**Core Concept:** Increased capillary permeability is a pathological condition where the blood capillaries lose their selective barrier function, leading to extravasation of plasma proteins, cells, and fluid into the surrounding tissues. This can result from various factors like inflammation, infection, or injury.

**Why the Correct Answer is Right:** Option D, "Increased vascular permeability", is the correct answer because it refers to the condition where the capillary permeability is increased due to factors like inflammation, infection, or injury. This leads to extravasation of plasma proteins, cells, and fluid into the surrounding tissues.

**Why Each Wrong Option is Incorrect:**

A. "Contraction of smooth muscle": While smooth muscle contraction does play a role in the regulation of capillary permeability, it is not the primary cause of increased capillary permeability.

B. "Increased vascular tone": Increased vascular tone affects blood flow and distribution, but does not directly cause increased capillary permeability.

C. "Increased vascular permeability": This option is incorrect because increased vascular permeability directly causes increased capillary permeability and is not the correct answer.

**Clinical Pearl / High-Yield Fact:** In clinical scenarios like sepsis or septic shock, increased capillary permeability contributes to the development of the "shock syndrome" by causing plasma leakage and hypovolemia, which can lead to hypotension and tissue hypoperfusion.

**Correct Answer:** D. Increased vascular permeability