Lecture 13: Water Balance

Question 1

Optimal function of animal depends on constant chemical composition of

Answer 1

body fluids

Question 2

examples of body fluids are:

Answer 2

• blood
• urine
• semen
• saliva

Question 3

___ is a major component of body fluid

Answer 3

..H2O

• affects [solute] (ions, small sugars, etc)
• and thus volume of individual cells suspended in body fluid

Question 4

control of water balance needs to be.. homeostatic:

Answer 4

homeostatic: OSMOREGULATION

Question 5

Body fluid concentration usually differed from surrounding environments: 2 concerns:

Answer 5

• balance uptake of water from & loss to external environment
• reduce build-up of toxic by-products of metabolism

Question 6

Body fluid concentration usually differed from surrounding environments: This requires:

Answer 6

• movement of sollutes (active/passive)

- movement of H2O (by passive osmosis)

Question 7

passive =

Answer 7

along a concentration gradient

Question 8

active =

Answer 8

add energy to move against concentration gradient

Question 9

what influences passive rate?

Answer 9

• membranes = barrier to solute flow
• selectively permeable
• how fast a solute gets into or out of cell depends on many things

Question 10

•How fast a solute gets into or out of the cell depends on:

Answer 10

• size of ion (larger takes longer)
• temperature of solution (lower takes longer)
• electrical charge of ion (prevents passage)
• concentration gradient (lower takes longer)

Question 11

osmolarity = (equation)

Answer 11

(#particles/molecule of solute) X (moles/litres) where moles = MW

Question 12

MW glucose (c6H12O6) = 180g (non-ionic) osmolarity =

Answer 12

– Doesn’t dissociate into smaller IONIC particles so the
number of particles/molecule = 1
– So 1M = 1 OsM

Question 13

MW NaCl = 58.44g (ionic) osmolarity =

Answer 13

– Does dissociate into smaller IONIC Na+ and Cl-
– so the number of particles/molecule = 2
– So 1M = 2 OsM

Question 14

Osmolarity:

Answer 14

• 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

Question 15

Tonicity:

Answer 15

• 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

Question 16

why is osmolarity important in physiology?

Answer 16

we can use it to describe the difference between extracellular fluid and the cell
-iso-, hypo- or hyper-osmotic

Question 17

If osmolarity of tissue surrounding cell =

Answer 17

iso-osmotic

Question 18

If tissue osmolarity < cell, means fewer solutes and thus higher H2O conc.;

Answer 18

hypo-osmotic

Question 19

If tissue osmolarity > cell

Answer 19

hyper osmotic

Question 20

organisms may have to alter physiology dependent on their

Answer 20

environment

Question 21

animal cells can’t survive net …

Answer 21

gain or loss of water

Question 22

Tensility is a term that refers to the

Answer 22

behaviour of a cell in a solution; By convention, tonicity always compares the solution to the cell

Question 23

external E of the cell is hypertonic:

Answer 23

H2O leaves the cell

Question 24

external E of the cell is Isotonic:

Answer 24

no net movement of water, both in & out

Question 25

external E of the cell i s hypotonic:

Answer 25

H2O moves into cell

Question 26

Osmoconformer:

Answer 26

are marine organisms that maintain an internal environment that is isosmotic to their external environment
-marine invertebrates and elasmobranchs

Question 27

osmoregulator:

Answer 27

maintains osmolarity in changing external surroundings.

- most marine & fw teleosts, mammals, birds

Question 28

limited osmoregulations:

Answer 28

brackish & fw invertebrates; some fish & amphibians

Question 29

the situation for a marine teleost:

Answer 29

E = high[salt] low [water]

Question 30

ATP-driven salt pumping:

Answer 30

• 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

Question 31

The situation for a fresh water teleost:

Answer 31

E = low[salt] high [water]

Question 32

Chloride cells in freshwater fish:

Answer 32

• 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)