Flashcards in Animal Physiology-Environment Deck (39)
What 3 processes does tissue temperature affect?
Enzyme-substrate affinity, catalytic rate and membrane fluidity
What do the following terms mean?
Homeothermy= Body temp. remains constant
Poikilothermy= opposite; Body temp. fluctuates with environment
Endothermy= Body heat is derived from metabolism
Ectothermy= Body heat is derived from the environment
e.g Mammals are endotherm homeotherms
Hummingbirds are endotherm and poikilotherms (can make their own heat but at night allow temp to drop to environmental temp)
What cost is there to being homeothermic (like mammals)?
High energy cost-> greatly increases food requirement
Sometimes costs are too high so methods such as hibernation are adopted
What is the basal metabolic rate (BMR)?
The basal metabolic rate (BMR) is defined as the metabolic rate of an animal, in the thermoneutral zone, that is neither digesting food nor engaged in reproduction or growth (basically just to stay alive)
What is the resting metabolic rate (RMR)?
The resting metabolic rate (RMR) incorporates all of these requirements except that the animal need not be postabsorptive or in the thermoneutral zone (easier to measure as animal can be digesting food etc)
What is the thermoneutral zone?
A range of ambient temperatures in which the animal does not need to utilise energy to maintain its body temp
-The lowest ambient temperature in the TNZ is termed the lower-critical temperature
-The highest ambient temperature in the TNZ is the upper critical-temperature
(These just depend on species + their size, bigger animals have a bigger range)
What happens to the resting metabolic rate when ambient temperature drops below or above the TNZ critical values?
The RMR increases as it actively tries to adjust body temp (cool itself down or warm itself up)
Dry heat transfer is the process of transferring heat without evaporation. What are the 3 processes in which this can be achieved?
Convection (e.g wind), Conduction (e.g ground) and Radiation (electromagnetic radiation)
What does the rate of dry heat transfer depend on?
Body temp (Tb) and Ambient temp (Ta), so if body temp is v. high and the ambient temp is low, the rate will be high. The difference between the temps is called the driving force
The polimotor response is part of a regulation mechanism to ensure an animal does not lose heat when the ambient temp drops (still within TNZ). Describe how it does this.
Hairs or feathers are erected by the arrector pili muscles under the sympathetic nervous system to form a layer where air is trapped to increase resistance against heat transfer
The postural response is part of a regulation mechanism to ensure an animal does not lose heat when the ambient temp drops (still within TNZ). Describe how it does this.
Animals position themselves to reduce the surface area exposed to the environment. E.g Possums curl up when cold. Penguins huddle together to achieve this result. Vultures also do this.
Blood flow is also used as a mechanism of maintaining body temp (still within TNZ). in cold environments. How?
Vasoconstriction keeps warm blood near the core of the body instead of at the surface of the skin. The opposite to this is vasodilation. Ears are often interesting in studying this due to their small mass to surface area ratio,
When the ambient temp drops below TNZ, thermogenic mechanisms are used to make heat from metabolism. Explain how shivering is a thermogenic mechanism.
Shivering is when the autonomous system activates groups of antagonistic skeletal muscles to contract. This causes hydrolysis of ATP to provide energy for the shivering. The energy is released as heat
What is involved in non-shivering thermogenesis?
Brown adipose tissue dissipates heat. It is mostly found in small mammals but is found in young larger mammals.. Protons move into the mitochondrial matrix via a uncoupling protein and this produces heat. This is all regulated by the hypothalamus
If ambient temp increases above TNZ, sweating and panting can be used to cool down. How does sweating work?
Sweat is lost through sweat ducts onto the skin surface increasing the rate of cutaneous evaporation by a factor of 50 or more by wetting the surface of the skin. Sweat is a saline solution therefore prolonged sweating can cause a significant depletion in the body’s pool of NA+ and Cl-.
Secretion by the sweat glands is activated by the sympathetic nervous system
How does panting work?
It increases the rate of evaporative cooling because water evaporates from the warm moist membranes lining the respiratory tract into the air that is breathed out
-Advantage to panting is that no salts are lost– only pure water vapour leaves the body however due to muscular effort requires energy leading to heat production
-Also can induce respiratory alkalosis – an elevation of the pH of the body fluids caused by excessive removal of carbon dioxide
Why do pigs 'wallow'?
Wallowing is the act of rolling around in the mud to cool down. Pigs are prone to over-heating due to few and inactive sweat glands, large insulation layer and high body mass to surface area ratio. The cooling effect lasts much longer than if just water was used
What is Vasomotor index?
How well an animal can control loss of body temp to its surroundings (positive correlation between VMI and body size)
Small mammals have a low VMI so keeping warm may be energetically expensive. What do they do to overcome this?
Hibernation or torpor (allowing body temp drop in a controlled manner)
How is hibernation and daily torpor similar and how do they differ?
Animals that exhibit one of these behaviours allow their body temp to drop to close to ambient temp for certain torpor bouts (lengths of time)
Hibernation: close to 10 degrees for several days/weeks
Daily Torpor: between 10-25 degrees for less than 24h
Does hibernation consist of one long continuous bout or several?
Several. The animal undergoes many bouts (raises its body temp back up to normal temp then back down again) throughout hibernation for a number of reasons; eliminate waste, food collecting, look out for predators, immune system activation.
By what percentage reduction of metabolic rate, ventilation rate and heart rate does a hibernating dormouse undergo?
98.8%, 99.4%, 97.4%- this happens rapidly during the first few hours of hibernation- proves that it saves energy
What may stimulate/trigger the commencement of hibernation?
Arrival of cold weather, accumulation of fat, circannual rhythm, lack of food
What is the difference between a facultative hibernator and an obligatory hibernator?
Facultative hibernators do it in response to environmental conditions- e.g water or food shortage- hamster
Obligatory hibernators do it as a response to an annual cycle which is under physiological control (melatonin)- e.g squirrels
Melatonin plays an important role in hibernation. How?
It indicates when winter is coming due to shortening days. As they shorten, melatonin increases until hibernation is entered. It then drops back down until just prior to an interbout (when the animal heats up temporarily). This also links to the use of brown fat as this is used to warm the animal back up in these periods so the breakdown of the fat is activated by melatonin
What is a bi-product of metabolism?
Free radicals- highly reactive molecules with an unequal balance of charges so can cause damage to cells
How can melatonin affect free radicals and how is this beneficial to the animal?
Melatonin is an anti-oxidant so can readily donate electrons to free radicals to stabilise them and prevent oxidative damage to cells
What two types of food hibernators are there?
Fat-storing- rely on lipid hydrolysis derived from white adipose tissue as fuel source- e.g squirrels
Food-storing- used cached food that is ingested during interbouts- e.g hamsters and chipmunks
What morphological changed are seen in fat-storing hibernators such as squirrels?
Villi in the small intestine undergo villous atrophy- this reduction in the size of the villi which decreases nutrient absorption. There is also a reduction in protein synthesis and digestive enzymes. This does not happen in food-storing hibernators as they still need to be able to digest food quickly