- Why did some organisms develop salt glands?
- How do the salt glands work?
- Animals and organisms that have salt glands
- Birds
- Reptiles
- Saltwater crocodiles
- Elasmobranchs
- Seaweed
- References
The salt glands or saline glands are highly specialized tubular organs found in various vertebrates and plant organisms, whose function is to excrete excess salt that they may have.
Throughout the evolutionary history of saltwater animals and those that inhabit areas close to the seas, they have developed salt glands to be able to ingest foods such as fish or algae with high salt content, as well as drink salt water.
Animals with saline glands have insufficient kidneys, which is why their body has been forced to develop this exocrine gland. On the other hand, those animals that are subjected to high concentrations of salts tend to develop larger saline glands.
Studies have been conducted and it has been shown that the salt glands have the ability to release a greater amount of sodium than human kidneys.
Why did some organisms develop salt glands?
The main reason why some organisms have developed saline glands is because their organisms do not tolerate high concentrations of salt due to increased serum osmolarity.
On the other hand, some of the hyposmotic animals that have salt glands do not have the ability to release sodium through the skin.
Such is the case of crocodiles, other reptiles and birds, who have had to opt for other systems of salt excretion.
This does not apply to elasmobranchs (sharks and rays), who are hyperosmotic in relation to seawater but still regulate their salt levels through the salt glands. This is the result of a convergent evolution.
How do the salt glands work?
The salt glands excrete salt intermittently, unlike the kidneys. This is because salt concentrations are not always high in vertebrates with saline glands. Therefore, excretion will depend on the levels of salt in the blood.
The main solute that is excreted is sodium and then chlorine, but certain amounts of potassium, calcium and bicarbonate are also excreted.
When salt levels increase, through the sodium-potassium pump, sodium is withdrawn from the blood to be entered into vacuoles into the cells of the glands and then excreted.
Animals and organisms that have salt glands
Birds
Some gulls and seabirds have these glands above their nostrils and have ducts through which the excretion material runs towards the tip of their beaks.
Reptiles
Sea turtles have these glands very close to their eyes, which is why sometimes you see some drops near their eyes and it gives the impression that they are crying.
Sea snakes have them under their tongues. They can also be found on some iguanas.
Saltwater crocodiles
They are separated from the reptile group because they are the only ones that have saline glands right on their tongue. For which previously it was believed that they did not possess them.
Elasmobranchs
The rays and the sharks. The latter possess the saline glands in the anus.
Seaweed
There are some marine algae that have saline glands to filter the large amount of salt that they can absorb from their roots and that can become toxic to them.
References
- Department of Zoology, U. o. (November 2003). Regulation of salt gland, gut and kidney interactions. Retrieved on August 10, 2017, from PubMed: ncbi.nlm.nih.gov
- Gonzales, DA (nd). Topic14: GLANDULAR STRUCTURES. Retrieved on August 10, 2017, from Morphology of vascular plants: biologia.edu.ar
- Hill, RW (1979). Comparative Animal Physiology: An Environmental Approach.
- María Luisa Fanjul, MH (1998). Functional biology of animals. Twenty-first Century Publishers.
- Babonis, L. (2011). Morphological and biochemical evidence for the evolution of salt glands in snakes. In DH Leslie S. Babonis, Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology (pp. 400-411). Elsevier.