Edema is due to-
**Core Concept**
Edema is a clinical manifestation characterized by the accumulation of excess fluid within the interstitial tissue spaces, leading to swelling. This condition can arise due to various factors, including increased hydrostatic pressure, lymphatic obstruction, or decreased oncotic pressure.
**Why the Correct Answer is Right**
The correct answer is related to the pathophysiology of edema, specifically the Starling forces that govern fluid movement across capillary walls. Increased capillary hydrostatic pressure (Pc) due to elevated venous pressure or cardiac failure leads to a greater force pushing fluid out of capillaries, resulting in edema. This is in accordance with the Starling equation: Q = (Pc - Pif) - (√πa - πi), where Q is the net fluid movement, Pc is capillary hydrostatic pressure, Pif is interstitial fluid pressure, πa is capillary oncotic pressure, and πi is interstitial fluid oncotic pressure.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it mentions decreased interstitial fluid oncotic pressure, which would actually reduce edema formation, not cause it.
**Option B:** This option is incorrect because it refers to lymphatic obstruction, which can indeed cause edema, but it is not the primary factor in this option.
**Option C:** This option is incorrect because it mentions increased interstitial fluid pressure, which would actually be a result of edema, not a cause.
**Clinical Pearl / High-Yield Fact**
When evaluating edema, it is essential to consider the patient's medical history, including cardiovascular diseases, kidney disorders, and liver cirrhosis, as these conditions can lead to increased capillary hydrostatic pressure and subsequent edema formation.
**Correct Answer:** D