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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



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.



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.
References in periodicals archive ?
Some of the things I was offered I simply couldn't digest due to my stoma, others were absurd, so I mostly lived off the fail safe option of Rice Krispies.
An estimated half of all ostomates develop skin complications around the stoma, and the majority of problems stem from bodily waste leaking in between the stoma and the seal.
Some of them have decided to keep their stoma permanently.
We called my stoma Beryl and my six-year-old is totally aware of it and even asks how Beryl is when she comes home from school.
Given our patient's chronic catheterization, chronic inflammation of the stoma and Monti ileal segment may likely be the pre-disposing factor for developing squamous metaplasia and SCC in situ.
In many cases, people with a new stoma are cleaning the site with different kinds of soaps and [are] applying preps and creams to the extent that if the skin becomes irritated, you're unsure about the contributing factors," Galindo says.
300 limited edition Medibears have been produced to be given to Salts patients, stoma care charities and other organisations, to help them through the difficult period surrounding surgery.
A series of X-ray was initiated after contrast liquid was injected through the stoma.
For me death or a stoma were not options I was comfortable with, I just wanted to know what else could be done about it.
I am really pleased and encouraged by Tom's initiative and I wholeheartedly agree with Tom that the Government should ensure that all UK airport security staff are trained regarding the preservation of stoma patients dignity.
To keep track of which stomate she had already counted, she used a computer with a photo-editing program and "painted" each stoma red.