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Medical Biochemistry > Nutrition, Vitamins, and Minerals > Flashcards

Nutrition, Vitamins, and Minerals Flashcards

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USMLE® Step 1 flashcards
1
Q

What are the lipid soluable vitamins? Water soluable?

A

Lipid soluable: A,D,K,E
Water Soluable: B vitamins, C

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2
Q

Vitamin A (functions, deficiencies, susceptible groups)

A

Functions:

  • visual cycle (rhodopsin and cone opsins)
  • synthesis of certain glycoproteins and mucopolysaccharides
  • retinoic acid - acts as hormone
  • antioxidant

Deficiency:

  • night blindness (early); xerophthalmia (advanced)
  • follicular hyperkeratosis
  • anemia (despite normal iron intake)
  • poor growth in children
  • increased susceptibility to infection and cancer

Susceptible groups: The poor (malnourishment.) Premature babies.

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3
Q

Vitamin D (functions, deficiencies, susceptible groups)

A

Functions:

  • maintaining bone
  • calcium homeostasis
  • acts as a hormone (receptors are present in many tissues, but full range of activity is unknown.)

Deficiency:

  • rickets in children
  • osteomalacia in adults
  • increased susceptibility to breast and other cancers, metabolic syndrome/diabetes, and infection.

Susceptible groups:

  • poor
  • elderly
  • alcoholics
  • the sun-deprived
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4
Q

Describe the synthesis of the active form of vitimin D.

A

7-dehydrocholesterol is converted to the active form of vitamin D: D3 (also known as calcitrol) in three steps in three organs (skin, kidney, then liver.)

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5
Q

What are the effects of vitamin D toxicity?

A
  • Bone loss
  • Excessive calcium
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6
Q

Vitamin K (functions, deficiencies, susceptible groups)

A

Function:

  • localization of enzymes required for blood clotting
  • Helps catalyze addition of γ-carboxyglutamate to clotting enzymes

Deficiency:

  • Results in easy bruising, bleeding
  • Hemorrhage

Susceptible groups:

  • Newborn infants (lack intestinal bacteria that make vitamin K)
  • Patients on long-term antibiotics (kills intestinal bacteria)
  • The elderly and others with defects in fat absorption
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7
Q

Vitamin E (functions, deficiencies, susceptible groups)

A

Function:

-Antioxidant: scavenge free radicals,protect membranes from damage, prevent oxidation of LDL

Deficiency:

  • Cardiovascular disease
  • Neurological symptoms

Susceptible groups:

-Patients with severe, prolonged defects in absorption (ex. celiac disease) or genetic defects (uncommon)

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8
Q

What is the major form of vitamin E in the human body?

A

Alpha-tocopherol (the only actively maintained form.)

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9
Q

Vitamin C (functions, deficiencies, susceptible groups)

A

Function:

  • cofactor for prolyl and lysyl hydroxylases involved in collagen formation
  • required for synthesis of certain stress hormones (response to trauma)
  • aids absorption of iron
  • has antioxidant activity

Deficiency:

  • Mild: bruising, immunocompromise
  • Severe: SCURVY (decreased wound healing, osteoporosis, hemorrhage and anemia, fatigue)

Susceptible groups:

  • people with poor diet
  • smokers
  • patients undergoing long-term treatment with aspirin, oral contraceptives, and corticosteroids
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10
Q

What are the 2 sub-categories of B vitamins? Which B vitamins belong to each group?

A

Energy releasing:

Thiamine (B1)

Riboflavin (B2)

Niacin (B3)

Biotin (B7)

Pantothenic acid (B5)

Pyridoxine (B6)

Hematopoietic:

Folate (B9)

Cobalamin (B12)

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11
Q

Vitamin B1/Thiamine (functions, deficiencies, susceptible groups)

A

Function:

  • Required cofactor for several enzymes in cellular energy metabolism (TPP)
  • Particularly critical in nervous system

Deficiency:

  • Mild: GI symptoms, depression, fatigue (poor, elderly)
  • Moderate: Wernicke-Korsakoff syndrome (alcoholics)
  • Severe: Beriberi (people with diet dependent only on polished rice, sometimes alcoholics)
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12
Q

What is Wernike/Korsakoff syndrome?

A

A Moderate/severe thiamine deficiency, most commonly seen in chronic alcoholics, Characterized by mental disturbance, unsteady gate, and uncoordinated eye movements. Occasionally congestive heart failure occurs.

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13
Q

What is beriberi?

A

Severe thiamine deficiency

  • Dry beriberi: extreme muscle weakness, poly-neuropathy, heart failure
  • Wet beriberi: as above + edema
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14
Q

Vitamin B2/Riboflavin (functions, deficiencies, susceptible groups)

A

Function:

-Precursor of FAD and FMN (coenzymes important in redox reactions of energy metabolism)

Deficiency:

-Ariboflavinosis: rash around nose, inflammation of mouth and tongue, burning and itchy eyes, light sensitivity

Susceptible groups:

-Alcoholics, deficiency is quite uncommon

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15
Q

Vitamin B3/Niacin (functions, deficiencies, susceptible groups)

A

Function:

-Precursor of NAD and NADP (coenzymes important in redox reactions of energy metabolism)

Deficiency:

-Pellagra: Characterized by dermatitis, diarrhea, and “dementia” (confusion, memory loss, mania)

Susceptible groups:

-People with corn or millet based diets

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16
Q

Vitamin B7/Biotin (functions, deficiencies, susceptible groups)

A

Function:

-Coenzyme for several carboxylases

Deficiency:

-Rare, but can be caused by eating a lot of raw eggs

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17
Q

Vitamin B5/Pantothenic Acid (functions, deficiencies, susceptible groups)

A

Function:

  • Required for the synthesis of CoA: CoA is a coenzyme for up to 70 different enzymes
  • Required for TCA cycle and metabolism of all fats and proteins

Deficiency:

-Very rare. Symptoms are typical of B vitamins

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18
Q

Vitamin B6/Pyridoxine (functions, deficiencies, susceptible groups)

A

Function:

  • Precursor of pyridoxyl phosphate (PLP) enzyme cofactor
  • Required for glycogen breakdown, and synthesis of GABA and heme

Deficiency:

  • Mild: irritability, nervousness, depression
  • Severe: peripheral neuropathy, convulsions, decreased glucose tolerance, hyper-homocysteinemia (cardiovascular risk), anemia

Susceptible Groups:

-Patients treated with certain drugs (isoniazid for TB)

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19
Q

What symptoms are common to most vitamin B deficiencies?

A
  • Symptoms show up first in rapidly dividing tissues. Skin: dermatitis, tongue:glossitis, GI:diarrhea
  • Nervous system also affected because of high energy demand: peripheral neuropathy (tingling of extremities,) depression, confusion, lack of coordination, malaise
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20
Q

Vitamin B9/Folate (functions, deficiencies, susceptible groups)

A

Function:

-precursor of tetrahydrofolate, co-enzyme involved in generating precursors for DNA and protein synthesis.

Deficiency:

  • neural tube defects in newborns of deficient mothers
  • macrocytic anemia
  • hyperhomocysteinemia(cardiovascular risk)

Susceptible groups:

  • pregnant women
  • the elderly
  • alcoholics
  • patients with certain long-term drug treatments (Anticonvulsant drugs and oral contraceptives)
  • people with genetic polymorphisms in folate metabolism
21
Q

Vitamin B12/Cobalamin (functions, deficiencies, susceptible groups)

A

Function:

  • coenzyme in methionine synthesis and in conversion of methylmalonyl CoA to succinyl CoA
  • needed in folate metabolism

Deficiency:

-Pernicious anemia (megaloblastic anemia) with demyelination

Susceptible groups:

  • the elderly
  • patients with malabsorption diseases
  • long-term vegetarians
22
Q

Calcium (functions, deficiencies, susceptible groups)

A

Functions:

  • Major component of bone
  • Signaling
  • Coagulation
  • Muscle contraction
  • Neurotransmission

Deficiency:

  • Mild: muscle cramps, osteoporosis
  • Severe: rickets

Susceptible groups:

  • Children
  • Adult women
  • The elderly
23
Q

Magnesium (functions, deficiencies, susceptible groups)

A

Functions:

  • Essential for many enzymes (which use MgATP as substrate)
  • Present at high levels in bone

Deficiency:

-Weakness, tremors, cardiac arrhythmia

Susceptible groups:

  • Alcoholics
  • Patients taking diuretics, or experiencing severe vomiting and diarrhea
24
Q

Iron (functions, deficiencies, susceptible groups)

A

Function:

  • O2/CO2 transport in hemoglobin
  • oxidative phosphorylation
  • cofactor in several nonheme iron proteins and cytochromes (redox properties of iron are important)

Deficiency:

  • Microcytic hypochromic anemia
  • Decreased immunity

Susceptible groups:

  • Children and menstruating women, pregnant women (increased demand)
  • The elderly
25
Q

Phosphorus (functions, deficiencies, susceptible groups)

A

Functions:

  • Mostly present in phosphates
  • Major component of bone (hydroxyapatite)
  • Constituent of nucleic acids, membrane lipids
  • Required in all energy-producing reactions

Deficiency (Rare, abundant in many foods):

  • Rickets
  • Muscle weakness and breakdown
  • Seizure
26
Q

Why does vitamin C deficiency cause mild anemia?

A

Reduction of Fe3+ (form released by food) to Fe2+ is promoted by vitamin C (Fe2+ is bioavailable form)

27
Q

What are the effects of iron toxicity?

A

Long-term: Hemochromatosis

  • iron overload leads to iron deposits in multiple tissues. Leads to compromised liver, pancreatic, and cardiac function.
  • ultimately can compromise mitochondrial function leading to lactic acidosis.

Acute: most common cause of death due to toxicity in children under 6 (Medscape), comes from consumption of adult iron supplements

28
Q

Copper (functions, deficiencies, susceptible groups)

A

Functions:

  • Assists iron absorption through ceruloplasmin
  • Cofactor for enzymes required in collagen synthesis, fatty acid metabolism, and elimination of reactive oxygen species

Deficiency (quite rare):

-Symptoms include anemia, hypercholesterolemia, fragility of large arteries, bone demineralization demyelination

Susceptible Groups:

  • Those with genetic disease (Menkes’ syndrome)
  • Patients consuming excessive zinc
29
Q

Zinc (functions, deficiencies, susceptible groups)

A

Function:

  • Cofactor for over 300 metalloenyzmes
  • Plays a structural role in many proteins (Zn finger domains)

Deficiency:

  • Poor wound healing
  • Dermatitis (earliest symptom)
  • Reduced taste acuity
  • Poor growth and impaired sexual development in children

Susceptible groups:

  • Alcoholics
  • The elderly
  • People with malabsorption or kidney disease
30
Q

Chromium (functions, deficiencies, susceptible groups)

A

Function:

-Component of chromodulin: facilitates insulin binding to its receptor

Deficiency:

-Impaired glucose tolerance (from reduced insulin effectiveness)

Susceptible populations:

-Those with impaired glucose tolerance (Cr3+ hasn’t yet proven helpful in treatment of type 2 diabetics.)

31
Q

Iodine (functions, deficiencies, susceptible groups)

A

Function:

-Incorporated into triiodothyronine (T3) and thyroxine (T4) (Regulates basal metabolic rate)

Deficiency:

  • Goiter: enlarged thyroid gland
  • Hyperthyroidism or hypothyroidism

Susceptible Groups:

-Developing world populations (Iodized salt has reduced incidence)

32
Q

Selenium (functions, deficiencies, susceptible groups)

A

Function:

  • Component of antioxidant enzymes (ex. glutathione peroxidase)
  • Component of deiodinase enzymes involved in T3 and T4 metabolism

Deficiency:

-Keshan disease: cardiomyopathy and cretinism

Susceptible Groups:

-People living in areas with little selenium in soil

33
Q

What are the most common nutrient deficiencies among alcoholics?

A

Folate, B6, and thiamine (many others are common)

34
Q

What are the most common nutrient deficiencies among children?

A

Iron and calcium

35
Q

What are the most common nutrient deficiencies among teenagers?

A

calcium and magnesium, possibly vitamin A, C, and B6

36
Q

What are the most common nutrient deficiencies among women?

A

iron, calcium, magnesium, vitamin B6, folate

37
Q

What are the most common nutrient deficiencies among the elderly?

A

Vitamins B6, B12, D, possibly zinc and chromium

38
Q

What is the function of manganese?

A

Cofactor or structural component for arginase, pyruvate carboxylase, superoxide dismutase.

39
Q

What is the function of molybdenum?

A

cofactor/structural component for xanthene oxidase

40
Q

What is the function of fluoride?

A

It is incorporated into bones and teeth, strengthening them

41
Q

What is the function of boron?

A

it is involved in bone formation.

42
Q

What is the function of sulfur?

A

It is a component of amino acids. It is also used in certain post-translational modifications.

43
Q

How is resting energy expenditure calculated?

A

For adult men:

(900 + 10w) * activity coefficient

For adult women:

(700 + 7w) * activity coefficient

w = weight in kg

Activity coefficients:

sedentary: 1.2

moderately active: 1.4

very active: 1.8

44
Q

How is BMI calculated?

A

BMI = Weight in kg divided by the square of height in meters = kg/m2.

45
Q

What are the value ranges associated with the WHO BMI dependent weight classifications?

A

<18.5 underweight

  1. 5—24.9 normal
  2. 0—29.9 Grade 1 overweight
  3. 0—39.9 Grade 2 overweight (obese)

≥40.0 Grade 3 overweight (morbidly obese)

46
Q

How is required energy expenditure for a given weight loss calculated?

A

Assuming all weight loss is in adipose tissue:

  • Adipose tissue is 85% fat, 15% water.
  • Therefore, 1 kg adipose tissue = 850 g fat.
  • 850 g * 9 kcal/g = 7650 kcal per kg of adipose tissue lost.

The calculations for weight gain are eqivalent.

47
Q

What is the energy content of a gram of each of the macronutrients?

A

protein: 4 Cal
carbohydrate: 4 Cal
fat: 9 Cal
alcohol: 7 Cal

48
Q

Why should “sweet” and starchy carbohydrate sources be distinguished?

A

Sucrose or high fructose corn syrup containing “sweets” are high in fructose. Fructose is metabolized primarily in the liver, and when the liver has to handle too much fructose, it turns it into TG that is deposited in the liver itself. Fatty liver (liver steatosis) leads to other metabolic derangements, including insulin resistance.

Medical Biochemistry (4 decks)

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