Lyons and Lourdon Flashcards
Polygamy
Male has more than 1 female mate
95% of mammalian species
Why is polygamy the major mating system
evolution of pregnancy and lactation means reproductive costs largely on female
What is the gonadorophin axis?
Brain (decapeptide) –> LH and FSH in pituitary gland –> Gonads –> behaviour
What are the principles of the neuroendocrine system (BRAIN)?
- produces low mol. weight peptides which act in anterior pituitary to release larger glycoprotein hormomes
- hormones of posterior pituitary secreted from nerve terminals in hypoT.
- many of these hormones also act via other pathways in the brain
What are the principles of the neuroendocrine system (Gonads)?
Produces sex steroids:
- act locally to regulate gonadal function
- act on body to differentiate development and physiology
- act on brain to regulate behaviour
How do peptides function in neuroendocrine system?
- peptides from the brain act on peripheral physiology via pituitary gland
- they also act directly on brain behaviour
- peptides involved in specific physiological function also act on sexual behavioural pathways in the CNS
What does GnRH control and how?
- GnRH causes release of LH and FSH
- sex steroids and gonadal peptides feedback to regulate pituitary activity
- GnRH also acts directly on brain and facilitates lordosis behaviour in females when injected
THEREFORE - peptide controls both pituitary gonadotrophins & sexual behaviour
What is lordosis, which hormone facilitates it?
characteristic sexually receptive behaviour in female rodents
- occurs in certain stage of oestrous cycle
- cannot exhibit without ovaries
- Oestradiol
How is the brain masculinesed?
- the brain is female by default
- oestrogen causes masculinisation of male brain and sexual dimorphism, but not in women
- BECAUSE, there is a short window of opportunity
- ovaries produce 100x less test than testis
What is the Aromatisation hypothesis?
- Aromatised oestrogen metabolites of testosterone masculinses the brain in the hypothalamus
- AFP system ‘swamped’ by oestrogen injection
- doubts over its validity
What does testosterone do?
Effects the brain, libido, deepens voice, increases lean muscle mass, male sex organs
How does testosterone secretion effect hormomes?
Developing testis secrete test, stimulates Wolffian Duct Formation & Mullerian Inhibiting Hormone, which causes Mullerian duct to generate leading to the absence of a uterus
What is the Jost hypothesis?
secretion of androgens & MIH by foetal testis during critical stages of development accounts for full range of sexually dimorphic urogenital traits observed at birth
MIH
Mullerian Inhibiting Hormone (MIH/AMH) is large molecularly, TGH-ß super family
How is gender determined in mammals?
- small region on tip of Y, location of SRY gene which is sex determining part
- SRY switches on sertoli cells in gonad, differentiating them
- they can support germ cells, and they stimulate development of Leydig cells
What do Leydig cells do
make testosterone
What do Sertoli cells do
- secrete substance initiating meiosis
- secrete testicular fluid
- conc. test locally
- release MIH
- protext spermatids from immune system
Castrate
XY:
- lack of androgen effect on long bone growth
- small penis, no body hair
- pubic hair originates from adrenal glands
Klinefelters
XXY:
- Small testis, low testosterone, limited breast development
- no spermatozoa produced (XXY cells don’t survive outside testis)
- scant body hair
XY digenesis
XY:
- X-linked supressor of SRY
- Male karyotype, undevelopeed female appearance
- no testi development, ovaries develop then degenerate
- normal vagina
- no ovaries = no sex steroids, no pubes/breasts
- tall
- ‘tall freak with vagina’
Testicular feminisation
XY:
- no androgen receptor
- testicular oestrogen drives breast development
- voluptous breasts, no testosterone signal opposing oestrogen
- MIH prevents uterus formation
- intra-abdominal testes as body can’t read test. signal
- short, blind-ending vagina
- raised as girls
Turner’s syndrome
XO:
- X missing
- ovaries or steak gonads
- Mullerian ducts present (no testis, no MIH)
- Wolffian duct absent (no test)
- Lack of germ cells = lack of sex steroid production
- no breasts, thick neck, socially awkward
Guevedoces
- raised girls
- puberty –> test rises to sufficient levels to virilise body
- testis descent, penis develops and grows
- cannot synthesis 5a-DHT because of mutation
5a-DHT
essential substrate of testosterone, far more potent
