1. 30-Sep-16Introduction to Endocrine system1 Endocrine System

2. 30-Sep-16Introduction to Endocrine system2 Introduction  Endocrine system  One of the system involved  In coordination of body functions  Systems involved include 1. Neural system  Release chemical substances (neurotransmitters) at axon terminals  Act locally to control cell function

3. 30-Sep-16Introduction to Endocrine system3 Introduction 2. Endocrine system  Glands or specialized cells  Release chemicals (hormones)  Into blood Have influence on cell function at another location 3. Neuro-endocrine  Neurons secrete substances (neurohormone)

4. 30-Sep-16Introduction to Endocrine system4 Introduction  Reach circulating blood  Influence cell function at another location 4. Paracrine  Cells secrete substances  Diffuse in ECF  Affect neighboring cells

5. 30-Sep-16Introduction to Endocrine system5 Introduction 5. Autocrine  Cells secrete substances  Affect the functioning of the same cell

6. 30-Sep-16Introduction to Endocrine system6 Hormones  Working definition  Hormone is chemical substance  Serve as regulators & coordinators of  Various biologic functions in the body  Highly potent, specialized organic molecules  Produced by endocrine cells  In response to specific stimuli

7. 30-Sep-16Introduction to Endocrine system7 Hormones  They exert their actions on specific target cells  The target cells are equipped with  Receptor that bind hormones  With high affinity & specificity  When bound hormone  Initiate characteristic biological responses by target cells

8. 30-Sep-16Introduction to Endocrine system8 Principal Endocrine Organs OrganHormone Pituitary glandTropic hormones (ACTH, GH, prolactin) HypothalamusHypophysiotropic hormones (releasing hormones, TRH); ADH, oxytocin Thyroid glandThyroxin, triiodothyronin Adrenal glandsMineralocorticoids (aldosterone), glucocorticoids (cortisol), catecholamines (epinephrine, norepinephrine) Parathyroid glandParathtyroid hormone (PTH) GonadsTestosterone, estrogen, progesterone Pancreatic isletsInsulin, glucagon, somatostatin

9. 30-Sep-16Introduction to Endocrine system9 Principal Endocrine Organs Other organsHormone HeartAtrial natriuretic peptide (ANP) Kidney1,25-dihydroxycholecalciferol (calcitriol), erythropoeitin Liver25-hydroxycholecalciferol (calcidiol), somatomedin Pineal glandMelatonin SkinCalciferol (vitamin D) GITGastrin, cholecyctokinin (CCK), secretin, vasoactive intestinal peptide (VIP) etc

10. 30-Sep-16Introduction to Endocrine system10 Structure & Synthesis  3 general classes of hormone 1. Protein & polypeptides  Include hormones secreted by  Anterior pituitary  The pancreas (insulin, glucagon)  Parathyroid gland (PTH)

11. 30-Sep-16Introduction to Endocrine system11 Structure & Synthesis 2. Steroids, include hormones secreted by  Adrenal cortex  Cortisol, aldosterone  Ovaries  Oestrogen, progesterone  Testes  Testosterone  Placenta  Oestrogen, progesterone

12. 30-Sep-16Introduction to Endocrine system12 Structure & Synthesis 3. Derivatives of amino acid tyrosine  Thyroid gland  Thyroxin, tri-iodothyronin  Adrenal medulla  Epinephrine & norepinephrine

13. 30-Sep-16Introduction to Endocrine system13 Peptide Hormones  Polypeptides and protein hormone  Synthesized on  Rough endplasmic reticulum of the endocrine cells  Usually synthesized as preprohormone  Larger protein  Has no biological activity Preprohormone Prohormone Hormone & Inactive fragments Hormone & Inactive fragments Synthesis in RER Cleaved into prohormone in ER Packaging in Golgi, cleaved into active hormone

14. 30-Sep-16Introduction to Endocrine system14 Peptide Hormones  This is then cleaved  To a prohormone  In endoplasmic reticulum Preprohormone Prohormone Hormone & Inactive fragments Hormone & Inactive fragments Synthesis in RER Cleaved into prohormone in ER Packaging in Golgi, cleaved into active hormone

15. 30-Sep-16Introduction to Endocrine system15 Peptide Hormones  The prohormone is then  Transferred to Golgi apparatus  For packaging  In the process enzymes cleave it into  An active hormone &  A larger inactive fragment Preprohormone Prohormone Hormone & Inactive fragments Hormone & Inactive fragments Synthesis in RER Cleaved into prohormone in ER Packaging in Golgi, cleaved into active hormone

16. 30-Sep-16Introduction to Endocrine system16 Peptide Hormones  Secretion of peptide hormones  Active hormone & inactive fragment  Occur by exocytosis when  secretory vesicles fuse with cell membrane  Ca ++ Ca ++

17. 30-Sep-16Introduction to Endocrine system17 Peptide Hormones  Granular content are then extruded into  Interstitial fluid  Blood stream  Stimulation a) In many cases the stimulus for the exocytosis is   Ca ++ in cytosol as a result of  Depolarization of plasma membrane  Ca ++ Ca ++

18. 30-Sep-16Introduction to Endocrine system18 Peptide Hormones 2. In other cases  Stimulation of the endocrine cell surface receptors   cAMP  Activation of protein kinase  Initiate release of the hormone  cAMP Prot kinase Activation Receptor

19. 30-Sep-16Introduction to Endocrine system19 Peptide Hormones  Peptide hormone are water soluble  Enter the circulatory system easily  Carried to target tissues  cAMP Prot kinase Activation Receptor

20. 30-Sep-16Introduction to Endocrine system20 Steroid Hormones  Usually synthesized from cholesterol  Chemical structure  Similar to that of cholesterol  They are lipid soluble,consist of  3 cyclohexyl ring and  1 cyclopentyl ring

21. 30-Sep-16Introduction to Endocrine system21 Structure of Steroid Hormones 19 3 2 1 8 7 6 5 4 10 9 15 14 13 12 11 18 17 16 Derivative of cholesterol Have 3 cyclohexyl rings( A, B, C) One cyclopentyl ring (D) AB C D Cyclopentanoperhydrophenanthrene

22. 30-Sep-16Introduction to Endocrine system22 Steroid Hormones  There is little hormone stored  In steroid forming cells  But there are large stores  Of cholesterol esters  Can be rapidly mobilized for steroid synthesis

23. 30-Sep-16Introduction to Endocrine system23 Steroid Hormones  Most of the cholesterol  Come from plasma  But cells have the ability to synthesize it

24. 30-Sep-16Introduction to Endocrine system24 Steroid Hormones  Steroid hormones are lipid soluble  Once they are synthesized  They diffuse across cell membrane  Into interstitial fluid

25. 30-Sep-16Introduction to Endocrine system25 Amine Hormones  Derivatives of tyrosine  From the thyroid & adrenal medulla glands  Formed by the action  Of cytoplasmic enzymes

26. 30-Sep-16Introduction to Endocrine system26 Amine Hormones  Thyroid hormones  Synthesized and stored in thyroid gland  Incorporated in thyroglobulin  Stored in large follicle within the gland  Secretion occurs when  The amines are split from thyroglobulin  Free hormone released in blood  Bound to thyroxine binding globulin (TBG)  Which slowly releases the hormone to target tissues

27. 30-Sep-16Introduction to Endocrine system27 Amine Hormones  Epinephrine & norepinephrine  Formed in the adrenal medulla  Secrete 4 times more epinephrine than norepinephrine  Stored in vesicles  Secreted by exocytosis  In plasma can exist  Free form or in conjugation with other substances