Assist prof. of Medical Physiology

1. Physiology of Endocrine Assist prof. of Medical Physiology Abdelaziz M. Hussein

2. Introduction

3. Introduction • Body functions are regulated by 2 systems;

4. Introduction nervous system

5. Introduction Endocrine gland Blood vessels Receptor Biological effect Target cell

6. Introduction • Endocrine glands are groups of cells that produce specific chemicals, called hormones, having well defined effects on body functions. • Also, called ductlessglands since their secretion is not conveyed along ducts but pass directly into blood and lymphatic vessels.

7. Introduction General features of hormones (def.) 1) A specific chemical substance 2) Secreted by ductless gland 3) In a catalytic amount (very small amounts), 4) Transported by the blood (directly or through lymphatics), To a specific target cells (which have a specific hormone receptors), 5) Where it produces: • physiologic, • morphologic and • biochemical responses

8. Neuro-endocrine system • Both nervous and endocrine systems form together a biological communication network for integration of the body response to a changing environment.

9. Neuro-endocrine system • Examples of this link: • 1) Hypothalamic neurosecretory cells, • A) Some neurons delivered substances through hypothalamo-hypophyseal portal vessels to the ant. pituitary to regulate its secretions. • B) Other hypothalamic neurons send their axons to the post pituitary, where they release neurosecretory products directly into the blood stream.

11. Neuro-endocrine system Hypothalamic neurosecretory cells

13. 2- Innervation of the endocrine glands: Most, endocrine glands, receive nerves that appear to control their blood supply and secretory activity. 3- Also, thyroid, gonadal and adrenocortical hormones act on the CNS to inhibit or stimulate the secretory activity of the hypothalamic neurons. Neuro-endocrine system

14. Neuro-endocrine system Secretion of adrenaline and noradrenaline from adrenal medulla by symp. N.F.

15. Neuro-endocrine system Feedback of Thyroid Hormones on Pituitary Gland

16. Hormone Secreting Tissues • Virtually all organs of the body exhibit endocrine function II- Organs with endocrine functions I-Endocrine glands • 1- Heart • 2- Kidney • 3- Liver • 4- Skin • 5-GIT • 6- Placenta • 1- Hypothalamus • 2- Pituitary gland • 3- Thyroid gland. • 4- Parathyroid glands • 5- Suprarenal glands • 6- Endocrine portion of the pancreas • 7- Primary sex organs:testes and ovaries • 8- Thymus gland • 9- Pineal gland

18. Local Hormones Some hormones act only locally, e.g.: 1- Paracrine hormones, which diffuse for a short distance through the interstitial space to affect neighbouring cells. 2- Autocrine hormones, which act on the same cells. 3- Juxtacrine, whereby one cell interact with specific receptor on juxta-posed cells. Example: PGs, histamine, serotonin, bradykinin, epinephrine, acetylcholine, endorphins, encephalins, GIT hormones.

19. Autocrine Hormones

20. Juxtacrine Hormones Biological effect

21. Paracrine Hormones Biological effect

22. Endocrine, Paracrine and Autocrine hormones

23. Protein H. Steroid H. P.P A.A Chemical nature of hormones • From cholesterol: • A) Adrenal cortical H. • B) Sex H. • C) D3. -Pituitary gland -Hypothalamus -Calcitonin. -Parathyroid H. -Pancreatic H. -GIT H. -Thyroid h. -Catechol. -Melatonin

24. Synthesis: Amino acid and steroid hormones are synthesized through series of enzymatic reactions Peptide hormones are synthesized as proteins in the ribosomes. Storage : Catecholamines and polypeptide hormones are stored in secretory granules thyroxin and steroid hormones not stored in granules & present in the free form within the cytoplasm . Synthesis & Storage of Hormones

25. Protein hormone synthesis

26. Protein hormone synthesis

27. Amine hormone synthesis • 2 groups of hormones derived from the amino acid tyrosine • Thyroid hormonesand Catecholamines

28. Amine hormone synthesis

29. Most endocrine glands produce their hormones continually at levels determined by: a)Body requirements. b)Rate of hormone inactivation. c)Rate of hormone clearance from the body. Synthesis & Storage of Hormones

30. Hormone Release 1. Catecholamine and polypeptide hormones are stored in secretory granules, are released by the process of exocytosis. 2. Thyroxin and steroid hormones are present in the free form within the cytoplasm and leave the cell by simple transfer through the plasma membrane.

33. Hormone Transport The released hormones enter the blood, where they may circulate in 2 forms: • 1. Free (unbound) part: the active part which binds to receptor. • 2. Bound part: carried by specific albumins and globulins which are synthesized in the liver. In general, steroid and thyroid hormones are bound to transport proteins, whereas polypeptide and other amine hormones circulate in a free form.

36. The plasma half-life of a hormone (time needed for the concentration of the hormone to decrease to its half) is correlated with the % of protein binding. For example, Thyroxin is 99.98% protein bound and has a plasma half-life of 6 days, Whereas aldosterone, a steroid hormone, is only 15% bound and its plasma half-life of 25 minutes. Hormone Transport

37. Thank You