Endocrine Ppt Exam 3

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  • Endocrine Ppt Exam 3

    1. 1. Hormones and the endocrine system
    2. 2. In addition to electrical signals in the nervous system, chemical signals in the endocrine system are a primary means by which anatomical, physiological, and behavioral changes are regulated in humans. The chemical signals in the endocrine system are hormones.
    3. 3. Chemical communication requires both a cell (or group of cells) that produces and releases the hormone and a cell (or group of cells) with an appropriate receptor that receives the hormone. The interaction between the hormone and the receptor activates mechanisms within the target cell that lead ultimately to anatomical, physiological, or behavioral changes.
    4. 4. Humans produce a wide array of hormones that regulate a large number of changes or responses. Most hormones in humans are produced by endocrine glands, which are aggregations of cells that secrete hormones into the extracellular fluid, from which they enter the blood. After entering the blood, the hormones may be transported throughout the body. The major human endocrine glands are shown in Figure 41.5.
    5. 5. * Some hormones in humans are secreted by endocrine cells that are not part of discrete endocrine glands.
    6. 6. The endocrine system contains both lipid-soluble and water-soluble hormones, which differ in how they bind to receptors in or on the target cells.
    7. 7. Lipid-soluble hormones Lipid-soluble hormones include the steroid hormones. They pass readily through the lipid-rich plasma membrane that surrounds the target cell, and bind to receptors in the cytoplasm or nucleus of the cell.
    8. 8. In most cases, lipid-soluble hormones stimulate the synthesis of new kinds of proteins by altering gene expression in the target cell. The synthesis of new kinds of proteins leads ultimately to anatomical, physiological, or behavioral changes. As an example, the mechanism of action of one lipid-soluble hormone (cortisol) is illustrated in Figure 15.8.
    9. 9. * Because lipid-soluble hormones stimulate the synthesis of new kinds of proteins, rather than serving to modify existing proteins, their actions are slower and last longer than those of water-soluble hormone.
    10. 10. Examples of lipid-soluble hormones include: 1) cortisol 2) androgens, especially testosterone 3) estrogens, especially estradiol, and progesterone
    11. 11. * Cortisol is produced by the adrenal glands specifically the adrenal cortex (The adrenal glands are located above the kidneys) It is important in regulating the body’s response to stress It causes a decrease in the metabolism of glucose in most cells, except the brain and muscles, and an increase in the metabolism of proteins and fats It also blocks immune system reactions.
    12. 12. 2) Androgens are produced by the testes of males They stimulate ted development and maintenance of male sexual characteristics and behavior. They also stimulate sperm production.
    13. 13. 3) Estrogen and progesterone are produced by the ovaries of females. They stimulate the development and maintenance of female sexual characteristics and behavior.
    14. 14. Water-soluble hormones Water-soluble hormones do not pass readily through the lipid-rich plasma membrane that surrounds the target cell. Instead, they bind with receptors on the surface of the target cell. The receptors are glycoprotein complexes.
    15. 15. The receptors have a binding domain that projects beyond the outside of the plasma membrane and a catalytic domain that projects into the cytoplasm of the cell. Directly or indirectly, most receptors initiate cellular responses by activating protein kinases, which catalyze the transfer of phosphate groups from ATP to specific proteins.
    16. 16. Phosphorylation of specific proteins causes them to become activated or de-activated, thereby leading ultimately to anatomical, physiological, or behavioral changes. As an example, the mechanism of action of one water-soluble hormone (epinephrine) is illustrated in Figure 15.18.
    17. 17. * By activating or de-activating existing proteins, many water-soluble hormones produce rapid changes or responses (in contrast to most lipid-soluble hormones).
    18. 18. Examples of water-soluble hormones include: 1) epinephrine (or adrenaline) 2) insulin 3) luteinizing hormone and follicle-stimulating hormone
    19. 19. * 1) Epinephrine is produced by the adrenal glands specifically the adrenal medulla. It is important in regulating the body’s immediate response to stress (the so- called “fight or flight” reactions). It causes increases in heart rate, breathing rate, blood pressure, and blood sugar concentration. It also divert blood flow to active skeletal muscles.
    20. 20. * 2) Insulin is produced by the pancreas gland. (The pancreas gland is located just below the stomach) It stimulates the uptake and metabolism of glucose, and increases the conversion of glucose to glycogen and fat.
    21. 21. * 3) Luteinizing hormone and follicle-stimulating hormone are produced by the anterior pituitary gland. ( The pituitary gland is located in a depression at the bottom of the skull just over the back of the roof of the mouth.) Luteinizing hormone stimulates the production and release of androgens by the testes. Luteinizing hormone and follicle-stimulating hormone stimulate the production and release of estrogens and progesterone by the ovaries.
    22. 22. * Luteinizing hormone and follicle-stimulating hormone are also known as gonadotropins.
    23. 23. Interaction between the nervous and endocrine systems As we discussed previously, the hypothalamus is part of the brain (specifically the diencephalon), and is thus part of the nervous system. As illustrated in Figure 41.5, the hypothalamus also functions as a key endocrine gland.
    24. 24. The hypothalamus is connected to the anterior pituitary gland by a specialized set of portal blood vessels, as illustrated in Figure 41.7. Neurohormones synthesized in neurons in the hypothalamus are secreted near capillaries that give rise to the portal blood vessels. The neurohormones are then transported in the blood vessels to the anterior pituitary gland, where they regulate secretion of the so-called tropic hormones.
    25. 25. *Tropic hormones produced by the anterior pituitary gland are hormones that control the activities of other endocrine glands.
    26. 26. As one example, gonadotropin-releasing hormone is a neurohormone produced by the hypothalamus. Gonadotropin-releasing hormone stimulates the production and release of the two tropic hormones, luteinizing hormone and follicle-stimulating hormone, by the anterior pituitary gland.
    27. 27. In turn, luteinizing hormone stimulates the production and release of androgens by the testes (in males), and luteinizing hormone and follicle- stimulating hormone stimulate the production and release of estrogens and progesterone by the ovaries (in females).
    28. 28. As a second example, corticotropin-releasing hormone is a neurohormone produced by the hypothalamus. Corticotropin-releasing hormone stimulates the production and release of the tropic hormone, corticotropin, by the anterior pituitary gland. In turn, corticotropin stimulates the production and release of cortisol by the adrenal cortex.
    29. 29. Multiple negative feedback loops may regulate the “chain of command” from the hypothalamus to the anterior pituitary gland to other endocrine glands, as illustrated in Figure 41.8. For example, when sufficient cortisol reaches the anterior pituitary gland in the circulating blood, it inhibits the further release of corticotropin. In addition, sufficient cortisol reaching the hypothalamus inhibits the further release of corticotropin-releasing hormone.
    30. 30. In some cases, a tropic hormone also exerts negative feedback control on the hypothalamus, inhibiting the production of the corresponding releasing hormone.
    31. 31. *With respect to sexuality, puberty is initiated by a reduction in the sensitivity of hypothalamic neurons to negative feedback control by gonadotropins and sex hormones. As a result, more gonadotropin-releasing hormone is produced by the hypothalamic neurons, resulting in higher levels of gonadotropins and this in sex hormones (androgens or estrogen/progesterone) The increase in sex hormones leads, in turn, to the profound anatomical and physiological changes associated with sexual maturation.
    32. 32. Recommended reading:  pp. 1054-1078

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