Question 1

The in-vivo synthesis of the active form of vitamin D begins with 7-dehydrocholesterol being converted to cholecalciferol in the ______.Cholecalciferol is next hydroxylated in the ______, followed by a second hydroxylation in the ______ to form 1,25-dihydroxycholecalciferol.

Accepted Answer

In-vivo synthesis of the active form of vitamin D begins in the skin, with ultraviolet light exposure driving the conversion of 7-dehydrocholesterol to cholecalciferol.Cholecalciferol is hydroxylated in the liver to 25-hydroxycholecalciferol, and 25-hydroxycholecalciferol is further hydroxylated in the kidney to form the active hormone 1,25-dihydroxycholecalciferol.

Question 2

The major function(s) of water-soluble vitamins in the body is/are:

Accepted Answer

Water-soluble vitamins function as coenzymes.

Question 3

Which vitamin is known chemically as pyridoxine?

Accepted Answer

Vitamin B₆ is known chemically as pyridoxine.Pyridoxine must be activated by phosphorylation to pyridoxal phosphate to function as a coenzyme.Most biochemical reactions that utilize pyridoxal phosphate involve transformations of amino acids.

Question 4

Wernicke-Korsakoff syndrome is commonly seen in ______ and is associated with a ______ deficiency.

Accepted Answer

Wernicke-Korsakoff syndrome is seen in association with a thiamine deficiency.Thiamine deficiencies are relatively common in alcoholics.Magnesium deficiency, which is also commonly seen in alcoholics, impairs thiamine activation.This can further exacerbate Wernicke's encephalopathy in the already thiamine-deficient alcoholic.Korsakoff's psychosis often presents with Wernicke's syndrome.

Question 5

Which of the following statements are true of vitamin B₃?
1)It is readily absorbed in the gut.
2)It is completely dependent on diet for a direct source.
3)There is abundant storage of B₃ in the body.
4)Urine contains nicotinamide and other metabolites of B₃.

Accepted Answer

Niacin, vitamin B₃, is unique with respect to the other vitamins, in that humans are only partially dependent on diet for a direct source.Both niacin and nicotinamide are readily absorbed in the gut.Niacin is transported in blood mainly in erythrocytes.There is little storage of niacin in the body, and urine contains nicotinamide and other metabolites of niacin.

Question 6

What vitamin is consistent with the following characteristics?
1)Foods high in this vitamin include milk, liver, eggs, meat, and some green, leafy vegetables.
2)This vitamin is a highly pigmented yellow compound that consists of flavin.
3)A deficiency can cause mouth lesions, glossitis, photophobia, eyelid spasm, and neurological alterations.

Accepted Answer

Riboflavin (Vitamin B₂) is a highly pigmented yellow compound that consists of flavin, attached to D-ribitol-riboflavin.Foods high in riboflavin include milk, liver, eggs, meat, and some green, leafy vegetables.A deficiency of riboflavin can cause mouth lesions, glossitis, photophobia, and neurological alterations, among others.

Question 7

The active form of vitamin K is important in which of the following steps of the coagulation pathway?

Accepted Answer

The active form of vitamin K is a cofactor in the reaction that carboxylates glutamic acid residues to form delta-carboxyglutamic acid residues on clotting factors II, VII, IX, etc.This carboxylation step is necessary for these factors to function normally.Once formed, the delta-carboxyglutamic acid residues permit binding of the coagulation protein to calcium, which initiates the ionic bridge formation through binding with phospholipids.

Question 8

Biotin acts as a coenzyme that participates in which metabolic pathway?
1)gluconeogenesis
2)fatty acid synthesis
3)amino acid catabolism

Accepted Answer

Biotin acts as a coenzyme participating in the metabolic pathways of gluconeogenesis, fatty acid synthesis, and amino acid catabolism.Biotin functions as a prosthetic group for carboxylation and carbon exchange reactions, such as seen with the action of acetyl-CoA.

Question 9

Which of the following statements are true regarding the laboratory analysis of vitamin status?
1)Measurement of urinary metabolites of a vitamin is one approach utilized for determining vitamin status.
2)Measurement of a biochemical function requiring the vitamin, with and without in-vitro addition of the cofactor form, is one approach utilized for determining vitamin status.
3)Detection of reduced serum concentrations of a vitamin is utilized to indicate a deficiency that interrupts cellular function.
4)Detection of vitamin values within a reference interval defined by population studies is utilized to indicate an adequate supply of that vitamin.

Accepted Answer

Laboratory evaluation of human vitamin status has been approached in several ways,
including measurement of urinary metabolites of the vitamin and measurement of a biochemical function requiring the vitamin (such as enzymatic activity), with and without in-vitro addition of the cofactor form.Measurement of enzyme activity is a common function evaluated for this purpose.Reduced serum concentrations of a vitamin do not always indicate a deficiency that interrupts cellular function, just as values within a reference interval defined by population studies do not always reflect adequate supply.

Question 10

It is reasonable to expect a request for the laboratory analysis of fat-soluble vitamins in which of the following conditions?

Accepted Answer

Because the fat-soluble vitamins (A, D, E, K) are absorbed as part of the chylomicron complex, their absorption depends on the presence of adequate bile and pancreatic secretions, as well as healthy bowel mucosa.Therefore, chronic malabsorptive states are often associated with a deficiency of one or more of these vitamins.The malabsorptive states include chronic bowel inflammatory conditions, impaired bile flow, pancreatic insufficiency, and alcoholic liver disease.Malabsorptive states are typically associated with the presence of steatorrhea.

Question 11

Hemolytic anemia may be associated with which vitamin deficiency?

Accepted Answer

Vitamin E plays an important role in protecting the erythrocyte membrane from oxidation.This antioxidant activity stabilizes erythrocyte membranes.With a deficiency of vitamin E, there is loss of this protective mechanism, increasing the chances of hemolysis associated with oxidative stress on the erythrocyte.

Question 12

Considering characteristics of lipid-soluble vitamins, ______ can be stored in liver parenchymal cells for a year or longer, ______ can be stored in body fat for several months, and ______ appears to only be stored for a period of days or weeks.

Accepted Answer

Vitamin A can be stored in liver parenchymal cells for a year or longer, and vitamin E can be stored in body fat for several months.Vitamins K and D, although fat soluble, appear to be stored only for days or weeks.

Question 13

Absolute vitamin deficiencies can be the result of:
1)a nutritional deficit
2)an inability to properly absorb a vitamin
3)an increased metabolism and clearance
4)a markedly increased utilization

Accepted Answer

Vitamin deficiencies can be absolute or can be due to an inability to utilize a vitamin optimally.Absolute vitamin deficiencies can be the result of a nutritional deficit, an inability to properly absorb a vitamin, increased metabolism and clearance, or markedly increased utilization.

Question 14

Which of the following statements are true of the major forms of vitamin K?
1)The phylloquinone form of vitamin K is found in fruits.
2)The phylloquinone form of vitamin K constitutes the dietary source of vitamin K.
3)The menaquinone form of vitamin K is produced in gram-negative bacteria.
4)The menaquinone form of vitamin K represents the bowel-derived source of vitamin K.

Accepted Answer

The two major forms of vitamin K are phylloquinone and the menaquinone forms.The phylloquinone form of vitamin K is found in plants and constitutes the dietary source of vitamin K.The menaquinone form of vitamin K is produced in gram-positive bacteria and represents the bowel-derived source of vitamin K.

Question 15

Vitamin A toxicity:

Accepted Answer

Vitamin A toxicity can occur in adults or children.Typically it is the result of overmedication with vitamin supplements but can also result from the use of topical retinoids for acne.Signs of vitamin A toxicity include dry, itchy skin; dermatitis; fissures of the lips; bone pain; edema; fatigue; renal disorders; intracranial hypertension; and hemorrhage.Further increased vitamin A intake increases bone resorption, can cause hypercalcemia, and may increase the risk of hip fracture.

Question 16

Vitamin B₁₂ is usually measured in the laboratory at the same time as which other vitamin, owing to their clinical similarities of deficiency and metabolic interactions?

Accepted Answer

Vitamin B₁₂ is known to reverse some forms of pernicious anemia.Folic acid is known to reverse other types of macrocytic anemia.Similar clinical symptoms result from deficiencies of these two totally different compounds, neither of which could replace the other.Thus the clinical similarities of deficiency and the metabolic interactions of vitamin B₁₂ and folic acid usually dictate their simultaneous assessment.

Question 17

In the general comparison of fat-soluble and water-soluble vitamins, ______ vitamins are generally expected to be stored longer in the body, and a deficiency of ______ vitamins may develop in a short period of time.

Accepted Answer

Generally, fat-soluble vitamins would be expected to be stored for long periods of time in the body because of their solubility in adipose tissue.Once stored, fat-soluble vitamins will be released slowly back into the circulation, prolonging their duration in the body.Paradoxically, vitamins D and K are fat-soluble vitamins that appear to be stored in the body for only days or weeks.Water-soluble vitamins do not dissolve in adipose tissue and do not persist in the body for long periods of time before they are excreted.Since there is no significant storage of water-soluble vitamins, deficiencies of water-soluble vitamins may appear rapidly.

Question 18

The need for laboratory evaluation of vitamin E status may be indicated by which of the following diets?

Accepted Answer

Dietary sources of vitamin E include vegetable oils, fresh leafy vegetables, egg yolk, legumes, peanuts, and margarine.Diets suspect for vitamin E deficiency are those low in vegetable oils or fresh, green vegetables and those high in unsaturated fats.

Quiz 43: Vitamins

The in-vivo synthesis of the active form of vitamin D begins with 7-dehydrocholesterol being converted to cholecalciferol in the .Cholecalciferol is next hydroxylated in the , followed by a second hydroxylation in the __ to form 1,25-dihydroxycholecalciferol.

The major function(s) of water-soluble vitamins in the body is/are:

Which vitamin is known chemically as pyridoxine?

Wernicke-Korsakoff syndrome is commonly seen in and is associated with a deficiency.

Which of the following statements are true of vitamin B₃? 1) It is readily absorbed in the gut. 2) It is completely dependent on diet for a direct source. 3) There is abundant storage of B₃ in the body. 4) Urine contains nicotinamide and other metabolites of B₃.

The active form of vitamin K is important in which of the following steps of the coagulation pathway?

Biotin acts as a coenzyme that participates in which metabolic pathway? 1) gluconeogenesis 2) fatty acid synthesis 3) amino acid catabolism

It is reasonable to expect a request for the laboratory analysis of fat-soluble vitamins in which of the following conditions?

Hemolytic anemia may be associated with which vitamin deficiency?

Considering characteristics of lipid-soluble vitamins, can be stored in liver parenchymal cells for a year or longer, can be stored in body fat for several months, and __ appears to only be stored for a period of days or weeks.

Absolute vitamin deficiencies can be the result of: 1) a nutritional deficit 2) an inability to properly absorb a vitamin 3) an increased metabolism and clearance 4) a markedly increased utilization

Vitamin A toxicity:

Vitamin B₁₂ is usually measured in the laboratory at the same time as which other vitamin, owing to their clinical similarities of deficiency and metabolic interactions?

In the general comparison of fat-soluble and water-soluble vitamins, vitamins are generally expected to be stored longer in the body, and a deficiency of vitamins may develop in a short period of time.

The need for laboratory evaluation of vitamin E status may be indicated by which of the following diets?