| 单词 | stoma | ||||||
| 释义 | stomasto·maS0773200 (stō′mə)stoma(ˈstəʊmə)sto•ma(ˈstoʊ mə)n., pl. sto•ma•ta (ˈstoʊ mə tə, ˈstɒm ə-, stoʊˈmɑ tə) sto•mas. sto·ma(stō′mə)stoma
stomastomaStomaa 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]stomastoma[sto´mah] (pl. stomas, sto´mata) (Gr.)At first the stoma will be slightly edematous and will appear larger than a healed stoma. The most common cause of abnormal swelling of the stoma is application of a collection device whose opening is too narrow to accommodate the stoma. To prevent edema and restricted blood supply, the opening of the collection device should be at least 1/8 inch larger than the circumference of the stoma. Prolapse of the stoma results from a surgical incision that is too large or from inadequately securing the stoma to the abdominal wall. Decreased development of the abdominal musculature and an increase in intraabdominal pressure are factors that make this more common in children than adults. It becomes evident when an increase in pressure within the abdominal cavity causes a segment of intestine to protrude a noticeable distance beyond its usual position. Coughing, sneezing, and vigorous peristalsis can contribute to stomal prolapse. When it occurs it is not necessarily an emergency situation; the intestine can be gently manipulated back into place by an experienced health care worker such as a nurse, enterostomal therapist, or surgeon. If the condition persists and causes serious problems, surgical repair may be necessary. Stenosis is one of the most common problems associated with a stoma. The cause is formation of scar tissue at the point at which the segment of intestine passes through the abdominal wall. Treatment may consist of progressive dilation of the opening to break down structures causing the stricture. Stomal stenosis must be relieved; otherwise the opening may become obstructed and drainage impeded or prohibited. The character of output from an intestinal stoma will depend on the location of the stoma along the intestinal tract. The farther along the tract the stoma is located, the more solid the fecal material should be. Patients are taught to distinguish between normal and abnormal output from the stoma. Periostomal skin care is essential to preserve the integrity of the skin, which can be exposed to the caustic action of urine or fecal material. The two major principles of periostomal skin care are cleanliness and provision of a protective barrier. If there is a proper seal to prevent seepage of either urine or feces around the stoma, irritation and breakdown of the skin occur much less frequently. Possible causes of skin problems include removing the appliance too roughly or changing faceplates too frequently, allergic reaction to a particular adhesive or other substance, and yeast infections. Soap and water are used to cleanse and thoroughly rinse the skin. The area is patted, not rubbed, dry. Protective barriers are available in a number of forms and shapes. The base usually is pectin, which repels moisture and other harmful substances. Specific aspects of care will depend on the type of stoma and the purpose for which it was created. All patients with a stoma (“ostomates”) will need instruction in self-care and continued support as they adjust to new ways to handle fecal or urinary waste. They will need to know how to obtain and care for collection devices, how to protect the skin around the stoma, and dietary restrictions to control odor and obstruction. They will also need to be aware of potential complications and signs and symptoms that should be reported. Goals for patient care include developing in these patients an attitude of independence and freedom from restrictions on their physical, social, and recreational activities after discharge from the hospital. There is a health care specialty designed to meet the needs of patients with stomas. Ostomy clubs composed of ostomates and their families and conducted under the guidance of enterostomal therapists are available in many communities. At regularly held meetings the members find assistance in resolving their physical problems, and gain psychological support from one another in adjusting to their new body image. Those members of the club who have been able to adjust to their stomas are frequently available for visits to patients who are in the hospital or have just returned home after surgery. Information about local resources available to the ostomate can be obtained from the American Cancer Society's Rehabilitation Program and from other agencies concerned with meeting the needs of patients with stomas. The United Ostomy Association, Inc., is a volunteer-based organization dedicated to providing education, information, support, and advocacy for people who have had or will have intestinal or urinary diversions. They can be contacted by writing to United Ostomy Association, Inc., 19772 MacArthur Blvd., Suite 200, Irvine, CA 92612-2405, or consulting their web site at http://www.uoa.org.  sto·ma, pl.sto·mas,sto·ma·ta(stō'mă, stō'maz, stō'mă-tă), Do not confuse this word with stroma. Avoid the mispronunciation stoma'ta of the plural of this word.stoma(stō′mə)stomaOstomy Surgery A surgically created opening of a hollow viscus organ to the outside of the body. See Colostomy, Urostomy.sto·ma, pl. stomas, pl. stomata (stōmă, -măz, -mă-tă)stomaA mouth or orifice, especially one formed surgically, as in a COLOSTOMY or ILEOSTOMY. stoma(pl. stomata) an opening in the epidermis of leaves (and sometimes stems) that allows gaseous exchange. The size of the stomatal aperture is controlled by two guard cells, whose shape can alter depending upon internal turgidity. See Fig. 290 . When flaccid, the thick inner wall causes the guard cells to straighten closing the stoma; when turgid the guard cells become curved, opening the stoma for gaseous exchange.The mechanism of guard cell operation is not fully understood. An older theory proposes that high CO2 values at night cause high acidity which encourages the enzymic conversion of sugar to starch, thus reducing the OSMOTIC PRESSURE in the guard cell sap, so that water is lost and the stoma closes. During daylight, PHOTOSYNTHESIS uses up the available CO2, the pH rises so favouring the conversion of starch to sugar, thus increasing the flow of water into guard cells by osmosis, causing the stoma to open. A newer theory has been built on the older one, and suggests that the changes in osmotic pressure are caused, not just by differences in levels of CO2, but by levels of potassium ions (K+) in the guard cells. According to this theory, K+ ions are actively pumped into the guard cells during the day so increasing the osmotic pressure and hence the turgidity. Stomasto·ma, pl. stomas, pl. stomata (stōmă, -măz, -mă-tă)stoma
Synonyms for stoma
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stoma - a minute epidermal pore in a leaf or stem through which gases and water vapor can pass