The need for communication
Changes in the external environment (stimulus) require a response to the change by the organism.
Internal environment- cells bathed in tissue fluid- this is their environment. Metablic reactions in the cells release substances that may be toxic, eg CO2 - change ph and stop enzyme activity.
Build up of toxins - stiumuls- response would be to reduce metabolic activity.
good communication system:
-cover whole body
-enable cells to communicate w eachother
-short term/long term responses
-neuronal+hormonal- interconnected network of neurones that conduct signals v quickly - across synapses - hormonal- signal transported in blood recognised by target cells- enables longer term responses
Homeostasis - maintenance of internal environment in a constant state despite external changes, eg
body temp, blood glucose conc, CO2 conc, blood salt conc, blood pressure
Negative feedback: process that brings about a reversal of a change in conditions back to the optimum state. Change detected-> signalled to cells->response reverses change.
stimulus- receptor- cell signalling- effector- response
Number of structures involved:
-sensory receptors= temp/blood glucose conc receptors - if they detect a change, signal sent
-communications system eg neuronal/hormonal- signalling between cells -used to transmit message from receptor to effector cells
-effector cells- liver/muscle cells- bring about response that reverses the change detected
Receptors detect change, response increases the change away from optimum state - eg when body gets too cold, enzymes become less active, less exogernic reactions, body temp dereases even more.
Sometimes beneficial- oxytocin- cervix stretches signal sent to pituitary gland which secretes oxytocin- the more it stretches the mroe oxytocin released- the more contractions.
It will never be constant but it can be around constant- eg body temp warm enugh for enzymes but cool enough not to denature protein structure.
Ectotherm- relies on external sources to regulate its body temp.
- use less food for respiration
- can go for long periods of time without food
- energy obtained from food can be used for growth
- less active in cooler temps+must warm up before they can be active
- may be inactive in winter- must have sufficient stores of food to keep alive
They must increase exchange of heat w environment:
-when an ectotherm is cold change its beh or physiology to increase absorption of heat
-when hot- decrease heat absorption of heat
Adaptations of ectotherms
Expose body to sun- enables more heat to be absorbed- snakes
Orientate body towards the sun- increases sa available for heat exchange- locusts
Orientate body away from sun- decrease SA available for heat exchange- locusts
Hide in burrow- decreases exposure to sun- less heat absorption - lizards
Alter body shape - expose less or more sa to sun- horned lizards
Increase breathing movements- evaporates more water- locusts
Uses internal sources of heat eg energy released from metabolic reactions- to regulate body temp
- fairly constant body temp whatever the temp is externally
- activity possible when environment temp is cool
- ability to inhabit cooler temps in the planet
- most of energy intake used to maintain body temp
- more food required to release energy needed
- less of the energy used from food used for growth
Temp regulation in endotherms
Sweat glands in skin- secrete more sweat when hot; evaporates- uses heat from blood to supply latent heat for evaporation - less sweat secreted when cold- less evaporation, less heat loss from blood
Lungs, mouth, nose: Panting increases evaporation of water from lungs/tongue-using latent heat- less heat, no panting, less evaporation
Hairs on skin: lay flat, little insulation of heat more heat lost by radiation- when cold stand up, trap layer of insulating air-reducing heat loss by radiation
Arterioles: vasodilation of arterioles allows more blood near capillaries near skin surface-more heat loss by radiation - when cold, vasoconstriction of arterioles- less blood near surface, less lost by radiation
Liver cells: reduced metabolic rate- less heat generated from exergonic reactions- less heat- more metabolic reactions -more heat from exergonic reactions
Skeletal muscles- less contractions vs more contractions in shivering - aerobic resp
Temp regulation in endotherms
Move into shade/hide in burrow v move into the sun
Orientate body twards the sun v orientate body away from the sun
Remain inactive and spread out limbs v move about for muscle contractoins and roll into ball when v cold
Control of temp regulation- negative feedback
rise in core temp, receptors detect, send signal to hypothalamus - neuronal/hornonal system send signals to effector cells (liver and muscle)- bring about a response which is a reversal of the change eg less heat generated/less heat lost
fall in core temp- receptors in hypothalamus detect- neuronal and hormonal systems send signals to muscle cells and liver cells- increase met reactions and contractions- body temp increases