Describe the physiological basis of thermogenesis

Describe the physiological basis of thermogenesis and the role of brown adipose tissue (BAT) in energy expenditure and metabolic regulation. How do uncoupling proteins in BAT mitochondria dissipate proton gradients, generating heat instead of ATP, and contribute to non-shivering thermogenesis? Furthermore, how does the activation of BAT by sympathetic nervous system stimulation, cold exposure, or endocrine factors like thyroid hormones and irisin increase energy expenditure, promote lipid metabolism, and improve metabolic health? Additionally, how do alterations in BAT activity and thermogenic capacity contribute to obesity, insulin resistance, and metabolic syndrome?