11 - The Gonads 2 Flashcards
In males, what can testosterone be converted into?
Reduction to DHT - dihydrotestosterone. More potent action of testosterone (super testosterone)
Aromatisation to oestrogens (17B-oestradiol)
How are testosterone and DHT transported in the blood?
SHBG - sex hormone binding globulin. 60%
Albumin 38%
Free 2% (bioactive)
How are testosterone and DHT transported in the seminiferous fluid?
Androgen binding globulin - ABG
Why must they be bound?
They are lipids
What are androgens?
Male sex hormones
What is the principal actions of androgens in the fetus?
Development of male internal and external genitalia.
Fetal growth
What are the principal actions of androgens in an adult?
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.
What is the definition of oestrogen?
Give examples
Any substance that induced mitosis in the endometrium. (Womb thickening)
17B-oestradiol = main one in women Oestrone = precursor Oestriol = main during pregnancy
What are the reproductive effects of oestrogen?
Stimulates proliferation of the endometrium
Triggers LH surge in menstrual cycle.
Growth of breasts and vagina secretions.
effects on skin
What are the other (non-reproductive) effects of oestrogen?
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.
Definition of progestogens?
Substances that make the endometrium secretory. i.e an embryo could implant into it.
eg. progesterone
What are the effects of progestogens?
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
Draw the hypothalamo-pituitary-testicular axis.
Drawing.
Which cells are responsible for androgen production?
What stimulates this?
Leydig Cells.
Stimulated by LH.
Reduced by testosterone (negative feedback)
Which cells are responsible for spermatogenesis?
What stimulates this?
Sertoli cells.
Stimulated by FSH
Reduced by inhibin (-ve feedback)
Does also require testosterone.
Draw the hypothalamo-pituitary-ovarian axis.
Drawing
At what 2 points in the menstrual cycle does positive feedback occur?
- When the follicles make oestrogen = more granulose cells = more oestrogen. (Autocrine)
- When the Graafian follicle is making so much oestrogen it positively feeds back on GnRH causing LH surge and ovulation.
Draw the graph for the hormones of the menstrual cycle and explain each phase.
Drawing
What is Amenorrhoea? What are the 2 types?
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.
What is oligomenorrhoea?
Infrequent cycles.
Less than every 6 weeks.
What is the definition of infertility?
When a couple cannot get pregnant after 12 months of regular unprotected sex.
What are the causes of infertility?
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)
What does PCOS cause?
Infrequent periods,
Hyper-androgenaemia (male hair pattern, acne)
Polycystic ovaries (increased number of enlarging ovarian follicles.
