Physiology I - Tulane University - New Orleans_ LA

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Physiology I - Tulane University - New Orleans_ LA Powered By Docstoc
					Physiology I • • •
In addition to feathers, birds have evolved many skeletal and physiological adaptations for flight Skeletal adaptations examined in lab Lecture will focus on physiological adaptations

• Skeletal Adaptations for Flight:
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Lightweight bones, strong and elastic Internal struts in wing bones Highly fused skeleton (synsacrum, head, hands) Powerful and highly modified joints in the forelimbs (carpometacarpus, alula) Streamlined shape of body

• Skeletal Adaptations for Flight:
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Keeled sternum or breastbone (carina) Furcula (clavicle or wishbone) No teeth, so no need for a heavy jaw (bill, gizzard) Pelvic and pectoral girdles large and strong Uncinate processes on ribs

• Physiological Adaptations for Flight:
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Efficient metabolism Efficient respiratory system (air sacs etc...) Uric acid excretory system Endothermy, 4-chambered heart, good circulation

• Physiological Adaptations for Flight:
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Powerful flight muscles, the pectoralis (wings down) and supracoracoideus (wings up) Shell forms late in egg development Sex organs atrophy outside breeding season

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Combination of feathers, skeletal, and physiological design strategies Produced a strong, elastic, lightweight airframe Produced an efficient power plant to run it Birds are very active animals, with amazing stamina Able to fly for hours at a time, for days on end Their metabolic furnace burns much brighter than our own

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Average body temperature is about 40 oC (104 oF), compared to our 98.6 oF (37 oC) Birds live precariously close to the thermal abyss Heat denatures proteins, three-dimensional shape uncurls into a string of amino acids Something you’ve seen every time you’ve fried an egg At ~ 46o C the rate of protein destruction exceeds the rate of protein synthesis Nervous and muscular systems of birds are turbocharged due to high body temp Supply and transport systems (circulatory, respiratory, excretory), have to keep pace High-powered metabolism generates a lot of heat Can kill them on a hot summer’s day Can keep them alive through a cold winter’s night Variety of physical and behavioral responses to heat and cold Can change the elevation of their feathers to shed or retain heat Fluffing the feathers traps a layer of warm air on a cold day Holding feathers very close, or extending them far out to expose bare skin, helps cool the bird down Keeled sternum spreads out the attachment point of the flight muscles Muscles have air channels inside which dissipate heat during flight Keeled sternum keeps muscle channels from collapsing when muscle contracts Heat loss is related to body size, the ratio between surface area and volume Consider the cline in body size of the English Sparrow? Hot humid climates favor smaller body (Mexican sparrows) Colder, dryer climates favor larger body (Canadian sparrows) Birds react to cold in many ways Seek shelter in cavities or dense vegetation Huddle together to keep warm Shiver, the same as we do, to generate additional heat Can sleep on one leg with their heads tucked under their wings to conserve heat (shorebirds, wading birds...)

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Most birds drop their body temperatures a degree or two at night Hummingbirds, chickadees and baby swifts are very tiny, severe SA/vol problem They have to turn the thermostat way down, leaving only the metabolic “pilot light” on They enter a state of torpor Hummingbirds have a very high surface area to volume ratio, and the highest metabolic rate of any vertebrate They don’t fly so much as buzz Beat their wings up to 80 times per second when they hover Flight muscles one-third their entire weight! Hummers radiate an enormous amount of heat When the weather gets too cold, they drop their body temperatures as much as 20-32oC If body temp falls to ~ 20oC below normal, enters a comatose state which uses an absolute minimum amount of energy Hovers unresponsive, on the energetic edge of death Takes about an hour to fully awaken in the morning from deep torpor Chickadees also resort to torpor to survive brief bouts of extreme cold Baby swifts can enter torpor to get through lean periods of little or no insects to eat Too hot is as big a problem for birds as too cold Birds don’t sweat Water simply evaporates through the skin, none of those messy sweat glands Birds seek shade or cool off in the water, just like us, to keep from overheating They can also lower their feathers to transfer heat directly from the body Birds can also pant, holding their mouths open to evaporate body moisture Many seabirds (ex. pelican) can also vibrate their gular pouch, which increases the evaporation of water from the throat and mouth Birds can also shed large amounts of heat through their legs and feet Can increase the blood flow to their extremities, especially long-legged birds like herons

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Can also reduce blood flow to the legs by constricting the blood vessels Direct the return flow of venous blood through a special shunt Flying turns up the heat even more Parakeets flying at 35 km/hr (22 mph) increase their body temperatures to 44oC (111oF)! Would cook themselves in midair, were it not for the cooling effect of the moving air Outstretched wings make nice heat exchangers Air streaming around them plasters their feathers tightly to their bodies, shedding even more heat A flying parakeet sheds three times as much heat as a parakeet at rest Passerines have very high basal metabolic rates (BMRs), the metabolic level of the bird at rest Passerine BMRs are 50-60% higher than non-passerine birds Birds have the highest BMR of any vertebrate But birds are seldom at rest They are usually expending enormous amounts of energy at a rapid rate A bird in flight can maintain a metabolic rate 10-25 times its BMR for hours at a time One consequence of heightened metabolic rate is that birds produce more metabolic water than other vertebrates Water is produced when carbohydrates and other organic compounds that contain hydrogen are oxidized Problem of excess metabolic heat is partly countered by the excess production of metabolic water Can be used for evaporative cooling (panting etc.) Supplement dietary water with visits to open water and using metabolic water Birds get water from many sources Much of their water comes from diet - fruits, meat and insects Most birds eat high energy foods Very few are leaf-eaters (folivorous)

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Supplement dietary water with visits to open water and using metabolic water Zebra Finch can survive in the desert without drinking Only dietary source is dry seeds (10% H2O) Relies on metabolic water for other 90%! Sustaining very high metabolic levels puts great demands on the bird’s transport systems Bringing fuel and oxygen to the tissues, carrying away waste is a big job for birds Mammals don’t have an especially efficient respiratory system When we exhale, there is always a residual pool of stale air left in the lungs Birds completely empty their lungs Don’t just inflate / deflate a gas bag Have evolved a flow-through ventilation system Brings oxygenated air into the lungs while stale air is being forced out Lungs are dense, compact structures Fed by a trachea that splits into two primary bronchi Each primary bronchus splits into 11 secondary bronchi Secondary bronchi split into 1,800 tertiary bronchi Tertiary bronchi in direct contact with the fine capillaries where gases are exchanged In geese, cranes, some shorebirds and other birds, the trachea can be unusually long Acts like a resonating tube to amplify calls and songs Human lungs are inflated by a muscular diaphragm Birds lower their sternum to increase chest capacity, contract it to squeeze air through the lungs Lungs work in conjunction with air sacs Air sacs are little sacks of tissue that run throughout the chest cavity Air sacs connect with the primary and second bronchi Most birds have 9 air sacs Big range in number of air sacs - 6 house sparrow; 7 loon, turkey; 12 storks, shorebirds Birds breathe in through their nares, or nostrils, usually located at the base of the bill Each respiratory cycle requires two complete breaths to push a given volume of air through the birds lungs

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First breath, inhaled air passes through the primary bronchi to the posterior air sacs When the bird exhales, this air is pushed into the lungs for gas exchange Second inhalation pushes air in lungs, now high in CO2, into the anterior part of the lungs and into the anterior air sacs Second exhalation pushes out all the stale air from the anterior air sacs Air sacs do not have a good supply of blood vessels Don’t play much of a role in gas exchange Critical, however, for keeping air flowing through the lungs Air sacs serve other functions as well Help cushion internal organs during flight Evaporative cooling via air sacs removes some excess metabolic heat, help prevent heat stress Pigeons and budgies shed 13-22% of their excess heat load through their air sacs Air sacs also provide water birds with additional buoyancy Some birds can control the volume of the air sacs for swimming and diving Analogous to the way bony fishes use their swim bladders Cervical air sacs of the male frigatebird function in courtship Male inflates his bright red air sacs to use in his courtship display Male Prairie Chicken uses his air sacs in the same way (film at eleven...) Supplying the bird’s demanding metabolism requires a strong circulatory system, to carry oxygen and fuel and to remove wastes Birds, like mammals, have a large 4-chambered heart Bird’s heart is half again to twice as large as heart of mammal of the same relative size Bird hemoglobin levels about the same as ours Avian hemoglobin is better at oxygen transport than our own Avian blood sugar levels are twice as high, consistent with their higher metabolic rates Resting heart rate of most birds ~ one-half that of mammals of the same size But birds have more powerful heart muscles Pump about the same volume of blood as a mammalian heart

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Avian heartbeats average about 220 beats per minute Some hummingbirds have an incredible 1200 beats per minute (20 beats per second!!) Avian blood pressure is also higher than most mammals Range from about 130 to 220 mm Hg in birds (100 in man, 175 horse) Avian blood pressures can run well over 300 mm of mercury Twice that of a human suffering from high blood pressure Chronic blood pressure of 150 will cause severe organ damage in humans Birds frequently stroke out If you catch a wild bird, especially a small passerine, they sometimes literally die of fright Cardinal was once observed dying of a heart attack during territorial battle with another male Male Prairie Warbler was seen stroking out during courtship displays Male birds in general have higher blood pressures than females! Pattern of avian blood flow similar to ours Oxygenated blood leaves the lungs and enters the left atrium Into the left ventricles and out into arteries Returning venous blood enters the right atrium, passes through the right ventricle, and out to the lungs Bird’s muscles must sustain an incredible rate of firing over prolonged periods to sustain powered flight Pectoralis muscle (~1/6th bird’s weight), contracts to create the power stroke Supracoracoideus muscles raise the wing by pulling down the attached tendon in the recovery stroke In most birds, flight muscles are a mixture of red and white muscle fibers Red muscle fibers rely on aerobic metabolism Supply power for endurance White muscle fibers rely on anaerobic metabolism Provides short bursts of energy needed for rapid takeoffs and high speed predator avoidance Hummingbirds have unusual flight muscles They use the recovery stroke as an additional power stroke

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Unusually large supracoracoideus, ½ the size of the pectoralis and (by relative weight) 5 times larger than other birds (11.5% of body mass!) Both hummer pectoralis and supra-coricoideus muscles are made up of red fibers Chickens and turkeys have lots of white fibers in their muscles White meat of their flight muscles lets them take off quickly But they quickly tire, can only fly for short distances before too much lactic acid accumulates in the muscles Their legs, on the other hand, are mostly dark meat Dark meat composed of red muscle fibers (the drumstick) Chickens have strong legs and can run very quickly Such powerful metabolic systems create substantial amounts of wastes Particular problem for an animal that needs to travel light Avian excretory system is a marvelous adaptation to shed weight for flight Many primitive and aquatic organisms concentrate liquid wastes as ammonia Ammonia requires large amounts of water to dissolve, not usually a big problem in the ocean Terrestrial animals evolved excretory systems relying on urea to concentrate liquid wastes Urea doesn’t require as much water to dissolve Birds have moved to an excretory system based on uric acid Uric acid requires very little water to dissolve It is also not toxic when concentrated, as is urea You’ve all seen bird wastes, probably a lot closer than you’d like! Darker portion is solid wastes, but light white portion is crystals of liquid waste, equivalent of our urine System may have evolved as an adaptation for egg laying in birds and reptiles Embryos have no way of getting nitrogen wastes out of the shells Must store those wastes in a non-toxic concentrated form that requires very little dissolved water Seabirds, and other birds with high levels of salt in their diet, can also excrete excess salt through special glands called salt glands All birds have them, but they are well developed in birds with high salt content in their diet

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These glands are supraorbital (above the eye) Glands excrete excrete excess salt from prey or from salt water that seabirds must usually drink Salt concentration can reach 5% or more, exceeding that of sea water (3.5%) Birds, in addition to their feathers and skeletal adaptations, have many physiological adaptations for flight