Avian Circulatory System (2023)

BIO 554/754

Avian Circulatory System

Birds have very efficient cardiovascular systems that permitthem to meet the metabolic demands of flight (and running, swimming, ordiving). The cardiovascular system not only delivers oxygen to body cells(and removes metabolic wastes) but also plays an important role in maintaininga bird's body temperature.The avian circulatory system consists of a heartplus vessels that transport:

  • nutrients
  • oxygen and carbon dioxide
  • waste products
  • hormones
  • heat
Birds, like mammals, have a 4-chambered heart (2 atria & 2 ventricles),with complete separation of oxygenated and de-oxygenated blood. The rightventricle pumps blood to the lungs, while the left ventricle pumps bloodto the rest of the body. Because the left ventricle must generate greaterpressure to pump blood throughout the body (in contrast to the right ventriclethat pumps blood to the lungs), the wallsof the left ventricle are much thicker & more muscular.
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Source: chickscope.beckman.uiuc.edu/explore/
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Cross-section through the ventricles of a chicken heart
(Source: trc.ucdavis.edu/mjguinan/apc100/modules/

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Dorsoventral (A) and lateral (B) thoracic radiographsfrom a grey heron, showing the normal avian cardiac silhouettes,
which are located nearly along the longitudinal axisof the body (Machida and Aohagi 2001).

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Heart of a Domestic Chicken. RA, right atrium; RV, right ventricle, LA, left atrium; LV, left ventricle; RAVV, right atrioventricular valve; LAVV, left atrioventricular valve;
IVS, interventricular septum; IAS, interatrial septum; SVC, superior vena cava. The left atrioventricular valve of birds has three cusps whereas the right AV valve is a single section of myocardium
(Figure modified from Lu et al. 1993).

Birds tend to have larger hearts than mammals (relative to bodysize and mass). The relatively large hearts of birds may be necessary tomeet the high metabolic demands of flight. Among birds, smaller birds haverelatively larger hearts (again relative to body mass) than larger birds.Hummingbirds have the largest hearts (relative to body mass) of all birds,probably because hovering takes so much energy.

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Electrical activity in the avian heart duringa cardiac cycle -- The P wave begins after sinus node depolarization nearthe top of the right
atrium, and the impulse spreads through the atria towardthe apex of the heart going caudally (down) and to the left (this resultsin a
small upright deflection in theelectrocardiogram, thePwave). The impulse then travels through the AV (atrioventricular) transmission
system to the ventricular myocardium (or heart muscle).Initial activation of the endocardium surrounding the apex of the leftventricle
(in a downward direction) causes a small, upright deflection,or R wave, in the ECG). Depolarization of the remainder of the ventricular
wall during this time is not detected in the ECG becauseextensive and complete penetration of the walls by Purkinje fibers resultedin a
single burst of mutually canceling electrical activity.Next, a large RS wave, or simply S wave, results from rapid, depolarizationof the
ventricle. Surface electrode placement = RA indicatesright axilla, or right wing; LA, left axilla, or left wing; & LL, leftleg (From: Oglesbee
et al. 2001).

Avian hearts also tend to pump more blood per unit time thanmammalian hearts. In other words, cardiac output (amount of blood pumpedper minute) for birds is typically greater than that for mammals of thesame body mass. Cardiac output is influenced by both heart rate (beatsper minute) and stroke volume (blood pumped with each beat). 'Active' birdsincrease cardiac output primarily by increasing heart rate. Ina pigeon, for example (Butler et al. 1977):

Heart rate
115 beats/min
670 beats/min
Stroke volume
1.7 ml
1.59 ml
Cardiac output
195.5 ml/min
1065 ml/min
Oxygen consumed
20.3 ml/min
200 ml/min

In general, bird hearts 'beat' at somewhat lower rates than mammalsof the same size but pump more blood per 'beat.' Among birds, heart ratevaries with size:

Resting heart rate
'Active' heart rate
Herring Gull
American Robin
Blue-throated Hummingbird

Source: Welty & Baptista. 1988. The Life of Birds.Saunders College Publishing, New York.

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Relationship between heart weight and heart rate at restgiven on a
bilogarithmic scale. The mean value for a given speciesis plotted
in this chart (Machida and Aohagi 2001).

Blood pumped by the avian heart enters the blood vessels. Themain types are:

  • arteries- carry blood away from the heart & toward the body cells
  • arterioles - 'distribute' blood (that is, direct blood where neededwith more going to active tissues & organs & less to less activetissues & organs) by vasodilating & vasoconstricting
  • capillaries - exchange of nutrients, gases, & waste productsbetween the blood & the body cells
  • venules (small veins) & veins-conduct blood back to the heart

Some of the major arteries in the avian circulatory system:

Carotids deliver blood to the head (& brain).

Brachials take blood to the wings.

Pectorals deliver blood to the flight muscles (pectoralis).

The systemic arch is also called the aorta & delivers blood to all areas of the body except the lungs.

The pulmonary arteries deliver blood to the lungs.

The celiac (or coeliac) is the first major branchof the descending aorta & delivers blood to organs & tissues inthe upper abdominal area.

Renal arteries deliver blood to the kidneys.

Femorals deliver blood to the legs & the caudalartery takes blood to the tail.

The posterior mesenteric delivers blood to manyorgans & tissues in the lower abdominal area.

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Source: http://numbat.murdoch.edu.au/Anatomy/avian/avian3.html

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Mitochondria are redistributed towards the cell membrane in the muscle fibers of Bar-headed Geese. (a) The proportion of mitochondria that were subsarcolemmal was higher in Bar-headed Geese than in low altitude species. Grey bar, Bar-headed Goose; unfilled bar, Barnacle Goose; black bar, Pink-footed Foose. (b,c) Representative transmission electron micrographs of muscle fibers from (b) Bar-headed Geese and (c) Barnacle Geese. Scale bar, 2 µm. Arrow, subsarcolemmal mitochondria; arrowhead, intermyofibrillar mitochondrion.

(Video) avian circulation

Adaptation for high-altitude flight -- Bar-headed Geese (Anser indicus) migrate over the Himalayas at up to 9000 m elevation, but it is unclear how they sustain the high metabolic rates needed for flight in the severe hypoxia at these altitudes. To better understand the basis for this physiological feat, Scott et al. (2009) compared the flight muscle of Bar-headed Geese to that of low altitude birds (Barnacle Geese, Pink-footed Geese, Greylag Geese, and Mallard ducks). Bar-headed Geese had more capillaries per muscle fiber than expected, and higher capillary densities and more homogeneous capillary spacing. Their mitochondria were also redistributed towards the sarcolemma (cell membrane) and adjacent to capillaries. These alterations should improve O2 diffusion capacity from the blood and reduce intracellular O2 diffusion distances, respectively. Bar-headed Geese have, therefore, evolved for exercise in hypoxia by enhancing the O2 supply to flight muscle.

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Bar-headed Geese

BBC Worldwide - Bar-headed Geese

AOS21-(430807) Evolution of blood-oxygen carrying capacity in hummingbirds from American Ornithological Society on Vimeo.

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The transport of O2 occurs along several steps of a cascading physiological pathway from atmospheric air to the mitochondria in tissue cells (e.g. muscle fibers). The effectiveness of this pathway at transporting O2 during hypoxia is imperative for flight at high altitudes, which depends upon several distinctive characteristics of birds in general and many unique features that have evolved in high flyers. The properties of O2 utilization and ATP turnover in the flight muscle are also important to consider in high fliers (Source: Scott 2011),

Some major veins in the avian circulatory system:

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Source: http://numbat.murdoch.edu.au/Anatomy/avian/avian3.html

The jugular anastomosis allows blood to flow fromright to left side when the birds head is turned & one of the jugularsconstricted.

The jugular veins drain the head and neck.

The brachial veins drain the wings.

The pectoral veins drain the pectoral muscles andanterior thorax.

The superior vena cavae (or precavae) drain theanterior regions of the body.

The inferior vena cava (or postcava) drains theposterior portion of the body.

The hepatic vein drains the liver.

The hepatic portal vein drains the digestive system.

The coccygeomesenteric vein drains the posteriordigestive system & empties in the hepatic portal vein.

The femoral veins drain the legs.

The sciatic veins drain the hip or thigh regions.

The renal & renal portal veins drain the kidneys.

The heart pumps & the vessels carry, of course, blood. Avianblood:

(Video) What Blood-Circulatory System Do AVIANS/BIRDS Have?

  • consists of plasma + formed elements
    • plasma is largely water (~85%) plus lots of protein (~9-11%); other constituentsof blood include glucose (blood glucose levels in birds are greater thanin mammals; about 200-400 mg/dl), amino acids, waste products, hormones,Avian Circulatory System (15)antibodies, & electrolytes.
    • the formed elements include red blood cells (or erythrocytes), white bloodcells (or leucocytes), and thrombocytes
      • bird red blood cells (shown to the right), unlike those of mammals, areelliptical in shape and nucleated. In most species, red blood cells areabout 6 x 12 micronsin size (mammalian RBC's are typically 5.5 - 7.5 microns in diameter).Typical concentrations are 2.5 to 4 million/cubic mm. Avian red blood cellshave a lifespan of 28-45 days (shorter than mammals, e.g., about 120 daysin humans). Red blood cells contain hemoglobin, the molecule responsiblefor transporting oxygen throughout the body, and are produced in the bonemarrow. However, many bird bones are pneumatic (penetrated by air sacs) and do not contain marrow. Hemopoietic bone marrow (red-blood-cell-producing marrow) is located in the radius, ulna, femur, tibiotarsus, scapula, furcula (clavicles), pubis,and caudal vertebrae.
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Skeleton of a Rock Pigeon (Columba livia) showing the bones (shaded) that contain red-blood-cell-producing marrow, including the radius and ulna of the wing, femur and tibiotarsus of the leg, furcula and scapula of the pectoral girdle, pubis of the pelvic girdle, and caudal vertebrae. Most other bones (except for very small ones) are pneumatized (Schepelmann 1990).

Examination and discussion of the cells in an avian blood smear, plus examination of a section of the cloacal bursa and discussion of its function.

Differences in the red blood cells of birds and mammals -- Mammals, which had developed an aerobic metabolism, emerged in the Triassic, when the oxygen content in the atmosphere was by approximately 50% lower than current levels and even lower than in the Jurassic period (when birds evolved). Under these conditions, natural selection favored the loss of nuclei in the red blood cells of mammals (making the cells smaller and allowing capilaries to become even smaller in diameter) and change to a biconcave shape (increasing the amount of surface area and enhancing diffusion into and out of the red blood cells). Birds, with their efficient respiratory system, evolved during the Jurassic when the oxygen content in the Earth atmosphere approached the present level, so there was no selective pressure to eliminate nuclei from their red blood cells or change in shape (Gavrilov 2013).

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The degree of oxygen saturation of hemoglobin (% of moleculesbinding with oxygen) depends on the partial pressure of oxygen (shown herefor various organisms in oxygen-hemoglobin dissociation curves). The P50is the partial pressure at which 50% saturation occurs; high-affinity hemoglobinhas a low P50 and a curve shiftedto the left, whereas a low-affinity hemoglobin has a high P50and a curve shifted to the right.
(Source: http://www.sfu.ca/biology/courses/bisc445/lectures/respiration_2_circulation.html)
      • bird thrombocytes (shown above with two red blood cells), also nucleated,are comparable to the non-nucleated platelets of mammalian blood. Thrombocytesare important in hemostasis (blood clotting).
      • White blood cells play an important role in protecting birds from infectiousagents such as viruses and bacteria. Birds have several types of whiteblood cells:
Avian White Blood Cells

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The lymphocyte is the most numerous white bloodcell. Lymphocytes are either T-lymphocytes (formed in the thymus)or B-lymphocytes (formed in the bursa of Fabricius). B-lymphocytes produceantibodies; T-lymphocytes attack infected or abnormal cells.The heterophil is the second most numerousWBC in most birds. Heterophils are phagocytic and use their enzyme-containinggranules to lyse ingested materials. Heterophils are motile and can leaveblood vessels to engulf foreign materials.Monocytes are motile cells that canmigrate using ameboid movements. Monocytes are also phagocytic.Eosinophils make up about 2 to 3 %of the WBC population of healthy birds. The function is these cells isunclear.

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Scanning electron microscope view of bird thrombocytes adhering to a collagen-lined plate (exposure to collagen causes bird thrombocytes, and mammalian platelets, to release chemicals that make them 'sticky'; the chemicals released by mammalian platelets are different from those released by bird thrombocytes and make platelets 'stickier' than thrombocytes). Avian thrombocytes are larger than mammalian platelets, have a nucleus, and, unlike mammalian platelets, do not form 3-dimensional aggregates. (Credit: Penn Medicine)

Can birds have heart attacks and strokes? -- Mammalian platelets are small, anuclear circulating cells that form tightly adherent (i.e., 'sticky') thrombi (clots or 'plugs') to prevent blood loss after vessel injury. Platelet thrombi that form in the coronary and carotid arteries of humans can also cause common vascular diseases such as myocardial infarction ('heart attacks') and stroke and are the target of drugs used to treat these diseases. Birds have high-pressure cardiovascular systems like mammals, but have nucleated thrombocytes in their blood rather than platelets. Schmaier et al. (2011) found that avian thrombocytes respond to many of the same activating stimuli as mammalian platelets (and so help stop blood loss from damaged vessels) but, unlike mammalian platelets, cannot form tighly adherent thrombi in arteries. Avian thrombocytes are larger than mammalian platelets and are less 'sticky' (because they release different chemicals) than mammalian platelets when exposed to collagen (connective tissue to which thrombocytes and platelets are exposed when there's a break in a blood vessel). When carotid arteries of mice are damaged, platelets form thrombi that can block blood flow (check this video showing the response of human platelets when exposed to a plate covered with collagen); similar damage to the carotid arteries of Budgerigars (similar in size and speed and pressure of blood flow to the carotid arteries of mice) did not cause the formation of thrombi (check this video showing the response of chicken thrombocytes when exposed to a plate covered with collagen). These results indicate that mammalian platelets, in contrast to avian thrombocytes, will form thrombi even in arteries where blood flow is rapid and under high pressure, an essential element in human cardiovascular diseases.


Heart disease linked to evolutionary changes that may have protected early mammals from trauma

Brain size & immunity -- Parasitism can negativelyaffect learning and cognition. Greater susceptibility to parasitism bymales may impair cognitive ability, and greater male investment in immunitycould compensate for greater susceptibility, in particular when males havea relatively large brain. Why might males be more susceptible to parasites?
  • Because of intense competition for access to mates.
  • Immunosuppression due to the negative effects of androgenson immune function.
Møller et al. (2004) analyzed covariationbetween relative size of immune defense organs and brain in birds. Therelative size of the bursa of Fabricius and the spleen in adults covariedpositively with relative brain size across species, and the relationshipbetween immune defense and brain size was stronger for males. Thus, speciesin which males have relatively large brains also have relatively largeimmune defense organs.
These findings support the hypothesisthat sex differences in brain function have evolved as a consequence ofdifferences in susceptibility to parasitism. Different components of theimmune system (bursa and spleen) may have evolved to mitigate the negativeimpact of parasites on brain function.

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Covariation between relative brain mass of juvenile birdsand relative mass of bursa of Fabricius in different bird species. Relativemass was calculated as residuals from a phylogenetically corrected regressionof log10-transformed organ mass on log10-transformed body mass. The linesare the linear regression lines for males and females, respectively (From:Møller et al. 2004).

B-lymphocytes, the cells that produce antibodies, are initially producedin the embryonic liver, yolk sac and bone marrow, then move through theblood to the bursa of Fabricius (BF).

Birds have a bursa of Fabricius (BF), which is an outpocketingof cloaca. Within the BF, B-lymphocytes mature then migrate to otherbody tissues. The bursa is a blind sac that extends from the dorsal sideof the cloaca, the common portal of the reproductive, urinary, and digestivesystems. Within the bursas of young birds are extensive leaf-like foldscomposed of simple, columnar epidermis and a loose connective tissue withlots of blood vessels and lymph nodules. Atrophy of the BF typically occursaround the time of sexual maturation.

(Source: http://www.upei.ca/~morph/webct/Modules/Lymphoid/bursa.html)

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In the BF, the B-cells mature and become functional and then move tothe blood, spleen, cecal tonsils, bone marrow, Harderian gland (Hg in diagrambelow), and thymus.

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In birds, most of the Ig diversification occurs by gene conversion in the bursa of Fabricius.
However, further Ig diversification is achieved by somatic hypermutation in secondary lymphoid organs (From: Kohonen et al. 2007).

B-lymphocytes produce three classes of antibodies after exposure toa disease organism: IgM, IgY (equivalent to mammalian IgG), and IgA. IgM appears after 4-5 days following exposure to a disease organism and thendisappears by 10-12 days. IgY is detected after 5 days following exposure,peaks at 3 to 3 1/2 weeks, and then slowly decreases. Ig A appears after5 days following exposure. This antibody is found primarily in the mucussecretions of the eyes, gut, and respiratory tract and provides "local"protection to these tissues.

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From: Szabo et al. 1998.

(Video) the avian heart

Antibodies do not have the capability to kill viruses or bacteria directly.Antibodies (especially IgY) perform their function by attaching to diseaseorganisms (like bacteria) and blocking their receptors. The disease organismsare then prevented from attaching to their target cells. The attached antibodiescan also facilitate the destruction of pathogens by phagocytes.

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IgY Ab = IgY antibody
Source: http://www.genwaybio.com/technology.htm

T-lymphocytes begin as the same stem cells as the B-cells, but are programmedin the thymus rather than the BF. The T-lymphocytes include a more heterogeneouspopulation than the B-cells. Some T-cells act by producing lymphokines(over 90 different ones have been identified); others directly destroydisease organisms. Some T-cells act to enhance the response of B-cells,macrophages, or other T-cells (helpers); others inhibit the activity ofthese cells (suppressors).

This video describes B cell development in the chicken. B cells produce antibodies that bind to infectious organisms (viruses, bacteria, and parasites) and play a vital role for the immune system to protect chickens, as well as us, from infectious disease.

How Did the Peacock Get His Tail? -- It's a questionthat has puzzled zoologists for more than a century. Charles Darwin firstnoted that the choosy peahen plays a crucial role in the evolution of thisextravagant sexual display. "We may conclude that…those males which arebest able by their various charms to please or excite the female, are underordinary circumstances accepted. If this be admitted, there is not muchdifficulty in understanding how male birds have gradually acquired theirornamental characters," Darwin wrote. Moller and Petrie (2002) now suggestthat plumage may specifically convey the strength of a male's immunesystem and his desirability as a mate. Hamilton and Zuk (1982) firstsuggested that 'showy' males were signaling to females that they were,if not parasite-free, then parasite "lite." But, there has been littleevidence to support this hypothesis. Moller believes it is because peoplehave been looking at the wrong parasites. "If you look at our own species,we are attacked by hundreds of different species of parasites," said Moller."So if you wanted to study our parasite burden, you'd have to identifyall the parasites, from tapeworms to head lice, see how abundant they areand how they affect us. It would be practically impossible, so we decidedto focus on the immune system." Moller and Petrie took blood samples frommale Blue Peafowl (Pavo cristatus) and recorded the numbers of B-and T-cells, and also measured the peacocks' tails and counted the numberof eye spots. They discovered that the condition and length of the peacock'stail was related to the production of B-cells, and the size of the eyespots to T-cell production. "Our main finding is that females are lookingat different aspects of a male's immune competence," said Moller. Males,in effect, are walking billboards advertising their health and status.And these things matter. Previous research has shown that in chickens andquail, at least, the immune system is under genetic control so offspringwill inherit their parents' ability to fight parasites. Thus, it pays forfemales to be choosy because their chicks, in turn, will survive betterand mate with other, equally picky females. -- SanjidaO'Connell, The Independent (London), September 9, 2002Avian Circulatory System (29)

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Tree Swallow

Immunosenescence in some immune components of free-living Tree Swallows -- A wide diversity of free-living organisms show increases in mortality rates and/or decreases in reproductive success with advancing age. However, the physiological mechanisms underlying these demographic patterns of senescence are poorly understood. Immunosenescence, the age-related deterioration of immune function, is well documented in humans and in laboratory models, and often leads to increased morbidity and mortality due to disease. However, little is known about immunosenescence in free-living organisms. Palacios et al. (2007) studied immunosenescence in a free-living population of Tree Swallows (Tachycineta bicolor), assessing three components of the immune system and using both in vivo and in vitro immunological tests. Immune function in female Tree Swallows showed a complex pattern with age; acquired T-cell mediated immunity declined with age, but neither acquired nor innate humoral immunity did. In vitro lymphocyte proliferation stimulated by T-cell mitogens decreased with age, suggesting that reduced T-cell function might be one mechanism underlying the immunosenescence pattern of in vivo cell-mediated response recently described for this same population. These results provide the most thorough description of immunosenescence patterns and mechanisms in a free-living vertebrate population to date. Future research should focus on the ecological implications of immunosenescence and the potential causes of variation in patterns among species.

The avian cardiovascular system is able to quickly respond tochanges in levels of activity (e.g., resting vs. flying) via changes inheart rate, cardiac output, & blood flow (by vasocontriction and vasodilationof vessels).

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Measurements of resting heart rate were obtained onlyafter each bird had ceased activity in the dark cage and remained quiet.
The heart rate in an excited state (during excitement)was measured when the animal became maximally excited because its
movement in the cage was restrained manually (Machidaand Aohagi 2001).

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Heart rate, diving depth and body angle of a female Common Eider (Somateria mollissima) during dives and when flying. (a, b) heart rates of 250 and 300 beats per minute, (c) heart rate ascending and descending slopes equal to or above 10 beats per minute per second (absolute values), (d) standard deviation of diving depth up to 0.1 m, and (e) change in body angle. The upward and downward pointing arrows indicate the point of take-off and landing, respectively (From: Pelletier et al. 2007).

Common Eider (male)

Many birds forage by diving underwater. So, what happens when a birddoesn't have access to air (oxygen)? The quintessential avian diver isthe EmperorPenguin, which can attain depths greater than500 meters while staying submerged for about 12 minutes. In shallower dives,an Emperor Penguin may stay submerged even longer, over 20 minutes. Divingbirds, including Emperor Penguins, must 'solve' several problems:

  • a bird obviously can't breathe when under water, so oxygen levels in thebody begin to decline &, therefore,
  • oxygen must be distributed to where it's most needed
  • heat conservation (this is a potential problem for deep-diving birds andbirds diving in cold water)
One 'solution' to the oxygen problem is that birds, like penguins, thatspend lots of time underwater store lots of oxygen in their muscles. Themuscles of some diving birds contain lots of myoglobin. Myoglobin bindsoxygen just like hemoglobin but actually has a higher affinity for oxygenthan does hemoglobin. This means that when blood passes through muscle,lots of oxygen is transferred from the blood to the muscle. The chart belowillustrates this. In Emperor Penguins, nearly half (47%) of all oxygenin the body is in the muscles.

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Source: http://eee.uci.edu/courses/bio112/diving.htm

As a result, when a penguin dives, muscle cells have access to lots of oxygen that allows them to remain active. Other tissues, of course, don't 'store' oxygen like muscle. Those tissues, such as the brain, still depend on oxygen being transported in the blood. However, because the skeletal muscles need less oxygen, more is available for other tissues like the brain.

Emperor Penguins

Emperor Penguins

Diving beyond the limits (Butler 2001) -- GentooPenguins around South Georgia feed on krill at depths of 80–90 m. KingPenguins feed on myctophid fish at depths of 100–250 m. A large proportionof the dives of both species are longer than their calculated aerobic divelimits. Part of this discrepancy is probably due to inaccuracies in determiningrates of oxygen consumption during diving. That this may well be the caseis suggested by the fact that the temperature in the abdominal cavity ofboth Gentoo and King penguins drops during dives and returns to normalwhen diving behavior ceases. For Gentoo Penguins, abdominal temperatureduring dives was, on average, 2.4°C lower than when the birds werenot diving. The lowest abdominal temperature recorded for each penguinwas, on average, 33.6°C for the Gentoos and 29.7°C for the Kings.So if the birds allow temperature to fall in some parts of the body (i.e.,they do not increase metabolic rate in an attempt to keep abdominal temperaturenormal), there will be a saving in energy both in terms of thermoregulatorycosts and in terms of reduced metabolic rates in those tissues (i.e, aQ10 effect, with Q10 being the factorial change inthe rate of a chemical reaction associated with a 10°C change in temperature).
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Traces of dive depth (top) and temperature in the abdominalcavity (bottom) during a foraging trip of a Gentoo Penguin (A; mass = 6.6 kg) during 1day at sea and a King Penguin (B; mass = 11.7 kg) during 5 days at sea. Note changein scale of the depth traces (Butler 2001).

Gentoo Penguins

Additional physiological responses allow diving birds to make the bestuse of available oxygen & minimize heat loss in cold water:

  • peripheral vasoconstriction (less blood & heat go to the surface ofthe body which reduces heat loss)
  • vasoconstriction of blood vessels supplying the digestive system (whichmeans less blood is delivered, but when diving the digestive system cantemporarily 'shut down' to conserve energy)
  • vasodilation of blood vessels supplying the central nervous system &heart (which means more blood is delivered)
What causes these things to occur? When a bird dives, special receptorsin the body detect an increase in levels of carbon dioxide (because thebird has stopped breathing). These receptors then stimulate the brain which,in turn, send nervous impulses that reduce heart rate & cause bloodvessels in different parts of the body to either vasoconstrict or vasodilate.

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Source: http://www.zoo.utoronto.ca/stephenson/Research/Diving.htm

(Video) Bird Circulatory System


How Penguins Avoid the Bends -- Penguins are Olympic-classdivers. After a deep breath, they can plunge hundreds of meters for manyminutes, bob up briefly, and dive again. This ought to cause the bends,or decompression sickness, but penguins seem immune. Now researchers havediscovered a diving habit that may help explain why: On their way up fromthe deep, Adélie and king penguins slow down and surface at an obliqueangle--in effect mimicking the careful decompression of human divers. Marineanimals have a variety of strategies toAvian Circulatory System (37)preventthe bends. In human divers, increased underwater pressure forces nitrogenin the air within body cavities to pass into the blood. If divers surfacebefore the nitrogen is cleared, they can suffer contorted joints, difficultbreathing, and even paralysis. Many whales and seals have blood and musclesadapted to conserve oxygen; they can also collapse their lungs before divingto squeeze out air. Penguins don't have it that easy: Their lungs don'tcollapse, and the buoyant divers need a good dose of oxygen to swim hard.To find out how penguins move about at depth, Katsufumi Sato and colleagues(Satoet al. 2002) attached data loggers to Adélie and king penguinsoff the shores of Antarctica and Crozet Island, about 1000 kilometers away.The instruments measured the depths, speed, and acceleration and decelerationeffects from wing strokes for more than 650 dives. From these data Sato'steam estimated air volumes in penguin lungs during their descents and ascents.The dive profiles revealed that the penguins flapped their flippers continuouslyon the way down. On return trips, after swimming halfway up, they stoppedand let their natural buoyancy give them a free ascent. But surprisingly,instead of shooting straight up the penguins veered at an oblique angle,thus significantly slowing their ascent, the team reports in the May issueof the Journal of Experimental Biology. This increases the amount of timethe penguins spend in shallow water with little prey, but it could providetime for nitrogen, under lower pressure, to return to the air inside bodycavities. Those findings intrigue marine biologist Dan Costa of the Universityof California, Santa Cruz: They've made careful and insightful measurementsof the fine-scale diving behavior of two penguins, supported with verysophisticated models of lung volume, and they may be correct. However,he cautions, there are alternate explanations for why penguins would slowtheir ascents, such as looking out for predators. -- NoreenParks, Academic Press Daily InScight

Literature Cited:

Butler, P. J. 2001. Divingbeyond the limits. News in Physiological Sciences 16: 222-227.

Butler, P. J., N. H. West, and D. R. Jones. 1977. Respiratoryand cardiovascular responses of the pigeon to sustained, level flight ina wind tunnel. Journal of Experimental Biology 71:7-26.

Gavrilov, V. M. 2013. Origin and development of homoiothermy: a case study of avian energetics. Advances in Bioscience and Biotechnology 4:1-17.

Hamilton, W. D. and M. Zuk. 1982 Heritable true fitnessand bright birds: a role for parasites? Science 218: 384-387.

Kohonen, P., K.-P. Nera, and O. Lassila. 2007. Avian model for B-Cell immunology - new genomes and phylotranscriptomics. Scandinavian Journal of Immunology 66: 113–121.

Lu, Y., T. N. James, M. Bootsma, and F. Terasaki. 1993. Histological organization of the right and left atrioventricular valves of the chicken heart and their relationship to the atrioventricular Purkinje ring and the middle bundle branch. Anatomical Record 235: 74-86.

Machida, N. and Y. Aohagi. 2001. Electrocardiography,heart rates, and heart weights of free-living birds. Journal of Zooand Wildlife Medicine 32: 47–54.

Møller, A. P., J. Erritzøe, & L. Z.Garamszegi. 2004. Covariation between brain size and immunity in birds:implications for brain size evolution.
Journal of Evolutionary Biology 18: 223-237.

Møller, A.P. and M. Petrie. 2002. Condition dependence,multiple sexual signals, and immunocompetence in peacocks. Behavioral Ecology13:248–253.

Oglesbee, B. L., R. L. Hamlin, H. Klingaman, J. Cianciola,and S. P. Hartman. 2001. Electrocardiographic Reference Values for Macaws(Ara sp.) and Cockatoos (Cacatua sp.). Journal of Avian Medicineand Surgery 15: 17-22.

Palacios, M. G., J. E. Cunnick, D. W. Winkler, and C. M. Vleck. 2007. Immunosenescence in some but not all immune components in a free-living vertebrate, the Tree Swallow. Proc. Royal Academy of London B, online early.

Pelletier, D., M. Guillemette, J.-M. Grandbois, and P. J. Butler. 2007. It is time to move: linking flight and foraging behaviour in a diving bird. Biology Letters 3: 357-359.

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Schepelmann, K. 1990. Erythropoietic bone marrow in the pigeon: development of its distribution and volume during growth and pneumatization of bones. Journal of Morphology 203: 21-34.

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Scott, G. R. 2011. Elevated performance: the unique physiology of birds that fly at high altitudes. Journal of Experimental Biology 214: 2455-2462.

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(Video) Circulation in birds | zoology by miller and harley

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What kind of circulatory system does a bird have? ›

Birds, having a closed circulatory system, are thought to have moved more agilely, allowing them to get food faster and possibly to prey on the insects. Figure 21.2. In (a) closed circulatory systems, the heart pumps blood through vessels that are separate from the interstitial fluid of the body.

How is the bird circulatory system different from a human's? ›

Because the bird heart pumps at a quicker rate, birds have more pulmonary veins than humans to help carry the blood. Notice the difference in the size of the ventricles. One can also observe the increased musculature surrounding the ventricles of the bird heart.

What are the differences between mammal and avian circulatory systems? ›

The mammalian lung has reciprocating ventilation with large terminal air spaces (alveoli) while the avian lung has a flow-through system with small air capillaries. As a result the environment of the pulmonary capillaries is very different between the mammals and birds.

What is the circulatory system of a chicken? ›

The circulatory system of the chicken is a closed circulatory system. That is to say, the life giving blood of the system is always contained in a vessel. The vessels we are talking about are arteries, veins and capillaries. Arteries carry the bright red oxygenated blood away from the heart to the capillaries.

Do birds have a single or double circulatory system? ›

Most non-avian reptiles have a three-chambered heart, but have little mixing of the blood; they have double circulation. Mammals and birds have a four-chambered heart with no mixing of the blood and double circulation.

Do all birds have a 4 chambered heart? ›

Birds and mammals, however, have a fully septated ventricle--a bona fide four-chambered heart. This configuration ensures the separation of low-pressure circulation to the lungs, and high-pressure pumping into the rest of the body.

How many valves does a bird heart have? ›

Once fully formed, the avian heart resembles the human heart, with four chambers and valves. However, the inner walls of the atria and ventricles are smoother in birds than in humans, and the avian valves are simpler than their human counterparts.

Where do birds produce blood? ›

Birds have bone marrow but not in all of their bones. Bone marrow is used to create red blood cells, the cells responsible for transporting oxygen taken in through the lungs, and delivering it to tissues where it is needed.

Which animal has the best circulatory system? ›

(d) Mammals and birds have the most efficient heart with four chambers that completely separate the oxygenated and deoxygenated blood; it pumps only oxygenated blood through the body and deoxygenated blood to the lungs.

What are the 3 types of circulatory systems? ›

3 Kinds of Circulation:
  • Systemic circulation.
  • Coronary circulation.
  • Pulmonary circulation.

What are 5 Differences between birds and mammals? ›

  • Mammals give birth to their young whereas birds lay eggs.
  • Birds have feathers whereas mammals have only fur or hair.
  • Birds have porous or hollow bones. ...
  • Birds have wings while mammals have paws, hands, and hooves.
  • Mammals produce sound using a larynx, but in birds this organ does not produce sounds.

What are the 3 differences between mammals and birds? ›

The definition of a bird requires feathers, a toothless beak, wings (usually allowing for flight), and the ability to lay hard-shelled eggs. Meanwhile, mammals have hair, give birth to live young, and the females produce milk from mammary glands — the structures for which the class is named.

How many ventricles does a bird have? ›

Figure 1 - The basic structures of animal hearts. Bird and mammal hearts have four chambers (two atria and two ventricles). A frog, which is an amphibian, has a heart with three chambers (one ventricle and two atria), and fish hearts have two chambers (one atrium and one ventricle).

What are the functions of a heart in a chicken system? ›

The heart is the muscular organ that pumps blood through the body of the bird.

Do birds have veins? ›

Birds have a cluster of veins and arteries that redirects blood flow so as to reduce heat loss. This cluster is referred to as a "heat exchanger." Warm blood flowing through arteries would normally flow into the bird's legs before returning to the heart.

Why do birds and mammals have double circulation? ›

Mammals and birds

Complete double ciruculatory systems allow for higher metabolic rates to be maintained as there is no mixing of oxygenated and deoxygenated blood. This means that blood leaving the heart to travel to the body is rich in oxygen. This is essential for the high-energy demands of birds and mammals.

What are the 2 types of circulatory system? ›

What Are the Parts of the Circulatory System? Two pathways come from the heart: The pulmonary circulation is a short loop from the heart to the lungs and back again. The systemic circulation carries blood from the heart to all the other parts of the body and back again.

Which animal has a single circulatory system? ›

Fishes have single circulation. They have a two-chambered heart comprising an atrium and a ventricle. In fishes, the heart pumps out the deoxygenated blood which undergoes oxygenation in the gills.

What animal has a 3 chambered heart? ›

amphibians and most reptiles have a heart with three chambers—two atria and a single ventricle. These animals also have separate circuits of blood vessels for oxygenating blood and delivering it to the body.

Who has 4 chambered heart? ›

Reason: Mammals and birds have a four-chambered heart.

What animals have 2 chambered hearts? ›

Fish and Insect Hearts

Fish hearts have just two chambers, an atrium and a ventricle (Figure 1). Insects often have just a tube that pumps hemolymph (the name for the insect equivalent of blood) freely around the entire body, with a vessel to help it move.

Are birds warm blooded or cold blooded? ›

All mammals and birds are capable of generating this internal heat and are classed as homoiotherms (ho-MOY-ah-therms), or warm-blooded animals. Normal temperatures for mammals range from 97° F to 104° F. Most birds have a normal temperature between 106° F and 109° F.

Why is bird poop black and white? ›

While mammals excrete nitrogenous wastes mostly in the form of urea, birds convert it to uric acid or guanine, which reduces water loss in comparison. Uric acid thus forms a white sticky paste. So the white part is actually bird pee; it is the dark center that is the poop.

What is the circulatory system of a fish? ›

Fish have a single circuit for blood flow and a two-chambered heart that has only a single atrium and a single ventricle. The atrium collects blood that has returned from the body and the ventricle pumps the blood to the gills where gas exchange occurs and the blood is re-oxygenated; this is called gill circulation.

What is the circulatory system in mammals? ›

It is the system comprising the heart and blood vessels. It is responsible for the transportation of deoxygenated blood to the heart and oxygenated blood from the heart to the whole body. In mammals, the circulatory is a closed type and blood is transported through blood vessels.

How do birds survive extreme cold? ›

All cold-climate birds pack on body weight in the late summer and fall in anticipation of the long, cold winter, but feathers also play an important role. All birds stay warm by trapping pockets of air around their bodies. The secret to maintaining these layers of air lies in having clean, dry and flexible feathers.

What is a bird blood temperature? ›

Like mammals, birds control their core body temperature in a fairly narrow range. For birds, that range is usually 39-43 degrees C (102-109 degrees F). Usually the ambient temperature is lower than the bird's body temperature, and the bird's metabolism produces heat to keep warm.

Which bird is cold-blooded? ›

There are no cold-blooded birds. A bird's average body temperature is higher than that of a human, at a constant level of between 41 and 43 degrees Celsius (106 to 109 degrees Fahrenheit), and birds have different methods of adapting to conserve or reduce their body heat depending on the weather conditions.

What is it called when you pee and poop at the same time? ›

A fistula is an abnormal hole in the bowel or the bladder. A recto-urethral fistula is a hole between the urethra (urinary channel) and the rectum. This hole leads to leakage of urine into the rectum and feces travelling into the bladder.

Is it normal to pee and poop at the same time? ›

The pelvic floor muscles relax when we defecate. However, they will not necessarily have to fully relax when we urinate. But when the pelvic floor musculature does relax, in addition to allowing stool to pass, it decreases the tension in our urinary sphincters, allowing urine to flow.

Why do birds not pee? ›

Birds convert nitrogen to uric acid instead: this is metabolically more costly but saves water and weight, as it is less toxic and doesn't need to be diluted so much. Birds therefore don't have a urethra, and don't pee - all waste leaves via the anus.

What are the 3 types of circulatory systems? ›

3 Kinds of Circulation:
  • Systemic circulation.
  • Coronary circulation.
  • Pulmonary circulation.

What animals have a closed circulatory system? ›

All mammals, including humans, have closed circulatory systems. So do all fish, birds, reptiles, and amphibians. Some invertebrates, like octopuses and squids, have closed circulatory systems, but many, like grasshoppers, have open circulatory systems.

Which animals have no closed circulation? ›

The correct answer is (C) Butterflies do not have a closed circulatory system. It has an open circulatory system. All the insects have an open Circulatory system lacking veins and arteries.

What are the 4 components of circulatory system in animals? ›

The cardiovascular system comprises the heart, veins, arteries, and capillary beds. The atrioventricular (mitral and tricuspid) and semilunar (aortic and pulmonic) valves keep blood flowing in one direction through the heart, and valves in large veins keep blood flowing back toward the heart.

What are the two types of circulatory system in animals? ›

In higher animals, there are two primary types of circulatory systems: open and closed. Arthropods and mollusks have an open circulatory system.

Which animal has a double circulatory system? ›

Double circulation is the sort of circulation where blood goes to the heart twice. It is fundamentally found in birds, warm blooded animals, and a few reptiles and fishes. Hence, out of the alternatives given in the question, alligator, lungfish, crocodile, birds, and mammals have double circulation.


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