Question 1

Calcitonin,a hormone secreted by the thyroid gland,helps regulate mineralization of bones and teeth.Without adequate levels of vitamin C,calcitonin cannot regulate blood calcium and phosphorus levels.

Accepted Answer

The first statement is true; the second is false.Although calcitonin is a hormone secreted by the thyroid gland and is critical to mineralization of bones and teeth,vitamin D,not C,is essential to this process.It helps to regulate the body's ability to absorb and regulate calcium and phosphorus levels.Calcium and phosphorus are each required for optimal use of the other.Note that vitamin D functions with both the parathyroid and the thyroid gland in these mechanisms.Although vitamin D is the major nutrient involved in this process,vitamin C also has a role.

Question 2

During early tooth development,vitamin A deficiency leads to enamel hypoplasia and defective dentin formation.Because of its effect on soft tissues and bone,vitamin A contributes to normal spacing of teeth.

Accepted Answer

Both statements are true.The effect of vitamin A on growth of soft tissues and bones naturally extends to the teeth and surrounding structures.Enamel hypoplasia,involving defective enamel matrix and incomplete calcification of enamel and dentin,can be due to vitamin A deficiency.The effect of this vitamin upon surrounding bone has a directly affects spacing patterns of the teeth within the bone and dentition.

Question 3

Each is true of retinoic acid,except one.Which is the exception?

Accepted Answer

Odontoblasts are not involved in enamel formation; they are involved in formation of dentin.Retinoic acid is the form of vitamin A involved in development of teeth,especially the formation of ameloblasts in enamel and odontoblasts in dentin.In general,vitamin A is necessary for growth of soft tissues and bones.In skeletal tissue,it is necessary for resorption of old bone and synthesis of new bone.

Question 4

Although vitamins are synthesized during metabolic processes,they also must be obtained through external sources because vitamins cannot be produced in adequate amounts to meet body needs.

Accepted Answer

Both the statement and the reason are correct and related.Vitamins must come from an outside source because they either cannot be produced by the body or cannot be produced in adequate amounts to meet body needs.Food is the ideal outside source.Supplements are also an option.

Question 5

Each is true of water-soluble vitamins,except one.Which is the exception?

Accepted Answer

Water-soluble vitamins serve as coenzymes,as opposed to enzymes,which are necessary for almost every cellular reaction the body.

Question 6

Fat-soluble vitamins are fairly stable when heated,as in cooking.In contrast to water-soluble vitamins,fat-soluble vitamins contain nitrogen.

Accepted Answer

The first statement is true; the second is false.Fat-soluble vitamins do not contain nitrogen.Some water-soluble vitamins,including B-complex,contain nitrogen.

Question 7

Each is true of vitamin requirements and deficiencies,except one.Which is the exception?

Accepted Answer

Nutrients are codependent; a deficiency of one can cause deficiency symptoms of another.Requirements for most vitamins,especially water-soluble vitamins,are increased during periods of stress because metabolic activity is elevated.

Question 8

Each form of vitamin A is involved in the prevention of night blindness,except one.Which is the exception?

Accepted Answer

Retinoic acid is the form of vitamin A involved in the development of teeth,especially the formation of ameloblasts in enamel and odontoblasts in dentin along with growth of bone.The remaining selections are involved in preventing ocular (eye)diseases.Retinol is converted into retinal in the eye.Retinal combines with opsin,a protein in the eye,to form the visual pigment,rhodopsin.Inadequate vitamin A may prevent rhodopsin production and result in night blindness.Opsin is a protein in the eye.

Question 9

Antioxidants prevent cell membrane damage by free radicals that are produced by cells and tissue using free oxygen.Research conclusively documents that the antioxidant beta-carotene is effective in preventing cancer.

Accepted Answer

The first statement is true; the second is false.Although it is established that antioxidants prevent cell membrane damage by free radicals,research is inconclusive in regard to the use of beta-carotene to prevent cancer.

Question 10

Each is a function of vitamin A,except one.Which is the exception?

Accepted Answer

Vitamin D,not A,is responsible for maintenance of more than 200 genes.Functions of vitamin A are many; the remaining selections correctly identify numerous important roles.Without the role of vitamin A in the production of the visual pigment,rhodopsin,and night blindness may result.

Question 11

International units (IUs)are the designation used to measure and recommend vitamin A levels because it better represents the absorption rates in humans than retinol activity equivalent (REA).

Accepted Answer

Neither the statement nor the reason is correct.Although IU is used for many vitamins,the retinol activity equivalent (RAE)was created for vitamin A because it better represents the absorption rates in humans.The IU reflects biological activity in animal studies,but it was determined that this measure does not always represent absorption rates in humans.

Question 12

Which vitamin acts most like a hormone?

Accepted Answer

Although vitamin D,also known as calciferol,has been called a vitamin,it is more appropriately classified as a hormone.Like hormones,vitamin D acts to control the function of other cell types.For example,it helps the body absorb and regulate skeletal calcium and phosphorus levels.

Question 13

Daily intake of water-soluble vitamins is important because although the body can store large amounts of these nutrients,they are better utilized when consumed daily.

Accepted Answer

The statement is correct,but the reason is not correct.The body stores only small amounts of water-soluble vitamins,hence daily intake is essential.

Question 14

Vitamin A can be stored in the liver for at least:

Accepted Answer

Vitamin A can be stored in the liver to meet basic needs for at least 1 year.

Question 15

Studies suggest that leukoplakia is caused by excess vitamin A (a fat-soluble vitamin),retinoids,and beta-carotene.Leukoplakia is an erythematous lesion that appears on the lateral borders of the tongue.

Accepted Answer

Both statements are false.Studies suggest that leukoplakia,a white plaque that forms on oral mucous membranes,can be resolved by vitamin A,retinoids,and beta-carotene.Despite the potential to resolve leukoplakia,relapse is common.Also pertinent,evidence does not indicate that any of these nutrients prevent malignant transformation.

Question 16

Fat-soluble vitamins are different from water-soluble vitamins because the body is able to store only small amounts of fat-soluble vitamins.

Accepted Answer

The statement is correct,but the reason is not correct.A major difference between fat-soluble and water-soluble vitamins is that the body is able to store larger amounts of fat-soluble vitamins.Vitamins A and D are stored for long periods; therefore,minor shortages might not be identified until drastic depletion has occurred.Observable signs and symptoms of a dietary deficiency are often not identified until they are in an advance state.

Question 17

Each is a fat-soluble vitamin,except one.Which is the exception?

Accepted Answer

Vitamin C is not a fat-soluble vitamin.It is water-soluble.The fat-soluble vitamins are A,D,E,and K.

Question 18

Inadequate intake of vitamin A occurs in lower socioeconomic groups because these individuals often lack resources to purchase and consume vegetables and fruits.

Accepted Answer

Both the statement and the reason are correct and related.Average intake in the United States meets the RDA for vitamin A intake,except in lower socioeconomic groups.This is most likely because these individuals lack resources to purchase,prepare,and consume an adequate supply of fruits and vegetables.Note that because vitamin A can be stored in the liver,most adults have sufficient quantities to maintain health.

Question 19

Supplementing dietary intake of beta-carotene is advised for patients with leukoplakia who smoke because research documents that exogenous beta-carotene protects lung tissues from dangers of smoking.

Accepted Answer

Neither the statement nor the reason is correct.Supplementation is not advised other than increasing consumption of fruits and vegetables because some studies show an increased risk of lung cancer among smokers using beta-carotene supplements.Currently,researchers are uncertain as to whether beta-carotene or some other component in fruits and vegetables leads to the resolution of leukoplakia.A statement by the American Cancer Society indicates that clinical studies do not support vitamin A supplementation for cancer prevention.

Question 20

Most milk in the United States is fortified because the calcium and phosphorus content is beneficial for absorption and use of vitamin A.

Accepted Answer

The statement is correct,but the reason is not correct.Ninety-eight percent of the milk in the United States is fortified with vitamin D because it is essential for absorption and use of both calcium and phosphorus.Although foods are not legally required to be fortified,another reason for fortification of milk is its popular consumption among children.Many regular and low-fat cheeses are also fortified with vitamin D as are many orange juices.In addition,fortification is optional,and one cannot assume that products are fortified without reading labels.

Quiz 8: Vitamins Required for Calcified Structures