stoma


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stoma

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

Stoma

 

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.

E. A. MIROSLAVOV

stoma

[′stō·mə]
(biology)
A small opening or pore in a surface.
(botany)
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 ?
I know a lot of people find it very hard to be told they need a stoma but I had been ill for so long that I was just pleased that having it fitted meant I was going to be pain-free.
Causes of stoma formation in all the patients were tuberculous, enteric and traumatic perforations with contamination of peritoneal cavity.
After dozens of ostomy bags were decorated, Rachael spent months crafting "Stan's Little Black Dress", named after the moniker given to her stoma, which will be displayed at an exhibition to raise awareness of bowel cancer.
I was fitted with a stoma bag following the operation, which removed my entire lower bowel and colon.
Conclusion: Early stoma closure, preferably during the same admission is a safe, cost effective and an attractive technique.
Stoma is in anomocytic type and has two epidermis cells (Fig.
In an ILEOSTOMY, the entire colon and rectum are removed and a stoma is created to allow the small intestine to expel faeces into a disposable bag.
There is one study in the French literature (Jeanroy-Beretta 2011) that offers a remarkable reading of the stoma from the point of view of a concern regarding shame and sexual modesty.
9) The diversion of faecal content by stoma formation is valuable for wound healing at the time of definitive surgery and also improves the continence in these patients with ARM because covering colostomy protects the operative site from faecal contamination and helps healing.
James, who lives in Dovecot, was given the bear by his stoma nurse at the hospital as he prepared for the operation which will hopefully tackle his health problems.
Noncontinent diversions are accomplished by ureteral anastomosis to the ileum or colon, with the stoma being formed by the bowel segment sutured to the outer skin (ileal conduit) (Costa, 2013; McDonald, 2011; Piras & Hurley, 2011).