# Lecture 2: Osmosis and Fluid Shifts Flashcards

1
Q

What is the diffusion?

A

The process by which solutes from a more concentrated compartment will have a higher probability of moving to the other side of the compartment (down the concentration gradient) until the 2 sides reach equilibrium

2
Q

What is osmosis? What is it driven by?

A

The process by which water is pulled to the more concentrated side of the membrane by the solute.
It’s driven by the osmotic pressure created by the solute.

3
Q

What are the 2 methods to find the osmotic pressure?

A
1. Measure it

2. Calculate it

4
Q

How can one measure osmotic pressure?

A

By using a machine that is made of two
compartments filled with two different solutions separated by a membrane. Solution A in one compartment has
100 moles of glucose; Solution B in the second compartment is water. Glucose is impermeable to the membrane.
Consequently, water will be “pulled” from Solution B into Solution A by the effective osmotic pressure through
the membrane. However, Solution A is in a fixed-volume compartment, so no water can enter. The machine can read the amount of pressure needed to keep the compartment’s volume fixed, and the effective osmotic pressure
would be equal and opposite to that value read by the machine’s pressure-sensor.

5
Q

What does the osmotic pressure depend on?

A

The concentration of particles

6
Q

What is the equation to calculate total osmotic pressure? What is it called?

A

π = icRT

i = # of dissociated particles

Van’t Hoff equation

7
Q

What is the difference between total and effective osmotic pressures?

A

Effective is only dependent on the concentration of IMPERMEABLE particles whereas total osmotic pressure is dependent on the concentration of ALL particles

8
Q

What is the equation to calculate effective osmotic pressure?

A

π = σicRT

9
Q

What is the equation for the reflection coefficient?

A

σ = 1- (permeability of solute/permeability of water)

10
Q

What is the reflection coefficient of a solute that is completely permeable to a particular membrane?

A

0

11
Q

What is the reflection coefficient a measure of?

A

The permeability of a membrane to a particular solute compared to water

12
Q

What is the reflection coefficient of a solute that is completely impermeable to a particular membrane?

A

1

13
Q

What is another word for permeable?

A

Diffusible

14
Q

Until what will water be pulled to one compartment in a U-tube?

A

Until the effective osmotic pressure equals the hydrostatic pressure (mass x gravity) of the water between the lines in the graph

15
Q

How can you increase osmotic pressure?

A

16
Q

If a membrane goes from semi-permeable to permeable to a certain solute, what happens?

A

Hydrostatic pressure will push water from the side with the least water to the other until equil is reached

17
Q

What is an example of the permeability of a membrane changing?

A

Runny nose due to histamines when you have allergies

18
Q

What is the body’s way of accommodating increased pressure in a compartment?

A

Increasing the compartment’s volume

19
Q

How to decrease the size of a cell?

A

By increasing the concentration outside the cell

20
Q

How to increase the size of a cell?

A

By decreasing the concentration outside the cell

21
Q

What is the osmolarity?

A

The moles of impermeable substance in solution that contribute to the effective osmotic pressure - basically the # of active particles

22
Q

What does it mean for the milieu to be isotonic with the cell?

A

Same concentrations of solutes, no water movement (or same amount of water going in and out)

23
Q

What is tonicity?

A

Effective osmotic pressure

24
Q

What is the osmolarity of all of the body fluid compartments in steady state?

A

300 mosm (actually 287)

25
Q

What happens when you drop a cell into a hyper-osmotic environment?

A

Water rushes out

26
Q

What happens when you drop a cell into a hypo-osmotic environment?

A

Water rushes in

27
Q

What happens when you drop a cell into a hyper-, iso-, or hypo-osmotic solution of a permeable solute?

A

The cell will be hypotonic in all cases and water will rush in with the solute

28
Q

What is the effective osmotic pressure of an RBC being dropped in pure water?

A

π = cRT to figure out π, measured in mmHg.
RT can be used as a constant for
the body when at 37 degrees at 19.3.
So (19.3)(300 mOsm/L)=5790 mmHg.
For comparison, thats roughly 50X more pressure than what a healthy contracted heart generates.

29
Q

Why do IV solutions have impermeable solutes added to them?

A

To counter-balance the effective osmotic pressure pulling water into the cell

30
Q

What happens if you remove solutes from the ECF?

A

Tonicity is decreased –> ECF is hypotonic to the ICF –> water is pulled out of ECF and into ICF –> osmolarity decreases in both the ECF and ICF

31
Q

What is the standard weight and TBW of the standard human?

A

70 kg

42 L

32
Q

What happens if you add water to the ECF?

A

Tonicity is decreased –> ECF is hypotonic to the ICF –> water is pulled out of ECF and into ICF –> osmolarity decreases in both the ECF and ICF

33
Q

What would happen if extra water would not be able to be excreted by the kidneys?

A

The cells in the brain can swell too much, pushing on the respiratory control center in the brainstem, ultimately leading to respiratory failure and death

34
Q

What happens if you add isotonic saline to the ECF?

A

No change in osmolarity, no change in the volume of ICF, and an increase in ECF volume

35
Q

What happens if you add pure NaCl to the ECF?

A

Tonicity is increased –> ECF is hypertonic to ICF –> water moves from ICF to ECF –> osmolarity of ICF and ECF increases

36
Q

What is the fluid movement between the capillary and the interstitial fluid driven by?

A

Changes in pressures called Starling Forces

37
Q

What are the 4 Starling Forces and their shorthands?

A
1. Capillary pressure (Pc) or Hydrostatic pressure (HPc)
2. Interstitial oncotic pressure (πi) or interstitial colloid osmotic (πif)
3. Interstitial hydrostatic pressure (HPi or Pif)
4. Plasma oncotic pressure (πc or πp) or plasma colloid osmotic pressure
38
Q

What is the hydrostatic/capillary pressure due to? Does it push fluid in or out of the capillary? What is its value?

A

The heart’s contraction
Out!
30-50 mmHg

39
Q

What is the interstitial oncotic pressure or colloid osmotic pressure due to? Does it push fluid in or out of the capillary?

A

Due to the proteins contained in the interstitial fluid

Out!

40
Q

What is the interstitial hydrostatic pressure due to? Does it push fluid in or out of the capillary?

A

Any space that has a fluid has one (but it’s much lower than the plasma hydrostatic pressure)
In!

41
Q

What is the plasma oncotic or plasma colloid osmotic pressure due to? Does it push fluid in or out of the capillary?

A

Due to proteins (mainly albumin) present in the blood

In!

42
Q

What pressure does the interstitial hydrostatic pressure oppose?

A

The plasma hydrostatic pressure

43
Q

What pressure does the interstitial oncotic pressure oppose?

A

The plasma oncotic pressure

44
Q

How can you find the net filtration pressure across the length of a capillary wall?

A
```Jv = Kf x [ (HPc-HPi) - (πc - πi) ]
Kf = Filtration coefficient = Surface area (SA) x Hydraulic permeability (Lp)```
45
Q

What could excess fluid in the interstitial space be due to? 3 examples

A
1. Too high plasma HP generated by the heart
2. Decreased capillary oncotic pressure
3. Block in the lymphatic system that drains the interstitial space
46
Q

Describe what happens in a capillary? 2 steps

A
1. First the hydrostatic pressure moves fluid into the interstitial fluid
2. The plasma oncotic pressure pulls fluid back out
47
Q

What is reverse osmosis? What is it used to do? How does it work?

A

When you exert pressure on a compartment to counter the movement of water due to osmosis
Used to purify water from sea water
The result is that the solute is retained on the pressurized side of the semipermeable membrane and the pure solvent is allowed to pass to the other side.

48
Q

What body fluid compartment does sweat come from?

A

Plasma

49
Q

What body fluid compartment is in contact with skin, kidneys, lungs, and the intestinal tract?

A

Plasma

50
Q

What is the difference between an ideal semipermeable membrane and a selectively permeable one?

A

Ideal: only fluid can move across, not solute
Selectively: fluid and some SELECTED solutes can move across

51
Q

What is the definition of diffusion?

A

Movement of solutes down their concentration gradient

52
Q

How many mosm in 1 mmol of NaCl?

A

2 mosm

53
Q

What is hydraulic permeability?

A

A measure of how permeable the membrane is to water

54
Q

Does molecular weight of particles affect the osmotic pressure?

A

Nope: 1 molecule of a large protein results in the same osmotic pressure as a molecule of Na+

55
Q

What drives fluid movement between the ICF and the interstitial fluid?

A

Change in osmolarity

56
Q

What drives fluid movement between the interstitial fluid and the plasma?

A

Difference in pressures (Starling forces)

57
Q

What drives oncotic pressures?

A

Protein concentrations

58
Q

How to calculate osmolality from concentration?

A

osm = concentration . active particles in osmotic pressure

59
Q

Why do proteins in plasma contribute only minimally to the total osmolality of plasma, yet they constitute the most significant force tending to draw fluid into the capillaries?

A

Effective osmotic pressure which governs fluid movement across membranes is dictated by impermeable solutes. Proteins in the plasma can’t cross the capillary endothelium while many of the other solutes that make up the ECF can. In this way proteins create the osmotic pressure seen across the capillaries.

60
Q

Can a cell be isosmotic but not isotonic? When?

A

Yes, when you place the cells in an isosmotic solution that can freely penetrate the membrane

61
Q

How to go from osm/kg to osm/L

A

They are equal!

62
Q

Relate osmolarity to the number of osmoles in a compartment

A

osmolarity = mosm/volume

63
Q

How do you know if fluid is moving in or out of the capillary?

A

Capillary hydrostatic pressure > Osmotic pressure —-> fluid leave the capillary

Capillary hydrostatic pressure fluid enters the capillary

64
Q

What is the effect of vasodilation on net filtration across the capillary wall?

A

It’ll cause more flow in the capillary and will push more fluid out

65
Q

What is the effect of increased arterial pressure on net filtration across the capillary wall?

A

It’ll increase capillary hydrostatic pressure and will push more fluid out

66
Q

The plasma oncotic pressure is always greater than the interstitial oncotic pressure: true or false?

A

FALSE!

67
Q

What would cause an RBC to shrink?

A

Put it in a hypertonic/hyperosmotic environment (eg: more than 150 mM of Na+)

68
Q

If Jv is positive, where is fluid going?

A

OUT of capillary!