?

Answer 5

At puberty, following FSH stimulation.

Question 6

Describe the stages of oogenesis.

Answer 6

• Germ cell to oogonia
• Mitotic division to primary oocytes
• First meiotic division begins but does not end, there is meiotic arrest until puberty or even for 50 years
• At puberty, secondary oocytes and the first polar body are made
• Second meiotic division makes the ovum and second polar body (only at fertilisation)

Question 7

What are polar bodies?

Answer 7

• They are formed because the oocyte does not divide evenly
• They are non-functioning egg cells that cant be fertilised
• They are smaller, haploid cells, which get less of the cytoplasm than the ovum

Question 8

Describe the anatomy of the testes

Answer 8

• The many coiled semineferous tubules lead to the Rete testis
• Sperm travels down the epididymis from the Vasa efferentia to the vasa deferens
• The vasa deferens is surrounded by smooth muscle, so ejaculation to the urethra can occur

Question 9

Describe the anatomy of the seminiferous tubules of the testes.

Answer 9

• The outside contains spermatogonia
• Spermatozoa are in the lumen
• Sertoli cells form the seminiferous tubules
• The leydig cells are found around the outside of seminiferous tubules

Question 10

Describe the function of the sertoli cells

Answer 10

-Synthesise FSH and androgen receptors
in response to FSH
- Produce various molecules including INHIBIN
- Are intimately associated with developing spermatocytes

Question 11

Describe the function of Leydig cells

Answer 11

• Synthesise LH receptors

- In response to LH are the principal source of testicular androgens (mainly testosterone)

Question 12

Describe the structure of the ovaries

Answer 12

• The graafian follicle contains the ovum, granulosa cells and thecal cells
• There are many follicles undergoing atresia (unfertilised)
• Ovarian stroma is the fluid
• There is a corpus luteum

Question 13

Describe the pathway of synthesis of androgens, oestrogen and progesterone

Answer 13

• Progesterone is produced first
• Then testosterone
• Testosterone can be converted to dihydrotestosterone (more potent than testosterone) or oestradiol (main human oestrogen)

Question 14

How is testosterone transported around the body?

Answer 14

• In the blood via sex hormone binding globulin (60%)
• 38% in the blood bound to albumin
• 2% in the blood is bioactive
• In the seminiferous fluid, it is carried by androgen binding globulin

Question 15

List the principle actions of androgens in the fetus

Answer 15

• Development of male genitalia

- Fetal growth (by acting on other hormones)

Question 16

List the principle actions of androgens in the adult.

Answer 16

• Spermatogenesis
• Growth and development of male genitalia and secondary sex characteristics
• Protein and bone anabolism
• Male sexual behaviour
• Growth spurt at puberty

Question 17

Define an oestrogen

Answer 17

Any substance which induces mitosis in the endometrium

Question 18

What is the main human oestrogen?

Answer 18

17 beta-oestradiol

Question 19

List the effects of oestrogen

Answer 19

• Stimulates mitosis of the endometrium
• Triggers LH surge resulting in ovulation
• Growth of breasts
• Feedback on gonadotroph releasing horomone
• Stimulates osteoblasts (results in osteoporosis after menopause)
• Metabolic actions
• Female behaviors

Question 20

Define progestogen

Answer 20

Any substance (natural or synthetic) inducing secretory changes in the endometrium

Question 21

What is the main progestogen in humans?

Answer 21

Progesterone

Question 22

What are the effects of progestogens?

Answer 22

• Stimulates secretory activity in the endometrium and cervix
• Negative feedback
• Increases basal body temperature
• Growth of breast

Question 23

Describe the feedback in the hypothalamo-pituitary-testicular axis

Answer 23

• Leydig cell produces testosterone (stimulated by LH), which performs negative feedback
• The sertoli cell produces inhibin (stimlated by FSH) which perfoms negative feedback
• Feedback is on hypothalamus (makes GnRH) and anterior pituitary (makes LH and FSH)

Question 24

Describe the process that occurs in the early follicular phase.

Answer 24

• New follicles begin growing under the influence of FSH

- These follicles begin to produce oestrodiol. As levels are only low, LH and FSH remains to stimulate growing

Question 25

What happens during the early mid follicular phase of the menstrual cycle?

Answer 25

- Oestradiol levels increase due to follicles growing, causing proliferation in the endometrium, as well as increasing the number of receptors for oestrogen and progesterone in the uterus - This causes one of the follicles to become larger - This follicle begins to produce large amounts of oestrogen, causing positive feedback - granulosa cells surrounding it are stimulated to produce more oestrogen. - LH and FSH are reduced by the high oestrogen levels, which results in only the graafian follicle surviving. The graafian follicle is no longer controlled by FSH

Question 26

What happens in the late follicular phase of the menstrual cycle?

Answer 26

- Oestrogen reaches a threshold where positive feedback in the hypothalamus/pituitary occur, and high levels of LH and FSH are produced - The LH surge triggers the egg to be released

Question 27

What happens in the luteal phase of the menstrual cycle?

Answer 27

- Once the egg is released, the corpus luteum is left. This produces progesterone - When there is no fertilisation, progesterone makes the womb lining thicker. - Negative feedback of LH and FSH occurs. This causes luteolysis and menstruation

Question 28

Describe the process that occurs in the endometrial cycle.

Answer 28

- In the proliferative phase, oestrogen is dominant, and the endometrium thickens. Glands enlargen - In the secretory phase, progesterone is dominant and this causes the endometrium to become secretory, secreting glycogen and the mucosa becomes engorged with blood - It then becomes necrotic and the lining is shed

Question 29

What is amenorrhoea?

Answer 29

The absense of the menstrual cycle

Question 30

What is the difference between primary and secondary amenorrhoea?

Answer 30

- Primary is where a woman has never had a period | - Secondary is where a woman has had periods but they stopped

Question 31

What is oligomenorrhoea?

Answer 31

Ingrequent cycles

Question 32

Define infertility

Answer 32

A couple cant get pregnant following 12 months of regular unprotected sex

Question 33

List the causes of infertility

Answer 33

- Pituitary failure - Prolactinoma - Testicular failure e.g. mumps, Klinefelter syndrome (XXY) - Ovarian failure e.g. Turner syndrome (XO) - Polycystic ovarian syndrome (PCOS)

Question 34

How many carbons are in cholesterol?

Answer 34

27

Question 35

What converts testosterone to oestrogen?

Answer 35

Aromatase

Question 36

What coverts testosterone to dihydrotestosterone?

Answer 36

5-alpha reductase

Question 37

What is the function of granulosa cells?

Answer 37

Produce oestrogen, stimulated by FSH.

Question 38

What is the function of thecal cells?

Answer 38

Stimulated by LH to produce the precursor for oestrogen, androstenedione.