11 - The Gonads 2

Question 1

In males, what can testosterone be converted into?

Answer 1

Reduction to DHT - dihydrotestosterone. More potent action of testosterone (super testosterone)

Aromatisation to oestrogens (17B-oestradiol)

Question 2

How are testosterone and DHT transported in the blood?

Answer 2

SHBG - sex hormone binding globulin. 60%

Albumin 38%

Free 2% (bioactive)

Question 3

How are testosterone and DHT transported in the seminiferous fluid?

Answer 3

Androgen binding globulin - ABG

Question 4

Why must they be bound?

Answer 4

They are lipids

Question 5

What are androgens?

Answer 5

Male sex hormones

Question 6

What is the principal actions of androgens in the fetus?

Answer 6

Development of male internal and external genitalia.

Fetal growth

Question 7

What are the principal actions of androgens in an adult?

Answer 7

Spermatogenesis
Growth and development of genitalia and facial hair
Muscle and bone growth
Male sexual behaviour
Puberty growth spurt
Can be mediated by conversion to oestrogen.

Question 8

What is the definition of oestrogen?

Give examples

Answer 8

Any substance that induced mitosis in the endometrium. (Womb thickening)

17B-oestradiol = main one in women
Oestrone = precursor
Oestriol = main during pregnancy

Question 9

What are the reproductive effects of oestrogen?

Answer 9

Stimulates proliferation of the endometrium

Triggers LH surge in menstrual cycle.

Growth of breasts and vagina secretions.

effects on skin

Question 10

What are the other (non-reproductive) effects of oestrogen?

Answer 10

Feedback on GnRH (-ve and +ve)
Stimulates osteoblasts (builds bone mass)
Metabolic actions (lowers lipid levels)
Behaviour
Salt and water reabsorption
Increases Plasma protein synthesis
Influences release of other hormones.

Question 11

Definition of progestogens?

Answer 11

Substances that make the endometrium secretory. i.e an embryo could implant into it.

eg. progesterone

Question 12

What are the effects of progestogens?

Answer 12

Stimulates secretion in endometrium and cervix.

Not as important:
-ve feedback on GnRH
Increases basal body temp.
Decreases renal NaCl reabsorption 
Stimulates growth of alveolar system in breast

Question 13

Draw the hypothalamo-pituitary-testicular axis.

Answer 13

Drawing.

Question 14

Which cells are responsible for androgen production?

What stimulates this?

Answer 14

Leydig Cells.
Stimulated by LH.
Reduced by testosterone (negative feedback)

Question 15

Which cells are responsible for spermatogenesis?

What stimulates this?

Answer 15

Sertoli cells.
Stimulated by FSH
Reduced by inhibin (-ve feedback)
Does also require testosterone.

Question 16

Draw the hypothalamo-pituitary-ovarian axis.

Answer 16

Drawing

Question 17

At what 2 points in the menstrual cycle does positive feedback occur?

Answer 17

1. When the follicles make oestrogen = more granulose cells = more oestrogen. (Autocrine)
2. When the Graafian follicle is making so much oestrogen it positively feeds back on GnRH causing LH surge and ovulation.

Question 18

Draw the graph for the hormones of the menstrual cycle and explain each phase.

Answer 18

Drawing

Question 19

What is Amenorrhoea? What are the 2 types?

Answer 19

The absence of menstrual cycles.
Primary - if the woman has never had a period.
Secondary - if the woman has had periods but they have stopped.

Question 20

What is oligomenorrhoea?

Answer 20

Infrequent cycles.

Less than every 6 weeks.

Question 21

What is the definition of infertility?

Answer 21

When a couple cannot get pregnant after 12 months of regular unprotected sex.

Question 22

What are the causes of infertility?

Answer 22

Pituitary failure (tumour) No LH and FSH
Prolactinoma (tumour in pituitary = make prolactin = inhibits LH and FSH)

Testicular failure (mumps, Klinefelter syndrome XXY)

Ovarian failure (Turner's syndrome XO)
Polycystic ovarian syndrome (PCOS)

Question 23

What does PCOS cause?

Answer 23

Infrequent periods,
Hyper-androgenaemia (male hair pattern, acne)
Polycystic ovaries (increased number of enlarging ovarian follicles.