One would think it has to do with the stomach being empty.
But last summer my stomach was basically removed. OK, it is still there, but nothing goes into it. The esophagas is now attached directly to the small intestine.
Andy yet, I still feel both hunger and fullness.
My university zoology prof said that feelings of hungriness and thirstiness are sensed at the cellular level, not in the digestive tract. If I knew what he knew, I could explain it to you, maybe.
My knowledge of this is very sketchy, but isn’t there an enzyme that’s secreted in the stomach that controls hunger? It seems that if your stomach had actually been removed (rather than bypassed) you wouldn’t be feeling hunger.
I had a morbidly obese cousin who had her stomach bypassed, but it didn’t affect her appetite. They then removed all or part of her stomach, and her appetite finally diminished – not soon enough to save her life though.
Hunger seems to be tied to blood sugar levels, although that’s undoubtedly not the whole story.
This story’s only been going on for 10-15 years now, so there’s still a lot that’s not known. I wouldn’t be surprised if there were three or four more major appetite controlling peptides, or maybe an oddball glycosylated steroid or some such, yet to be discovered.
There are also things like leptin, insulin and catecholamines which are tied into hunger and fullness. Considering that several of these peptides weren’t even discovered until the 90s (ghrelin wasn’t discovered until 1999, leptin in 1994) we are probably going to discover even more in the future.
I have read that the hunger and fullness signals have evolved to have several backup and overlapping signal methods so doing something like removing the stomach may just result in different hormones and peptides being used to pick up the slack.
Incidentally, there are some individuals afflicted with an absence of the full feeling. My wife had to take care of a couple of folks like these in a group home setting. Kinda’ weird, 'cuz they’d literally eat til they… you know… unless someone stopped them or they realized they’d overdone it due to sheer quantity.
An episode of CSI featured Prader-Willi Syndrome - one of it’s main features is that is causes hyperphagia - excessive eating.
From this site:
There are quite a few hormones affecting in hunger and satiety. Thirst is controlled by a totally different mechanism that involves cellular signals to the brain, which activates not only that dry feeling in your throat but also some muscular things in your digestive tract, whcih is why thirst is often confused with hunger. One of the quickest ways to get un-thirsty is to drink water until you can feel it expanding your stomach b/c the pressure sensitive nerves there have the fastest feedback loop to the brain thirst centers. Anyway, about hunger, a lot of the replies here are right about what hormones are involved. Cholecystekinin (CCK b/c it’s a pain to spell) is released by your stomach in the presence of fat and causes the sphincter b/w your stomach and you small intestine to close, causing food to stay in your stomach longer. This is why fatty foods make you feel fuller. CCK and ghrelin and things like that do seem to be involved in incredibly complicated secondary backup systems to make sure you eat enough but not too much. The main characters in the drama, however, are insulin and leptin. Insulin is released from pancreatic cells and allows your body to absorb sugar from the bloodstream into your cells. Well, not directly, it usually goes through the liver first, but that’s the overall effect. In doing so, it eventually lowers your blood sugar levels and makes you hungry again. Usually, in a normal healthy person, the time it takes for this to happen and then for the cells to use that amount of sugar is the time you feel sated b/w meals. Leptin is the opposite, a satiety signal. It’s released from fat cells in direct proportion to the amount of fat on your body, so the body knows how much it has stored and can adjust intake to account for that. It’s actions are closely tied to your HPA (hypothalamic-pituitary-adrenal) axis, which controls the amount of glucocorticoids circulating in your system, which in turn can loop back onto insulin pathways. Of course, this is all downstream of some more complicated stuff in the brain, involving NPY, AGRP, beta-endorphins, alpha-MSH, CRF, and a bunch of other hormones. So now, I know you’re thinking “Well that’s great but what I really wanted to know is what actually causes the hollow feeling I wake up with”. And the answer, of course, is that it could be any number of the things I’ve mentioned, or all of them, or, well, you got the point. This is why obesity is such a problem - the system is so complicated that figuring out where it’s broken for each individual person is impossible. The unfortunate result is that, while diet and exercise are only successful 5% of the time, gastric surgery or some sort has a 95% success rate. It’s an awful thing to do to your body but the results are undeniable.
Sorry this was so pompous, I’ve just finished my thesis on it.
-Jurph’s wife
Cholecystokinin, and yes it is a pain to spell. 