chapter 49 - Osmosis

where is water found in a multicellular body

intracellular and extracellular compartments

animals exchange water/ions from the extracellular compartment with the environment to maintain

osmotic balance

water and ion exchange occurs in

specialized epithelial cells

in vertebrates

kidneys play a key role in exchange

what is the main cation in the extracellular fluid

sodium

what is the main anion in the extracellular fluid

chloride

most vertebrates regulate

total solute concentration and concentration of important ions

how does osmotic movement occur?

less concentrated (more dilute) → more concentrated (less dilute)

osmotic pressure

solution’s tendency to take in water by osmosis

osmolarity

number of osmotically active moles of solute per liter of solution

tonicity

solutions ability to change the volume of a cell by osmosis (relative to a cell or another fluid)

hypotonic

lower osmotic pressure than the cell

isotonic

equal osmotic pressure to the cell

hypertonic

greater osmotic pressure than the cell

osmotic conformers

do not regulate osmotic concentrations, many marine invertebrates (hagfish is the only vertebrate), evolved for ECF to be isotonic with the environment

in an animal in a freshwater environment, which way will water move?

water will move into the animal

challenges of freshwater vertebrates

body of a fish is hypertonic to the environment, passively absorbs water, passively loses ions

soutions to freshwater vertebrates

adaptations preventing entry of water into the body, produce high volume of dilute urine to get ride of excess water, actively absorb ions through gills

challenges of marine fish

body is hypotonic to environment, loses water to surrounding environment, passively absorbs ions through skins,

solutions for marine fish

drinks high volumes of sea water actively excretes excess ions through gills and more concentrated urine

terrestrial vertebrates

have more water in their bodies than surrounding air, inherently dehydrating, evaporation from skin and lungs, respiration and removal of wastes

what do advanced urinary systems in terrestrial vertebrates do?

help with water conservation while still eliminating harmful waste

what are amino acids and nucleic acids catabolized into?

nitrogenous wastes

what is the first step of eliminating nitrogenous wastes from the body?

deamination (removal of the amino group and addition of H+ to form ammonia)

excretion of waste: aquatic fish

no metabolic cost but very toxic, toxicity of ammonia is not an issue because its diluted with ample water

what do bony fish and larval amphibians excrete?

ammonia via gills and in very dilute urine

excretion of waste terrestrial vertebrates

convert ammonia to urea or uric acid, mammals largely produce urea and birds/reptiles produce uric acid

urea

moderate toxicity, can be more safely concentrated, some metabolic cost to synthesize

uric acid

extremely low toxicity, more effective at water conservation, extrememely metabolically expensive to produce.