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The Endocrine System

The Endocrine System. Endocrine system . Includes all cells and endocrine tissues that produce hormones or paracrine factors. Endocrine vs Nervous System. Nervous system performs short term crisis management Endocrine system regulates long term ongoing metabolic

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The Endocrine System

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  1. The Endocrine System

  2. Endocrine system • Includes all cells and endocrine tissues that produce hormones or paracrine factors

  3. Endocrine vs Nervous System • Nervous system performs short term crisis management • Endocrine system regulates long term ongoing metabolic • Endocrine communication is carried out by endocrine cells releasing hormones • Alter metabolic activities of tissues and organs • Target cells • Paracrine communication involves chemical messengers between cells within one tissue

  4. Control of Endocrine Activity • Endocrine reflexes are the counterparts of neural reflexes • Hypothalamus regulates the activity of the nervous and endocrine systems • Secreting regulatory hormones that control the anterior pituitary gland • Releasing hormones at the posterior pituitary gland • Exerts direct neural control over the endocrine cells of the adrenal medullae

  5. Three Methods of Hypothalamic Control over the Endocrine System Figure 18.5

  6. Hypothalamic Control of Adenohypophysis • Hypothalamus regulates secretion of hormones • Secretes releasing factors to release hormones • Secretes inhibiting hormones to turn off secretion of hormones

  7. The Hypothalamus • The hypothalamus sends a chemical stimulus to the anterior pituitary to releasing hormones stimulate the synthesis and release of hormones • TRH - Thyrotropin releasing hormone (TRH) >> release of TSH • CRH - Corticotropin releasing hormone (CRH) >> release of ACTH • GnRH - Gonadotropin releasing hormone (GNRH) >> release of FSH and LH • GHRH – Growth hormone releasing hormone >> release of GH

  8. Hypothalamic Stimulation–from CNS

  9. Figure 25.3a–c The Pituitary Gland - Hypophysis • Attached to the hypothalamus by the infundibulum • Two basic divisions of the pituitary gland • Anterior pituitary or Adenohypophysis • Posterior pituitary or Neurohypophysis

  10. The Pituitary Gland - Hypophysis • Releases nine important peptide hormones • All nine bind to membrane receptors and use cyclic AMP as a second messenger

  11. Anterior Pituitary • Pars distalis - largest division of the adenohypophysis • Contains five different types of endocrine cells • Somatotropic cells -secrete growth hormone (GH) • Mammotropic cells - secrete prolactin (PRL) • Thyrotropic cells - secrete thyroid-stimulating hormone (TSH) • Corticotropic cells - secrete adrenocorticotropic hormone (ACTH) and melanocyte-stimulating hormone (MSH) • Gonadotropic cells - secrete follicle-stimulating hormone (FSH) and luteinizing hormone (LH) • Tropic hormones • TSH, ACTH, FSH, and LH • Regulate the secretion of hormones by other endocrine glands

  12. Hormones of the Adenohypophysis • Thyrotropin releasing hormone promotes the release of TSH • Thyroid stimulating hormone (TSH) triggers the release of thyroid hormones • Corticotropin releasing hormone causes the secretion of ACTH • Adrenocorticotropic hormone (ACTH) stimulates the release of glucocorticoids by the adrenal gland

  13. Hormones of the Adenohypophysis • Follicle stimulating hormone (FSH) - stimulates follicle development and estrogen secretion in females and sperm production in males • Luteinizing hormone (LH) causes ovulation and progestin production in females and androgen production in males • Gonadotropin releasing hormone (GNRH) promotes the secretion of FSH and LH

  14. Hormones of the Adenohypophysis • Prolactin (PH) –stimulates the development of mammary glands and milk production • Growth hormone (GH or somatotropin) - stimulates cell growth and replication • Melanocyte stimulating hormone (MSH) -stimulates melanocytes to produce melanin

  15. Posterior Pituitary • Structurally part of the brain • Contains axons of hypothalamic nerves • Manufactures antidiuretic hormone (ADH) • Decreases the amount of water lost at the kidneys • Elevates blood pressure • Manufactures oxytocin • Stimulates contractile cells in mammary glands • Stimulates smooth muscle cells in uterus Figure 25.5

  16. Table 25.1

  17. Feedback Control of Endocrine Secretion Figure 18.8a

  18. Negative Feedback Controls: Long & Short Loop Reflexes Figure 7-14: Negative feedback loops in the hypothalamicanterior pituitary pathway

  19. Negative Feedback Controls: Long & Short Loop Reflexes Figure 7-15: Control pathway for cortisol secretion

  20. Thyroid • Lies near the thyroid cartilage of the larynx

  21. Thyroid Follicles and Thyroid Hormones • Thyroid gland contains numerous follicles • Release several hormones such as thyroxine (T4) and triiodothyronine (T3) that regulate metabolism • increases protein synthesis • promotes glycolysis, gluconeogenesis, glucose uptake • C cells produce calcitonin - helps regulate calcium concentration in body fluids

  22. The Thyroid Follicles Figure 18.12b

  23. Thyroid hormones • Held in storage • Bound to mitochondria, thereby increasing ATP production • Bound to receptors activating genes that control energy utilization • Exert a calorigenic effect • C cells produce calcitonin - helps regulate calcium concentration in body fluids

  24. Four parathyroid glands • Embedded in the posterior surface of the thyroid gland • Chief cells produce parathyroid hormone (PTH) in response to lower than normal calcium concentrations • Parathyroid hormones are regulators of calcium levels in healthy adults

  25. Homeostatic Regulation of Calcium Ion Concentrations Figure 18.15

  26. Adrenal Cortex • Synthesizes and releases steroid hormones called corticosteroids • Different corticosteroids are produced in each of the three layers • Zona glomerulosa – mineralocorticoids (chiefly aldosterone) • Zona fasciculata – glucocorticoids (chiefly cortisol) • Zona reticularis – gonadocorticoids (chiefly androgens)

  27. Adrenal Cortex • Secretes over 30 different steroid hormones (corticosteroids) • Mineralocorticoids • Aldosterone: maintains electrolyte balance • Glucocorticoids • Cortisol: • Stimulates gluconeogenesis • Mobilization of free fatty acids • Glucose sparing • Anti-inflammatory agent • Gonadocorticoids • testosterone, estrogen, progesterone

  28. Mineralocorticoids • Regulate the electrolyte concentrations of extracellular fluids • Aldosterone – most important mineralocorticoid • Maintains Na+ balance by reducing excretion of sodium from the body • Stimulates reabsorption of Na+ by the kidneys • Aldosterone secretion is stimulated by: • Rising blood levels of K+ • Low blood Na+ • Decreasing blood volume or pressure

  29. Glucocorticoids (Cortisol) • Help the body resist stress by: • Keeping blood sugar levels relatively constant • Maintaining blood volume and preventing water shift into tissue • Cortisol provokes: • Gluconeogenesis (formation of glucose from non-carbohydrates) • Rises in blood glucose, fatty acids, and amino acids

  30. Gonadocorticoids (Sex Hormones) • Most gonadocorticoids secreted are androgens (male sex hormones), and the most important one is testosterone • Androgens contribute to: • The onset of puberty • The appearance of secondary sex characteristics • Sex drive in females • Androgens can be converted into estrogens after menopause

  31. Pancreatic Islets • Clusters of endocrine cells within the pancreas called Islets of Langerhans or pancreatic islets • Alpha cells secrete glucagons • Beta cells secrete insulin • Delta cells secrete GH-IH

  32. Insulin and glucagon • Insulin lowers blood glucose by increasing the rate of glucose uptake and utilization • Glucagon raises blood glucose by increasing the rates of glycogen breakdown and glucose manufacture by the liver

  33. Regulation of Blood Glucose Concentrations Figure 18.19

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