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  • Different portions of the plant (root, stem, leaves, seeds) often contain different concentrations of a toxic substance.

  • The age of a plant contributes to variability. Young plants may contain more or less of some constituents than mature plants.

  • Climate and soil influence the synthesis of some toxins.

  • Plants contain substances that may exert toxic effects on skin, lung, cardiovascular system, liver, kidney, bladder, blood, nervous system, bone, and the endocrine and reproductive systems.

  • Contact dermatitis and photosensitivity are common skin reactions with many plants.

  • Gastrointestinal effects range from local irritation to emesis and/or diarrhea.

  • Cardiac glycosides in plants may cause nausea, vomiting, and cardiac arrhythmias in animals and humans.

  • Venomous animals produce poison in a highly developed secretory gland or group of cells and can deliver their toxin during biting or stinging.

  • Poisonous animals are those whose tissues, either in whole or in part, are toxic. Poisoning usually takes place through ingestion.

  • The bioavailability of a venom is determined by its composition, molecular size, amount or concentration gradient, solubility, degree of ionization, and the rate of blood flow into specific tissues.

  • The distribution of most venom fractions is rather unequal, being affected by protein binding, variations in pH, and membrane permeability, among other factors.

  • A venom may be metabolized in several or many different tissues.

  • Because of their protein composition, many toxins produce an antibody response; this response is essential in producing antisera.


History is replete with stories of the earliest humans using plant extracts and animal venoms for hunting, war, assassination, and political intrigue for millennia. The toxic properties of plants and animals often enhance their ability to survive. Some toxic compounds are used primarily to aid an animal in obtaining food while plants have developed toxic properties to specifically ward off being used as food. Toxins have been utilized as tools to study human biochemistry and physiology in order to pave the way for new pharmaceuticals. In fact, some components are in active development for clinical use.


The plant kingdom contains potentially 300 000 species, and the toxic effects of plants serve primarily as defense mechanisms against natural predators. Toxic effects on humans can range from simple hay fever caused by exposure to plant pollen all the way to serious systemic reactions caused by ingestion of specific plants. Table 26–1 lists some of the poisoning syndromes plants can produce. Many variables that can affect the concentration of a plant’s toxin and that can be a major factor in the severity of reaction one will experience on exposure include what part of the plant exposure is from, the age of the plant, amount of sunlight and soil quality that the plant has grown in, and genetic differences within a species. Also, plant toxins fall under a number of different chemical structures, which is useful in understanding related toxins. ...

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