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What is Endocrinology?
The study of how the body is regulated by chemicals synthesized in one
region of the body which then travel elsewhere in the body to control cell
function
A gland = a part of the body which secretes a product e.g. mucus
glands making mucus in the intestine, salivary glands making saliva.
Endocrine glands make specific chemicals called hormones, which act
as chemical messengers. Lymph nodes are often loosely called “glands”
(“my glands are swollen”) but are not true glands at all
An example is the production of adrenaline from the inner part of the
adrenals (and from nerve endings) that increases markedly with shock
or stress, helping the body to cope by increasing the heart rate,
preparing muscles for action etc
The endocrine system is thus a signaling system in the body working
by production of chemical messengers which travel around the body
to instruct cell how to function (switch on their action, switch off etc).
It is a more gradual signaling system than the nervous system for
example.
Interaction of the pituitary gland with other glands in the
body
Brain
Hypothalamus
Input from body and
environment
e.g. stress
temperature
water balance
hunger/food
weight
season
blood sugar
stalk
Pituitary gland
thyroid
adrenals
Three hormone systems
involving the pituitary
gland
ovaries/testes
Brain
Hypothalamus
Input from body and
environment
e.g. stress
temperature
water balance
hunger/food
weight
season
blood sugar
stalk
Pituitary gland
Growth
hormone
prolactin
vasopressin
Another three
hormone systems
involving the pituitary
gland
Why worry about pituitary hormones? Isn’t
it enough to worry about growth hormone?
The normal pituitary gland may be damaged in various
ways in individuals with growth-hormone –secreting
pituitary adenomas
Position
of
normal
pituitary
Normal
pituitary
damaged by
treatment
Normal pituitary or
the pituitary stalk
squashed by growth
hormone-secreting
adenoma
Brain
The pituitary –
adrenal pathway
Hypothalamus
stalk
Pituitary gland
ACTH – releasing
hormone
ACTH – making
cell
adrenals
Adrenal stimulating
hormone (ACTH)
Cortisol (hydrocortisone) released into
blood stream
Acts on many different cell types in the body
Hydrocortisone
Very important hormone produced in the adrenal glands
under stimulation by the pituitary (ACTH stimulation)
Often called “steroids” or “corticosteroids”.
Synthetic corticosteroids are more potent weight for weight
than hydrocortisone (e.g. prednisone, dexamethasone etc).
For example 1mg prednisone = 5mg hydrocortisone
Actions: Essential for life. Enables us to respond to stress,
maintains blood pressure, immune function, blood sugar etc
Regulation of the thyroid
Hypothalamus
TSH – releasing
hormone
stalk
Pituitary cell
making thyroid
stimulating
hormone
Pituitary gland
Thyroid stimulating
hormone (TSH) in
bloodstream
Thyroid
gland
Thyroxine
Circulates in the bloodstream and reacts
with almost all cells in the body
Thyroxine
Often called “T4”, and now days measured in the blood as the serum
“free T4”. Thyroid hormones act on tissues to control our metabolic
rate (energy levels, body temperature etc)
Thyroid
gland
T3
T4
Converted to T3
in liver tissue
Main thyroid
hormone
acting on
tissues
Control of the ovaries and testes (gonads)
Hypothalamus
Gonadotrophin
stimulating
hormone
stalk
Pituitary cell
making
gonadotrophins
(LH & FSH)
Pituitary gland
Egg (ovum)
formation)
LH
FSH
Oestrogen
secretion
LH
FSH
(trophin = “to drive”)
LH = luteinising
hormone, FSH =
follicle stimulating
hormone
Sperm
formation
Testosterone
secretion
Ovary
testicle
Hormone replacement
individualised patient by
patient
Sex hormone replacement treatment
(HRT)
Ovarian function
• LH & FSH can be used by
injection to stimulate
ovulation and enable
conception
• Oestrogen replacement
e.g. 1. Use of the pill
(oestrogen and
progesterone) in younger
women
2. Estrogen tablets or
patches in older
women
Testicular function
• LH & FSH can be used by
injection to stimulate
sperm production for
fertility (± sperm storage)
• Testosterone replacement
e.g. 1. Injections
2. Patches
3. Tablets
Vasopressin
Front part of
the pituitary
gland (“anterior
pituitary”)
Deficiency in vasopressin
causes diabetes insipidus
(frequent urination and
thirst, dehydration if fluid
intake not maintained)
Back part of
the pituitary
gland
(“posterior
pituitary”)
Releases vasopressin
(ADH)
Vasopressin acts on the
kidney to retain water in the
body by concentrating the
urine
Treatment of diabetes insipidus
Diabetes insipidus is relatively uncommon compared with anterior
pituitary hormone deficiency, since vasopressin is made in the
hypothalamus and travels down nerve endings to the posterior
pituitary, and damage to the hypothalamus is rare
Nasal spray taken up to 3
times/day
Nasal drops blown into nose
Tablets (not funded in NZ –
may be able to obtain under
special circumstances)
What about growth hormone itself?
As might be expected, sometimes the treatment of acromegaly is so
damaging to the pituitary that the natural secretion of growth
hormone becomes defective
Do we need growth hormone in adult life?
Answer = yes. It is not a hormone that is essential for life like
hydrocortisone or thyroid hormone, but it helps maintain energy,
muscle mass, cognitive function, reduced fat mass etc. Deficiency as
an adult can lead to a major reduction of quality of life in some (but
not all) individuals
Pharmac has a funded program for treating adults (and children) with
growth hormone if they are very deficient and have impaired quality
of life. Four out of 215 adults treated with GH in NZ are individuals
previously treated for acromegaly who are now profoundly GH
deficient
Hormone replacement therapy can be very successful…..