Homeostasis Flashcards
What is a sensory receptor
detects changes in the internal and external environment of an organism
What is homeostasis
maintenance of stable body conditions, a dynamic equilibrium with small fluctuations
What is an effector
A muscle or gland that reacts to a motor stimulus to bring about change in response to a stimulus
Features of a negative feedback system
- change is detected, effectors work to reverse change and restore initial conditions
- reverse the stiumulus
Examples of a negative feedback system
blood sugar level control
Features of positive feedback systems
- change is detected, effectors are stimulated to reinforce the change and increase the response
Examples of positive feedback systems
- blood clotting= platelets stick and attract more until clot formed
- child birth= baby head against cervix stimulates oxytocin, which stimulates uterus contraction, causing head to press and repeat
What is thermoregulation
the maintenance of a relatively constant core body temperature to maintain optimum enzyme activity
Processes that can cause temperature to change, and what they are
- exothermic chemical reactions
- latent heat of evaporation= cool as water evaporates
- radiation= transmission of electromagnetic waves too and from the air, water or ground
- convection= heating and cooling by currents of air and water (warm rises, cold sinks)
- conduction= heating as a result of the collision of molecules
What are ectotherms
- use their surroundings to warm their bodies
- core body temperature dependent on their environment
Examples of ecotherms
invertebrates, fish, reptiles, amphibians
Why do ectotherms not need to thermoregulate
- IF they live in water, the high heat capacity of water means the temperature is relatively constant
What are on endotherms
- rely on metabolic processes to warm up
- have adaptations to enable maintenance of body temperature
Examples of endotherms
- mammals
- birds
Behavioural responses to change temperatures
- increase/decrease radiation from the sun = BASKING
- lie in sun exposing maximum surface area
- press bodies against warm ground= conduction
- cool down by seeking shade, press against cold surfaces, minimal surface area exposed to the sun
Physiological responses to warming
- dark colours to absorb more radiation
- some ectotherms alter heart rate to increase or decrease metabolic activity
How are temperature changes detected
- peripheral temperature receptors in the skin detect changes in the surface temperature
- temperature receptors in the hypothalamus detect the change if temperature of blood deep in the body
- combination of the 2 gives the body sensitivity and allows it to respond
- temperature receptors in the hypothalamus act as the thermostat in the body
- should be kept within 1 degrees of 37
Principles of thermoregulation in endotherms
- use internal exothermic metabolic activities to keep warm
- use energy requiring physiological processed to keep cool
- also rely on behavioural responses (basking, digging burrows etc., and humans can change clothes and air con)
- some endotherms hibernate or aestivate
- endotherms mainly rely on physiological adaptations - skin, muscles, receptors
How organisms cool down
- vasodilation= arterioles dilate near the skin, increases radiation
- increased sweating= as it evaporates, heat is lost, cools blood below the surface (some organisms sweat glands restricted to less hairy areas)
- reducing insulation= erector pili muscles relax, causing hair/feathers to lie flat to the skin, avoiding trapping an insulating layer
- some endotherms in hot climates have anatomical adaptations= to maximise sa:vol ratio, e.g. large ears, wrinkly skin, pale fur
Ways organisms warm up
- vasoconstriction= arterioles near skin constrict, little radiation occurs
- decreased sweating= reduce cooling by evaporation
- raising body hair/feathers= erector pili muscles contract, trapping an insulating layer
- shivering= rapid, involuntary contracting and relaxing, metabolic heat warms up body
anatomical adaptations (of endotherms)
- adaptations to minimise sa:vol e.g. small ears
- Thick layer of insulating fat e.g. blubber
- hibernation
Examples of adaptations of polar bears
- small ears and fur on feet to insulate from ice
- fur traps an insulating layer
- skin under fur is black to increase absorption of warming radiation
- thick layers of fat under skin
- dig dens to insulate
What is the heat loss centre
- activated when temperature of blood flowing through the hypothalamus increases
- sends impulses through autonomic motor neurons to effectors in skin and muscles
- triggers responses that lower core temperature
What is the heat gain centre
- activated when the temperature of the blood flowing through the hypothalamus decreases
-sends impulses through the autonomic nervous system to effectors in skin and muscles that trigger responses to raise core temperature
