Water Transport and Osmosis

Question 1

water mass in body

Answer 1

• 60% of total body weight
• 70kg-42 liters of water
• ICF is 2/3 of that-28 L, 40%
• ECF is 1/3- 14 L, 20%

Question 2

ICF maintenance

Answer 2

• osmosis

- optimal concentration of solutes means optional function of cells

Question 3

ECF distribution

Answer 3

• extravascular- 75 % of ECF- 11L

- intravascular- 7% of body weight- 5L (25% of ECF (plasma))

Question 4

intravascular distribution

Answer 4

• hematocrit
• 55% blood volume is plasma (3L)
• 45 % cellular (2L)
• plasma is 25% of ECF

Question 5

movement of water across membrane

Answer 5

• facilitated diffusion through aquaporins-RBC and kidney, aqueous humor in eye and CSF in brain
• fluid exchange in lung and formation of bile
• formation of interstitial fluid in all muscle
• can be unmediated too

Question 6

osmosis

Answer 6

• process of net movement of water caused by a concentration difference between two compartments
• goes to a side with a higher concentration of solute (higher osmolarity)
• particle numbers, not size
• high water chemical potential means low osmolarity

Question 7

osmotic pressure

Answer 7

• amount of pressure that would have to be applied to force water back to its original chamber
• DF of water from chemical gradient (in lower Osm compartment)
• hydrostatic pressure developed in right compartment that is equal and opposite DF and leads to no net movement of water is equal to the osmotic pressure difference between the solutions

Question 8

hydrostatic pressure

Answer 8

• force of gravity down on water molecules
• hydrostatic pressure gradient from gravity opposes the DF from the chemical gradient of water in the low Osm compartment

Question 9

osmotic pressure 2

Answer 9

• water will flow from lower osm to higher in a U tube until solute concentrations is almost equal and the hydrostatic pressure formed by the rising water opposes the remaining osmotic pressure
• magnitude of osmotic pressure is related to solute concentration
• osmotic pressure higher in more concentrated solutions
• difference in osmotic pressure is a DF- drives water from low osm to high osm

Question 10

edema

Answer 10

-increase hydrostatic- intra to extra

or decrease osmotic- blocks intra to extra

Question 11

low osmotic pressure

Answer 11

• lower osmolarity

- higher water concentration

Question 12

high osmotic pressure

Answer 12

• higher osmolarity

- lower water concentration

Question 13

osmosis goes from

Answer 13

• lower osmotic pressure to higher osmotic pressure
• because gradient is a DF and gradient goes from high to low, so water goes the other way
• higher osmotic pressure on one side pulls water to that side

Question 14

isotonicity

Answer 14

• same osmolarity

- nothing happens to cell

Question 15

hypotonicity

Answer 15

• lower osmolarity outside cell

- water comes into the cell

Question 16

hypertonicity

Answer 16

• higher osmolarity outside the cell

- water leaves the cell

Question 17

add water to plasma

Answer 17

• increase ECF volume
• decreases ECF osm
• water moves into ICF and increases ICF volume and decreases osm

Question 18

add isotonic solution to plasma

Answer 18

• increases ECF volume without changing osm

- no effect on ICF volume and osm

Question 19

adding hypertonic saline to plasma

Answer 19

• increases ECF osm
• water leaves ICF into ECF
• decreases ICF volume and increases ICF osm
• increases ECF volume

Question 20

response to cell shrinking

Answer 20

• cell is normal 300 osm/ so is plasma
• plasma osm to 450- water out of cell
• now both osm are 450 but cell lost volume
• activates two ion transporters which bring ions into cell, osm increases in cell
• water follows the ions in
• volume restored but osm not

Question 21

sweat

Answer 21

100 osm

• Na and Cl diffuse back and just water leaves
• ECF osm increases
• water flows from cells and cellular volume decreases and osmolarity increases-which then can pull more water back
• we also have other mechanisms like thrist

Question 22

response to cell swelling

Answer 22

• osm normal 300
• plasma drops to 200 osm
• water comes into cell
• ion transporters put ions out of cell
• water follows
• volume restored but osm remains 200

Question 23

movement of fluid during dehydration

Answer 23

• sweat comes from blood
• fluid drawn from blood (plasma) to form sweat
• fluid lose by the blood leads to loss by rest of ECF (ECF osm increases)
• ECF osm draws water from ICF
• cell volume decreases and triggers water retention by kidneys