Transcript The Metric System

Body Fluid
Compartments
Chapter Reading:
Chapter 25 pages 292-301
1
Lecture outline
I. Water compartments of the body
A.Intracellular
B. Extracellular
i. Interstitial
ii. Plasma
iii. Transcellular
II. Compare/contrast water compartments
A. Size
B. composition
C. Osmolality
III. How do we have different composition/ movement of solutes
A. Different permeability
B. Types of transport across the membrane for solutes--Protein transporters
C. Review of Simple diffusion of solutes
IV. Movement of water
A. Osmosis-movement across cell membranes due to unequal particles
B. Hydrostatic pressure- movement across capillaries
V. Examples of when water vs. solute moves
VI. Definition of osmotic pressure
A. Examples of osmotic pressure differences in body fluid compartments
VII. Tonicity vs osmolality
A. Examples of tonicity and osmolality
2
• Why do you need to understand body fluid
compartments and osmolarity calculations?
Many of you will be applying IV care for patients,
and sometimes doctors make mistakes, so you
need to be able to catch these errors. Most
medical solutions are calculated in units that
don’t require a periodic table of elements, but if
someone miscalculates a solution, and you
inject it, and the patient crashes, you are just as
liable, and you will be sued.
3
Water
• Water makes up 45-75%
of our body weight
– 70 kg man X 0.60 = 42 kg
= 42 L
– How much of your own
weight is water? 2.2lb/1kg
• Divide this into two
compartments
– Intracellular water
– Extracellular water
4
Compartments
?
Lumen of stomach
• Intracellular Fluid
(30-40% Body Wt)
• Extracellular Fluid
These are
stomach
epithelial cells
?
– Interstitial fluid (the water
immediately outside cells,
between and around cells)
(16%)
– Plasma fluid (the water
inside blood vessels, but not in
(4-5%)
– Transcellular fluid (the
blood cells)
?
?
?
water enclosed in chambers
lined by epithelial
membranes) (1-3%)
5
• If you manipulate one body fluid compartment, it has an
effect on another compartment. Body fluid
compartments have different sizes and volumes, and
different compositions. What is dissolved in the fluid is
different. It does not matter about size and
composition…if you can count every particle in that
compartment, in all the compartments you should get the
same number of particles: 300 million particles per
liter, expressed as “300 million osmoles” or “300 miliosmoles”. It could also be described as having “an
osmolarity of 300”.
6
• That means that there are 300 million particles
(or 300 milliosmoles, abbreviated 300 mOsm) of
things in each compartment. If one compartment
has more particles than another one next to it,
and if those particles cannot reach equal
numbers on their own because the cell
membrane blocks their passage, water will try to
dilute the compartment with the higher number
of particles until they are at the same number of
particles per liter. Water always moves across
the compartments because cell membranes
7
always allow water to pass.
Body Fluids compartments
 Different compositions (different amounts of individual
particles)
 Different volumes,
 Same osmolalities (total number of particles)
0.3 Osmolal = 300 mOsmolal (actually closer to 280mOsmolal)
Plasma
Interstitial
Intracellular
8
• If the plasma is diluted to 260 mOsm, and the cells next to a blood
vessel are still at 300 mOsm, the cells now have more particles.
What will move, in order to dilute the cells? Water. Why? Because
particles suck! The cells will draw the water to it. Water will move
from the plasma to the adjacent cells. What happens to the cells?
They will lyse (rupture). When would that ever happen in real life? A
contestant on a radio game show drank a lot of water for a week,
and was not allowed to go to the bathroom much. She developed a
headache, went home, and died. She was OVER hydrated, so the
original 300 particles per liter in her plasma were now at 300
particles per 2 liters, since the excess water increased her blood
volume. That means there were only 150 particles per liter, so
overall, there were now fewer particles in the plasma than in the
adjacent cells. Her brain cells sucked up the water until they
ruptured and exploded in her skull.
9
• Thus, we learn that if a person is overhydrated, the plasma will be diluted below
300 mOsm, but the cells still have 300 mOsm
in particles. So, the cells will draw in more
water from the plasma and the cells will
enlarge and rupture. Therefore, she should
have been given an IV that was hypertonic
(greater than 300 mOsm) to balance out the
number of particles in the plasma so it matched
the number of particles in the cells.
10
• The opposite is true for someone who is dehydrated. Since the
original number of particles was 300 million particles per liter, and
then the patient became dehydrated, they would now have 300
million particles per half a liter (since they lost plasma volume due to
dehydration), so their plasma is actually at 600 mOsm per liter.
Therefore, if a patient is dehydrated, you will give an IV that was
hypotonic (less than 300 mOsm, be careful of the drip rate) to
balance out the number of particles per liter within the plasma and
within the adjacent cells. If, a doctor accidentally tells you to give a
dehydrated patient an IV solution that is hypertonic (greater than
300mOsm), the plasma will have more particles than the cells, and
the cells will have the water sucked out of them, which also causes
death. Understanding body fluid compartments is important!
11
• There are 100 trillion cells in your body, 25% of them are RBCs.
Dead RBCs are the reason why your pee is yellow and your poop is
brown! You will understand why, later in the semester.
• About 50% of your body weight is from water. How can you
calculate your water weight? For every 2.2 pounds, you are 1
kg in weight. Then multiply that number by 0.6 to see how
much water is in your body.
• Water makes up 45-75% of our body weight
– 70 kg man X 0.60 = 42 kg = 42 L of water is in his body
– How much of your own weight is water? 2.2lb/1kg
12
• The total amount of water in your body is divided into two
compartments
– Intracellular water is inside of your cells. Most of your water
is here.
– Extracellular water is outside of your cells. There are three
types.
• Interstitial fluid (the water immediately outside cells,
between and around cells) (16%)
• Plasma fluid (the water inside blood vessels, but not in
blood cells)
(4-5%)
• Transcellular fluid (the water enclosed in chambers lined
by epithelial membranes, including the GI tract and
synovial joints) (1-3%)
13
• All compartments are not the same size.
Which is the biggest? Intracellular
• What’s the smallest? Trancellular
• The inside of each cell is low sodium, low in
free calcium, high in potassium, high in
proteins (there are four times as many proteins
in cells than there are in plasma).
• Outside of cells (in the plasma) are high in
sodium and free calcium, low in potassium
and proteins.
14
Different compositions across the
membrane: How can this be?
15
• As stated, if you could count all the solutes
(particles) inside and outside of the cell, they are
the same number (300 mOsm). Why does it
need to be that way?
• All particles pull water to them, whether the
particle is glucose, calcium, a protein, salt, etc.
We don’t want a net gain or loss of fluid across
the cell membrane or the cell will shrink or burst.
Not all compartments have the same volume
liquid, but they all have the same number of
particles per liter.
16
• If the numbers of particles are always the
same, how can we have higher numbers
of potassium ions inside of the cell
compared to the outside of the cell? Won’t
the potassium ions want to move down
their concentration gradient towards
equilibrium? Yes, they will want to, but the
cell membranes are semi-permeable and
will prevent the potassium (and other
particles) from crossing.
17
• If you have a cell containing 300 mOsm of potassium
(K+) immersed in pure water, will it shrink or burst? The
potassium cannot flow out of the cell to equalize its
numbers inside and outside of the cell because it is
blocked in by the cell membrane. That means there are
more particles on the inside of the cell than in the pure
water it is soaking in. The particles in the cell will suck
water into the cell until the cell bursts. In theory, if the
substance we are talking about was a particle other than
potassium, and one that can cross the cell membrane
whenever it wants to, it would simply diffuse across the
cell membrane until it reached equilibrium, so the cell
would not burst.
18
• What particles can cross the cell
membrane?
• Gases (O2, CO2)
• Lipids and lipid-loving (hydrophobic or
lipophylic) substances, such as alcohol
19
Functions of Membrane- Selective
Permeability and Transport
• Selectively permeableallows some substances
to pass between
intracellular and
extracellular fluids
• Only small uncharged
molecules or fat soluble
molecules can pass
through membrane
without help- diffusion
(passive transport)
• Facilitated diffusion (still
passive transport)
• Active transport
http://www.northland.cc.mn.us/biology/BIOLOGY1111/animations/active1.swf
20
Membrane Function
• Passive transport
includes diffusion
across a membrane
– diffusion is tendency of
molecules to spread out
spontaneously from
area of high
concentration to area of
low concentration
• at equilibrium molecules
diffuse back and forth-no
net gain or loss
This only happens if the solute is
permeable across the cell membrane!
http://www.northland.cc.mn.us/biology/BIOLOGY1111/animations/active1.swf
21
• If movement across the cell membrane
does not require energy to be spent,
the movement is called passive
transport. There are two kinds of
passive transport: simple diffusion and
facilitated diffusion. If movement
across the cell membrane requires
energy to be spent, the movement is
called active transport. The energy
molecule that is spent is called ATP. 22
• A water-loving (hydrophilic) substance
needs a special channel in the cell
membrane to cross, and it will cross the
cell membrane either by simple
diffusion (no ATP required), or it may
need a transport protein to carry it into
or out of the cell by one of two
processes: facilitative diffusion (no ATP
required) or active transport (ATP is
required).
23
• Facilitated diffusion is when an ion
wants to travel down its concentration
gradient, but there is a channel in the cell
membrane that opens and closes by a
protein which enlarges or shrinks to open
or block the channel (remember, this is still
passive transport, so it does not need
ATP).
24
• Active Transport is when a substance needs to
move against its concentration gradient (it is
moved from an area of low concentration on one
side of the cell membrane to an area of high
concentration on the other side of the cell
membrane). It accomplishes this because a
protein embedded in the cell membrane grabs
onto the substance and drags it across the cell
membrane (this requires ATP).
25
• Passive Transport:
• Simple Diffusion
Facilitated Diffusion
26
How does water move?
• Two ways:
• Osmosis
• Hydrostatic pressure
27
Movement of water
• Always passive and unsaturable
• Pores (aquaporins) serve as conduits
(ubiquitous AQP1 vs. collecting duct AQP2)
• Osmosis
– a chemical potential energy difference
dependent on the water concentration on
two sides of the membrane
– Easier for physiologists to measure the
solute concentration (more solute means
less water; less solute means more water)
– Driving force for water movement across cell
membranes
• Hydrostatic pressure
– The pressure of the fluid exerted on the
vessels, or container (change in
energy/mole)
– Animal cell membranes are “flexible” so it
is not a driving force across cell
membranes
– IT IS a driving force for moving plasma water
across walls of capillaries
If you squeezed on this
bottle to get the water to
shoot out, what kind of
pressure would this
simulate?
28
Hydrostatic Pressure
• Squeeze a water bottle to shoot the water out, this is
hydrostatic pressure. Hydrostatic pressure is the
pressure of the water exerting on the vessel wall. If
you push harder, the water will shoot farther. The
hydrostatic pressure of water being filled in a balloon will
exceed the capacity of the balloon and pop. That is how
water moves between cells and into cells so that plasma
becomes interstitial fluid. The plasma leaks out between
the endothelium of the capillaries. If you have a swollen
ankle and apply an ace wrap, you are applying
hydrostatic pressure to force interstitial fluid back into the
plasma. Hydrostatic pressure is not the movement
across a cell membrane. That is osmosis.
29
Osmosis
• Osmosis is movement of water across
the cell membrane because of the
particle different on each side. Osmotic
pressure can be measured. If there is
more water on one side of a membrane
than the other side of the membrane, the
water will move down its concentration
gradient, which is the same condition of
moving from low particles to high particles.
30
• Dialysis tubing is used in laboratory demonstrations about osmosis
because it is not permeable to glucose but water can cross it. It
helps you learn about the body because glucose also cannot get
across the body’s cell membranes, but water can. In a laboratory
demonstration, water will move into the tubing until it reaches a
certain column height. It does not continue to climb higher and
higher in the column indefinitely, because gravity will be exerting
forces on it too. Eventually, the water will reach a certain height and
then stop. The point at which is does this is when the hydrostatic
pressure caused of the gravity is equal to the osmotic pressure of
the water trying to get into the tube. If we did this experiment in outer
space, all of the water would cross over the membrane and the
column would rise until all the water is gone.
31
• Imagine that you take some aspirin and wash it
down with water. If the aspirin particles can get
across the cell membrane, there will be no net
gain or loss of water in the compartment.
• But if you eat a bunch of cellulose (fiber), it
cannot cross a cell membrane. There will be
more particles in the GI tract lumen, so the GI
lumen will suck water from the nearby cells into
the intestinal lumen. That is how laxatives work!
They will extract fluid from the body and in
excess, they may cause dehydration.
32
• Osmotic pressure is the amount of
hydrostatic pressure required to stop
osmosis from moving water from low to
high concentration across a cell
membrane. Osmotic pressure is attributed
to the osmolarity of a solution. The
solution with the highest number of
particles will have the highest
hydrostatic pressure.
33
Membrane
Function
• Osmosis is
movement of water
to an area with more
solute
– if cell membrane
permeable to water
but not solute
– direction of osmosis is
determined by
differences in total
solute concentrations
– Hypo-osmotic
– Hyper-osmotic
– Water always moves!
Watch your body fluid
compartments
When would this stop?
What if we were in space?
http://student.ccbcmd.edu/~gkaiser/MYANIMATIONS.pdf
34
Review: Implications of Concentration and
Osmolality Differences Across Membranes
• First, let’s focus
on a solute that
can move across
the membrane.
• Let’s say these
green particles
are aspirin
molecules in the
stomach.
• How would
these molecules
move across the
body fluid
compartments?
• Diffusionrandom
movement of
particles from
“high to low”
Plasma
GI tract
http://www.indiana.edu/~phys215/lecture/lecnotes/diff.html
35
Review: Implications of Concentration and
Osmolality Differences Across Membranes
•
•
•
•
•
Now, let’s say
you’ve eaten fiber
(cellulose)
You can’t absorb
it!
There are more
particles in one
body fluid
compartment
What will happen?
Water movement
– Osmosis
– Hydrostatic
pressure
This is the basis for
how diuretics and
laxatives work!
Plasma
GI tract
http://www.indiana.edu/~phys215/lecture/lecnotes/diff.html
36
Osmotic Pressure
• Osmosis occurs when water moves from a
solution w/ fewer particles to one with more
particles because the particles can’t move
across the membrane!
– Remember “particles suck (....in water).”
• osmotic pressure is the amount of pressure
required to stop osmosis from happening
(hydrostatic pressure).
• Water is likely to enter a solution that
contains lots of particles that are
impermeable across a membrane– thus the
solution is said to have a high osmotic
pressure!
37
Osmotic Pressure:
the amount of hydrostatic pressure (force of fluid exerted on
the vessel wall) required to counter osmosis
Osmotic pressure is
attributed to the
osmolarity
of a solution
Isosmotic - has same
osmolarity as body fluids
Hyperosmotic - higher
osmolarity than body fluids
Hyposmotic- lower
osmolarity than body fluids
Figure 4-10;38
Guyton & Hall
• In a U-shaped tube separated by a membrane, water moves to the
side with more particles (Particles suck). If a compartment has a
high number of particles, there is a low amount of water there,
so water will move from there to the area with fewer particles.
Scientists can count how many particles there are in a solution. If a
membrane prevents the particles from moving down their
concentration gradient, water will move from low concentration (low
particles) to high particles. Osmotic pressure is the amount of
hydrostatic pressure you need to apply to stop the water from
moving (from the top of the tube where the particles are highest).
PhysioEx has an osmosis activity. Set up two beakers, one with high
and one with low particles, apply a force to the top of the high
particle beaker, and measure how much force is needed to push it
down until there is no net gain or loss of fluid on the side that has a
lot of particles.
39
• What will happen to a cell placed in the
following solutions?
• Isosmotic (300 mOsm): no net gain or
loss of water.
• Hyperosmotic (600 mOsm): particles
suck, so solution will suck the water
from the cell, which will shrink.
• Hyposmotic (100 mOsm): particles
suck, so cell will suck water from the
solution and burst.
40
• The above example assumes that the particles in the cell
cannot diffuse out, which is usually the case.
• However, there are particles (such as urea) that can
cross a membrane. Urea will diffuse out of one
compartment and into another, down its concentration
gradient. As it does so, water will also be diffusing back
and forth down its own concentration gradient. In this
case, although the water will go back and forth while it is
seeking equilibrium, there is no net gain or loss of water
from each compartment. The solute (urea) will diffuse
quickly. There are only transient changes in water if a
particle is diffusing across a membrane.
41
Example with Diabetes
• Increased sugar in the blood
• Relatively less water due to increased
solute concentration
• Describe the movement of water when the
mOsmolal changes!
intercellular
Interstitial
(extracellular)
300
S
S
S
S
S
G.I.
Tract
304mOsm
Water flow
Plasma
(extracellular)
Transcellular
(extracellular)
42
Example with Diabetes
• When you eat, sugars are absorbed into plasma.
Normally, insulin transports these sugars into the cells,
but in a diabetic with no insulin, the sugars stay in high
concentration in the plasma. That raises the plasma
above 300 mOsm, while the interstitial fluid is still at 300.
Where will water go? Water will move from the interstitial
fluid into the plasma. Now, the interstitial space has less
water, but the same number of particles, so it may be at
300 particles per HALF a liter, instead of 300 particles
per liter. To calculate the number of particles per liter,
multiply by 2 and you will see that the interstitial space
has actually become 600 mOsm.
43
• The interstitial space now has more particles than the
intercellular area next to it. Water will then go from the
cells into the interstitial space (which gets the water
sucked out of it again from the high plasma osmolality),
and the person gets dehydrated. Diabetics have excess
sugar circulating in the plasma, and the kidneys cannot
filter all of it, so the sugar builds up in the nephron
lumen. Water from the capillaries is drawn into the
nephron lumen (higher mOsm), so more urine is
produced. Sugar will also spill into the urine and can be
detected in a urinalysis (UA).
44
• When a person becomes dehydrated, it
triggers the brain to release anti-diuretic
hormone (ADH), which stimulates the
thirst center in the brain, encouraging the
person to drink more water. The
condition where a person drinks a lot of
water because they are thirsty is called
polydipsea, and is characteristic of a
person with diabetes.
45
Test yourself- by picking which one
of these is correct
•
What happens with diabetes mellitus?
a) Cells lose water to ECF via osmosis; ECF osmotic
pressure rises; Solute concentrations increase in ECF.
b) Solute concentrations increase in ECF; Cells lose water to
ECF via osmosis; ECF osmotic pressure rises;
c) Water is lost from the ECF; Solute concentrations increase
in ECF; ECF osmotic pressure rises; Cells lose water to
ECF via osmosis.
d) Solute concentrations increase in ECF; ECF osmotic
pressure rises; cells lose water to ECF via osmosis
What if the question described an athlete who was dehydrated?
46
Note this poor child’s swollen
distended belly.
How does that relate to her
lack of dietary protein?
Kwashiorkor- “disease of deposed
child” (no longer suckled).
•Corn has no tryptophan
•Economically disadvantaged
countries that use cornmeal
•Hospitals and nursing homes, too!
•Failure to grow
•Lethargy
•Depressed mentality
Low plasma protein. So, the fluid moves into the interstitial
•Edema caused by.......
space (seemingly increased conc) and then into an area of
low resistance—the peritoneal cavity
Used with permission given by A. Imholtz
http://academic.pg.cc.md.us/~aimholtz/
47
Example with Malnourishment
• We need all of our essential amino acids, and problems
can occur if you are deficient in only one amino acid. All
compartments, including the plasma, should be 300
mOsm. There are many plasma proteins; the most
abundant is albumin, which is made in the liver. If your
diet is deficient in an amino acid, the liver cannot make
enough plasma proteins. If albumin numbers decline,
particles in the plasma decrease. Plasma is now 200
mOsm. Other compartments will suck the water from the
plasma and edema will result. Therefore, lack of dietary
protein causes a low mOsm in the blood plasma. Since
there are more particles in the interstitial space, water
will move from the plasma to the interstitial compartment.
48
• The peritoneal cavity is an area of low resistance; there is not much
there to hold back something that is pressing from the inside. The
fluid goes from the plasma into the peritoneal compartment, and the
belly becomes distended with fluid (ascites). It is not to be
confused with a full stomach; ascites is characteristic of malnutrition
and other diseases. Edema (excess interstitial fluid) also occurs
in legs, since there is no pressure there to keep it in. Ascites is not
just a problem of poor countries. Other people who often get ascites
are alcoholics and the elderly who don’t eat their protein.
• When malnourished, the body will break down the proteins in the
muscles to get what is needed elsewhere. Alcoholics drink their diet;
the liver becomes so scarred that it can’t make proteins.
49
Acites
• Ascites puts pressure on the bile duct (called portal
hypertension), preventing the release of bilirubin, so
this yellow pigment enters the tissues, turning the skin
yellow, especially the white parts of the eyes. This yellow
appearance of the skin is called jaundice. When excess
bilirubin enters the brain, it causes nerve cell death. This
is why alcoholics still seem drunk when they are sober.
Bilirubin is the result of RBC death. Parts of the RBC can
be recycled (such as the iron), but the bilirubin (part of
hemoglobin) needs to be eliminated. Bilirubin is what
causes the color of urine and feces.
50
Our book refers to tonicity more than
osmolality....are they interchangeable?
• NO!!!!!!!
• Tonicity refers to whether a
solution will cause changes in
cell volume (effective
osmolality—that means, not
permeable)
• Osmolality refers to the
number of particlesregardless of permeability
• Is the solute an effective
(impermeant) or ineffective
(permeant) osmole?
• Some solutes (primarily urea)
are freely permeable to cell
membranes (exhibit passive
transport). A hyperosmotic
solution may cause only
transient shifts in the body under
steady-state conditions.
Figure 25-5; Guyton and Hall
51
Tonicity vs. Osmolality
• Tonicity and osmolality are not the same word.
Tonicity refers to the number of particles in 1kg
of water. Will there be a shift of water across the
cell membrane? Most of the time, particles don’t
move so the water does. If this was always the
case, tonicity and osmolality are the same
number. But substances, such as urea, can
move across a cell membrane, so there is only a
transient shift in water. In these cases, the
resulting osmolality and tonicity are different.
52
For example:
• 300mmol/L sucrose
• isosmotic to our bodily fluids!
300mmol/Kg sucrose
300mmol/kg sucrose
is also isotonic- no
change in cell volume
It’s osmolality is also
its effective osmolality
(tonicity).
53
• Place a cell in isotonic solution: There are
equal particles and no net gain or loss of
water.
• This solution is considered to be Isotonic
and isosmotic.
54
What about 600mOsmolal Sucrose?
•Hyper-osmotic
•Hypertonic
55
• Place a cell in hypertonic solution: The cell
will shrink.
• This solution is hypertonic and
hyperosmotic.
56
• Place a cell in hyposmotic solution: The
cell will swell
• This solution is hypotonic and hyposmotic.
57
Let’s see what happens with urea
400mmol/Kg urea
Hyper-osmotic
Isotonic (long-term)
58
• But place a cell in a solution with 400 mOsm of
urea. The urea will move into the cell until it
equalizes.
• The water will transiently shift from the solution
to the cell until it equalizes, with no net gain or
loss of water from the cell. The cell will not
shrink, nor will it swell.
• This solution is isotonic but hyperosmotic.
• Urea is important for proper kidney function, so it
needs to be able to cross a membrane. That’s
59
why you can make concentrated urine.
Study Tip:
• How to remember what a cell does in hypertonic water?
• Hypertonic has an “e” in it. Make the letter e with your
body. See how you have to curl up and shrink to make
this letter? A cell will curl up and shrink in hypertonic
solution.
• How to remember what a cell does in hyportonic water?
• Hyportonic has an “o” in it. Make the letter o with your
arms over your head. See how you have made yourself
bigger? A cell will swell up in hyportonic solution.
60