MadSci Network: Anatomy
Query:

Re: why dont our body cells have contractile vaculoes?

Date: Wed Nov 1 11:09:16 2006
Posted By: Elizabeth E Hansen, Grad student, MSTP - Microbiology
Area of science: Anatomy
ID: 1162235425.An
Message:

Hi Amanda,
You asked why our cells don’t have contractile vacuoles.  That’s a really
interesting question!  I’ll do my best to answer it. 

Contractile vacuoles are found in single celled protozoans, like amoebas,
where they function to maintain normal cell volume by extruding water.  You
can find a definition of contractile vacuoles online:
“A membrane-bound organelle found in certain protists that pumps fluid in a
cyclical manner from within the cell to the outside by alternately filling
and then contracting to release its contents at various points on the
surface of the cell. It functions in maintaining osmotic equilibrium.” From
Answers.com
This is just one strategy that organisms take to regulate their volume. 
Our cells have different strategies that are more complex.  This is in part
because we are not single celled organisms, so water cannot just be taken
from or extruded into the extracellular space without consequences for
neighboring cells.  

From the textbook Molecular Cell Biology (Fourth Edition) ed. Harvey Lodish
•	Most biological membranes are more permeable to water than to ions or
other solutes, and water moves across them by osmosis from a solution of
lower solute concentration to one of higher solute concentration.
•	Animal cells swell or shrink when placed in hypotonic or hypertonic
solutions, respectively. To maintain their normal cytosolic osmolarity and
hence cell volume, animal cells must export Na+ and other ions that leak or
are transported from the extracellular space into the cytosol.
•	The rigid cell wall surrounding plant cells prevents their swelling and
leads to generation of turgor pressure in response to the osmotic influx of
water.
•	In response to the entry of water, protozoans maintain their normal cell
volume by extruding water from contractile vacuoles.
•	Aquaporin in the erythrocyte plasma membrane and other water-channel
proteins increase the water permeability of biomembranes.
•	Opening and closing of K+ and Cl− channels and the resulting changes in
cytosolic solute concentrations of guard cells cause stomata in leaves to
open and close.
As you can see, there are many ways that cells can move water in and out.

I hope this answers your question!  Thanks,
Liz



Current Queue | Current Queue for Anatomy | Anatomy archives

Try the links in the MadSci Library for more information on Anatomy.



MadSci Home | Information | Search | Random Knowledge Generator | MadSci Archives | Mad Library | MAD Labs | MAD FAQs | Ask a ? | Join Us! | Help Support MadSci


MadSci Network, webadmin@madsci.org
© 1995-2006. All rights reserved.