Question

In Zollinger-Ellison syndrome, proper regulation over gastrin production and H+ secretion is lost. Normally, what type of physiologic control is exhibited once the proper gastric pH is reached? A. Baroreceptor (pressure-regulated) B. Positive feedback control C. Negative feedback regulated D. Pulsatile regulation

Short answer

C. Negative feedback regulated

Step-by-step solution

Identify the condition's effect

In Zollinger-Ellison syndrome, there is a loss of regulation over gastrin production and H+ secretion.

Understand normal physiological control

Normally, the body regulates gastric pH to maintain a balance. Once the proper gastric pH is reached, the body must adjust the secretion to avoid an imbalance.

Type of feedback in normal conditions

To identify the correct type of feedback, determine how the body responds to reaching the correct gastric pH.

Define Negative Feedback

Negative feedback occurs when the body reduces the output or activity to return to a set point, such as reducing H+ secretion when gastric pH is within the normal range.

Compare against other options

Other options such as baroreceptor (pressure-regulated), positive feedback, and pulsatile regulation do not fit the described normal control of gastric pH.

Key concepts

Negative Feedback

Negative feedback is a vital mechanism used by the body to maintain homeostasis, or internal stability. A great example of this is the regulation of gastric pH. When the stomach reaches its optimal pH level, the body needs to reduce or stop further secretion of acids to prevent excessive acidity. This is achieved through negative feedback.

In negative feedback, the body detects a deviation from the optimal condition and initiates responses to correct it. For instance, if the gastric pH becomes too low (too acidic), sensors in the stomach lining send signals to reduce the production of hydrochloric acid (H+ ions). This helps to bring the pH level back to normal.

The opposite can also happen. If the pH level rises (becomes less acidic), the body can increase acid production via signal pathways. This back-and-forth adjustment is what keeps our systems in check.

Gastrin Production

Gastrin is a hormone largely responsible for triggering the secretion of gastric acid. It is produced by G-cells in the lining of the stomach and the upper part of the small intestine. When food enters the stomach, it stimulates gastrin production which in turn stimulates the gastric glands to secrete more hydrochloric acid and digestive enzymes.

However, this process must be tightly controlled. In a healthy individual, once the gastric pH reaches its optimum level, the secretion of gastrin is diminished, thanks to the negative feedback mechanism. This stop in production prevents unnecessary acidity.

In Zollinger-Ellison syndrome, though, this regulatory mechanism is disrupted. Tumors called gastrinomas produce excessive amounts of gastrin regardless of the gastric pH, leading to overproduction of gastric acid. This results in severe acidity and can cause peptic ulcers.

Gastric pH Regulation

Maintaining an optimal gastric pH is crucial for digestive health. The stomach produces hydrochloric acid to break down food and activate digestive enzymes, but this acid must be kept in balance to prevent damage to the stomach lining.

Gastric pH regulation involves a complex interplay of various factors. Gastrin, as mentioned before, stimulates acid production. But other factors, like somatostatin, work to inhibit acid secretion when the pH drops too low. This is a clear example of negative feedback regulation. When the gastric pH reaches its optimal range, somatostatin production increases, signaling the stomach to reduce acid secretion.

Contrary to how it functions normally, in Zollinger-Ellison syndrome, these feedback mechanisms are overridden by the continuous production of gastrin by tumors. The unchecked acid secretion leads to an abnormally low pH and many related complications.