**Core Concept**
Physiological antagonism occurs when two substances produce opposite effects on the same physiological function or process. This type of antagonism is often seen in hormone pairs that regulate metabolic pathways, where one hormone stimulates a process, and the other inhibits it.

**Why the Correct Answer is Right**
Glucagon and insulin are physiological antagonists because they regulate blood glucose levels through opposing mechanisms. Glucagon, secreted by the pancreas, raises blood glucose levels by stimulating glycogenolysis and gluconeogenesis. In contrast, insulin, also secreted by the pancreas, lowers blood glucose levels by facilitating glucose uptake in cells and inhibiting glycogenolysis and gluconeogenesis. This reciprocal relationship between glucagon and insulin ensures that blood glucose levels remain within a narrow range.

**Why Each Wrong Option is Incorrect**
**Option A:** Adrenaline and isoprenaline are pharmacological antagonists, not physiological antagonists. Adrenaline and isoprenaline are both beta-adrenergic agonists, and their effects can be reversed by beta-blockers like propranolol.

**Option C:** Isoprenaline and propranolol are pharmacological antagonists, not physiological antagonists. Isoprenaline is a beta-adrenergic agonist, while propranolol is a beta-blocker that reverses its effects.

**Clinical Pearl / High-Yield Fact**
The glucagon-insulin axis is a classic example of physiological antagonism in endocrinology. Understanding this reciprocal relationship is crucial for managing diabetes and other metabolic disorders.

**Correct Answer:** ✓ Correct Answer: B. glucagon and insulin