chapter ten the regulation of internal body states
TRANSCRIPT
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Chapter TenThe Regulation of Internal Body States
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Temperature Regulation
Homeostasis-keeping body variables within a fixed range
Set Point-a single value that the body works to maintain
Homeothermic-mammals and birds use physiological mechanisms to maintain an almost constant body temperature despite large variations in the temperature in the environment
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Advantages of Consistent Body Temperature
Generally, we rest with temperature around 37o C
Advantages
Higher than air temperature so we don’t have to rely on inefficient methods to cool the body
Body is as warm as it can be without damaging necessary proteins
Rapid muscle contractions are more possible at this temperature
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Temperature Regulation
Brain Mechanismspreoptic area is most critical
Behavioral MechanismsSeeking a warm place when cold, etc.
FeverProstaglandins stimulate a rise in temperature in response to
invading bacteria and viruses
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Thirst and Related Processes
When the body needs water=thirst
Related Processes
Vasopressin-hormone released from posterior pituitary
constricts blood vessels
enables kidneys to reabsorb water
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Types of Thirst
Osmotic Thirst
When solutes become concentrated outside the cell and water is extracted from inside cells
OVLT-organum vasculosum laminae terminalis
detects osmotic pressure
sends information to hypothalamus
paraventricular nucleus
supraoptic nucleus
lateral preoptic area
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Figure 10.6 The consequence of a difference in osmotic pressure(a) A solute such as NaCl is more concentrated outside the cell than inside. (b)
Water flows by osmosis out of the cell until the concentrations are equal. Neurons in certain brain areas detect their own dehydration and trigger thirst.
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Figure 10.3 Major subdivisions of the hypothalamus and pituitary
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Types of Thirst
Hypovolemic Thirst
thirst resulting from low blood volume
Mechanisms
Baroreceptors-attached to large veins detect pressure of blood returning to the heart
Renin released by kidneys assists in creating high levels of angiotensin II which constricts blood vessels and signals brain to stimulate thirst
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Table 10.1
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Digestive System
Digestion
Begins with saliva in the mouth
Down esophagus
Stomach tears up food using acids and enzymes
Small Intestine-digested materials absorbed through small intestine
Large intestine-absorbs water and minerals
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Influences on Food Selection
Food Preferencecarnivores-meatherbivores-plantsomnivores-meat and plants
FlavorFamiliarityPotential conditioned taste aversions-the tendency to form a dislike
to any food that has become associated with illnessEx: People receiving chemotherapy will develop a dislike for
fluids they consume during therapy
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Bodily Influences on Hunger
Mouthoral sensations
StomachVagus nerve-transmits information on stomach distentionSplanchnic nerve-transmits information on nutrient content of
food being consumedIntestines
duodenum-once food reaches here, CCK is released and signals to stop eating
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Glucose, Insulin, and Glucagon
Glucose-primary energy source for cells
Insulin-assists glucose entering cells
When high, hunger levels drop
Glucagon-stimulates liver to convert glycogen to glucose
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The Hypothalamus and Eating Regulation
Lateral HypothalamusDamage to this area = animal refuses foodaxons extend to nucleus of the tractus solitarius in the medulla
possibly altering taste sensationsaxons extend to forebrain facilitating ingestion and swallowingactivates a circuit that excites dopamine cells initiating
reinforcement of behaviorssends axons to spinal cord controlling autonomic responses
such as digestive secretions
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The Hypothalamus and Eating Regulation
Paraventricular NucleusDamage here = eating larger than normal meals
Ventromedial HypothalamusLesions to the VMH lead to finicky eating and sometimes to
overeatingThe overeating is due to eating more frequently than normal
Causesincreased stomach motility and secretionsleads to a lasting increase in insulin production
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Satiety Signals and Eating Disorders
Hormones
Leptin-produced by fat cells and signal no need to eat
Neuropeptide Y-neuromodulator that inhibits the PVN of the hypothalamus and results in an increase in meal size
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Figure 10.24 Relation among weight, leptin, NPY, and eatingOrdinarily, high levels of body fat produce leptin, which inhibits eating. Obese mice fail to produce leptin. Obese humans produce leptin but fail to
respond to it.
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Genetics, Metabolic Rate, and Body Weight
Genetics-heritability of .4 to .7
Metabolic Rate-the higher the rate the more difficulty someone will have gaining weight
Ideas for Weight Loss
Increase exercise
Reduce consumption
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Eating Disorders
Anorexia
defined-unwilling to eat, significantly underweight
occurs mostly in women during adolescence
Bulimia
defined-alternating between dieting and overeating
May be associated with alterations in PYY, CCK and serotonin