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21 Cards in this Set

  • Front
  • Back
Salts dissociate in solution into charged ions
Electrolyte balance important
Imbalance can alter membrane potential or disrupt cellular activities
Electrolytes (2)
Water moves between adjacent body compartments by osmosis down an osmotic gradient
Changes in salt concentration in one compartment will lead to changes in fluid distribution between compartments
Shrinking or swelling cells can rupture plasma membranes leading to cell death
Obligatory exchanges
Many vital processes have the potential to disturb salt and water balance
Obligatory exchanges are required as part of respiration or elimination of wastes
Nitrogenous wastes
Product of protein and nucleic acid degradation
Toxic at high concentrations
3 forms
Ammonia and ammonium ions
Uric acid
Freshwater fish
Gain water and lose salt when ventilating gills
Kidneys produce copious dilute urine
Specialized gill epithelial cells transport Na+ and Cl- from water into fish’s capillaries
Saltwater fish
Gain salts and lose water across gills
Produce very little urine
Drink seawater to replace water lost
Expend energy to transport excess salt out of body through gill epithelial cells
Exchanges during ingestion
Food contains minerals and water
Unusable parts of food are excreted as solid waste with accompanying water and salt loss
Marine reptiles and birds ingest seawater when consuming prey or drinking – salt glands used to excrete excess salt
Salt glands
Contain a network of secretory tubules that actively transport NaCl from the interstitial fluid into the tubule lumen
Body temperature
Endotherms use body water to cool off
Sweating and panting use the evaporation of water to draw heat out of the body
Sweat is hypoosmotic to blood
Fluid left behind in body has lower volume and higher salt concentration
Water is generated as a by-product of ATP production – “metabolic water”
Some animals rely on this for all or nearly all of their water requirements
In other animals, this water is excess that must be eliminated
Excretion or retention of metabolic water can be considered a type of obligatory exchange
Regulate or conform
Osmoregulators maintain constant internal salt concentrations and osmolarities
Drink or excrete as needed to maintain 300 mosm/L
All terrestrial animals, freshwater animals, and many marine animals
Requires considerable expenditure of energy
Osmoconformers match osmolarity of blood and other fluids to seawater at 1000 mosm/L
Most marine invertebrates and some vertebrates
Less tendency to gain or lose water across skin or gills
Expend less energy to compensate for water gain
Generally limited to marine environment
An organ acts like a filter to remove water and small solutes from blood while leaving behind blood cells and large solutes
Produces filtrate
Material in filtrate recaptured and returned to blood
Supplements solutes removed by filtration
Simplest filtration mechanism in invertebrates
Series of branching tubules filters fluids from body cavity using beating of ciliated cells (flame cells)
Protonephridia (2)
Solutes reabsorped
Excess water and some wastes emptied through openings in body wall called nephridiopores
Osmoregulatory – nitrogenous wastes diffuse out of body
Metanephridial system
Pairs located in each body segment
Tubular network beginning in funnel-like structure called nephrostome
Collect coelomic fluid containing nitrogenous wastes
Na+, Cl- and others reabsorbed along tubule
Nitrogenous wastes excreted through nephridiopores in body wall
Malpighian tubules
Insects use secretion and not filtration
Cells lining tubules actively transport potassium ions and uric acid from hemolymph into lumen
Creates osmotic gradient drawing water and solutes into tubule
Moves to hindgut where water and solutes reabsorbed
Nitrogenous wastes and others excreted together with feces through anus
Specialized tubules composed of epithelial cells
Participate in both salt and water homeostasis
Nitrogenous waste elimination
Most vertebrate kidneys are filtration kidneys
Filtration controlled by mechanical forces
Functional unit of the kidney
As many as several million in each kidney
Consists of
Renal corpuscle forms filtrate
Tubule performs secretion and reabsorption
Tubule empties into collecting duct