Introduction and Body Fluid
Compartments
Vivek Bhalla, MD
Division of Nephrology
Stanford University School of Medicine
August 28th, 2015
Anatomy of the Renal Block
Physiology
Pathophysiology
Urology
Body Fluids -1
Glomerular Diseases – 3 Histology Lab
GFR, Clearance -1
Acute Kidney Injury – 1
Sodium / Diuretics – 2
Chronic Kidney Disease
–3
Potassium – 2
Renal Lab -2
Acid – 2
Transplant Pathology-1
Water – 2
Vascular Diseases – 1/2
Steady State - 1
Plumbing- 1/2
Malignancy – 1
The Roles of the Kidneys
• Control the volume and composition of the body
compartments i.e. keep us in chemical balance
• Remove organic waste products
• Make necessary hormones
– (our own personal Lance Armstrong)
Learning Objectives (3)
• Memorize (unfortunately) the concentrations of the principal ions
in the extracellular and intracellular fluid.
• Know the difference between intracellular fluid, extracellular fluid,
plasma, and interstitial fluid, and how to estimate the volume of
each of these compartments in a patient.
• Understand the composition of two common intravenous fluids
used in medicine – 5% Dextrose (“D5W”) and 0.9% Sodium
Chloride (“Normal Saline”)
Claude Bernard
The fluid surrounding our cells
Extracellular Fluid (ECF)
“le milieu intérieur”
The fixity of the milieu supposes a perfection of the organism such that
the external variations are at each instant compensated for and
equilibrated.... All of the vital mechanisms, however varied they may be,
have always one goal, to maintain the uniformity of the conditions of life
in the internal environment .... The stability of the internal environment is
the condition for the free and independent life.
The Roles of the Kidneys
Internal milieu
• Control the volume and composition of the body
compartments i.e. keep us in chemical balance
• Remove organic waste products
• Make necessary hormones
– (our own personal Lance Armstrong)
ECF = Water in the Fish Tank
Cells
Environment
Learning Objective (Renal Physiology)
How the kidney regulates the
volume and ionic composition
of the extracellular fluid (the fish tank)
How? Not What? (Renal Physiology)
Example
The plasma K+ concentration is 6.5 mEq/L (normal 4.5 mEq/L)
Approach #1:
What are the common causes of a high plasma K+ concentration?
Approach #2: How does my body regulate the plasma K+ concentration?
Common causes are those which frequently affect the regulatory machinery.
Basic Body Compartments
Intracellular Fluid
Extracellular Fluid
Bacteria…..Not Us!
Intracellular Fluid
Extracellular Fluid
100 mOsm
< 10 mOsm
Our Body Composition…Our Fish Tank
Intracellular Fluid
Extracellular Fluid
290 mOsm
290 mOsm
140 meq/L
Na+
4.5 meq/L
K+
40 neq/L
H+
Definitions…Need to Memorize
Total body water (TBW) – all the fluid in and out of cells
Intracellular fluid - inside cells; 2/3 rd of TBW
Extracellular fluid - outside cells; 1/3 rd of TBW
Plasma - in blood vessels, about 1/4 th of ECF
Interstitial - between cells
Definitions
Interstitial Fluid
Plasma
Intracellular Fluid
Extracellular Fluid
Rough Estimates – 70 kg, person
Interstitial Fluid
Plasma Blood
Intracellular Fluid
28 Liters
11 L
3L
Extracellular Fluid
14 L
Total Body Water = 60% of total body weight = 42 L
Let’s Repeat That
Total body water (TBW) – all the fluid in and out of cells
70 kg * 60% = 42L
Intracellular fluid - inside cells; 2/3 rd of TBW
42 L* 2/3 = 28L
Extracellular fluid - outside cells; 1/3 rd of TBW
42 L* 1/3 = 14 L
Plasma - in blood vessels, about 1/4 th of ECF
14 L* ~1/4 = 3L
Interstitial - between cells
14 L – 3L= 11L
Body Compartments…Let’s Repeat That
Composition of Body Compartments
Pop Quiz
The [Na+] outside the cell is approximately…
1. 150 mEq/L
2. 100 mEq/L
3. 50 mEq/L
4. 10 mEq/L
Our Body Composition…Our Fish Tank
Intracellular Fluid
Extracellular Fluid
290 mOsm
290 mOsm
140 meq/L
Na+
4.5 meq/L
K+
40 neq/L
H+
K+
Na+
Na+-K+ ATPase pump
Pop Quiz
If you infuse a saline solution (salt in water)
into a person’s vein (intravenous infusion),
where does the Na+ go?
1. Into the vascular (plasma) space
2. Into the vascular and interstitial spaces
3. Throughout the body water (vascular space plus interstitial
space plus cells)
Definitions…Need to Memorize
mmole = 1/1000 of a mole of ions or molecules
mEq = 1/1000 of a mole of charge
so 1 mmole of Na+ is the same as 1 mEq of Na+
but 1 mmole of Ca++ is the same as 2 mEq of Ca+ +
mosmole = 1/1000 of a mole of particles in solution
so 1 mmole/liter of glucose gives a 1 mosmolar solution
but 1 mmole/liter of NaCl gives a 2 mosmolar solution
? a glucose solution of 5mmoles/liter is how many mEq/liter?
Zero….glucose has no charge
Example # 1
Calculate the osmolality of a 5% dextrose solution…
5% dextrose is:
5 grams / 100 milliliters
= 50 grams / liter
50 grams/liter divided by 180 grams/mole:
= 0.278 moles/liter
= 278 millmoles/liter
= 278 mOsm
Why do we use a dextrose solution of 5 grams/100 ml?
You can’t infuse pure water
(the red cells would blow up)
start with
280 mOsm
in the plasma
but rapidly infuse pure water
and the plasma osmolality
goes down in the vein where
the water is infused
<200 mOsm
in the plasma
280 mOsm
inside the cell
Add sugar…
Pop Quiz
If you infuse 5% dextrose intravenously,
the sugar will be metabolized (remember
biochemistry). Where will the water go?
1. into the vascular space
2. into the vascular and interstitial spaces
3. throughout the body water (vascular space plus interstitial
space plus cells)
Example # 2
Calculate the NaCl concentration in grams per liter (g/L)
required to get an osmolality of 290 milliosmoles per liter
(mOsm/L)…
We want:
290 mOsm/L
Since each NaCl breaks up into 2 ions in solution, then we will need:
145 mmol/L
After a small correction (technicality), the answer is:
~ 155 mmol/L
0.155 moles/liter * 58.5 grams/mole :
~ 9.0 g/L
= 0.9 grams/100 mL
= 0.9% saline
= “Normal Saline”
Pop Quiz
If you infuse 1 liter of “normal” saline
intravenously, the ECF volume will…
1. increase by about 2 liters
2. increase by about 1 liter
3. increase by about 1/3 liter
4. decrease by about 1 liter
But…
If you infuse 1 liter of 5% dextrose in H2O
intravenously, the ECF volume will…
1. increase by about 2 liters
2. increase by about 1 liter
3. increase by about 1/3 liter
4. decrease by about 1 liter
Rough Estimates – 70 kg, person
Interstitial Fluid
Plasma Blood
Intracellular Fluid
28 Liters
11 L
3L
Extracellular Fluid
14 L
Total Body Water = 60% of total body weight = 42 L
Body Compartments
Pop Quiz
Most of the body water is?
1. Outside the cells
2. Inside the cells
Pop Quiz
The standard 70 kg genderless teaching
person contains about…
1. 20 liters of extracellular fluid
2. 15 liters of extracellular fluid
3. 10 liters of extracellular fluid
Renal Physiology
Quantitative
But
Not
Precise
Pop Quiz
A 70 kg patient has a plasma [Na+] of 165 mEq/L. About
how much water must you give to bring the [Na+] down to
150 mEq/L?
1. 7 liters
2. 4 liters
3. 1.5 liters
Why Does this Stuff Matter?
Need to be Quantitative but not Precise
Don’t Memorize This!
Take Home Points (3)
• Memorize (unfortunately) the concentrations of the principle ions
in the extracellular and intracellular fluid.
• Know the difference between intracellular fluid, extracellular fluid,
plasma, and interstitial fluid, and how to estimate the volume of
each of these compartments in a patient.
• Understand the composition of two common intravenous fluids
used in medicine – 5% Dextrose (“D5W”) and 0.9% Sodium
Chloride (“Normal Saline”)