Exploring the Physiology of Hunger: Hormones, Neurons, and Energy Levels

In summary, the physiology of hunger involves a complex interplay of hormones, neurons, and organs. Ghrelin and leptin are two key hormones that play a role in the process of hunger, with ghrelin stimulating appetite and leptin promoting satiety. However, the exact trigger for hunger is not fully understood. Hunger is also influenced by energy levels, with ghrelin potentially sensing the body's energy needs. The hypothalamus and its neurons, such as AgRP, POMC, and NPY, play a crucial role in regulating hunger. The stomach, pancreas, and intestines also play a role in signaling hunger and satiety. Hunger, appetite, and satiety are complex and interconnected processes
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mktsgm
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I have been studying about the physiology of hunger. I have studied about the hormones that are involved in the process of hunger, like ghrelin, leptin, pancreatic polypeptide, cholecystokinin, cholecystokinin (CCK) and the neurons like AgRP, POMC and neuropeptide Y (NPY) etc.

I understand that ghrelin urges us to eat. Leptin gives us satiation.

But I am confused as to how hunger is triggered at first instance.
  1. What senses what, to trigger hunger?
  2. Is it ghrelin that initiates the whole process? Is energy level determines hunger/
  3. If so how ghrelin (or whatever initiates it) senses the energy need?
  4. Is energy need is synonymous (only) to the ATP level?
  5. How and at which state the hypothalamus (AgRP, POMC & NPY) is involved?
  6. What is the role of stomach, pancreas & intestines?
  7. How to distinguish hunger, appetite and satiety?
I have gone through many articles in ncbi articles. They look mostly convoluted (for me) and it is very difficult to distinguish the start from the end.

Can anyone throw some light on simple terms on the connection among the energy level, ATP, hunger hormones and hunger neurons so that I get clarity on complete physiology on hunger?
 
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But I am confused as to how hunger is triggered at first instance.
The question seems to seek a simple answer, but as your comments and other questions make clear, it's not really a simple question. Hunger is a name for an imprecisely defined set of emergent phenomena, the processes contributing to which are extremely complex.

The only responsible simple answers will include the proviso that it's not simple.

Here's an article that may or may not strike you similarly to others you've read: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2777281/

It doesn't mention orexin/hypocretin, which is a mediator of appetite as well as of muscle tone. You can see the resemblance between the words "orexin" and "anorexia". It's a functional name.

Hunger, appetite, satiety -- it's complicated.
 
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https://nba.uth.tmc.edu/neuroscience/s4/chapter04.html
Chapter 4: Central Control of Feeding Behavior
Patrick Dougherty, Ph.D., Department of Anesthesiology and Pain Medicine, MD Anderson Cancer Center
Feeding by its nature is intermittent, yet the need for energy in tissues is constant. Thus, mechanisms have evolved for the ebb and flow of nutrients after feeding and during the post-absorptive period; and the maintenance of near-normal function during fasting. The remarkable stability of body weight in persons with access to adequate food supplies is testament to the precision by which metabolic needs are monitored and maintained. Aberrations in these controls can produce serious and even life-threatening conditions.
 
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This discusses hormones, genetics in terms of obesity and hunger.
 
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1. What hormones are involved in hunger and satiety?

The main hormones involved in hunger and satiety are ghrelin, leptin, and insulin. Ghrelin is produced by the stomach and stimulates hunger, while leptin is produced by fat cells and signals satiety. Insulin, which is produced by the pancreas, helps regulate blood sugar levels and can also impact hunger and satiety.

2. How do neurons play a role in hunger and satiety?

Neurons in the brain, specifically in the hypothalamus, play a crucial role in regulating hunger and satiety. These neurons receive signals from hormones and other neurotransmitters, and send signals to the rest of the body to either increase or decrease appetite.

3. What is the role of energy levels in hunger?

Energy levels, specifically the body's energy stores, play a significant role in regulating hunger. When energy levels are low, the body produces ghrelin to signal hunger and promote food intake. On the other hand, when energy levels are high, leptin is produced to signal satiety and decrease appetite.

4. How does the brain control hunger and satiety?

The brain controls hunger and satiety through a complex network of neurons, hormones, and other signaling molecules. The hypothalamus, in particular, plays a crucial role in integrating these signals and sending out appropriate responses to regulate appetite and food intake.

5. Can external factors influence hunger and satiety?

Yes, external factors such as stress, emotions, and environmental cues can influence hunger and satiety. For example, stress can increase the production of ghrelin, leading to increased appetite and food intake. Similarly, environmental cues like the sight or smell of food can trigger hunger even when the body does not necessarily need more energy.

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