The Vertebrate Endocrine System

Abstract

Osmoregulation is the process of physiological adjustment of the volume of water and the concentrations of solutes in the cells and body fluids of organisms, including the vertebrates. Such responses are usually necessitated by changes that can occur as a result of the animal’s interactions with its external environment but also can be due to metabolic changes and disturbances, including disease. Changes in the animal’s fluid content and composition occur continually in potentially hostile osmotic environments such as the sea, freshwater rivers and lakes, and terrestrial habitats, which can even include hot dry deserts. Several types of physiological responses may be involved in maintaining homeostasis of the body fluids. They are mediated, depending on the species, by such organs and tissues as the kidneys, urinary bladder, gut, salt-secreting glands, skin, gills and the blood vascular system. The nature and duration of their physiological responses, coordination with each other and the environmental events, necessitates the transmission of chemical messages that are provided by neighbouring cells, nerves and the endocrine glands. Osmoregulation can involve all of these coordinating processes. However, the hormones secreted by the endocrine glands have special roles that probably reflect their more persistent and ubiquitous effects.