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Nutrition and Metabolism > Vitamins > Flashcards

Vitamins Flashcards

1
Q

Definition of vitamins

A

Complex organic substances required in the diet in small amounts, compared to other dietary components like protein, carbohydrate and fat. Absence leads to deficiency

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2
Q

Definition of vitamer

A

Different structural form of a vitamin

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3
Q

Water soluble vitamins and properties

A

B
C

Not stored extensively
Needed regularly
Generally not toxic in excess (within reason)

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4
Q

Fat soluble vitamins and properties

A

A
D
E
K

Stored
Not absorbed/excreted easily
May be toxic in excess (A, D)

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5
Q

Overarching property of all B vitamins

A

All act as coenzymes in metabolic pathways

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6
Q

Sources of thiamine (B1)

A

Whole grain, pork, poultry, fish, vegetables, dairy
Requirement high if carbohydrate intake high
Thiaminases (raw fish) and antithiamine (tea, coffee) render it inactive

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7
Q

Biochemical role of B1

Deficiency

A

Thiamine pyrophosphate, essential cofactor for pyruvate dehydrogenase

Pyruvate =pyruvate dehydrogenase=> Acetyl CoA

Deficiency leads to lactate accumulation in muscles

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8
Q

3 forms of thiamine deficiency presentation

A

Infantile beri beri
sudden onset, cardiovascular symptoms

Acute cardiac beri beri
Congestive heart failure, enlarged heart, liver engorged neck veins with sudden heart failure

Chronic dry beri beri
Symmetrical ascending peripheral neuropathy
Weakness, numbness ataxic gait, painful extremeties

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9
Q

What is Wernicke’s encephalopathy

Where is it often seen and why

A

Cerebral beri beri
Confusion, ataxia, polyneuropathy, disorientation

Often seen in alcoholics
Inhibition of AT of B1 from intestines
Inhibition of enzyme that converts thiamin => TPP

Will develop into Korsakoff’s psychosis

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10
Q

Korsakoff’s psychosis

A

Loss of memory of recent events

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11
Q

Why do alcoholics often have vitamin B deficiencies

A

Inadequate vitamins, nutrients from alcohol
GI tract malfunctions
Cirrhotic liver affects storage, transport and metabolism of many vitamins
Storage and transport of fat soluble vitamins impaired

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12
Q

Riboflavin (B2) properties

A

UV sensitive, in milk, associated with proteins
Protein bound, if diet adequate in protein, adequate in B2
Low status in alcoholics, elderly, some adolescents
Not toxic in excess

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13
Q

Function of riboflavin

A

FAD, FMN in redox

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14
Q

Riboflavin deficiency

A

Rare, except in alcoholics

Symptoms, mild: cheilosis, angular stomatitis, cateracts

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15
Q

Niacin, vitamer of B3

A

Found in small amounts in cereals

High protein diets don’t need niacin, formed from tryptophan

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16
Q

Function of niacin B3

A

As NAD and NADP in redox reactions

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17
Q

Deficiency of B3

A

Pellagra
Affects maize eating people in EU, US. Fatal if severe

Photosensitive dermatitis
Diarrhoea
Dementia

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18
Q

Function of pyridoxine (B6)

A

Active form: pyridoxal phosphate
Essential for AA metabolism (transamination, deamination)
Haem synthesis

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19
Q

Pyridoxine (B6) deficiency

A

Caused by presence of antagonists

Isoniazid in TB combines with PP => inactive, B6 given

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20
Q

Therapeutic uses/toxicity

A

Used in a variety of settings (Downs, autism), doesn’t really help

Deficiency can lead to seizures, but not all seizures are caused by B6 deficiencies

OD can lead to peripheral neuropathy

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21
Q

Function of cobalamin (B12)

A

Carrier of methyl groups in mammalian metabolism

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22
Q

Function and structure of folate (B9)

A

Carrier of 1C units (not necasserily methyl)

Active form: tetrahydrofolate, maintained by dihydrofolate reductase

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23
Q

Source of folate

A

Mainly in green veg, liver, whole grain

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24
Q

Absorption of B12, B9

A

B12 only in animal tissue
Binds to IF secreted from gastric cells
Needed for absorption and transport of B12

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25
Q

Metabolic functions of folate

A

IC transfer reactions in
purine, pyramidine synthesis
AA metabolism (homocysteine => methionine)

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26
Q

Metabolic functions of B12

A

Conversion of homocysteine => methionine

In branched chain AA metabolism

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27
Q

The relationship between folate and B12

A

Folate
Dehydrofolate
(DHF reductase)
Tetrahydrofolate

Enters pool of ICTH derivatives, all interconvertible except MeTHF

MeTHF converted back to tertrahydrofolate via B12 (homocysteine => methionine)

From the pool of ICTHF derivatives, purines, pyrimidines and amino acids can be formed

28
Q

What happens when there is a B12 deficiency in the pool of ICTHR derivatives system

A

MeTHR form is irreversible, it cannot be converted back into another form
B12 deficiency traps THF in the MeTHF form proving functional THF deficiency
Explains why hematological picture of B12 deficiency is identical to folate deficiency

Results in lack of 5, 10 methylene THF and DNA synthesis
Haemopoietic cells die in marrow immature

29
Q

Neurological changes in inadequate myelin synthesis in B12 deficiency

A

Numbness in fingers hands and forearms
Tingling hand and feet
Loss of position sense
Unsteadiness, ataxia, confusion, moodiness, depression
Spinal cord, brain and peripheral nerve lesions

30
Q

Causes of B12 deficiency

A

Absent, defective IF
Gastric atrophy
Gastrectomy
Coeliac, Crohns disease

31
Q

Causes of folate (B9)

A

Topical sprue
Durgs
Ethanol

32
Q

Link between folate and neural tube defects

A

Folic acid reduces incidence of neural tube defects

33
Q

Function of panthenoic acid (B5)
Sources
Deficiency

A

Component of CoASH in metabolism and transfer of C chains (FA oxidation)

Ubiquitous, deficiency rare

34
Q

Sources of biotin (B7)

A

Widely distributed in peanuts, chocolate, egg yolk

Normally sufficient quantities provided by intestinal bacterial synthesis

35
Q

Function of biotin (B7)

A

Prosthetic group for carboxylations
Pyruvate => oxaloacetate
Acetyl CoA => malonyl CoA

36
Q

Deficiency of biotin (B6)

A

Rare on normal diet unless eating raw egg whites

Long term antibiotic therapy wipes out intestinal flora

37
Q

Sources of ascorbic acid (VC)

A

Citrus, tomatoes, berries

38
Q

Function of ascorbic acid

A

Antioxidant nutrient
Hydroxylation of proline and lysine in collagen formation, needed to maintain Fe II needed for proline and lysine hydroxyls activity i reduced active state

Reduction of dietary Fe in stomach for absorption
Possibly in vivo as an antioxidant protecting vitamins A, E, K from oxidation

39
Q

Vitamin C deficiency

A

Scurvy

Well fed human has a 6 month store
Signs of scurvy after 3 months on vitamin C free diet
Impaired wound healing, hemorrhages and anaemia, joint pain

40
Q

Vitamin C status in the Uk

A

Low status in elderly, alcoholics, adolescents on junk food

Smokers need twice the normal intakes as the turnover is greatly increased by smoking

41
Q

The risks of megadoses of vitamin C

A

Oxalate kidney stones in susceptible individuals
Diarrhoea
Systemic conditioning

42
Q

Causes of deficiency of fat soluble vitamins

A

Dietary deficiency
Low fat diet
Usually by choice in developed societies
Fat malabsorption

43
Q

Definition of primary deficiency

A

Inadequate intake in diet

44
Q

Definition of secondary deficiency

A

Secondary causes that lead to the inadequate absorption of vitamins

45
Q

Sources of vitamin A

A

As retinol in animal liver and fish liver oils, whole milk, egg yolk

As carotenoids in green, yellow, orange vegetables and fruit

46
Q

Forms of vitamin A

A

Retinoic acid, hormone
Retinal, in vision
B carotene, antioxidant

47
Q

Functions of vitamin A

A

Control of protein synthesis

In vision

48
Q

Functions of vitamin A

Control of protein synthesis

A

Retinoic acid binds specific receptor protein in cytosol
Binds chromatin, affects synthesis of proteins involved in cell growth and differentiation
Acts similarly to steroid hormone

49
Q

Function of vitamin A

In vision

A

At low intensity light, II cis retinal participates in conversion of light energy to impulses in optic nerve in rod cells in retina

50
Q

Transport and storage of vitamin A

A

From the gut => liver in chylomicrons

From liver => tissues bound to a specific retinal binding protein and pre albumin

51
Q

Vitamin A deficiency

A

Rarely seen in developed countries but more common in developing countries
Usually associated with inadequate protein diets
Affects synthesis of retinal binding protein and transport to tissue
Administrations of vitamin A does not often help

52
Q

Night blindness as a result of vitamin A deficiency

A

Followed by progressive keratinization of cornea

xerophthalmia) and keratomalacia (irreversible blindness

53
Q

Toxicity/teratogenicity of vitamin A

A

Dermatitis, hair loss, mucous membrane defects, hepatic disfunction, thinning and fracture of long bones
Unlikely with normal sources but possible with supplements

54
Q

Sources of vitamin E

A

Vegetable oils, wheat germ oil, nuts, green vegetables
Canned and frozen foods severely depleted
Includes family of tocopherols
Natural occurring antioxidant

55
Q

Function of vitamin E

A

Prevention oxidation of unsaturated/polyunsaturated FA (PUFA)
PUFA susceptible to free radical attack
Destruction disrupts membrane structures and cell integrity
Some PUFAs are precursors of prostaglandins and so PG metabolism also disturbed

56
Q

Free radical scavenging in vitamin E

A

PUFA susceptible to free radical attack
Generates other radicals
Reaction of FA radical w O2 => peroxyl radical
Leads to chain reaction by attacking other PUFA
Reacts with Vitamin E, terminates chain reaction
Vitamin E = radical itself, stable
Can be reduced to original form by other antioxidants

57
Q

Vitamin E deficiency

A

Premature, low birth weight infants, Vitamin E does not cross placenta easily
Human milk, poor source of Vitamin E
Found in formula milk
Hemolytic anaemia due to fragility of RBC

58
Q

Vitamin D

A

Group of similar compounds

59
Q

D3 (Cholecalciferol) sources and function in the body

A

Naturally occurring in animals
In skin by UV on 7-dehydrocholesterol

Functions by binding => intracellular receptors that eventually interact with DNA
Act like steroid hormones

60
Q

D2 (ergocalciferol) sources and function in the body

A

Derived from ergosterol in plants, fungi and mould
Milk and dairy, fortified margarine, eggs
Formed from ergosterol by activation of UV

Acts to maintain correct levels of Ca, PO4 3- in blood, proper mineralization of the bone achieved

61
Q

Vitamin D deficiency in children and adults

A

Rickets in children
Mineral:matrix ratio is low in bone
Bending of long bones and kyphosis
Tootheruption delayed

Osteomalacia in adults
Muscle weakness, bone pain, decalcification of long bones
Nearly always due to Vitamin D deficiency, rarely Ca deficiency

62
Q

Vitamin D toxicity

A

Excessive consumption = toxic
Hypercalcaemia, GI tract disturbances and calcification of soft tissue
Fatal when severe

63
Q

Sources of Vitamin K

A

Green leafy veg best, small amounts in milk, meat, eggs and cereals
Considerable amount from bacterial flora jejunum, ileum

64
Q

Vitamin K deficiency

A

Defective blood clotting, depends on cascade system of interacting proteins
Deficiency resulting in increased clotting time, rare except in long term antibiotic theraoy

65
Q

Hemorrhagic disease of new borns

A

Poor placental transfer, no fut flora
Some affected babies develop intracranial haemorrhages
50% die, 50% have neurological malfunction

Nutrition and Metabolism (14 decks)

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