Case Scenario 1:
A 48-year-old female patient came to the OPD with complaints of depressed mood, irritability, and dark yellow urine. Her lab reports show:
- Sodium (Na⁺): 132 mEq/L
- Potassium (K⁺): 4.0 mEq/L
- Elevated Antidiuretic Hormone (ADH) levels
- a.What is the most probable diagnosis based on the given findings?
b. Describe the regulation of water and electrolyte balance.
d. Mention any three roles of water in the human body.
Answer:
a. Probable Diagnosis: Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH).
- This condition leads to excess ADH, causing water retention.
- Result: Dilutional hyponatremia (Na⁺ = 132 mEq/L, below normal).
- Symptoms such as irritability, mood changes, and concentrated urine are consistent with SIADH.
- b. Regulation of Water and Electrolyte Balance:
Water and electrolyte balance is maintained through hormonal and renal mechanisms:
- Antidiuretic Hormone (ADH):
- Secreted by posterior pituitary.
- Increases water reabsorption in distal tubules and collecting ducts of kidneys.
- Triggered by increased plasma osmolality or decreased blood volume.
- Aldosterone:
- Secreted by adrenal cortex.
- Increases Na⁺ reabsorption and K⁺ excretion in the kidneys.
- Renin-Angiotensin-Aldosterone System (RAAS):
- Activated by low blood pressure or sodium.
- Promotes aldosterone release, thus conserving Na⁺ and water.
- Atrial Natriuretic Peptide (ANP):
- Secreted by atria in response to high blood volume.
- Promotes natriuresis (Na⁺ excretion) and water loss.
- Thirst Mechanism:
- Triggered by osmoreceptors in the hypothalamus, stimulating water intake.
- c. Roles of Water in the Human Body:
- Solvent:
- Acts as a universal solvent for biochemical reactions.
- Transport Medium:
- Helps transport nutrients, hormones, and waste products.
- Thermoregulation:
- Maintains body temperature through sweating and heat exchange.
- Lubrication and Protection:
- Present in synovial fluid, cerebrospinal fluid, etc.
- Maintaining Cell Shape and Turgor:
- Provides structural support to cells.
Case Scenario 2:
A 66-year-old man was brought to the Emergency Department with severe vomiting and diarrhoea. On examination, he had low blood pressure, dry and shriveled lips and tongue, and lax skin turgor. Laboratory tests revealed electrolyte imbalance.
a. What is the most likely diagnosis based on the clinical picture?
b. Compare the composition of major electrolytes in extracellular and intracellular fluid.
c. Define dehydration and classify its types.
Answer:
a. Probable Diagnosis:
The most likely diagnosis is dehydration with electrolyte imbalance due to fluid loss from vomiting and diarrhoea.
Signs include:
- Hypotension (due to fluid volume depletion)
- Dry mucous membranes and skin turgor loss
- Electrolyte disturbances (commonly Na⁺, K⁺, Cl⁻ losses)
- b. Comparison of Electrolyte Composition:
| Electrolyte | Extracellular Fluid (ECF) | Intracellular Fluid (ICF) |
| Na⁺ (Sodium) | High (~140 mEq/L) | Low (~10–15 mEq/L) |
| K⁺ (Potassium) | Low (~4–5 mEq/L) | High (~140 mEq/L) |
| Cl⁻ (Chloride) | High (~100 mEq/L) | Low (~2–10 mEq/L) |
| HCO₃⁻ (Bicarbonate) | High (~24 mEq/L) | Low (~10 mEq/L) |
| Mg²⁺ and Phosphates | Low | High |
| Proteins | Low in plasma; absent in ISF | High |
c. Dehydration:
Definition:
Dehydration is the excessive loss of body water, with or without electrolyte loss, leading to an imbalance in fluid compartments.
Types of Dehydration:
- Isotonic Dehydration (most common):
- Equal loss of water and electrolytes (e.g., diarrhea).
- No shift between ECF and ICF.
- Hypertonic Dehydration:
- Greater water loss than sodium (e.g., fever, sweating, diabetes insipidus).
- Water shifts from ICF → ECF → cell shrinkage.
- Hypotonic Dehydration:
- Greater sodium loss than water (e.g., Addison’s disease, diuretic overuse).
- Water shifts from ECF → ICF → ECF volume decreases further.