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Types of capillaries

Continuous capillaries

• They are the most common types of capillaries in the body tissue (muscular
and neural capillaries).

• The capillary circumference is formed of one or more endothelial cells whose
edges are sealed together by tight junctions or fascia occludens.

• The endothelial lining is continuous without any interruptions or fenestrations.
Exchange between the lumen and the surrounding tissues occur by:

• Passive diffusion. For example gases and small ions.
• Pinocytotic vesicles. Example proteins and some lipids.
• Passage between the intercellular spaces. Example white blood cells.
Fenestrated capillaries

• They occur in small intestine, endocrine glands and kidneys.
• The endothelial cells are perforated by fenestrations or pores traversed by

diaphragms.
• The basement membrane is continuous across the fenestrations. Their

permeability is much greater than that of continuous capillaries.
• The pericytes are rarely found around their endothelium.
Discontinuous capillary

• They occur in liver, bone marrow and spleen. The basal lamina is
discontinuous across the pores or fenestrations leaving a wide gap within the
endothelial lining.

Blood sinusoids
• The blood sinusoids are capillaries of wide diameter and irregular outline.
• They are more permeable than capillaries and are found in the liver, spleen,
bone marrow and some endocrine glands.
• The endothelium of the sinusoids may be continuous, fenestrated or
discontinuous.

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