hypothalamus and homeostasis psy391s march 13, 2006 john yeomans
TRANSCRIPT
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Hypothalamus and Homeostasis
PSY391S
March 13, 2006
John Yeomans
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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.
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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.
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Posterior Pituitary
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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).
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Circumventricular Organs
Arcuate N.Posterior Pituitary
Subcommissuralorgan
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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.
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Temperature Control Systems
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Temperature
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Hypothalamus maintainstemperature best.
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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.
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Water and Salt Regulation
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Thirst
Water Loss:respiration,sweating,urination,defecation,bleeding.
Salt loss.
Water Intake:drinking,feeding,
Salt content.
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Renin-Angiotensin
Kidney
Blood
Adrenals
14 AA
10 AA
8 AA
7AA
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Neural controlof blood pressure Hormonal control of
blood pressure and tonicity
Behavioral controlof water and salt.
Vasoconstriction &H20 reuptake in kidney
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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.
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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.
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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.
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Feeding and Obesity
John Yeomans
PSY391S
March 15, 2006
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Hypothalamus and Feeding
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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.
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ob/ob or db/db mice
- (-/-) (+/+)
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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.
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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.
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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.