Depending on the salt concentration of the environment the species takes in or puts out salt to stay in equilibrium.
Many marine animals have a salt gland which is used to excrete excess salt. Animals like sharks have their gland located near their rectum, while birds and reptiles have theirs located near eyes, nostrils, or mouth. Marine mammals lacking salt glad avoid drinking saltwater because their kidneys are unable to produce urine that is hypertonic.
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There are salt glands because this allows marine vertebrates to drink saltwater and maintain homeostasis. This is done by active transport via the sodium-potassium pump in the basolateral membrane. Salt is moved from the blood into the gland and excreted as a concentrated solution.
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