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The respiratory pathway is concerned principally with the gaseous waste products of metabolism carbon dioxide and ammonia , which move to the external environment by diffusing from the cells of origin. Benzoyl peroxide and parabens applied to the skin may be toxic. Exotoxins are neutralized by homologous antibodies— i. Views Read Edit View history. Atmospheric pressure annelids In annelid: Therefore, it includes chemicals used in industry, as well as chemicals found in or near households. Respiratory system cetaceans In cetacean:

Reptile Classification

Respiratory system

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. Like many mammals, birds and Amphibians, their embryonic life consists of an amnion, chorion, as well as an allantois.

The incubation period may vary depending on the species and other factors like the temperature of the surroundings. Usually, hatchlings are able to take care of themselves almost immediately after coming out of the eggs. But, the females of some species are known to protect their eggs and hatchlings. For example, female Pythons coil themselves around the eggs in order to protect them and regulate their temperature.

Similarly, crocodiles are known to guard their young after the eggs hatch. TDSD or temperature-dependent sex determination can be observed in many Reptiles. In TDSD, the incubation temperature determines the sex of the offspring. This characteristic is most commonly seen in crocodiles and turtles, but can also occur in tuataras and lizards. Different food habits can be observed between the four sub-groups. Animals belonging to the Crocodilia, Squamata and Sphenodontia sub-groups are carnivores, feeding on a wide range of prey from vertebrates to fish and insects.

The Testudines are herbivorous in nature with their diet comprising of fruits, shrubs, leaves, grass and marine plant materials like kelp and algae. The populations of many Reptilian species are facing rapid decline due to various factors like deforestation, loss of habitat, hunting for hide and to use them for edible purposes. Various Reptile populations have faced extinction in some specific locations.

Due to these reasons, many species are protected by law in most of the countries where they are found. Many Reptile species, including various lizards and turtles, are very popular all over the world as exotic pets. There is a widespread popularity even for the venomous snakes, especially among keen animal lovers. However, there is a common misconception that these animals do not need as much care as required by mammal pets. The truth is that, Reptiles need to be taken care of properly; otherwise, they cannot survive in captivity.

They should be kept in large tanks or cages where they can move freely. It is not advisable to keep more than one to two animals in a single enclosure. Their tanks should have suitable substrate and the animals should be provided with special heating lamps to allow them to bask and maintain their body temperature. The temperature of the tanks needs to be monitored with the help of thermostats. Heating pads can also be used for this purpose. Custom made cages can also be used for this purpose as these mimic the natural habitat of a specific species in the best manner possible.

It is advisable to place stones, pieces of wood and small plants in their tanks to provide them with basking spots. Using a fogger to mist the enclosure may be advisable for certain species.

When keeping snakes or poisonous lizards as pets, one should keep in mind not to handle them with bare hands. One should do extensive research and read appropriate books regarding how to best take care of them before petting any Reptilian animal.

These pets can survive as much as mammalian pets of similar size when properly taken care of. The Ringneck Snake is a species of small North American snakes that belong to the harmless colubrid family.

The Banded Water Snake also called the southern water snake is a species of aquatic snake widely distributed in parts of the United States. The Water Monitor is a species of giant monitor lizard found in parts of South and Southeast Asian countries.

These semi-aquatic reptiles are common t. The African Fat-tailed Gecko is a species of lizard abundantly spread throughout the western regions of the continent of Africa. Often confused with i. Black caimans found in South America are the fourth largest extant member of the crocodile family.

These robust reptiles were almost hunted to extinct. Dwarf caimans found in South America are the smallest crocodilian belonging to the alligator family. It is one of the two members in its genus, the ot. The Emerald Tree Boa is a non-venomous boa species that is considered to be one of the most beautiful snakes in the world. They are known for their cr. Common leopard geckos, also known as the spotted fat-tailed gecko, are terrestrial lizards found in Asia.

Reproduction in whole or in part without permission is prohibited. Reptile Classification According to the taxonomy, they belong to the kingdom Animalia, phylum Chordata and the clade Amniota.

The Reptilia class is further divided into several extant sub-groups: There are around species in this sub-group, including turtles, tortoises and terrapins.

This subgroup includes the two living tuatara species from New Zealand. This is the biggest sub-group of the Reptilia class, having over 9, species including lizards, worm lizards and snakes. This subgroup consists of 25 different species including crocodiles, alligators, caimans and gavials.

Reptile Defense Mechanism The useful defenses of these animals help them to survive in their wild habitat. Camouflage Birds and larger Reptiles are among the main predators of many smaller lizards and snakes. Tail Shedding and Regenerating Various lizards like skinks and geckos can shed their tail when captured by it. Defense in Snakes The principal defense mechanism in various snake species is their ability to deliver poison through their fangs. Evolution of Reptiles These animals originated around million to million years ago with the first reptiles evolving from the advanced reptiliomorph labyrinthodonts.

Reptile Anatomy Eyes Most Reptiles are unable to see properly during nighttime as their vision is mainly adapted to the daylight conditions. Skin The horny epidermis layer makes their skin watertight, allowing these animals to inhabit dry land. Respiratory System Reptiles use their lungs for breathing.

Digestive System Majority of these animals have short digestive tracts because their diet mainly consists of meat, which is very simple to digest. Nervous System The basic nervous system in the Reptiles is similar to that in the Amphibians. Skeletal System Most of these animals are tetrapods, meaning they have four legs. Excretory System Their excretory system consists of two small kidneys.

Their major toxic effect is depression of the central nervous system, which results in muscular incoordination and slurred speech Table 3. For sleeping pills containing barbiturates , chloral hydrate , paraldehyde, and meprobamate, however, the margin of safety is much narrower, and the major toxicity is severe depression of the central nervous system, leading to respiratory and cardiovascular failure Table 3.

Like benzodiazepines, antipsychotic drugs such as chlorpromazine, perphenazine, and haloperidol have a relatively large therapeutic index, rarely causing fatalities. They occasionally may block the action of the parasympathetic and sympathetic nervous systems and thus produce such undesired effects as dry mouth and blurred vision from the former and a drop in blood pressure upon standing in the latter Table 3.

Nasal decongestants, antihistamines, and cough medicine , which are found in over-the-counter preparations for treating the symptoms of colds, have a low potential to produce toxicity. Nasal decongestants, such as ephedrine , mimic the action of epinephrine by stimulating the sympathetic nervous system, and consequently, an overdose of ephedrine produces symptoms related to stimulation of the sympathetic and central nervous systems Table 3. Depression of the central nervous system and parasympathetic blockade are two common toxicities of antihistamines such as diphenhydramine Table 3.

Depression of the central nervous system is also the major toxicity of dextromethorphan and codeine, both used to suppress coughing. Benzoyl peroxide and parabens applied to the skin may be toxic. Among the most toxic antiseptics are hexachlorophene, benzalkonium, and cetylpyridinium chloride, any of which can cause injuries to internal organs. Systemic toxicity double vision, drowsiness, tremor, seizures, and death with hexachlorophene is more likely to occur in babies because the relatively thin stratum corneum of their skin is highly permeable.

Deficiencies as well as excesses of vitamins are harmful. Excessive vitamin A retinol, or retinoic acid , known as hypervitaminosis A , can result in skin lesions, edema, and liver damage. Overconsumption by Alaskan natives of polar bear liver, a rich source of vitamin A, has produced acute toxicities, characterized by irresistible sleepiness and severe headaches. Chronic poisoning with vitamin A can cause neurological symptoms, including pain , anorexia, fatigue, and irritability Table 3.

Excess vitamin C can lead to kidney stones. Apart from irritation of the skin and respiratory tract, the most severe toxicity of vitamin K excess is the increased destruction of red blood cells, which leads to anemia and the accumulation of bilirubin, one of the products of hemoglobin degradation Table 3. Excess bilirubin can result in brain damage in newborns, a condition known as kernicterus.

Because the blood—brain barrier is not well developed in newborns, bilirubin enters and damages the brain. Due to the blood—brain barrier, kernicterus is not seen in adults. Iron , a metal that is necessary for normal health, can also cause poisoning. The toxicity of iron is a result of its corrosive action on the stomach and intestine when present in high concentrations. As a result, intestinal bleeding occurs, which can lead to the development of shock.

Among tricyclic antidepressants, amitriptyline and imipramine account for most of the fatal cases of poisoning. These drugs have a number of effects, including blockage of the parasympathetic system and damage to the central nervous system, the latter producing symptoms such as fatigue, weakness, lowered body temperature, seizures, and respiratory depression Table 3.

Death is usually caused by damage to the heart. Lithium salts, used to treat manic depression, have a relatively low therapeutic index. Mind-altering drugs commonly abused include amphetamines, cocaine , phencyclidine, heroin , and methaqualone. These drugs are primarily toxic to the central nervous system; amphetamine and cocaine cause stimulation of the system hallucinations and delirium , and heroin causes the depression of the system depressed respiration and coma.

In contrast, phencyclidine and methaqualone are biphasic, producing first depression drowsiness and then stimulation of the central nervous system delirium and seizures. Amphetamines also affect the gastrointestinal tract anorexia, nausea, vomiting, diarrhea and stimulate the cardiovascular system increased blood pressure and heart rate, palpitations, and abnormal heart rhythm.

In addition to hallucinations and delirium, cocaine causes euphoria, sexual arousal, confusion, and sympathetic stimulation. Phencyclidine is also known to cause aggression and psychotic behaviour, while methaqualone produces excessive dreaming and amnesia.

Digitalis overdose usually begins with gastrointestinal symptoms, such as anorexia, nausea, and vomiting, followed by sensory symptoms, such as pain and visual disturbances Table 3. There are also effects on the central nervous system, characterized by delirium and hallucinations. The major toxicities of beta blockers e. Sympathetic stimulation relaxes smooth muscles in the tracheobronchial wall and makes the heart beat faster and more forcefully. Blockage produced by propranolol or metoprolol can cause bronchoconstriction and heart failure Table 3.

Drugs for treating asthma, such as theophylline and aminophylline, are structurally similar to caffeine. Like caffeine, which is a stimulant, theophylline and aminophylline also stimulate the central nervous system. Therefore, excitement, delirium, rapid breathing, increased heart rate, and seizures occur with an overdose. With excessive stimulation of the heart, palpitations and irregular heart rhythm arrhythmia can result, leading to sudden death.

Biotoxins can be conveniently grouped into three major categories: The geographic distribution of poisonous organisms varies greatly; poison-producing microorganisms tend to be ubiquitous in their distribution. Poisonous plants and animals are found in greatest abundance and varieties in warm-temperate and tropical regions. Relatively few toxic organisms of any kind are found in polar latitudes. Knowledge of the evolutionary significance and development of most biotoxins is largely speculative and poorly understood.

In some instances they may have developed during the evolution of certain animal species as part of the food procurement mechanism e. Biotoxins may also function as defensive mechanisms, as in some snakes, fishes, arthropods e. The defense may be quite complex—as in the protection of territorial rights for reproductive purposes—and inhibitory or antibiotic substances may be produced that result in the exclusion of competitive animal or plant species.

Certain marine organisms and terrestrial plants may release into the water, air, or soil inhibitory substances that discourage the growth of other organisms; well-known examples include the production of antibiotic substances by microorganisms. Similar chemical-warfare mechanisms are used in battles for territorial rights among the inhabitants of a coral reef , a field, or a forest. Thus biotoxins play important roles in the regulation of natural populations.

Of increasing interest has been the discovery that certain substances, which may be toxic to one group of organisms, may serve a vital function in the life processes of the source organism. Venom-producing animals and stinging and dermatogenic i. Biotoxic agents may produce their injurious effects by becoming involved in the food supply; ingestion of a poisonous microbial organism, plant, or marine animal or one of their toxic by-products may cause intoxication.

An example is that of the shore fishes of many tropical islands; otherwise valuable food fishes are frequently contaminated by a poison called ciguatoxin. The poison, a potent neurotoxin nerve poison , is accidentally ingested by the fishes in their food; such fish can no longer be used for either human or animal consumption.

Some of the effects produced by biotoxins on humans are of an acute nature, and the injuries they cause are readily discernible.

The effects of some of the mycotoxins poisons produced by fungi and poisons produced by plants, however, are long-term and chronic; they result in the development of cancerous growths and other chronic degenerative changes that are sometimes difficult to detect. Microbial poisons are produced by the Monera bacteria and blue-green algae and Protista algae, protozoa, and others , and the Fungi.

Various classifications have been proposed for the microbial poisons, but none is entirely satisfactory. The problems encountered when dealing with these organisms result from a lack of precise knowledge concerning their biological nature and their phylogenetic relationships; in addition, their poisons show great diversity and chemical complexity.

The following outline, however, is useful in dealing with this subject. The main differences in these toxins lie in their chemical structure. Poisonous proteins from bacteria are sometimes referred to as bacterial exotoxins.

The exotoxins are generally produced by gram-positive organisms i. The exotoxins usually do not contain any nonprotein substances, and most are antigenic ; i. The exotoxins may appear in the culture medium in which the bacteria are growing during the declining phases of growth; in some cases they are released at the time of normal destruction of the cells after death autolysis.

The exotoxins are less stable to heat than are the endotoxins, and they may be detoxified by agents that do not affect endotoxins. They are more toxic than endotoxins, and each exotoxin exerts specific effects which are collectively known as pharmacological properties.

Exotoxins are neutralized by homologous antibodies— i. Endotoxins are antigens composed of complexes of proteins, polysaccharides large molecules built up of numerous sugars , and lipids fats.

The protein part determines the antigenicity, or quality of being reacted against as a foreign substance in a living organism. The polysaccharide part determines the immunological specificity, or limitations on the types of antibodies that can react with the endotoxin molecule and neutralize it the immunological reaction. Some of the lipids possibly determine the toxicity. Endotoxins are derived from the bacterial cell wall and, when cells are grown in culture , are released only on autolysis.

Endotoxins are not neutralized by homologous antibodies and are relatively stable to heat; all of them have the same pharmacological properties. The Cyanobacteria, or blue-green algae , are among the most primitive and widely distributed of all organisms.

They have extreme temperature tolerances. Some strains of a species are toxic; other strains of the same species are not. Water blooms of blue-green algae have been responsible for the death of fishes, waterfowl, cattle, horses, swine, and other animals. Blue-green algae have also been implicated as causes of human intoxications. Fungi are plantlike members of the kingdom Fungi Mycota that do not contain chlorophyll. A significant number are known to produce poisons of various types.

Toxic fungi can be roughly divided into two main categories on the basis of their size: The toxic microfungi are members of one of two classes: Ascomycetes , or the sac fungi, and the Deuteromycetes , or the imperfect fungi i. The large toxic mushrooms, or toadstools, are mostly members of the class Basidiomycetes , although some Ascomycetes, such as the poisonous false morel Gyromitra esculenta , may attain a size as large as some of the mushrooms.

The ability of certain fungi, such as ergot Claviceps purpurea and some mushrooms, to produce intoxication has long been known. During the 19th century it was recognized that molds are responsible for such diseases as yellow-rice toxicoses in Japan and alimentary toxic aleukia in Russia. The eruption of so-called turkey X disease in England in and the resulting discovery of the substance known as aflatoxin see Table 4 stimulated study of the subject of mycotoxicology.

Poisonous mushrooms , or toadstools as they are commonly called, are the widely distributed members of the class Basidiomycetes, although only a few are known to be poisonous when eaten see Table 5 ; some of the poisons, however, are deadly.

Most deaths attributed to mushroom poisoning result from eating members of the genus Amanita. Wild mushrooms should be eaten only if they have been accurately identified by an experienced person; the safest procedure is to eat only cultivated species. The problem of toxicity in mushrooms is complex; no single rule or test method exists by which the toxicity of a mushroom can be determined.

The most poisonous species closely resemble some of the most prized edible species; in addition, toxicity within a given wild species may vary from one set of ecological conditions or from one geographical locality to the next. Moreover, although some mushrooms that are poisonous when fresh are edible when cooked, dried, salted, or preserved in some other way, others remain poisonous in spite of all preparation procedures.

It has also been observed that some people may become poisoned by eating mushrooms that apparently do not affect others. As with microfungi, the mushroom poisons vary in their chemical and biological properties from species to species. The dinoflagellates , important producers of the primary food supply of the sea, are microscopic one-celled organisms that are dependent upon various inorganic nutrients in the water and upon radiant energy for photosynthesis, the process by which they produce their own food supplies.

Although dinoflagellates inhabit both marine waters and freshwaters, most species are marine. Dinoflagellates are most often found in cool or temperate waters. During periods of planktonic blooms times of high concentrations of microscopic organisms in the water dinoflagellates multiply in large numbers.

These planktonic blooms, sometimes referred to as red tide because they discolour the water, are often associated with weather disturbances that may bring about changes in water masses or upwellings.

During periods of bloom large numbers of toxic dinoflagellates may be ingested by shellfish; the poisons accumulate in their digestive glands.

Animals and humans may in turn be poisoned by eating poisoned shellfish. Certain species of dinoflagellates are capable of producing some of the most toxic substances known. The two species of dinoflagellates most commonly involved in human intoxications have been Gonyaulax catenella along the Pacific coast of North America and G.

Intoxications from these organisms are known as paralytic shellfish poisoning. The symptoms, which begin with a tingling or burning sensation, then numbness of the lips, gums, tongue, and face, gradually spread. Gastrointestinal upset may be present. Other symptoms include weakness, joint aches, and muscular paralysis; death may result. There is no specific treatment or antidote. The poison, variously called paralytic shellfish poison, mussel poison, and saxitoxin , is a complex nonprotein nitrogen-containing compound.

Paralytic shellfish poisoning is best avoided by following local public-health quarantine regulations. Respiratory irritation may result from the inhalation of toxic products in the windblown spray from red-tide areas containing the toxic dinoflagellate Gymnodinium breve , which is found in the Gulf of Mexico and Florida; the nature of the poison is unknown.

Deaths of large numbers of brackish-water pond fishes because of Prymnesium parvum have been reported in Israel; the poison is known as prymnesin. The study of plant poisons is known as phytotoxicology. Most of the poisonous higher plants are angiosperms , or flowering plants, but only a small percentage are recognized as poisonous. Several systems have been devised for the classification of poisonous plants, none of which is completely satisfactory.

Poisonous plants may be classified according to the chemical nature of their toxic constituents , their phylogenetic relationship, or their botanical characteristics. The following classification, which is based on their toxic effects, has been found to be useful: Plant poisons, or phytotoxins, comprise a vast range of biologically active chemical substances, such as alkaloids , polypeptides, amines, glycosides, oxalates, resins, toxalbumins, and a large group of miscellaneous compounds whose chemical structure has not yet been determined.

Alkaloids, most of which are found in plants, are characterized by the presence of nitrogen and their ability to combine with acids to form salts.

They are usually bitter in taste. It has been estimated that about 10 percent of the plant species contain some type of alkaloid. Only a few of the 5, alkaloids characterized thus far do not produce any biological activity; most cause a strong physiological reaction when administered to an animal. Amines are organic compounds containing nitrogen. A polypeptide is a string of three or more amino acids.

A few polypeptides and amines are toxic to animals. Some glycosides , which are compounds that yield one or more sugars and one or more other compounds— aglycones nonsugars —when hydrolyzed chemically degraded by the introduction of water molecules between adjacent subunits , are extremely toxic to animals.

Toxicity resides in the aglycone component or a part of it. Oxalates are salts of oxalic acid, which under natural conditions is not toxic but becomes so because of the oxalate ion. Resins , a heterogeneous assemblage of complex compounds, differ widely in chemical properties but have certain similar physical properties.

Some resins are physiologically very active, causing irritation to nervous and muscle tissue. Toxalbumins are highly toxic protein molecules that are produced by only a small number of plants. Ricin , a toxalbumin from the castor bean Ricinus communis , is one of the most toxic substances known. Under certain ecological conditions plants may become poisonous as a result of the accumulation of toxic inorganic minerals such as copper, lead, cadmium, fluorine, manganese, nitrates, or selenium.

Photosensitization, an unusual toxic reaction resulting from the ingestion of certain plants, may be of two types. The toxic substance may be obtained directly from the plant, which thereupon acts on the skin primary photosensitivity , or the toxicity may result from liver damage caused by the metabolism of a toxic plant and failure of the breakdown products to be eliminated by the liver hepatic photosensitivity.

In either case the animal reacts by becoming restless; in addition, the skin reddens, and a severe sloughing of the skin develops. A large number of poisonous plants occur throughout the world; a few representative species and their poisons are listed in Table 6.

Poisonous animals are widely distributed throughout the animal kingdom; the only major group that seems to be exempt is the birds.

What Is a Reptile?