1. Physiology of Electrolytes
Cindy McKinney, Ph.D.
Block 2, 2012
Musculoskeletal System
Supplemental Dr. Reilly

2. Learning Objectives
Electrolytes
 Detail the normal concentrations of the following blood and cellular
components
 Detail intracellular or extracellular location
 Sodium (Na+), Potassium (K+), Glucose, Calcium (Ca+2), Magnesium (Mg
+2),
Hydrogen ion (H+), Bicarbonate (HCO3-), Chloride (Cl-), Albumin,
Creatinine and
Urea
 State normal arteriole blood gases
 Interpret a normal urine dipstick and what the measures mean

3. Learning Objectives
Bone Marrow and Blood Components
 Describe production of RBCs –what tissues and what times produced
 State normal and abnormal Hematocrit (Hct)
detail possible genetic, pathophysiological disturbances that lead to abn
RBC production
 Define the normal range for each of the following and state what an abnorma
elevated or abnormal value may indicate:
-Hemoglobin
-White Blood Cell (WBC) count
-Red Blood Cell (RBC) count
-White Blood Cell differential count
-Platelet Count
-Reticulocyte Count

4. Reading
• Guyton Electrolytes

5. Body Fluid Spaces
(TBW)
Water is a major component of
the
fluid space (50-70% of body
ICF ECF
weight)
Ultrafiltrate of
plasma
Plasma---without proteins and
cells
(RBCs)
= 25% of ECF
Contained w/in cell=2/3
of body water
=1/3 body water Interstitial Fluid= 75% pf ECF
---baths the
cells

6. Composition of body fluids
Not uniform between compartments---ICF and ECF have different
concentrations of
of solutes
one example: interstitial fluid being an ultrafiltrate of plasma contains
little protein
Concentrations of solutes can be expressed as:
moles/L
Eq/L
Osm/L
Because biological concentrations are low you will usually see these values as:
mmoles/L
mEq/L
mOsm/L

7. Composition of body fluids
Remember your high school chemistry:
One mole=6 x 1023 molecules of solute; one millimole (mmole)= 1/1000
mole=1 x 10-3 mole
so: 1 mmol/L glucose =1 x 10-3 mole/L glucose
An equivalent describes the amount of charged solute (Na+ ion as an example)
in solution
= number of moles of solute x its valence
Examples: one mole of KCl in solution dissociates to one equivalent of
K+ and Cl-
KCL
K+ + Cl- one equivalent
one mole of CaCl2 in solution dissociates in two equivalents of Ca and
one Cl

8. Composition of body fluids
One osmole is the number of particles from a solute in solution
Osmolarity measures the concentration of particles in solution osmoles/L
(Note: a solute (like glucose) that does not dissociation in solution
osmolarity = molarity)
Examples: 1 mmol/L NaCl dissociates into two particles Na+ and Cl- osmolarity
what is the osmolarity of a 1mmol/L solution of NaHCO3-?
pH is used to express the H+ concentration in a body fluid= -Log10 [H+]
Normally [H+] is very low  40 x 10-9 Eq/L
Body pH is maintained in a narrow range of 7.35-7.45.

9. Electroneutrality
Each body fluid compartment obeys “principle of macroscopic neutrality”
Thus: each compartment must have equal positive=negative charges for
NO NET CHARGE
Even if there is a potential difference between compartments-- balance is
still maintained
within the compartment

10. Approximate Compositions of Solutes in
the ICF compared to ECF
ICF ECF
Solute
Solute
Concentration Concentration
Na+
14 Na+
140 mEq/
mEq/L L
K+
120 K+
4 mEq/
mEq/L L
Ca+2 (ionized 1x Ca+2
2.5 mEq/
10-4 mEq/L L
Cl-
10 Cl-
105 mEq/
mEq/L L

11. Other solutes in solution
Other solutes in cellular compartments
Solute Concentration and
Units
Mg+2 0.9 mmol/L
Albumin (protein) 4.5 g/dL
Creatinine 1.2 mg/dL
Urea (BUN) 12 mg/dL
Glucose 80 mg/dL

12. Sodium
Major cation in ECF and vital mineral
(electroneutrality balanced with HCO3= or Cl-)
Most sodium found in blood or lymph fluid (85%)
Sodium levels are controlled by kidney (hormone aldosterone)
Small amount lost in sweat
Too much sodium can raise blood pressure

13. Potassium
Major cation of the ICF---electroneutrality balanced by anions (proteins and
organic
phosphates like ATP, ADP, AMP)
Necessary for proper functioning of heart, nerve fibers, muscles and GI tract
Mostly acquired via diet
[K+]inside and [Na+]outside generate the membrane potential across a cell
Balance between K+ and Na+ maintained by ion pumps and cell membrane

14. Calcium
Calcium (Ca+2) is an important cation in biological systems; major
anions are HCO3-, PO4-3, SO4-
signal transducer for hormone interactions (second messenger
systems) and
neurotransmitter release , muscle contraction, capacitation
reaction (fertilization), bone formation
Bone is the main mineral storage reservoir
Intracellular Ca+2 stores are in mitochondria and the endoplasmic
reticulum

15. Magnesium
Magnesium (Mg+2) is an essential nutrient and present in every cell
adult daily requirement=300-400 mg/day
Mg+2-ATP is the biologically active form of ATP –Mg+2 facilitates activity
Mg+2 also plays a role in stability of DNA and RNA another PO4- compounds.
Over 300 enzymes require the presence of Mg+2 for catalytic activity
-all enzyme synthesizing or utilizing ATP
-synthesis of DNA and RNA
Biological membranes are impermeable to Mg+ (can close certain types of Ca+2
Hypomagnesemias—loss of balance due to muscle weakness; drug side effect
Hypermagnesemias---loss of kidney function (kidney excretes excess Mg quick

16. Bicarbonate (HCO3-)
CO2 + H2O
H2CO3
H+ + HCO3- (major blood buffering
system) Carbonic Anhydrase (CA)
Volatile Acid
Acid-base Homeostasis (pH buffering)
70-75% CO2 in body is converted to H2CO3 and then to HCO3-
-protects tissues of the CNS where pH changes are disastrous
- regulates pH in GI tract
HCO3- standard concentration in blood at a CO2 =40 mm Hg, full O2 and 37C

17. Osmolarities are equal between
compartments
Remarkably—with all the concentration differences between the ICF and ECF
the
osmolarities are equal
this is due-- in part-- because water can flow freely across cell
membranes
and between compartments
water movement in and out balances the osmolarities in the two
spaces
flows from low concentration to higher concentration

18. Basic Metabolic Panel (BMP)
Set of 7 (Chem-7) or 8 (Chem-8) chemical tests
Monitors:
electrolytes and fluid status
kidney function
 blood sugar levels
 responses to medications

19. Chem-7 or Chem-8
Four electrolytes:
Sodium (Na+)
Potassium (K+)
Chloride (Cl-)
Bicarbonate (HCO3- or pCO2)
Blood urea nitrogen (BUN)
Creatinine
Glucose
Calcium (Ca+2) Chem-8

20. Fishbone Diagram of Chem-7
Na+ Cl- BUN Blood Glucose
K+ HCO3-Creatinine
Quick reference for common values

21. Comprehensive Metabolic Panel
Fourteen Blood tests:
General: serum glucose
Kidney Function
Assessment
calcium
blood urea nitrogen
creatinine
Protein Tests: human serum albumin (HSA)
total serum protein
Liver Function
Assessment
Alkaline phosphatase (ALP)
Electrolytes: Sodium (Na+)
Alanine aminotransferase
(ALT or SPGT)
Potassium (K+)
Aspartate
aminotransferase (AST or SGOT)

22. Blood Urea Nitrogen (BUN)
Liver produces urea in the urea cycle—waste product from digestion of
protein
-Normal value 7-21 mg/dL of blood
BUN value is an indicator of renal health
if GFR and blood volume decrease (hypovalemia) then BUN will
increase

23. Lipid Panel
• Total Cholesterol
• High Density Lipoproteins (LDLs) cholesterol
• Low Density Lipoprotein (LDLs) cholesterol
• Very Low Density Lipoprotein (VLDLs)
• Triglycerides

24. Urine Dipstick:

25. Urine Specific Gravity
Urine specific gravity—measures amount of solutes dissolved in urine compare
Assessment of the kidney’s ability to concentrate or dilute urine
directly proportional to urine osmolality (solute concentration)
Normal value range: 1.002-1.035 if kidney function is normal
Decreased <1.005
-inability to concentrate urine or excessive hydration (TBW expansion fr
-nephrogenic diabetes insipidus, acute glomerulonephritis, acute tubul
-falsely low sp.gr. can be associated with alkaline urine (pH>7.4)
- after 12 fast w/o food and water, urine sp.grshuld be >1.022
if not—renal concentrating ability is impaired
-nephrogenic diabetes insipidus or generalized renal issue

26. Urine Specific Gravity
Fixed: 1.010
- the glomerular filtrate in Bowman’s Space ranges from 1.007-1.010
-measurements below tis range indicate hydration, above indicates
relative dehydration
-In End-Stage Renal Disease (ESRD) tends towards 1.010
-Chronic Renal failure, chronic glomerulonephritis
Increased: >1.035
-indicates a concentrated urine with a large volume of solutes
-dehydration (fever, vomiting, diarrhea) SIADH, adrenal insufficiency,
pre-renal renal failure, hyponatremia with edema, liver failure,
nephrotic syndrome
-elevation can also occur with glycosuria (diabetes or IV infusion)
proteinuria

27. Urine pH (4.5-8.0)
Kidneys –important role in acid-base regulation---maintain urine pH 5.5-6.5
-can vary between 4.5-8.0
Glomerular filtrate is usually acidified in nephron tubules and collecting ducts fro
a pH equivalent to plasma (7.4) to a pH of 6 in final voided urine
pH control is important in Bacteriuria, renal stones and drug therapy
High Urinary pH (alkline urine)
-vegetarian diet, low carbohydrate diet or ingestion of citrus fruit (alkali ash pro
-systemic alkalosis (metabolic or respiratory)
-renal tubular acidosis (RTA 1 distal), Fanconi anemia
-urinary tract infections (urea splitiing organisms)
-drugs (amphotercin B, CA inhibitors, salicylate OD

28. Urine pH (4.5-8.0)
Low urinary pH (Acidic urine)
- high protein diet or fruits like cranberries
-systemic acidosis (metabolic or respiratory)
-diabetes mellitus, starvation, diarrhea, malabsorption syndromes
-PKU, alkaptouria, renal tuberculosis

29. Protein
Normal daily protein excretion should not exceed 150 mg/24 h or 10 mg/100
ml
Proteinuria is production of >150 mg/day with nephritic syndrome =3.5 g/
day
True protein evaluation:
Renal- increased renal tubular secretion, increased GFR (glomerular disease),
glomerular
disease, nephrotic syndrome, malignant hypertension
Functional proteinuria (albuminuria)- fever, cold exposure, stress,
pregnancy, eclampsia,
shock, severe exercise
Other- orthostatic proteinuria, electric current injury, hypokalemia, Cushing’s

30. Leukocytes (White Cell Counts)
Determines presence of whole or lysed WBC in the urine (pyuria) by
measuring
leukocyte esterase activity
Positive leukocyte esterase correlates well with pyuria
HOWEVER: diagnosis may be missed (in up to 20% cases) if a negative
urinalysis dipstik
Is used to exclude UTI
False Positive: contaminated specimen, trichomonas vaginalis, drugs or
foods that color
the urine red (grape juice)
False Negative: intercurrent or recent antibiotic therapy (gentamicin,

31. Nitrites
Nitrates in the urine are converted to nitrites in the presence of gram-
negative bacteria
like E.coli and Klebsiella
A positive nitrites test is a surrogate marker for bacteria in urine
Positive test strongly suggests infection (but does not exclude it)
False negative: drugs or foods that color urine red

32. Blood
Dipstick is able to detect hemolyzed blood and non-lysed blood in urine
Positive: may indicate hematuria from trauma, infection, inflammation, infa
kidney stones, neoplasia, clotting disorders or chronic infection
Hemaglobinuria: maybe associated with intravascular hemolysis, burns, su
eclampsia, sickle cell crisis, multiple myeloma, alkaloids (
or transfusion reactions

33. Ketones
Ketones: (end-point of incomplete fat matabolism) accumulate in plasma
and are
excreted in the urine ---acetoacetone, aceto-acidic acid, β-
hydroxybuturate
Ketonuria is associated with low carbohydrate (high fat/protein) diets,
stravation,
Diabetes, alcoholism, eclampsia, and hyperthyroidism
Ketonuria is also associated with overdose of insulin, isonizid and
isopropyl alcohol

34. Glucose
Glucose not normally present in urine (filtered but reabsorbed in proximal
tubule)
-<0.1% of glucose filtered appears in the urine (<130 mg/24h)
Glycosuria occurs in patients with elevated glucose levels in the presence
of reduced
threshold and reduced glucose reabsorption (Tm exceeded) in renal
disese and
Pregnancy
Glucosuoria also seen with certain drugs: cephalosporins, penicillins,
methyl DOPA,
steroids and thiazides

35. Bilirubin
Bilirubin ( a product of liver function) can appear in the urine with liver diseases
and jaundice ---it may be seen before clinical signs develop
Formed by RBC degradation in the liver and then conjugated to glucuronide for
excretion in
Bile. In intestine converted to
stercobilin –excreted in feces
urobilinogen—excreted from kidney
Failure of bilirubin to reach the intestines (obstruction) will result in bilirubinuria
Positive test confirms conjugated hyperbilirubunaemia
Raised hyperbilirubinaemia with appearance in urine( bilirubinuria) ---
heptacellular disease,
Cirrhosis,viral or drug induced hepatitis, biliary tract obstruction, pancreatic
involvement with

36. Urobilinogen
Normally oresent in urine in low concentrations—0.2-1.0 mg/dL or <17
μmole/L
Urobilinogen is a product of bilirubin conversion by gut bacteria in the
duodenum
-excreted mostly in feces or transported back to liver for bile
production
-remaining is excreted in urine (<1%)
Urobilinogen concentration increases in urine of patients with: cirrhosis,
infective
hepatitis, extravascular hempysis, hemolytic anemia, pernicious anemia,
malaria,

37. Key Concepts
Intracellular and extracellular ion concentrations are different
extracellular: glucose, Na+. K+ HCO3- are a quick measure of
homeostasis
Lipids: reveal diet and genetic make-up
BUN and creatinine give you an estimate of renal function
Urine dipstick: can tell you about infection, liver and kidney function,
diabetes mellitus or
Inspidus, metabolic state of the body (starvation changes)
What are the different components of blood and a CBC panel?

38. Homework
• Know the “normal” values of the major
ICF and ECF anions and cations
(Chem panel)