The parathyroid glands respond to which type of stimulus?
A hormonal
B neural
C humoral
D positive
The correct answer and explanation is:
The correct answer is C: humoral.
The parathyroid glands primarily respond to humoral stimuli. This type of stimulus involves the regulation of hormone release in response to changes in the levels of certain ions or other substances in the blood. Specifically, the parathyroid glands are highly sensitive to the concentration of calcium in the blood. When blood calcium levels drop, the parathyroid glands detect this decrease through calcium-sensing receptors on their surface. In response to low calcium levels, they release parathyroid hormone (PTH) into the bloodstream.
PTH plays a critical role in maintaining calcium homeostasis by increasing blood calcium levels. It does so by several mechanisms: it stimulates the release of calcium from bones, enhances calcium reabsorption in the kidneys, and promotes the activation of vitamin D, which in turn increases calcium absorption from the intestines. When blood calcium levels return to normal, the secretion of PTH is reduced, thus providing a feedback mechanism to maintain calcium balance.
This humoral regulation is crucial for preventing conditions like hypocalcemia, where low calcium levels can lead to muscle spasms and other health issues. In contrast to hormonal, neural, and positive feedback mechanisms, humoral control is based on the direct influence of blood components, making it a key regulatory pathway for maintaining balance in the body’s internal environment.