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The Endocrine System

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PART 1. The Endocrine System. The Endocrine System: An Overview. A system of ductless glands Secrete messenger molecules called hormones Interacts closely with the nervous system Endocrinology Study of hormones and endocrine glands. Endocrine Organs. Scattered throughout the body

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The Endocrine System

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  1. PART 1 The Endocrine System

  2. The Endocrine System: An Overview • A system of ductless glands • Secrete messenger molecules called hormones • Interacts closely with the nervous system • Endocrinology • Study of hormones and endocrine glands

  3. Endocrine Organs • Scattered throughout the body • Pure endocrine organs • Pituitary, pineal, thyroid, parathyroid, and adrenal glands • Organs containing endocrine cells • Pancreas, thymus, gonads, and the hypothalamus • Richly vascularized

  4. Location of the Major Endocrine Glands Figure 25.1

  5. Hormones • Classes of hormones • Amino acid-based hormones • Steroids – derived from cholesterol • Basic hormone action • Circulate throughout the body in blood vessels • Influences only specific tissues – target cells • A hormone can have different effects on different target cells

  6. Control of Hormones Secretion • Secretion triggered by three major types of stimuli • Humoral – simplest of endocrine control mechanisms • Secretion in direct response to changing ion or nutrient levels in the blood • Parathyroid monitors calcium • Responds to decline by secreting hormone to reverse decline

  7. Control of Hormones Secretion • Neural • Sympathetic nerve fibers stimulate cells in the adrenal medulla • Induces release of epinephrine and norepinephrine • Hormonal • Stimuli received from other glands • Certain hormones signal secretion of other hormones • Hypothalamus secretes hormones  stimulates pituitary  stimulates other glands

  8. Control of Hormones Release: Three Mechanisms Figure 25.2a–c

  9. Control of Hormones Secretion • Always controlled by feedback loops • Blood concentration declines below a minimum • More hormone is secreted • Blood concentration exceeds maximum • Hormone production is halted

  10. The Pituitary Gland (Hypophysis) • Secretes nine major hormones • Attached to the hypothalamus by the infundibulum • Two basic divisions of the pituitary gland • Adenohypophysis • Neurohypophysis

  11. The Pituitary Gland Figure 25.3a–c

  12. The Adenhypophysis • Pars distalis • The largest division of the adenohypophysis • Contains five different types of endocrine cells • Somatotropic cells • Secrete growth hormone (GH) • Mammotropic cells • Secrete prolactin (PRL)

  13. The Adenhypophysis • Pars distalis endocrine cells (continued) • 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)

  14. The Paris Distalis • Tropic hormones • TSH, ACTH, FSH, and LH • Regulate the secretion of hormones by other endocrine glands • The five endocrine cell types group into three categories when stained • Acidophils • Basophils • Chromophobes

  15. Hypothalamic Control of Hormone Secretionfrom the Adenohypophysis • Hypothalamus • Regulates secretion of hormones • Secretes releasing factors to release hormones • Secretes inhibiting hormones to turn off secretion of hormones

  16. Hypothalamic Control of Hormone Secretionfrom the Adenohypophysis Figure 25.4

  17. The Neurohypophysis • Structurally part of the brain • Secretes two hormones • Antidiuretic hormone (ADH) • Oxytocin Figure 25.5

  18. Table 25.1

  19. The Thyroid Gland • Located in the anterior neck • Largest pure endocrine gland • Composed of follicles and areolar connective tissue • Produces two hormones • Thyroid hormone (TH) • Calcitonin

  20. The Thyroid Gland Figure 25.6a

  21. The Thyroid Gland Figure 25.6b, c

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