So, I  recall that one of the 'factoids' I was given during my undergrad days was related to heart chambers and oxygen requirements. Not verbatim but something along these lines:

Amphibians have 2 chambered hearts and as this is less efficient (than a fully chambered heart), they require an extra 50% or so oxygen than can be taken orally. Therefore, they diffuse oxygen through their moist skin to make up for this. Mammals have a 4 chambered heart, which is efficient enough for them to utilise the oxygen taken orally, not requiring a supplement.

The third part of this was that crocs (the example used for reptiles), having a 3 chambered heart used oral oxygen better than amphibians but not as well as mammals and therefore had an oxygen requirement of around 25% that needed to be accounted for. They don't have moist, permeable skins, so they aquired the extra oxygen by absoring it through the anus.

Does anyone know if this is in anyway true, or was my old lecturer expelling oxygen from his fundament?? See, if this is true(ish), I think it's a great factoid to drop into most, if not all, conversations, which I haven't dared (as yet) as I'm not sure about it...

"Another scone, vicar? They really are delightful. Mrs Etherington from the village really does do us proud on these occasions, does she not? By the way, are you aware that a crocodile needs to..."

I thought crocs are hypothesised to have arisen from an ancestor with a four-chambered heart (Summers 2005). I have no idea about the oxygen absorption though...

Summers, A. P. 2005. Evolution - Warm-hearted crocs. Nature 434(7035):833-834.

Dave, your lecturer was either very confused or your memory is failing you.

Amphibians and reptiles (except crocodilians) have a 3 chambered heart: or rather an incomplete septum between the ventricles.  All crocodiles have a fully-divided 4 chambered heart, and in fact are the only animals known to have active control over heart valves (cog-wheel valve leading to the pulmonary artery, and foramen of Panizza joining the two main aortas from the ventricles).  This enables them to alter circulation through the heart during diving, basically diverting the pulmonary flow into the systemic one to concentrate blood into the essential areas when it isn't being renewed.  Crocodiles also have haemoglobin with very high affinity for oxygen (so much so that Hb Scuba has been engineered from crocodile haemoglobin as a potential solution to supplying additional oxygen to heart transplant patients during surgery).

The absorption of oxygen through the cloaca isn't a crocodile trait (they don't need it) but has recently been confirmed in some aquatic turtle species (eg. Fitzroy River Turtle).

Adam,

Many thanks for clearing that one up, I'll probably put it down to messing about in the lecture theatre and making up my own 'world of biology'...

I'll have to try and dig out my notes at some point to see if demensia is kicking in...