National League for Nursing (NLN PAX) Practice Exam

The liver plays a critical role in maintaining blood glucose levels, particularly during fasting periods. When a person fasts for 24 hours and does not consume carbohydrates, the liver primarily meets the body's glucose requirements through the conversion of glycogen into glucose. This process, known as glycogenolysis, occurs when glycogen, which is stored in the liver, is broken down into glucose and released into the bloodstream to provide energy for cells that rely on glucose, such as red blood cells and certain parts of the brain.

While the breakdown of fat reserves and synthesizing glucose from amino acids are important metabolic processes that occur during prolonged fasting or starvation, the immediate response to a short-term fast like 24 hours primarily relies on existing glycogen stores. The liver's glycogen reserves are typically sufficient to maintain glucose levels for about 24 hours. After these stores are depleted, the body would then begin utilizing other methods, such as gluconeogenesis from amino acids or fat-derived substrates, to produce glucose.

Thus, the correct answer reflects the immediate source of glucose when a person fasts for a short duration without carbohydrates, highlighting the liver's ability to mobilize its glycogen reserves to sustain essential energy demands.