The deposition of insoluble materials, such as bacteria, colloids, oxides and water-borne debris, onto the surface of a media such as water softening resins, reverse osmosis or ultrafiltration membrane. Should I be worried? The money supply is the amount of money in circulation, usually measured as M1 or M2. Proponents of water softening systems tend to call water "hard" which contains between 3 and 10 grains of hardness. While in ground water, MTBE persists and moves freely. May include consumption of tap water with high levels of alum used in most municipal water treatment processes.
Sessile sponges rely on the ebb and flow of ambient water. By contrast, the jellyfish, which can be quite large, has a low oxygen need because its content of organic matter is less than 1 percent and its metabolizing cells are located just beneath the surface, so that diffusing distances are small.
Organisms too large to satisfy their oxygen needs from the environment by diffusion are equipped with special respiratory structures in the form of gills, lungs, specialized areas of the intestine or pharynx in certain fishes , or tracheae air tubes penetrating the body wall, as in insects.
Respiratory structures typically have an attenuated shape and a semipermeable surface that is large in relation to the volume of the structure.
Within them there is usually a circulation of body fluids blood through the lungs, for example. Two sorts of pumping mechanisms are frequently encountered: In air-breathing vertebrates, alternately contracting sets of muscles create the pressure differences needed to expand or deflate the lungs, while the heart pumps blood through the respiratory surfaces within the lungs.
Oxygenated blood returning to the heart is then pumped through the vascular system to the various tissues where the oxygen is consumed. Two common respiratory organs of invertebrates are trachea and gills. Diffusion lungs, as contrasted with ventilation lungs of vertebrates, are confined to small animals, such as pulmonate snails and scorpions.
This respiratory organ is a hallmark of insects. It is made up of a system of branching tubes that deliver oxygen to, and remove carbon dioxide from, the tissues, thereby obviating the need for a circulatory system to transport the respiratory gases although the circulatory system does serve other vital functions, such as the delivery of energy-containing molecules derived from food.
The pores to the outside, called spiracles , are typically paired structures, two in the thorax and eight in the abdomen. Periodic opening and closing of the spiracles prevents water loss by evaporation, a serious threat to insects that live in dry environments.
Muscular pumping motions of the abdomen, especially in large animals, may promote ventilation of the tracheal system. Although tracheal systems are primarily designed for life in air, in some insects modifications enable the tracheae to serve for gas exchange under water.
Of special interest are the insects that might be termed bubble breathers, which, as in the case of the water beetle Dytiscus , take on a gas supply in the form of an air bubble under their wing surfaces next to the spiracles before they submerge.
Tracheal gas exchange continues after the beetle submerges and anchors beneath the surface. As oxygen is consumed from the bubble, the partial pressure of oxygen within the bubble falls below that in the water; consequently oxygen diffuses from the water into the bubble to replace that consumed.
The carbon dioxide produced by the insect diffuses through the tracheal system into the bubble and thence into the water. The bubble thus behaves like a gill. There is one major limitation to this adaptation: As oxygen is removed from the bubble, the partial pressure of the nitrogen rises, and this gas then diffuses outward into the water. The consequence of outward nitrogen diffusion is that the bubble shrinks and its oxygen content must be replenished by another trip to the surface.
A partial solution to the problem of bubble renewal has been found by small aquatic beetles of the family Elmidae e. Several species of aquatic beetles also augment gas exchange by stirring the surrounding water with their posterior legs. An elegant solution to the problem of bubble exhaustion during submergence has been found by certain beetles that have a high density of cuticular hair over much of the surface of the abdomen and thorax.
The hair pile is so dense that it resists wetting, and an air space forms below it, creating a plastron , or air shell, into which the tracheae open. As respiration proceeds, the outward diffusion of nitrogen and consequent shrinkage of the gas space are prevented by the surface tension —a condition manifested by properties that resemble those of an elastic skin under tension—between the closely packed hairs and the water.
Since the plastron hairs tend to resist deformation, the beetles can live at considerable depths without compression of the plastron gas. One extraordinary strategy used by the hemipteran insects Buenoa and Anisops is an internal oxygen store that enables them to lurk for minutes without resurfacing while awaiting food in relatively predator-free but oxygen-poor mid-water zones. The internal oxygen store is in the form of hemoglobin-filled cells that constitute the first line of oxygen delivery to actively metabolizing cells, sparing the small air mass in the tracheal system while the hemoglobin store is being depleted.
The book lungs contain blood vessels that bring the blood into close contact with the surface exposed to the air and where gas exchange between blood and air occurs.
In addition to these structures, there may also be abdominal spiracles and a tracheal system like that of insects. Since spiders are air breathers, they are mostly restricted to terrestrial situations, although some of them regularly hunt aquatic creatures at stream or pond edges and may actually travel about on the surface film as easily as on land. The water spider or diving bell spider , Argyroneta aquatica —known for its underwater silk web , which resembles a kind of diving bell—is the only species of spider that spends its entire life underwater.
Research has shown that the inflated web serves as a sort of gill, extracting dissolved oxygen from the water when oxygen concentrations inside the web become sufficiently low to draw oxygen in from the water.
As the spider consumes the oxygen, nitrogen concentrations in the inflated web rise, causing it to slowly collapse. Most of the life cycle of the water spider, including courtship and breeding, prey capture and feeding, and the development of eggs and embryos, occurs below the water surface.
Many immature insects have special adaptations for an aquatic existence. Thin-walled protrusions of the integument , containing tracheal networks, form a series of gills tracheal gills that bring water into close contact with the closed tracheal tubes. The nymphs of mayflies and dragonflies have external tracheal gills attached to their abdominal segments, and certain of the gill plates may move in a way that sets up water currents over the exchange surfaces.
Dragonfly nymphs possess a series of tracheal gills enclosed within the rectum. Periodic pumping of the rectal chamber serves to renew water flow over the gills. Removing the gills or plugging the rectum results in lower oxygen consumption. Considerable gas exchange also occurs across the general body surface in immature aquatic insects. The insect tracheal system has inherent limitations. Gases diffuse slowly in long narrow tubes, and effective gas transport can occur only if the tubes do not exceed a certain length.
It is generally thought that this has imposed a size limit upon insects. Gills are evaginations of the body surface. Some open directly to the environment; others, as in fishes , are enclosed in a cavity.
In contrast, lungs represent invaginations of the body surface. Many invertebrates use gills as a major means of gas exchange; a few, such as the pulmonate land snail , use lungs. Almost any thin-walled extension of the body surface that comes in contact with the environmental medium and across which gas exchange occurs can be viewed as a gill.
Gills usually have a large surface area in relation to their mass; pumping devices are often employed to renew the external medium.
Although gills are generally used for water breathing and lungs for air breathing, this association is not invariable, as exemplified by the water lungs of sea cucumbers. The marine polychaete worms use not only the general body surface for gas exchange but also a variety of gill-like structures: The tufts, used to create both feeding and respiratory currents, offer a large surface area for gas exchange.
In echinoderms starfish, sea urchins, brittle stars , most of the respiratory exchange occurs across tube feet a series of suction-cup extensions used for locomotion. The gills of mollusks have a relatively elaborate blood supply, although respiration also occurs across the mantle, or general epidermis. Clams possess gills across which water circulates, impelled by the movements of millions of microscopic whips called cilia.
In the few forms studied, the extraction of oxygen from the water has been found to be low, on the order of 2 to 10 percent. The currents produced by cilial movement, which constitute ventilation , are also utilized for bringing in and extracting food.
At low tide or during a dry period, clams and mussels close their shells and thus prevent dehydration. Metabolism then shifts from oxygen-consuming aerobic pathways to oxygen-free anaerobic pathways, which causes acid products to accumulate; when normal conditions are restored, the animals increase their ventilation and oxygen extraction in order to rid themselves of the acid products.
In snails , the feeding mechanism is independent of the respiratory surface. Cephalopod mollusks, such as squid and octopus , actively ventilate a protected chamber lined with feathery gills that contain small blood vessels capillaries ; their gills are quite effective, extracting 60 to 80 percent of the oxygen passing through the chamber.
In oxygen-poor water, the octopus may increase its ventilation fold, indicating a more active control of respiration than appears to be present in other classes of mollusks. Many crustaceans crabs, shrimps, crayfish are very dependent on their gills. As a rule, the gill area is greater in fast-moving crabs Portunids than in sluggish bottom dwellers; decreases progressively from wholly aquatic, to intertidal, to land species; and is greater in young crabs than in older crabs.
Often the gills are enclosed in protective chambers, and ventilation is provided by specialized appendages that create the respiratory current. As in cephalopod mollusks, oxygen utilization is relatively high—up to 70 percent of the oxygen is extracted from the water passing over the gills in the European crayfish Astacus.
A decrease in the partial pressure of oxygen in the water elicits a marked increase in ventilation the volume of water passing over the gills ; at the same time, the rate of oxygen utilization declines somewhat. Although more oxygen is extracted per unit of time, the increased ventilation increases the oxygen cost of breathing. The increased oxygen cost, together with the decrease in extraction per unit of volume, probably limits aquatic forms of crustaceans to levels of oxidative metabolism lower than those found in many air-breathing forms.
This is largely due to the lower relative content of oxygen in water and the higher oxidative cost of ventilating a dense and viscous medium compared with air. Not all crustaceans meet a reduction in oxygen with increased ventilation and metabolism. The square-backed crabs Sesarma become less active, reducing their oxidative metabolism until more favourable conditions prevail.
In most vertebrates the organs of external respiration are thin-walled structures well supplied with blood vessels. Such structures bring blood into close association with the external medium so that the exchange of gases takes place across relatively small distances. There are three major types of respiratory structures in the vertebrates: The gills are totally external in a few forms as in Necturus , a neotenic salamander , but in most they are composed of filamentous leaflets protected by bony plates as in fish.
Some fishes and numerous amphibians also use the body integument, or skin, as a gas-exchange structure. Both gills and lungs are formed from outpouchings of the gut wall during embryogenesis. Such structures have the advantage of a protected internal location, but this requires some sort of pumping mechanism to move the external gas-containing medium in and out. The quantity of air or water passing through the lungs or gills each minute is known as the ventilation volume.
The rate or depth of respiration may be altered to bring about adjustments in ventilation volume. The ventilation volume of humans at rest is approximately six litres per minute. This may increase to more than litres per minute with increases in the rate of respiration and the quantity of air breathed in during each respiratory cycle tidal volume.
Certain portions of the airways trachea, bronchi, bronchioles do not participate in respiratory exchange, and the gas that fills these structures occupies an anatomical dead space of about millilitres in volume. Of a tidal volume of millilitres, only millilitres ventilate the gas-exchange sites. The maximum capacity of human lungs is about six litres. During normal quiet respiration, a tidal volume of about millilitres is inspired and expired during every respiratory cycle.
The lungs are not collapsed at the close of expiration; a certain volume of gas remains within them. At the close of the expiratory act, a normal subject may, by additional effort, expel another 1, millilitres of gas. Even after the most forceful expiratory effort, however, there remains a residual volume of approximately 1, millilitres. By the same token, at the end of a normal inspiration, further effort may succeed in drawing into the lungs an additional 3, millilitres.
The gills of fishes are supported by a series of gill arches encased within a chamber formed by bony plates the operculum. A pair of gill filaments projects from each arch; between the dorsal upper and ventral lower surfaces of the filaments, there is a series of secondary folds, the lamellae , where the gas exchange takes place. The blood vessels passing through the gill arches branch into the filaments and then into still smaller vessels capillaries in the lamellae.
Deoxygenated blood from the heart flows in the lamellae in a direction counter to that of the water flow across the exchange surfaces. In a number of fishes the water-to-blood distance across which gases must diffuse is 0. The countercurrent flow of blood through the lamellae in relation to external water flow has much to do with the efficiency of gas exchange. Laboratory experiments in which the direction of water flow across fish gills was reversed showed that about 80 percent of the oxygen was extracted in the normal situation, while only 10 percent was extracted when water flow was reversed.
The uptake of oxygen from water to blood is thus facilitated by countercurrent flow; in this way, greater efficiency of oxygen uptake is achieved by an anatomical arrangement that is free of energy expenditure by the organism.
Countercurrent flow is a feature of elasmobranchs sharks, skates and cyclostomes hagfishes , lampreys as well as bony fishes. A number of vertebrates use externalized gill structures.
Some larval fishes have external gills that are lost with the appearance of the adult structures. A curious example of external gills is found in the male lungfish Lepidosiren. At the time the male begins to care for the nest, a mass of vascular filaments a system of blood vessels develops as an outgrowth of the pelvic fins. The fish meets its own needs by refilling its lungs with air during periodic excursions to the water surface.
When it returns to the nest, its pelvic-gill filaments are perfused with well-oxygenated blood, providing an oxygen supply for the eggs, which are more or less enveloped by the gill filaments. It is theoretically possible for a skin that is well supplied with blood vessels to serve as a major or even the only respiratory surface. In terrestrial animals a moist integument also provides a major avenue of water loss.
A number of fishes and amphibians rely on the skin for much of their respiratory exchange; hibernating frogs utilize the skin for practically all their gas exchanges. The lungs of vertebrates range from simple saclike structures found in the Dipnoi lungfishes to the complexly subdivided organs of mammals and birds.
An increasing subdivision of the airways and the development of greater surface area at the exchange surfaces appear to be the general evolutionary trend among the higher vertebrates.
In the embryo, lungs develop as an outgrowth of the forward portion of the gut. The lung proper is connected to the outside through a series of tubes; the main tube, known as the trachea windpipe , exits in the throat through a controllable orifice, the glottis. At the other end the trachea subdivides into secondary tubes bronchi , in varying degree among different vertebrate groups.
The trachea of amphibians is not divided into secondary tubes but ends abruptly at the lungs. The relatively simple lungs of frogs are subdivided by incomplete walls septa , and between the larger septa are secondary septa that surround the air spaces where gas exchange occurs.
The diameter of these air spaces alveoli in lower vertebrates is larger than in mammals: Because many women don't discover that they're pregnant until this time, experts recommend that all women of childbearing age take a daily supplement of micrograms mcg of folic acid. Several foods, including enriched bread, pasta, rice and some breakfast cereals, are fortified with mcg of folic acid per serving.
Folic acid may be listed on food packages as folate, which is the natural form of folic acid found in foods. If you're actively trying to conceive, most pregnancy experts believe supplementation of at least mcg of folic acid a day is the best approach for women planning pregnancy. Your body doesn't absorb folate as easily as it absorbs synthetic folic acid, and most people don't get the recommended amount of folate through diet alone, so vitamin supplements are necessary to prevent spina bifida.
And, it's possible that folic acid will also help reduce the risk of other birth defects, including cleft lip, cleft palate and some congenital heart defects.
It's also a good idea to eat a healthy diet, including foods rich in folate or enriched with folic acid. This vitamin is present naturally in many foods, including:. If you have spina bifida or if you've given birth to a child with spina bifida, you'll need extra folic acid before you become pregnant. If you're taking anti-seizure medications or you have diabetes, you may also benefit from a higher dose of this B vitamin.
But check with your doctor before taking additional folic acid supplements. Spina bifida care at Mayo Clinic. Mayo Clinic does not endorse companies or products. Advertising revenue supports our not-for-profit mission. This content does not have an English version.
This content does not have an Arabic version. Overview Spina bifida is a birth defect that occurs when the spine and spinal cord don't form properly. Spina bifida myelomeningocele Myelomeningocele is a severe form of spina bifida, in which the membranes and the spinal nerves protrude at birth, forming a sac on the baby's back.
Request an Appointment at Mayo Clinic. Centers for Disease Control and Prevention. Spina Bifida Fact Sheet. National Institute of Neurological Disorders and Stroke. Routh JC, et al. Design and methodological considerations of the Centers for Disease Control and Prevention urologic and renal protocol for the newborn and young child with spina bifida. Ferri's Clinical Advisor McLone DG, et al. Pathophysiology and clinical manifestations of myelomeningocele spina bifida.
Alpha-fetoprotein AFP , single marker screen, maternal, serum. Mayo Foundation for Medical Education and Research; Fetal spina bifida surgery.
Overview of the management of myelomeningocele spina bifida. Dietary supplement fact sheet: Office of Dietary Supplements. Shepard CL, et al. Pregnancy among mothers with spina bifida. Journal of Pediatric Urology. Swaroop VT, et al. Orthopedic issues in myelomeningocele spina bifida. Current selection criteria and perioperative therapy used for fetal myelomeningocele surgery. Mayo Clinic, Rochester, Minn. Patel DM, et al. Sleep-disordered breathing in patients with myelomeningocele.
Driscoll SY expert opinion. Ruano R expert opinion. Granberg CF expert opinion. Dukhovny S, et al. Open neural tube defects: