water transport

Question 1

how much of your body weight is in a 70kg person?

how much of that is intracellular and how much is extracellular?

Answer 1

60%- 42 L
intracellular- 2/3 or 28L
extracellular- 1/3 or 14L
(60:40:20 rule)

Question 2

why is intracellular fluid volume so important?

Answer 2

to maintain the concentrations of solutes at a narrow level for optimal function of the cell

Question 3

what are the two compartments of the extracellular fluid and how much fluid is contained in them?

Answer 3

intravascular fluid (25%) and extravascular fluid (75%)

Question 4

how is the ECF volume balanced?

Answer 4

by the excretion of water by the kidney to match the consumption of water by the mouth.

Question 5

what two pathways can water move across the cell membrane? which one is faster?

Answer 5

by simple diffusion and by facilitated diffusion mediated by aquaporins (much faster)

Question 6

what is osmosis?

Answer 6

the process of net water movement across a membrane caused by a concentration difference between compartments. always passive transport.

Question 7

what constitutes a low chemical potential of water?

Answer 7

a high concentration of solute (high osmolarity)

Question 8

what is osmotic pressure?

Answer 8

the amount of pressure that would have to be applied to force water back to its original chamber during osmosis

Question 9

when is a water solute system at equilibrium?

Answer 9

when the hydrostatic pressure and the osmotic pressure are equal and opposite

Question 10

what are the proportions of blood components?

Answer 10

55% is plasma, 45% is formed elements

Question 11

what does isotonic mean? what happens to a cell placed into this type of solution?

Answer 11

any solution with an osmotic pressure equal to plasma (iso-osmolar). there will be no net diffusion of water across the membrane

Question 12

what does hypertonic mean? what will happen to a cell placed into this type of solution?

Answer 12

any solution with an osmotic pressure greater than plasma (hyper-osmolar). there will be osmosis out of the cell and it will shrink.

Question 13

what does hypotonic mean? what will happen to a cell placed into this type of solution?

Answer 13

any solution with an osmolarity less than plasma (hypo-osmolar). there will be osmosis into the cell and it will swell and possibly burst

Question 14

what would happen to the ICF and ECF when distilled water is added intravenously into the body?

Answer 14

the ECF volume increases and its osmolarity decreases. water from the ECF will flow to the ICF and will increase its volume and decrease its osmolarity.

Question 15

what would happen to the ICF and ECF when isotonic saline is given intravenously?

Answer 15

the volume of the ECF will increase but there will be no osmosis between the compartments because there will be no change in the ECF osmolarity.

Question 16

what would happen to the ICF and ECF when hypertonic saline is given intravenously?

Answer 16

The ECF osmolarity will increase and water will flow from the ICF to the ECF along its concentration gradient. ICF will have a higher concentration and a lower volume while the ECF will have a higher concentration and higher volume

Question 17

how does a cell respond to hypertonic ECF to maintain homeostasis?

Answer 17

the shrinkage initiated by the solution activates solute transporters that transfer ions into the cell. There will be an influx of water into the cell restoring volume

Question 18

which is more important to the body, maintaining ECF volume or ICF volume?

Answer 18

ICF volume

Question 19

how does a cell respond to hypotonic ECF to maintain homeostasis?

Answer 19

the swelling triggers activation of efflux transporters that decrease the osmolarity in the cell to be more isotonic to its surrounding solution. This drives more water out of the cell.

Question 20

why would a cell sacrifice intracellular osmolarity for a consistent volume?

Answer 20

to ensure that there is a constant intracellular concentration of regulatory factors.

Question 21

how is thirst and water retention triggered?

Answer 21

sweating results in volume depletion and increased concentration of ECF. When brain cells shrink due to this newly established gradient, they secrete antidiuretic hormone which triggers thirst and water retention by the kidneys.