Temperature Thirst Hunger Basal metabolism is the rate of energy that is used while the body is at rest We expend a lot of energy daily Most energy expended is to maintain our body temperature Homeostasis is a balance our body strives to keep its systems in If the set point varies the body works to get the set point back For the most part homeostasis has been replaced by allostasis Allostasis takes into account the fact that depending on what you re doing your set point may change Amphibians frogs reptiles are what is known as poikilothermic Their body temperature is the same as the environmental temperature Mammals are known as homoeothermic We maintain a constant body temperature no matter what the environmental temperature is One reason we evolved to do this is because a certain internal temperature is absolutely necessary for a lot of internal chemical processes to occur Also it allows us to be active no matter what the external temperature is There are both physiologic and behavioral mechanisms that allow us to do this Physiologically when it s hot we sweat animals that can t sweat pant or lick themselves Blood vessels that are close to the skin surface will dilate allowing air temperature to cool blood If it s cold one will get rhythmic muscle contractions shivering goosebumps don t do much because we don t have a lot of hair Blood vessels near the skin surface constrict to keep blood warmer Behaviorally if it s hot we ll take off a coat If cold we ll put on one We seek out hot or cold places depending on external temperature Most critical area of the body for temperature regulation is the hypothalamus Incredibly important Pre optic area of the hypothalamus is an area that is anterior of the anterior hypothalamus POA AH Helps monitor temperature in a couple of ways Temperature sensitive cells in skin and spinal cord that send POA temperature information Also monitors its own temperature Keeps body at a constant temperature If this area is damaged one will see wild fluctuations in temperature as the person cannot keep a constant temperature Interesting phenomena that are temperature related When an organism is exposed to a bacteria or a virus it is very common to have a fever A fever is a temperature related event Macrophages are particular immune cells that secrete an immune chemical called cytokines known as cytokine IL1 that travels to the hypothalamus and with the help of prostaglandin there is an increase in temperature Fevers are beneficial for a couple of reasons it s a part of sickness behavior If one is sick the immune system needs to have as much energy as it can in order to fight whatever is making you sick The other reason is that many bacteria and viruses are heat sensitive and will die if the body is warmer than usual Playing possum is also related to temperature regulation basically playing dead There are some species of predators that hunt based on movement so there are some prey for which this would be useful A possum can t play possum forever eventually it has to move What makes the animal have to move is temperature body temperature rises because they re not moving so they have to move before it gets too high Official name is tonic immobility We re about 70 water Every chemical reaction in our body depends on the concentration of chemicals in water Water regulation is incredibly important for us The body needs enough fluids to maintain a circulatory system and normal blood pressure Amount of water in system is monitored very closely Animals balance very well how much they take in and how much they take in Animals living close to water will excrete copious amounts of water Animals who don t will not Two components to body s water First is concentration of fluids in cells osmotic thirst Second is the total fluid volume in blood hypovolemic thirst The concentration of solutes relative to the amount of fluid in the system stays at a constant level When that balance is altered such that solutes increase and fluids decrease one experiences an osmotic pressure fluid moves from an area of high concentration to an area of low concentration Solutes can increase because one eats or sweats If solutes increase osmotic pressure occurs so water comes out of the cells and into the body s fluids When water leaves those cells one gets thirsty How is the brain aware of this process Two important areas OVLT and SFO They send information to the hypothalamus They have receptors around the third ventricle Information from the OVLT and the SFO go to particular parts of the hypothalamus called the supra optic area of the hypothalamus and the PVN of the hypothalamus which control the release of a chemical called ADH ADH will cause us to excrete more concentrated urine Some of the information sent by OVLT and SFO goes to the lateral pre optic area Makes you thirsty Drink water until things even out again A couple of things help you stop before you overdose on water Body monitors the number of swallows you take and the amount of stomach distension So there s a cut off point when it realizes that s enough water and stops your thirst If blood volume and blood pressure are low one will experience hypovolemic thirst Hypovolemic thirst is detected via a couple of mechanisms There are baroreceptors in the large blood vessels that will detect changes in blood pressure and increase thirst as a result A second mechanism if pressure drops kidneys will release the hormone renin which goes through a couple of different hormonal changes The end result is the hormone angiotensin II Angiotensin II will cause blood vessel restriction which should ideally increase one s blood pressure Angiotensin II also stimulates cells in the SFO that send information to the pre optic area which increases drinking Interesting part is that one has a preference for fluids that are a little salty to help replace salt found in blood In addition one will get from the adrenals the hormone aldosterone this causes the kidneys to conserve salt and help trigger the craving for salt In order for us to access everything we need to survive we need to eat Once we eat the food has to be broken down via digestion so we can get the proteins vitamins minerals etc Digestion begins in the mouth Saliva contains enzymes that break down the carbohydrates Food goes down esophagus to stomach In the stomach one finds other enzymes that help digest proteins Once that has occurred there is a sphincter that separates the stomach from the