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Question

Please read the article and help explain refering to the comments in the()

The liver stores glucose by converting it to glycogen.(I understand so far) It holds perhaps a 12-hour supply of glucose in its glycogen(typo, did it mean liver? If it converts to glycogen how can it be held in glycogen?) . Once you finish digesting all of the carbohydrates that you last ate, the liver starts converting its stored glycogen back into glucose and releases it to maintain glucose in the blood. (Understood)Lipolysis (lip-what?) also starts breaking down fat in the fat cells and releasing fatty acids into the bloodstream. Tissues that do not need to use glucose for energy (for example, muscle cells) start burning the fatty acids. This reduces the glucose demand so that nerve cells get the glucose. (ok, how does this affect your body?)
Once the liver runs out of glycogen, the liver converts to a process called gluconeogenesis. Gluconeogenesis turns amino acids into glucose. (I got lost)

Answer 1

What we're talking about here is how your body gets energy. As you probably know, there are generally three major sources (you see them on all the food labels): fats (also called lipids), carbohydrates (things like sugar, including glucose), and proteins (things made of amino acids - your excerpt doesn't much talk about them, so we'll ignore them from here on out too).

Now, if you left all the sugars in your bloodstream, it would throw a lot of things out of whack. Your body tries to always maintain a certain balance. So when there's lots of glucose in your blood, the liver takes it out and turns it into something else (glycogen in this case). Then, when there's too little glucose in your blood, the liver takes that other stuff and turns it back into glucose. Handy.

Glucose is particularly important because there are some cells in your body (like your brain) that pretty much ONLY run on glucose. So if that runs out then you start to be in big trouble. Your brain is a HUGE user of energy, consuming about 20% of your body's oxygen and as much as 30% of your body's energy all by itself.

And that's why, when blood sugar starts running down, your body tries to save much of what's left for your brain. Fat cells are broken into those fatty acids as an alternate energy source for all your other tissues. Your liver starts trying to turn other things that are lying around into glucose... amino acids in this case, which come from those proteins. And so it goes until you eat something sugary again.

Don't let the vocabulary hang you up. Some of these terms you'll see over and over again, so let's define some of them now:

-LYSIS is breaking something up. You may have heard of cells being 'lysed', or of the 'lysosome' organelle which breaks down stuff in the cell. Any time you see some variant of this, it means it's destroying something else. So glycolysis breaks glucose down, lipolysis breaks lipids down, and so on.

-GENESIS is exactly the opposite - building something up. If you're making it from scratch, they may stick 'neo' (meaning new) in there too. So gluconeogenesis is making new glucose. You can tell just from how the word is put together.

Particularly in this section, you'll probably want to keep on the lookout for GLUCO- (having to do with glucose specifically or carbohydrates in general) and LIPO- (having to do with lipids or fats). You'll see it other places too: the 'liposome' is the organelle in a cell that holds lipids, for example.

Hope that helps! Sounds like you're actually getting most of what's going on!

Answer 2

Our bodies rely primarily on three sources of energy from food: carbohydrates (sugars/starch), lipids (fats and oils), and amino acids (from protein). Some tissues, such as muscle tissue, posses the ability to obtain energy from all three sources. Other tissues, however, can obtain energy from only glucose. The brain is one such tissue. For this reason, it is important to have glucose around so that the brain can function. Without any glucose around, your brain will cease to function (this is a bad thing).

Therefore, the body must constantly maintain glucose levels in order to ensure that the brain always gets enough glucose. As you have mentioned, glucose levels are regulated through various mechanisms. First, glycogen can act as a short term store for glucose and can release glucose to meet the demands of the body. When glycogen stores run low, the body starts breaking down fat tissue (in a process called lipolysis) which provides fuel (fatty acids) to muscle cells. Fueling muscle cells with fatty acids instead of glucose prevents them from using up the remaining stores of glucose, leaving the rest of the glucose for the brain.

If glucose stores get very low, the liver will break down proteins to amino acids. These amino acids can then be made into glucose (the pathway, called gluconeogenesis, is basically the opposite of glycolysis, the pathway which breaks glucose down into smaller molecules). Gluconeogenesis ensures that the brain can get an adequate supply of glucose and keep functioning under conditions of very low glucose.