Respiration and Circulation inReptiles

Elizabeth TimpeHerpetology - EEB 3265/5265

23 February 2010

Lecture Outline Respiration and Circulation in

Reptiles Oxygen transport

Diving in aquatic and semi-aquatic species Adaptations for O2 uptake

Pulmonary Extra-pulmonary (or nonpulmonary)

Hibernation and respiration Changes in blood flow through the heart Characteristics of blood*

*will not be covered in todays lecture

Pulmonary Uptake of O2 Compared to amphibians, O2 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 O2

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 O2

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 lungswith air

Reduces evaporative water loss across the lung surface Especially important in desert reptiles

Pulmonary Uptake of O2

Periodic breathing pre-adapts reptilesfor 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 O2 Some largely aquatic reptiles have evolved

additional adaptations for prolongedsubmergence 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 Dont have to rely on anaerobic metabolism to

support activity

Pulmonary Uptake of O2

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

*Read Lutcavage and Lutz (1997) review of sea turtle diving physiology(see bibliography)

http://en.wikipedia.org/wiki/File:Hawksbill_Turtle.jpg

Pulmonary Uptake of O2

Cheloniidae(marine turtles) Shallow water divers, seldom >300 m Store O2 in lungs, used during dive

Dermatochelyidae(leatherback sea turtles) Deep water divers, up to 1000 m At great depths, lungs would collapse Most O2 is stored in the blood

Highest hematocrits Highest hemoglobin concentrations Highest myoglobin concentrations

Pulmonary Uptake of O2 File snake (Acrochordus granulatus)

High blood volumes High hematocrits

However high hematocrits = increases blood viscosity, decreasesblood flow rate, decreases O2 flow to the tissues

Storing O2 in the blood does not mean increased capacity for activity,but may allow for increased time submerged

High O2 affinity High O2 affinity = high tendency for hemoglobin to bind with O2 Allows animal to take up more O2 into the blood, but inhibits release

of O2 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 O2 Some aquatic species of reptiles have surprisingly high

capacities for EP gas exchange Sea snakes - O2 uptake through skin

Aquatic turtles - O2 uptake through the pharynx or thecloaca

Bagatto and Henry (1999) sliders vs. softshell turtles Sliders (Trachemys) - dependent on aerial breathing, little EP O2

uptake, excrete CO2 into water, have short dives (~5 min), takemultiple breaths when at the surface, high tolerance for lactic acid,anaerobic metabolism if needed

Softshells (Apalone) - rely on EP O2 uptake to stay active whensubmerged, make long dives (12-23 mins), single breath of air whensurfacing, cannot tolerate lactic acid buildup, and therefore cannotrely on anaerobic metabolism to stay submerged longer

Extra-pulmonary uptake of O2

Australian chelid turtles have muscularcloacal 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 O2 underwater Cloacal bursae surface area = 16x that of smooth surface of

similar volume Dependent on O2 levels in water (prefer colder, fast flowing

waters)

Extra-pulmonary uptake of O2 The total amount of EP O2 uptake is hard to

determine for most species Estimates for inactive sea snakes = 5-22% Boa constrictor = ~3%

Cutaneous uptake is more important to smallindividuals or small species High surface to volume ratio

Cutaneous uptake may increase up to 120% foractive snakes compared to inactive snakes

Extra-pulmonary uptake of O2 Partitioned O2 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 O2 from water, 90% from air Aquatic CO2 exchange was much greater (~40%)

Hibernation and Respiration in Reptiles

For reptiles that hibernate underwater, cutaneousgas 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 O2 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 takeup significant amounts of O2 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 orother 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 intheir 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 dont 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 samespecies

Explains why turtles have a greater capacity to survive anoxicconditions 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 thepulmonary 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 separatedblood 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?

Snake, lizard, and turtlehearts are different thanthose 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 fromleft atrium -> cavum arteriosum

3) Ventricle contracts, muscular ridge that separates cavumvenosum from cavum pulmonare is not pressed againstthe wall of the heart, so blood flows over the ridge fromcavum venosum -> cavum pulmonare, blood ->pulmonary artery -> lungs

4) Cavum venosum is empty, and oxygenated blood fromcavum arteriosum -> cavum venosum throughintraventricular canal. Muscular ridge is pressedagainst the wall of the heart, completely separating cavumvenosum from cavum pulmonare

- There is no mixing of oxygenated and deoxygenated blood

Circulatory Adaptations

The reptilian heart is no less efficient than themammalian heart

Reptilian system allows for shunting of bloodinto different pathways under specialcircumstances

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 ofblood away from the lungs to the body, particularlythe 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 theright ventricle

Most of the deoxygenated blood in the right ventricle normally by-passes the entrance to the left aortic arch, goes through thepulmonary artery to the lungs. Left aortic arch receivesoxygenated blood from the right aortic arch through a connectioncalled the foramen of Panizzae

Exhibits right to left shunting during diving and left to rightshunting during surfacing

Circulatory Adaptations