Lecture12_hormones - Hypothalamus Homeostasis Internal...

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Hypothalamus & Homeostasis
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“Internal” senses The nervous system is endowed with external senses for monitoring the world around us: Vision Hearing Vestibular Touch Taste Smell We also possess “internal” senses for monitoring the state of our own bodies: Temperature Hydration Nutrition Oxygenation Sleep Social status / self image
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Homeostasis Homeo ” = self “stasis” = stability, lack of movement. “Homeostasis” essentially means “keeping the self stable.” There are many “internal states” that our bodies need to keep within a stable range of values: Temperature Hydration & Electrolytes Nutrient levels Oxygen levels Sleep status The hypothalamus is on of the main brain centers for regulating such forms of homeostasis
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Autonomic nervous system The autonomic nervous system controls body functions and behaviors that we do not consciously or voluntarily regulate There are two divisions of the autonomic nervous system that “oppose” one another for control of body systems: The sympathetic division promotes active states that often involve increased metabolism and consumption of the body’s energy The parasympathetic division promotes resting states that often involve decreased metabolism an conservation of the body’s energy
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Regulation of body temperature Humans are endotherms (animals that generate their own body heat) Core human body temperature is 36-38 ° C If the body gets cold, it turns on “heaters” If the body gets hot, its turns on “air conditioners”
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Closed-loop control by a thermostat A home thermostat has three main components: 1) A set switch for specifying the desired temperature 2) A thermometer for measuring the actual temperature 3) A control switch that regulates a heater and/or air conditioner to adjust the actual temperature in the appropriate way if it differs from the desired temperature We may say that this system achieves homeostasis (holding a stable temperature) through negative feedback , because the heater and air conditioner both exert influences that turn themselves off (which is the hallmark of negative feedback).
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In response to cold stress, neuro- endocrine cells in the preoptic area (POA) of the hypothalamus produce thyrotropin releasing hormone (TRH) TRH is released into the blood from hypothalamic neuron axons, and travels a short distance through the vessels of the hypophyseal portal system to the anterior pituitary gland Neuroendocrine cells in the anterior pituitary release a specific tropic hormone called thyroid stimulating hormone (TSH) into the bloodstream TSH travels through the bloodstream to the thyroid gland (in the neck), where it triggers release of thyroid hormones that increase metabolic rate and sympathetic nervous actvity Hormone release from the anterior pituitary (or adenohypophysis ) in response to cold stress
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