Salt gland

Source: Wikipedia, the free encyclopedia.
For the "salt gland" in halophyte plants, see hydathode.

Sea turtles excrete salts through tear ducts. "Crying" is visible when out of water.

The salt gland is an

epithelial cells. The diameter and length of these glands vary depending on the salt uptake of the species.[1]

Salt glands maintain

basolateral membrane, moves salt from the blood into the gland, where it is excreted as a concentrated solution
.

In birds

Salt gland of a bird and its inner structure
Magellanic penguin

The avian salt gland has two main ducts: a medial and a lateral. Salt gland activations occurs from increased osmolarity in the blood, stimulating the hypothalamic information processing, sending a signal through the

osmoreceptors
and volume receptors.

The supraorbital gland is a type of lateral nasal gland found in some species of marine birds, particularly penguins, which removes sodium chloride from the bloodstream. The gland's function is similar to that of the kidneys, though it is much more efficient at removing salt, allowing penguins to survive without access to fresh water. The supraorbital gland is also possessed by the European herring gull - allowing the seagull to drink seawater without becoming ill, although it prefers to drink fresh water when available.[4] Contrary to popular belief, the gland does not directly convert saltwater to freshwater. The term supraorbital refers to the area just above the eye socket (which is known as the orbit).

Living in saltwater environments would naturally pose a large problem for penguins because the ingestion of

capillary bed
in the head. This capillary bed constantly strains out the salt in the saltwater that a penguin takes in. Since the byproduct of the gland has roughly five times as much salt as would normally be found in the animal's fluids, the supraorbital gland is highly efficient.

The penguin excretes the salt byproduct as a brine through its bill. Often, the fluid drips out, and this gives the appearance of a runny nose. However, the fluid may also be sneezed out. In the absence of saltwater, caused by captivity, the supraorbital gland will lie dormant as it has no other purpose. Having a dormant supraorbital gland does not negatively affect the health of a penguin.

In reptiles

The need for salt excretion in reptiles (such as marine iguanas and sea turtles) and birds (such as petrels and albatrosses) reflects their having much less efficient kidneys than mammals.[5] Unlike the skin of amphibians, that of reptiles and birds is impermeable to salt, preventing its release.[6]

The evolution of a salt gland in early reptiles and birds allowed them to eat aquatic plants and animals with high salt concentrations. This evolutionary development does not account for the gland in

elasmobranchs, suggesting convergent evolution
.

Some theories suggest

phylogeneticists disagree with the association.[citation needed
]

See also

Look up salt gland in Wiktionary, the free dictionary.


References

  1. S2CID 28638773
    .
  2. ^ O’Driscoll, K.J.; Staniels, L.K.; Facey, D.E. "Osmoregulation and Excretion". Archived from the original on 8 July 2007. Retrieved 6 July 2007.
  3. PMID 16351835
    .
  4. ^ Dewey, Tanya; Spencer, Shane. "ADW: Larus argentatus: INFORMATION". Animal Diversity Web. Retrieved 8 April 2023.
  5. ^ "Plants Poisonous to Livestock - Cornell University Department of Animal Science". Ansci.cornell.edu. Retrieved 14 July 2011.
  6. ISBN 978-0-520-23854-1
    .

Further reading

  • Evans, D. H. 1993. Osmotic and Ionic Regulation. pp. 315–336. In Evans, D. H. 1993. The Physiology of Fishes. CRC Press, Boca Raton, Florida.
  • Goldstein, D. L. 2002. Water and Salt Balance in Seabirds. pp. 467–480. In Schreiber, E. A. and J. Burger. (eds.) 2002. Biology of Marine Birds. CRC Press, Boca Raton, Florida.
  • Schmidt-Nielsen, K. 1959. Salt Glands. pp. 221–226. In Wessells, N. K. (comp.) 1974. Vertebrate Structures and Functions. W. H. Freeman and Company, San Francisco, CA.
  • Wǖrsig, B. G., T. A. Jefferson and D. J. Schmidly. 2000. The Marine Mammals of the Gulf of Mexico. Texas A&M Press, College Station, TX.
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