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

Hypothalamus

Pituitary gland

Brain

Input from body and environmente.g. stress temperature water balance hunger/food weight season blood sugar

stalk

thyroidadrenals

ovaries/testes

Three hormone systems involving the pituitary

gland

Hypothalamus

Pituitary gland

Brain

Input from body and environmente.g. stress temperature water balance hunger/food weight season blood sugar

stalk

Growth hormone

prolactin

vasopressinAnother three

hormone systems involving the pituitary

gland

Why worry about pituitary hormones? Isn’t it enough to worry about growth hormone?

Normal pituitary or the pituitary stalk squashed by growth hormone-secreting adenoma

The normal pituitary gland may be damaged in various ways in individuals with growth-hormone –secreting

pituitary adenomas

Normal pituitary damaged by treatment

Position of normal pituitary

Hypothalamus

Pituitary gland

Brain

stalk

adrenals

The pituitary – adrenal pathway

ACTH – releasing hormone

ACTH – making cell

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

Hypothalamus

Pituitary gland

Regulation of the thyroid

stalk

Thyroid gland

TSH – releasing hormone

Pituitary cell making thyroid stimulating hormone

Thyroid stimulating hormone (TSH) in bloodstream

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)

T4

T3Main thyroid hormone acting on tissues

Converted to T3 in liver tissue

Thyroid gland

Hypothalamus

Pituitary gland

Control of the ovaries and testes (gonads)

stalk

Gonadotrophin stimulating hormone

Pituitary cell making gonadotrophins (LH & FSH)(trophin = “to drive”) LH = luteinising hormone, FSH = follicle stimulating hormone

LHEgg (ovum) formation)

FSH

Oestrogen secretion

Ovary

LH

testicle

Testosterone secretion

FSH

Sperm formation

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”)

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

Deficiency in vasopressin causes diabetes insipidus (frequent urination and thirst, dehydration if fluid intake not maintained)

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…..