Which of the following is the most common site of peripheral resistance in the systemic circulation?

Question

Accepted Answer

A. Arterioles. ## Vascular Resistance Distribution

**Key Point:** Arterioles are responsible for approximately 60% of total peripheral resistance in the systemic circulation, making them the primary site of vascular resistance regulation.

### Resistance by Vessel Type

| Vessel Type | % of Total Resistance | Diameter | Wall Thickness | Function |
|---|---|---|---|---|
| Arteries | ~10% | Large | Thick | Pressure reservoir |
| **Arterioles** | **~60%** | Small | Muscular | **Primary resistance site** |
| Capillaries | ~20% | Smallest | Thin | Exchange |
| Venules | ~5% | Small | Thin | Drainage |
| Veins | ~5% | Large | Thin | Capacitance |

### Mechanism of Arteriolar Resistance

**High-Yield:** Resistance is inversely proportional to the fourth power of radius: $R = \frac{8\eta L}{\pi r^4}$ (Poiseuille's law). Small changes in arteriolar diameter produce massive changes in resistance.

1. **Structural features** — Arterioles have thick, muscular walls rich in smooth muscle
2. **Sympathetic innervation** — Dense autonomic nerve supply allows rapid vasoconstriction/vasodilation
3. **Metabolic responsiveness** — Direct response to local metabolic factors (O₂, CO₂, H⁺, adenosine)
4. **Pressure gradient** — Arterioles experience the largest pressure drop (~60 mmHg) across the vascular tree

### Clinical Pearl

Antihypertensive drugs (ACE inhibitors, ARBs, calcium channel blockers, alpha-blockers) primarily target arteriolar smooth muscle to reduce peripheral resistance and lower blood pressure.

**Mnemonic:** **RAVE** — Resistance occurs At Vessels that are small and muscular = **Arterioles** are the primary site of Vascular resistance in the systemic circulation.

Answer

B. Capillaries

Answer

C. Venules

Answer

D. Arteries

Which of the following is the most common site of peripheral resistance in the systemic circulation?

Explanation

Vascular Resistance Distribution

Resistance by Vessel Type

Mechanism of Arteriolar Resistance

Clinical Pearl

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Vessel Type	% of Total Resistance	Diameter	Wall Thickness	Function
Arteries	~10%	Large	Thick	Pressure reservoir
Arterioles	~60%	Small	Muscular	Primary resistance site
Capillaries	~20%	Smallest	Thin	Exchange
Venules	~5%	Small	Thin	Drainage
Veins	~5%	Large	Thin	Capacitance