Expert: Walter Hintz - 4/8/2007

Question
QUESTION: In what way is the circulatory system of: the human, the fish and the worm, designed to suit their respective environments?  I understand the circulatory system of each but would like to know what is is about the design of each that makes it work in the respective environments.
ANSWER: Hi Barbra
Let's start with humans.  All mammals are warm blooded and warm blooded animals require  a 4 chambered heart and a separate circulatory system for gas exchange.  This is the pulmonary system in mammals.  Without a four chambered heart the animal would be subject to the external temperatures like reptiles are.
Fish have a two chambered heart and no separate pulmonary system. Since the O2 content of water is less than the 21% in the air less surface area is needed for gas exchange and the gills are constantly bathed in water facilitating the exchange of O2 and CO2.  Fish are subject to external temperatures and move when temperatures vary but water temperature does not change rapidly.
I assume you are thinking about earthworms.  There are a lot of different worms.  Earthworms have semiclosed circulatory system with a dozen "hearts " in segments in  the head end.  Gas exchanges occur through the skin.  Like fish they are cold blooded and move deeper in the soil with temperature changes.


---------- FOLLOW-UP ----------

QUESTION: Thank you for your assistance.  As a follow up, are you saying that because the human is warm blooded, it requires more oxygen (to allow for the regulation of body temperature)and that the fish and earthworm, which are cold blooded creatures, require less oxygen? And that the design of the 4 chambered heart in a human allows for a greater amount and quicker delivery, of oxygen to the cells of the body?

As for earthworms, I thought that I had read that they receive oxygen through the closed circulatory system that makes one simple loop through their bodies. Isn't that correct?

Answer
Thermoregulation requires a greater metabolic rate and therefore more O2.. Fish and worms need less O2 since the body temperature is whatever the environmental temperature is.  A 4 chambered heart allows for a separate circulation, the pulmonary system.  The heart in mammals is a double pump.  The right heart pumps blood to the lungs while the left heart services the rest of the body.