139
chapter seven
Water balance
Miwa Suzuki and Rudy M. Ortiz
7.1 Osmotic challenges for marine mammals
Constancy of the milieu interieur is critically important for Metazoan organisms because
the cells can only live within a narrow range of physicochemical conditions necessary for
proper cellular functions. Water and salt are fundamental for life and the main determinants of the osmolality of the extracellular fluid. In most vertebrates, water and salt balance
is rigidly controlled to maintain the osmolality at about one-third of seawater by changing the transport of water and electrolytes to meet the demands induced by the external environments. When early vertebrates ascended upon dry land they evolved robust
Contents
7.1 Osmotic challenges for marine mammals ..................................................................... 139
7.2 Knowledge .......................................................................................................................... 140
7.2.1 Constancy of internal environment .................................................................... 140
7.2.2 Morphological adaptations ................................................................................... 143
7.2.2.1 Gastrointestinal tract—The entrance for water .................................. 144
7.2.2.2 Kidney—The principal regulator .......................................................... 144
7.2.2.3 Other organs—Synergies to conserve body water ............................ 146
7.2.3 Source of water ....................................................................................................... 147
7.2.3.1 Diet is the main source of free water ................................................... 147
7.2.3.2 Water balance during fasting ................................................................ 148
7.2.3.3 Drinking of seawater and freshwater .................................................. 149
7.2.4 Infusion experiments: Water, electrolytes, and organic molecules ................ 151
7.2.4.1 Loading of hypertonic/hyperosmotic saline ...................................... 151
7.2.4.2 Loading of isotonic water ...................................................................... 152
7.2.4.3 Loading of freshwater ............................................................................ 152
7.2.4.4 Loading of organic molecules ............................................................... 153
7.2.5 Hormonal control ................................................................................................... 153
7.2.5.1 Arginine vasopressin ............................................................................. 153
7.2.5.2 Renin–angiotensin aldosterone system ............................................... 155
7.2.5.3 Natriuretic peptides ................................................................................ 156
7.3 Toolbox ................................................................................................................................ 156
7.3.1 General tools ........................................................................................................... 156
7.3.2 Isotopic dilution ..................................................................................................... 157
7.3.3 Genome analysis .................................................................................................... 159
7.4 Unresolved questions ........................................................................................................ 159
Glossary ........................................................................................................................................ 160
References ..................................................................................................................................... 161
chapter seven
Water balance
Miwa Suzuki and Rudy M. Ortiz
7.1 Osmotic challenges for marine mammals
Constancy of the milieu interieur is critically important for Metazoan organisms because
the cells can only live within a narrow range of physicochemical conditions necessary for
proper cellular functions. Water and salt are fundamental for life and the main determinants of the osmolality of the extracellular fluid. In most vertebrates, water and salt balance
is rigidly controlled to maintain the osmolality at about one-third of seawater by changing the transport of water and electrolytes to meet the demands induced by the external environments. When early vertebrates ascended upon dry land they evolved robust
Contents
7.1 Osmotic challenges for marine mammals ..................................................................... 139
7.2 Knowledge .......................................................................................................................... 140
7.2.1 Constancy of internal environment .................................................................... 140
7.2.2 Morphological adaptations ................................................................................... 143
7.2.2.1 Gastrointestinal tract—The entrance for water .................................. 144
7.2.2.2 Kidney—The principal regulator .......................................................... 144
7.2.2.3 Other organs—Synergies to conserve body water ............................ 146
7.2.3 Source of water ....................................................................................................... 147
7.2.3.1 Diet is the main source of free water ................................................... 147
7.2.3.2 Water balance during fasting ................................................................ 148
7.2.3.3 Drinking of seawater and freshwater .................................................. 149
7.2.4 Infusion experiments: Water, electrolytes, and organic molecules ................ 151
7.2.4.1 Loading of hypertonic/hyperosmotic saline ...................................... 151
7.2.4.2 Loading of isotonic water ...................................................................... 152
7.2.4.3 Loading of freshwater ............................................................................ 152
7.2.4.4 Loading of organic molecules ............................................................... 153
7.2.5 Hormonal control ................................................................................................... 153
7.2.5.1 Arginine vasopressin ............................................................................. 153
7.2.5.2 Renin–angiotensin aldosterone system ............................................... 155
7.2.5.3 Natriuretic peptides ................................................................................ 156
7.3 Toolbox ................................................................................................................................ 156
7.3.1 General tools ........................................................................................................... 156
7.3.2 Isotopic dilution ..................................................................................................... 157
7.3.3 Genome analysis .................................................................................................... 159
7.4 Unresolved questions ........................................................................................................ 159
Glossary ........................................................................................................................................ 160
References ..................................................................................................................................... 161