Also found in: Dictionary, Thesaurus, Medical, Wikipedia.


1. Botany an epidermal pore, present in large numbers in plant leaves, that controls the passage of gases into and out of a plant
2. Zoology anatomy a mouth or mouthlike part
3. Surgery an artificial opening made in a tubular organ, esp the colon or ileum
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



a slitlike opening in the epidermis of aboveground organs of plants. The stoma is bordered by two guard cells, which are usually bean-shaped. The walls of the guard cells that face the stoma are thick, while the opposite walls are thin. The stoma leads to a large intercellular space, the substomatal cavity. The stoma is often surrounded by two or more cells that differ in shape from ordinary epidermal cells.

Stomata are found in the epidermis of all aboveground parts of the plant containing chlorophyll but are especially numerous in leaf epidermis (100–300 per sq mm). They regulate the exchange of gas and water vapor between the atmosphere and the cells of the plant by increasing and decreasing in width. Stomatal movement is effected by changes in the turgor of the guard cells. When turgor is increased, the thin parts of their walls stretch and are drawn away from the stoma. The walls that face the stoma are distended in the same direction, and the stoma opens. When the turgor of the guard cells decreases, the stoma closes. Change in the turgor of the guard cells occurs as a result of reversible conversion of starch, which is osmotically inactive, into osmotically active sugars. However, according to some data, potassium ions play an important, possibly leading, role in regulating the turgor of the guard cells. Scientists are currently investigating these data with the intention of formulating a new hypothesis of the mechanism of stomatal movement.

At night, the stomata of most plants are closed, and gas exchange and transpiration are minimal. During the day, when the weather is fair, the stomata are open. Carbon dioxide gas readily enters the internal tissues of the plant, and oxygen formed as a result of photosynthesis is released with water vapor into the atmosphere.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


A small opening or pore in a surface.
One of the minute openings in the epidermis of higher plants which are regulated by guard cells and through which gases and water vapor are exchanged between internal spaces and the external atmosphere.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
"The estates teams on both sites have been working with our colleagues in community engagement to upgrade our accessible toilets to the stoma friendly standards put out by Colostomy UK."
The operation meant she was able to live a near normal life but sometimes when her stoma bag is full, she needs to get to a toilet urgently.
SEEK WAIVER The second-hand clothes dealer appealed to the government to release the waiver certificate to their umbrella body, Stoma World Kenya, to enable it to order more bags from donors.
Maria Brown, associate practitioner in Stoma Care said: "This event is part of the continuing care we provide to our patients.
Wearing a stoma pouch shouldn't restrict your ability to live life to the full, and finding the right pouch to suit your lifestyle and needs can mean the difference between struggling and not struggling.
The stoma should always be beefy red in color as this indicates adequate perfusion.
We studied patients operated from August 2017 to November 2018 for intestinal obstruction after previous stoma surgery in department of General Surgery, SMIMER Hospital, Surat.
Stoma ve Yara Bakim Hemsireligi'ne hiz kazandiran ikinci buyuk gelisme, 2008 yilinda Yara Ostomi Inkontinans Hemsireleri Dernegi (YOlHD)'nin kurulmasidir.
After stoma closure, surgical site infection is also a frequent complication, with a reported incidence rates up to 40% in patient with conventional linear sutured closure of the stoma wound.
The multidisciplinary team consists of specialist colorectal surgeons, oncologists, diagnostic radiologists, social workers and stoma therapists.
Now Harry has had his stoma bag removed and his bowel reconnected in a bid to try to get him ready for starting school in September.