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Flashcards in nitrates Deck (12)
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1

toxicity of nitrates

  • no big effect at low levels, toxic at high levels
  • nitrate not very toxic but very toxic when converted to nitrite
  • about 5% of nitrate is converted to nitrite in body

2

most common route of exposure for nitrates

oral exposure:

  • drinking contaminated water 
  • diet - used as preservatives in food, in some vegetables

3

why is nitrite toxic

  • May cause cancer (debates ongoing)
  • Binds with iron (Fe2+) to oxidise it to Fe3+
    • This is bad in Hb because it makes it form Methaemoglobin so it can no longer bind oxygen as well
  • When exposed to high levels (more than 14mg/kg or 0.9g in an adult) symptoms develop

4

why are infants more susceptible to nitrate poisoning

infants have high GI pH which promotes conversion of nitrate to nitrite. Methaemoglobin reductase has 1/2 the activity of an adult

5

who is most susceptible to nitrate poisoning

infants, foetus, fish and cattle most susceptible

6

symptoms of nitrite poisoning

correlate to lack of oxygen carrying ability

  • mild: skin discolouration, weakness, headache
  • moderate: fatigue, dizziness, confusion
  • severe: acidosis, seizures, respiratory distress, coma, cardiac arrest

 

7

why are cattle more at risk of nitrite poisoning

Cattle can consume toxic amount of nitrate within an hour

8

why are foetus more susceptible to nitrate poisoning

  • Fetal haemoglobin (2 alpha, 2 gamma) has a higher affinity for oxygen than adult haemoglobin
  • More readily oxidised by NO2 to methaemoglobin

9

why are fish more at risk of nitrite poisoning

Nitrates increase plant growth (weed and algae) which decreases O2 levels

10

carbon monoxide poisoning: symptoms, treatment and whos at risk

  • Toxicity at levels as low as 0.02% and can kill in minutes
  • Signs of toxicity include headache, shortness of breath, confusion
  • Treatment is high pressure oxygen (hyperbaric chamber)
  • Disrupts normal oxygen transport by occupying the binding site.
  • Binds with high affinity meaning it is hard to remove.
  • Fetal Hb has greater affinity for CO so smoking as a pregnant mother is v dangerous for foetus

11

why do we need to treat nitrite poisoning

  • Have to convert Fe3+ back to Fe2+
  • Methaemoglobin reductase (MetHb Reductase) is a naturally occurring enzyme in RBCs that maintains methaemoglobin levels < 2%
  • Need treatment when enzyme is saturated by an overload of methaemoglobin

12

treating nitrite poisoning via methylene blue

  • Reduces Fe3+ in metHb back to Fe2+
  • This causes the methylene blue to become oxidised.
  • Oxidised methylene blue is reduced by the enzyme methylene blue reductase.
  • The enzyme is recycled using NADPH as a co-factor