**Core Concept**
The Bainbridge reflex is a physiological response to increased atrial stretch, resulting in a reflex increase in heart rate. This reflex is mediated by stretch receptors in the atria, which send signals to the brainstem to increase sympathetic outflow to the heart.

**Why the Correct Answer is Right**
The Bainbridge reflex is a classic example of a reflex increase in heart rate in response to atrial distension. When the atria are stretched, specialized stretch receptors, known as atrial stretch receptors or volume receptors, are activated. These receptors send signals to the medulla oblongata through the vagus nerve, which in turn increases sympathetic outflow to the heart, leading to an increase in heart rate. This reflex helps to maintain cardiac output in the face of increased blood volume or pressure.

**Why Each Wrong Option is Incorrect**
**Option A:** The J reflex, also known as the J wave or Osborn wave, is an electrocardiographic phenomenon observed in hypothermia, not a reflex increase in heart rate.
**Option C:** The Cushing reflex, also known as Cushing's reflex, is a physiological response to increased intracranial pressure, characterized by a triad of increased blood pressure, bradycardia, and irregular breathing, not a reflex increase in heart rate.
**Option D:** The Bezold-Jarisch reflex is a reflex decrease in heart rate in response to activation of the baroreceptors in the heart, not an increase in heart rate.

**Clinical Pearl / High-Yield Fact**
The Bainbridge reflex is an important physiological mechanism that helps to maintain cardiac output in the face of increased blood volume or pressure. It is also a useful clinical pearl to remember when interpreting ECGs in patients with atrial distension or volume overload.

**✓ Correct Answer: B. Bainbridge reflex**