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Hormone Control:
The Hypothalamus

Hormone control is a complex process, but some simple parts of the process are understood. The "command center" seems to lie in a central part of the brain just below the oldest, most central structure, the thalamus.  To locate the thalamus, if you haven't been there yet, take the "R complex" tour (or for an even more basic introduction to these most central parts of the brain, start with the "3-brains-in-one" tour.)  Just to remind you, the thalamus looks like this:

As you'll remember, the thalamus is that central yellow structure.  Just below it, then, is where we look for the command center:  the "hypo-thalamus" (literally, the under-thalamus)  However, these structures are right in the very center of the brain, so to see them, we need to look at a brain with one half removed.  Imagine if the brain in the picture above was cut from the front to the back, on a line from "nose" to the center of the back of the head (medical students know this as a "saggital section").  Here's what you'd see: you're right in the center of the brain.  To keep you oriented, there's a rough outline of the thalamus position in yellow.  All the colored parts below are the separate segments of the hypothalamus:

The thalamus itself does not appear  because we are directly in the center of the brain in this drawing, where the thalamus narrows to a small bridge. You can see that bridge cut cross-ways marked by the yellow dot.  If you'd like to see an enlargement of this view, click here

Otherwise, notice that the many parts of the hypothalamus (all the colored pieces) sit directly above a stalk of tissue that looks like an odd shaped golf club -- that's the pituitary gland.  It's the first lieutenant to the commander (the hypothalamus).   The pituitary issues orders to the major glands: the thyroid, which sets the body's "idle" speed through its product, thyroid hormone;  the adrenal gland, maker of adrenalin;  and the gonads -- testes or ovaries.  If you'd like to see a diagram of all the messenger chemicals involved in this command system (TRH and TSH; CRF and ACTH; GnRH and LH/FSH) click here.  

Now for one final view, that may help you grasp just where in the brain we are in the picture above.  Imagine if you just spun your camera around to the front of this brain and looked at this same region -- remember, this is the very center of the brain: 

In this view the brain's former owner would have a left ear, visible on the right margin of the picture (remember, we're looking from the front).  Tricky?  Imagine there's a person standing in front of you and the whole front half of her just disappeared, back to about the ear.  So, there's the thalamus again, outlined on the left side in yellow -- it's pretty big.  And below it you can see the hypothalamus, in all its segments.  (We're too far back to see the pituitary hanging below.  If you've really got the three dimensions, you'll see the "bridge" between the two sides of the thalamus in this picture, and you might even see why when the brain is cut right in the very middle as in the drawing above, the only part of the thalamus you can really see is the little bridge!).   

This ends our brain tour of the hypothalamus.  You may have already learned that this "master gland" is involved in the "hormones and mood" story in a big way, although much of that story remains to be explained.  When we do "get it", you can be pretty sure the hypothalamus will be right at the center of the explanation.   

 

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