homeostasis Flashcards
(21 cards)
why do multicellular organisms need communication systems
~to respond when their internal & external environment changes
~to coordinate organ function
what is cell signalling
communication between cells: electrical signals carried by neurons or chemical signals as hormones
what is homeostasis
internal environment is maintained within set limits around an optimum
define positive and negative feedback
negative feedback: self-regulatory mechanisms return internal environment to optimum when there is a fluctuation
positive feedback: a fluctuation triggers changes that results in an even greater deviation from the normal level
what are receptors and effectors
receptors: specialised cells located in sense organs that detect a specific stimulus
effectors: usually muscles or glands which enable a physical response to a stimulus
what is an ectotherm
organism that cannot increase its reparation rate to increase the internal production of heat
-relies on external sources to regulate its body temp
-responds to body changes behaviourally e.g sun basking
what is an endotherm
organism that can regulate its body temperature independently of external sources. thermoreceptors send signals to the hypothalamus, which triggers a physiological or behavioural response
outline behavioural methods endotherms use to regulate their body temperature
-basking in sun
-pressing against warm surfaces
-digging burrows
-hibernation/aestivation
-panting
how does the autonomic nervous system enable endotherms to thermoregulate
negative feedback. peripheral thermoreceptors detect changes in skin temperature. thermoreceptors in hypothalamus detect changes in blood temperature
-hypothalamus sends impulses to effectors in skin ( vasodilation/constriction, piloerection, sweating) & muscles (shivering)
explain the role of the skin in thermoregulation
-vasodilation/constriction of arterioles supplying skin capillaries controls heat loss to skin surface
-hair erector muscles contract & follicles protrude to trap air for insulation
-evaporation of sweat cools skin surface
it is more difficult for moths and bumble bees to maintain their body temp than mammals and birds explain why
-larger SA:VOL ratio
-rely on behavioural changes to regulate temp instead of physiological
-mammals have thicker insulation
-insects greater rate of heat loss
in humans when core body temp falls below 35, positive feedback causes this decrease in temperature to continue this process is known as hypothermia
explain how positive feedback accelerates this process
-positive feedback exaggerates effector
-so temp continuous to decrease causing slower metabolic reactions
-less kinetic energy to cells
-causes less internal heat to be generated
-causes body temp to lower further
peripheral temp receptors detect the temp of internal organs
false
receptors in the hypothalamus detect core body temp
true
blood temp is detected by receptors in the hypothalamus
true
temperature receptors send impulses to the medulla oblongata, which regulates body temp
false
describe 3 reasons why homeostasis is important
-to maintain the body’s internal temp so enzymes are in optimum temp for functioning properly
-maintains osmotic potential of the blood to prevent cytolysis
-maintains water levels in body
what is the set point
-the physiological value around which the normal range fluctuates
explain the role of negative feedback in the control of plasma glucose concentration
-change from norm initiates corrective mechanisms
-fluctuation in plasma glucose conc detected by islet cells in pancreas
-initial decreases stimulates increased secretion of glucagon
-increase stimulates increased secretion of insulin
-increased/ decreased uptake of glucose by cells is normal again
explain how normal core body temp is maintained when a person moves into a cold room
-shiver
-vasoconstriction
-putting on warmer clothes
-erectile pili muscles
-heat gain centre activated
how does maintaining a constant body temp allow metabolic reactions in cells to proceed with maximum efficiency
-body temp is 37 which is optimal for enzymes which catalyse metabolic reactions
-when temp too high enzymes denature / change shape so cant bind
-when temp to low not allot of kinetic energy so not enough collisions occur
