Introduction to endocrinology

Basic Introduction to the vast science of the endocrine glands and their interactions. A brief review into the physiological processes that result in endocrine disorders.

1. Introduction to Endocrinology

2. Course Plan Introduction Pituitary gland, Hypothalamus and their disorders Hypothyroidism Hyperthyroidism Diabetes Mellitus Acute Complications of Diabetes Mellitus Chronic Complications of Diabetes Mellitus Disorders of the Adrenal Cortex Phaeochromocytoma Calcium and the Parathyroids

3. Introduction Endocrinology is the understanding of hormone secretion, hormone action, and principles of feedback control . The endocrine system is evaluated primarily by measuring hormone concentrations . Most disorders of the endocrine system are amenable to effective treatment once the correct diagnosis is determined .

4. Introduction The term endocrine was coined by Starling Hormones secreted internally (endocrine) Externally (exocrine) i.e. into a lumen , such as the gastrointestinal tract. The term hormone - derived from a Greek phrase meaning “to set in motion,” aptly describes the dynamic actions of hormones as they elicit cellular responses and regulate physiologic processes through feedback mechanisms.

5. Introduction The Endocrine organs Hypothalamus P ituitary gland Thyroid gland Parathyroid glands Adrenal glands Pancreatic islet cells (Endocrine Pancreas) Gonads Others – Eg . The gastrointestinal tract The classic endocrine organs

6. Introduction Other hormones Kidney (Erythropoietin, Renin) Heart (ANP) Lungs (PG, ACE) GIT (Many GI hormones) Placenta (Many hormones during Pregnancy)

7. Hormones 5 major classes Amino acid derivatives  dopamine, catecholamine, and thyroid hormone; Small neuropeptides  gonadotropin-releasing hormone ( GnRH ), thyrotropin-releasing hormone (TRH), somatostatin, and vasopressin; Large proteins  insulin, luteinizing hormone (LH), and PTH produced by classic endocrine glands; Steroid hormones such as cortisol and estrogen; Vitamin derivatives such as retinoids (vitamin A) and vitamin D.

8. Hormones A variety of peptide growth factors , most of which act locally, share actions with hormones . As a rule – protein based hormones act on the ‘cell surface receptors’ and steroid based hormones act on ‘intracellular nuclear proteins’

9. 9 (a) Humoral : in response to changing levels of ions or nutrients in the blood (b) Neural : stimulation by nerves (c) Hormonal : stimulation received from other hormones Mechanisms of hormone release

10. Endocrine glands Sites of hormone action Exocrine glands

11. Autocrine glands Sites of hormone action Neurotransmission

12. Functions Maintenance of growth & development – Growth hormone, Thyroxine , insulin, Glucocorticoid, & Gonadal hormones Maintenance of internal environment – ADH, Mineralocorticoids , PTH Regulation of energy balance and metabolism –Insulin, glucagon , Leptin & Ghrelin Reproduction & species propagation – Gonadal & Pituitary hormones

13. Interactions between hormones When two or more hormones work together to produce particular result their effects are said to be synergistic . These effects may be additive or complementary. Additive : Same effect of the hormones on one target organ, for example, epinephrine and norepinephrine on heart rate Complementary : Work on different stages of a physiological procedure, for example, FSH (initiation) and testosterone (maintenance) on spermatogenesis 1. Synergistic effects

14. Interactions between hormones 1. Synergistic effects

15. Interactions between hormones A hormone is said to have a permissive effect on the action of a second hormone when it enhances the responsiveness of a target organ to the second hormone or when it increases the activity of the second hormone. Estrogen – Expression of progesterone receptors on uterus – progesterone effect on the uterus. Glucocorticoids – effects of catecholamines on cardiovascular system Thyroid hormones- effects of catecholamines on cardiovascular system 2. Permissive effect

16. Interactions between hormones In some situations the actions of one hormone antagonize the effects of another. Lactation during pregnancy is prevented because the high concentration of estrogen in the blood inhibits the action of prolactin and hence milk secretion. 2. Antagonistic effect

17. Example of an endocrinal axis Regulation by negative feedback and direct control is shown, along with the equilibrium between active circulating free hormone and bound or metabolized hormone.

18. Endocrinal axes

19. Regulation Feedback control , both negative and positive, is a fundamental feature of endocrine systems. Each of the major hypothalamo -pituitary-hormone axes is governed by negative feedback, a process that maintains hormone levels within a relatively narrow range

20. Regulation As an example, a small reduction of thyroid hormone triggers a rapid increase of TRH and TSH secretion,  thyroid gland stimulation and increased thyroid hormone production. When thyroid hormone reaches a normal level, it feeds back to suppress TRH and TSH. Feedback regulation also occurs for endocrine systems that do not involve the pituitary gland, Eg . glucose inhibition of insulin secretion

21. Overview of Endocrine disorders

22. Overview of Endocrine disorders

23. Presentation

24. Investigations

25. Thank you