Organismal Physiology Lecture No. 10: Methods Of Circulation
Thursday October 11 , 2012
-Circulation is a pressure-driven bulk flow of fluid that transports: O 2 CO 2 nutrients, organic wastes,
hormones, agents of the immune system, heat, and hydraulic pressure for organ function. The notion
that most primitive animal phyla lack circulatory systems is inherently flawed because circulatory
systems do not necessarily need to involve blood as the vascular fluid. Cardiac output is about 5L/min, a
huge amount of work performed by the heart.
Circulation In Sponges:
-Sponges belong to the phylum Perifora and have dominated the world’s oceans from 600 mya to the
present day. A sponge is essentially a pump, which, at approximately every 5 seconds, will pump the
volume of its body size through its system. Sponges accomplish this because they possess massive
cardiac tissue. Incoming water comes through the entire body of the animal and then shoots out
through the top of the animal because it helps deliver oxygen and nutrients to the system as well as
helps with feeding.
-The general morphology of sponges comprises of: osculi (tiny pores through which water enters) and
choanocytes (tiny cells within the tissue of the animal that drive the pumping of water). Choanocytes
have caller cells, which have central flagella that drive the water by beating in a single plane and rotating
the water inwards. In a single sponge, there may be up to hundreds of thousands or maybe millions of
these flagella. This mechanism of circulation is very useful in spawning when sponges may deliver their
sperm or eggs (dioecious) into the water column.
Circulation In Jellyfish:
-From the phylum Cnidaria (corals are a benthic form of colonial cnidarians); jellyfish are very
transparent and show no apparent signs of circulatory function. In jellyfish, there is a whole series of
canals (radial canals, circular canals) that branch out to get the fluid throughout the animal’s system.
Jellyfish only have a single-celled tissue layer on the outside and the inside. They move fluid around their
system by cilia.
Vertebrate & Invertebrate Circulatory Systems:
-As recently stated, sponges and jellyfish have circulatory systems that are regulated not by pumping
mechanisms, but by single-celled driving forces such as flagella and cilia respectively. Rotifers, which are
some of the tiniest organisms present in freshwater, have not evolved a circulatory system partly due to
the fact that their incredibly small size has made diffusion a more useful process than for most animals
on the planet. Linking Circulation To Gas Exchange & Aerobic Respiration:
-Diffusion is a useless process if you are a big animal (diffusion time is one hour) when compared to
diffusion for small organisms, which diffuse in 0.1 seconds. There is a huge jump from a 10 micron to a
2mm diffusion distance. Because diffusion is too slow for most organisms, circulation becomes a very
-The speed of transport is the driving force because mitochondria need oxygen in order to make ATP.
Diffusion is too slow, but in the case of respiratory surfaces such as gills (for aquatic organisms) or lungs
(for terrestrial organisms), diffusion does readily occur. Therefore the circulatory system is simply the
process that connects gas exchange and aerobic respiration.
Different Hearts For Differ