Which statement about insulin is correct?
A) Insulin is produced by the liver when the blood glucose concentration is high. Its target cells are in the pancreas.
B) Insulin is produced by the liver when the blood glucose concentration is low. Its target cells are in the pancreas.
C) Insulin is produced by the pancreas when the blood glucose concentration is high. Its target cells are in the liver.
D) Insulin is produced by the pancreas when the blood glucose concentration is low. Its target cells are in the liver.
▶️ Answer/Explanation
Ans: C
Key facts about insulin:
- Produced by β-cells in the pancreas (not the liver).
- Secreted in response to high blood glucose levels.
- Target cells are primarily in the liver, where it promotes glucose uptake and glycogen synthesis.
Thus, the correct statement is C: Insulin is produced by the pancreas during high blood glucose and acts on liver cells.
What describes how the body maintains a constant internal temperature on a hot day?
A) Vasoconstriction increases blood flow to the skin surface capillaries.
B) Vasoconstriction decreases blood flow to the skin surface capillaries.
C) Vasodilation increases blood flow to the skin surface capillaries.
D) Vasodilation decreases blood flow to the skin surface capillaries.
▶️ Answer/Explanation
Ans: C) Vasodilation increases blood flow to the skin surface capillaries.
Explanation:
- Vasodilation is the process where blood vessels widen, increasing blood flow to the skin surface. This helps release excess heat through radiation and sweating.
- On hot days, the body uses this mechanism to maintain its core temperature by transferring heat to the environment.
Why other options are incorrect:
A) Vasoconstriction would reduce heat loss (occurs in cold conditions, not hot).
B) While this describes vasoconstriction correctly, it’s the opposite of what happens in heat.
D) Vasodilation always increases blood flow – the description is contradictory.
Key concept: The body uses vasodilation as its primary cooling mechanism, making C the only correct answer.