GH/TH and Gestational Diabetes(5 pages)
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GH/TH and Gestational Diabetes
- Lecture number:
- Lecture Note
- University of Southern California
- Bisc 307l - General Physiology
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BISC 307L 2nd Edition Lecture 19 Current Lecture Growth Hormone Effects: Indirect effects are due to induction of IGF synthesis and secretion within target cells. Among these target cells, IGF production in the liver was particularly important because of the amount of IGF production spilling out of the liver and becoming a circulating growth hormone for the rest of the body. For most other tissues, IGF acts locally as a paracrine hormone to stimulate the growth of that tissue. Those are the indirect and most powerful effects. Direct – widespread. Stimulates: many anabolic reactions protein & RNA synthesis lipolysis: in adipose tissues Overall • lean body mass due to increase in muscle growth, fat content in adipose tissue • Increased organ size, especially in bones, heart, and lungs • Effects on long bones important in determining height Control of Growth Hormone Secretion: Control follows the classical hypothalamic and anterior pituitary pathway. If we start with growth hormone secretion from somatotropes of the Anterior Pituitary, the release of GH is directly stimulated by GHRH. There is also a hypothalamic release- inhibiting hormone, called SS. So there is dual hypothalamic control of the secretion of GH from the ant pit. GH affects many different target cells, indirectly. GH works through 3 different stimuli for growth – direct effect of circulating growth hormone on target cells, an indirect effect mediated through IGH produced in the target tissue, and an indirect effect mediated by IGF produced by the liver and circulating through the body as a hormone. So IGF acts as both a circulating hormone and a paracrine hormone. The negative feedback is typical – the peripheral hormones, IGF and GH, feedback and inhibit the releasing hormone and the GH itself, as shown by the dashed arrows. Patterns of GH secretion originate in the hypothalamus. Can see that there is a strong age dependent pattern to GH release. In fetal life, it doesn’t have much effect, but it has a strong effect in prenatal life. After birth, GH secretion is highest in childhood, reaching a peak at puberty. Then it starts a slow and steady decline from that point throughout the rest of life. In midlife and advanced age, GH is still secreted but at lower levels. A fall in plasma glucose from a high level (like after a meal) will cause an increase in secretion of GH. Insulin will take care of moving the fuel molecules from the plasma into glycogen stores and fat stores as we’ve discussed. Then what happens? That energy, stored in those forms, can be utilized to power tissue growth by a subsequent bout of secretion of growth hormone. Makes it possible for food you ate to actually go into RNA protein synthesis and growth and maintenance of tissue. Growth Hormone Pathologies Dwarfism: Caused by a deficiency in growth hormone secretion, or a deficiency in GH or IGF Receptors(because GH works through IGF), in childhood. Not very common anymore, because recombinant human growth hormone has become available to ...
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