Capillary Bed Diagram – Metarteriole, Sphincters, Venule

All 9 parts on the diagram

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The capillary bed 6

Arteriole Its bands of smooth muscle can narrow it to control the flow.
Metarteriole It feeds the capillaries and runs on into the thoroughfare channel.
Precapillary sphincters Smooth muscle rings that open and close to let blood into capillaries.
Capillaries Their walls are one cell thick, so gases and nutrients pass through.
Thoroughfare channel Blood can take it and bypass the capillaries when the sphincters close.
Venule Capillaries drain into venules, which join to form veins.

Kinds of capillary 3

Continuous capillary The most common kind; the cells are joined with only small gaps.
Fenestrated capillary The pores let more fluid through, as in the kidney and gut.
Sinusoid capillary Large gaps let even blood cells and proteins through. As in the liver and bone marrow.

How this list was compiled: Every name and detail checked on 2026-09-29 against OpenStax Anatomy and Physiology 2e, section 20.1 Structure and Function of Blood Vessels (arteriole, metarteriole, precapillary sphincters, capillary bed, thoroughfare channel, venule; continuous, fenestrated and sinusoid capillaries and where each is found), https://openstax.org/books/anatomy-and-physiology-2e/pages/20-1-structure-and-function-of-blood-vessels, and against Wikipedia, text only: Capillary, Metarteriole and Precapillary sphincter. Licence: own work

The drawing: Drawn for this site on 2026-09-29 from plain geometry; nothing traced. Licence: own work

How it works

A capillary bed is the network where blood from an arteriole reaches the tissues before it drains into a venule. The top drawing is one bed; the bottom one cuts three kinds of capillary across.

Read the full guide

Follow the blood, then compare the walls

Numbers 1 to 6 follow the blood through a bed: in through the arteriole and metarteriole, past the precapillary sphincters into the capillaries, or straight on through the thoroughfare channel, and out through the venule. Numbers 7 to 9 are the three kinds of capillary wall, from tightest to leakiest.

Sphincters open, blood fills the capillaries; sphincters close, blood takes the thoroughfare channel past them.

Questions and answers

What is a capillary bed?

A network of capillaries between an arteriole and a venule. Blood enters through the metarteriole, passes through the capillaries where exchange with the tissues happens, and leaves through the venule.

What do precapillary sphincters do?

They are rings of smooth muscle at the start of each capillary. When they relax, blood flows into the capillaries; when they contract, blood bypasses them through the thoroughfare channel.

What are the three types of capillaries?

Continuous capillaries, the most common, with an unbroken wall; fenestrated capillaries, with pores, found in the kidneys and gut; and sinusoid capillaries, with wide gaps, found in the liver and bone marrow.