Metabolism & Nutrition

This unit is pretty short. If you really want to learn a lot about this topic, you should consider taking our nutrition class.

You learned back in Unit 18 that blood plasma contains nutrients, and you learned a bit about what they are back then. Now we have just finished the digestive system, and you learned a bit more about what the nutrients actually are. But we still haven't really talked about the importance of the nutrients we ingest. In other words, what items do we have to obtain in our diets, and what can we handle not taking in? If we don't get enough of one particular nutrient, is it possible for our cells to synthesize it from what we did take in? Finally, when have we taken in enough nutrients? Is it possible to take in too many?

If I restate the questions above into major categories, you should see that there are three main topics for investigation in this unit:

	What are the main types of nutrients?
	Which nutrients must we ingest and which can we make? (If we must ingest them, they are called essential nutrients).
	What quantity of nutrients is enough in a given day?

You can follow the links at the top to investigate each topic. But first, read a little more information below.

The foods we eat are large, but the material absorbed by our intestines and sent into our blood is small (as you learned in last week's unit). In order for us to get all the nutrients we need for absorption, we must eat large food that contains the right material within it. Therefore, we can talk about macronutrients and micronutrients. Macronutrients are the big food items, while micronutrients are the tiny, absorbed items.

Also, although we need to absorb these teeny micronutrients, sometimes, like right after a meal, we have plenty of them. To maintain homeostasis in numbers of micronutrients, we actually need to assemble them back together into larger molecules for storage until needed. Then, when needed, we break these larger molecules (macromolecules) back down again. Therefore, we are constantly building and breaking macromolecules... all of the building and breaking reactions that go on within a person are collectively referred to as one's metabolism. The building chemical reactions are anabolic, while the breaking chemical reactions are catabolic. I think it is easy to remember which reaction is which if you associate catabolic reactions with cutting reactions. Besides, you probably remember learning this before.

Finally, many metabolic reactions described in this unit occur in the LIVER. It should make sense to you that one organ is specialized for coordinating metabolic function in our bodies-- and that organ is the liver. Over the pages of this unit you will see many places where the liver is mentioned, so I just wanted to make sure that you understood why.