# Stoma

In botany, a stoma (plural "stomata"), also called a stomate (plural "stomates")[1] (from Greek στόμα, "mouth"),[2] is a pore, found in the epidermis of leaves, stems, and other organs, that facilitates gas exchange. The pore is bordered by a pair of specialized parenchyma cells known as guard cells that are responsible for regulating the size of the stomatal opening.

The term is usually used collectively to refer to the entire stomatal complex, consisting of the paired guard cells and the pore itself, which is referred to as the stomatal aperture.[3] Air enters the plant through these openings by gaseous diffusion and contains carbon dioxide which is used in photosynthesis and and oxygen which is used in respiration. Oxygen produced as a by-product of photosynthesis diffuses out to the atmosphere through these same openings. Also, water vapor diffuses through the stomata into the atmosphere in a process called transpiration.

Stomata are present in the sporophyte generation of all land plant groups except liverworts. In vascular plants the number, size and distribution of stomata varies widely. Dicotyledons usually have more stomata on the lower surface of the leaves than the upper surface. Monocotyledons such as onion, oat and maize may have about the same number of stomata on both leaf surfaces.[4]:5 In plants with floating leaves, stomata may be found only on the upper epidermis and submerged leaves may lack stomata entirely. Most tree species have stomata only on the lower leaf surface.[5] Leaves with stomata on both the upper and lower leaf are called amphistomatous leaves; leaves with stomata only on the lower surface are hypostomatous, and leaves with stomata only on the upper surface are epistomatous or hyperstomatous.[5] Size varies across species, with end-to-end lengths ranging from 10 to 80 µm and width ranging from a few to 50 µm.[6]

Stoma in a tomato leaf shown via colorized scanning electron microscope image
A stoma in cross section
The underside of a leaf. In this species (Tradescantia zebrina) the guard cells of the stomata are green because they contain chlorophyll while the epidermal cells are chlorophyll-free and contain red pigments.

## Function

Electron micrograph of a stoma from a Brassica chinensis (Bok Choy) leaf

### CO2 gain and water loss

Carbon dioxide, a key reactant in photosynthesis, is present in the atmosphere at a concentration of about 400 ppm. Most plants require the stomata to be open during daytime. The air spaces in the leaf are saturated with water vapour, which exits the leaf through the stomata in a process known as transpiration. Therefore, plants cannot gain carbon dioxide without simultaneously losing water vapour.[7]

### Alternative approaches

Ordinarily, carbon dioxide is fixed to ribulose-1,5-bisphosphate (RuBP) by the enzyme RuBisCO in mesophyll cells exposed directly to the air spaces inside the leaf. This exacerbates the transpiration problem for two reasons: first, RuBisCo has a relatively low affinity for carbon dioxide, and second, it fixes oxygen to RuBP, wasting energy and carbon in a process called photorespiration. For both of these reasons, RuBisCo needs high carbon dioxide concentrations, which means wide stomatal apertures and, as a consequence, high water loss.

Narrower stomatal apertures can be used in conjunction with an intermediary molecule with a high carbon dioxide affinity, PEPcase (Phosphoenolpyruvate carboxylase). Retrieving the products of carbon fixation from PEPCase is an energy-intensive process, however. As a result, the PEPCase alternative is preferable only where water is limiting but light is plentiful, or where high temperatures increase the solubility of oxygen relative to that of carbon dioxide, magnifying RuBisCo's oxygenation problem.

### CAM plants

C3 and C4 plants(1) stomata stay open all day and close at night. CAM plants(2) stomata open during the morning and close slightly at noon and then open again in the evening.

A group of mostly desert plants called "CAM" plants (Crassulacean acid metabolism, after the family Crassulaceae, which includes the species in which the CAM process was first discovered) open their stomata at night (when water evaporates more slowly from leaves for a given degree of stomatal opening), use PEPcarboxylase to fix carbon dioxide and store the products in large vacuoles. The following day, they close their stomata and release the carbon dioxide fixed the previous night into the presence of RuBisCO. This saturates RuBisCO with carbon dioxide, allowing minimal photorespiration. This approach, however, is severely limited by the capacity to store fixed carbon in the vacuoles, so it is preferable only when water is severely limited.

### Opening and closure

Opening and closing of stoma.

However, most plants do not have the aforementioned facility and must therefore open and close their stomata during the daytime, in response to changing conditions, such as light intensity, humidity, and carbon dioxide concentration. It is not entirely certain how these responses work. However, the basic mechanism involves regulation of osmotic pressure.

When conditions are conducive to stomatal opening (e.g., high light intensity and high humidity), a proton pump drives protons (H+) from the guard cells. This means that the cells' electrical potential becomes increasingly negative. The negative potential opens potassium voltage-gated channels and so an uptake of potassium ions (K+) occurs. To maintain this internal negative voltage so that entry of potassium ions does not stop, negative ions balance the influx of potassium. In some cases, chloride ions enter, while in other plants the organic ion malate is produced in guard cells. This increase in solute concentration lowers the water potential inside the cell, which results in the diffusion of water into the cell through osmosis. This increases the cell's volume and turgor pressure. Then, because of rings of cellulose microfibrils that prevent the width of the guard cells from swelling, and thus only allow the extra turgor pressure to elongate the guard cells, whose ends are held firmly in place by surrounding epidermal cells, the two guard cells lengthen by bowing apart from one another, creating an open pore through which gas can move.[8]

When the roots begin to sense a water shortage in the soil, abscisic acid (ABA) is released.[9] ABA binds to receptor proteins in the guard cells' plasma membrane and cytosol, which first raises the pH of the cytosol of the cells and cause the concentration of free Ca2+ to increase in the cytosol due to influx from outside the cell and release of Ca2+ from internal stores such as the endoplasmic reticulum and vacuoles.[10] This causes the chloride (Cl) and organic ions to exit the cells. Second, this stops the uptake of any further K+ into the cells and, subsequently, the loss of K+. The loss of these solutes causes an increase in water potential, which results in the diffusion of water back out of the cell by osmosis. This makes the cell plasmolysed, which results in the closing of the stomatal pores.

Guard cells have more chloroplasts than the other epidermal cells from which guard cells are derived. Their function is controversial.[11][12]

### Inferring stomatal behavior from gas exchange

The degree of stomatal resistance can be determined by measuring leaf gas exchange of a leaf. The transpiration rate is dependent on the diffusion resistance provided by the stomatal pores, and also on the humidity gradient between the leaf's internal air spaces and the outside air. Stomatal resistance (or its inverse, stomatal conductance) can therefore be calculated from the transpiration rate and humidity gradient. This allows scientists to investigate how stomata respond to changes in environmental conditions, such as light intensity and concentrations of gases such as water vapor, carbon dioxide, and ozone.[13] Evaporation (E) can be calculated as;[14]

${\displaystyle E=(e_{i}-e_{a})/Pr}$

where ei and ea are the partial pressures of water in the leaf and in the ambient air, respectively, P is atmospheric pressure, and r is stomatal resistance. The inverse of r is conductance to water vapor (g), so the equation can be rearranged to;[14]

${\displaystyle E=(e_{i}-e_{a})g/P}$

and solved for g;[14]

${\displaystyle g=EP/(e_{i}-e_{a})}$

Photosynthetic CO2 assimilation (A) can be calculated from

${\displaystyle A=(C_{a}-C_{i})g/1.6P}$

where Ca and Ci are the atmospheric and sub-stomatal partial pressures of CO2, respectively. The rate of evaporation from a leaf can be determined using a photosynthesis system. These scientific instruments measure the amount of water vapour leaving the leaf and the vapor pressure of the ambient air. Photosynthetic systems may calculate water use efficiency (A/E), g, intrinsic water use efficiency (A/g), and Ci. These scientific instruments are commonly used by plant physiologists to measure CO2 uptake and thus measure photosynthetic rate.[15] [16]

## Evolution

Tomato stoma observed through immersion oil

There is little evidence of the evolution of stomata in the fossil record, but they had appeared in land plants by the middle of the Silurian period.[17] They may have evolved by the modification of conceptacles from plants' alga-like ancestors.[18] However, the evolution of stomata must have happened at the same time as the waxy cuticle was evolving – these two traits together constituted a major advantage for early terrestrial plants.

## Development

There are three major epidermal cell types which all ultimately derive from the outermost (L1) tissue layer of the shoot apical meristem, called protodermal cells: trichomes, pavement cells and guard cells, all of which are arranged in a non-random fashion.

An asymmetrical cell division occurs in protodermal cells resulting in one large cell that is fated to become a pavement cell and a smaller cell called a meristemoid that will eventually differentiate into the guard cells that surround a stoma. This meristemoid then divides asymmetrically one to three times before differentiating into a guard mother cell. The guard mother cell then makes one symmetrical division, which forms a pair of guard cells.[19] Cell division is inhibited in some cells so there is always at least one cell between stomata.[20]

Stomatal patterning is controlled by the interaction of many signal transduction components such as EPF (Epidermal Patterning Factor), ERL (ERecta Like) and YODA (a putative MAP kinase kinase kinase).[20] Mutations in any one of the genes which encode these factors may alter the development of stomata in the epidermis.[20] For example, a mutation in one gene causes more stomata that are clustered together, hence is called Too Many Mouths (TMM).[19] Whereas, disruption of the SPCH (SPeecCHless) gene prevents stomatal development all together.[20]  Activation of stomatal production can occur by the activation of EPF1, which activates TMM/ERL, which together activate YODA. YODA inhibits SPCH, causing SPCH activity to decrease, allowing for asymmetrical cell division that initiates stomata formation.[20][21] Stomatal development is also coordinated by the cellular peptide signal called stomagen, which signals the inhibition of the SPCH, resulting in increased number of stomata.[22]

Environmental and hormonal factors can affect stomatal development. Light increases stomatal development in plants; while, plants grown in the dark have a lower amount of stomata. Auxin represses stomatal development by affecting their development at the receptor level like the ERL and TMM receptors. However, a low concentration of auxin allows for equal division of a guard mother cell and increases the chance of producing guard cells.[23]

## Types

Different classifications of stoma types exist. One that is widely used is based on the types that Julien Joseph Vesque introduced in 1889, was further developed by Metcalfe and Chalk,[24] and later complemented by other authors. It is based on the size, shape and arrangement of the subsidiary cells that surround the two guard cells.[25] They distinguish for dicots:

• actinocytic (meaning star-celled) stomata have guard cells that are surrounded by at least five radiating cells forming a star-like circle. This is a rare type that can for instance be found in the family Ebenaceae.
• anisocytic (meaning unequal celled) stomata have guard cells between two larger subsidiary cells and one distinctly smaller one. This type of stomata can be found in more than thirty dicot families, including Brassicaceae, Solanaceae, and Crassulaceae. It is sometimes called cruciferous type.
• anomocytic (meaning irregular celled) stomata have guard cells that are surrounded by cells that have the same size, shape and arrangement as the rest of the epidermis cells. This type of stomata can be found in more than hundred dicot families such as Apocynaceae, Boraginaceae, Chenopodiaceae, and Cucurbitaceae. It is sometimes called ranunculaceous type.
• diacytic (meaning cross-celled) stomata have guard cells surrounded by two subsidiary cells, that each encircle one end of the opening and contact each other opposite to the middle of the opening. This type of stomata can be found in more than ten dicot families such as Caryophyllaceae and Acanthaceae. It is sometimes called caryophyllaceous type.
• hemiparacytic stomata are bordered by just one subsidiary cell that differs from the surrounding epidermis cells, its length parallel to the stoma opening. This type occurs for instance in the Molluginaceae and Aizoaceae.
• paracytic (meaning parallel celled) stomata have one or more subsidiary cells parallel to the opening between the guard cells. These subsidiary cells may reach beyond the guard cells or not. This type of stomata can be found in more than hundred dicot families such as Rubiaceae, Convolvulaceae and Fabaceae. It is sometimes called rubiaceous type.

In monocots, several different types of stomata occur such as:

• gramineous (meaning grass-like) stomata have two guard cells surrounded by two lens-shaped subsidiary cells. The guard cells are narrower in the middle and bulbous on each end. This middle section is strongly thickened. The axis of the subsidiary cells are parallel stoma opening. This type can be found in monocot families including Poaceae and Cyperaceae.
• hexacytic (meaning six-celled) stomata have six subsidiary cells around both guard cells, one at either end of the opening of the stoma, one adjoining each guard cell, and one between that last subsidiary cell and the standard epidermis cells. This type can be found in some monocot families.
• tetracytic (meaning four-celled) stomata have four subsidiary cells, one on either end of the opening, and one next to each guard cell. This type occurs in many monocot families, but also can be found in some dicots, such as Tilia and several Asclepiadaceae.

In ferns, four different types are distinguished:

• hypocytic stomata have two guard cells in one layer with only ordinary epidermis cells, but with two subsidiary cells on the outer surface of the epidermis, arranged parallel to the guard cells, with a pore between them, overlying the stoma opening.
• pericytic stomata have two guard cells that are entirely encircled by one continuous subsidiary cell (like a donut).
• desmocytic stomata have two guard cells that are entirely encircled by one subsidiary cell that has not merged its ends (like a sausage).
• polocytic stomata have two guard cells that are largely encircled by one subsidiary cell, but also contact ordinary epidermis cells (like a U or horseshoe).

## Stomatal crypts

Stomatal crypts are sunken areas of the leaf epidermis which form a chamber-like structure that contains one or more stomata and sometimes trichomes or accumulations of wax. Stomatal crypts can be an adaption to drought and dry climate conditions when the stomatal crypts are very pronounced. However, dry climates are not the only places where they can be found. The following plants are examples of species with stomatal crypts or antechambers: Nerium oleander, conifers, and Drimys winteri which is a species of plant found in the cloud forest.[26]

## Stomata as pathogenic pathways

Stomata are obvious holes in the leaf by which, as was presumed for a while, pathogens can enter unchallenged. However, it has been recently shown that stomata do in fact sense the presence of some, if not all, pathogens. However, with the virulent bacteria applied to Arabidopsis plant leaves in the experiment, the bacteria released the chemical coronatine, which forced the stomata open again within a few hours.[27]

## Stomata and climate change

### Response of stomata to environmental factors

Photosynthesis, plant water transport (xylem) and gas exchange are regulated by stomatal function which is important in the functioning of plants.[28] Stomatal density and aperture (length of stomata) varies under a number of environmental factors such as atmospheric CO2 concentration, light intensity, air temperature and photoperiod (daytime duration). [29][30]

Decreasing stomatal density is one way plants have responded to the increase in concentration of atmospheric CO2 ([CO2]atm).[31] Although changes in [CO2]atm response is the least understood mechanistically, this stomatal response has begun to plateau where it is soon expected to impact transpiration and photosynthesis processes in plants.[28][32]

### Future adaptations during climate change

It is expected for [CO2]atm to reach 500–1000 ppm by 2100.[28] 96% of the past 400 000 years experienced below 280 ppm CO2 levels. From this figure, it is highly probable that genotypes of today’s plants diverged from their pre-industrial relative.[28]

The gene HIC (high carbon dioxide) encodes a negative regulator for the development of stomata in plants.[33] Research into the HIC gene using Arabidopsis thaliana found no increase of stomatal development in the dominant allele, but in the ‘wild type’ recessive allele showed a large increase, both in response to rising CO2 levels in the atmosphere.[33] These studies imply the plants response to changing CO2 levels is largely controlled by genetics.

### Agricultural implications

The CO2 fertiliser effect has been greatly overestimated during Free-Air Carbon dioxide Enrichment (FACE) experiments where results show increased CO2 levels in the atmosphere enhances photosynthesis, reduce transpiration, and increase water use efficiency (WUE).[31] Increased biomass is one of the effects with simulations from experiments predicting a 5–20% increase in crop yields at 550 ppm of CO2.[34] Rates of leaf photosynthesis were shown to increase by 30–50% in C3 plants, and 10–25% in C4 under doubled CO2 levels.[34] The existence of a feedback mechanism results a phenotypic plasticity in response to [CO2]atm that may have been an adaptive trait in the evolution of plant respiration and function.[28][30]

Predicting how stomata perform during adaptation is useful for understanding the productivity of plant systems for both natural and agricultural systems.[29] Plant breeders and farmers are beginning to work together using evolutionary and participatory plant breeding to find the best suited species such as heat and drought resistant crop varieties that could naturally evolve to the change in the face of food security challenges.[31]

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Ad Stoma was a fort in the Roman province of Moesia. As Tabula Peutingeriana shows it is situated between Histriopolis and Salsovia; 60 miles from Histriopolis and 24 miles from Salsovia.

Bryopsida

The Bryopsida constitute the largest class of mosses, containing 95% of all moss species. It consists of approximately 11,500 species, common throughout the whole world.

The group is distinguished by having spore capsules with teeth that are arthrodontous; the teeth are separate from each other and jointed at the base where they attach to the opening of the capsule. These teeth are exposed when the covering operculum falls off. In other groups of mosses, the capsule is either nematodontous with an attached operculum, or else splits open without operculum or teeth.

Cholecystostomy

A cholecystostomy or cholecystotomy is a procedure where a stoma is created in the gallbladder, which can facilitate placement of a tube for drainage, first performed by American surgeon, Dr. John Stough Bobbs, in 1867. It is sometimes used in cases of cholecystitis where the person is ill, and there is a need to delay or defer cholecystectomy. The first endoscopic cholecystostomy was performed by Drs. Todd Baron and Mark Topazian in 2007 using ultrasound guidance to puncture the stomach wall and place a plastic biliary catheter for gallbladder drainage.

Colostomy

A colostomy is an opening (stoma) in the large intestine (colon), or the surgical procedure that creates one. The opening is formed by drawing the healthy end of the colon through an incision in the anterior abdominal wall and suturing it into place. This opening, often in conjunction with an attached stoma appliance, provides an alternative channel for feces to leave the body. Thus if the natural anus is not available for that job (for example, in cases where it has been removed in the fight against colorectal cancer or ulcerative colitis), an artificial anus takes over. It may be reversible or irreversible, depending on the circumstances.

Epidermis (botany)

The epidermis (from the Greek ἐπιδερμίς, meaning "over-skin") is a single layer of cells that covers the leaves, flowers, roots and stems of plants. It forms a boundary between the plant and the external environment. The epidermis serves several functions: it protects against water loss, regulates gas exchange, secretes metabolic compounds, and (especially in roots) absorbs water and mineral nutrients. The epidermis of most leaves shows dorsoventral anatomy: the upper (adaxial) and lower (abaxial) surfaces have somewhat different construction and may serve different functions. Woody stems and some other stem structures such as potato tubers produce a secondary covering called the periderm that replaces the epidermis as the protective covering.

Hydathode

A hydathode is a type of pore, commonly found in angiosperms, that secretes water through pores in the epidermis or leaf margin, typically at the tip of a marginal tooth or serration. Hydathodes occur in the leaves of submerged aquatic plants such as Ranunculus fluitans as well as herbaceous plants of drier habitats such as Campanula rotundifolia. They are connected to the plant vascular system by a vascular bundle. Hydathodes are commonly seen in water lettuce, water hyacinth, rose, balsam, and many other species.

Hydathodes are made of a group of living cells with numerous intercellular spaces filled with water, but few or no chloroplasts, and represent modified bundle-ends. These cells (called epithem cells) open out into one or more sub-epidermal chambers. These, in turn, communicate with the exterior through an open water stoma or open pore. The water stoma structurally resembles an ordinary stoma, but is usually larger and has lost the power of movement.

Hydathodes are involved in the process of guttation, in which positive xylem pressure (due to root pressure) causes liquid to exude from the pores. Some halophytes possess glandular trichomes that actively secrete salt in order to reduce the concentration of cytotoxic inorganic ions in their cytoplasm; this may lead to the formation of a white powdery substance on the surface of the leaf.

Hydathodes are of two types:

passive hydathodes, formed when a leaf vein terminates in an epithem (an area of thin-walled parenchyma).

active hydathodes, formed when epidermal cells lose water actively.

Ileostomy

Ileostomy is a stoma (surgical opening) constructed by bringing the end or loop of small intestine (the ileum) out onto the surface of the skin, or the surgical procedure which creates this opening. Intestinal waste passes out of the ileostomy and is collected in an artificial external pouching system which is adhered to the skin. Ileostomies are usually sited above the groin on the right hand side of the abdomen.

Jejunostomy

Jejunostomy is the surgical creation of an opening (stoma) through the skin at the front of the abdomen and the wall of the jejunum (part of the small intestine). It can be performed either endoscopically, or with formal surgery.A jejunostomy may be formed following bowel resection in cases where there is a need for bypassing the distal small bowel and/or colon due to a bowel leak or perforation. Depending on the length of jejunum resected or bypassed the patient may have resultant short bowel syndrome and require parenteral nutrition.A jejunostomy is different from a jejunal feeding tube which is an alternative to a gastrostomy feeding tube commonly used when gastric enteral feeding is contraindicated or carries significant risks. The advantage over a gastrostomy is its low risk of aspiration due to its distal placement. Disadvantages include small bowel obstruction, ischemia, and requirement for continuous feeding.

Nettastomatidae

The duckbill eels or witch eels are a family, Nettastomatidae, of eels. The name is from Greek netta meaning "duck" and stoma meaning "mouth".

Duckbill eels are found along the continental slopes of tropical and temperate oceans worldwide. They are bottom-dwelling fish, feeding on invertebrates and smaller fish. They are slender eels, up to 125 centimetres (4.10 ft) in length, with narrow heads and large, toothy, mouths. Most species lack pectoral fins.

Ostomy pouching system

An ostomy pouching system is a prosthetic medical device that provides a means for the collection of waste from a surgically diverted biological system (colon, ileum, bladder) and the creation of a stoma. Pouching systems are most commonly associated with colostomies, ileostomies, and urostomies.Pouching systems usually consist of a collection pouch plastic bag, known as a one-piece system or, in some instances involves a mounting plate, commonly called a flange, wafer or a baseplate, and a collection pouch that is attached mechanically or with an adhesive in

an airtight seal, known as a two-piece system. The selection of systems varies greatly between individuals and is often based on personal preference and lifestyle. Ostomy pouching systems collect waste that is output from a stoma. The pouching system allows the stoma to drain into a sealed collection pouch, while protecting the surrounding skin from contamination.Ostomy pouching systems are air- and water-tight and allow the wearer to lead an active lifestyle that can include all forms of sports and recreation.Ostomy pouching systems are also sometimes referred to as an appliance, where the term appliance refers to a prosthesis, as a mechanical replacement for a biological function.

Peristome

Peristome (from the Greek peri, meaning 'around' or 'about', and stoma, 'mouth') is an anatomical feature that surrounds an opening to an organ or structure. Some plants, fungi, and shelled gastropods have peristomes.

Protostome

Protostomia (from Greek πρωτο- proto- "first" and στόμα stoma "mouth") is a clade of animals. Together with the deuterostomes and xenacoelomorpha, its members make up the Bilateria, mostly comprising animals with bilateral symmetry and three germ layers. The major distinctions between deuterostomes and protostomes are found in embryonic development and is based on the embryological origins of the mouth and anus.

In most, but not all protostomes, the mouth forms first, then the anus, whereas the reverse is true in deuterostomes.

Stoma (disambiguation)

A stoma is a pore, found in the epidermis of leaves, stems, and other organs, that facilitates gas exchange.

Stoma may also refer to:

Stoma (medicine), an opening which connects a portion of the body cavity to the outside environment

"Stoma", single by Welcome (band)

"Stoma", track on 2010 album The Age of Hell by Chimaira

"Stoma", track on 2015 soundtrack album Rosetta: Audio/Visual Original Score

Saulius Stoma, a Lithuanian politician

Sternberg Test of Mental Ability (STOMA), an intelligence test by Robert Sternberg

Stoma (medicine)

In anatomy, a stoma (plural stomata or stomas) is any opening in the body. For example, a mouth, a nose, and an anus are natural stomata. Any hollow organ can be manipulated into an artificial stoma as necessary. This includes the esophagus, stomach, duodenum, ileum, colon, pleural cavity, ureters, urinary bladder, and renal pelvis. Such a stoma may be permanent or temporary. Surgical procedures that involve the creation of an artificial stoma have names that typically end with the suffix "-ostomy", and the same names are also often used to refer to the stoma thus created. For example, the word "colostomy" often refers either to an artificial anus or the procedure that creates one. Accordingly, it is not unusual for a stoma to be called an ostomy (plural ostomies), as is the norm in wound, ostomy, and continence nursing.

Stroma of ovary

The stroma of the ovary is a unique type of connective tissue abundantly supplied with blood vessels, consisting for the most part of spindle-shaped stroma cells. These appear similar to fibroblasts. The stroma also contains ordinary connective tissue such as reticular fibers and collagen. Ovarian stroma differs from typical connective tissue in that it contains a high number of cells. The stoma cells are distributed in such a way that the tissue appears to be whorled. Stromal cells associated with maturing follicles may acquire endocrine function and secrete estrogens. The entire ovarian stroma is highly vascular.On the surface of the organ this tissue is much condensed, and forms a layer (tunica albuginea) composed of short connective-tissue fibers, with fusiform cells between them.

The stroma of the ovary may contain interstitial cells resembling those of the testis.

Tracheal tube

A tracheal tube is a catheter that is inserted into the trachea for the primary purpose of establishing and maintaining a patent airway and to ensure the adequate exchange of oxygen and carbon dioxide.

Many different types of tracheal tubes are available, suited for different specific applications:

An endotracheal tube is a specific type of tracheal tube that is nearly always inserted through the mouth (orotracheal) or nose (nasotracheal).

A tracheostomy tube is another type of tracheal tube; this 2–3-inch-long (51–76 mm) curved metal or plastic tube may be inserted into a tracheostomy stoma (following a tracheotomy) to maintain a patent lumen.

A tracheal button is a rigid plastic cannula about 1 inch in length that can be placed into the tracheostomy after removal of a tracheostomy tube to maintain patency of the lumen.

Ureterostomy

A ureterostomy is the creation of a stoma (a new, artificial outlet) for a ureter or kidney.The procedure is performed to divert the flow of urine away from the bladder when the bladder is not functioning or has been removed.Indications may include: bladder cancer, spinal cord injury, malfunction of the bladder, and birth defects such as spina bifida.

Urostomy

A urostomy is a surgical procedure that creates a stoma (artificial opening) for the urinary system. A urostomy is made to avail for urinary diversion in cases where drainage of urine through the bladder and urethra is not possible, e.g. after extensive surgery or in case of obstruction.

Ventriculostomy

Ventriculostomy is a neurosurgical procedure that involves creating a hole (stoma) within a cerebral ventricle for drainage. It is done by surgically penetrating the skull, dura mater, and brain such that the ventricle of the brain is accessed. When catheter drainage is temporary, it is commonly referred to as an external ventricular drain, or EVD. When catheter drainage is permanent, it is usually referred to as a shunt. There are many catheter-based ventricular shunts that are named for where they terminate, for example, a ventriculo-peritoneal shunt terminates in the peritoneal cavity, a ventriculoatrial shunt terminates within the atrium of the heart, etc. The most common entry point on the skull is called Kocher's point, which is measured 11 cm posterior to the nasion and 3 cm lateral to midline. EVD ventriculostomy is done primarily to monitor the intracranial pressure as well as to drain cerebrospinal fluid ("CSF"), primarily, or blood to relieve pressure from the central nervous system (CNS).

Strictly speaking, "ventriculotomy" does not require the use of tubing. For example, a "third ventriculostomy" is a neurosurgical procedure that creates a hole in the floor of the third ventricle and usually has no indwelling objects.

Other types ventriculostomy include ventriculocisternostomy developed by the Norwegian doctor Arne Torkildsen.

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