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ENDOCRINE SYSTEM. General Overview. Major Control System Ductless Glands; Produce Hormones Diffuse into Blood Slow Initial Effects, but Effects Persist much longer Hormones act on specific Targets Regulated by Negative Feedback. Classification of Glands.

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  2. General Overview • Major Control System • Ductless Glands; Produce Hormones • Diffuse into Blood • Slow Initial Effects, but Effects Persist much longer • Hormones act on specific Targets • Regulated by Negative Feedback

  3. Classification of Glands • Endocrine – ductless glands that secrete hormones into the blood stream • Exocrine – ducted glands that secrete their products onto a surface

  4. Hormones - General Function • Modify activity of target cells • Targets have specific receptors for the particular hormone • Distributed by blood

  5. Location of Receptors • Cell Surface • cell membrane • Intracellular • Cytoplasm • Nucleus

  6. There are Two Types of Hormones • Steroid Hormones • Attach to intracelluar receptor • Directly activate genes • Non-steroid Hormones • Attach to receptor on plasma membrane • A second messenger formsinside the cell to change cell’s activity

  7. Mechanisms of Hormone Action • Steroids (Synthesized from Cholesterol) • Hormone enters cell • Hormone forms complex with receptor • Complex binds to DNA in nucleus • Transcription of mRNA • New protein is synthesized in cytoplasm (Translation) • E.g. Testosterone

  8. Mechanisms of Hormone Action continued • Non-Steroids (Proteins/Peptides/Amine) • Hormone does not enter cell & acts as 1st messenger • Hormone binds to receptor on cell membrane • Enzyme is activated • 2nd messenger is produced • 2nd messenger affects cell function • E.g. Pituitary hormones

  9. How do Cells Respond to Hormones? • Precise response depends on target cell type •  or  rates of normal cellular processes: • Activates/deactivates enzymes • Stimulates protein synthesis • Opens/closes ion channels • Stimulates mitosis

  10. What Stimulates Endocrine Glands? • Hormonal - • Tropic hormones alter activity of other endocrine glands • Most common • Humoral • Changing levels of ions or nutrients trigger release of hormones • Neural • Nerve Impulses stimulate hormone release

  11. What if Hormone Levels are too High or too Low? • Cells can change the number of receptors they have: • Up Regulation • Low hormone levels • Number of receptors increases • Target’s responsiveness increases • Down Regulation • Excess hormone levels • Number of receptors decreases • Target’s responsiveness decreases

  12. Hypothalamus Pituitary Anterior Posterior Thyroid Gland Parathyroid Glands Adrenal Glands Cortex Medulla Pancreas Pineal Gland Thymus Gonads Endocrine Organs

  13. Hypothalamus • Integrates Nervous & Endocrine systems • Releasing Factors (hormones) stimulate secretion by Anterior Pituitary • Inhibiting Factors (hormones) are antagonistic to Releasing • Portal Circulation carries hormones to Anterior Pituitary • Nervous tissue carries hormones to Posterior Pituitary

  14. Pituitary Gland • Attached to Hypothalamus via infundibulum • Protected by sella turcica of sphenoid • Divided into 2 lobes: • Anterior (glandular) • Posterior (neural)

  15. Anterior Pituitary • “Master Gland” (makes & secretes various tropic hormones) • Tropic Hormones • Act on other Endocrine Glands • Serve as Hormonal Stimuli • Stimulate release of another hormone

  16. Anterior Pituitary continued • Human Growth Hormone (GH): • Target: All/Most Body Cells (esp. Bone & Muscle) • Action: Promotes Growth & Repair • Prolactin (PRL): • Target: Mammary Tissue • Action: Promotes milk production

  17. Anterior Pituitary continued • Thyroid Stimulating Hormone (TSH) • Target: Thyroid Gland • Action: Stimulates production of Thyroid Hormone

  18. Anterior Pituitary continued • Adrenocorticotropic Hormone (ACTH) • Target: Adrenal Cortex • Action: Controls production/secretion adrenal cortex hormones • Gonadotropic Hormones • Follicle Stimulating Hormone (FSH) • Target: Gonads (Ovaries/Testes) • Action: Production of gametes & sex hormones

  19. Anterior Pituitary continued • Luteinizing Hormone (LH/ICSH) • Target: Gonads • Functions: • Production of sex hormones • Prepare uterus for implantation • Develop corpus luteum in ovary

  20. Posterior Pituitary • Does NOT synthesize Hormones • Neural rather than glandular • Stores & Releases two hormones produced by hypothalamus • Oxytocin • Target: Uterus & Mammary Glands • Action: Stimulates Contractions to eject fetus & milk

  21. Posterior Pituitary continued • Antidiuretic Hormone (ADH) also called vasopressin • Target: Kidneys • Action: • Conserve Water (decrease urine volume) • Increase BP

  22. Thyroid Gland • Thyroid Hormone • T3 (Triiodothyronine), T4 (Thyroxine) • Target: All body cells • Action: Increase metabolic rate, regulate body temperature • Calcitonin • Target: Bone/Inhibits Osteoclasts • Action: Decrease blood Ca2+ (Hypocalcemia if excessive)

  23. Parathyroid Glands • Parathyroid Hormone • Target: Bone/Stimulates Osteoclasts • Action: Increase blood Ca2+ (Hypercalcemia if excessive)

  24. Adrenal Glands • Adrenal Cortex (outer/glandular) • Cortisol • Target: Many tissues • Action: make glucose, decrease inflammation • Aldosterone • Target: Kidneys • Action: Maintain Na+/K+ blood levels

  25. Adrenal Glands continued • Adrenal Medulla (inner/nervous) • Epinephrine/Adrenalin (Fear/Flight) • Norepinephrine/Noradrenalin (Anger/Fight) • Targets:Heart, Liver, Muscles, Blood Vessels, etc. • Functions: Prepare for sudden threat

  26. Pancreas • Endocrine (Islets of Langerhans) & Exocrine • Glucagon • Target: Liver • Action: Raises blood glucose • Insulin • Target: Most/All Cells • Action: Promotes glucose transport into cells (decreases blood glucose)

  27. Pineal & Thymus Glands • Pineal Gland (Endocrine & CNS) • Melatonin • Target: Hypothalamus • Action: Sets biological rhythms & promotes sleep • Thymus (atrophies at puberty) • Thymosins • Target: T cells of immune system • Action: T cell maturation (immunocompetence)

  28. Gonads • Ovaries • Estrogen • Target: Uterus, Ovaries, other • Action: prepare for fetus, secondary sexual characteristics • Progesterone • Target: Uterus • Action: maintains pregnancy, prevents uterine contractions

  29. Gonads continued • Testes • Testosterone • Target: Various body parts • Action: Secondary sexual characteristics

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