Hormones carry messages from glands to cells in different body organs via the bloodstream.
The chemical structure of hormones is very similar to that of neurotransmitters.
As members of the endocrine system, glands manufacture hormones. Hormones circulate
freely in the bloodstream, waiting to be recognised by a target cell, their intended
destination. The target cell has a receptor that can only be activated by a specific
type of hormone. Once activated, the cell knows to start a certain function within
its walls. Genes might get activated or energy production resumed.
The pituitary gland, located deep in the brain, is often called the ‘master gland’
because some of the hormones it releases also regulate and stimulate other glands
to secrete hormones. The hypothalamus controls the pituitary and, thus, the whole
of the endocrine system.
Other principal glands include:-
- pineal gland - produces melatonin which is involved in sleep
- thyroid gland - makes thyroid hormones, principally thyroxine and triiodothyronine
which regulate the rate of metabolism and affect the growth and rate of function
of many other systems in the body
- pancreas - produces insulin which also affects metabolism
- adrenal glands - produce adrenaline, noradrenaline and glucocorticoids such as cortisol
when acute stress (‘fight or flight’) is experienced
- testes (male gonads) - testosterone
- ovaries (female gonads) - oestrogen and progesterone
There are two types of hormones: steroids and peptides.
In general, steroids are sex hormones related to sexual maturation and fertility.
Steroids are made from cholesterol either by the placenta when we're in the womb
or by our adrenal gland or gonads (testes or ovaries) after birth. Cortisol, an example
of a steroid hormone, breaks down damaged tissue so it can be replaced. Steroids
determine physical development from puberty on to old age, as well as fertility cycles.
If we are not synthesisng the correct steroidal hormones, we can sometimes supplement
them pharmaceutically as with oestrogen and progesterone.
Peptides regulate other functions such as sleep and sugar concentration. They are
made from long strings of amino acids, so sometimes they are referred to as ‘protein’
hormones. Growth hormone, for example, helps us burn fat and build up muscles. It
is secreted by the pituitary. Another peptide hormone, insulin, starts the process
to convert sugar into cellular energy.
Hormones and gender
For the first few weeks of pre-natal development all foetuses have the same undeveloped
sex organs, both male (Wolffian system) and female (Műllerian system).
6 weeks into foetal development, if there is a Y chromosome present the protein hormone
H-Y Antigen is released which encourages the development of testes. The first hormone
to be be released by the testes is anti-Műllerian hormone - also known as Műllerian
Inhibiting Substance (MIS) - which actively absorbs the female parts and thus prevents
any further development of female sex organs. The testes then produce androgens which
work to masculinise the foetus by stimulating the development of male sex organs,
thickening the spermatic cord. After 3 months of pre-natal development, if there
has been development of testes and, consequently, the production of male sex hormones,
the Wolffian system will develop fully into male sex organs. In the absence of male
sex hormones, the Műllerian system will develop fully into female sex organs.
At puberty, under the influence of hypothalamic and pituitary hormones, male gonads
release testosterone while female gonads release oestrogen and progesterone. This
results in the development of secondary sexual characteristics such as breasts and
pubic hair.
The sex hormones - sometimes referred to as reproductive hormones - can affect people
right throughout life.
Testosterone has often been associated with aggression and risky behaviour in males.
John Kalat (1998) found that males aged 15-25, who have the highest levels of testosterone,
also show the highest levels of violence as measured by crime statistics. Interestingly
Hans J Eysenck
(1976) linked testosterone with his temperamental dimension of Psychoticism.
It appears that male cerebral hemispheres work more independently than females; Herbert
Lansdell (1962) attributed this lateralisation to testosterone.
Pamela Regan (1996) demonstrated that women’s sexual desires are regulated by their
menstrual cycle - with oestrogen causing it to increase and progesterone to decrease.
Katarina Dalton, the endocrinologist who first gained worldwide acceptance of Pre-Menstrual
Syndrome (PMS) in 1964, catalogued irritability, anxiety, sadness, moodiness, depressed
feelings, feeling out of control, insomnia and a decline in alertness as just some
of the symptoms of the fluctuations of oestregen and progesterone at this time. She
also found that crime, suicides and accidents tended to cluster around the pre-menstrual
interval. O R Floody’s 1968 review of research into PMS very much confirmed Dalton’s
findings, with pre-menstrual women generally more irritable and hostile and more
likely to commit crime.
Hormones and problems in gender development problems
Some evidence suggests that, when there is a discrepancy between genetic and physical
gender,
hormonal problems during pre-natal development may be involved. Pseudo-hermaphrodites
are chromosomally one sex but appear physically like the other sex. This is caused
by Congenital Adrenal Hyperplasia - a rare condition occurring in both males and
females which cause the adrenal glands to underproduce cortisol. As a consequence,
the pituitary releases adrenocorticotrophic hormone (ACTH) which then causes the
adrenal glands to increase in thickness (hyperplasia) which is accompanied by the
production of androgens whether testes are present or not, resulting in either:-
- Androgenital Syndrome occurs when an XX foetus is exposed to excessive amounts of
androgens which masculinise the female foetus and result in the development of male
rather than female sex organs. The size of the penis ranging from being a very over-enlarged
clitoris to being a large penis capable of full erection is often enlarged; however,
the testes are usually underdeveloped. The baby will look male but is chromosomally
female. As the brain has been subject to masculinising hormones, these pseudo-hermaphrodites
will tend to behave in more ‘masculine’ ways.
The condition can be caused by excessive
activity of the mother’s adrenal glands producing androgens during pregnancy.
- Androgen Insensitivity Syndrome - aka Testicular Feminising Syndrome - is the result
of an XY foetus becoming feminised by a lack of exposure to male hormones, with the
consequence that, even though the internal female parts have been absorbed, the body
tries to develop female sex organs. The condition is due to a recessive gene and
is often diagnosed when a hernia (lump in the abdomen) turns out to be a testis.
(As there is a high probability the testes will become malignant, they are usually
removed surgically.) These pseudo-hermaphrodites have only a very short vagina and,
having no womb, are infertile and cannot menstruate. They are often taller than most
women.
However, Daphne Went, famously, was an XY pseudo-hermaphrodite who lived successfully
as a woman despite having a Y chromosome and 2 testes where most women have ovaries.
At puberty she did not develop pubic hair or start to menstruate in spite of developing
breasts and female contours as a result of oestregen. Daphne went on to marry. When
she failed to conceive, she consulted her doctor and eventually was presented with
the disturbing facts that she was a he and had no internal female organs. According
to E Goldwyn (1979), in spite of the terrible shock, still felt she was a woman and
decided to live as one, she and her husband adopting 2 children.
Daphne is thought
to be one of about 500 sufferers in the UK.
