lecture27.ppt hypothalamus and pituitary gland
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The document discusses the hypothalamic-pituitary-adrenal (HPA) axis and how it regulates stress responses. It describes how the hypothalamus secretes hormones that signal the pituitary gland, which in turn signals the adrenal glands to release cortisol and other hormones into the bloodstream. While some changes may occur with aging, such as alterations in circadian rhythm, the HPA axis compensates to keep hormone levels stable. Under stress, the HPA axis coordinates both specific and nonspecific responses through neural, endocrine, and immune signaling to mobilize the body's defenses.
lecture27.ppt hypothalamus and pituitary gland
- 1. The Hypothalamo-Pituitary- Adrenal Axis MCB 135K April 7, 2006
- 3. Exocrine and Endocrine Secretions • Cells communicate with each other through three types of chemical messengers • Neural Communication: neurotransmitter secreted at the synaptic junction • Endocrine Communication: hormones, secreted into the blood circulation, are carried to the target tissues throughout the body • Paracrine Communication: products of secretion enter the extracellular fluid to affect neighboring cells
- 4. Exocrine and Endocrine Secretions Continued • Exocrine secretions: the products of secretion are released into a body cavity as for example, the saliva into the mouth, the digestive enzymes into the intestinal cavities • Autocrine communication: cells secrete chemical messengers that in some situations bind to receptors on the original cells.
- 5. Historical Notes • Exocrine secretions were known by Hippocrates and ancient Romans • The endocrine secretions were first identified at the turn of the 20th century. The first to speak about internal secretions, that is, secretions released into the blood circulations, was the French physiologist CE Brown-Sequard (1817-1894).
- 6. Historical Notes Continued • Brown-Sequard suggested that the internal secretions -- using those of the testes as an example -- influence general metabolism, muscle strength, reproductive and brain function. • He also suggested that when the internal secretion products were diminished -- as with aging -- some of the functions they regulated were lost. • But, replacement therapy would restore the lost functions.
- 7. In 1905, the internally secreted substances were called “hormones” by the British physiologist E.H. Starling. The original ideas of Brown- Sequard gave rise to two different fields of physiology: Endocrinology Neuroendocrinology Biotechnology ?? Replacement therapy ??
- 8. Neuroendocrine Interelations • The hypothalamus Pituitary Connection with cortex, thalamus, limbic system, reticular formation, etc. Secretes hypophyiotropic hormones Secretes anterior and posterior pituitary hormones
- 9. Hypophysiotropic hormones CRH: corticotropic releasing hormone GHRH: growth hormone releasing hormone GHIH: growth hormone inhibitory hormone Somatostatin PRH: prolactin releasing hormone GnRH: gonadotropin releasing hormone TRH thyrotropin (TSH)-releasing hormone Pituitary Hormones ACTH: adrenocorticotropin hormone LH: lutenizing hormone FSH: follicle stimulating hormone PL: prolactin TSH: thyroid stimulating hormone GH: growth hormone **Please see Figures 10.7-10.9 in text** Figure 10.1
- 12. Figure 10.2
- 13. Figure 10.3 Diagram of a section of the adrenals illustrating the various zones and hormones
- 16. Actions of Adrenaline/Noradrenaline Target
- 17. Figure 10.5 Schematic diagram of corticosteroid action in target cell
- 18. •Gene expression & new protein synthesis •Relatively long latency of onset •Medium & long term cell program •Organization of cell networks for complex functions •Activation/repression of pre- existing cell proteins •Rapid onset of action •Rapid adaptation to changes in the milieu •Dynamic modifications of long term cell programs
- 19. Table 10.1 Factors Influencing Evaluation of Endocrine Function in Aging Physiologic Metabolism Body Composition Nutrition Exercise Stress Inter-endocrine Relations Secretory Rate Transport to target site Hormone Metabolism Activity T4 T3 T DHT Number & Affinity Of Receptors
- 20. Changes with Aging in the Hypothalamo-Pituitary-Adrenal Axis No significant changes in healthy, non-stressed, elderly The few changes that occur are rapidly compensated for (e.g. decreased secretion of GCs from the adrenal cortex) but also less rapid metabolism in the liver & less urine excretion Therefore the circulating levels remain constant Also, normal ACTH & cortisol responses to CRH administration Some alterations of the circadian rhythm
- 21. Old rats Young rats Figure 10.4 Corticosterone titers in young (3-5 mo) and aged (24-28 mo) rats
- 22. Cortisol, norepinephrine, and epinephrine STRESS
- 25. END
- 28. Figure 10.7 Diagrammatic representation of the anterior pituitary
- 29. Figure 10.8 Diagrammatic representation of the posterior pituitary
- 30. Exposure to Stress Generates: • Specific responses: vary with the stimulus (specialized responses) and generate different responses with each different stimulus. • Nonspecific responses: (also called non- specialized) are always the same – regardless of the stimulus – mediated through stimulation of neural, endocrine, and immune axis