Protonephridia: Excretory System Overview

Which organisms primarily possess protonephridia as part of their excretory system?

What is the primary function of flame cells in the protonephridial system?

What do the canal cells in the protonephridium do during the process of waste filtration?

What drives the movement of waste fluids into the protonephridia?

How did the evolution of protonephridia likely begin?

Protonephridia (Excretory System)

A protonephridium is a network of dead-end tubules in Platyhelminthes, Nemertea, and Rotifera.
The ends of the tubules are called flame cells (ciliated) or solenocytes (flagellated).
They function in osmoregulation and ionoregulation.
Terminal cells are located at the blind end of the protonephridium.
These cells have cilia that create a current, pushing waste fluids from the animal's interior through perforations in the terminal cells.
Small molecules pass through the perforations, but larger proteins remain inside the animal.
Solutes travel through the tube, formed by canal cells, and exit the animal through a nephridiopore.
Canal cells reabsorb useful molecules as the solutes move through the tubule.
Protonephridia are common in basal organisms like flatworms.
They likely initially evolved to manage hypotonic environments, removing excess water.
These structures can also play secondary roles in excretion and ion regulation.
Excretory tubules in flatworms are sometimes called "blind tubules".
These consist of a hollow cup-shaped cell containing cilia or flagellum.
Cilia or flagellar movement draws in waste products and expels them from the body.

This quiz explores the structure and function of protonephridia, the excretory system found in certain basal organisms such as Platyhelminthes, Nemertea, and Rotifera. Learn how these networks of tubules, with their specialized cells, contribute to osmoregulation and the excretion of waste. Test your knowledge on the various roles and evolutionary significance of protonephridia.