Answer is option A (receptor).
These nerve endings represent a receptor in the negative feedback mechanism.
Explanation:
Homeostasis in the human body is the tendency of the body to maintain its internal environment suitable for normal and optimal functioning by adjusting the changes occurring in internal variables such as body temperature, blood pressure, etc using feedback mechanisms. The two feedback mechanisms involved in homeostasis are positive feedback (the output of the system stimulates the system to increase the output further) and negative feedback mechanisms (the output of the system stimulates the system to decrease the output).
The various components in the feedback loop include;
stimulus - an initiation event that causes changes in a variable.
variable - a physiological factor that is kept at a normal range.
receptors - monitor the variable, detect changes in the variable value and report to control center.
control center - it compares the variable value to the normal range and if any deviation is found, the effectors are activated.
effectors - return the value to the normal range by making adjustments in the same direction (positive feedback) or opposite direction (negative feedback) of the stimulus.
In the body’s thermoregulation mechanism, a negative feedback loop is used in which the variable is body temperature. The nerve endings in the skin that are sensitive to changes in temperature are called heat-sensitive thermoreceptors. They detect changes in body temperature and produce nerve impulses that signal the hypothalamus in the brain. The hypothalamus is the control center that compares the body temperature with the normal range and activates and controls different effectors such as muscles, blood vessels, adrenal glands, sweat glands, etc. These effectors controlled by the hypothalamus perform certain physiological activities that can return the body temperature to normal range.
When body temperature drops, the hypothalamus activates and control the effectors such as blood vessels to constrict in order to decrease the flow of heat to the skin, muscles to shiver in order to increase the production of heat, adrenal glands to secrete hormones (norepinephrine and epinephrine) in order to increase metabolic rates and heat production. All these effects cause the body temperature to increase and return to normal.
When body temperature rises, the hypothalamus activates and controls the effectors such as blood vessels to dilate in order to increase the flow of heat to the skin, sweat glands to release sweat, which on evaporation cools the skin. All these effects cause the body temperature to decrease and return to normal.
