Communication and homeostasis Flashcards
Why do multicellular organisms need communication systems?
- As species have evolved to become increasingly complex, their cells become increasingly specialised.
- Organisms need to coordinate the function of different cells and systems to operate effectively and respond to changes
- Few body systems can work alone.
Factors that need to be kept constant inside body
- Blood-glucose concentration
- Internal temperature
- Water potential
- Cell pH
Why is it important to keep the conditions within cells relatively constant?
- Vital for cells to function normally and to stop them being damaged
- e.g. Enzymes denatured
- Glucose in blood needs to be controlled so there is always enough for respiration
Name the process by which cells communicate with each other
Cell signalling
Define cell signalling
- A complex system of intercellular communication
2. Where one cell releases a chemical which has an affect on another cell
Give 2 examples of systems whose purpose is cell signalling and outline how signals are transferred
Nervous
- signals transferred LOCALLY
eg. between neurones and synapses - signal is a neurotransmitter
Endocrine
- signals transferred across LARGE DISTANCES
eg. pituitary cells secrete ADH which acts on permeability of kidney tubules (DCT & collecting duct) - signal is hormone
Compare neuronal vs hormonal communication (transmission, response, effect, communication molecules)
Hormonal system
- Communication by hormone chemicals
- Transmission by blood, usually relatively slow
- Hormones travel to all parts of the body, but only target organs respond
- Response is widespread, slow, long-lasting
- Effect may be permanent and irreversible
Nervous system
- Communication by nervous impulses
- Transmission by neurones, very rapid
- Nerve impulses travel to specific parts of the body
- Response is localised, rapid, short-lived
- Effect is temporary and reversible.
negative feedback
- Sensory detectors detect small change. Effectors work to reverse the change and restore conditions to base level.
- The mechanism by which homeostasis is achieved
eg. control of blood sugar levels by insulin and glucagon
eg. osmoregulation using ADH
positive feedback
- A change in the internal environment of the body is detected by sensory receptors and effectors are stimulated to reinforce the change and increase the response
eg. blood clotting cascade
eg. childbirth oxytocin hormone which stimulates uterus contraction
homeostasis
maintaining a constant internal environment
maintains a dynamic equilibrium, with small fluctuations over a narrow range of conditions
4 factors that need to be kept constant in animals
pH of blood
core body temp
conc of urea and sodium ions in the blood
describe the blood clotting cascade as an example of positive feedback
blood vessel is damaged
platelets stick to damaged region
release factors that initiate clotting and attract more platelets
continues until clot forms
effector
Muscle or gland which carries out body’s response to a stimulus
receptor
- Extrinsic glycoproteins that bind chemical signals, triggering a response by the cell
- Detect changes in the internal and external environment of an organism
endotherm
‘inside heat’
- rely on metabolic processes to warm up
- relatively stable core body temp regardless of temp or environment
- mammals and birds
- survive in wide range of environments
- metabolic rate is 5x higher than ectotherms so need to consume much more food
ectotherm
‘outside heat’
- use surroundings to heat body up
- core body temp heavily dependant on environment
- all invertebrates, fish, amphibians and reptiles
- many ectotherms living in water do not need to thermoregulate as due to high heat capacity of water there is little variation in temp of internal environment
- on land can be big issue as air temp varies between seasons and over 24hrs. Many adaptations needed to cope
thermoregulation
the maintenance of a relatively constant core body temp to maintain optimum enzyme activity
why are ‘warm blooded’ and ‘cold blooded’ inappropriate terms
all blood is warm
explain why temp needs to be maintained within a narrow range with cells
enzymes that control the rates of chemical reactions are very sensitive to changes in temperature. Denatured if temp is too high.
Describe 5 ways in which heat is transferred between and organism and their environment
- exothermic reactions
- latent heat of evaporation (objects cool down as water evaporates from surface)
- radiation
- convection
- conduction
how do organisms generate heat internally
from metabolic processes
eg. waste heat from cell respiration
pros and cons of being an ectotherm
+ low metabolic demands
+ more of the food eaten can be used for growth
+ do not need to thermoregulate if live in water
- can’t live in a variety of environments. restricted to tropical or temperate regions on land
- core body temp heavily dependent on environment
- activity levels are reduced severely when it is cold eg. night or winder
how do ectotherms regulate their internal temp?
behavioural + physiological responses
behavioural
- bask in sun
- orientate/ extend bodies to maximise SA exposed to sun
- conduction by pressing bodies against warm ground
- contract muscles and vibrate, increasing cellular metabolism
- to cool down: seek shade, dig burrows, move into water, minimise movements
physiological
- lizards are darker colours if they live in colder climates to max radiation
- some ectotherms can alter their heart rate to increase/ decrease metabolic rate
pros and cons of being an endoderm
+ can live in a variety of environments
+ can maintain relatively constant internal environment regardless of external conditions
+ can maintain high activity levels at night and winter
- high metabolic demands
- more energy used to maintain body temp so less is available for growth
how do endotherms detect temp changes (internal and external)
internal - temp receptors in hypothalamus detect temp of blood deep in body
external - temp receptors in skin
how do endotherms regulate their internal temp?
behavioural + physiological responses
behavioural
- same as ectotherms but also
- hibernation (dormant in cold weather) or aestivation (dormant through the hottest weather) to avoid cold/heat stress
- humans wear extra layers, have insulation in housing etc.
physiological
- vasodilation/constriction
- sweating
- hair insulating later
- shivering
how to endotherms lower core body temp (cool down)
Vasodilation
- arterioles near skin surface dilate
- arteriovenous shunt vessels constrict,
- forcing blood through capillary networks close to skin surface
- increased heat radiation to air
Increased sweating
- sweat glands all over skin release sweat
- evaporation of sweat from skin surface, heat is lost, cooling body
(or panting in harrier animals)
Hair/feathers
- erector pili muscles in skin relax,
- so hair lies flat on skin surface
Additional adaptations
to increase SA:Vol ratio eg. big ears, wrinkly
to reflect radiation eg. pale fur/feathers
how endotherms increase core body temp (warm up!)
Vasoconstriction
- arterioles near skin surface constrict
- arteriovenous shunt vessels dilate,
- minimises blood flow through capillary networks close to skin surface
- very little heat radiation to air
Decreased sweating
- sweat production stops entirely
- greatly reduced evaporation from skin surface, although some evaporation from lungs continues
Hair
- erector pili muscles in skin contract,
- so hair stands erect on skin surface, creating insulating layer
Shivering
- involuntary contracting and relaxing of voluntary muscles in body
- metabolic heat from exothermic reactions heats up body
Additional adaptations
to decrease SA:Vol ratio eg. small ears
insulating fat eg. blubber in whales
hibernation (to build up fat stores and lower metabolic rate)
What are the two control centres controlling thermoregulation in endotherms?
heat loss centre
- activated when temp of blood flowing through hypothalamus is high
- sends impulses through autonomic motor neurones to effectors on skin and muscles to stimulate response to lower temp
heat gain centre
- activated when temp of blood through hypo is low
- sends response through autonomic nervous system to effectors in skin and muscles to raise core temp
