Anal pore

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Diagram of a Ciliate with various cell structures (including anal pore) labelled

The anal pore or cytoproct is a structure in various single-celled eukaryotes where waste is ejected after the nutrients from food have been absorbed into the cytoplasm.[1]

In ciliates, the anal pore (cytopyge) and

pellicle that are not covered by ridges, cilia or rigid covering. They serve as analogues of, respectively, the anus and mouth of multicellular organisms. The cytopyge's thin membrane allows vacuoles to be merged into the cell wall and emptied.[citation needed
]

Location

The anal pore is an exterior opening of microscopic organisms through which undigested food waste, water, or gas are expelled from the body. The anal pore is located on the

posterior half of the cell. The anal pore itself is actually a structure made up of two components: piles of fibres, and microtubules
.

This structure is found in different unicellular eukaryotes like paramecium organelles.

Function

Digested nutrients from the vacuole pass into the cytoplasm, making the vacuole shrink and moves to the anal pore, where it ruptures to release the waste content to the environment outside of the cell. The cytoproct is used for the excretion of indigestible debris contained in the food vacuoles.

Most

aboral
end. An anal pore is not a permanently visible structure; it appears at the time of defecation and then disappears afterward.

In

pellicle that is not covered by ridges and cilia
, and the area has thin pellicles that allow the vacuoles to be merged into the cell surface to be emptied.

In ciliates, the anal cytostomes and cytopyge pore regions are not covered by either ridges or cilia or hard coatings like the other parts of the organism. As a food vacuole approaches the cytoproct region it actually starts to flatten out the surrounding cells, and a thin-membrane vacuole allows it to be combined in the cell wall. Once the vacuole attaches to the plasma membrane of the cell wall, the vacuole is emptied. The waste excreted by the cell can come as a membrane-bound packaged ball, or as a stream of debris behind the organism.

Directly after secretion of the waste products, deep invagination (deep, canyon-like structure that was the vacuole) is still present. About 10 to 30 seconds after secretion, the vacuole detaches, and a new thin plasma membrane is formed. After a minute has gone by the organisms cytoproct is closed up again and the process is ready to be repeated.

In marine animals

Anatomical diagram of a cydippid comb jelly.

sensory organ which is thought to control osmotic pressure. These animals are also with animal pore. Ctenophores have sometimes been interpreted as homologous with the anus of bilaterian animals (worms, humans, snails, fish, etc.). Furthermore, they possess a third tissue layer between the endoderm and ectoderm, another characteristic reminiscent of the Bilateria. Ctenophores possess a functional through-gut from which digested waste products and material distributed via the endodermal canals are expelled to the exterior environment through terminal anal pores, which are specialized to control outflow from the branched endodermal canal system. Ctenophores have no true anus; the central canal opens toward the aboral end by two small pores, through which a small amount of egestion can take place.[citation needed]

Bathocyroe fosteri
with anal pore.

References

Bibliography