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24.1 Hormones

24.1 Hormones. A hormone is a chemical signal that is produced in one part of the body and that acts at a distant site Three advantages to using chemical signals 1. Can spread to all tissues via the blood 2. Can persist much longer than electric signals 3. Many can act as hormones

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24.1 Hormones

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  1. 24.1 Hormones • A hormone is a chemical signal that is produced in one part of the body and that acts at a distant site • Three advantages to using chemical signals • 1. Can spread to all tissues via the blood • 2. Can persist much longer than electric signals • 3. Many can act as hormones • Different hormones can target different tissues

  2. Hormones are produced by endocrine glands • These glands do not have ducts • Hormones are secreted directly into the blood • Hormones are under the control of the neuroendocrine system • The hypothalamus is the main switchboard • Issues commands to the nearby pituitary gland • Pituitary sends chemical signals to the various hormone-producing glands in body

  3. Fig. 24.1 Major glands of the human endocrine system

  4. Hormones are effective because they are recognized by specific receptors • These are on or in target cells • The path of communication of a hormone signal • 1. Issuing the command • By the hypothalamus • 2. Transporting the signal • By the blood • 3. Hitting the target • Binding to the receptor • 4. Having an effect • A change in cell activity

  5. Fig. 24.2 How hormonal communication works

  6. 24.2 How Hormones Target Cells • Steroid hormones • Manufactured from cholesterol • Lipid-soluble and thus can across the lipid bilayer of the cell membrane • Bind to receptors within the nucleus usually • The hormone-receptor complex binds to DNA causing changes in gene activity • Anabolic steroids • Synthetic compounds resembling testosterone • Cause muscle cells to produce more protein

  7. Fig. 24.3 How steroid hormones work

  8. Fig. 24.4 • Peptide hormones • Short peptides or full-sized proteins • Bind to receptors embedded in the cell membrane • Induce a change in cytoplasmic end of the receptor protein • Triggers events within the cytoplasm

  9. Fig. 24.5 • Trigger a cascade of enzymic activation within cell • The change in cellular activity is facilitated by second messengers such as cAMP

  10. 24.3 The Hypothalamus and the Pituitary • The pituitary gland is located in a bony recess in the brain below the hypothalamus • It produces nine major hormones • It is actually two glands • Posterior lobe • Anterior lobe

  11. The Posterior Pituitary • Stores and releases two short peptide hormones • Vasopressin(antidiuretic hormone, ADH) • Regulates water conservation by the kidney • Oxytocin • Initiates uterine contractions during childbirth • Causes milk letdown • Both synthesized within hypothalamus neurons • Transported down nerve axons to the posterior lobe

  12. Fig. 24.6 Posterior pituitary

  13. The Anterior Pituitary • A complete gland that produces seven major hormones • 1. Thyroid-stimulating hormone (TSH) • 2. Luteinizing hormone (LH) • 3. Follicle-stimulating hormone (FSH) • 4. Adrenocorticotropic hormone (ACTH) • 5. Growth hormone (GH) • 6. Prolactin • 7. Melanocyte-stimulating hormone (MSH)

  14. Fig. 24.7 The role of the pituitary

  15. Fig. 24.8 • Secretes releasing and inhibiting hormones into capillaries • Hypothalamo-hypophyseal portal system carries the hormones to the pituitary • The hypothalamus controls the anterior pituitary

  16. Fig. 24.9 • Regulated by the hormones whose secretion they stimulate! • Hypothalamus and anterior pituitary are themselves controlled by negative feedback inhibition Thyrotropin-releasing hormone Gonadotropin-releasing hormone Corticotropin-releasing hormone

  17. 24.4 The Pancreas • The pancreas gland is located behind the stomach • Secretes a number of digestive enzymes into the small intestine through a narrow tube • Islets of Langerhans govern blood glucose levels • Insulin • Secreted by beta cells • Storage hormone that promotes accumulation of glycogen in liver and triglycerides in fat cells • Glucagon • Secreted by alpha cells • Cause release of stored glucose and fat breakdown

  18. Fig. 24.10

  19. Diabetes mellitus • Affected individuals cannot take up glucose from the blood • Type I • ~ 5-10% of diabetics • Autoimmune disorder in which immune systems attacks the Islets of Langerhans • Develops before age 20 (juvenile-onset diabetes) • Treated by daily injections of insulin • Type II • ~ 90-95% of diabetics • Caused by abnormally low number of insulin receptors • Develops after age 40 (adult-onset diabetes) • Typically in obese individuals • Treated by diet and exercise

  20. 24.5 The Thyroid, Parathyroid and Adrenal Glands • The thyroid gland lies just below the Adam’s apple in front of the neck • Its two most important hormones are • Thyroxine • Increases metabolic rate and promotes growth • Contains iodine • Lack of iodine in diet causes goiters • Calcitonin • Stimulates calcium deposition in thebone

  21. Fig. 24.11 The thyroid gland secretes thyroxine Goiter

  22. The parathyroid glands are four small glands attached to the thyroid • Produce parathyroid hormone (PTH) • One of only two hormones essential for survival • Acts as a fail-safe mechanism ensuring that calcium levels never fall too low • Calcium ions are key to muscle contractions • When levels are low, PTH stimulates osteoclast cells to break down bone matrix • This raises calcium levels in the blood • PTH also acts on kidneys to reabsorb calcium ions from the urine

  23. Fig. 24.12 Maintenance of proper calcium levels in the blood

  24. The adrenal glands are two glands, one located just above each kidney • Each composed of two parts • Medulla – Inner core • Adrenaline and norepinephrine • Released in times of stress to stimulate rapid deployment of body fuel • Cortex – Outer shell • Cortisol – Stimulates carbohydrate metabolism and reduces inflammation • Aldosterone – Stimulates the kidney to uptake sodium and other ions from the urine • This is the other hormone that is absolutely essential for survival

  25. 24.6 A Host of Other Hormones • Steroid sex hormones • Estrogen, progesterone and testosterone • Produced by gonads to regulate sexual development • Atrial natriuretic hormone • Secreted by the right atrium of the heart • Stimulate kidneys to excrete salts and water in the urine • Erythropoietin • Secreted by the kidney • Stimulates the bone marrow to produce RBC

  26. Molting and Metamorphosis in Insects • Molting is triggered by the molting hormone, also called ecdysone • The production of ecdysone is itself controlled by the brain hormone • These two hormones are balanced by a third hormone, the juvenile hormone • If present in high levels, it inhibits the formation of the pupa and adult forms

  27. Fig. 24.13 The hormonal control of metamorphosis in the silkworm moth, Bombyx mori

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