Which of the following is called as capacitance vessels
**Core Concept**
Capacitance vessels are a crucial component of the vascular system, responsible for regulating blood volume and pressure. These vessels are characterized by their thin walls, allowing them to distend and accommodate large volumes of blood. The capacitance function is primarily maintained by the venous system, with the majority of capacitance vessels being veins.
**Why the Correct Answer is Right**
Capacitance vessels, particularly veins, have a unique property that enables them to act as blood reservoirs. When blood pressure increases, these vessels distend, increasing their capacitance and allowing blood to seep into the surrounding tissues. This process helps to maintain blood pressure within a narrow range. The venous system, comprising over 60% of the total vascular bed, plays a vital role in regulating blood volume and pressure.
**Why Each Wrong Option is Incorrect**
**Option A:** Arteries are not considered capacitance vessels, as they have thicker walls and are primarily involved in conducting blood away from the heart. They do not have the same degree of distensibility as veins.
**Option B:** Capillaries are too narrow and have too little blood volume to act as capacitance vessels. Their primary function is to facilitate the exchange of oxygen, nutrients, and waste products between the blood and tissues.
**Option C:** Venules are a subset of veins but are not typically considered capacitance vessels. They are smaller in diameter and have a higher resistance to blood flow compared to larger veins.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that the capacitance function is primarily maintained by the venous system. This is why veins are often affected in conditions such as congestive heart failure, where the body's ability to regulate blood volume and pressure is compromised.
**Correct Answer: D. Veins**