Date post: | 03-Jan-2016 |
Category: |
Documents |
Upload: | nora-lloyd |
View: | 217 times |
Download: | 0 times |
Communication: Homeostasis
Syllabus points
• Outline the need for communication systems within multicellular organisms, with reference to the need to respond to changes in the internal and external environment and to coordinate the activities of different organs.
• State that cells need to communicate with each other by a process called cell signalling.
• State that neuronal and hormonal systems are examples of cell signalling.
• Define the terms negative feedback, positive feedback and homeostasis.
• Explain the principles of homeostasis in terms of receptors, effectors and negative feedback.
• Describe the physiological and behavioural responses that maintain a constant core body temperature in ectotherms and endotherms, with reference to peripheral temperature receptors, the hypothalamus and effectors in skin and muscles.
Need for Communication
• Arctic fox – external environment
Need for Communication
• Internal environment
Major Systems of Communication
• Neuronal system• Endocrine system
Homeostasis
• Ability to maintain a steady state within a constantly changing environment contributes towards the success of living organisms.
“The constancy of the internal environment is the condition of a free life” – Claude Bernard 1857 (French
physiologist concerned with self regulation)
Homeostasis
The maintenance of a constant internal environment:
• Temperature• Concentration of dissolved substances• Blood sugar level• Water level• pH• Carbon dioxide concentrationAll rely on feedback in order to be kept
constant
Alterations to the environment…
Why is it important to control the following?
• Core body temperature
• Plasma water potential
• Plasma Glucose concentration
• Plasma CO2 concentration• Blood pressure
Feedback
All rely on feedback in order to be kept constant
Negative Feedback reversal of a change in the internal environment to return to a steady state or optimum position
Stimulus
Receptor
Communication Pathway
Effector
Response
Pathway for Feedback System
Regulation Negative Feedback
Detected by receptors
Detected by receptors
Change from resting level
Change from resting level
Effectors bring about a
return to resting level
Effectors bring about a
return to resting level
Resting
level
Positive Feedback
• Process that increases any change detected by the receptors and does not lead to homeostasis.
• Very rare in biological systems and leads to unstable and extreme states
Thermoregulation
All animals derive heat from 2 sources: external environment and chemical energy within cells
• Ectothermic: (‘ecto’ = outside) rely more on heat derived from the environment. All animals excepts birds and mammals.
• Endothermic: rely on internal sources of heat
Adaptations to resist changes in temperature leads to thermoregulatory classification of animals: ecto- and endotherms
Endotherms produce significant amounts of heatHow do they do it?
Inefficient metabolism -- leaky cells (uncoupling oxidative phosphorylation.)Production of waste heat -- shivering.Burning fuel without doing work -- brown fat.
Thermal GradientRadiation: Heat transferred by electromagnetic waves. Bodies
unable to absorb much radiated heat but transfer it to other bodies– 50% of total heat loss in man– Main route for controlled heat loss in animals
Convection: heat transferred via air. In endotherms air is warmer than body, therefore a convection current is created bringing in more cool air to body. This can be deterred by fur, feathers, hair or clothing
Conduction: Physical contact between two bodies. This is insignificant for most terrestrial animals
Evaporation: heat lost by body surface as water converts to water vapour– 1 cm3 requires the loss of 2.45 KJ from body – Cannot be controlled
General metabolism
Musclecontraction
Radiation and conduction from the environment
Radiation, conduction and convection to the
environment
Evaporation of sweat
Expiration and excretion
Heat Balance in Endotherms
Endotherms (mammals and birds) maintain a constant body
temperature through mechanisms aimed at balancing their heat gains and heat losses
Consider the ways in which this resting lioness is gaining
and losing heat
Radiation from the sun
Radiation and conduction from warmer parts of the environment
Radiation and conduction to
cooler parts of the environment
Convection of heat by air movements
Evaporation of water from
lungs and body surface
In terms of temperature control, provide an explanation for the relationship between ear size and habitat for the three different foxes
Suggest why the red fox has an ear size that is intermediate betweenthat of the Fennec and Arctic foxes
What is the significance of this behavioural and physiological response for thermoregulation in the mouse?
Endotherms
Advantages: • Constant body temperature
regardless of environmental temperature
• Activity is possible when external temp is cool
Disadvantages:• Significant amount of energy intake
is used to maintain body temperature in the cold
• More food required• Less of energy from food is used for
growth
Thermoregulation in Mammals
• Receptors– Sensory cells detect changes in skin temperature and blood
temperature flowing through hypothalamus – Two different types of receptor (warm and cool)
• Coordinator– Two areas in the hypothalamus:
Heat gain centre – involved in limiting amount of heat
loss from body and with heat generation from metabolism
Heat loss centre – controls activities that will reduce body temperature
• Effectors– Sweat glands, muscles, movement of hair, liver cells, blood
flow in arterioles to capillaries• Negative Feedback System
Negative Feedback in Temperature Control
Increase (usually due to exercise)
Detected by the hypothalamus
Heat loss mechanisms
• Skin
• Blood flow (vasodilation)
• Body hairs
• Liver cells
• Skeletal movement
• Breathing via mouth, nose and
lungsHeat retention/gain mechanisms
• Skin
• Blood flow (vasoconstriction)
• Body hairs
• Liver cells
• Skeletal movement
• Breathing via mouth, nose and
lungs
Detected by the hypothalamus
Decrease (usually due to a fall in environmental temperature)
Heat energy lost from body as
water evaporates.
More heat lost by conduction and radiation.
Insulating layer of air reduced. More heat lost by conduction.
Less metabolic heat gained.
Less heat lost by conduction and radiation.
Insulating layer of air trapped. Less heat lost by convection.
Generates metabolic heat.
Energy released as heat rather
than ATP
NormalBody
Temperature
Temperature rises
Temperature falls
Detected byThermoregulatory
center
Coordination Of
response
message viahormone
Impulse viaMotor neurones
1. Reduce metabolic rate
LiverCorrective action
1. Hairs lie flat2. More sweat3. More blood flow toSkin (vasodilation)
SkinCorrective action
Less heat produced More heat lost
Temperature falls
Detected byThermoregulatory
center
Coordination Of
response
message viahormone
1. Increase metabolic rate
LiverCorrective action1. Hairs raised
2. Less/no sweat3. Less blood flow toSkin (vasoconstriction)
SkinCorrective action
Impulse via Motor neurones
1. Shivering
MuscleCorrective action
Less heat lost More heat produced
Temperature rises
NormalBody
Temperature
Temperature rises
Temperature falls
Detected byThermoregulatory
center
Coordination Of
response
message viahormone
Impulse viaMotor neurones
1. Reduce metabolic rate
LiverCorrective action
1. Hairs lie flat2. More sweat3. More blood flow toSkin (vasodilation)
SkinCorrective action
Less heat produced More heat lost
Temperature falls
Detected byThermoregulatory
center
Coordination Of
response
message viahormone
1. Increase metabolic rate
LiverCorrective action1. Hairs raised
2. Less/no sweat3. Less blood flow toSkin (vasoconstriction)
SkinCorrective action
Impulse via Motor neurones
1. Shivering
MuscleCorrective action
Less heat lost More heat produced
Temperature rises
Stimulus
Receptor Coordination
Effectors
Response
Stimulus
Receptor
Coordination
Effectors
Response
Ectotherms can use behavior to resist changesin temperature.
But, endotherms also use behavior, and do so preferentially,and ectotherms have anatomical and physiological adaptations.
Anatomical adaptation in certain fast swimming fish make it possible to conserve metabolic heat in core and elevate muscle temp.
In most fish, cold arterial bloodflows centrally to serve muscles.
In “hot” fish, arterial blood flows under skinAnd forms countercurrent heat exchangersWith veins as it enters muscle.
Ectotherms also display variousPhysiological adaptations:Examples are heat production in flying insects, shivering inbrooding pythons, and CVadaptations in marine iguanas.
Water off GalapagosIs cold.Marine iguanas warm bybasking. When they enter water to feed, heartrate and therefore bloodflow to skin decreasesconserving heat in the core.Reverse when they return to land.
Thermoregulation in an Ectothermic Reptile – The Desert Lizard
Desert lizards, like many other reptiles, gain or lose heat by thermoregulatory
mechanisms that involve:• Burrowing behaviour when the ambient behaviour is
low (25oC to 30oC) or high (above 38oC)• Shifting between sun and shade• Postural adjustments that maximise or minimise the
exposure of the body surface to the sun• Physiological adjustments: vasodilation of skin
capillaries during basking behaviour and vasoconstriction during periods of low temperature; dispersion or contraction of black pigment cells in the skin with the lizards becoming lighter as the temperature increases
Postural adjustments and seeking out shade are behavioural mechanisms used by desert lizards to regulate their body temperature
1. Early morning; lizard emerges from its cool burrow (body temperature around 20°C)
2. Lizard basks in the morning sun and body temperature rises to around 38°C
3. Lizard maintains a relatively constant body temperature(38-40°C) by moving between the sun and shade as ambient temperatures rise towards mid-day
4. Lizard spends much time in the shade during the heat of the afternoon
5. Lizard spends mostof its time in the sun in the early evening and is very active before returning to its burrow for the night
alternating betweensun and shade
sheltering alternating betweensun and shade
basking
retreat toburrow for the night
EctothermsAdvantages:• Body temperature fluctuates with external temperature. • They are unable to increase respiration rates to generate
heat internally and therefore rely on external sources of heat to keep warm.
• Behavioural and structural mechanisms important in limiting variation in body temperature
• Need less food than endotherms to supply their metabolic needs
Disadvantages: • Less active in cooler temperatures, warm up in morning
before active• Not capable of activity during winter so must have sufficient
stores of energy to survive over winter• Found in limited range of environments.
Temperature Regulation
Behavioural changes:• To warm up: Bask in sun or lie on warm surface• To cool down: Stay underground or lie in the
shade
Physiological or anatomical adaptations:• Horned lizard: can alter surface area by
expanding or contracting its rib cage• Frilled lizard uses its frill to help absorb heat• Locusts increase their abdominal breathing
movements to increase evaporation of water and aid cooling.