Edema (Oedema) - Body Swelling

What is Edema?

Edema is the medical term for swelling caused by excess fluid accumulating in the body's tissues. About 60% of lean body weight is water; normally, fluid balance between blood vessels and surrounding tissue is tightly regulated. When this balance is disturbed, fluid leaks into the interstitial (tissue) space and causes swelling.

When fluid collects in a body cavity it is called an effusion: hydrothorax (pleural cavity), hydropericardium (pericardial cavity), or ascites (abdominal/peritoneal cavity)
Anasarca is the most severe form - generalized, whole-body edema with profound swelling of subcutaneous tissues and fluid in multiple body cavities

How Edema Forms - The Mechanism

Two main opposing forces normally keep fluid in balance (Robbins & Kumar Basic Pathology):

Hydrostatic pressure - blood pressure pushes fluid OUT of capillaries into tissue
Colloid osmotic (oncotic) pressure - plasma proteins (mainly albumin) pull fluid BACK into capillaries

Normally, the tiny net outflow of fluid is drained back by lymphatic vessels. Edema develops when:

Hydrostatic pressure increases too much, OR
Osmotic pressure decreases (low protein), OR
Lymphatics are blocked and cannot drain

Causes of Edema

Category	Examples
Increased hydrostatic pressure	Congestive heart failure, liver cirrhosis, deep vein thrombosis, venous obstruction, prolonged immobility
Reduced plasma proteins (hypoproteinemia)	Nephrotic syndrome (kidney disease), advanced liver disease, malnutrition, protein-losing gut disease
Lymphatic obstruction	Inflammation, cancer, post-surgery, radiation damage
Sodium retention	Renal insufficiency, excess salt intake, increased aldosterone
Inflammation	Acute/chronic infection, injury, angiogenesis

Types of Edema (by location)

Type	Where it occurs	Key feature
Peripheral/Dependent edema	Legs, ankles, feet	Worsens with standing; leaves a finger dent (pitting edema)
Periorbital edema	Around the eyes	Seen in kidney disease (nephrotic syndrome)
Pulmonary edema	Lungs	Lungs become 2-3x heavier; frothy sputum; can be fatal
Cerebral edema	Brain	Life-threatening; can cause brain herniation and death
Anasarca	Whole body	Severe, generalized; seen in heart/kidney/liver failure
Ascites	Abdominal cavity	Fluid in the belly; common in cirrhosis
Lymphedema	Arms/legs	Due to blocked lymphatics; non-pitting, firm

Common Diseases Causing Whole-Body Swelling

Heart failure - the heart cannot pump effectively, fluid backs up
Kidney disease (nephrotic syndrome) - protein leaks into urine, low blood protein causes swelling
Liver cirrhosis - reduced albumin production + portal hypertension
Malnutrition (kwashiorkor) - severe protein deficiency
Deep vein thrombosis - blocked veins cause local swelling
Allergic reactions (angioedema) - histamine causes rapid swelling, especially face/throat
Hereditary angioedema - C1 inhibitor deficiency causes uncontrolled fluid leakage into tissues (per Janeway's Immunobiology)
Hypothyroidism (myxedema) - non-pitting swelling from mucopolysaccharide deposits

Pitting vs. Non-Pitting Edema

Pitting edema: Pressing a finger leaves an indent. Caused by simple fluid - seen in heart, kidney, liver disease.
Non-pitting edema: No indent left. Caused by protein/cellular deposits - seen in lymphedema, myxedema (thyroid disease).

Clinical Significance

Subcutaneous edema often signals underlying cardiac or renal disease and impairs wound healing
Pulmonary edema can be life-threatening, interfering with breathing and predisposing to pneumonia
Brain edema is a medical emergency - can cause brain herniation and death

- Robbins & Kumar Basic Pathology, pp. 77-78

In summary: The main condition where the body swells up is edema, which results from excess fluid in tissues. Its cause determines the treatment - whether addressing heart failure, kidney disease, low protein, blocked lymphatics, or inflammation.

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