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93 Cards in this Set
- Front
- Back
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Anatomy of the Tracheal System |
- System of air filled tubes that provide a direct link between aerobically transpiring tissue and the atmosphere
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Tracheal System |
- Trachae and tracheoles are formed from invaginations of the ectoderm - Regulated by opening and closing of the spiracles |
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Respiratory system of insect |
1. Ventilation of the tracheole system 2. Diffusion of gas (very fast over short distances) |
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Fick's first law of diffusion |
- Rate of diffusion = KO2 x Area/length x (Po2 out - Po2 in) - K = krogh's coefficient; determines how fast O2 will travel through a particular medium |
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Convection |
- Some parts of the tracheal system are flexible - Abdominal pumping increases pressure in haemolymph --> collapse and expand the tracheal system to help push air in and out |
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Convection (cont'd) |
- Convective movement of air ventilates the tracheae between spiracles - Raises the PO2 and lowers PCO2 in the tracheal trunks to near atmospheric levels --> decreases diffusion length |
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How does convection limit insect size |
- Since the diffusion path is lowered, then insect size is lowered as well |
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Discontinuous gas exchange |
- It does not promote homeostasis - Internal level of O2 and CO2 fluctuate, as well as pH |
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Hygric Hypothesis |
- Insects have high SA:V ratio so there's a lot of SA to lose water from - Closing spiracles could cut off site of evaporation to short period of gas loss |
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Chthonic Ho |
- Underground insects where they have high CO2 and O2 levels - Hold breath |
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Oxidative damage Ho |
- Maximum override of O2 delivery --> high oxygen levels at rest - Tracheal system is too efficient - Create ROS |
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Disproving the Hygric hypothesis |
- No real correlation between arid and tropical regions - Some insects lose a lot of water but still have discontinuous breathing... - Wouldn't make sense if it was only to prevent water loss |
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Disproving Chthonic Hypothesis |
- Only the queen ant has discontinuous breathing - Worker ants do not - Some cockroaches that burrow underground don't have DGC... No correlation |
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Moth Pupa and Oxidative Hypothesis - Disproving |
- Experiment: moth pupa maintain the same ambient oxygen levels even when PO2 increases - It might be because the tracheal system is small and DGC didn't evolve to protect against oxidative damage |
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Emergent property hypothesis |
- DGC arose due to interaction between CO2 and O2 chemoreceptors during low MR |
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Neural Hypothesis |
- DGCs arose in the absence or down regulation of brain activity - Ganglionic activity? |
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Testing the low MR hypothesis (Gas exchange results) |
- Decapitate the head => absent brain activity - Chilled head => reduced head activity - Silver rod chills the head to zero degrees -> experiences DGC when the brain is off --> as temperature slowly rises, switch back to continuous breathing |
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If MR drives DGCs then... |
- there would a threshold of MR where DGC becomes continuous |
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What do we observe instead? |
- At the same metabolic rate, continuous and DGC are both observed... - Therefore, DGC is not driven by MR |
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DGCs and circadian rhythm |
- When insects are inactive, DGCs are observed - Can be induced by inactivating brain activity |
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Aquatic insect physiology |
- Many aquatic insects dive underwater with a bubble of air - Surface of air bubble acts like a gill: "gas permeable air-water interface allowing O2 to diffuse into the bubble" |
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What limits diffusion into air bubble |
- Thickness - Layer of stagnant water - Total area for diffusion |
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How does the air bubble shrink? |
- High O2 in bubble diffuses out to the water - High N2 in bubble diffuses out to the water |
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What do insects do to prevent air bubble shrinkage? |
- Since the insect is respiring, it will decrease PO2 in the bubble so it won't diffuse out into the water - However, this increases PN2 in the bubble and causes the bubble to shrink because partial pressure gradient inside is higher than outside |
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Two models of how bubble shrinks |
- Volume decreases but SA doesn't change - Volume decreases but SA changes |
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Which model is correct? |
- Stuck oxygen probe into insect bubble - Under ventilated gas-gill, bubble decreases but SA doesn't change drastically |
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Barheaded Geese - What do they have to overcome? |
- Very high altitudes - Low oxygen, air is cold and dry - Little drag, so they have high energetic demands |
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What do they actually do? |
- They take advantage of mountain passes and valleys - They have a great wing span to reduce wing loading --> Greater lift
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Why do bar headed geese fly at night? |
- They take advantage of cooler air -> denser -> more lift - They avoid the areas with high winds - They typically stay around 500m of the ground
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What is the roller coaster strategy of flight |
- It is energetically favourable to stay low to the ground because wind is thin at top - Cheaper to lose altitude and to stay at high altitudes for short amount of time |
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What are the two things that matter the most for bar headed geese? |
1. Total Ventilation 2. Muscle Diffusion Capacity |
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Ventilation - Poikilocapnic hypoxic ventilatory response |
- Bar headed geese have very HIGH tidal volumes and low frequency of breathing - Breathing deeper and slower => less dead space ventilation |
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When you add CO2... |
Bar headed geese ventilation was even greater! - They are INSENSITIVE to CO2 |
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Some anatomical features of bar headed geese |
- Larger lungs - more SA for gas exchange - Large SA and thin barrier for diffusion - Air sacs bellow: don't have restraints |
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Perfusion |
- They increase their stroke volume - Their heart can expand to 2 1/2 its size - Birds that were born in high altitudes have LEFT SHIFTED O2 saturation curves --> This means their hemoglobins have HIGH affinity to oxygen |
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High affinity hemoglobin in bar headed geese |
- They don't begin to desaturate and release their oxygen until high levels of hypoxia
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Effect of Temperature on Bar headed geese |
- Cold temperature shifts curve to the left - Hypocapnia (low CO2 in blood) enhances O2 loading - Metabolic acidosis in tissues enhance O2 unloading - Results in VERY high levels of oxygen delivery
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Tissue Diffusion in bar headed geese |
- They have more type 2a fibres near surface (oxidative fibres) - More mitochondria -> increase aerobic capacity in flight muscle - More capillaries per muscle fibre - More mitochondria are near the sarcolemma - The ventricles of the heart have higher O2 diffusion capacity |
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Cellular metabolism in bar headed geese |
- There seems to be no difference in enzyme activity and respiration rate - But there is a difference in MR...
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How is MR of bar headed geese different than other birds? |
- Most birds will depress metabolic functions -> reduces heat production and increases heat loss (usually through the beak) - Bar headed geese do not do this until they experience very severe hypoxia conditions - You can make them run for 15 minutes at 7% O2! |
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Effect of temperature on physiology |
- Enzyme and metabolic rate - pH of neutrality - Membrane fluidity - Locomotion |
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Van Hoff Equation |
Q10 = (k2/k1)^10/(t2-t1) k2 and k1 = rates of reaction at temperatures t2 and t1 - Compares the rate of a reaction at two different temperatures.. if the temp difference is 10 degrees, this is the Q10 |
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Q10 |
Q10 = k2/k1 - For most chemical reactions, this is a value of 2 or 3 - That means, for every 10 degree change, reaction rate doubles or triples |
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How do Q10 values vary? |
- They change based on acclimization of animal - Adaptability of animals |
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What is an endotherm? |
- Internal heat is generated by animal to maintain a high body temperature
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What is an ectotherm? |
- Environment determines the body temp. |
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Homeotherm? |
- Fish that live in stenothermal (stable) environments - Relatively constant body temperature |
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Poikilotherm |
- Variable body temp. - Echidnas are endotherms but regulate their body temp at variable levels |
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Heterotherms? |
Exhibits regional or temporal endothermy - TEMPORAL: based on time; lower body temperature at night (birds at night) - REGIONAL: Retaining heat in certain parts of the body (ie. shark muscle) |
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Thermoneutral zone in homeotherms |
- Range over which body temp and metabolic rate remains constant - End of this thermoneutral zone is usually seen at low temperatures where metabolic rate increases |
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Thermal preference in ectotherms |
- Ectothermic animals have a preferred body temp - High temp for lizards and lower for sharks |
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Behavioral response to temp. associated with hypoxia |
- Animals choose lower temp. when exposed to hypoxia - This phenomenon can be seen in ectotherms and endotherms |
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Thermal tolerance |
- Optimal temperature = largest difference between maximal and minimal oxygen consumption - Temperate fish have very high thermal tolerance |
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Temperature and Aerobic Scope Relationship |
- optimal temp determines aerobic scope of animal |
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Effect of climate change |
- Forces animals to move north to higher altitudes - Aerobic scope limitations - As temperature increases, critical max temperature increases - Temp. sensitive fish could be affected |
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COLD AND FREEZE TOLERANCE - What are the challenges of winter? |
- Food availability - Behavioural thermoregulators |
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Overwintering cycle |
- This is common for many animals - Shuts down metabolism and prepares for lack of food availability |
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Challenges of low temp. |
- Really important for ectotherms - Refer to Topt graph.. if temps are low, enzyme function is compromised - Change in membrane fluidity |
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Chill coma state is reversible Progression from cold damage to freeze damage - Supercooling point is when the animal freezes.. |
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What is chill coma? |
- Reversible state of muscle paralysis - Prolonged time in this state can lead to chilling injury - Low temp = reduced rate of ventilation ==> less oxygen supply to tissues ==> less ATP supply ==> LOW aerobic scope |
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What can cause chill coma? |
- Ion pump failures - As temp decreases, the rate of ion movement decreases |
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What is freezing? |
- Note: water does not freeze at 0 degrees - It only melts at 0 degees When water solidifies, it releases heat |
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What determines the supercooling point? |
- Presence of nucleators or antifreeze proteins --> controls where ice can form; antifreeze keeps ice crystals small - Size of water pool - High sugar content in blood can DEPRESS the supercooling point! |
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Why is freezing bad? |
- Causes osmotic shock as water leaves the cell - Enzymes denature - Cell membrane breaks |
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Biochemical adaptations of ectotherms to cold |
- Polyols & sugars ==> they are hydrophilic and can make hydration shells around proteins to protect them - Heat shock proteins (chaperones) - Antifreeze & nucleator proteins |
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Freeze Tolerance Adaptations |
- Ice nucleating agents: controls where ice form - Aquaporins - gets rid of water from the cell to prevent ice formation - Polyols and sugars - depresses supercooling point and protects proteins from freeze damage - Antifreeze proteins - reduce ice crystals |
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Goldenrod gall flies |
- They have high concentration of sugars to depress supercooling point |
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Effects of repeated freeze thaws (Mussels) |
Mussels from high intertidal zone experience longer periods of emersion and freezing events - They are more cold tolerant |
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What is the basis for this cold tolerance? |
- They go anaerobic during low tide -> reduce heart rate - Results show mussels from high intertidal that go anaerobic has higher survival time |
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What is Endothermy? |
- Ability to maintain body temp. above ambient temperature via heat produced from internal sources |
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Types of Endothermy |
--> Constant - constant production of endogenous heat throughout most of animal body (from the viscera) --> Temporal - temporary heat production by exercise (ie. snakes shivering) --> Regional - constant or temporary endogenous heat produced in one part of the body |
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Heat generation in billfish |
- Heat is generated in a "heater" tissue in billfish - T-tubule receptor stimulates Ca2+ channels which stimulates ATP -> ADP - Energetically expensive |
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Name 5 sources of heat - (1) Locomotion |
Heat produced by voluntary muscle contraction |
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(2) Shivering thermogenesis |
- Heat as byproduct of involuntary contraction (ie. brooding pythons) |
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(3) High resting metabolic rates |
Heat as byproduct of leaky membranes - Na/K ATPase is leaky.. means visceral tissues must work harder to maintain potential difference --> heat is released |
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(4) Brown adipose tissue |
- Heat as byproduct of a specialized tissue regulated by hypothalamus (ie. placental mammals, or animals that go into hibernation) |
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(5) Non shivering thermogenesis in skeletal muscle |
- Heat production stimulated by norepinephrine in animals w/o brown adipose tissue (ie. some birds and a marsupial) |
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What are some traits that were co-evolved? |
- Insulation - Circulation - Control over cellular heat production - Colouration - Sweat - Behaviour - Enzyme activity - Protein structure, function, synthesis |
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Advantages of Endotherms |
- Thermal independence from the environment - Increased growth rates - Faster biochemical reactions |
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Disadvantages of endotherms |
- Very energetically expensive - Lots of water loss --> when water gets to lungs, it is heated up to 37 degrees and humidified --> when exhale, water is lost |
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Theories on evolution of endothermy: (1) Performance of enzymes |
- Enzymes became optimized for a working temperature - Selection acted so they could thermoregulate
ADVANTAGE: allows enzymes to work in a variety of environments |
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(2) Niche expansion |
- Higher metabolic rates and body temp. facilitated expansion of geographic range and ecological niche |
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(3) Small body size and nocturnal activity |
- Large ectothermic ancestors were warm homeotherms (bigger animals have low SA:V so they can keep heat better) - Therefore, molecular machinery became suited for high stable temps - When climate cooled, selection acted to stay warm and become nocturnal --> increase metabolic heat production
WEAKNESS: this doesn't explain birds or endotherms... |
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(4) Aerobic capacity model |
- Selection acted on the ability to maintain high levels of locomotor activity - Could escape from predators, catch prey - Better survival - Basal metabolic rate (BMR) INCREASED to support locomotion - Byproduct of heat from BMR used for thermoregulation - WE ASSUME that BMR is linked with aerobic performance...
WEAKNESS: However, most of BMR comes from viscera, not the muscles... so theory isn't so good |
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(5) Intensive parental care #1 |
- Selection acted for survival of juveniles - Heat produced by metabolism was used to incubate eggs - Development of leakier membranes - Incubation at higher and stable temps allowed for faster growth of juveniles
--> explains birds and mammals
WEAKNESS: selecting leaky membranes is not ideal... its like a "furnace that can't be turned off" - leaky membranes couldn't have been the act of direct selection |
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(6) Intensive parental care #2 |
- Selection acted to improve survival of juveniles by increasing BMR to support increased locomotion - Increased BMR required to feed juveniles - Long term energy would pressure heat production from sustainable organs like the viscera, and not the muscles |
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Do enzymes work better at higher temps? |
- Depends - Can test by using assays to test rate of reaction |
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Were large ancestors warm homeotherms? |
- Tested dinosaurs for presence of turbinates (high SA structures that pick up water and allows for heat and water exchange when animal exhales) - Dinosaurs did not have turbinates, but they could have had other ways to minimize water loss |
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Does increased metabolic rates in ectotherms cause higher body temp? |
- Graph says no - Quadrupled MR, but no change in body temp. |
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Does BMR relate to litter size? |
No. Doesn't seem to increase the number of offspring |
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Wooly caterpillar paper key notes |
- Population of caterpillars died after multiple freeze thaw events - No metabolic rate changes - Figures show mortality rate vs. consecutive freezes |
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Insect paper - Matthews |
- DGCs can be induced by reversibly inactivating the brain with a cold probe - Supports the neural hypothesis |
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Crocodile paper |
Using calculations, they found that body temp increases with mass in animals - Large dinosaurs that had 10000kg would have a body temp. that fluctuates between 31-36 degrees - MR usually decreases with mass according to scaling laws - However, when body temp. increases with mass, and with normal Q10 (2-3), the metabolic scaling effect may be countered by Q10, and MR per unit mass may actually increase! - Dinosaurs may have had way higher MRs than modern reptiles |
