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Questions and Answers
Which vitamin mentioned in the text is absorbed by carrier mediated processes when ingested in small amounts?
Which vitamin mentioned in the text is absorbed by carrier mediated processes when ingested in small amounts?
What is the main form of thiamin mentioned in the text?
What is the main form of thiamin mentioned in the text?
Which source of thiamin is not mentioned in the text?
Which source of thiamin is not mentioned in the text?
What factor can affect the absorption of thiamin from foods, according to the text?
What factor can affect the absorption of thiamin from foods, according to the text?
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Which type of enzymes are responsible for destroying thiamin in raw fish, according to the text?
Which type of enzymes are responsible for destroying thiamin in raw fish, according to the text?
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What happens to water-soluble vitamins when blood levels exceed the renal threshold?
What happens to water-soluble vitamins when blood levels exceed the renal threshold?
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What facilitates the destruction of the vitamin according to the text?
What facilitates the destruction of the vitamin according to the text?
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Which process prevents the destruction of the vitamin?
Which process prevents the destruction of the vitamin?
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Where does most of the free thiamin get phosphorylated to TDP?
Where does most of the free thiamin get phosphorylated to TDP?
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What is the main form in which thiamin exists in erythrocytes?
What is the main form in which thiamin exists in erythrocytes?
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Where is small amounts of thiamin stored in the body?
Where is small amounts of thiamin stored in the body?
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How is thiamin dephosphorylated in the body?
How is thiamin dephosphorylated in the body?
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What is the role of thiamin in nerve membranes?
What is the role of thiamin in nerve membranes?
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What vitamin is released in response to nervous system stimulation?
What vitamin is released in response to nervous system stimulation?
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Which of the following is a symptom of dry beriberi?
Which of the following is a symptom of dry beriberi?
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What is a symptom associated with wet beriberi?
What is a symptom associated with wet beriberi?
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What can cause acute thiamin deficiency in infants?
What can cause acute thiamin deficiency in infants?
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How does thiamin deficiency affect nerve conduction in the limbs?
How does thiamin deficiency affect nerve conduction in the limbs?
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What is the function of TDP in the hexose monophosphate shunt?
What is the function of TDP in the hexose monophosphate shunt?
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Which complex does TDP function as a coenzyme for?
Which complex does TDP function as a coenzyme for?
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In which reactions do TPP-dependent α-keto acid dehydrogenases play a role?
In which reactions do TPP-dependent α-keto acid dehydrogenases play a role?
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What is the consequence of a deficiency in branched-chain α-keto acid dehydrogenase complex?
What is the consequence of a deficiency in branched-chain α-keto acid dehydrogenase complex?
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Which enzyme is responsible for deamination of leucine, isoleucine, and valine?
Which enzyme is responsible for deamination of leucine, isoleucine, and valine?
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What is the main product of the Pentose Phosphate Pathway (hexose monophosphate shunt)?
What is the main product of the Pentose Phosphate Pathway (hexose monophosphate shunt)?
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What is the main cause of B1 deficiency due to alcoholism?
What is the main cause of B1 deficiency due to alcoholism?
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Which neurologic disorder is often associated with B1 deficiency due to alcoholism?
Which neurologic disorder is often associated with B1 deficiency due to alcoholism?
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What symptoms are associated with Wernicke’s encephalopathy resulting from B1 deficiency?
What symptoms are associated with Wernicke’s encephalopathy resulting from B1 deficiency?
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What might excessive intake of B1 (100 x greater than recommendations) lead to?
What might excessive intake of B1 (100 x greater than recommendations) lead to?
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What assessment method can be used to measure the activity of a B1-dependent enzyme?
What assessment method can be used to measure the activity of a B1-dependent enzyme?
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Why might thiamin deficiency be prevalent in congestive heart failure?
Why might thiamin deficiency be prevalent in congestive heart failure?
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Study Notes
Vitamin B1 (Thiamine)
- Vitamin B1 is destroyed by divalent minerals like Ca and Mg, but protected by reducing compounds like vit C and citric acid.
- Absorption of thiamine occurs in the jejunum and ileum through active transport (ThTr1 and ThTr2) and passive diffusion.
- Thiamine is phosphorylated within intestinal cells and stored in the liver as thiamine diphosphate (TDP).
Digestion, Absorption, Transport, and Storage
- Thiamine is transported in plasma, bound to albumin or TMP, and 90% is stored in erythrocytes as ThDP.
- Cellular uptake occurs through facilitated diffusion into RBCs and active transport in other tissues.
- The body stores approximately 30 mg of thiamine, primarily in the liver, muscles, heart, and brain, with the muscles containing about half of the body's thiamine.
Functions and Mechanisms of Action
- Thiamine plays coenzyme roles in E transformation, synthesis of pentoses and NADPH, and membrane and nerve conduction.
- It functions as a coenzyme in the pyruvate dehydrogenase complex, α-ketoglutarate dehydrogenase complex, and branched-chain α-keto acid dehydrogenase complex.
- Thiamine is also involved in the synthesis of pentoses and NADPH through the pentose phosphate pathway.
Sources and Destruction
- Thiamine is widely distributed in foods, with rich sources including pork, salmon, legumes, and grain products.
- It is destroyed in alkaline environments and by heat, and can be affected by antithiamin factors like thiaminases and polyhydroxyphenols.
Deficiency: Beriberi
- Chronic low thiamine intake with high CHO intake can cause dry beriberi, characterized by muscle weakness, peripheral neuropathy, and symmetrical foot drop.
- Wet beriberi results in more extensive cardiovascular system involvement, including cardiomegaly and peripheral edema.
- Acute beriberi can occur in infants, causing anorexia, vomiting, and lactic acidosis.
Deficiency Risk Factors
- Alcoholism is a main cause of thiamine deficiency due to reduced absorption, low food intake, and increased requirements.
- Elderly individuals and those with congestive heart failure are also at risk of thiamine deficiency.
Toxicity
- There is no UL for thiamine, and side effects are rare, but high doses (> 500 mg/d) may cause headache, convulsions, cardiac arrhythmias, and anaphylactic shock.
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Description
Test your knowledge on water soluble vitamins which are easily absorbed by simple diffusion when ingested in large amounts. Learn about the sources and forms of Vitamin B1 (Thiamin) and understand their importance in human nutrition.
