In human physiology, which of the following situations is the best example of a negative feedback mechanism that stabilizes an internal condition?

Introduction / Context:
Negative feedback is one of the most important principles in human physiology and homeostasis. It refers to control mechanisms in which the response of a system counteracts or reverses an initial change. This question asks you to identify which situation is a clear example of negative feedback that helps stabilize an internal condition, such as blood sugar level.

Given Data / Assumptions:
- The body uses feedback systems to maintain stable internal conditions (homeostasis).
- Negative feedback reduces or reverses the original change.
- Positive feedback amplifies or increases the original change.
- Examples include hormonal control of blood glucose and control of blood clotting and labor contractions.

Concept / Approach:
In negative feedback, a rise in a variable triggers responses that lower it, or a fall triggers responses that raise it. The goal is to keep the variable near a normal set point. In blood glucose regulation, eating raises blood sugar. Insulin secretion then promotes uptake and storage of glucose, which lowers blood sugar back toward normal. This clearly opposes the initial rise and therefore is negative feedback. By contrast, positive feedback mechanisms, such as labor contractions and blood clotting, intensify the original change rather than stabilizing it.

Step-by-Step Solution:
Step 1: Identify what happens to blood sugar after a meal. It rises above the fasting level. Step 2: Recognize that insulin release from the pancreas increases after a meal and promotes glucose uptake by cells and storage as glycogen. Step 3: Note that this response lowers blood sugar toward its normal range, which counteracts the original rise in glucose. Step 4: Compare this pattern with positive feedback examples such as labor contractions and blood clotting, where the response becomes stronger and stronger instead of stabilizing. Step 5: Conclude that the scenario with insulin lowering blood sugar best fits the definition of negative feedback.

Verification / Alternative check:
In physiology textbooks, blood glucose regulation is a classic example of negative feedback. Diagrams show rising glucose stimulating insulin release, and rising insulin bringing glucose down. When glucose falls too low, insulin secretion decreases and other hormones such as glucagon may increase, which again brings glucose back toward normal. This cycle shows a continuous tendency toward stability, which is the hallmark of negative feedback.

Why Other Options Are Wrong:
Option B: During labor, contractions stimulate release of more oxytocin, which in turn causes stronger contractions. This amplifying loop is a classic positive feedback mechanism, not negative feedback.
Option C: A rise in blood sugar followed by glucagon driven increase in glucose would amplify the original change, so this would be positive feedback and is also not physiologically accurate after a meal.
Option D: Blood clotting is a positive feedback process where formation of a clot triggers more clotting until the damaged vessel is sealed, so it does not stabilize a variable around a set point.

Common Pitfalls:
Students often confuse negative feedback with a harmful effect because of the word negative. In control systems, negative simply means that the response is in the opposite direction of the initial change. Another common mistake is to think that any feedback in the body is negative, but labor contractions and blood clotting are important examples of positive feedback that drive rapid change rather than stability.

Final Answer:
The correct answer is After you eat a meal, insulin is released and helps lower elevated blood sugar levels back toward normal. because this mechanism counteracts the initial rise in blood glucose and stabilizes the internal environment, which is the definition of negative feedback.