Sea Underwater Blood

[KeenTeen17]

I have just been doing some past papers for my biology revision ready for the exam on Thursday and a question has come up about what happens to the blood supply of the organs, skin and intestines while they are underwater. I said it decreases because the seal conserves oxygen whilst underwater because it is a mammal and can't breathe underwater so needs to hold its breath.

Am I right?

[KeenTeen17]

sorry the title should say SEAL!

[Lancashire Lad]

Seals have large spleens which are able to, in effect, store oxygenated blood. They alter their blood oxygen content when diving. During a dive the seals haematocrit (the volume of red blood cells in a given volume of blood) rises, (and subsequently falls back to normal post dive). In some seals (Weddell for example) the spleen contracts during the dive, to force oxygenated blood into the circulatory system.

Seals undergo normal mammalian bradycrdia (lowering of heart rate) during the dive, and tachycardia (raising of heartrate) post dive, along with vasoconstriction of certain blood vessels enabling the necessary provision of oxygenated blood to oxygen sensitive tissues during the dive.

So, in a nutshell, the seal is able to alter its circulatory system to provide oxygenated blood to the organs and tissues which most need it during the dive. However, compared with surface situation, blood flow to all tissues and organs (except the brain) is reduced during a normal (voluntary) dive.

Regards
Mike.

[Jason Green]

Can't really answer your question, but Good Luck, KT!

[Hobjob]

I can add a little to Lancashire Lad's answer.

Seals (and I think most diving mammals, and I assume all pinneds - seals, sea lions and walruses) have a much larger blood volume per body volume than land mammals (as well as the larger spleen noted above).

They have more haemoglobin that land mammals, as above

They also empty their lungs much more than land mammals
Emptying the lungs means less nitrogen to be absorbed at depth, and so no bends. We get round this by substituting helium

The muscles have much higherl levels of myoblobin - the oxygen storing chemical of the muscles. This delays the onset of anaerobic respiration in the muscles, which is much less efficient and auses more lactic acid.

They can also shut down the blood supply to non-essential parts of the body very efficiently when getting short of oxygen - notably muscles, where they have already stored a good dollop of oxygen. That way the brain can be protected (and IRRC the palcenta too in pregnant females). There is a clever name for this that escapes me.

They also have some other chemical adaptions for efficient areobic oxygenation from fat stores - sorry no details.

The slowing of the heart - bradycardia - that occurs in mammals on diving is even graced with the term "Diving reflex". It is very marked in seals, and I suspect all diving mammals, but present in humans too. Heart rate can drop to one tenth.

Their hearts and aortae are also braoder and flatter than the characteristic roundness in land mammals - thought to be able to withstand pressure better.

Another nugget to drop in for extra marks about seals is that they have delayed implantation - embryonic diapause - so that after getting pregnant they rest and regain conditon before starting to grow their baby ready for the next breeding season. In South Africa this means they can make use of the sardine run. Impala can do the same thing - sorry more trivia!

Good luck

[poschiavanus]

I was going to post something long and complicated: the missing 'l' threw me completely. I think everyone is basically saying that your answer is right (reduced blood flow to skin). As usual the truth is much more complicated than examiners would like!

To add a rider to Hobjobs last fact (ignore this KT17, its too close to exams). Its not just seals which show delayed implantation. Many mammals from different orders do this. The ones I can recall of the top of my head is Roe Deer, and some mustelids. Its not just a case of regaining condition. Gestation period is more or less determined by the size of the mammal and its primary mode of nutrition. Optimum breeding times are determined by factors such as food availability and so on. The ability to postpone birth until optimum conditions for the newborn is not surprisingly advantageous. Also kangaroos and wallabies (from what I can remember) induce a form of delay if they still have joeys in the pouch (i.e., its hormonally controlled). There are lots of other wonderful aspects of early mammalian development which are under maternal hormonal control like the Bruce and Cattanach effects, but I think are the topic for another post.

posch

[KeenTeen17]

thanks for all the info guys. Im surprised because I probably confused you with the title of the thread

Thats what I put as an answer on this past paper - their blood supply decreases. It was only a 2 marker question

I think you guys have given me the answer to a 10 marker!

[poschiavanus]

Well hopefully a bit more than a 10 marker. Diving physiology and the more esoteric aspects of mammalian reproduction were final degree year stuff when I were a lad.

posch

[KeenTeen17]

wow. thanks again everyone, I think 10 marks is an understatement. this thread is probably a dissitation