The Endocrine System

1. The Endocrine System • chemical messages (hormones) that are released into the blood • Hormones control several major processes • Reproduction - gametogenesis, sexual desire • Growth and development • Maintenance of homeostasis - salts, water, blood pressure, RBCs • Regulation of metabolism - digestion, stress responses

2. Endocrine System Characteristics • Access to every cell • Each hormone acts only on specific cells (target cells) that have matching receptors • Endocrine control slower than nervous system • Endocrine and nervous systems interact

3. Classification of Hormones: Steroid • Steroid Hormones: • Lipid soluble, derived from cholesterol • Enter target cells • Activate specific genes to produce proteins • Slower acting: minutes to hours

4. Steroid Hormones: How does a steroid hormone cause changes in cells?

5. Hormones: Nonsteroid • Amino acid-based hormones proteins, peptides, amines • Water soluble • Bind to receptors on target cell surface • Work via second messengers to activate existing enzymes • Faster action: seconds to minutes

6. Non-Steroid Hormones: How does a non-steroid hormone cause changes in cells?

7. Control of Hormone Release • Hormone levels are maintained by negative feedback • Low hormone levels or a stimulus triggers the release of more hormone • Hormone release stops once an appropriate level in the blood is reached

8. 1. Hormonal Stimulus • Endocrine glands are activated by other hormones • Most common signal- coordinates response of several glands Figure 9.2a

9. 2. Humoral Stimulus • Changing blood levels of certain ions stimulate hormone release • PTH - to raise Ca++ • Calcitonin - to decrease Ca++ • Insulin - to decrease glucose Figure 9.2b

10. 3. Neural Stimulus • Nerve impulses stimulate hormone release • Usually by sympathetic nervous system Figure 9.2c

11. Location of Major Endocrine Organs Figure 9.3

12. Pituitary - Hypothalamus Relationship • Release of anterior pituitary hormones is controlled by hormones from hypothalamus • Hypothalamus produces two hormones that are stored in the posterior pituitary • posterior pituitary releases hormones when neurally stimulated by hypothalamus

13. Hormones of the Posterior Pituitary • Oxytocin • Stimulates contractions of the uterus during labor • Causes milk ejection • Antidiuretic hormone (ADH) • Can inhibit urine production • In large amounts, causes vasoconstriction

14. Hormones of the Anterior Pituitary • Six anterior pituitary hormones; common characteristics: • Proteins (or peptides) • Act through second-messenger systems • Regulated by hormonal stimuli, mostly negative feedback

15. Growth Hormone (GH) • General metabolic hormone • Major effects are directed to growth of skeletal muscles and long bones • Causes amino acids to be built into proteins • Causes fats to be broken down for a source of energy

16. Functions of Other Anterior Pituitary Hormones • Prolactin (PRL) • Stimulates milk production following childbirth • Function in males is unknown • Adrenocorticotropic hormone (ACTH) • Regulates the adrenal cortex (affects salt, glucose levels) • Thyroid-stimulating hormone (TSH) • Influences thyroid gland

17. Functions of Other Anterior Pituitary Hormones • Gonadotropic hormones - appear at puberty • Follicle-stimulating hormone (FSH) • Stimulates follicle development (ovaries) and sperm development (testes) • Luteinizing hormone (LH) • Triggers ovulation • Stimulates testosterone production in males

18. Thyroid Gland • Found at the base of the throat • Produces two hormones • Thyroid hormone - controls metabolism • Calcitonin - affects Ca++ levels in blood

19. Calcitonin • Decreases blood calcium levels by causing calcium deposition in bone (in children) • Antagonistic to PTH, parathyroid hormone Figure 9.9

20. Adrenal Glands • Two glands • Cortex – outer glandular region in three layers • Medulla – inner neural tissue region • Sits on top of the kidneys

21. Hormones of the Adrenal Cortex • Mineralocorticoids (mainly aldosterone) • Regulate mineral content in blood, water, and electrolyte balance via kidney action • Glucocorticoids (cortisone, cortisol) • Promote normal cell metabolism • Help resist long-term stressors • depress inflammatory response • Androgen, estrogen

22. Hormones of the Adrenal Medulla • Produces two similar hormones (catecholamines) • Epinephrine • Norepinephrine • prepare the body to deal with short-term stress

23. Roles of the Hypothalamus and Adrenal Glands in the Stress Response Figure 9.12

24. Pancreatic Islets • pancreas is a mixed gland • islet cells produce hormones: • Insulin – allows glucose to cross plasma membranes into cells • Glucagon – allows glucose to enter the blood • Somatostatin Figure 9.13

25. Diabetes • Diabetes mellitus - “sweet siphon” • Type I - lack of insulin • juvenile • Type II - resistant to effects of insulin • Adult onset

26. Other Hormone Sources • Thymus: thymosin and thymopoietin, assist maturation of T lymphocytes • Pineal gland: melatonin • Heart: atrial natriuretic hormone (ANH) • Digestive system: gastrin, secretin, cholecystokinin • Kidney: erythropoietin, renin