Which of the following enzymes functions at the lowest pH?
Trypsin
Pancreatic amylase
Pepsin
Salivary amylase
The Correct Answer is C
A. Trypsin functions in the small intestine, where the environment is slightly alkaline. Therefore, this enzyme does not function at a low pH.
B. Pancreatic amylase also functions in the small intestine, where the pH is neutral to slightly alkaline.
C. Pepsin functions in the stomach, where the environment is highly acidic (pH 1.5 to 2). Pepsin is the correct answer because it works optimally at this low pH.
D. Salivary amylase functions in the mouth, where the pH is neutral or slightly alkaline.
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Correct Answer is B
Explanation
A. It stimulates angiotensin II secretion: Antidiuretic hormone (ADH) does not directly stimulate angiotensin II secretion; instead, it acts on the kidneys to promote water reabsorption.
B. It promotes water conservation: ADH promotes water conservation by increasing water reabsorption in the kidneys, reducing urine output, and thus helping to maintain fluid balance.
C. It inhibits salivation and thirst: ADH does not inhibit salivation or thirst; in fact, it can increase thirst to encourage fluid intake when dehydration is detected.
D. It stimulates hypothalamic osmoreceptors: While ADH affects hypothalamic osmoreceptors indirectly by promoting water retention, its primary function is to act on the kidneys to conserve water.
Correct Answer is C
Explanation
A. Posterior pituitary releases hormones such as ADH (antidiuretic hormone), but it does not have aldosterone receptors.
B. Proximal convoluted tubule is involved in reabsorption, but it does not have aldosterone receptors.
C. Distal convoluted tubule: Aldosterone receptors are found in the cells of the distal convoluted tubule. Aldosterone increases sodium reabsorption and potassium excretion in this part of the nephron, which helps regulate blood pressure and electrolyte balance.
D. Adrenal medulla produces catecholamines (e.g., adrenaline) but does not contain aldosterone receptors.