Flashcards in Homeostasis Deck (31):
How do organisms control their own external environment?
-a feature of an increase in complexity is the ability of organisms to control their internal environment
-by maintaining a relatively constant internal environment for their cells, organisms can limit the external changes these cells experience
-this maintenance of a constant internal environment is called homeostasis
-the internal environment is made up of tissue fluids that bathe each cell, supplying nutrients and removing wastes
-maintaining the features of this fluid at the optimum levels protects the cells from changes in the external environment, thereby giving the organism a degree of independence
What is homeostasis?
-homeostasis is the maintenance of an internal environment within restricted limits in organisms
-it involved trying to maintain the chemical make-up, volume and other features of blood and tissue fluid within restricted limits
-homeostasis ensures that the cells of the body are in an environment that meets their requirements and allows them to function normally despite external changes
-this does not mean that there are no changes
-on the contrary, there are continuous fluctuations brought about by variations in internal and external conditions, such as changes in temperature, pH and water potential
-these changes, however, occur around an optimum point and so maintain organisms in a balanced equilibrium
Why is homeostasis essential for the proper functioning of organisms?
-the enzymes that control the biochemical reactions within cells, and other proteins, such as channel proteins are sensitive to changes in pH and temperature
-any change to these factors reduces the rate of reaction of enzymes or may even prevent them working altogether, for example, by dewatering them, even small fluctuations in temperature or pH can impair the ability of enzymes to carry out their roles effectively, maintaining a fairly constant internal environment means that reactions take place at a suitable rate
-changes to the water potential of the blood and tissue fluids may cause cells to shrink and expand even to even to bursting point as a result of water leaving or entering by osmosis, in both instances the cells cannot operate normally
-the maintenance of a constant blood glucose concentration is essential in ensuring a constant water potential, a constant blood glucose concentration also ensures a reliable source of glucose concentration also ensures a reliable source of respiration by cells
-organisms with the ability to maintain a constant internal environment are more independent of changes in the external environment, they may have a wider geographical range and therefore have a greater chance of finding food, shelter, etc. mammals for example with their ability to maintain a constant temperature are found in most habitats ranging from hot arid deserts to cold, frozen polar regions
What the stages of control of any self-regulating system involved a series of stages?
-the optimum point
What is the optimum point?
-the optimum point, the point at which the system operates bets, which is monitored by a receptor
What is a receptor?
-receptor, which detects any deviation from the optimum point i.e. a stimulus and informs the coordinator
What is a coordinator?
-coordinator, which coordinates information from receptors and sends instructions to an appropriate effector
What is an effector?
-effector, often a muscle or gland which brings about the changes needed to return the system to the optimum point
-this return to normality creates a feedback mechanism
What is a feedback mechanism?
-feedback mechanism, by which a receptor responds to a stimulus created by the change to the system brought about by the effector
What is the coordination of control mechanisms?
-most systems including biological ones, use negative feedback
-negative feedback is when the change produced by the control system leads to a change in the stimulus detected by the receptor and turns the system off
-positive feedback occurs when a deviation from an optimum causes changes that results in an even greater deviation from the normal
-one example occurs ion neurones where a stimulus leads to a small influx of sodium ions
-this influx increases the permeability of the neurone membrane to sodium ions more ions enter causing a further increase in permeability and even more rapid entry of ions, in this way, a small stimulus can bring about a large and rapid response
-control systems normally have many receptors and effectors, this allows them to have separate mechanisms that each produce a positive movement towards an optimum
-this allows a greater degree of control of the particular factor being regulated
-having separate mechanisms that controls departures in different directions from the original state is a general feature of homeostasis
-it is important to ensure that the information provided by receptors is analysed by the coordination before action is taken
-for example, temperature receptors in the skin may signal that the skin itself is cold and that the body temperature should be raised
-however, information from regions in the hypothalamus in the brain may indicate that blood temperature is already above normal
-this situation might arise during strenuous exercise when blood temperature rises but sweating cools the skin
-by analysing the information from all detectors, the brain can decide the best course of action - in this case not to raise the body temperature further
-in the same way, the control centre must coordinate the action of the effectors so hat they operate harmoniously
-for example, sweating would be less effective in cooling the body if it were not accompanied by vasodilation
What are endotherms?
-animals such as birds and mammals derive most of their heat from the metabolic activities that tale place inside their bodies
-they are therefore known as endotherms meaning inside heat
-some animals obtain a proportion of their heat sources outside their bodies, namely the environment
-they are therefore known as ectotherms meaning outside heat
What are ectotherms?
-many ectotherms gain heat from the environment, so their body temperatures fluctuates with that of the environment
-they therefore control their body temperature by adapting their behaviour to changes in the external temperature
-reptiles, such as lizards are ectotherms
How do ectotherms control their body temperature?
-Exposing themselves to the sun
-gaining warmth from the ground
How do ectotherms control their body temperature by exposing themselves to the sun?
-in order to gain heat lizards ordinate themselves so that the maximum surface area of their body is exposed to the warming rays of the sun
How do ectotherms control their body temperature by taking shelter?
-lizards will shelter in the shade to prevent over-heating when the suns radiation is at its peak
-at night they retreat into burrows in order to reduce heat loss when the external temperature is low
How do ectotherms control their body temperature by gaining warmth from the ground?
-lizards will press their bodies against areas of hot ground to warm themselves up
-when the required temperature is reached, they raise themselves off the ground on their legs
How do endotherms regulate their body temperature?
-endotherms gain most of their heat from internal metabolic activities
-their body's temperature remains relatively constant despite fluctuations in the external temperature
-like ectotherms, endothermic animals use behaviour to maintain a constant body temperature
-unlike ectotherms, however, they also use a wide range of physiological mechanisms to regulate their temperature
How do animals conserve and gain heat in response to a cold environment?
-mammals and birds that live in cold climates have evolved a number of adoptions in order to survive in these environments
-one of the most important is having a body with a small surface area to volume ratio
-it is from within the volume that heat is produced and from the surface area that heat is lost
-mammals and birds in cold climates therefore tend to be relatively large, for example, the polar bear and penguin
-compared with animals in warmer climates they also have smaller extremities, such as ears, and thick fur, features, or fat layers to insulate the body
Which mechanisms allow mammals to make more rapid body temperature changes?
-raising of hair
-increased metabolic rate
-decrease in sweating
How does vasoconstriction allow mammals to make more rapid body temperature changes?
-the diameter of the arterials near the surface of the skin is made smaller
-this reduces the volume of blood reaching the skin surface through the capillaries
-most od the blood entering the skin passes beneath the insulating layer of fat and so loses little heat to the environment
How does shivering allow mammals to make more rapid body temperature changes?
-the muscles of the body undergo involuntary rhythmic contraction that produce metabolic heat
How does raising of hair allow mammals to make more rapid body temperature changes?
-the hair erector muscles in the skin contract, raising the hairs on the body
-this enables a thicker layer of still air, which is a good insulator and conserving heat in mammals with thick fur
How does increased metabolic rate allow mammals to make more rapid body temperature changes?
-in cold conditions more of the hormones that increase metabolic rate are produces
-as a result metabolic activity, including respiration is increased and so more heat is generated
How does decrease in sweating allow mammals to make more rapid body temperature changes?
-sweating is reduced or ceases altogether in cold conditions
How does behavioural mechanisms allow mammals to make more rapid body temperature changes?
-sheltering from the wind, basking in the sun and huddling together all help animals maintain their core body temperature
How do animals lose heat in response to a warm environment?
-long-term adoptions to life in a warm climate include having a large surface area to volume ratio and lighter coloured fur to collect heat
Which mechanisms allow mammals to lose heat in response to a warm environment?
-lowering of body hair
How does vasodilation allow animals to lose heat in response to a warm environment?
-the diameter of the arterials near the surface of the skin becomes larger
-this allows warm blood to pass close to the skin surface through the capillaries
-the heat from this blood is then radiated away from the body
How does increased sweating allow animals to lose heat in response to a warm environment?
-to evaporate water from the skin requires energy in the form of heat
-in relatively hairless mammals, such as humans, sweating is a highly effective means of losing heat
-in mammals with fur, cooling is achieved by the evaporation of water from the mouth and tongue, during painting
-the high latent heat of vaporisation of water makes sweating an efficient way of losing heat
How does lowering of body hair allow animals to lose heat in response to a warm environment?
-the hair erector muscles in the skin relax and the elasticity of the skin causes them to flatten against the body
-this reduced the thickness of the insulating layer and allows more heat to be lost to environment when the internal temperature is higher than the external temperature