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Physiology II-9
Energy Balance
| Question | Answer |
|---|---|
| What is energy input into the body? | Consumed dietary nutrients |
| What is energy output from the body? | 25% work and 75% heat |
| What is the basal metabolic rate? | Minimal waking rate of internal energy expenditure |
| How is the basal metabolic rate determined? | Thyroid hormone, physical & mental rest, comfortable room temperature, last meal more than 12 hours prior |
| What is external work? | Skeletal muscle movement for interaction with the environment |
| What is internal work? | Energy expenditure required to sustain life - internal muscle contraction and cellular work (mechanical, chemical, transport) |
| What is a neutral energy balance? | Energy input = energy output (work+heat) - body weight remains the same |
| What is a positive energy balance? | Energy input is more than energy output - body weight increases |
| What is a negative energy balance? | Energy input is less than energy output - body weight decreases - stored energy used to supply energy needs |
| What structures in the hypothalamus regulate food intake? | Arcuate nucleus, lateral hypothalamic area (LHA), paraventricular hypothalamic nucleus (PVN) |
| What structures in the arcuate nucleus regulate food intake? | Neuropeptide Y (NPY)-secreting neurons and melanocortin-secreting neurons |
| How do NPY-secreting neurons regulate food intake? | Increase food intake and appetite |
| How do melanocortin-secreting neurons regulate food intake? | Decrease food intake and appetite |
| What structure in the lateral hypothalamic area (LHA) regulates food intake? | Orexins |
| How do orexins regulate food intake? | Increase appetite and food intake |
| How does the paraventricular hypothalamic nucleus (PVN) regulate food intake? | Secretes neuropeptides like CRH to decrease appetite and food intake |
| What structure in the brain stem regulates food intake? | Nucleus tractus solitarius (NTS) |
| How does the nucleus tractus solitarius (NTS) regulate food intake? | Satiety centre receives input from LHA and PVN - important for short-term meal regulation |
| Which structure is the satiety centre for food intake regulation? | Nucleus tractus solitarius (NTS) |
| How is food intake regulated over the long term? | Leptin and insulin |
| How does leptin regulate food intake? | Secreted by adipocytes, decreases appetite and food intake by inhibiting NPY-secreting and stimulating melanocortin-secreting neurons |
| How does insulin regulate food intake? | Secreted by pancreas in response to rise in glucose concentration, stimulates cellular uptake & nutrient storage, inhibits NPY-secreting neurons |
| How is food intake regulated over the short term? | Ghrelin, PYY 3-36, and CCK |
| How does ghrelin regulate food intake? | "Hunger hormone" stimulates appetite, secreted in stomach prior to meals and decreases after food intake, stimulates NPY-secreting neurons |
| How does PYY 3-36 regulate food intake? | "Satiety signal" regulates meal termination, secreted in intestines, increases during meal, inhibits NPY-secreting neurons |
| How does CCK regulate food intake? | "Satiety signal" regulates meal termination, produced by duodenum in response to fat and protein, stimulates NTS (satiety centre) of brainstem |
| What is anorexia nervosa? | Distorted body image and aversion to food, altered hormone secretion and low body temperature |
| What are physiological consequences of increased body temperature? | Increased speed of chemical reactions, nerve malfunction, irreversible protein denaturation |
| What results from a 41℃ fever? Convulsions | |
| What results from a 43.3℃ fever? Death | |
| What are physiological consequences of decreased body temperature? | Decreased speed of chemical reactions and decreased rate of metabolism |
| What is a normal internal core temperature? | 37.8℃ |
| What is a normal skin temperature? | 20℃ to 40℃ |
| What is the innate biological rhythm of temperature? | Cyclical variation by 1℃ during the day |
| What is heat input? | Heat gain from external environment and internal heat production |
| What is heat output? | Heat loss from body surface to external environment |
| What is heat radiation? | Emission of heat from a surface as electromagnetic heat waves, lose half of body heat this way |
| What is heat conduction? | Transfer of heat between objects in direct contact with each other, gain and lose heat by conduction to air |
| What is heat convection? | Transfer of heat by currents through air or water, combines with conduction to dissipate heat from body, convection currents carry heat away from body |
| What is evaporation? | Loss of heat required to transform water from liquid to a gas, passively and actively through sweating |
| How does the hypothalamus thermoregulate? | Integrates thermosensory inputs centrally and peripherally |
| What activates the posterior region of the hypothalamus to thermoregulate? | Cold |
| What activates the anterior region of the hypothalamus to thermoregulate? | Heat |
| What is shivering? | Rhythmic, oscillating skeletal muscle contractions produce primary involuntary heat production |
| What is nonshivering thermogenesis? | Increased metabolic heat in newborns by metabolizing brown fat |
| How does the body attempt to thermoregulate a high core temperature? | Decreased muscle tone |
| How does the hypothalamus interact with the cardiac control centre for thermoregulation? | Hypothalamus dominates over cardiac control centre, can affect MAP |
| What causes a fever? | Macrophages release endogenous pyrogen, which raises thermal set point of hypothalamic thermoregulatory centre |
| Why does a feverish person feel cold? | Person feels cold until new set point of hypothalamic thermoregulatory centre is reached |
| What is hyperthermia? | Increased body temperature above normal range, excluding fever |
| What is heat exhaustion? | Results from overactivity of heat-loss mechanisms - extensive sweating, vasodilation, decreased blood pressure, and fainting |
| What is heat stroke? | Breakdown of thermoregulatory ability increases temperature and lack of compensatory heat-loss mechanisms |
| What is frostbite? | Tissue damage resulting from excessive cooling, ice crystals form in cells leading to cell death |
| What is hypothermia? | Body temperature below normal range, decreasing rate of metabolic processes and depressing CNS, respiratory, and cardiac function |
Created by:
ugrn
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