BIO 304 · Human Anatomy & Physiology
Fluid, Electrolyte & Acid-Base Balance
Urinary System · Module 15
A reference for the Fluid & Acid-Base video. Body fluid lives in compartments. Electrolytes are the ions that matter. Acid-base balance is a fast respiratory layer plus a slow renal layer working together.
How to use this sheet Toggle the toolbar above. Notes prints the full reference for review. Study prints as a fill-in-the-blank worksheet , print it, then write each definition while you watch the video or read your book. Quiz me is on-screen typing practice; type the term, click Reveal to check yourself.
- Distinguish intracellular fluid from extracellular fluid by volume and composition.
- Identify the major roles and regulators of sodium, potassium, calcium, and phosphate.
- Classify an acid-base disturbance as metabolic or respiratory and acidosis or alkalosis.
Click any image to enlarge.
Fluid & Electrolytes
Body fluid (60% of body weight)
- Intracellular fluid (ICF, ~40%)high K+, phosphate, Mg²⁺, protein
- Extracellular fluid (ECF, ~20%)high Na+, Cl-, HCO₃-
- Plasma (~5%)ECF inside blood vessels; has plasma proteins
- Interstitial (~15%)ECF outside vessels; bathes cells
Sodium (Na+)
- Normal serum135-145 mEq/L
- Main extracellular cationsets ECF osmolarity
- RegulatorsADH (water), aldosterone (Na+ reabsorption), ANP (Na+ excretion)
- Hyponatremiacerebral edema; seizures if rapid
- Hypernatremiacellular shrinkage; thirst
Potassium (K+)
- Normal serum3.5-5.0 mEq/L
- Main intracellular cationtiny serum changes have big effects
- Regulatoraldosterone (excretion); insulin (intracellular shift)
- Hypokalemiaflat T waves, U waves, muscle weakness, arrhythmia
- Hyperkalemiapeaked T waves, wide QRS, cardiac arrest
Calcium (Ca²⁺)
- Normal serum8.5-10.5 mg/dL (or ionized 1.1-1.3 mmol/L)
- 99% in bone1% in blood; ionized fraction biologically active
- RegulatorsPTH (raises Ca²⁺), calcitonin (lowers, minor), vitamin D (gut absorption)
- Hypocalcemiatetany; Chvostek/Trousseau signs; QT prolongation
- Hypercalcemiastones, bones, groans, psychiatric overtones
Phosphate (PO₄³-)
- Inversely related to Ca²⁺PTH lowers phosphate
- Vital in bone & ATPenergy currency
Acid-Base
Normal values
- Arterial pH7.35-7.45 (tight!)
- PaCO₂35-45 mmHg (respiratory component)
- HCO₃-22-26 mEq/L (metabolic component)
Buffer systems (instant)
- Bicarbonate (HCO₃-/H₂CO₃)main extracellular buffer
- Phosphateintracellular and urinary
- Protein (hemoglobin, plasma)absorbs or releases H+
Respiratory regulation (minutes)
- Hyperventilationblows off CO₂; raises pH
- Hypoventilationretains CO₂; lowers pH
- Driven bymedullary chemoreceptors sensing CSF pH
Renal regulation (hours to days)
- Excretes H+as titratable acid (phosphate buffer) and ammonium
- Reabsorbs HCO₃-or generates new HCO₃- as needed
- Slower but finallong-term compensator
Four primary disturbances
- Metabolic acidosispH low, HCO₃- low · DKA, lactic acidosis, renal failure, diarrhea
- Metabolic alkalosispH high, HCO₃- high · vomiting, diuretics, hyperaldosteronism
- Respiratory acidosispH low, PaCO₂ high · COPD, narcotics, NM disease
- Respiratory alkalosispH high, PaCO₂ low · anxiety, salicylates, high altitude
Anion gap
- AG = Na+ - (Cl- + HCO₃-)normal ~12
- High AG metabolic acidosisMUDPILES — methanol, uremia, DKA, propylene glycol, INH, lactic acidosis, ethylene glycol, salicylates
- Normal AG (hyperchloremic)diarrhea, RTA
Step 3 . Retrieval check
Now explain it back, in your own words.
In 60 words or more, pull together what the video just taught you. Include the key concepts. This is the point where the learning actually sticks. After you submit, your spaced-recall cards for this topic unlock.
Zoomed image
Spaced recall unlocked
Nice work finishing the video.
Your spaced-recall cards for this topic are ready. Open the pre-work to activate them and start drilling.