Salt Gland Function in the Green Sea Turtle Chelonia Mydas

Abstract

When salt-gland-cannulated green sea turtles were stimulated by the intravenous injection of various salt loads the secretion osmolality rose quickly from a basal value of 300–400 mosmol kg−1 to a plateau of 1680–2000. The height of the plateau and the duration of the response were dependent on the amount of salt given. An increase in flow rate accompanied the initial rise in concentration, but the flow rate thereafter declined while the plateau concentration was held. The fluid was protein-free, and was mainly composed of Na+ and Cl−, in similar relative concentrations to those in sea water, but had substantial amounts of K+, Mg2+ and HCO3− and negligible amounts of glucose. Urea concentrations did not change with osmolarity, and were similar to that of plasma, suggesting that the walls of the salt gland ducts are permeable to urea. The composition of the tearswas uninfluenced by the concentration of the injected solutions, and its ionic content did not directly depend upon the identity of the added salts. The two eyes of individual turtles frequently did not function in synchrony. The average amount of the salt load remaining in a turtle at the end of salt gland activity, 4.5 mmol ion kg body mass−1, was very similar to the median load required to stimulate the salt gland (4.0 mmol ion kg body mass−1). This suggests that there is a threshold salt load level of around 4–5 mmol ion kg body mass−1 that determines salt gland on/off activity. The flow/concentration relationships of the salt gland fluid are consistent with water reabsorption from a primary isosmotic secretion being the major mechanism for concentrating the tears. A high maximal secretory rate is indicated for theprimary fluid, 0.32 ml g salt gland−1min−1, equivalent to that of the mammalian kidney. Calculations suggest that 83% of the initial fluid is recovered, Na+ is passively concentrated, Cl− and Mg2+ concentrations are enhanced, and that the duct walls are either impermeable to glucose or that glucose is actively taken up.

Ecophysiological steps of marine adaptation in extant and extinct non‐avian tetrapods

“…Non‐marine tetrapods are allocated to Step M0 based on all data that we could locate without screening. Data compiled from the literature (Dunson & Taub, 1967; Dunson, 1968, 1969, 1970, 1974; June et al ., 1973; Dunson & Dunson, 1974, 1979; Taplin et al ., 1982; Nicolson & Lutz, 1989).…”

Sectional anatomic and magnetic resonance imaging features of the head of juvenile loggerhead sea turtles (Caretta caretta)

“…In addition, specific organs that play an integral part in the adaptation of turtles to the marine environment, such as the salt glands, are also located in the head. 16 Several types of head lesions in stranded loggerhead sea turtles have been described, including meningeal hemorrhages, heterophilic meningitis, encephalitis, bone fractures due to traumatic lesions of the head, and oral and esophageal lesions caused by hooks. 17 Meningitis and encephalitis caused by parasitism by intravascular spirorchiid trematode eggs have been identified in green and loggerhead turtles.…”

Osteological and vascular morphology and electrolyte homeostasis of sea turtles

“…Potassium is found in contents of excreted tear fluids of sea turtles [23], not phosphorous and sulfur. Lacrimal glands are involuntary organs and the ratio of potassium and sodium in tear fluids is fixed [37]. This fixed composition suggests that lacrimal glands are not responsible for excreting these excess electrolytes obtained from prey items.…”

“…Sea turtles use salt glands to eliminate excessive salts. The homeostatic burden is reflected in an increase or a decrease in fluid secretion from the salt glands [31,37,42,43]. Lesion or disorder in salt glands result failure to maintain electrolyte homeostasis and may cause death of sea turtles [39].…”