Vitamins & Micronutrients

Name the 8 water-soluble and 4 fat-soluble vitamins.

Water Soluble - Vitamin C, Vitamin B1 (Thiamine), Vitamin B2 (Riboflavin), Vitamin B3 (Niacin), Vitamin B5 (Pantothenic acid), Vitamin B6 (Pyridoxine), Vitamin B7 (Biotin), Vitamin B9 (Folic acid), Vitamin B12 (Cobalamin).

Fat Soluble - Vitamin A, Vitamin D, Vitamin E, Vitamin K.

2. Name the two active forms of Vitamin A.

Retinol and Retinoic Acid

3. What receptor do the two active Vitamin A forms bind to? What are the main functions of Vitamin A?

Receptor: Retinoic acid binds to the retinoic acid receptor (RAR), and retinol binds to cellular retinol-binding proteins (CRBP).

Functions: Vision (via retinal in the visual cycle), immune function, cellular differentiation, and epithelial health.

4. What are the common symptoms of hypervitaminosis A?

Symptoms include headache, dizziness, nausea, bone pain, liver damage, dry skin, and in severe cases, intracranial hypertension.

5. Describe the process in which cholecalciferol (Vitamin D3) gets converted into the biologically active form (calcitriol)

Cholecalciferol (Vitamin D3) is synthesized in the skin or ingested through diet.

It is hydroxylated in the liver to form 25-hydroxyvitamin D (calcidiol).

Calcidiol is further hydroxylated in the kidneys by 1α-hydroxylase to form the active form, 1,25-dihydroxyvitamin D (calcitriol).

6. What is the main role of Vitamin D?

Vitamin D helps regulate calcium and phosphorus levels, promoting bone health and mineralization.

7. What are the three clinical manifestations of Vitamin D deficiency?

Rickets (in children).

Osteomalacia (in adults).

Hypocalcemia-related muscle weakness or tetany.

8. T/F: Tocopherols are more potent forms of Vitamin E than tocotrienols.

True

9. Name the enzyme and the clotting factors that Vitamin K plays a role in activating.

Enzyme: γ-glutamyl carboxylase.

Clotting Factors: II (Prothrombin), VII, IX, and X.

10. What medication is Vitamin K used to reverse the effects of during an acute bleed?

Warfarin

11. Name a few health functions of Vitamin C.

Collagen synthesis, antioxidant activity, iron absorption, and immune system support.

12. What is the condition called when patients have a Vitamin C deficiency? What are some common symptoms of this deficiency?

Condition: Scurvy.

Symptoms: Bleeding gums, petechiae, joint pain, anemia, and impaired wound healing.

13. FITB: The B vitamins are a collection of water-soluble ___________ used in various metabolic pathways.

Coenzymes

14. What are the two main biochemical roles of thiamine pyrophosphate?

Coenzyme in carbohydrate metabolism (e.g., pyruvate dehydrogenase, α- ketoglutarate dehydrogenase).

Role in transketolase activity in the pentose phosphate pathway.

15. Describe the two syndromes that can result from thiamine deficiency.

Wernicke-Korsakoff Syndrome: Symptoms include confusion, lack of coordination and memory impairment.

Beriberi Syndrome: Seen in areas where polished rice is major dietary component. Causes peripheral neuropathy, muscle weakness, and edema due to cardiac dysfunction.

16. What are the two active forms of Vitamin B2 (Riboflavin)? What are the main roles of this vitamin?

Active Forms: Flavin mononucleotide (FMN) and Flavin adenine dinucleotide (FAD).

Roles: Energy production in redox reactions (e.g., electron transport chain) and metabolism of fats, carbohydrates, and proteins.

17. What is the deficiency of Vitamin B3 called and what are the symptoms?

Deficiency: Pellagra.

Symptoms: Dermatitis, Diarrhea, Dementia, and eventually Death (4 D's).

18. How is pantothenic acid related to coenzyme A?

Pantothenic acid is a precursor for the synthesis of coenzyme A, which is essential in fatty acid metabolism and energy production.

19. What drug can induce Vitamin B6 (pyridoxine) deficiency and must be supplemented when patients take this medication?

Drug: Isoniazid (used for tuberculosis).

20. What is the biochemical role of Vitamin B7 (biotin)?

Acts as a coenzyme in carboxylation reactions, such as in gluconeogenesis, fatty acid synthesis, and amino acid metabolism.

21. List some of the manifestations that can occur from folic acid deficiency.

Megaloblastic anemia, fatigue, glossitis, neural tube defects in fetuses, and increased homocysteine levels.

22. What is the active form of folic acid and what are the 3 groups that play a role in carbon transfer in amino acid synthesis?

Active Form: Tetrahydrofolate (THF).

Groups: Methyl, methylene, and formyl groups.

23. What biochemical role does cobalamin have, and what can a deficiency in this vitamin cause?

Role: Cobalamin (Vitamin B12) is a coenzyme in DNA synthesis and methylation reactions, and it converts homocysteine to methionine.

Deficiency: Can cause megaloblastic anemia, peripheral neuropathy, and subacute combined degeneration of the spinal cord.

24. Describe what can occur when there are derangements in sodium, potassium, magnesium, calcium, phosphate, and iodine.

Sodium: Hyponatremia → confusion, seizures; Hypernatremia → dehydration symptoms.

Potassium: Hypokalemia → arrhythmias, muscle weakness; Hyperkalemia → cardiac arrest risk.

Magnesium: Hypomagnesemia → tremors, tetany; Hypermagnesemia → hypotension, lethargy.

Calcium: Hypocalcemia → tetany, seizures; Hypercalcemia → nephrolithiasis, bone pain.

Phosphate: Hypophosphatemia → weakness, bone pain; Hyperphosphatemia → soft tissue calcification.

Iodine: Deficiency → goiter, hypothyroidism; Excess → thyroid dysfunction.

1. Major Roles of Steroids in Metabolism

Steroids are involved in regulating various physiological processes:

  • Energy metabolism: Steroids like glucocorticoids (e.g., cortisol) promote gluconeogenesis, glycogenolysis, and lipolysis to provide energy.

  • Electrolyte balance: Mineralocorticoids (e.g., aldosterone) regulate sodium and potassium balance by acting on the kidneys.

  • Immune function: Steroids modulate immune responses, often suppressing inflammation and immune activity.

  • Growth and development: Steroids like androgens and estrogens influence growth, reproduction, and sexual differentiation.

2. Major Steroid Hormone Classes

  • Glucocorticoids (e.g., cortisol): Involved in stress response and energy metabolism.

  • Mineralocorticoids (e.g., aldosterone): Regulate electrolyte and fluid balance.

  • Androgens (e.g., testosterone): Support male characteristics and reproductive activity.

  • Estrogens (e.g., estradiol): Support female characteristics and reproductive activity.

  • Progestogens (e.g., progesterone): Involved in pregnancy and menstrual cycle regulation.

3. Hormonal Stimulation and Steps of Steroid Biosynthesis

  1. Hormonal stimulation: Tropic hormones like ACTH (adrenocorticotropic hormone) or LH (luteinizing hormone) trigger steroid biosynthesis in response to physiological needs.

  2. Steps of steroid biosynthesis:

    • Cholesterol uptake: Cholesterol serves as the precursor for all steroid hormones.

    • Conversion to pregnenolone via the enzyme cholesterol side-chain cleavage enzyme (CYP11A1) in the mitochondria.

    • Sequential enzymatic reactions modify pregnenolone into specific steroid hormones like cortisol, aldosterone, testosterone, or estradiol.

4. Steroid Hormone Synthesis in Major Sites

  • Adrenal Cortex:

    • Zona glomerulosa: Produces mineralocorticoids (e.g., aldosterone).

    • Zona fasciculata: Produces glucocorticoids (e.g., cortisol).

    • Zona reticularis: Produces androgens (e.g., dehydroepiandrosterone or DHEA).

  • Gonads:

    • Ovaries: Produce estrogens and progesterone.

    • Testes: Produce testosterone.

  • Placenta: Synthesizes progesterone and estrogens during pregnancy.

5. Mechanism of Action of Steroid Hormones

  • Lipid solubility: Steroid hormones easily cross the cell membrane.

  • Binding to intracellular receptors: In the cytoplasm or nucleus, they bind to specific steroid hormone receptors.

  • Transcription regulation: The hormone-receptor complex binds to DNA at hormone response elements, modulating the transcription of specific genes.

  • Protein synthesis: Changes in gene expression lead to the production of proteins that mediate the physiological effects of the hormone.

6. How Glucocorticoids and Mineralocorticoids Work

  • Glucocorticoids:

    • Increase gluconeogenesis and mobilization of energy stores.

    • Suppress inflammation and immune system activity.

    • Aid in stress response.

  • Mineralocorticoids:

    • Act on the renal distal tubules to increase sodium reabsorption, potassium excretion, and water retention.

    • Help maintain blood pressure and fluid balance.

7. Examples of Corticosteroid Use in Medicine

  • Glucocorticoids:

    • Anti-inflammatory: Used in conditions like asthma, rheumatoid arthritis, and inflammatory bowel disease.

    • Immunosuppressive: To prevent organ transplant rejection or treat autoimmune diseases.

    • Adrenal insufficiency: Replacing cortisol in Addison’s disease.

  • Mineralocorticoids:

    • Treat conditions like Addison's disease (e.g., fludrocortisone is used to replace aldosterone).

  • Combined therapies:

    • Hormonal therapy in cancers like prostate or breast cancer.

    • Treatment of congenital adrenal hyperplasia (CAH).