Gonads (2) 11 Flashcards
What is testosterone a precursor for?
- 17b-oestradiol and oestrone
- dihydrotestosterone
What is the difference between dihydrotestosterone and its precursor?
- it is far more potent but acts on the same androgen receptors
- it is produced in the target tissue that has the 5alpha-reductase enzyme
Which tissues have the 5alpha-reductase enzyme?
- prostate
- testes
- skin
- brain
- pituitary
How are oestrogens formed from the precursor?
Testosterone is aromatised by aromatase to form oestrone and 17b-oestradiol
What tissues is aromatase found in?
- adrenals
- testes
- liver
- skin
- brain
- adipose
How is testosterone and DHT transported in blood?
- Sex hormone binding globulin (SHBG) = 60%
- Albumin = 38%
- Bioactive (free) = 2%
Where is the other testosterone transport?
Testosterone can be found in seminiferous fluid (semen) bound to Androgen binding globulin (ABG)
What are the actions of androgens on the foetus?
- stimulate internal and external genitalia formation
- stimulate general growth
- affect behavioural characteristics
- can be converted to oestrogens to bind to receptors in the brain for behavioural changes
What are the actions of androgens in adults?
- SPERMATOGENESIS
- growth/development of genitalia, secondary sex glands and secondary sex characteristics (beard/pubic hair)
- stimulation of protein anabolism
- Pubertal growth spurt (GH)
- Behavioural (CNS) effects
- Feedback regulation (to control LH/FSH)
Definition of oestrogens
Any substance (natural or synthetic) that induces mitosis in the endometrium
What is the main hormone in the menstrual cycle?
17b-oestradiol
What is the main hormone in pregnancy
Oestriol
What is the precursor to 17b-oestradiol and oestriol?
oestrone
What are the principal actions of oestrogens?
- mitosis of endometrium
- final maturation of follicle and stimulation of LH surge
- effects on vagina and cervix (secretions)
- Stimulates growth of breast ductile system
- decreases sebaceous gland secretion
- increased salt/water reabsorption
- increased plasma protein sysnthesis
- Metabolic actions on lipids e.g. increase HDL levels
- stimulates osteoblasts
- influences other hormones
- behavioural effects
Progestogens Definition
Any substance (natural or synthetic) that induces secretory changes in the endometrium
What is the main Progestogen?
PROGESTERONE
-17hydroxyprogesterone
What are the principal actions of progestogens?
- stimulate secretory activity in the endometrium and cervix
- stimulate growth of breast alveolar system
- decrease renal Na+/Cl- reabsorption
- associated with increase in body temperature
- -ve feedback for GnRH
What is the steroid hormone mechanism of action?
Have a genomic effect via intracellular receptors. The receptor-hormone complex acts as a transcription factor. May act on G-protein like receptors to not have a genomic effects
Describe major points in the hypothalamo-pituitary-testes axis.
1) hypothalamus produces GnRH
2) GnRH causes LH and FSH production in the pituitary
3) LH acts on Leydig cells to produce testosterone
4) testosterone has a -ve feedback on LH and GnRH production
5) FSH acts on sertoli cells to produce Inhibin
6) Inhibin has a -ve feedback to reduce FSH, LH and GnRH
Give an example of auto-positive feedback
oestrogens produced by a granulosa cell with bind to Oestrogen receptors on the same cell and produce more oestrogens having activated the aromatase enzyme by a secondary messenger. Therefore, granulosa cells multiply and get bigger and plasma oestrogen levels increase
What hormone does the graffarian follicle produce?
17b-oestradiol
What is Amenorrhoea
Absence of menstrual cycles
Primary = never happened Secondary = did but stopped
What is Oligomenorrhoea
Infrequent menstrual cycles (less than every 6-8 weeks)
What is infertility?
Inability to get pregnant following 12 months of regular unprotected sex
What are the causes of infertility?
- pituitary failure (e.g.tumour)
- prolactinoma (excess prolactin with galactoria symptom)
- testicular failure
- ovarian failure
Polycystic Ovarian Syndrome (infrequent periods/hyper-androgenaemia/ polycystic ovaries)
