Final answer:
The brain and the liver do not need insulin for glucose entry. While insulin is chiefly responsible for glucose uptake into most body cells, these two organs can absorb glucose independently of insulin, critical for maintaining energy supply and regulating blood glucose.
Step-by-step explanation:
The two things in the body that do not need insulin for glucose entry are the brain and the liver. Insulin's primary function is to facilitate the uptake of glucose into body cells, but certain cells and tissues have the ability to take up glucose without the presence of insulin. Specifically, the brain requires a constant supply of glucose, which it can utilize without the need for insulin. The liver, on the other hand, plays a key role in regulating blood glucose levels and can take up or release glucose irrespective of insulin levels. Other tissues and cells capable of taking up glucose without insulin include red blood cells, the kidneys, and the lining of the small intestine.
In contrast, insulin is critical for glucose uptake in most other tissues, such as muscle and adipose (fat) tissue. During the absorptive state after a meal, insulin is released, promoting the uptake of glucose into these cells for immediate use or storage. Over time, the body's ability to properly use insulin is crucial for maintaining normal blood glucose levels and preventing conditions such as diabetes.