Blood flow from arteries to capillaries is regulated by

Options

A. arterioles
B. pre capillary sphincters
C. valves in the heart
D. tunica externa of arteries

Answer

To solve the question "Blood flow from arteries to capillaries is regulated by," we will analyze the options provided and determine which one correctly identifies the mechanism of regulation.

### Step-by-Step Solution:

1. **Understanding Blood Flow Regulation**: Blood flow from arteries to capillaries is influenced by various structures in the circulatory system. The regulation of blood flow is crucial for ensuring that tissues receive adequate oxygen and nutrients.

2. **Analyzing the Options**:
- **Option 1: Arterioles**: Arterioles are small blood vessels that lead from arteries to capillaries. They have muscular walls that can constrict or dilate, thereby regulating blood flow and pressure. This makes them a key player in controlling blood flow to capillary beds.
- **Option 2: Pre-capillary Sphincters**: These are rings of smooth muscle located at the junction of arterioles and capillaries. They can open or close to regulate blood flow into the capillary beds, but they primarily control flow at the capillary level rather than from arteries to capillaries.
- **Option 3: Bulbs in the Heart**: This option is not relevant as "bulbs" are not a recognized term in the context of blood flow regulation. The heart does pump blood but does not directly regulate flow from arteries to capillaries.
- **Option 4: Tunica Externa of Arteries**: The tunica externa is the outer layer of blood vessels and provides structural support. It does not play a direct role in regulating blood flow.

3. **Selecting the Correct Answer**: Given the analysis, arterioles (Option 1) are the primary regulators of blood flow from arteries to capillaries due to their ability to constrict and dilate, thus controlling the volume of blood that enters the capillary beds.

### Final Answer:
The correct answer is **Option 1: Arterioles**.

---