Gonadotropins and Hypothalamic Pituitary Axis

Question 1

What is the function of the gonadotropins?

Answer 1

Hormones released to control the reproductive system

Question 2

What is released from the hypothalamus? What does it act on?

Answer 2

Gonadotropin-releasing hormone (GnRH) and acts on the anterior pituitary

Question 3

What is released from the anterior pituitary by GnRH?

Answer 3

Luteinizing hormone and follicle-stimulating hormone

Question 4

What is the effect of LH in males?

Answer 4

Stimulates the Leydig cells in the testes to produce testosterone

Question 5

What is the function of testosterone? (8 points)

Answer 5

Spermatogenesis in the testes
Libido
Secondary sexual characteristics e.g. pubic, axillary and facial hair
External genitalia growth
Voice deepening
Muscle growth
Bone growth
Promotion of anabolic reactions

Question 6

What effect does FSH have in males?

Answer 6

Drives spermatogenesis in the testes
Androgen binding protein
P450 aromatase
Growth factors
Inhibins

Question 7

What does androgen binding protein do in males?

Answer 7

Maintains high testosterone levels in seminiferous tubules

Question 8

What does P450 aromatase do in males?

Answer 8

Converts testosterone to oestradiol

Question 9

What does growth factor do in males?

Answer 9

Support sperm cells and spermatogenesis - increased number of sperm cells and promotes motility and fertility potential of sperm

Question 10

What does inhibins do in males?

Answer 10

Selectively negatively feeds back for FSH, NOT LH

Question 11

What function does LH and FSH have in females?

Answer 11

Both stimulate the ovaries to produce mature gametes and secrete and synthesise oestrogens and progestins

Question 12

What cells does LH bind to in females?

Answer 12

1. Theca cells - develop follicles for menstruation
2. After ovulation, binds to cell of corpus luteum

Question 13

How is oestrogens produced in females?

Answer 13

LH binds to theca cells > progestins and androgens produced > androgens enter granulosa cells > converted to oestrogen

Question 14

What is the action of FSH on granulosa cells?

Answer 14

Increases enzyme production which catalyse production of steroid hormones
Increased activins - positive feedback on ant. pituitary
Increased inhibins - selective negative feedback
Convert androgens to oestrogen

Question 15

How does varying levels of oestrogen affect the feedback system to the HPA?

Answer 15

Moderate oestrogen levels causes negative feedback
High levels of oestrogen causes positive feedback
High levels of oestrogen and progesterone causes negative feedback

Question 16

What age does normal puberty start in girls and boys?

Answer 16

8-14 girls
9-15 boys
Takes about 4 years start to finish

Question 17

What is the effect of puberty on girls?

Answer 17

Development of breast buds, pubic hair and menstruation (2 years from start of puberty)

Question 18

What is the effect of puberty on boys?

Answer 18

Testicles and penis enlargement
Pubic hair
Deepening of voice

Question 19

What are the two causes for delayed puberty?

Answer 19

Hypogonadotrophic hypogonadism
Hypergonadotrophic hypogonadism

Question 20

What is hypogonadotrophic hypogonadism?

Answer 20

Deficiency in LH and FSH

Question 21

What is hypergonadotrophic hypogonadism?

Answer 21

Lack of response to LH and FSH by gonads (testes and ovaries)

Question 22

What are the causes of hypogonadotrophic hypogonadism? (8 points)

Answer 22

Previous damange to hypothalamus or pituitary
GH deficiency
Hypothyroidism
Hyperprolactinaemia (high prolactin)
Serious chronic conditions e.g. CF, IBD
Excessive exercise / dieting
Constitutional delay in growth and development
Kallman syndrome

Question 23

What are the causes of hypergonadotrophic hypogonadism?

Answer 23

Previous damage to gonads
Congenital absence of testes or ovaries
Kleinfelter’s syndrome
Turner’s syndrome