Types of Osmotic Exchanges

The osmotic exchanges that take place between an animal and its environment are of two different types:

• Obligatory exchanges and
• Regulated exchanges

In obligatory exchange osmotic exchanges occur mainly in response to physical factors over which the animal has little or no physiological control. Whereas in regulated exchanges, the osmotic exchanges are physiologically controlled and it serve to aid in maintaining internal homeostasis. Regulated exchanges generally serve to Animals that maintain osmolarity of their body fluids constant irrespective of the medium in which they live are termed osmoregulators.

Animals that do not actively control the osmotic condition of their body fluids and instead conform to the osmolarity of the medium in which they live are termed osmoconformers. Most vertebrates, except elasmobranches and hagfishes are strict osmoregulators, maintaining the composition of body fluids within small osmotic range. Marine invertebrates are in osmotic balance with seawater. The concentration of Na⁺, K , ca²⁺, Mg²⁺ and Cl^- in their body fluids is close to the concentration of these ions in the seawater, in which they live.