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5 HIAA in urine is due to ?
a. Pheochromocytoma
b. Carcinoid Syndrome
c. Phenyl Ketonuria
d. Alkaptonuria
The correct answer is b. Carcinoid Syndrome.
Explanation:
5-Hydroxyindoleacetic Acid (5-HIAA) is the primary metabolite of serotonin, a chemical that nerves and brain cells produce. An increase in 5-HIAA in the urine is most commonly associated with carcinoid tumors, which are a type of neuroendocrine tumor that secretes large amounts of serotonin.
Carcinoid Syndrome is characterized by a group of symptoms that include flushing, diarrhea, asthma, and, less frequently, heart failure. These symptoms are due to the excessive production of serotonin by carcinoid tumors, primarily found in the gastrointestinal tract or the lungs. The excess serotonin is metabolized in the liver to 5-HIAA, which is excreted in the urine. Therefore, measuring 5-HIAA levels in urine is a diagnostic test for carcinoid syndrome.
Degradation Products in Each Condition:
Pheochromocytoma: This condition involves tumors of the adrenal gland that produce excessive catecholamines, including epinephrine (adrenaline) and norepinephrine. The degradation products increased in this condition are metanephrine and normetanephrine, which are metabolites of epinephrine and norepinephrine, respectively. These can be measured in plasma or urine to diagnose pheochromocytoma.
Carcinoid Syndrome: As mentioned, the key degradation product increased is 5-HIAA, a metabolite of serotonin. This is because carcinoid tumors often produce high levels of serotonin.
Phenylketonuria (PKU): In this genetic disorder, there's a deficiency of the enzyme phenylalanine hydroxylase, leading to an accumulation of phenylalanine in the body. The degradation product increased in PKU is phenylalanine itself, as it cannot be adequately metabolized to tyrosine. This can lead to neurological damage if not treated early.
Alkaptonuria: This is another genetic disorder characterized by the body's inability to break down the amino acids phenylalanine and tyrosine properly, due to a deficiency of the enzyme homogentisate 1,2-dioxygenase. The degradation product increased in alkaptonuria is homogentisic acid. Accumulation of homogentisic acid leads to its oxidation and polymerization, causing darkening of the urine upon standing (alkaptonuria), and can also lead to ochronosis, the bluish-black discoloration of connective tissues.
Each of these conditions is associated with a distinct metabolic abnormality and increased specific degradation products, which can be used for diagnostic purposes.