Capillary Diagram – Continuous, Fenestrated and Sinusoid

All 10 parts on the diagram

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Continuous capillary 7

Lumen In the narrowest capillaries one red blood cell only just squeezes through.
Red blood cell Also called an erythrocyte. It is drawn here to show how small a capillary is.
Endothelial cell A capillary wall is a single layer of endothelial cells. In the smallest capillaries one cell wraps right round to meet itself.
Basement membrane The endothelium rests on it. In a continuous and a fenestrated capillary it is complete. It is also called the basal lamina.
Intercellular cleft Water and other very small molecules pass through these clefts. They move between the blood plasma and the tissue fluid.
Tight junction Tight junctions join the endothelial cells. In most capillaries they are incomplete, which leaves the clefts; in the brain they seal the gap.
Transport vesicles They carry material across the cell. Continuous capillaries outside the brain are rich in them.

Fenestrated and sinusoid 3

Fenestrations (pores) Fenestrations make a capillary permeable to larger molecules. Fenestrated capillaries are common in the small intestine and the kidneys.
Intercellular gaps A sinusoid has large gaps between its endothelial cells. They are wide enough for plasma proteins and even cells to pass.
Incomplete basement membrane In a sinusoid it does not go all the way around. Sinusoids are found in the liver, spleen and bone marrow.

How this list was compiled: Every name and detail checked on 2026-09-30 against OpenStax Anatomy and Physiology 2e, section 20.1 Structure and Function of Blood Vessels (capillaries: endothelial layer, basement membrane, lumen, tight junctions, intercellular clefts, transport vesicles, fenestrations, sinusoids with intercellular gaps and incomplete basement membranes, and where each type is found), https://openstax.org/books/anatomy-and-physiology-2e/pages/20-1-structure-and-function-of-blood-vessels, and against Wikipedia, Capillary and Lumen (anatomy), text only. Licence: own work

The drawing: Drawn for this site on 2026-09-30 from plain geometry; nothing traced. Not to scale. Licence: own work

How it works

The first drawing cuts a continuous capillary across and enlarges a piece of its wall. The second sets a fenestrated capillary beside a sinusoid, so the three kinds of capillary can be told apart by their walls.

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Three walls, from tight to leaky

Numbers 1 to 4 are the capillary cut across: the lumen, a red blood cell, the endothelial cells and the basement membrane round them. Numbers 5 to 7 are in the enlarged piece of wall. In the second view the round capillary on the left is fenestrated (number 8) and the wide, flattened one on the right is a sinusoid (numbers 9 and 10). The walls are drawn far thicker than life.

Tell the kinds apart by what breaks the wall: only clefts in a continuous capillary, pores in a fenestrated one, wide gaps in a sinusoid.

Questions and answers

What are the three types of capillaries?

Continuous, fenestrated and sinusoid. A continuous capillary has a complete endothelial lining. A fenestrated capillary also has pores in that lining. A sinusoid is flattened, with wide gaps between its cells and an incomplete basement membrane.

What is a continuous capillary made of?

A single layer of endothelial cells resting on a basement membrane. Tight junctions join the cells, and where a junction is incomplete it leaves an intercellular cleft that lets water and very small molecules through.

Where is each type of capillary found?

Continuous capillaries, the most common kind, are in almost all tissues with a blood supply. Fenestrated capillaries are common in the small intestine and the kidneys. Sinusoids are in the liver, spleen and bone marrow.

Which capillary is the leakiest?

The sinusoid. Its openings are large enough for plasma proteins and even whole cells to pass, and blood moves through it very slowly, which leaves more time for exchange.