5.1.1- communication & homeostasis

what are vital for the body to be able to maintain this dynamic equilibrium and how does it work?

- receptors and effectors
- sensory receptors detect changes in the internal and external environment of an organism
- info from the sensory receptors is transmitted to the brain and impulses are sent along the motor neurones to the effectors to bring about changes to restore equilibrium in the body

what are the physical processes which cause organisms to constantly heat up or cool down?

- exothermic chemical reactions

- latent heat of evaporation: objects cool down as water evaporates from the surface

- radiation: transmission of electromagnetic waves to and from air, water or ground

- convection, heating and cooling by currents of air or water, warm air or water rises and cooler air or water sinks setting up convection currents around an organism

- conduction: heating as a result of the collision of molecules, air is not a good conductor of heat but the ground and water are

what are ectotherms?

- organisms whose core body temp is heavily dependent on their environment
- incl all invertebrate animals along with fish, amphibians and reptiles

why do ectotherms which live in water not need to thermoregulate?

- due to the high heat capacity of water which means that the temp of their environment doesn't change much as a lot of energy is needed to heat water

why do ectotherms which live in land have a bigger problem with thermoregulation?

- as the temp of the air can vary dramatically both between seasons and even over a 24hr period
- as a result ectotherms have evolved a range of strategies to enable them to cool down or warm up

what is a negative feedback system?

- a small change in one direction is detected by sensory receptors and as a result effectors work to reverse this change and restore conditions to their base level

- increase detected, response lowers level back to ideal conditions
- decrease detected, response raises level back to ideal conditions

-e.g. control of blood glucose levels by insulin and glucagon, temp control, water balance of the body

what are endotherms?

- organisms who rely on their metabolic processes to warm up and maintain a stable core body temp regardless of the temp of the environment
- mammals and birds

what are the differences between ectotherms and endotherms in terms of survival?

- endotherms can survive in a wide range of environments
- metabolic rate of endotherms is a lot higher than in ectotherms meaning they need to consume more food to meet their metabolic needs than ectotherms of a similar size

what can ectotherms not do and as a result what do they do instead?

- ectotherms cannot control their body temp using their metabolism so they have evolved a range of behavioural responses that enable them to overcome limitations imposed by the temp of their surroundings

what is homeostasis?

- how the body maintains a stable internal environment with small fluctuations with a narrow range of conditions

what is a positive feedback system?

- change in internal environment of the body is detected by sensory receptors and effectors are stimulated to reinforce the change and increase the response

- e.g. blood clotting cascade effect

what is thermoregulation?

- maintenance of a relatively constant core body temp to maintain optimum enzyme activity

what is a behavioural response for increasing the radiation ectotherms absorb from the sun?

- they may bask in the sun or orientate their bodies so that the maximum sa is exposed to the sun and can even extend areas of their body to increase sa exposed to sun

e.g. lizards may bask for long periods to get warm enough to move fast and hunt their prey

what behavioural response allows ectotherms to increase their body temp?

- through conduction by pressing their bodies against the warm ground
- also as a result of exothermic metabolic reactions e.g. contracting muscles and vibrating increasing cellular respiration to raise body temp or vibrating wings to warm muscles before taking flight

what behavioural response allows ectotherms to cool down?

- ectotherms shelter from the sun by seeking shade, hiding in cracks in rocks or digging burrows
- they will press their bodies against cool shady earth or stone or move into available water
- orientate their bodies so that minimum sa is exposed to the sun and minimise movements to reduce metabolic heat generated

do dark or light colours absorb more radiation?

- dark colours absorb more radiation than light colours

what is a physiological response from ectotherms?

- some ectotherms living in colder climates may be darker coloured than ectotherms living in hotter climates so they can get warmer an absorb more radiation from the sun

what can ectotherms also alter which is a physiological response?

- alter heart rate to increase or decrease metabolic rate

what is an advantage of ectotherms over endotherms?

- ectotherms need less food than endotherms as they req less energy to regulate their temps and so they can survive in some difficult habitats where food is in short supply

- by using a variety of behavioural and physiological strategies many can maintain a relatively stable core temp

what is a disadvantage of ectotherms compared to endotherms?

- metabolism is slower at lower environmental temps

- less able to hunt for food when body temp is low

what are peripheral temperature receptors?

- they are receptors which detect changes in the surface temp
- found in skin

where are temperature receptors located and what do they do?

- located in the hypothalamus and detect temp of blood deep in the body

what are the processes called which helps endotherms cool down or warm up?

- endotherms warm up by their internal exothermic reactions and cool down by energy requiring physiological responses

- also have passive ways of heating up and cooling down to reduce energy demands on their bodies

- some animals become dormant (hibernate) through the coldest weather

what are human behavioural adaptations to help control body temp?

- wearing more clothes to stay warm or less to cool down, houses are heated up or cooled down to maintain ideal temp

what do endotherms mainly rely on to maintain a stable core body temp?

- mainly rely on physiological responses regardless of the environmental conditions

- these adaptations incl the peripheral temp receptors, thermoregulatory centres of the hypothalamus, skin and muscles

what responses do endotherms make when cooling down?

- vasodilation
- increased sweating
- reducing insulating effect of hairs or feathers

how does vasodilation cool endotherms down?

- arterioles near the surface of the skin dilate when the temp rises
- the vessels that provide a direct connection between the arterioles and venules (arteriovenous shunt vessels) constrict
- this forces blood through the capillary networks close to the surface of the skin
- the skin flushes and cools as a result of heat loss b y radiation
- if the skin is pressed against cool surfaces then the cooling results from conduction

how does increased sweating cool endotherms down?

- as the core temp increases, rates of sweating also increase
- as the sweat evaporates from the surface of the skin, heat is lost which cools the blood below the surface

how does reducing the insulating effect of hair or feathers cool endotherms down?

- as body temp increases, the erector pili muscles (hair erector muscles) in the skin relax
- as a result the hair or feathers of the animal lie flat to the skin
- this avoids trapping an insulating layer of hair (this has litle effect in humans)
- large ears and wrinkly skin ensure relatively large sa:v ratio to maximise cooling
- pale fur or feathers reflect radiation rather than absorb

what are the ways endotherms can warm up?

- vasoconstriction
- decreased sweating
- raising the body hairs or feathers
- shivering

how does vasoconstriction warm up endotherms?

- arterioles near the surface of the skin constrict
- the arteriovenous shunt vessels dilate so very little blood flows through the capillary networks close to the surface of the skin
- this results in the skin looking pale and very little radiation takes place
- warm blood is kept well below the surface

how does decreased sweating warm up endotherms?

- as core temp falls, rate of sweating decreases and sweat production will stop
- this greatly reduces cooling by the evaporation of water from the surface of the skin

how does raising body hair or feathers warm up endotherms?

- as the body temp decreases, the erector pili muscles in the skin contract, pulling the hair or feathers of the animal erect
- this traps an insulating layer of air and so reduces cooling through the skin (in humans this has very little effect)

how does shivering warm up endotherms?

- as the core body temp falls the body begins to shiver
- this is the rapid involuntary contracting and relaxing of large voluntary muscles in the body, the metabolic heat from the exothermic reactions warm up the body

what anatomical adaptations do polar bears have which demonstrate how endotherms survive in cold conditions?

- have small ears to minimise sa:v ratio to reduce cooling, skin underneath is black which absorbs warming radiation
- they have a thick layer of insulating fat underneath their skin
- have fur on feet to insulate them from ice

what are the 2 control centres which control thermoregulation?

- both located in the hypothalamus

heat loss centre: activated when the temp of the blood flowing through the hypothalamus increases, sends impulses through autonomic motor neurones to effectors in the skin and muscles triggering responses that act to lower core temp

heat gain centre: activated when temp of blood flowing through the hypothalamus decreases, sends impulses through ans to effectors in skin and muscles triggering responses that raise the core temp

what is a summary of the control of body temp by peripheral temp receptors, hypothalamus and ans?

- decrease in blood detected by heat gain centre of hypothalamus and peripheral temp receptors in skin, responses /negative feedback e.g. vasoconstriction etc and temp of blood restored to normal