## Core Concept
The systemic capillaries are crucial for the exchange of oxygen, carbon dioxide, nutrients, and waste products between the blood and tissues. The changes in blood composition as it passes through systemic capillaries involve the loss of oxygen and the gain of carbon dioxide, along with the exchange of nutrients and waste products.

## Why the Correct Answer is Right
The correct answer involves understanding what does NOT typically change in the blood as it passes through systemic capillaries. In systemic capillaries, the partial pressure of oxygen (pO2) decreases, and the partial pressure of carbon dioxide (pCO2) increases. Oxygen is released from hemoglobin to the tissues, and carbon dioxide, a waste product, diffuses into the blood. The pH of the blood decreases slightly (becomes more acidic) due to the increase in CO2, which forms carbonic acid. However, one parameter that remains relatively constant or does not change significantly in the context provided is the concentration of glucose, as glucose is continuously being taken up by cells but also being produced and released into the bloodstream through various mechanisms.

## Why Each Wrong Option is Incorrect
- **Option A:** Typically, there is a decrease in pO2 as oxygen diffuses out of the blood and into the tissues.
- **Option B:** There is an increase in pCO2 as carbon dioxide diffuses from the tissues into the blood.
- **Option D:** The pH decreases slightly (becomes more acidic) due to increased CO2 levels.

## Clinical Pearl / High-Yield Fact
A key point to remember is the role of systemic capillaries in gas exchange and the maintenance of acid-base balance. The buffering system in blood, including hemoglobin, helps mitigate large changes in pH. Understanding these changes is crucial for assessing tissue perfusion and respiratory function.

## Correct Answer Line
**Correct Answer: C.**