Endocrine System

1. Endocrine System PA 481: Anatomy & Physiology Tony Serino, Ph.D. Biology Department Misericordia Univ.

2. Endocrine System • Controls and modifies the internal environment by releasing chemicals (hormones) into the blood • Slower response time but longer duration of action compared to nervous system

3. Chemical Messengers (hormones) • Hormone –secreted by cell into blood and acts on another cell some distance away • Neurohormone –secreted by neuron into blood to affect a target cell some distance away • Local hormones –secreted by cell into interstitial fluid to affects cells nearby • Paracrines –affect neighboring cells • Autocrines –affect the secreting cell • Pheromones –secreted by cell onto body surface to affect cells of another individual

4. Hormones • Chemical Classification • Amines –single or few amino acids, most water soluble • Epinephrine, Thyroxine (but water insoluble), Melatonin • Proteins –short to long chains of amino acids; water soluble • GH, FSH, LH, Insulin, Glucagon, ADH, etc. • Steroids –derivatives of cholesterol; water insoluble • Estrogen, Testosterone, Progesterone, Cortisol, Aldosterone

5. Steroid Hormones

6. Characteristics Common to all Hormones • Must have target cell with appropriate receptor molecules • Receptor-hormone complex must trigger events in target cell that changes its physiology • Mechanisms for deactivating the hormone response must be present

7. Controlling Hormone Response • Half-life of the hormone • Physiological range • Modifying target cell response • Up and down regulation • Turning off secretion • Negative feedback • Control by other hormones, neurons and metabolites

8. Control of Hormone Secretion

9. Mechanisms of Hormone Action 2nd messengers Water Soluble Water Insoluble Carrier protein

10. 2nd Messengers: cAMP

11. 2nd Messengers: IP3 and Ca++-Calmodulin

12. Steroid Hormone Transduction

13. Different Styles of Secretion • Prohormone –a hormone that is made as a larger (inactive form) that must be changed prior to secretion (allows for storage of hormone in secreting cell)Ex.: proinsulin, pro-opiomelanocortin • Prehormone –a hormone that is secreted in an inactive form that must be changed near or in the target cellEx.: Thyroxine, Angiotensinogen

14. Proinsulin

15. Types of Endocrine Disorders • Hypersecretion • Too much secretion of the hormone • Hyposecretion • Too little secretion of hormone • Hyporesponsiveness • Normal secretion, but little to no response by target cells

16. Endocrine Glands

17. Control of Growth • Growth periods: prenatal and postnatal (consists of pre-puberal (especially the first 2 years –infancy) and puberty • Several factors influence growth: genetics, diet, health, and hormonal balance • Prenatal growth dominated by insulin secretion, post-natal dominated by GH, thyroxine, and sex hormones

18. GH secretion and effects GH secretion stimulated by exercise, fasting, sleep (diurnal rhythm), stress, decreased plasma glucose, increased plasma AA (such as after a high protein meal) Increase protein synthesis Increase differentiation (increase mitosis)

19. GH interactions with other Hormones • Thyroxine: essential and permissive for GH • Needed to maintain energy levels for growth • Increases sensitivity of target cells to GH effects • Insulin: essential for GH effects • Dominant hormone for pre-natal growth • Estrogen and Testosterone: surge at puberty stimulates GH release, synergistic with GH anabolism; also trigger epiphyseal closure • Cortisol: anti-growth effects; decrease GH secretion, cell division, and increase catabolism

20. GH pathologies • Hypersecretion: • Gigantism –in children with responsive epiphyseal plates • Acromegaly –in adults, with closed epiphyseal plates

21. GH pathologies • Hypofunction: • Dwarfism –in children • Pituitary –decreased GH secretion • Laron –decreased responsiveness due to lack of GH receptors 28 yo woman withpituitary dwarfism; 45” tall Achondroplastic Dwarfism (genetic dwarf) due to failure of cartilage to form in epiphyseal plate