Final answer:
Gluconeogenesis primarily occurs in the liver and secondarily in the kidney, brain, and muscle under conditions such as fasting, starvation, and low carbohydrate intake, ensuring a constant glucose supply for the brain and other organs.
Step-by-step explanation:
Gluconeogenesis, the synthesis of new glucose from certain non-carbohydrate sources, occurs mainly in the liver and to a lesser extent in the kidney. This metabolic pathway is critical for maintaining blood glucose levels during periods such as fasting, starvation, and low carbohydrate intake. It can also occur secondarily in the brain and muscle tissues under specific conditions. The liver's central role in gluconeogenesis is underscored by its ability to store large amounts of glycogen and utilize glycerol derived from the hydrolysis of triacylglycerols (TAG) to synthesize glucose. Additionally, during times of low blood sugar, hormones such as glucocorticoids and ACTH stimulate the liver to produce glucose.
The body resorts to gluconeogenesis to ensure that organs like the brain, which depend exclusively on glucose for energy, receive a constant supply, even when dietary carbohydrates are scarce. Moreover, conditions such as pregnancy, lactation, and febrile diseases may also induce gluconeogenesis to meet the increased metabolic demands.