Water Transport/ Osmosis

Question 1

What accounts for most of the mass of the cell, and the human body?

Answer 1

Water accounts for 60% of body weight.

Question 2

Where are the two places that water resides in the human body?

Answer 2

intracellular and extracellular

Question 3

How is ICF volume maintained?

Answer 3

It is maintained within narrow limits by solute transport mechanisms that drive water into, or out of, the cell via osmosis

Question 4

What two compartments is extracellular fluid volume distributed to?

Answer 4

intravascular and extravascular

Question 5

How is ECF volume maintained? Why is maintenance so important?

Answer 5

It is regulate within normal limits by balancing the excretion of water by the kidneys to match the consumption of water.

This is essential for blood pressure regulation

Question 6

How is water transported across the membrane?

Answer 6

Simple diffusion and by specific channels called Aquaporins (facilitated diffusion)

Question 7

What is the definition of osmosis?

Answer 7

the net movement of H20 by a concentration difference of water between two compartments

Water moves “down” its concentration gradient (usually via aquaporins)

Question 8

Is H20 more likely to flow to an area of low osmolarity or high osmolarity?

Answer 8

To an area of high osmolarity because high osmolarity indicates high solute concentration.

Question 9

What is the main factor driving the net diffusion of water accross a semipermeable membrane?

Answer 9

solute and water concentration gradients

Question 10

What is osmotic pressure?

Answer 10

It is the amount of pressure that would have to be applied to force water back into its original chamber before osmosis occurred to equillibrate the two chabers

Question 11

What is hydrostatic pressure?

Answer 11

Pressure due to the force of gravity that is generated when water flows from one chamber to the next in order to equillibrate the chambers

(see page 73 of notes for picture)

Question 12

What opposes hydrostatic pressure gradient in the vascular compartment?

Answer 12

The hydrostatic pressure gradient that drives fluid from the vascular compartment is opposed by the osmotic pressure gradient that results from the presence of impermeable protein solutes in the plasma

Question 13

What causes edema?

Answer 13

the imbalance of the opposing forces (hydrostatic pressure and osmotic pressure).

Question 14

What is the osmolarity of plasma in human blood?

Answer 14

300mOsm/L

Question 15

What is ICF contribution to Total Body Weight?

Answer 15

40%

Question 16

What is the ECF contribution to Total Body Weight?

Answer 16

20%

Question 17

What is isotonicity?

Answer 17

ECF and ICF osmolarity both equal 300mOs/L.

No concentration gradient exists, and therefore there is no net movement of water.

Question 18

What is hypotonicity?

Answer 18

When ICF osmolarity > ECF osmolarity.

There is more solute inside the cell and water enters the cell in order to equillibrate the two compartments

Question 19

What occurs to cells in a hypotonic solution?

Answer 19

They swell due to the influx of water and can lyse.

Question 20

What is hypertonicity?

Answer 20

When ICF osmolarity < ECF osmolarity.

There is more solute outside the cell and water leaves the cell in order to equillibrate the two compartments.

Question 21

What occurs to cells in a hypertonic solution?

Answer 21

They shrink due to the efflux of water and can crenate.

Question 22

Explain the response to cell shrinking:

Answer 22

1. An increase in extracellular osmolarity sets up a gradient
2. The cell shrinks as water leaves the cell
3. Shrinkage activates two ion transporters and ions enter the cell.
4. Via osmosis, water enters the cell and returns omolarity to normal (ICF=ECF)

Question 23

Explain the response to cell swelling:

Answer 23

1. A decrease in extracellular osmolarity sets up a gradient
2. The cell swells as water enters the cell
3. Swelling activates two ion transporters and ions leave the cell
4. Via osmosis, water exits the cell and returns omolarity to normal (ICF=ECF)

Question 24

Are the transporters activated during cell shrinkage response the same as the transporters activated during the cell swelling response the same?

Answer 24

No, they are different ion transporters

Question 25

Explain the movement of water between compartments during dehydration:

Answer 25

1. Sweat is derived from blood (fluid is drawn from blood to forms sweat)
2. Fluid lost from the blood is replaced by interstitial fluid (plasma proteins draw water into the vasculature by osmosis)
3. Extracellular osmolarity is now higher which draws water out of the cells via osmosis
4. The cell volume decrease triggers water retention in the kidneys
5. total body water is restored.

Question 26

What are the ultimate results of sweating?

Answer 26

• volume depletion

- inc in ECF osmolarity

Question 27

Does sweat have a high or low osmolarity?

Answer 27

Low - 100 mosm

Question 28

What will occur if distilled water is added to the blood stream?

Answer 28

• Increase in both ICF and ECF volumes

- Decrease in both ICF and ECF osmolarities

Question 29

What will occur if an isotonic solution is added to the blood stream?

Answer 29

-just and inc in ECF volume

Question 30

What should you give a patient that is severely dehydrated?

Answer 30

-isotonic solution

Question 31

What will occur if hypertonic solution is added to the bloodstream?

Answer 31

• Increase in both ICF and ECF osmolarities
• Dec in ICF volume
• Inc in ECF volume

Question 32

What’s another word for extravascular fluid?

Answer 32

Interstitial