Animal Body Science - Lectures on Osmoregulation

Bio 224 – animal body systems – osmoregulation
Two concepts to remember.
Osmosis: the movement of solvent particles across a semipermeable membrane from a dilute solution into a
concentrated solution
• The solvent moves to dilute the concentrated solution and equalize the concentration on both sides of
the membrane.
Diffusion: the movement of particles from an area of higher concentration to lower concentration
• The overall effect is to equalize concentration throughout the medium
Osmosis
the unit of osmotic concentration is the osmole (Osm)
• Number of Osm of solute per liter (L) of solution.
o Also termed Osm/L or “osmolar”
• A milliosmole (mOsm) = 1/1,000 0f an osmole
• A microosmole (uOsm) = 1/1,000,000 of an
osmole
Single Na+
A single Na+ contributes as mich to the osmolarity as a
large molecule.
• One mole of glucose, which does not ionize,
• One mole of NaCl
The osmol represents the pressure equivalent to the
amount of solute that dissociates in solution.
• Osmosis can be made to do work:
o Osmotic water movement generates a hydrostatic pressure.
o Osmotic pressure (pie)
• Mechanical pressure required to prevent movement of water across a
semipermeable membrane.
o 1.0 Osm solutions has a Pi of 22.4 atm at 0’C

, Tonicity




There are three classifications of tonicity relative to another.




Animals and their relationship with water
• Terrestrial:
o Unrestricted access
o Limited access
• Aquatic:
o Sea water
§ 1,000 mOsm
o Fresh water
§ <5 mOsm
Water and solutes in the Internal Media
• Water
o The universal solvent.
o 70% of the weight of an animal body
• Ions
o Na+, K+, Ca++, Cl-, Mg++, PO4-
• Organic molecules.
o Carbohydrates
o Proteins
o Lipids