2.5
Reações Tóxicas: Visão Geral
Quando substâncias tóxicas penetram no corpo humano, elas se dispersam por vários tecidos, passando por mudanças metabólicas. Esse processo gera metab…
Os produtos químicos tóxicos que entram no corpo são distribuídos para os tecidos, onde podem ser metabolizados. Os metabólitos reativos podem interagir covalentemente com as moléculas-alvo para produzir toxicidade.
A toxicidade local ocorre no local da exposição. Um exemplo é a desnaturação de proteínas por substâncias cáusticas.
A toxicidade sistêmica geralmente requer absorção e distribuição do tóxico, que pode funcionar interrompendo uma via bioquímica específica.
Alguns efeitos tóxicos podem ser locais e sistêmicos. Por exemplo, a exposição ao chumbo tetraetila pode causar irritação na pele e sua absorção na circulação pode afetar o SNC.
As lesões no SNC são irreversíveis devido à capacidade limitada dos neurônios cerebrais de se regenerarem. Lesões em órgãos como o fígado podem ser reversíveis devido à sua capacidade de regeneração.
A maioria dos efeitos tóxicos são rápidos. Por exemplo, o excesso de acetilcolina nas sinapses, devido à inibição da acetilcolinesterase mediada por malatião, produz sintomas imediatos.
Alguns produtos químicos tóxicos, como o amianto, exibem longos períodos de latência antes de levar ao mesotelioma - um câncer do revestimento de certos tecidos.
View the full transcript and gain access to JoVE Core videos
Q1: What is the difference between local and systemic toxicity?
Local toxicity occurs at the site of exposure, such as protein denaturation caused by caustic substances. Systemic toxicity requires absorption and distribution of the toxicant throughout the body, where it may disrupt specific biochemical pathways. Some toxins produce both effects—for example, tetraethyl lead causes skin irritation locally and damages the central nervous system systemically.
Q2: How do reactive metabolites cause toxic effects in the body?
When toxic chemicals enter the body, they distribute to tissues where they undergo metabolic changes. These processes yield reactive metabolites that covalently bind with specific target molecules, resulting in toxicity. This covalent interaction disrupts normal cellular function and produces the harmful effects characteristic of toxic exposure.
Q3: Why are injuries to the central nervous system typically irreversible?
Damage to the central nervous system is usually irreversible because brain neurons have limited regenerative capacity. Unlike organs such as the liver, which can repair and regenerate damaged tissue, neurons cannot effectively replace themselves after injury. This fundamental difference makes CNS toxicity particularly serious and long-lasting.
Q4: What determines whether toxic effects appear immediately or after a delay?
The onset of toxic effects varies depending on the toxin's mechanism. Some chemicals, like malathion, produce immediate symptoms by inhibiting acetylcholinesterase and causing excess acetylcholine at synapses. Others, such as asbestos, exhibit long latency periods before causing diseases like mesothelioma. The chemical's interaction with target molecules determines whether effects are rapid or delayed.
Q5: How does organ regenerative capacity affect the reversibility of toxic injury?
The reversibility of toxic effects depends significantly on the affected organ's regenerative ability. Organs like the liver can repair and recover from toxic damage due to their inherent regenerative capacity. In contrast, organs with limited regenerative ability, such as the brain, sustain permanent injury from toxic exposure.
Q6: What role do covalent interactions play in producing toxic effects?
Reactive metabolites produced during the metabolism of toxic chemicals covalently bind with specific target molecules in tissues. These covalent interactions disrupt normal cellular function and biochemical pathways, producing toxicity. The strength and specificity of these molecular interactions determine the severity and type of toxic effect observed.
Q7: Can a single toxin cause both local and systemic effects?
Yes, certain toxins trigger both local and systemic effects. Tetraethyl lead exemplifies this dual action: it causes skin irritation at the exposure site and disrupts the central nervous system when absorbed into the bloodstream. Understanding both local and systemic mechanisms is essential for comprehensive toxicity assessment and prevention of further absorption of poison.