endocrine biochemistry mbbs basic science
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1. **Question**: Which of the following hormones is derived from cholesterol?
a) Insulin
b) Cortisol
c) Growth hormone
d) Prolactin
**Correct Answer**: b) Cortisol
**Explanation**: Cortisol is a steroid hormone derived from cholesterol, synthesized in the adrenal cortex.
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2. **Question**: The enzyme responsible for the conversion of T4 (thyroxine) to T3 (triiodothyronine) is:
a) Thyroid peroxidase
b) Deiodinase
c) 11β-hydroxylase
d) 3β-hydroxysteroid dehydrogenase
**Correct Answer**: b) Deiodinase
**Explanation**: Deiodinase enzymes are responsible for the conversion of T4 to the more active T3.
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3. **Question**: Which of the following is the precursor molecule for the synthesis of thyroid hormones?
a) Tyrosine
b) Phenylalanine
c) Iodine
d) Glycogen
**Correct Answer**: a) Tyrosine
**Explanation**: Thyroid hormones (T3 and T4) are synthesized from the amino acid tyrosine and iodine.
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4. **Question**: Insulin resistance primarily affects which of the following metabolic pathways?
a) Glycogen synthesis
b) Lipid oxidation
c) Glucose uptake
d) Protein degradation
**Correct Answer**: c) Glucose uptake
**Explanation**: Insulin resistance impairs glucose uptake in cells, particularly in muscle and adipose tissue.
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5. **Question**: The main site of synthesis for cortisol is:
a) Liver
b) Adrenal cortex
c) Pancreas
d) Kidney
**Correct Answer**: b) Adrenal cortex
**Explanation**: Cortisol is synthesized in the zona fasciculata of the adrenal cortex.
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6. **Question**: Which of the following is NOT a steroid hormone?
a) Aldosterone
b) Testosterone
c) Estrogen
d) Thyroxine
**Correct Answer**: d) Thyroxine
**Explanation**: Thyroxine (T4) is an amino acid-derived hormone, not a steroid.
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7. **Question**: Which of the following hormones acts by a second messenger system involving cyclic AMP (cAMP)?
a) Insulin
b) Thyroid hormone
c) Glucagon
d) Estrogen
**Correct Answer**: c) Glucagon
**Explanation**: Glucagon acts via the cAMP second messenger system to stimulate glycogen breakdown and increase blood glucose.
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8. **Question**: The principal action of parathyroid hormone (PTH) is to:
a) Stimulate calcium uptake from the intestines
b) Decrease calcium excretion by the kidneys
c) Increase phosphate excretion by the kidneys
d) All of the above
**Correct Answer**: d) All of the above
**Explanation**: PTH raises blood calcium levels by promoting calcium release from bones, increasing calcium reabsorption in the kidneys, and enhancing calcium absorption in the intestines.
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9. **Question**: The precursor molecule for the synthesis of catecholamines (epinephrine and norepinephrine) is:
a) Phenylalanine
b) Tyrosine
c) Tryptophan
d) Glutamine
**Correct Answer**: b) Tyrosine
**Explanation**: Catecholamines are synthesized from the amino acid tyrosine.
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10. **Question**: Which enzyme is responsible for the synthesis of insulin from proinsulin?
a) Peptidyl transferase
b) Prohormone convertase
c) Glycogen synthase
d) Deiodinase
**Correct Answer**: b) Prohormone convertase
**Explanation**: Prohormone convertase enzymes cleave proinsulin to insulin and C-peptide.
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11. **Question**: Which of the following hormones stimulates gluconeogenesis in the liver?
a) Insulin
b) Cortisol
c) Growth hormone
d) Prolactin
**Correct Answer**: b) Cortisol
**Explanation**: Cortisol promotes gluconeogenesis in the liver, increasing blood glucose levels.
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12. **Question**: Which of the following is a primary function of aldosterone?
a) Stimulate sodium reabsorption in the kidneys
b) Stimulate calcium absorption in the intestines
c) Increase heart rate
d) Regulate blood glucose levels
**Correct Answer**: a) Stimulate sodium reabsorption in the kidneys
**Explanation**: Aldosterone increases sodium reabsorption in the distal tubules and collecting ducts of the kidneys.
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13. **Question**: Which enzyme is responsible for the conversion of angiotensin I to angiotensin II?
a) Renin
b) Angiotensin-converting enzyme (ACE)
c) Aldosterone synthase
d) 11β-hydroxylase
**Correct Answer**: b) Angiotensin-converting enzyme (ACE)
**Explanation**: ACE converts angiotensin I to the active form, angiotensin II, which increases blood pressure.
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14. **Question**: What is the mechanism of action of glucagon?
a) Activation of the PI3K/Akt pathway
b) Activation of adenylyl cyclase to increase cAMP levels
c) Inhibition of phosphodiesterase
d) Stimulation of protein synthesis
**Correct Answer**: b) Activation of adenylyl cyclase to increase cAMP levels
**Explanation**: Glucagon activates adenylyl cyclase to increase cAMP levels, stimulating glycogen breakdown and increasing blood glucose levels.
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15. **Question**: Which of the following is the function of the hormone leptin?
a) Decrease appetite
b) Increase appetite
c) Regulate calcium metabolism
d) Increase glucose uptake in cells
**Correct Answer**: a) Decrease appetite
**Explanation**: Leptin is an adipocyte-derived hormone that decreases appetite by acting on the hypothalamus.
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16. **Question**: Which of the following is a direct effect of insulin?
a) Inhibition of glycogen synthesis
b) Promotion of lipolysis
c) Promotion of glucose uptake by muscle and adipose tissue
d) Stimulation of gluconeogenesis
**Correct Answer**: c) Promotion of glucose uptake by muscle and adipose tissue
**Explanation**: Insulin promotes the uptake of glucose into cells, particularly muscle and adipose tissue.
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17. **Question**: Which of the following is true about thyroid hormone?
a) It increases basal metabolic rate
b) It is synthesized in the anterior pituitary
c) It is water-soluble
d) It binds to a receptor in the cytoplasm
**Correct Answer**: a) It increases basal metabolic rate
**Explanation**: Thyroid hormone increases the basal metabolic rate by stimulating metabolic processes in tissues.
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18. **Question**: What is the effect of increased parathyroid hormone (PTH) secretion on bone?
a) Bone resorption is increased
b) Bone formation is increased
c) Bone matrix is unaffected
d) Bone mineralization is promoted
**Correct Answer**: a) Bone resorption is increased
**Explanation**: PTH stimulates osteoclast activity, leading to increased bone resorption and the release of calcium into the bloodstream.
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19. **Question**: Which of the following is a precursor for the synthesis of the steroid hormone estrogen?
a) Cholesterol
b) Tyrosine
c) Progesterone
d) Cortisol
**Correct Answer**: a) Cholesterol
**Explanation**: Estrogen is synthesized from cholesterol through a series of enzymatic steps in the gonads.
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20. **Question**: The primary action of somatostatin in the endocrine system is to:
a) Stimulate insulin secretion
b) Inhibit growth hormone secretion
c) Promote glucagon release
d) Increase thyroid hormone production
**Correct Answer**: b) Inhibit growth hormone secretion
**Explanation**: Somatostatin inhibits the release of growth hormone from the pituitary gland and insulin from the pancreas.
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21. **Question**: What is the principal biochemical action of cortisol?
a) Decreasing blood glucose
b) Promoting protein synthesis
c) Increasing blood glucose
d) Reducing sodium reabsorption
**Correct Answer**: c) Increasing blood glucose
**Explanation**: Cortisol increases blood glucose levels by promoting gluconeogenesis in the liver and inhibiting insulin action.
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22. **Question**: Which of the following hormones is responsible for regulating the circadian rhythm?
a) Cortisol
b) Melatonin
c) Prolactin
d) Growth hormone
**Correct Answer**: b) Melatonin
**Explanation**: Melatonin, secreted by the pineal gland, regulates sleep-wake cycles and circadian rhythms.
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23. **Question**: Which of the following is the primary role of the hormone ghrelin?
a) Stimulate insulin secretion
b) Increase appetite
c) Decrease appetite
d) Increase energy expenditure
**Correct Answer**: b) Increase appetite
**Explanation**: Ghrelin, produced in the stomach, stimulates appetite and increases food intake.
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24. **Question**: Which of the following hormones promotes lipogenesis in adipose tissue?
a) Glucagon
b) Insulin
c) Cortisol
d) Growth hormone
**Correct Answer**: b) Insulin
**Explanation**: Insulin promotes lipogenesis, the storage of fat, in adipose tissue by stimulating the uptake of glucose and its conversion into fatty acids.
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25. **Question**: Which of the following is the function of aldosterone in the renal system?
a) Increase potassium excretion
b) Decrease sodium reabsorption
c) Promote water ex
cretion
d) Increase sodium reabsorption
**Correct Answer**: d) Increase sodium reabsorption
**Explanation**: Aldosterone acts on the kidneys to promote sodium reabsorption and potassium excretion, which helps regulate blood pressure.
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