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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
Metabolic functions of folate
IC transfer reactions in purine, pyramidine synthesis AA metabolism (homocysteine => methionine)
26
Metabolic functions of B12
Conversion of homocysteine => methionine | In branched chain AA metabolism
27
The relationship between folate and B12
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
What happens when there is a B12 deficiency in the pool of ICTHR derivatives system
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
Neurological changes in inadequate myelin synthesis in B12 deficiency
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
Causes of B12 deficiency
Absent, defective IF Gastric atrophy Gastrectomy Coeliac, Crohns disease
31
Causes of folate (B9)
Topical sprue Durgs Ethanol
32
Link between folate and neural tube defects
Folic acid reduces incidence of neural tube defects
33
Function of panthenoic acid (B5) Sources Deficiency
Component of CoASH in metabolism and transfer of C chains (FA oxidation) Ubiquitous, deficiency rare
34
Sources of biotin (B7)
Widely distributed in peanuts, chocolate, egg yolk | Normally sufficient quantities provided by intestinal bacterial synthesis
35
Function of biotin (B7)
Prosthetic group for carboxylations Pyruvate => oxaloacetate Acetyl CoA => malonyl CoA
36
Deficiency of biotin (B6)
Rare on normal diet unless eating raw egg whites | Long term antibiotic therapy wipes out intestinal flora
37
Sources of ascorbic acid (VC)
Citrus, tomatoes, berries
38
Function of ascorbic acid
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
Vitamin C deficiency
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
Vitamin C status in the Uk
Low status in elderly, alcoholics, adolescents on junk food | Smokers need twice the normal intakes as the turnover is greatly increased by smoking
41
The risks of megadoses of vitamin C
Oxalate kidney stones in susceptible individuals Diarrhoea Systemic conditioning
42
Causes of deficiency of fat soluble vitamins
Dietary deficiency Low fat diet Usually by choice in developed societies Fat malabsorption
43
Definition of primary deficiency
Inadequate intake in diet
44
Definition of secondary deficiency
Secondary causes that lead to the inadequate absorption of vitamins
45
Sources of vitamin A
As retinol in animal liver and fish liver oils, whole milk, egg yolk As carotenoids in green, yellow, orange vegetables and fruit
46
Forms of vitamin A
Retinoic acid, hormone Retinal, in vision B carotene, antioxidant
47
Functions of vitamin A
Control of protein synthesis | In vision
48
Functions of vitamin A | Control of protein synthesis
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
Function of vitamin A | In vision
At low intensity light, II cis retinal participates in conversion of light energy to impulses in optic nerve in rod cells in retina
50
Transport and storage of vitamin A
From the gut => liver in chylomicrons | From liver => tissues bound to a specific retinal binding protein and pre albumin
51
Vitamin A deficiency
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
Night blindness as a result of vitamin A deficiency
Followed by progressive keratinization of cornea | xerophthalmia) and keratomalacia (irreversible blindness
53
Toxicity/teratogenicity of vitamin A
Dermatitis, hair loss, mucous membrane defects, hepatic disfunction, thinning and fracture of long bones Unlikely with normal sources but possible with supplements
54
Sources of vitamin E
Vegetable oils, wheat germ oil, nuts, green vegetables Canned and frozen foods severely depleted Includes family of tocopherols Natural occurring antioxidant
55
Function of vitamin E
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
Free radical scavenging in vitamin E
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
Vitamin E deficiency
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
Vitamin D
Group of similar compounds
59
D3 (Cholecalciferol) sources and function in the body
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
D2 (ergocalciferol) sources and function in the body
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
Vitamin D deficiency in children and adults
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
Vitamin D toxicity
Excessive consumption = toxic Hypercalcaemia, GI tract disturbances and calcification of soft tissue Fatal when severe
63
Sources of Vitamin K
Green leafy veg best, small amounts in milk, meat, eggs and cereals Considerable amount from bacterial flora jejunum, ileum
64
Vitamin K deficiency
Defective blood clotting, depends on cascade system of interacting proteins Deficiency resulting in increased clotting time, rare except in long term antibiotic theraoy
65
Hemorrhagic disease of new borns
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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