Homeostasis Flashcards
Homeostasis definition
process of coordinating physiology of an animal to maintain as constant internal environment as possible
Applicable to temperature and chemical systems
Why is temperature important
Affects rates of biochemical processes
Influences viscosity of cellular materials and fluids- warmer=more runny
Protein conformation
Temperature definition
Intensity of molecular motion
Heat definition
The energy contained in the entire system as a result of the motion of the molecules
Large objects at the same temperature have a greater amount of heat – more molecules
Heat interactions between homeothermic animals and the environment
generates heat as a waste product of its metabolism.
Some of the heat is stored so raising its body temperature above ambient.
Some heat radiates from the skin.
Some heat is lost as air next to the rabbit is heated and moves away via convection.
Some heat is lost by evaporation of water from the respiratory membranes or skin.
Some heat is conducted away through to the ground.
The environment also interacts with the rabbit – there is direct radiation from the sun and other surrounding structures and wind can affect rates of convection by increasing the loss of hot air above the skin.
Conduction
Transfer of heat through a material substance that is microscopically motionless
Convection
Transfer of heat between an object and a fluid or air directly in contact with the body’s surface that is macroscopically active
Radiation
Bodies emit electromagnetic radiation at infrared wavelengths
Evaporation
Latent heat of vaporisation removes heat from a body through evaporation of water from its surface
4 main ways of transferring heat
Conduction
Convection
Radiation
Evaporation
What is body surface temperature proportional to
Thickness and nature of outer layer of body and ambient (or environmental) temperature
Conduction - physics
Heat is transferred through microscopic movement of atoms and molecules
Movement of atoms will cause movement of adjacent atoms via interatomic collisions
Equivalent to diffusion of molecules
t2 – t1 = thermal gradient
Different materials have different conductivities, e.g. air has low conductivity so is a good insulator
Convection- physics
Heat is transferred through macroscopic movement of atoms and molecules
Movement of air or fluid molecules will cause movement of heat away from a surface
t2 – t1 = thermal gradient requires ambient fluid to be cooler
hc depends on many different aspects of the structure of the body and on the rate of fluid flow
Evaporation - physics
Water absorbs a lot of heat when it is converted from a liquid to a gas
Latent heat of vaporisation [evaporation] is ~2400 J/g
Evaporating water from the skin or other bodily surfaces is a very effective way of removing heat
Radiation - physics
All bodies above absolute temperature (0 K or -273°C) emit electromagnetic radiation in the infrared wavelengths at the speed of light
Jackrabbits can regulate blood flow to the vessels in their large pinnae
Act as radiators but also allows for convective heat loss
Total intensity of radiation increases as surface temperature increases
Pairs of bodies emit and receive thermal-radiation simultaneously
Can be absorbed or reflected depending on colour
A model animal
Rate of heat loss depends on degree of insulation in the outer layer of body
Body core temperature (TB) is achieved by combined effect of metabolic heat production, insulation and environmental temperature
High metabolic rate and good insulation can keep TB > TA for longer
Poikilothermic animals
unable to maintain a body temperature based on internal heat production. These can either keep their body temperature at the same temperature as their environment and have no need to thermoregulate. Other animals can raise their body temperature above ambient using various behavioural means.
Poikilothermy
animal’s body temperature is in equilibrium with the thermal conditions of the environment
Poikilothermy relates to variability in body temperature
Ectothermy
reflects the external sources of heat that determine body temperature
Homeothermy (endothermy)
animal’s body temperature is regulated to a relatively constant value by physiological means
Heterothermy
reflects an animal’s ability to regulate its core body temperature, or a portion of its body, by either temporal or regional variation and that body temperature varies
Which animals of Poikilothermic
Invertebrates
Lower vertebrates
Which animals are homeothermic
Birds
Mammals
Conformers
are in equilibrium with the ambient temperature but are at its mercy – any changes can affect their metabolic rate (which is temperature dependent). One solution is to find a niche in an environment that doesn’t change very much over time or at all. Therefore, deep-sea fish live under constant high pressure but water temperature may be cold but it doesn’t fluctuate.
Regulators
either use behavioural or metabolic mechanisms to maintain their body temperatures. The lizard basking on a rock uses heat radiated from the sun to warm its body and moves out of the sun when it is warm enough but its body temperature over the course of a day is not stable. Birds regulate body temperature at a constant level using metabolic sources of heat.
Eurythermal animals
Can tolerate a wide temperature range
Stenothermal animals
Can tolerate only a small range of temperatures
Thermal tolerance
Optimal evolutionary fitness is a function of life history and peak bodily performance is often at an optimal body temperature. High temperatures are typically more deleterious to performance than lower temperatures – within the Pejus range a small increase in temperature has a large adverse effect (compare with a decrease in temperature of the same magnitude). Thermal tolerance has both low and high critical temperatures that can adversely affect survival if they are crossed.
Which of the following organisms will have the greatest heat energy at 38°C: Capybara, Chinchilla, Harvest mouse, or Mara?
Capybara
What three ways can mammals lose heat by evaporation?
Cutaneous evaporation
Respiratory evaporation
True or false? Convection involves the loss of heat through direct contact with another surface.
True
Why do were consider a dormouse a heterotherm?
exhibit physiological mechanisms that allow them to modify their body temperature over a long period of time
Define a wide thermal tolerance?
Animals can tolerate a wide range of environmental temperatures
Different species have different thermal tolerances
Often reflect differences in enzyme activity
Different responses to changes in temperature
Acute
Chronic
Evolutionary
Acute responses of ectotherms
Temperature
Ectotherms derive heat from external sources and if they poikilothermic they will change temperature as the ambient temperature changes. This impacts on cell metabolism and body performance but changes in temperature produce an asymmetric curve around an optimal temperature. Reducing temperature slows performance and metabolic rate but small increases in temperature can have dramatic adverse effects on performance. These changes are characterized by curvilinear responses and a higher temperatures the effects can be abrupt.
What are acute physiological processes largely determined by
the physical properties of molecular interactions and the metabolic rate of an animal
How are acute responses quantified
Determining the Q10 value for a response
Q10 = RT/R(T-10)
RT is the rate at any given body temperature
R(T-10) is the rate at the temperature at a body temperature 10 °C lower
the slope of the regression line on a semi-logarithmic plot.
How are acute responses quantified
Determining the Q10 value for a response
Q10 = RT/R(T-10)
RT is the rate at any given body temperature
R(T-10) is the rate at the temperature at a body temperature 10 °C lower
the slope of the regression line on a semi-logarithmic plot.
Which physiological responses experience a breakpoint
Metabolism
Heart rate
Gill ventilation
What is LD50
Temperature where 50% of the population can survive
Proteins and temperature
Protein denaturation and coagulation- prevents eg enzyme activity
Proteins and temperature
Protein denaturation and coagulation- prevents eg enzyme activity
Why can different species withstand different changes in temperature
1) Different animal may have unique metabolic pathways that are critically sensitive to temperature
-May explain differences between species but diversity of habitat temperature means that variability in metabolic processes just isn’t observed
2) Small changes to amino acid sequences changes temperature sensitivity
-Enzymes in icefish may be denatured at 6ºC because they different in their amino acid profile to eurythermal fish that live at higher temperatures and are denatured at 30-35ºC
Arrhenius principle
Metabolic rate increases exponentially against temperature
Heat shock proteins
family of proteins that are produced by cells in response to exposure to physiologically stressful conditions (temperature, UV light, and during wound healing.
Perform chaperone function by stabilizing new proteins to ensure correct folding or by helping to refold proteins that were damaged by the cell stress
Q10 effect on proteins
Consider a simple metabolic pathway
X → Y Y → Z
Q10 = 1.7 Q10 = 3.0
As temperature increases the conversion of Y → Z will be almost twice as fast as the rate that it can be converted from X
Concentration of Y decreases and the production of Z decreases
Y may also be important in other metabolic processes, which then slow and perhaps fail
Lipids and temperature
Fluidity of lipids is temperature sensitive – as temperature increases they become more fluid, as it cools they can solidify
High temperatures cause lipids to become less organised
These changes in fluidity can affect the biochemical processes mediated by proteins embedded in the membrane
Low temperatures and lipids
As temperatures decrease there is a greater risk of ice crystal formation in cells that physically damage structures
Reduced temperatures may slow elements of key biochemical pathways and if the rate of reaction is too low then vital processes may be stopped
If axon conduction stops then this can affect important autonomic processes, such as breathing
Ironically, cold temperatures can delay death by slowing biochemical processes even after breathing or heart function have ceased.
Thermal selection and seasonality
Only species that are fixed to one location (e.g. sessile sponges or coral) lack any ability to control body temperature through some kind of behaviour
Water readily conducts heat and temperature can change on short or long term time periods
Simplest method of temperature control is to move to locations that are at the preferred body temperature
Temperature regulation in ectotherms and size
Body temperature rises as body mass increases
As animals grow their surface layers become better insulators so more metabolic heat is retained and a higher body temperature can be maintained- thermal inertia
Acute responses and behavioural changes
Behaviour
Posture
Increased surface area and colour to absorb sun’s radiation
Shading by vegetation
Short flights to increase convective heat losses
Albedo- lightening in colour eg frogs
Physiological changes in ectotherms when diving
Reduced heart rate
vasoconstriction
Physiological changes in ectotherms when too hot
Evaporative cooling via respiration
Distribution of blood
Chronic responses and temperature
Changes in metabolic rate
