MLT130 CC Osmolality & Electrolytes & Trace Elements

What are the 2 major body compartments (at cellular level)?

1. Intracellular fluid (ICF) 2. Extracellular fluid (ECF)

Four Colligative Properties

1. Vapor pressure depression 2. Boiling point elevation 3. Melting point depression 4. Osmotic pressure

Osmolality Reference Range

275-295 mOsm/kg (milliosmoles per kilogram)

Bicarbonate (HCO₃)

2nd major EC anion Sometimes ordered as Total CO₂ RR = 22-28 mmol/L 95% total plasma CO₂ is bicarbonate

Normal Urine Concentration

300-900 mOsm/kg. can range from 50-1200 MOsm/kg due to kidney\'s ability to concentration/dilute urine to maintain tight control of plasma osm.

Total Body Water

50-60% body weight in males 45-50% in females (more fat cells)

Function of ADH on the kidneys

ADH acts in the distal portion of the renal tubule (Distal Convoluted Tubule) as well as on the collecting duct and causes the retention of water, but not solute. ADH activity effectively dilutes the blood (decreasing the concentrations of solutes such as sodium).

Major body anions

Chlorine (Cl⁻) bicarbonate or hydrogen carbonate (HCO₃⁻) Hydrogen Phosphate (HPO₄⁻2) Sulfate (SO₄ ⁻2)

Hypernatremia

Dehydrated - blood is dry. Increased blood levels of sodium, is associated with values of >150 mmol/L and is always hyperosmolar, (a greater deficiency of EC than of sodium)

Low Na = Dilutional

Dilutional = high water which appears that low Na Ex. decrease OSM

Low levels of Osmolality - disorders

Excessive fluid intake Hyponatremia Overhydration Paraneoplastic Syndromes assoc. with lung cancer Syndrom of inappropriate ADH secretion

Osmolal Gap RR

Gap <10 mOsm/kg = NOT normal Gap >30 mOsm/kg = grave prognosis (↑↑ alcohol)

ADH (antidiuretic hormone)

High levels of ADH prevent urination Low levels of ADH body produces large levels of urine

ANP (Atrial natriuretic peptide)

Hormone that has opposite effect from aldosterone. High BP in heart, ANP gets release from atria which increases GFR & decrease Na reabsorption in nephrons which promotes rapid diuresis & Na excretion (natriuresis) in response to persistent hypervolumia

What are the major contributors to OP in each compartment?

ICF = Potassium (K+) ECF = Sodium (NA+) IV = plasma proteins (esp. albumin) = oncotic pressure

Hypokalemia Process

In metabolic alkalosis, K+ moves from ECF into the cells as H+ moves in the opposite direction.

Causes of Hypernatremia

Ingestion of large amount of sodium salts admin of hyperton NaCl or NaHCO3 primary hyperaldosteronism (conn syndrome) excessive sweating diabetes insipidus osmotic diuresis

ECF has 2 subdivisions

Interstitial Fluid Intravascular (IV) fluid

Electrolytes

Ions are charged particles. Substances that dissociate into ions when placed in solution.

FP depression occurs because...

It is important to realize that freezing point depression occurs because the concentration of water molecules in a solution is less than the concentration in pure water. The nature of the solute doesn\'t matter.

Renin-Angiotensin-Aldosterone Pathway

JGA cells sense low plasma volume/low BP in afferent arteriole. this releases renin which converts angiotensin to stimulate aldosterone to be released from AC, which increases NA reabsorption in DCT/CT in exchange for potassium excretion which increases plasma Na+, water follows to increase volume & BP

Potassium Regulations

Kidney can regulate increase K+ so it directly activates aldosterone. Kidney regulates EC K+ filtered glom to reabsorbed in PCT.

Chloride

Major EC anion RR = 99-109 mmol/L Chloride function w/Na+ to maintain water & OP balance, therefore [CL-] changes with [Na+] wieh fludi shifts between ICF & ECF

Potassium

Major intracellular cation (98% within cells) Plasma K+ = Low. RR 3.5-5.0 mmol/L NA+/K+ pump keeps NA+ EC K& K+ IC in balance (Na-K-ATPase Pump) Body uses more ATP to run NA+/K pump for any other energy required function.

Measuring Osmolality

Measure colligative properties = proteries affected by number of particles in solution (freezing, point, boiling point, vapor pressure) Common method = Freezing point depression Instrument = osmometer

Osmolality/Osmolarity

Measure of number of dissolved particles (solutes) in a solution

Hypokalemia Conditions

Metabolic alkalosis, diuretic admin, increased GI loss, increase urinary loss.

Hyponatremia

Na <136 mmol/L = refection of Na:plasma volume ratio, not total body Na content

Regulation of body sodium performed by kidneys

Na filters thru glomerulus and 70% of NA is reabsorbed by AT in PCT. NA reabsorption in DCTR/CT under aldosterone control.

RR - Rule of 4

Na+ 140 K+ 40 Cl¯ 104 HCO₃ 24

Distribution 4 Major Electrolytes

Na⁺ = major extracellular cation K⁺ = major intracellular cation Cl⁻ = major extracellular anion HCO₃ = both in/out (ECF>ICF)

Four major electrolytes

Na⁺, K⁺, Cl⁻, HCO₃⁻ (total CO₂) These 4 are measured on lytes order

Anions

Negative charge ion

What happens when osmolality is increased?

OSM increases, the body releases ADH, this causes kidneys to reabsorb H₂O, resulting in more concentrated urine. the reabsorbed H₂O dilutes the blood, allowing to fall back to normal.

Hypertonic - OSM

OSM level high (increased sodium) in ECF the solute increases in ECF the water decreases to ICF water shifts from ECF to ICF to est. osmotic balance. Cells may SHRINK)

Hypotonic - OSM

OSM level low (decreased sodium) in ECF the solute decreases in ECF the water increases to ICF water shifts from ECF to ICF to re-establish osmotic balance. (Cells May SWELL)

osmolal gap

Osmolal Gap = Measured osmolality-calculated osmolality. an increased osmolal gap indicates presence of unaccounted solutes, which include ingested volatiles such as methanol, ethylene glycol, and isopropanol, high trig., high proteins. -increased gaps are also observed in metabolic conditions e.g. ketoacidosis, presence of ketone bodies adds to the measured osmolality

Dilutional Hyponatremia

Patients who retain excess water in assoc with weight gain or excess edema

Cations

Positive charge ion

Calculate Plasma Osmolality from NA, Glu, Urea

Posm = 1.86[NA+] + [glucose]/18 + [bun]/2.8 +9

Sodium = Major ECF cation

RR plasma = 136-145 mmol/L (mEq/L) Function: maintain H2O distribution & plasma OP (osmotic pressure). Sodium also functions with (K+) to maintain resting membrane potential & allow neuromuscular excitability in muscle & nerve cells.

Potassium Functions

Regulates many cells processes (enzyme co-factor) Neuromuscular excitability: resting membrane potential depends on proper ratio of EC NA+ to IC K+ (balance resting potential)

Principle of FP depression

Serum (or urine) placed in controlled cooling bath becomes supercool to -7°C (below FP) - it is vibrated rapidly which releases heat of fusion the sample reaches FP the you measure FP temp

What are the two molecules that are major contributors to osmotic (plasma) pressure of ECF

Sodium & chloride (NaCl)

Major Body Cations

Sodium (NA⁺) Potassium (K⁺) Magnesium (Mg ⁺2) Calcium (Ca⁺2)

Sodium functions

Sodium also functions (with potassium) to maintain resting membrane potential & allow neuromuscular excitability in muscle & nerve cells

Who are the contributors that maintain plasma osmolality?

Sodium, Water, ADH Glucose & Urea

Major contributor to osmolality in ECF

Sodium. high or low levels of sodium - levels of water increase/decrease, to maintain osmotic balance - net movement of water into cells -> cells either shrink or swell

Hormone ANP, BNP, CNP

Stimulus: ↑ ECF Site: collecting duct Effect: ↓NaCl & H₂O reabsorption

Hormone ADH

Stimulus: ↑ Plasma osmol ↓ ECF Site: distal tubule & collecting duct Effect: ↑ H₂O reabsorption

Hormone Aldosterone

Stimulus: ↑Angiotensin II, ↑ plasma K⁺ Site: distal tubule, collecting ducts Effect: ↑ NaCL & H₂O reabsorption

Hormone Urodilatin

Stimulus: ↑ECF Site: collecting duct Effect: ↓NaCl & H₂O reabsorption

Hormone Angiotensin II

Stimulus: ↑renin Site: Proximal tubule Effect: ↑ NACl & H₂O reabsorption

Decreased ECF Sodium

Symptoms of low Na not evident til <125mmol/L. Decrease ECF Na which causes water shifts in ECF to ICF causing braine cells to swell, severe symptoms

SIADH

The syndrome of inappropriate antidiuretic hormone hypersecretion (SIADH). Excessive release of antidiuretic hormone (ADH or vasopressin) from the posterior pituitary gland or another source. The result is hyponatremia and sometimes fluid overload. Found in patients diagnosed with pneumonia, brain tumors, head trauma, strokes, meningitis, encephalitis, or small-cell carcinoma of the lung.

Major contributors of OP can upset?

any of the major contributors in OP (K+, NA+, IV) When any of these have an upset balance of solutes in each compartment - this will lead to change in water distribution to balance osmotic pressure

Interstitial fluid

between cells & outside cells, by no within blood vessels; separated from ICF by plasma membrane (PM)

Colligative Properties

colligative properties of solutions are properties that depend upon the concentration of solute molecules or ions, but not upon the identity of the solute.

Sodium - decrease ↓ plasma Na⁺

decrease in sodium = decrease plasma osm (↓solute ↑H₂O in ECF) causes H₂O to move from ECF to ICF to equalize OP - which leads to decreased plasma volume

OSM increases with ...

dehydration

High Levels of Osmolality - disorders

dehydration, diabetes insipidus ethylene glycol poisoning, hyperglycemia hypenatremia, Uremia Methanol poisoning stroke or head trama resulting in dificient ADH secretion

Low Na = Depletional

depletional = renal or nonrenal loss = true NA loss

Low Na - artifactual (pseudo)

displacement of plasma water due to thigh lipids or proteins

Major \"lytes\" in ECF & ICF

each compartment (ICF & ECF) = electroneutral where sum positive = sum negative.

Hyponatremia

hypo [deficiency] + new latin natrium [sodium] + emia [blood]

Depletional-type hyponatremia - name conditions

hypoosmotic hyponatremia - due to excessive loss of Na. Also, osmotic diuresis, adrenal insufficiency & diuretics

Sodium - increase ↑ plasma Na⁺

increase in sodium will increase plasma osm (↑ solute ↓H₂O in ECF) causes H₂O to move from ICF to ECF which leads to increased plasma volume

ICF (intracellular fluid)

inside cell

Electrolytes (lytes)

ions that carry electric charge; substances that dissociate into ions when placed in solution

Osmolality

is a test that measures the concentration of all chemical particles found in the fluid part of blood. (plasma osmolality)

Dilutional Hyponatremia conditions

liver failure, congestive heart failure (CHF), renal failure, nephrotic syndrome, inappropriate ADH secretion

ECF (extracellular fluid)

outside cell

OSM decreases with ...

overhydration

Hypokalemia

plasma K+ concentration <3.5 mmol/L. Is caused by movement of K+ into the cell from the ECF space, increased output, or decreased intake.

Osmotic Pressure (OP)

presence of solutes (especially lytes) holding water in a compartment (water follows solute)

ADH

related mechanism: increases water reabsorption in response to high plasma osmolality

Osmotic Pressure (OP)

water moves randomly between compartments by osmosis (from high conc. to low conc. across semiperm. membrane.

Intravascular Fluid (IV)

within blood vessels (capillaries surround cells/tissue beds); separated from interstitial by capillary wall