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Which of the following is an example of negative feedback loop in humans?
A
secretion of tears after falling of sand particles into the eye
B
salivation of mouth at the sight of delicious food
C
secretion of sweat glands and constriction of skin blood vessels when it is too hot
D
constriction of skin blood vessels and contraction of skeletal muscles when it is too cold
Detailed Solution
In a negative feedback loop, a change in a controlled condition brings about responses that oppose the change and return the condition to its set point.
Body temperature is controlled by the thermoregulatory centre in the hypothalamus.
When it is too cold, the hypothalamus brings about constriction of the skin blood vessels (vasoconstriction), which reduces heat loss, and contraction of skeletal muscles (shivering), which produces heat.
The body temperature rises back to normal, and the responses then stop. This is a negative feedback loop.
When it is too hot, the correct responses are sweating and dilation (not constriction) of the skin blood vessels, so that statement is wrong as written.
Secretion of tears and salivation at the sight of food are reflex actions, not feedback loops.
So the example of a negative feedback loop is the constriction of skin blood vessels and contraction of skeletal muscles when it is too cold.
Body temperature is controlled by the thermoregulatory centre in the hypothalamus.
When it is too cold, the hypothalamus brings about constriction of the skin blood vessels (vasoconstriction), which reduces heat loss, and contraction of skeletal muscles (shivering), which produces heat.
The body temperature rises back to normal, and the responses then stop. This is a negative feedback loop.
When it is too hot, the correct responses are sweating and dilation (not constriction) of the skin blood vessels, so that statement is wrong as written.
Secretion of tears and salivation at the sight of food are reflex actions, not feedback loops.
So the example of a negative feedback loop is the constriction of skin blood vessels and contraction of skeletal muscles when it is too cold.