Respiration and Circulation in Reptiles

Respiration and Circulation in
Reptiles
Elizabeth Timpe
Herpetology - EEB 3265/5265
23 February 2010

Lecture Outline
Respiration and Circulation in
Reptiles
• Oxygen transport
– Diving in aquatic and semi-aquatic species
• Adaptations for O 2 uptake
– Pulmonary
– Extra-pulmonary (or nonpulmonary)
• Hibernation and respiration
• Changes in blood flow through the heart
• Characteristics of blood*
*will not be covered in today’s lecture

Pulmonary Uptake of O 2
• Compared to amphibians, O 2 uptake through the skin
in most reptile species is minimal
– Few exceptions discussed in this lecture
• Reptiles rely largely on lungs for gas exchange
– Have large lung volumes
• 10x more volume compared to mammals of similar size
• However, reptiles lungs are much simpler
– lack aveoli
– lung surface areas are only ~1% that of mammals of similar
size
• Remember, reptiles have a much-reduced metabolic rate
– 1-10% that of mammals

Pulmonary Uptake of O 2
• Most snakes have only one lung (the right one;
Fig 7-6, pg 276 in textbook)
– Some primitive lineages have a smaller vestigial
left lung
– Maina et al. (1998)
• In the sandboa (Eyrx [Gongylophis] colubrinus)
• Anterior half of the lung is used for gas exchange
• Posterior part is an air storage organ.

Pulmonary Uptake of O 2
• Adaptiveness of large lung volume in reptiles
– Store large volumes of air in the lungs
• Used for aerobic metabolism
– Have periodic, irregular breathing
• Allows for less frequent breathing
• Saves a lot of energy
– Do not have to continuously contract muscles to fill lungs
with air
• Reduces evaporative water loss across the lung surface
– Especially important in desert reptiles

Pulmonary Uptake of O 2
• Periodic breathing pre-adapts reptiles
for diving
– Even terrestrial or arboreal reptiles can
remain under water for long periods of time
– Apnea during a dive in an extension of their
normal breathing pattern
• Allows the marine iguana to readily adapt to its
diving lifestyle
• Allows snakes, crocodilians, and turtles to stay
under water for long periods

Pulmonary Uptake of O 2
• Some largely aquatic reptiles have evolved
additional adaptations for prolonged
submergence
– Alligators
• Submerged for up to 2 hours
• Support aerobic metabolism from stored oxygen in
blood and lungs
– Marine snakes
(Hydrophiinae and Acrochordidae)
• Have unusually large lungs that stores large
amount of oxygen for long dives
• Don’t have to rely on anaerobic metabolism to
support activity

Pulmonary Uptake of O 2
• Sea Turtles
– Stay submerged the longest of all reptiles
– Highest metabolic scopes of all reptiles
– Can swim for long periods of time without
resting
– Have complex lungs with large surface areas
and large volumes
http://en.wikipedia.org/wiki/File:Hawksbill_Turtle.jpg
*Read Lutcavage and Lutz (1997) review of sea turtle diving physiology
(see bibliography)

Pulmonary Uptake of O 2
• Cheloniidae
(marine turtles)
– Shallow water divers, seldom >300 m
– Store O 2 in lungs, used during dive
• Dermatochelyidae
(leatherback sea turtles)
– Deep water divers, up to 1000 m
– At great depths, lungs would collapse
– Most O 2 is stored in the blood
• Highest hematocrits
• Highest hemoglobin concentrations
• Highest myoglobin concentrations

Pulmonary Uptake of O 2
• File snake (Acrochordus granulatus)
• High blood volumes
• High hematocrits
– However high hematocrits = increases blood viscosity, decreases
blood flow rate, decreases O 2 flow to the tissues
– Storing O 2 in the blood does not mean increased capacity for activity,
but may allow for increased time submerged
• High O 2 affinity
– High O 2 affinity = high tendency for hemoglobin to bind with O 2
– Allows animal to take up more O 2 into the blood, but inhibits release
of O 2 from blood to the tissues
• Lowest aerobic scopes of any snake
• Therefore blood characteristics in the file snake are related
to prolonged dive time and not increased activity

Extra-pulmonary uptake of O 2
• Some aquatic species of reptiles have surprisingly high
capacities for EP gas exchange
– Sea snakes - O 2 uptake through skin
– Aquatic turtles - O 2 uptake through the pharynx or the
cloaca
• Bagatto and Henry (1999) sliders vs. softshell turtles
– Sliders (Trachemys) - dependent on aerial breathing, little EP O 2
uptake, excrete CO 2 into water, have short dives (~5 min), take
multiple breaths when at the surface, high tolerance for lactic acid,
anaerobic metabolism if needed
– Softshells (Apalone) - rely on EP O 2 uptake to stay active when
submerged, make long dives (12-23 mins), single breath of air when
surfacing, cannot tolerate lactic acid buildup, and therefore cannot
rely on anaerobic metabolism to stay submerged longer

Extra-pulmonary uptake of O 2
• Australian chelid turtles have muscular
cloacal bursae
– Sacs branching off the cloaca
• Have muscles to pump water in-out
• Huge number of papillae, increasing respiratory
surface area
• Example: Rheodytes leukops
– Can obtain all their O 2 underwater
– Cloacal bursae surface area = 16x that of smooth surface of
similar volume
– Dependent on O 2 levels in water (prefer colder, fast flowing
waters)

Extra-pulmonary uptake of O 2
• The total amount of EP O 2 uptake is hard to
determine for most species
– Estimates for inactive sea snakes = 5-22%
– Boa constrictor = ~3%
• Cutaneous uptake is more important to small
individuals or small species
– High surface to volume ratio
• Cutaneous uptake may increase up to 120% for
active snakes compared to inactive snakes

Extra-pulmonary uptake of O 2
• Partitioned O 2 uptake among differ EP organs in turtles
– King and Heatwole (1994) - Elseya latisternum
• 49% - buccopharyngeal cavity
• 33% - cloacal bursae
• 18% - through skin
– Podocnemys
• 90% - cloacal bursae
– Sternotherus
• 70% - through skin
• 30% - buccopharyngeal cavity
– Bagatto et al. (1997) - Kinosternon and Staurotypus
• Less than 10% of O 2 from water, 90% from air
• Aquatic CO 2 exchange was much greater (~40%)

Hibernation and Respiration in Reptiles
• For reptiles that hibernate underwater, cutaneous
gas exchange is the only process available
– Costanza (1989) - garter snakes hibernate underwater
(up to 80 cm) in abandoned wells
• Metabolic rates depressed by 80%
• Took up enough O 2 cutaneously to remain aerobic
• Did not accumulate lactic acid even though submerged up
to 5 months
• If exposed to anoxic conditions, snakes died

Hibernation and Respiration in Reptiles
• Freshwater turtles - some species can take
up significant amounts of O 2 cutaneously
• Examples - softshell turtles, musk turtles, map turtles
• Favor highly oxygenated water
• Metabolize aerobically; low tolerance for lactic acid buildup
• Freshwater turtles - some species hibernate in mud or
other anoxic/hypoxic conditions
• Examples - painted turtles
• Metabolize anaerobically; high tolerance for lactic acid buildup
• Found much further north than softshells, musk, and map
turtles
• Hibernation in anoxic environments is common
• Geographic variation between populations of painted turtles in
their tolerance of anoxic conditions

Hibernation and Respiration in Reptiles
• Tolerance of anoxic conditions in turtles is due to the
buffering capacity of their shells
• Calcium carbonate released from shell neutralizes the lactic acid that
accumulates
• Essential for surviving long winters underwater, buried in mud
• Juvenile turtles don’t have the buffering capacity of adults
• Reese et al. (2004) - juv. snapping turtles, painted turtles and map
turtles had survival rates in anoxic water 1/3 that of adults of the same
species
• Explains why turtles have a greater capacity to survive anoxic
conditions than underwater-hibernating frogs
http://upload.wikimedia.org/wikipedia/commons/9/90/Defensive_turtle.jpg

Circulatory Adaptations
• Mammals have a completely separated
circulatory system, with no mixing of blood in the
pulmonary and systemic circuits
(veins--> r. auricle--> r. ventricle--> pulmonary artery-->
lungs--> pulmonary veins--> l. auricle--> l. ventricle-->
aorta--> systemic arteries)
• Reptiles do not have the same type of separated
blood flow, with some mixing occurring
• Questions
– 1) How is the pattern of reptilian circulation adapted to
the animals’ oxygen transport requirements?
– 2) Is the reptilian pattern less efficient than the
mammalian pattern?

Circulatory Adaptations
• Snake, lizard, and turtle
hearts are different than
those of crocodilians
• Snake, lizard, turtle heart
(Figures, 3rd page of handout)
– Two atria (auricles)
– Single ventricle
• 3 chambers
– Cavum venosum
– Cavum arteriosum
– Cavum pulmonare

Circulatory Adaptations
1) Ventricle relaxes, blood from veins -> right and left atria
2) Blood from right atrium -> cavum venosum; blood from
left atrium -> cavum arteriosum
3) Ventricle contracts, muscular ridge that separates cavum
venosum from cavum pulmonare is not pressed against
the wall of the heart, so blood flows over the ridge from
cavum venosum -> cavum pulmonare, blood ->
pulmonary artery -> lungs
4) Cavum venosum is empty, and oxygenated blood from
cavum arteriosum -> cavum venosum through
intraventricular canal. Muscular ridge is pressed
against the wall of the heart, completely separating cavum
venosum from cavum pulmonare
- There is no mixing of oxygenated and deoxygenated blood

Circulatory Adaptations
• The reptilian heart is no less efficient than the
mammalian heart
• Reptilian system allows for shunting of blood
into different pathways under special
circumstances
• These shunts are of two kinds:
– 1) left to right shunt: results in recirculation of
more blood to the lungs
• Important in aerial breathing
– 2) right to left shunt: results in redirection of
blood away from the lungs to the body, particularly
the brain
• Important during apnea

Circulatory Adaptations
• In crocodilians:
(Figures on last page of handout)
– A completely divided ventricle with two chambers, superficially
similar to that of birds and mammals
– The right aortic arch (to the brain) arises from the left
ventricle, while the left aortic arch (to the body) arises from the
right ventricle
– Most of the deoxygenated blood in the right ventricle normally bypasses
the entrance to the left aortic arch, goes through the
pulmonary artery to the lungs. Left aortic arch receives
oxygenated blood from the right aortic arch through a connection
called the foramen of Panizzae
– Exhibits right to left shunting during diving and left to right
shunting during surfacing