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PowerPoint 8

by: Brittany Woody

PowerPoint 8 PSB4504

Brittany Woody

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PowerPoint and lecture notes for powerpoint 8 on thermoregulation
Developmental Psychobiology
Dr. Donald J. Stehouwer
Class Notes
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This 8 page Class Notes was uploaded by Brittany Woody on Monday March 7, 2016. The Class Notes belongs to PSB4504 at University of Florida taught by Dr. Donald J. Stehouwer in Spring 2016. Since its upload, it has received 16 views.


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Date Created: 03/07/16
Monday, February 22, 2016 PowerPoint 8 The Neonatal Niche - Neonates face problems not face by adults; unique to neonates because of their size, anatomy, and physiology - Neonates adopt their own strategies to cope with these unique problems - Coping strategies are both behavioral and physiological - Homeothermy: the physiological and behavioral maintenance of a relatively constant internal body temperature (homeotherms typically show fluctuations, e.g. circadian rhythms, in temperature); humans - Endothermy: physiological and behavioral thermoregulation, but body temperatures may fluctuate widely; - Ectothermy: use only behavioral means to regulate temperature; butterflies - Poikilothermy: the fluctuation of internal body temperature closely related to environmental temperature; most fish - Cold blooded: poikilothermy > ectothermy > endothermy > homeothermy: warm blooded - Heat gain: volume (size) of thermogenic tissue; basal metabolic rate (how active is tissue); shivering or other thermogenesis - Heat loss: surface area; insulation (fat, feathers, hair); panting, sweating, etc - Infants have small bodies for heat generation and heat loss - Peripheral thermoreceptors are found in the skin; related to behavior - Central thermoreceptors are found in the anterior hypothalamus; controls seasonal fluctuations in body temperature - These thermoreceptors are important for behavioral and physiological thermoregulation both in the short term and in the long term - Short term thermoregulation is regulated predominantly by autonomic and somatic motor activity 1 Monday, February 22, 2016 - Autonomic: • shivering when cold, sweating when hot • peripheral vasodilation when hot, constriction when cold • piloerection (fur standing up) and panting in non-human mammals • adrenal gland: release catecholamines to increase basal metabolic rate - Somatic: seeking warm (sun) or cool (shade or water) areas • • minimizing or maximizing surface area - Long term (e.g. seasonal or as adaptation to different climates) thermoregulation is predominantly regulated by hormonal regulation of metabolism - Thyrotropin releasing hormone (TRH) is secreted from the hypothalamus to stimulate release of thyroid-stimulating hormone (TSH, also thyrotropin), which stimulates release of thyroxine from the thyroid gland • tissues respond with an increase in their basal metabolic rate - Autonomic and hormonal responses to thermal challenges are mediated primarily by the medial pre optic area - Behavioral responses to thermal challenges are mediated principally by the lateral hypothalamus - Maintenance of thermal homeostasis is arguably the greatest factor influencing both energy balance (via calories spent for thermogenesis and the need for fat stores) and water and mineral balance (water lost via evaporation through the skin, metabolic processes necessary for homeothermy and panting) - Allometric growth: parts of the body grow at different rates - Problems faced by altricial neonates: • sensory and motor immaturity • CNA immaturity • Physiological immaturity (autonomic control, homeostatic regulation) • morphological immaturity (small size, allometric growth) 2 Monday, February 22, 2016 - Thermoregulatory problems of altricial mammals: • cannot shiver • has precarious energy balance; do not have extra energy because all energy is used on growth • small size • cannot vasoconstrict in response to cold • no hair; humans depend on adults for clothing • little body fat and thin skin for insulation - The problem with being small: surface area to volume ratio; if length increases linearly, surface area and volume increase exponentially; surface area increases more slowly than volume • surface area to volume ratio increases with age; more surface area per volume • at ambient room temperature, a newborn rat would have to increase its metabolic rate 6-fold to maintain its core temperature • newborn rat and dead rat lose heat at the same rate when put in cold water • hypothermia is used as anesthesia for rats; hard to overdose and less bleeding - Brown adipose tissue (BAT) is not used as long term storage for nutrients but is metabolically active; densely vascularized; dense mitochondria; increased metabolism allows newborns to raise body heat - Bears use brown fat during hibernation - Brown fat accounts for 5 to 6 percent of the body weight of the newborn rabbit. It is concentrated around the neck and between the should blades - Human infant at birth has a thin sheet of brown adipose tissue between the should blades and around the neck, and small deposits behind the breastbone and along the spine - Brown fat is located near heart and spinal cord to maintain these most vital organs - Basal metabolic rate (BMR): minimum metabolic rate at thermoneutral temperature; mid 70s to mid 80s in naked adult humans 3 Monday, February 22, 2016 - Cold stress will result in increased metabolism which will lead to increased oxygen consumption, hypoglycemia, hypoxia, and respiratory distress - Newborn rats can be cooled until their heart stops and then rewarmed to start it again; adult rats cannot start their heart back up; newborn humans can survive in water longer than adult humans - In mild cold temperatures, newborns will attempt to thermoregulate; in very cold temperatures, they will shut down their metabolism - Rats who are transected at level 3 are unable to maintain their core temperature in warm environments; have thermogenic response and heat up - Transected animals have an increased oxygen consumption in warm temperatures; intact animals show thermogenic response but then shut down to return to BMR - Blood glucose levels are initially higher in transected animals; blood glucose levels decrease in transected and intact animals, but are overall lower in intact animals - Intact animals shut down as blood glucose level drops because they are able to monitor glucose stores; transected animals maintain high metabolism in both temperatures even as glucose stores decrease - Intact animals injected with insulin do not illicit a thermogenic response; made them hypoglycemic - Lesions in hypothalamus do not affect animals; mechanisms responsible for thermoregulation is located somewhere rostral to transection but not in hypothalamus - Temperatures were taken rectally; rectal temperature is most accurate in adult rats, but not in newborns; newborns are warmest under brown fat (upper back) and rectal temperatures are coolest - Oxygen consumption (metabolic rate) compared to environmental temperature of differently aged rats: • 21 days old:steady decrease in metabolic rate as temperature decreases • 23 hours old: increase of oxygen consumption at 30 then declining as temperature decreases; have nursed so they can produce thermogenic response • 4 hours: temperature does not have an affect on metabolic rate; they do not have energy to produce thermogenic response because they have not nursed yet 4 Monday, February 22, 2016 - 5- 10 day old rats require huddling with littermates to stay warm; they have not developed thick fur or developed thermogenesis; older rats are also larger - 5 and 10 day old rats lose temperature rapidly if separated from litter; temperature decreases more slowly if with only three littermates - 15 and 20 day old rats can maintain their temperature when alone and when with three littermates - Newborn rats thermoregulate as one group when they huddle (clump) - Huddles form convection currents when moving around their clump; positive thermotaxis; if a pup is cold, they dive into the top of the huddle, pushing others out; those who were pushed out jump back to top when they get cold - In warmer temperatures, the current reverses and rats jump out of top to get to the cooler area - Rat- shaped robots programmed to move randomly resemble real rat behaviors; formed clumps; both got stuck in corners; shape of rats facilitates clumping behavior - Reptiles move to thermoneutrality: area between hot and cold - Reptiles and infant rats cannot generate a fever when injected with bacteria - Fish and reptiles spend more time in heat when injected with infectious agent - Newborn rabbits prefer higher temperatures (40.5 degrees C) when injected with pyrogen vs. saline (36.5 degrees C) Human Infants: - Heat Production • The ability to increase metabolic rate in response to cold stress begins around 28— 30 weeks postconceptional age. Postconceptionally older infants can increase heat production, but the response is weaker than in the adult. 4’16 Limited stores of metabolic substrates (glucose, glycogen, fat, etc.) • • Heat production needs met primarily through non-shivering thermogenesis; however, the amount of brown fat stores are inversely related to gestational age. • Heat production obligates oxygen consumption, challenging the immature cardiovascular and pulmonary systems. 5 Monday, February 22, 2016 • Large surface-to-mass ratio and large surface heat loss relative to heat-producing ability result in high metabolic rate. • Large evaporative loss due to status of skin maturation; evaporative loss itself may exceed heat production abilities. • Shivering response not well developed. Cannot initiate increased tone and shivering to increase heat production. - Insulation • Limited layer of subcutaneous fat, limited development of muscle and other tissues that provide insulation. • Small body diameter results in thinner layer of still air boundary layer, reducing insulation through this mechanism. - Vasomotor Response • Competent abilities to regulate skin blood flow documented in infants weighing >1 kg; however vasoconstriction abilities are outmatched by propensity for heat loss.4 - Sudomotor Response Sweat production observed in infants of 29 weeks gestational age; maturation of • response enhanced by extrauterine development. Response is slower and less efficient than in older child or adult, and occurs at a higher environmental temperature.24 - Motor Tone and Activity • Lower postconceptional aged and ill infants prone to decreased motor tone and less activity, resulting in decreased heat production. Infant with poor tone cannot use flexion posture effectively to reduce surface area and hence heat loss. - Behavioral • Limited ability to effectively communicate thermal needs or thermal comfort to caregiver. • Cues are subtle and nonspecific. • Cannot use volitional actions such as altering clothing, increasing ambient temperature, using motor activity to increase heat production, drinking warm or cool beverages to modify temperature. 6 Monday, February 22, 2016 - Brown fat is stimulated by sympathetic innervation (not blood-borne signals) - Ultrasonic Vocalizations in newborn rats: • emitted by isolated pups in first two weeks • isolation necessary and sufficient condition to elicit vocalization • retrieved by dam; mom rat gets newborn if they are making vocalizations • called “isolation distress”: distress implies that it is an emotional response; this would make a good model for separation anxiety in humans - Vocalizations as “cries” • implies emotional response • analogue of separation anxiety? - Alternative explanation? • part of thermogenic response; physiological reason not psychological • exaptation: adaptations that are selected as a consequence of another; ultrasonic vocalization may be used as part of thermogenic response, but also results in dam (mother) retrieval • not “cries,” but more like “grunts” • laryngeal braking: closing larynx; prevent passage of air - enhances gas exchange - facilitates return of blood to heart - Valsalva maneuver: tightening of abdominal muscles; like humans grunting when lifting weights or playing tennis; abdominal compression response - Thermoregulation summary: Problem: Cannot shiver to produce heat Solution: Brown adipose tissue (BAT) Problem: Precarious energy balance Solution: Thermoregulate over narrow temperature range, shut down to conserve energy if temperature is out of range, tolerate lowered temperature 7 Monday, February 22, 2016 Problem: Small size, large surface area:volume ratio Solution: Clump to reduce surface area:volume ratio Problem: Poor insulation Solution: Clump, nest insulation (mother builds nest), thermotaxis, ultrasound response to isolation, mother is source of heat while nursing, most rodents live in burrows for warmth (also to escape predators) - Thermogenesis is not a precursor to adulthood; it is specifically neonatal; it persists in adults as a machismo of hibernation - Huddling may be both for thermogenesis and as a social behavior 8


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