Hormonal control of development and behaviour Flashcards
what are the major glands in the human body that make up the endocrine system?
pineal
hypothalamus
pituitary
thyroid
parathyroid
thymus
adrenal
pancreas
ovary
testis
where is testosterone released?
by the testes and adrenal glands in males
by the adrenal glands in females
what mainly controls the hormones?
hypothalamus
what does the hypothalamus and pituitary gland do?
hypothalamus controls the release of hormones in the brain
pituitary gland releases hormones into the blood
these hormones stimulate release of other hormones by glands throughout the body
what are the main areas that produce hormones?
pineal gland
hypothalamus
pituitary gland
adrenal gland
pancreas
ovaries
testes
what does the hypothalamus do?
found in the top of the brain stem in the diencephalon within the forebrain
controls the production of hormones
controls the release of hormones by other glands in the body
controls the release of hormones from the anterior pituitary gland into the bloodstream
produces the posterior pituitary hormones and directly controls their secretion e.g. oxytocin
what are the parts of the pituitary gland?
the anterior and posterior
what does the anterior pituitary gland do?
master gland
controls other endocrine glands
connected to the hypothalamus through a system of capillaries
what does the posterior pituitary gland do?
controls neurons via a neural network
it is an extension of the hypothalamus
what does oxytocin do?
stimulates ejection of milk
how does the endocrine system differ from the neural system?
hormones work must slower than action potentials
slower communication system than neurones
hormones released into the blood and travel through the blood to the different organs
organs have receptors that respond to certain hormones to ensure that each hormone gets to the right place
explain how the hormone gonadotropin is produced
in the brain, neural signals stimulate the hypothalamus to release gonadotropin-releasing hormone via the hypothalamic portal system
this hormone releases gonadotropin from the anterior pituitary gland into the bloodstream
gonadotropin travels to the testes in males and ovaries in females
this releases oestrogens, androgens and progestins which affects the body tissue and consequently how humans develop
what happens if there is too much gonadotropin?
If there is too much gonadotropin then a message will get sent to the brain to stop the release of any more
positive feedback loop
when is gonadotropin released and what is the effect?
Gonadotropin is released while the foetus is developing within the mother (primary development) and during puberty around 12-13 years old (secondary development).
During puberty, gonadotropin will affect the testes by causing a massive release of testosterone in males and will affect the ovaries by causing a massive release of oestrogen in females.
how does the Y chromosome differ to the X chromosome?
Y chromosome is smaller
only has 500 genes
contains the sry gene which results in the production of a protein which turns the primordial gonads into testes
what happens at 6 weeks after conception?
At 6 weeks after conception, the gonads of males and females are identical.
If a Y chromosome is present, the medulla of the primordial gonad develops into a testis
If no Y chromosome is present, the cortex of the primordial gonad develops into an ovary
All human fetuses have the antecedents of both male and female reproductive ducts
what is the male reproductive system called?
Wolfian system
what is the female reproductive system called?
Mullerian system
how does the Wolffian system develop?
Testes release testosterone which release a hormone which stimulates the Wolfian system
Receptors that respond to an increase of testosterone which strengthens the Wolfian system
Testes also release the anti-Mullerian hormone is produced to get rid of the Mullerian system in males
Thus creating a fully developed Wolfian system
how does the Mullerian system develop?
Gonads automatically turn into ovaries if there is no Y chromosome as there is no Sry gene and therefore no testosterone
Mullerian system will get stronger due to there being no anti-Mullerian system
how is dihydrotesterone produced?
Dihydrotesterone = testerosterone + 2 water molecules
Testosterone –> dihydrotestosterone occurs with the help of an enzyme
how do external differences in male and female genitalia develop?
The conversion of testosterone to dihydrotesterone (DHT) leads to the differentiation of external genitalia in males
Without dihydrotestosterone, female genitalia develops
what are some gender differences in the brain?
- Men’s brain are 15% larger than women’s brains - generally males are bigger
- Women’s hemisphere’s share more functions than men - brain is more plastic so can compensate for damage more easily than males
- Different size in medial preoptic area of hypothalamus - affects sexual behaviour in males and females - males have more sexually dimorphic nuclei in the preoptic area - due to testosterone
explain studies into the medial preoptic area of the hypothalamus in male and female rats
- Rhees et al. (1990) found a critical period of the 5th to 18th day after birth
- Sexually dimorphic nuclei in the preoptic area bigger in males than females
- Females rats injected with testosterone had increased sexually dimorphic nuclei
- De Jonge et al (1989) found that lesions of the SDN decrease masculine sexual behaviour
- The size of this nucleus is controlled by the amount of androgens present during fetal development
- According to Rhees, Shryne and Gorski (1990), the critical period for masculinisation of the SDN appears to start on the 18th day of gestation and end once the animals are five days old. Normally, rats are born on the twenty-second day of gestation
explain Warne & Zajac’s study into causes of differences in females and males (1998)
- Human females protected from mothers estradiol by placenta
- Found that estradiol released by ovaries in women only causes changes in the brain between males and females
- Testosterone cannot cross blood brain barrier whereas estradiol can cross the blood brain barrier
- Aromatisation of testosterone changes the chemical structure slightly to produce estradiol which can be transported across and into the brain
- This causes masculinisation of the brain
- Blocking aromatisation blocks masculinisation
- Ovaries do not produce estradiol until puberty and the placenta protects females from mother’s estradiol during development
- Therefore no estradiol in females so the brain does not have as many sexually dimorphic nuclei
explain Alexander & Hines’ study into causes of differences in females and males (2002)
- Looked at vervet monkeys in a zoo
- Gave loads of toys in the cage
- Found male monkeys more likely to play with cars
- Found female monkeys more likely to play with dolls
- So there must be a biological factor that determines whether males and females like gender specific toys
what does organisational effect mean?
the effect on the brain
what does activational effect mean?
Brain must be developed in a certain way before it can be activated
explain the study into the organisational and activational effect of testosterone
Ovaries removed from rats so no estrogen and no testosterone
Immediately after birth, rats were given testosterone or nothing at all
When fully grown/ puberty, rats were given testosterone or oestrogen and progesterone
Rats with only oestrogen when fully grown: found increased female sexual behaviour - indicates the activational effect of estrogen - without any intervention, female genitalia is produced
Rats with only testosterone when fully grown: found no female or male sexual behaviour - indicates organisational effect of testosterone
Rats with testosterone at birth (affects brain development) and at puberty: found increased male sexual behaviour - indicates organisational effect of testosterone
what are some examples of hormonal disorders?
Androgen insensitivity syndrome
Congenital Adrenal Hyperplasia
Turner’s syndrome
Persistent Mullerian duct syndrome
Lack of enzyme converting testosterone to dihydrotestosterone
what is androgen insensitivity syndrome?
People with androgen insensitivity syndrome have receptors on the Wolfian system that are not sensitive to androgens
So the wolffian system does not develop and withers away even if they have XY chromosomes
But they are sensitive to the anti-mullerian hormones as it is not an androgen meaning that the mullerian system does not develop either and withers away
This leaves the individual with no internal reproductive system.
The external genitalia are also not sensitive to DHT but the external genitalia will continue to develop as female genitalia meaning the individual will have external female features but genetically are XY.
what is Congenital Adrenal Hyperplasia?
CAH results from overactivity of the adrenal gland which produces an overload of testosterone in both males and females.
what are the effects of CAH on hyperandrogenised athletes?
Increase in testosterone levels are most noticeable in females but is it fair to have a limit of testosterone for female and not for male athletes?
what is Turner’s syndrome?
Results from abnormal sex chromosomes - only 1 X chromosome (XO chromosome)
If there is only 1 X chromosome then neither ovaries or testes develop
Individuals develop normal female internal sex organs and external genitalia but no ovaries so cannot produce eggs
what is persistent Mullerian duct syndrome?
Insensitivity to the anti-Mullerian hormone
An XY individual will respond to androgens and Wolfian system will develop
But when the testes release the anti-Mullerian hormone, the Mullerian system continues to develop due to either a failure to produce anti-Mullerian hormone or the absence of receptors for this hormone (Warne & Zajac)
Both male and female systems continue to develop in males as the presence of testosterone will stimulate the Wolffian system and the absence or insensitivity to the anti-mullerian hormone the mullerian system will continue to develop.
The presence of the additional female sex organs usually interferes with normal functioning of the male sex organs.
what is lack of enzyme converting testosterone to dihydrotestosterone?
Deficiency of the 5a-reductase 2 enzyme
Impairs the differentiation of external genitalia (Shabir et al 2015)
Until puberty, the individual develops externally as a female due to lack of dihydrotestosterone to produce male genitalia
A proportion of the male populate within the Dominican Republic suffer from 5a-reductase deficiency
They only form a penis at about 12 years old when the hypothalamus releases gonadotropin-releasing hormones to initiate puberty and secondary gender differentiation.
