Pathology Cheat Sheet
Fluid Follows Forces
Oedema, hyperaemia and congestion for NEET-PG: Starling forces, transudate vs exudate, nutmeg liver, brown induration, and cardiac heart failure cells.
MedNext Academy | 3 min read
Fluid Follows Forces
Oedema, hyperaemia and congestion for NEET-PG: Starling forces, transudate vs exudate, nutmeg liver, brown induration, and cardiac heart failure cells.
Oedema, hyperaemia and congestion: how disturbed Starling forces and blood flow produce fluid shifts and tissue changes.
High-yield lines
- At the arterial capillary end hydrostatic pressure exceeds oncotic pressure and fluid leaves, while at the venous end oncotic pressure draws most of it back.
- Transudate is protein-poor fluid with specific gravity below 1.012 from altered haemodynamic forces.
- Exudate is protein-rich inflammatory fluid with specific gravity above 1.020 and many cells.
- Increased hydrostatic pressure from heart failure or venous obstruction and reduced oncotic pressure from hypoalbuminaemia both produce transudative oedema.
- Nephrotic syndrome causes oedema through urinary albumin loss and consequent low plasma oncotic pressure.
- Lymphatic obstruction, as in filariasis or after lymphadenectomy, produces protein-rich lymphoedema.
- Hyperaemia is active arteriolar dilatation giving warm red tissue, whereas congestion is passive impaired venous outflow giving cool dusky tissue.
- Chronic pulmonary congestion produces brown induration with haemosiderin-laden heart failure cells that are Prussian blue positive.
- Chronic hepatic congestion in right heart failure produces the nutmeg liver with dark centrilobular zones and pale periportal parenchyma.
- Petechiae are pinpoint haemorrhages under 2 mm associated with thrombocytopenia or vasculitis.
- The renin-angiotensin-aldosterone system drives secondary sodium and water retention that worsens oedema in cardiac and renal failure.
- Anasarca is severe generalised oedema, and fluid in serous cavities is termed an effusion.
Mapped competency codes
- PA6.1
- PA6.2
Continue into the full chapter
This summary maps to PA6-hemodynamic-disorders.
Frequently Asked Questions
How do transudate and exudate differ?
Transudate is protein-poor with specific gravity below 1.012 from altered hydrostatic or oncotic pressure, while exudate is protein-rich with specific gravity above 1.020 and abundant cells from inflammation.
What causes the nutmeg liver?
Chronic passive venous congestion, usually from right heart failure, producing dark congested centrilobular zones alternating with paler periportal parenchyma.
What are heart failure cells?
Haemosiderin-laden alveolar macrophages seen in chronic left heart failure or mitral stenosis, staining positive with Prussian blue.
Why does nephrotic syndrome cause oedema?
Heavy urinary loss of albumin lowers plasma oncotic pressure, so fluid is not drawn back into capillaries and accumulates in the interstitium.
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