There are two types of glands - exocrine glands which secrete chemicals through ducts and endocrine glands which secrete hormones directly into the bloodstream. Hormones have different types and properties depending on their chemical structure, with steroid hormones being hydrophobic and able to influence gene expression. The hypothalamus and pituitary gland work together to regulate hormone release, with the hypothalamus secreting tropic hormones and the pituitary gland secreting tropic and other hormones in response. Sexual development is determined by sex hormones like testosterone and their influence on internal and external genital development.

2.  2 types of glands: exocrine and endocrine.
 Exocrine glands secrete chemicals in ducts
e.g. sweat glands and enzyme secreting
acinar cells of pancreas.
 Endocrine glands secrete chemicals
(hormones) directly into the bloodstream.
 Hormones circulate in the blood until they
reach the receptors they act on where they
have their physiological effect.

3.  3 types: amino acid derivatives,
peptides/proteins, steroids.
 Because of the overall protein nature of the first
2 types they are generally hydrophilic and
cannot penetrate the cell membrane: their
receptors are usually on the cell surface
(thyroxine is an exception) and because of this
they have short lasting effects (think of
adrenaline).
 Steroid hormones are cholesterol derived
molecules that are hydrophobic and usually act
on receptors in the cell cytoplasm or nucleus
where they influence gene expression and thus
can have long lasting effects.
 Sex hormones are steroids.

4.  Synthesised primarily in the gonads, (testes
for men and ovaries for women).
 3 main classes: androgens, oestrogens and
progestins of which testosterone, oestradiol
and progesterone are the most common of
each respective class.
 Zona reticularis of adrenal cortex also
synthesises sex steroids but in smaller
amounts.
 Main role of testes and ovaries is to produce
sperm and ova respectively, which are
haploid sex cells created via meiosis.

5.  Divided into anterior and posterior (aka
adneohypohysis and neurohypophysis).
 Adenohypophysis derived from tissue that forms
roof of mouth, fuses with neurohypophysis.
 Adenohypophysis secretes tropic hormones which
stimulates hormone secretion of other glands.
 Secretes: Gonadotropin (LH and FSH)
Somatotropin (GH)
Thyrotropin
Adrenocorticotropic hormone (ACTH)
Prolactin

6.  Neurohypophysis formed from small
outgrowth of hypothalamus.
 Secretes vasopressin and oxytocin.
 Vasopressin’s primary function is to increase
kidney water reabsorption and increase
blood pressure.
 Oxytocin is involved in uterine smooth
muscle contraction during labor, breast
smooth muscle contraction during suckling
and recently has been implicated in
establishing feelings of trust and closeness.

7.  Hypothalamus secretes tropin releasing
hormones (e.g. gonadotropin releasing hormone)
into the hypothalamopituitary portal system
from which they reach the adenohypophysis and
stimulate the secretion of the respective tropin
hormone (In this case gonadotropin).
 Neurohypophysis hormone secretion is such that
the hormones themselves are synthesised in the
cell bodies of neurons in the paraventricular and
supraoptic nuclei of the hypothalamus and are
then transported along the axons of these
neurons down into the neurohypophysis where
they are eventually secreted into the
bloodstream from there.

9.  Via neural signals (all except adenohypohysis)
e.g. sympathetic nervous system stimulating
adrenaline release from adrenal glands.
 Via other hormones e.g. adenhypophysial tropic
hormones, but also via the same hormones
through negative feedback acting to stabilise
hormone levels in blood.
 Via nonhormonal chemicals e.g. high glucose
stimulating insulin release and low calcium
stimulating PTH release etc. as the hormones in
question are involved in maintaining
physiological levels of these chemicals anyway.
 Hormones (especially those secreted and
controlled by the pituitary gland) tend to be
secreted in pulses throughout the day.

11.  All humans preprogrammed to develop as
females.
 Default mechanism is that cortex of
primordial gonads grows to become an ovary.
 SRY (Sex determining Region of the Y
chromosome) gene on Y chromosome results
in synthesis of SRY protein which stimulates
medulla to grow instead and the formation of
testes instead of ovaries.
 This crucial determining event takes place 6
weeks post fertilisation.

12.  The internal reproductive duct is determined
3 months post fertilisation.
 If genotype is XY, testes secrete testosterone
and mullerian inhibiting substance. The
former promotes the development of
wolffian (male) internal reproductive ducts
and the latter inhibits the development of
mullerian (female) ducts.
 If genotype is XX, mullerian ducts develop by
default with no needed output from ovaries
and no testosterone or MIS to halt their
development.

14.  External genitalia develops from bipotential
precursor in the 2nd month.
 Testosterone secreting XY genotypes
stimulate the precursor to develop into the
penis, urethra and scrotum.
 XX genotypes result in the formation of the
vagina, clitoris and labia majora and minora
by default due to the absence of
testosterone.

16.  Puberty is the period wherein an individual
becomes sexually mature and starts to
develop secondary sex characteristics.
 Secondary sex characteristics are the
physical traits that distinguish men from
women
 Gonadotropin induces sex steroid production
which initiate sexual maturity while
somatotropin and adrenocorticotropic
hormone (ACTH) result in anabolic changes
and the development of secondary sex
characteristics respectively.

18.  Male and female brains are phenotypically different
in terms of size, various tract and nucleus size etc.
 We are still unsure as to how and when the different
concentrations of sex steroids between men and
women influence the development of these
differences in the brain.
 However, female rats ovariectomised at birth and
given androgen injections upon reaching sexual
maturity displayed male sexual behaviour but failed
to exhibit as much female sexual behaviour if
injected with progesterone and oestradiol. The same
complementary scenario was seen with male rats
undergoing the complementary treatment.
 This perinatal critical time period has been estimated
at 11 days, at least for mice.

19.  Castration has been seen to significantly reduce
sexual interest and behaviour in adult human
males to different degrees.
 It is thought that this variation is the result of
the adrenal cortex producing different amounts
of testosterone in different individuals post
orchidectomy.
 Conversely and logically, adminstering
testosterone to castrated individuals restores
their libido and sexual behaviour.
 However testosterone cannot restore fertility
(gonadotropins and normal spermatogenesis are
needed for that).

20.  Female guinea pig sexual behaviours have
been seen to vary with the different
hormone concentrations of their menstrual
cycles.
 Human females are much more complex and
libido varies for different women at different
points in their cycles.
 Testosterone has been implicated in sexual
drive as replacing low levels helps increase
libido.
 However many women lacking sexual interest
have normal testosterone levels.

21.  Anabolic steroids are testosterone derived or
testosterone related artificially synthesised
molecules.
 They stimulate anabolism, including muscle
mass growth, bone growth (remodeling not
height), body hair production etc. (i.e.
amplifying secondary sex characteristics)
 Because they are similar to testosterone,
they have negative feedback effects on the
pituitary and hypothalamus resulting in
decreased gonadotropin release leading to
testicular atrophy and sterility in men.

22.  In women they lead to amenorrhoea and
sterility along with masculinisation of body
features.
 Other shared symptoms include muscle
pains, spasms, haematuria, water retentions,
nausea, vomiting and psychotic behaviours.
 Chronic usage of anabolic steroids also
decreases life expectancy in rodents.
 No concrete evidence that they significantly
increase aggression and sexual behaviour.

23.  Oestradiol reduces brain damage caused by
neurodegenerative disorders.
 Has neurotrophic effects ranging from
reducing inflammation, increasing axonal
generation and promote synaptogenesis
among others.
 Clinical trials have so far, unfortunately,
been inconclusive.

24.  Sexual behaviours in humans are under
complex control via association cortex.
 Dimorphic nuclei identified in hypothalamus.
 Much larger in male rats than in female ones.
 Difference due to oestradiol from aromatised
testosterone acting on neurons there.
 In humans, preoptic, suprachiasmatic and
anterior nuclei of hypothalamus are different
between men and women.

25.  The medial preoptic area is heavily involved
in male sexual behaviour.
 Lesions covering this area result in complete
cessation of male-associated sexual
behaviours in both males and females.
 Acts via dopamine dependent neural
pathways.
 Medial preoptic area projects to lateral
tegmental field via tract. Destruction of this
tract or various parts of it also lead to
complete or specific loss of male-associated
sexual behaviour.

26.  Sexual behaviour controlled by VentroMedial
Nucleus (VMN).
 Lesions reduce female-associated sexual
behaviour in rodents.
 Oestrogen and progesterone complement one
another when acting on VMN to induce
receptive sexual behaviour in rodents.
 Cell bodies of VMN project to periaqueductal
grey area of the tegmentum via white matter
tract.
 Damage to this tract results in decrease of
sexual behaviours.

27.  Genes heavily implicated in sexual identity
as twin studies show higher rates of
concordance between monozygotic than
dizygotic twins when it comes to
homosexuality.
 The fraternal birth order effect stipulates
that a man has a significantly increased
chance of being homosexual the more older
brothers he has. Autoimmunity induced by
successive male pregnancies is implicated as
the underlying mechanism.

28.  Transsexualism is an example of confrontation
between a person’s gender identity and their
actual sex wherein people think they are
actually of the opposite sex and are trapped in
their pre-determined body.
 Transsexuals engage in various, often harmful,
behaviours to try and change their body into that
of their desired sex.
 No such behaviour has been observed in other
animals.
 Interestingly a transsexual’s sexual interest is
Independent of their gender identity.