**Core Concept**
Healthy, intact capillaries are a crucial component of the microcirculation, allowing for the exchange of oxygen, nutrients, and waste products between the bloodstream and tissues. Capillary permeability is tightly regulated to prevent excessive fluid loss and maintain tissue homeostasis. The integrity of capillary walls is essential for maintaining blood pressure and preventing edema.

**Why the Correct Answer is Right**
The correct answer is related to the fact that healthy, intact capillaries have tight junctions between adjacent endothelial cells, which prevents the free diffusion of molecules and maintains the integrity of the capillary wall. This is achieved through the presence of occluding junctions, also known as tight junctions, which are formed by the interaction of transmembrane proteins such as claudins and occludin. These tight junctions create a barrier that restricts the passage of ions and small molecules, while allowing the free diffusion of oxygen and carbon dioxide.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it suggests that healthy, intact capillaries are permeable to all types of molecules, which is not true. While capillaries do allow for the exchange of oxygen, nutrients, and waste products, they are not permeable to all types of molecules.

**Option B:** This option is incorrect because it suggests that healthy, intact capillaries are characterized by a lack of tight junctions, which is not true. Tight junctions are a critical component of healthy, intact capillaries and play a key role in maintaining the integrity of the capillary wall.

**Option D:** This option is incorrect because it suggests that healthy, intact capillaries are characterized by a high degree of permeability, which is not true. While capillaries do allow for some degree of permeability, they are not as permeable as some other types of blood vessels, such as venules.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that the integrity of capillary walls is essential for maintaining blood pressure and preventing edema. Damage to capillary walls, such as that which occurs in conditions like diabetes and hypertension, can lead to increased permeability and edema.

**Correct Answer: C.**