hormones and sex Flashcards
what are hormones
signalling molecule transported by the vascular system
regulate development, physiology, and behaviour
produced by organs (endocrine system) and receptors in all tissues
under control of the brain (hypothalamus) but complex feedback architecture undermines concept of a control hierarchy
endocrine glands
- hypothalamus (controls pituitary gland and others)
- pituitary
- thyroid
- parathyroids
- adrenal
- pancreas
- ovary
- testis
hormone vs neurotransmitter (6)
neurotransmitter
fast onset
short distance
nerve pathways
short duration
digital - neural signalling
targeted actions
hormone
slow onset
long distance - all over body, complements CNS/PNS action
anywhere in circulatory system
long duration
analogue - continuously variable
diffuse actions - begin at a level and then inc/dec accordingly
hormone action loop
- disturbance occurs (input)
- measuring by hormones
- comparison to desired state
- error noticed
- controller commands effector (using hormones)
- effector (hormone) returns to desired state
pathway hormones use
vascular system - in blood
from secreting cell to target cell - specific receptors
hypothalamus function
master controller - knows current state of body and can make adjustments to physiology and behaviour via several routes (inc hormones)
controls pituitary gland - anterior and posterior - for hormone release and sensing
hypothalamus - feedback loops
context + sensory inputs = detected by hypothalamus → visceral & somatic motor, neuroendocrine, and bevhavioural responses
context = cortex, amygdala, hippocampal formation
sensory input = visceral and somatic sensory pathways, chemosensory and humoral signals
hypothalamus = compares input to set points and makes changes in response
anterior vs posterior pituitary gland
anterior = TSH, ACTH, FSH + LH, endorphin etc.
posterior = oxytocin, ADH
anterior = 2 step release = neurosecretory cell –> blood vessels –> stimulate endocrine cells for hormone release
posterior = single step = neurosecretory cell secretes hormones –> blood vessels
hormone function (2) and common features
regulate physiology → motivational states - arousal, aggression, hunger, fear, fatigue etc.
regulate processes → digestion, metabolism, respiration, reproduction, sleep, menstrual cycle etc.
common features = feedforward and feedback signalling, bidirectional influences between body and brain
define chromosomal sex
fixed
most humans have 22 pairs of autosomes (like one another) and one pair of allosomes (not comparable_
allosome pair = XX or XY
historically considered to define phenotypic sex
define phenotypic sex
modifiable (e.g. hormone treatment)
internal and external genitalia and secondary sex characteristics
XX = ovaries, oviducts, uterus, cervix, vagina etc.
XY = testicles, epididymis, vas deferens, seminal vesicles etc.
often used interchangeably with gender and can influence perceptions
define gender
constructed
individuals subjective perception of their sex
emerging from self-appraisal in context or social or cultural norms
genetic and biological contributions are complex
turner syndrome
[XO] = missing X chromosome - affects females
shorter height, impaired ovary function
ovaries produce oestrogen and progesterone - reduced levels lead to under development of secondary sex characteristics
therefore diagnosed at puberty
infertility or reduced fertility
treatment = oestrogen and progesterone
Klinefelter’s syndrome
[XXY] = extra X chromosome - affects males
[XXXY] variation also possible
taller height, impaired testicular function, language problems, impaired executive function, delayed motor development, reduced body/face hair, feminine fat distribution
testicles produce testosterone - reduced levels = underdevelopment of secondary sex characteristics
therefore evident and diagnosed at puberty
treatment = testosterone
XYY syndrome
extra Y chromosome - affects males
taller than XY males, risk of learning or speech development problems - often mild symptoms and IQ in normal range
most are never diagnosed
normal fertility
treatment = supported learning
function of sex chromosomes
XX = important for full female sex characteristics development
if missing = underdeveloped
XY = needed for full male sex characteristics development
not possible to have only a Y chromosome
[X] = 1500 genes, [Y] = 80 genes
[X] = info for general development and survival, not just sex characteristics
[Y] = mainly just genes for male gonadal development and sperm function
“functional wasteland” - most DNA seems to be not coding for any specific genes - other than SRY gene
SRY gene
sex-determining region on Y chromosome
sex-linked - only found on Y - on short arm
important for diversion toward male biological development in utero - at around 6-8 weeks old foetus
SRY present = forms testes
SRY not present = forms ovaries
chemically blocking SRY in XY = genetic male with ovaries
injecting SRY protein in XX = genetic female with testes
why do men have nipples
formed before SRY gene activates → evolutionary baggage
no strong pressure to drop them from main body plan (Y chromosome instruction doesn’t stop this) as they don’t do any harm
chromosomal testing in sports
1992 Olympics tested for SRY gene to determine male/female of athletes
* with SRY = not allowed to compete as females
* found later that 8 female athletes had SY gene - had insensitivity to androgen (testosterone is a form of this)
* but they were phenotypically female - so had no advantage
screening replaced in 2000 with hormone based testing
* debate with transgender athletes
phenotypic sex - hormones control of other hormones
sex hormones inhibit release of other sex hormones - hold off until puberty
inhibit anterior pituitary and hypothalamus function → reduced sensitivity to hormones enables altered state of system
activity of hypothalamus to AP is pulsatile (increases and decreases)- released GnRH to AP → leads to LH and FSH release
* increased pulsatility towards puberty → increased LH and FSH → sex hormone release
* females after puberty, changes in pulsatility of GnRH release → regulates the menstrual cycle (slow in luteal phase, increasing through follicular and pre-ovulatory stages)
phenotypic sex - control and abnormality
chromosomal sex (presence//absence of SRY gene) gives rise to internal and external genitalia
abnormalities - evident at puberty - when gonads are needed to release sex hormones
under control of brain - beginning with hypothalamus
historical perspectives of brain differences with sex (3)
historical view (<1990s) = sex hormones lead to differentiation of male and female brains → similar to primary and secondary sex characteristics
then suggested wider range of influences on the development of male and female brains, beyond that of the sex hormones
recently (2010+), idea of “predetermined” differences → functional significance have been challenges
gender studied in neuroscience
definition is too simplistic - binary, doesn’t capture external social context for gender
WHO definition encapsulates behaviour too
neurobiological basis for gender?
* not if it is socially constructed
* but behaviour does emerge from the brain - so must be linked somehow (not just behaviour tho)
* can study relationship between biological sex and behaviour though → brain, experience, and behaviour links
* could inform understanding of gender and identity - wouldn’t give answers though
male vs female brains - size and structure
male brains weigh10% more
* mostly explained by body mass differences
differences in white and grey matter
some differing structures → uncertain how these came about
differing functions are unclear
plasticity of brain - susceptible to differential influences, probs occur from birth
bad research into male/female brain differences (4)
motivations → they are different so brain must be too
bad design → so many areas that some are bound to be different - make enough comparisons you will find a difference
questionable comparisons → sexual dimorphism greater in one species than another
publication bias → more likely if difference is found
why is brain sex differences relevant
different incidence levels in males vs females of neurological disorders
e.g. autism
unsure if sex is a determining factor or not
view of default development of brain
body development - default female pattern is modified towards a male pattern by sex hormones - this is extended to the brain too
only evidence for this with hypothalamic nuclei - involved in sexual and reproductive behaviours
hormones act perinatally to drive differentiation of hypothalamic nuclei
what could be responsible for the masc/fem of the brain (3)
sex hormones:
no
* if it was we would be able to see this with brain imaging studies
* would expect greater variability in male brains than female
human brain mosaic
no
* study found variation across individuals within a gender category was greater than between categories
* some features tended to be more male or female but individuals had a combination of these - not consistent to one or the other - cancels out
environmental
potentially
* brain is plastic
* differentiated from an early stage
e.g. girls vs boys toys
is there conclusive research into difference between male and female brain?
no - not sexually dimorphic - indicates binary which isn’t there
- sex only explain 1% of total variance independent of size
- most research doesn’t differentiate between male and female brains - viewed as irrelevant difference
- idea of connectivity differences between hemispheres - corpus callosum in men is larger but so is rest of brain so this isn’t relevant
- function with lateral connectivity - brain size can explain differences
- lack of cultural inclusivity in research
- similar emotion circuits for empathy
