Comparitive phys test 2

Tuna are considered a high performance fish species while sole are typically viewed as sluggish. Compare these two species regarding the following: gill morphology, Ucrit, myocardial properties, ventilatory mode, and coronary blood supply.

-Gill morphology: Tuna have complex gill morphology containing closely spaced, thin, lamellae that increases surface area for gas exchange. sole have thicker lamellae that are further apart.

-Ucrit: tuna have a very high ucrit while sole have a very low ucrit.

-Myocardial properties: Tuna have very developed compact myocardium with high mitochondrial counts, while sole have only spongy myocardium.

-Ventilatory mode: Tuna are obligate ram ventilators, and sole are buccal pump ventilators.

-Coronary blood supply: Tuna have a well-developed coronary circulation that supports the compact myocardium and keeps the heart well oxygenated, while sole have little to no coronary circulation.

Describe the cardiac anatomy of a fish and the route that a single erythrocyte takes as it travels through its circulatory system.

A single red blood cell will start by becoming deoxygenated in the tissues and picking up CO2. The deoxygenated erythrocyte traveling through the venous circulation will enter the heart which is only ever receiving deoxygenated blood. The blood will enter the heart through the atrium and be loaded into the ventricle and then pumped into the gills where gas exchange occurs. The now oxygenated blood will travel through the common dorsal aorta to the brain and other tissues to oxygenate them.

What are the different layers of tissue in the heart? What accounts for their quantitative variation across different species? What are the trade-offs associated with having more of one than another?

The heart contains both spongy and compact myocardium. The quantity of compact myocardium is closely associated with the animal’s activity levels, with animals with large amounts of compact myocardium being more active. If an animal is going to have compact myocardium they must also evolve a well-developed coronary blood supply to perfuse the tissues of the heart, if an animal does not have compact myocardium then they will have a very minimal supply of oxygen to the heart receiving only deoxygenated blood, which must be picked up by the high surface area spongy myocardium.

What hypothesis do Farrell and Steffensen test and how do they test it? What was the outcome of their experiment?

Farrell and Steffensen wanted to determine if coronary circulation is essential for maximum aerobic performance. They accomplished this by surgically placing a silk thread around the coronary artery of a fish and measuring the Ucrit before and after ligating the coronary artery. They found that when they ligated the coronary artery, that ucrit was reduced by 35.5%, supporting that the coronary artery and its circulation is necessary for maintaining maximum aerobic performance.

Describe the conventional hypothesis concerning lung evolution in fishes?

Conventional wisdom says that lungs evolved in fish living in hypoxic conditions to allow these animals to acquire extra oxygen to support their aerobic metabolism.

What problems did Farmer identify in this hypothesis?

Fossil record evidence suggests that lungs had evolved in marine fish in the open ocean rather than in hypoxic areas. Living fish with lungs are found in well-oxygenated water or rely on their gills for majority of oxygen uptake. Finally the fish lung does not function most effectively for gas exchange as blood returning from the lungs mixes with deoxygenated venous blood before being pumped into the tissues.

What is her hypothesis concerning lung evolution in fishes?

The new hypothesis says that the lung had evolved to supply oxygen to the heart of bony fish to support high levels of activity by delivering adequate oxygen to the coronary circulation.

What testable predictions can be made based on this hypothesis?

Fossilized lunged fish should be evenly distributed in oxygen-rich and oxygen-poor environments and should show characteristics of an active lifestyle. The use of lungs should be related to activity levels rather than aquatic oxygen supplies.

What does she believe the implications are for the evolution of the tetrapod heart?

She thought that the division of the tetrapod’s atria and/or ventricle may compromise the cardiac oxygenation from the lung. She also thought that amphibians may rely on their cutaneous circulation to supply oxygen to their hearts, and that lizards, turtles, and snakes, may rely on intracardiac shunting to supply oxygen to their hearts. Further she thought that animal lineages who have lost the ability to shunt should have evolved an extensive coronary circulation.

Describe why gravity is such a problem in regard to blood distribution and interstitial fluid accumulation in giraffes.

The height of giraffes creates a problem for the animal as the brain and head are located far above the heart, which requires the animal to be able to perfuse their brain with oxygenated blood via high arterial blood pressure while also requiring them to avoid fluid accumulation in the legs and ankles due to gravity pulling fluid to the core of the earth, which even further causes venous return problems for the animal.

How do giraffes manage to insure adequate blood flow to their brain?

Most animals require about 100mmhg of pressure within the brain for proper perfusion, for giraffes to get this pressure up to their head they must have a very high (around 200) blood pressure coming from their heart. They have larger hearts with thick ventricular walls that help to generate necessary pressures and specialized valves in the jugular helps regulate flow up the neck and to the brain.

How do they prevent high intravascular pressures when lowering their head to feed from the ground?

The animal must be making cardiovascular adjustments to handle the changing head position with respect to the heart to ensure that blood and fluid are where they are required to be at all times. Giraffes have extensive valving in the jugular close to the head with less valves lower down the jugular and very thick non-compliant tissue around the base of the skull. This allows for the head and neck to act in the same way as the ankles in preventing backflow and fluid accumulation when an animal bends its head down to feed.

What did their measurements of interstitial and colloid osmotic pressure tell them?  What specific adaptations do giraffes have to prevent edema in their legs and feet?

The measurements of these pressures told researchers that both interstitial and colloid osmotic pressures are highest in the feet but capillary colloid osmotic pressures are equal everywhere. Giraffes have extremely tight thick connective tissue in the foot skin that essentially makes the interstitial space non-compliant for fluid buildup in these areas, which forces the fluid to be pushed back up towards the heart rather than being able to stay in the ankles. The giraffes get the fluid back into the circulatory system by using skeletal muscle pumping.

Answer the following questions concerning the cardiovascular physiology of sauropod dinosaurs by Seymour and Lillywhite.

 Describe the physiological problems they were trying to elucidate.

The researchers were investigating the problem of tall upright necks requiring extremely high arterial blood pressures and enormous hearts. Specifically, they were trying to understand the physiological characteristics that sauropod dinosaurs would have required to adequately perfuse their head given their extreme body and neck size.

What did they conclude about the likelihood that sauropods were endothermic and could lift their heads? What led them to this conclusion?

They concluded that it is unlikely that sauropod dinosaurs were endotherms holding their necks erect as this would have required a left ventricle weighing 2 tons and with a 20-inch wall thickness. With such a large heart this would require 62% of the animal’s resting metabolic rate to be utilized for cardiac metabolism and the requirement of 700mmHg of mean arterial blood pressure. No other animal exists to explain how they could have been endothermic, which lead them to conclude that ectothermy would have been more likely as this would allow lower stroke volumes and arterial blood pressures than endothermy which would allow the heart to be of a more reasonable size. With the heart at a reasonable size the animal would likely be able to raise its head as its using less metabolic energy to simply pump its heart.

What alternatives to cardiac hypertrophy did they believe allow sauropods to solve their cardiovascular challenge?

Some alternative hypothesizes to cardiac hypertrophy are the possible presence of multiple accessory hearts going up the neck to support the blood flow to the head, but this has not been supported with fossil evidence. Another alternative was the possibility of siphon action pulling blood into the head, but this would require the heart to be in the neck (not supported by the fossil record) and would cause air to be sucked into a wound on the head if that case were to occur. Ectothermy or partial ectothermy would successfully solve the problem regarding the size of the heart but would not solve the mechanical inefficiency problem regarding the cost of propelling the blood versus the cost of overcoming the stiffness of the thick ventricular wall.

What hypothesis is Secor et al testing and why are they testing it?

They hypothesized that snakes rapidly up and down-regulate their gut endothelium due to constant maintenance of the gut being energetically expensive. They are testing this hypothesis to understand the metabolic costs associated with intermittent vs continuous feeding.

What happens to oxygen consumption rate after a meal in rattlesnakes?  How does this compare to the oxygen consumption rate of a typical mammal after a meal?  What accounts for these differences in oxygen consumption rate?

After a meal, the oxygen consumption rate should drastically increase as the metabolic rate for the animal increases by about 800%, compared to the increase in the metabolic rate of a typical mammal of only about 25-50%. This difference can be attributed to the fact that the snake must expend lots of ATP to simply upregulate the gut mucosa for digestion, while the mammals’ gut is already primed for digestion, so energy is only being expended on digestion and absorption.

How does the transport capacity of amino acids compare to that of glucose in the small intestine of the rattlesnake?  Why does this make sense?

Amino acid uptake was always higher than glucose uptake and saw a large jump in amino acid uptake after the 3^rd day post-meal. Amino acid transport capacity also stays elevated longer post-meal than glucose transport capacity. This makes sense, as snakes are carnivorous and are eating other animals that are made up mostly of amino acid containing proteins, and are not eating foods high in glucose, like fruits. There is still a slight elevation in glucose transport, which has been hypothesized to be related to preventing glucose from diffusing into the gut lumen down its concentration gradient.

What morphological changes occur in rattlesnake intestine after feeding? What might these changes serve?

The serosa and distal portions of the gut experience very little morphological change after feeding, while the anterior mucosa experiences an explosion in size after feeding. This is because the mucosa is the inner layer of the gut that functions to digest the meal using projections called enterocytes. These enterocytes individually increase their volume after feeding reaching a maximum volume around a week after feeding, which increases the total surface area for digestion and absorption.

What happens to the heart of digesting Burmese pythons after it ingests a large meal? What is the physiological function of these changes?

The heart of a Burmese python after feeding experiences cardiac hypertrophy that increases the wet mass of the heart (and other metabolic organs) that is reversible during fasting periods. This allows the Burmese python to obtain post-feeding metabolic rates that are 40x larger than their fasting metabolic rates, and the high VO2 needed to sustain these high metabolic rates.

How do we know that the changes that were seen resulted from hypertrophy and not hyperplasia?

Cardiac hypertrophy is increasing the size of cells while cardiac hyperplasia is increasing the number of total cells. We know that the changes in the heart of the snake during digestion was due to hypertrophy rather than hyperplasia because the concentration of mass specific DNA decreases during digestion, and increases again after digestion, suggesting that the size of the cells are increasing, but new cells are not being made – if new cells were being made the mass specific DNA would stay the same.

What is symmorphosis?

Symmorphosis is a unifying principle of animal design that states that animals are built to have exactly what they need to survive and reproduce, with no more and no less. It assumes that animals incur selective penalties for maintaining structures in excess of their demand. Changes in demand for the organism can be resolved by plasticity during the growth and maintenance of tissues or systems.

What question were Taylor and Weibel attempting to answer in their study? What were their hypotheses?

They wanted to determine if the respiratory system is optimally built to satisfy the oxygen requirement of an animal. Essentially they wanted to know if the size of different structures within the respiratory system were adapted to the oxygen requirements of the animal. They hypothesized that structural patterns are a rate-limiting factor for oxygen flow at each level, that structural design is optimized to do exactly what is needed, and the structural design is adaptable (within limits, via plasticity).

Describe Taylor and Weibel’s experimental approach, including the physiological parameters they measured and the two study systems they investigated them in?

They used a comparative approach that both looked at similar sized animals and with different aerobic performances (cow vs horse for example) and looked at the relationship between size variation and metabolic rate changes. On these different groups they measured VO2 max, diffusion capacity in the lungs, and mitochondrial and muscle fiber distribution.

What did Taylor and Weibel conclude?

They found that all the variables they measured were consistent with the principle of symmorphosis, though most did not scale with body mass in the predicable way. This is because there was a little bit of variation as not everything is scaled to the ¾ body mass. For the most part, those animals that had high rates of metabolism had the supporting structures to satisfy that. An exception to this was lung diffusion capacity, which was found to be isometric.

Do Lindstedt and Jones agree with the conclusions of Taylor and Weibel? Why or why not?

Lindstedt and Jones did not fully agree with Taylor and Weibel, as they thought that systems (like the renal and respiratory) could be optimized, but 3 patterns may create constraints against optimization of the structures. These three constraints are that systems often have multiple functions making optimization difficult to demonstrate, that excess may be used as a safeguard against failure of a structure to function which makes it difficult to attribute excess to being more or less optimal in this instance, and that structures that exhibit plasticity are more likely optimized than ones without plasticity.

Why are Lindstedt and Jones concerned about tautology in the context of symmorphosis?

They are concerned because optimization has many constraints, including if a structure or system has multiple functions, whether safety and excesses in a system have been optimized, and that structures with plasticity will more likely be optimally designed. They also ask the question of why can’t adequate be adequate because in nature, things just need to be “good enough.” They also wonder if symmorphosis is really testable.

What are Garland’s primary criticisms of symmorphosis?

Garland gave 8 reasons why organisms are not optimal:

1)      Organisms are not “designed” and natural selection is not engineering.

2)      Organismal design is limited by the starting material.

3)      There is little empirical evidence supporting energetic efficiency as a “goal” of selection.

4)      Environments change faster than animals do.

5)      All animals are equally likely to be killed by stochastic events.

6)      Genetic drift will cause deviations from optimal when the trait isn’t under strong selection.

7)      Behavior evolves more rapidly than physiology and may have more influence over what animals

can and cannot do.

8)      Sexual selection can lead to irrational animal designs.

What is an animal’s metabolic rate?

Metabolic rate is the rate at which an animal converts chemical energy into work and heat in the units of calories or joules.

Where does metabolic heat come from?

Metabolic heat comes from inefficiencies of energy capture as matter is transformed by cells or is released when an animal does work on a component in its environment.

What is the difference between direct calorimetry and indirect calorimetry?

Direct calorimetry directly measures the metabolic heat production by surrounding the animal with ice and assessing how much the ice is melted by the animal. Indirect calorimetry uses other parameters including carbon dioxide production and oxygen consumption as a proxy to determine metabolic heat production but can sometimes have variable accuracy when an animal uses multiple fuel types.

 

What is the respiratory exchange ratio and what is its normal value in a typical animal?  How is it affected by metabolic fuel utilization?

The respiratory exchange ratio is the rate of CO2 production over the rate of O2 consumption (VCO2/VO2). In a typical animal, its normal value is between 0.7 and 1 , with differences being accounted for by the utilization of different fuel types. The respiratory exchange ratio is 0.71 for lipids, 0.83 for proteins, and 1 for carbs in a typical animal.

Describe the relationship between body mass and metabolic rate. How does this relationship compare between endotherms and ectotherms?

The mass-specific metabolic rate is higher in smaller animals than it is in larger animals. This follows for endotherms and ectotherms but is seen at a higher scale in endotherms as they have a 10x higher metabolic rate than an ectotherm of the same size.

List four ways an animal may use to achieve homeothermy.

Homeothermy can be achieved via behavior adaptations like changing physical position or wearing clothes, or by insulation like blubber, by coloration of fur, and by changes in blood flow distribution.

List one cost and one benefit of endothermy.

One cost of endothermy is that it requires more energy intake so endotherms spend more time foraging. One benefit is that endotherms are freed from the “tyranny” of the Q10, which is the change in any reaction rate per 10 degree change in temperature, allowing for greater niche exploitation.

Explain why the smallest vertebrate known cannot possibly be endothermic.

SA to volume ratio would mean that the smallest vertebrate would be very susceptible to heat loss due to the high SA available for radiating heat. This animal would have to be constantly heating their body to maintain endothermy which would be very energy expensive. Heat production is largely related to mitochondria function, an extremely small endothermic animal would need so many mitochondria packed into each cell that it would no longer be effective for other normal cell functions.

Explain why it is so difficult for a water-breathing vertebrate to be endothermic homeotherms.

It is difficult because of the respiratory medium. Water has a high heat capacity making it very difficult for an animal to avoid losing metabolic heat to the water. Tuna is an exception to this because they increase their metabolic flux to maintain endothermy and defend their temperature.

What is the origin of metabolic heat?

Metabolic heat is a normal by-product of metabolism and is released when glucose is turned into ATP. 62% of chemical energy produced by a cell is lost as heat.

What are the two main strategies utilized by vertebrates to increase metabolic heat production? Give one example of each.

1.       Increase metabolic flux by increasing ATP consumption rate

   Ex: Tunas use this as they swim continuously to increase metabolix flux by increasing ATP turnover

2.      Reducing the efficiency of free energy capture by increasing the amount of metabolic flux required to produce ATP.

      Ex: futile cycling of H+ and Na+/K+ used by birds and mammals

What two mechanisms most likely explain systemic endothermy specifically in birds and mammals? Give one example of each.

Mammals increase metabolic heat production by increasing the size of tissues which are more metabolically expensive, like the liver, brain, heart, and kidneys. Additionally, they possess futile cycling, like that of H+ caused by leaky mitochondrial membranes that allows for increased metabolic heat to production without the production of extra ATp.

What is non-shivering thermogenesis, which vertebrates do it, and in what tissue does it occur? Describe the cellular mechanisms underlying it and how it results in increased heat production.

Non-shivering thermogenesis is the process of increasing metabolic heat production without work in the muscles. Non-shivering thermogenesis occurs in neonatal and hibernating mammals within the brown adipose tissue. The sympathetic nervous system releases noradrenaline when exposed to cold which binds to a receptor on the cell membrane that activates second messenger pathways that eventually change the phosphorylation state of lipases that will digest triglycerides into free fatty acids. These free fatty acids will act as a proton buffer, which allows them to easily pass into the mitochondrial matrix when the FFA is protonated. In the high pH matrix, the FFA will release the proton into the matrix and be transported back out to the cytoplasm with an uncoupling protein transporter. This cycle essentially bypasses ATP synthase, making electron transport less efficient, which means that the electron transport chain must go faster to satisfy the basal metabolic requirements of the cell which in turn leads to higher levels of heat being produced.

Name the three general types of muscle.  For each, state one place where they are found in vertebrates.  Which types are striated? Which types are under voluntary control and which are under involuntary control?

The 3 types of muscles are skeletal muscles, cardiac muscles, and smooth muscles. Skeletal muscles surround the skeleton, cardiac muscles make up the walls of the heart, smooth muscles make up the gastrointestinal tract. Skeletal muscles and cardiac muscles are both striated muscles with a striped appearance. Skeletal muscles are under voluntary control while cardiac and smooth muscles are under involuntary control.

Name the two most important contractile proteins in muscle. Which one has an active site for hydrolyzing ATP?

Myosin and Actin. Myosin has an active binding site for hydrolyzing ATP.

What role does Ca²⁺ play in cross-bridge cycling?  Which organelle regulates Ca²⁺?  How causes calcium to leave this organelle? How does the Ca²⁺ reenter it?

Ca²⁺ is required to activate crossbridge cycling by binding to troponin which shifts tropomyosin out of the actin active sites which allows for the myosin heads to bind and begin muscle contraction. Calcium is regulated by the sarcoplasmic reticulum. Ca²⁺ is released from the reticulum when an action potential travels down the sarcolemma and down the t-tubules, depolarizing them. When these positive charges are present in the t-tubules, DHPRs on the t-tubules change shape and allow for the RyR calcium channel to be open, allowing calcium to diffuse from the SR to the cytoplasm to stimulate muscle contraction. Ca²⁺ is returned to the sarcoplasmic reticulum via ATP-requiring SERCA transporters that actively transport calcium back into the SR.

During muscle contraction, what processes require ATP?

ATP is required to power myosin and actin cross-bridge cycling. Specifically, when ATP is bound to myosin, it dissociates from actin which allows for the myosin heads ATPase to hydrolyze the ATP into ADP and inorganic phosphate which allows the myosin head to cock in preparation for actin re-association. ATP is also used in the reuptake of calcium from the cytoplasm into the SR, done by active transportation via SERCA transporters.

Easy answer: ATP is required for myosin and actin cross-bridge cycling and calcium active transport into the SR using SERCA transporters.

What are the three types of skeletal muscle fibers? How do they compare with respect to force production and fatigue resistance?

The three types of skeletal muscle fibers are slow oxidative fibers, fast oxidative glycolytic fibers, and fast glycolytic fibers. Slow oxidative fibers have low force production with high fatigue resistance, fast oxidative glycolytic fibers have intermediate force production and intermediate fatigue resistance, and fast glycolytic fibers have high force production and low fatigue resistance.

Define the following and provide one vertebrate example of each:  poikilothermy, homeothermy, heterothermy, endothermy,  ectothermy.

Poikilothermy: The temperature of environment determines body temperature and in turn their metabolic rate animals may use physiological and behavioral thermoregulation (Icefish)

Homeothermy: Endotherms that are good at temperature regulation (Humans)

Heterothermy: The ability of an animal to exhibit characteristics of both ectothermy and endothermy allowing animals to adjust their metabolism and temperature regulation depending on the environmental conditions (13 lined ground squirrel)

Endothermy: The ability of an organism to generate metabolic heat internally, done by birds and mammals. Endotherms fall into two groups, either thermoregulating endotherms or non-thermoregulating endotherms. (Birds)

Ectothermy: Animals that use the heat in their surroundings to change their body temperature (lizards)

Why is evaporative cooling such an effective way of dumping heat?

Evaporative cooling, like that done with panting or sweating, is the process of increasing the rate at which water evaporates from the body surface and is an extremely effective mechanism for releasing excess metabolic heat. We know that water absorbs heat very well due to its high heat capacity, thus actively increasing the release of water will also increase the release of heat. While evaporative cooling is very effective it is important to consider the tradeoff between this form of cooling and the potential for dehydration due to excess water loss.

Why is the observed distribution of the body temperatures measured in living lizards so much narrower than those measured in an identical, non-living model?

Behavioral thermoregulation within the living lizards allows this much more narrow distribution of temperatures and show that these lizards have a preferred body temperature that they will attempt to maintain through behavioral means.

What are two ways that animals change their heat conductance to the environment?

Animals will change their positioning to change the amount of heat conductance to their environment, like a lizard spreading out on a warm rock to warm its body up, as a form of behavioral thermoregulation. Animals will also regulate the amount of blood flow at their skin to regulate heat exchange. Rabbits will increase blood flow to their large ears which allows them to release more heat into the environment after exercise or other instances of high heat production.

In simple terms, what does Q₁₀ describe?  What is the actual numerical value for biochemical processes, generally?

Q₁₀ is the change in reaction rates per 10 degrees change in temperature. The Q₁₀ for general biochemical process is 2-3.

How is metabolic rate affected by body temperature? Why?

For endotherms, metabolic rate is inversely proportional body temperature. When the body temperature of an endotherm drops, metabolic rate must increase to produce the metabolic heat required to get the body back to optimal temperature. For endotherms and poikilotherms there is an positive exponential relationship between metabolic rate and body temperature. When the body temperature of these animals increases the metabolic rate increases because the reaction rate of the biochemical processes within the animal also increases.

How would cold acclimation affect metabolic rate in a lizard? What is the function of this acclimation response?

Cold acclimation allows for a lizard that has been at a low temperature for a long period of time to have a higher metabolic rate than that of a lizard at the same temperature that is acclimated to a warmer climate. This acclimation effectively blunts the effect of the drastic temperature change on the lizards metabolic activity.

Describe the effects of temperature on enzyme activities. How is it that different animals living in different thermal environments all maintain similar enzyme-substrate affinities for many different enzymes?

Low temperature decreases the functional properties and thus activity of an enzyme. Animals are able to maintain similar enzyme-substrate affinities despite different thermal environments via the evolution of different enzyme homologs which function within different ranges of temperature depending on the animals average habitat temperature but within the same enzyme-substrate affinity for all enzymes at all temperatures.

How does temperature affect the fluidity of plasma membranes? What is the consequence the change? What is homeoviscous adaptation and how is it adaptive?

Plasma membranes fluidity is dependent on temperature, membranes are less fluid in low temperatures and more fluid in high temperatures. Changing the fluidity of the phospholipids in the plasma membrane will change the mobility of substances through the plasma membrane which is extremely important for both membrane and overall cell function. Homeoviscous adaptation is the maintenance of membrane fluidity at a constant level regardless of the temperature of the tissues, which allows for animals to maintain the fluidity that optimizes the function of the plasma membrane irrespective of the ambient temperature, allowing animals to withstand a variety of temperatures without impacting their plasma membranes function.

What is a thermoneutral zone and which animals have one?

The thermoneutral zone is the range of temperatures at which the ambient temperature of the environment does not raise the metabolic rate of the animal, thus this is the range at which the cost of living is the lowest. Endotherms like birds and mammals have a thermoneutral zone.

How does increasing insulation affect the thermoneutral zone? How does decreasing it affect it?

Increasing insulation shifts the thermoneutral zone to lower temperatures, allowing an animal to tolerate colder climates without increasing metabolic heat production. Decreasing insulation shifts the thermoneutral zone to higher temperature allowing for easier heat dissociation in warm climates.

Explain why marine mammals potentially have a problem with overheating while on land. How do they avoid overheating? (be sure to express your answer in terms of the physical properties of air versus water).

Marine mammals have extensive insulation in the form of blubber which prevents heat from the core to dissipate. This is a very effective strategy in water which has a much higher specific heat than air and sinks heat out of objects, as the blubber can reduce this heat conduction from the core to water. Air is a much worse conductor of heat which can cause marine mammals to retain too much of this metabolic heat and risk overheating. Marine mammals can avoid overheating by changing blood distributions in their skin in and out of water. When a marine mammal is in water the blood vessels constrict to prevent heat loss and when the animal is in air the blood vessels open to increase the temperature of the skin thus increasing the heat loss to the environment.

Describe the basic anatomical arrangement of a countercurrent heat exchanger and how it conserves heat in the leg of the European rook. 

The countercurrent heat exchanger in the leg of a European rook consists of a large, thick-walled artery carrying warm blood from the core, in close contact with the surrounding thin-walled veins returning from the legs with colder blood. This close association between the veins and artery allows for heat exchange to occur between the blood in these vessels rather than into the environment. This lets the warm arterial blood exchange heat with the cool venous blood before that blood is returned to the core, keeping the feet relatively cool, minimizing the heat that is lost from the feet.

Why does dehydration become a major problem for endotherms in extremely warm climates? How have camels solved this problem?

Dumping heat via active evaporative cooling like panting or sweating can lead to massive water loss and dehydration, especially for animals in extremely warm climates. Dehydrated camels were able to bypass this issue by a process of deep cycling their body temperature to conserve water. Essentially the camels drop their temperature at night such that when the sun begins to rise at dawn the body temperature is at its lowest. Over the day the camel will accumulate this heat, raising its body temperature up to 7 degrees C, until the sun goes back down, and the environment is more optimal for convection and radiation to carry the heat out of the camel without water loss.

Describe the strategy used by the gazelle to tolerate extremely warm ambient temperatures.

Gazelles can tolerate extremely warm ambient temperatures via higher hyperthermia tolerance and a brain cooling heat exchange system. Gazelles have nasal turbinate’s (conchae) that increase in complexity going down the nasal passages which greatly increases the surface area for heat exchange. When hot, the animal will send lots of blood to the nasal passages which will pass through the nasal turbinates and become greatly cooled while the animal pants. The now cool venous blood comes in contact hot arterial blood at the high surface area heat exchange structure, where heat exchange can occur, cooling down the arterial blood before it goes to the brain.

Despite the fact the blood leaving the gills in tuna is the same temperature as the water flowing across them, their swimming muscles are warmer than the water. Explain how this is achieved.

Tuna’s swimming muscles are warmer than the water that they are in because the red swimming muscles have a countercurrent heat exchanger where heat produced when the muscle contracts is picked up by the venous blood and is transferred to the ingoing arterial blood, rather than continuing out to the periphery of the body where the heat would be quickly lost. This allows for heat to be both produced and retained in this red swimming muscle.