A tubule is a very small tube or fistula

Fistula

In medicine, a fistula is an abnormal connection or passageway between two epithelium-lined organs or vessels that normally do not connect. It is generally a disease condition, but a fistula may be surgically created for therapeutic reasons.-Locations:Fistulas can develop in various parts of the...

r structure.

A system of surface-connected membranes in muscle that enables a nerve impulse to travel to the interior of the muscle fibre.

In anatomy

Anatomy

Anatomy is a branch of biology and medicine that is the consideration of the structure of living things. It is a general term that includes human anatomy, animal anatomy , and plant anatomy...

, a tubule is a minute tube lined with glandular epithelium

Epithelium

Epithelium is one of the four basic types of animal tissue, along with connective tissue, muscle tissue and nervous tissue. Epithelial tissues line the cavities and surfaces of structures throughout the body, and also form many glands. Functions of epithelial cells include secretion, selective...

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Tubules can be found on poisonous sea creatures.

These are tiny tubes in the biologial structure of the living items.

The cells of the tubules remove certain molecules and ions from the blood and deposit these into the fluid within the tubules.