What is Endocrinology?

1. 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.

2. Interaction of the pituitary gland with other glands in the body

3. Brain Hypothalamus Input from body and environment e.g. stress temperature water balance hunger/food weight season blood sugar stalk Pituitary gland thyroid adrenals ovaries/testes Three hormone systems involving the pituitary gland

4. 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

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

6. 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

7. Brain The pituitary – adrenal pathway Hypothalamus stalk ACTH – releasing hormone Pituitary gland ACTH – making cell Adrenal stimulating hormone (ACTH) adrenals Cortisol (hydrocortisone) released into blood stream Acts on many different cell types in the body

8. 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

9. 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

10. 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 Main thyroid hormone acting on tissues T3 T4 Converted to T3 in liver tissue

11. Control of the ovaries and testes (gonads) Hypothalamus Gonadotrophin stimulating hormone stalk Pituitary cell making gonadotrophins (LH & FSH) (trophin = “to drive”) LH = luteinising hormone, FSH = follicle stimulating hormone Pituitary gland Egg (ovum) formation) LH FSH LH FSH Sperm formation Oestrogen secretion Testosterone secretion Ovary Hormone replacement individualised patient by patient testicle

12. 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

13. Vasopressin Front part of the pituitary gland (“anterior pituitary”) Back part of the pituitary gland (“posterior pituitary”) Releases vasopressin (ADH) Deficiency in vasopressin causes diabetes insipidus (frequent urination and thirst, dehydration if fluid intake not maintained) Vasopressin acts on the kidney to retain water in the body by concentrating the urine

14. 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)

15. 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

16. Hormone replacement therapy can be very successful…..