Final answer:
The signal to eat is commonly caused by an increase in ghrelin levels, stimulating appetite. When blood glucose levels decrease, it also signals a need to consume energy. On the other hand, increased leptin and serotonin levels contribute to feelings of satiety and inhibit further eating. So the correct answer is option (A).
Step-by-step explanation:
Among the factors that signal us to eat, ghrelin levels increase, which is associated with stimulating appetite. Conversely, leptin levels rise to signal satiation and therefore reduce hunger. When blood glucose levels decrease, this acts as a stimulus to initiate eating because the body requires energy. Serotonin levels, on the other hand, normally have an inhibitory effect on eating, counteracting the urge to consume more food. Thus, when serotonin levels increase, they actually contribute to reducing hunger, not inducing it.
When someone feels hungry, typically their ghrelin levels are high, as this hormone's role is to stimulate hunger. Leptin, which is produced by fat cells, sends signals to the brain when there are sufficient energy reserves, thus inducing a feeling of fullness. So, during hunger, leptin levels would be relatively low. Biological factors such as the deregulation of neurotransmitters including serotonin and dopamine, as well as imbalances in hormones like leptin and ghrelin, are linked to eating behaviors and may lead to disorders affecting appetite and eating habits.
An understanding of these hormones and neurotransmitters, as well as how they interact to regulate appetite and satiation, is important for grasping the complexity of eating behaviors and the potential for disorders that can arise from these signaling mechanisms being out of balance.