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Hypothalamus and Homeostasis

Hypothalamus and Homeostasis. PSY391S March 13, 2006 John Yeomans. Hypothalamus Functions. “We are the accumulation of mechanisms that allowed our ancestors to survive and reproduce their genes” (Sagan) Hypothalamus is an accumulation of tiny nuclei for survival and reproduction.

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Hypothalamus and Homeostasis

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  1. Hypothalamus and Homeostasis PSY391S March 13, 2006 John Yeomans

  2. Hypothalamus Functions • “We are the accumulation of mechanisms that allowed our ancestors to survive and reproduce their genes” (Sagan) • Hypothalamus is an accumulation of tiny nuclei for survival and reproduction. • Hormones and neural signals to and from viscera. • Motivated behaviors to respond to internal challenges. • Homeostasis maintains internal environment. Reproduction changes environment.

  3. Hormonal and Neural Signals • Hypothalamus controls pituitary hormones acting on many organs. • Hypothalamus receives hormonal inputs by way of circumventricular organs. • Hypothalamus coordinates neural and hormonal signals for visceral control (Autonomic NS) and motivated behaviors. • Hypothalamus receives neural inputs from descending limbic/olfactory systems and ascending taste/visceral systems.

  4. Posterior Pituitary

  5. Hormones to Brain • Blood-brain barrier (glia surrounding brain vessels) prevents entry of large molecules in most brain regions. • Leaky capillaries in 6 tiny nuclei near ventricles allow entry of hormones. • Circumventricular organs have receptors for many circulating hormones (e.g. leptin, angiotensin II, gonadal hormones).

  6. Circumventricular Organs Subcommissural organ Arcuate N. Posterior Pituitary

  7. Endotherms • Birds and mammals control body temperature near 37ºC. • Advantages: Constant physiology, better brain function, bigger brains, and adaptation to extreme environments. • Costs: More insulation needed (fat, feathers, fur), more energy needed, more internal controls.

  8. Temperature Control Systems

  9. Temperature

  10. Hypothalamus maintains temperature best.

  11. Fluid Regulation • Body made up of ~65% H2O, for cell chemistry, and for movement of nutrients and cells (e.g. blood and lymph). • Salt concentration maintained at 0.9%. • Intracellular and extracellular compartments separated by semipermeable membranes that control ions and other chemicals.

  12. Water and Salt Regulation

  13. Thirst Water Loss: respiration, sweating, urination, defecation, bleeding. Salt loss. Water Intake: drinking, feeding, Salt content.

  14. Renin-Angiotensin 14 AA 10 AA 8 AA Blood Kidney Adrenals 7AA

  15. Neural control of blood pressure Hormonal control of blood pressure and tonicity Vasoconstriction & H20 reuptake in kidney Behavioral control of water and salt.

  16. Energy Sources • Carbohydrates-->Glucose • Proteins-->Amino acids • Fats-->Fatty acids • These are stored in the body: • Fat cells (long-term) 80-90% of total • Muscle and liver glycogen (starch) • Blood glucose, fatty acids and amino acids. (short-term) • Ketones used if blood glucose low.

  17. Insulin and Glucagon • Pancreas hormones made by beta and alpha cells of Islets of Langerhans. • High blood glucose activates insulin; low blood glucose activates glucagon. • Insulin activates transport of glucose into body cells (not brain). • Glucagon converts glycogen into glucose. • This keeps blood glucose levels stable.

  18. Brain Energy • Uses glucose and O2 only (Ketones in starvation). • Does not need insulin so always gets glucose. • Brain uses over 20% of glucose and O2. • Fainting helps brain get these when blood pressure drops.

  19. Feeding and Obesity John Yeomans PSY391S March 15, 2006

  20. Hypothalamus and Feeding

  21. Brain Lesions and Stimulation • LH and PVN lesions--> less eating; VMH and arcuate lesions--> more eating. • LH stimulation-->eating; VMH-->aversion. • PVN-->NPY and NE increases feeding; 5HT decreases feeding. • Therefore, LH and PVN for feeding, VMH for satiety.

  22. ob/ob or db/db mice (-/-) (+/+) -

  23. Leptin and Obesity • ob/ob and db/db mice are obese, and eat fats as if starving. • ob/ob mice have mutation in leptin gene. • Leptin is peptide produced in fat cells in proportion to size. • db/db mice have mutation in leptin receptor gene. • Leptin receptors in arcuate n. and LH.

  24. Short-Term Feeding Signals • Taste and smell (accept or reject). • Stomach--ghrelin, distension, vomiting (area postrema). • Intestines, pancreas, gall bladder--hormones (CCK, insulin, PYY3-36), • Liver-->vagus to N. Solitary Tract, area postrema-->parasympathetic and sympathetic. • Hypothalamus--hormone receptors, neural systems, motivated behaviors.

  25. Human Obesity • Starvation-->hunger, depression and poor health. Exercise healthier, but harder. • Surgery--liposuction, stomach resection. Still hungry. • Leptin insensitivity. Leptin is high, but hypothalamus doesn't respond. • Serotonin (fenfluramine, SSRIs) works, but has side effects.

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