Primary Motives: Hunger and Thirst

Hunger and thirst are two basic physiological drives that guide survival behaviors in humans and animals.

Hunger is triggered when the brain detects changes in nutrients, such as glucose, lipids, amino acids, and hormones like ghrelin and leptin in the body.

The hypothalamus primarily regulates hunger. The lateral hypothalamus initiates the drive to eat, while the ventromedial hypothalamus signals satiety or fullness.

Environmental cues, such as the sight, smell, and taste of food, can also influence hunger.

Alternately, the double-depletion hypothesis explains thirst motivation, suggesting that cellular and extracellular dehydration trigger thirst.

Cellular dehydration occurs when the body loses water from its cells, which osmoreceptors detect in the hypothalamus to regulate water balance.

Additionally, extracellular dehydration happens when water loss reduces blood volume, lowering blood pressure.

The drop in blood pressure stimulates the secretion of hormones like antidiuretic hormone from the pituitary glands and renin from the kidneys, further promoting the sensation of thirst.