Water Movement Across Membranes

Front 1

Why is water movement thru membranes 100x faster than predicted from the oil:water partition constant?

Back 1

1. Water can pass b/w adjacent phospholipids --> not have to dissolve in lipid phase/ 2. Aquaporins --> channnels for water movement

Front 2

Thru which membranes will water move the slowest?

Back 2

Ones with hi long chain saturated fatty acid compositions

Front 3

Does water movement ever require active transport?

Back 3

No. It's always passive (goes down its concentration gradient)

Front 4

What 2 forces act on water movement thru membranes?

Back 4

1. Chemical force due to its concentration gradient (osmotic force)/ 2. hydrostatic force due to pressure difference across the membrane

Front 5

What can pass thru a semipermeable membrane?

Back 5

just water

Front 6

You have a chamber separated by a semipermeable membrane. Different sides have different concentrations of solute. Where does water flow?

Back 6

From the side with low [solute] to the side with hi [solute] until both sides have the same concentration.

Front 7

So what is the definition of osmosis?

Back 7

The movement of water down its concentration gradient thru a membrane

Front 8

What is osmolality (C)?

Back 8

Moles of particles per liter

Front 9

What is osmotic pressure?

Back 9

The amount of pressure needed to prevent osmosis

Front 10

Osmotic Pressure (pi) = ?

Back 10

R * T * C ; where C is osmolality, R is gas constnat, T is temperature(kelvins)

Front 11

What is the van't Hoff Equation?

Back 11

delta pi = delta (C) * R * T; where delta (C) is osmolality difference between two solutions

Front 12

What is the osmolality of pure water?

Back 12

0

Front 13

What is the osmolality of 2 M glucose?

Back 13

2 osmolar

Front 14

What is the osmolality of 2 M calcium phosphate (Ca3(PO4)2) assuming that it is completely soluble in water?

Back 14

10 osmolar

Front 15

What may keep solutes from reaching their full osmotic potential?

Back 15

Interactions between molecules

Front 16

How do we correct the van't Hoff equation to take into account non-ideal

Back 16

put in a fudge factor (phi) called the osmotic activity coefficient that is specific to different salts, so the new equation is now: pi = R * T * C * phi

Front 17

You have a membrane separating two solutions with identical solute composition but different concentrations. The membrane is equally permeable to water and the solute. What is the osmotic pressure difference?

Back 17

Zero. The solute and water both pass thru the membrane and equilibrate at the same rate.

Front 18

You have a membrane separating two solutions with identical solute composition but different concentrations. The membrane is MORE permeable to water than to the solute. What is the osmotic pressure difference?

Back 18

Net osmotic flow and observed osmotic pressure would be reduced but not zero.

Front 19

Reflection coefficient (sigma) = ?

Back 19

delta(pi)observed / delta(pi)theoretical, where delta(pi)theoretical is osmotic pressure against a semipermeable membrane with pure water on the other side and delta(pi)observed is osmotic pressure actually observed against a biological membrane with pure water on the other side

Front 20

True or false: a reflection coefficient is defined for a particular membrane and solute.

Back 20

TRUE

Front 21

What does a reflection coefficient of 1 tell you?

Back 21

The membrane is totally impermeable to a particular solute. It is reflected.

Front 22

What does a reflection coefficient of ~0 tell you?

Back 22

The solute's permeability is close to water's, so it'll move thru it at approximately the same rate.

Front 23

True or false: a reflection coefficient can be <= 0

Back 23

FALSE. It has to be between 0 and 1.

Front 24

Between 2 isosmotic solutions, which has more molecules per unit volume?

Back 24

Neither, they have the same osmolarity

Front 25

Solution A is hyperosmotic compared to solution B. Which has more molecules per unit volume?

Back 25

A

Front 26

Solution A is hypoosmotic compared to solution B. Which has more molecules per unit volume?

Back 26

B

Front 27

Does a cell swell or shrink in an isotonic solution?

Back 27

Neither, it remains the same size.

Front 28

Does a cell swell or shrink in an hypertonic solution?

Back 28

Shrink

Front 29

Does a cell swell or shrink in an hypotonic solution?

Back 29

Swell

Front 30

Is the following solution isotonic, hypotonic, or hypertonic? A cell has 200 mOs of impermeable solutes. The extracellular solution has 200 mOs of impermeable solutes.

Back 30

Isotonic. Since the intracellular and extracellular concentrations are equal, there is no need for water movement.

Front 31

Is the following solution isotonic, hypotonic, or hypertonic? A cell has 200 mOs of impermeable solutes. The extracellular solution has 100 mOs of impermeable solutes.

Back 31

Hypotonic. Water will flow into the cell to equilibrate the intracellular and extracellular concentrations.

Front 32

Is the following solution isotonic, hypotonic, or hypertonic? A cell has 200 mOs of impermeable solutes. The extracellular solution has 300 mOs of impermeable solutes.

Back 32

Hypertonic. Water will flow out of the cell to equilibrate the intracellular and extracellular concentrations.

Front 33

Is the following solution isotonic, hypotonic, or hypertonic? A cell has 200 mOs of impermeable solutes. The extracellular solution has 100 mOs of impermeable solutes and 100 mOs of permeable solutes.

Back 33

Hypotonic. Initially there is no water movement since the intracellular and extracellular concentrations are equal. Then, the permeable solutes will equilibrate across the cell membrane bringing the intracellular concentration to 300 mOs while the extracellular concentration is still 200 mOs. Therefore, water will flow into the cell to equilibrate the new concentrations.

Front 34

Is the following solution isotonic, hypotonic, or hypertonic? A cell has 200 mOs of impermeable solutes. The extracellular solution has 100 mOs of impermeable solutes and 200 mOs of permeable solutes.

Back 34

Isotonic. Initially the [extracellular] > [intracellular] ,so water will flow out of the cell. Then, permeable solute will equilibrate across the membrane bringing the [intracellular] up to 300 mOs, which is equal to the [extracellular] thereby bringing water back into the cell and back to its initial volume.

Front 35

In the above example which would cause the cell to initially shrink more: a hi or low reflection coefficient.

Back 35

Hi because the permeable solute would lag behind the water movement longer thereby allowing more water to leave the cell until the solute can equlibrate across the membrane.

Front 36

What's ultrafiltration?

Back 36

The use of hydrostatic pressure to move water against it concentration gradient.

Front 37

Can albumin leak out of capillaries?

Back 37

Yes, at a finite rate due to the presence of large pores

Front 38

True or false: capillary permeability is the same regardless of body region

Back 38

False. It is optimized to different organ functions.

Front 39

Do small molecules contribute to osmotic pressure difference in capillaries?

Back 39

No. The pores are so large that small molecules move freely thru them. Their reflection coefficients are 0.

Front 40

What is oncotic pressure (or colloid osmotic pressure)?

Back 40

The osmotic pressure difference due to large proteins (ie albumin) in the plasma

Front 41

In which direction does oncotic pressure act on water movement?

Back 41

Into the capillary

Front 42

What is the oncotic pressure typically?

Back 42

25 mm Hg

Front 43

What force acts to move water out of the capillaries?

Back 43

Hydrostatic pressure

Front 44

Where is hydrostatic pressure higher?

Back 44

At the arteriol end (32 mm Hg), while the venous end is lower (15 mm Hg)

Front 45

What is Starling's Law?

Back 45

The net pressure at the arteriol end serves to move water out of the capillaries for filtration, while the net pressue at the venous end serves to move water into the capillary for absorption.

Front 46

How does a vein thrombosis affect hydrostatic pressure?

Back 46

It increases hydrostatic pressure at the venous end.

Front 47

So does a vein thrombosis result in edema?

Back 47

Yes, the increased hydrostatic pressure forces decreases absorption, resulting in more water outside of the capillary.

Front 48

In addition to physically increasing the hydrostatic pressure as in a vein thrombosis, how else can edema be caused?

Back 48

Increase the permeability of the capillaries (due to damage from burns, trauma, insect bites, sprains), which would decrease the oncotic pressure, which keeps water in the capillaries and ultimately results in accumulation of water outside of the capillaries.

Front 49

What is kwashiorkor?

Back 49

Edema in the belly

Front 50

What causes kwashiorkor?

Back 50

Severe protein malnutrition reduces plasma protein concentrations and thus reduces oncotic pressure. Lower oncotic pressure results in a lower force acting to keep fluid in the capillaries, so fluid accumulates outside of the capillaries in the belly.