In human physiology, what is the normal pH range of blood in a healthy adult?

Introduction / Context:
Blood pH is a vital parameter in human physiology because it reflects the acid base balance of the body. Enzyme activity, oxygen transport, and many metabolic processes work efficiently only within a narrow pH range. Even small deviations can be dangerous. This question checks whether you know the normal pH range of human blood, a common topic in biology, medicine, and nursing entrance exams. Understanding the typical pH values also helps in appreciating conditions such as acidosis and alkalosis.

Given Data / Assumptions:
- The question asks for the normal pH level in human blood. - Several close numerical ranges are given as options. - We assume arterial blood in a healthy adult at rest.

Concept / Approach:
The pH scale runs from 0 to 14, where 7 is neutral, values lower than 7 are acidic, and values higher than 7 are basic or alkaline. Human blood is slightly alkaline, not neutral. In healthy individuals, the pH of arterial blood is maintained within a very narrow range around 7.4 by buffer systems, the lungs, and the kidneys. The widely accepted normal range is about 7.35 to 7.45. Values below this range indicate acidosis, whereas values above it indicate alkalosis. Because cells and enzymes are sensitive to pH, the body tightly regulates this value.

Step-by-Step Solution:
Step 1: Recall that normal human blood is slightly alkaline rather than exactly neutral, so the pH should be greater than 7. Step 2: Remember the commonly quoted normal arterial blood pH range, which is approximately 7.35 to 7.45. Step 3: Compare this known range with the given options. Option A exactly matches 7.35 to 7.45. Step 4: Recognize that the other options shift the range higher or lower in ways that do not correspond to normal physiological values. Step 5: Conclude that 7.35 to 7.45 is the correct normal pH range for healthy human blood.

Verification / Alternative check:
Medical textbooks, nursing manuals, and standard physiology references all list normal arterial blood pH as around 7.4 with an acceptable range of about 7.35 to 7.45. Clinical laboratories also use this range when reporting results. Values outside this interval usually trigger alerts and clinical evaluation. This independent confirmation from multiple authoritative sources supports Option A as the correct answer and rules out the other intervals as abnormal for a healthy adult.

Why Other Options Are Wrong:
Option B (7.45 to 7.55) is slightly more alkaline than the normal range. Persistent values in this range may indicate mild alkalosis, not normal physiology. Option C (7.60 to 7.70) is strongly alkaline and generally incompatible with normal metabolism. Such high pH levels are considered severe alkalosis and can be life threatening. Option D (7.00 to 7.10) is near neutral or mildly acidic and indicates acidosis. Normal blood pH is higher than 7.3, so this range is definitely not normal.

Common Pitfalls:
A frequent mistake is to assume that because blood is often described as neutral, its pH must be exactly 7. Another pitfall is to think that a wider range of pH values is acceptable for normal physiology. In reality, the body maintains blood pH within a very narrow interval, and even small shifts can affect heart rhythm, brain function, and breathing. Students should memorise the approximate values 7.35 to 7.45 and remember that blood is slightly alkaline, not neutral or strongly basic.

Final Answer:
The correct answer is: 7.35 to 7.45.