Lecture 13: Water Balance Flashcards
Optimal function of animal depends on constant chemical composition of
body fluids
examples of body fluids are:
- blood
- urine
- semen
- saliva
___ is a major component of body fluid
..H2O
- affects [solute] (ions, small sugars, etc)
- and thus volume of individual cells suspended in body fluid
control of water balance needs to be.. homeostatic:
homeostatic: OSMOREGULATION
Body fluid concentration usually differed from surrounding environments: 2 concerns:
- balance uptake of water from & loss to external environment
- reduce build-up of toxic by-products of metabolism
Body fluid concentration usually differed from surrounding environments: This requires:
- movement of sollutes (active/passive)
- movement of H2O (by passive osmosis)
passive =
along a concentration gradient
active =
add energy to move against concentration gradient
what influences passive rate?
- membranes = barrier to solute flow
- selectively permeable
- how fast a solute gets into or out of cell depends on many things
•How fast a solute gets into or out of the cell depends on:
- size of ion (larger takes longer)
- temperature of solution (lower takes longer)
- electrical charge of ion (prevents passage)
- concentration gradient (lower takes longer)
osmolarity = (equation)
(#particles/molecule of solute) X (moles/litres) where moles = MW
MW glucose (c6H12O6) = 180g (non-ionic) osmolarity =
– Doesn’t dissociate into smaller IONIC particles so the
number of particles/molecule = 1
– So 1M = 1 OsM
MW NaCl = 58.44g (ionic) osmolarity =
– Does dissociate into smaller IONIC Na+ and Cl-
– so the number of particles/molecule = 2
– So 1M = 2 OsM
Osmolarity:
- relative concentration of two solutions
- refers to osmotic pressure
- influences the ability of water to cross a membrane
- in hyper osmotic environments concentration of solutes outside of the cell is higher than inside of the cell, cell will shrink
Tonicity:
- effect of a solution on the cell volume
- depends on solutes and membrane permeability
- in hypertonic environment cell will shrink
- in hypertonic environment, water will enter the cell which will expand and possibly burst
why is osmolarity important in physiology?
we can use it to describe the difference between extracellular fluid and the cell
-iso-, hypo- or hyper-osmotic
If osmolarity of tissue surrounding cell =
iso-osmotic
If tissue osmolarity < cell, means fewer solutes and thus higher H2O conc.;
hypo-osmotic
If tissue osmolarity > cell
hyper osmotic
organisms may have to alter physiology dependent on their
environment
animal cells can’t survive net …
gain or loss of water
Tensility is a term that refers to the
behaviour of a cell in a solution; By convention, tonicity always compares the solution to the cell
external E of the cell is hypertonic:
H2O leaves the cell
external E of the cell is Isotonic:
no net movement of water, both in & out
external E of the cell i s hypotonic:
H2O moves into cell
Osmoconformer:
are marine organisms that maintain an internal environment that is isosmotic to their external environment
-marine invertebrates and elasmobranchs
osmoregulator:
maintains osmolarity in changing external surroundings.
- most marine & fw teleosts, mammals, birds
limited osmoregulations:
brackish & fw invertebrates; some fish & amphibians
the situation for a marine teleost:
E = high[salt] low [water]
ATP-driven salt pumping:
- Na+/K+ ATPase builds whopping Na gradient
- Cl- transported using Na gradient (Cl-/Na+ symporters)
- Cl- builds up and escapes through apiecel Cl- channels
- Na+ follows Cl- charge by sneaking through leaky tight cell junctions
The situation for a fresh water teleost:
E = low[salt] high [water]
Chloride cells in freshwater fish:
- Also have lots of mitochondria and Na+/K+ ATPase
- No Na+/Cl- symporters
- Cell cytoplasm very low in Na+ & Cl-
- Apical membranes have ion pumps to pop ions IN
- Cell junctions very tight (no ion leak)
