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Pond, Caroline M.
(2011).
DOI: https://doi.org/10.1007/978-1-4614-0965-6_8
Abstract
Gene products and metabolic pathways comprising and controlling adipose tissues are traced from their invertebrate origins through lower vertebrates to mammals and birds. Many functions of the mammalian liver and pancreas take place in adipose-like tissues in lower animals. Mammalian white adipose tissue is split into numerous depots, many with site-specific properties adapted to paracrine interactions, insulation or structural roles. Paracrine provision of lipids to the immune system with fatty acid sorting optimizes cellular nutrition even during fasting or on deficient or imbalanced diets, averts competition with other tissues and utilizes scarce resources efficiently. Non-shivering thermogenesis occurs in avian muscles and mammalian brown adipose tissue, recently shown to be developmentally related to muscle not white adipose tissue. The biochemical mechanisms of thermogenesis evolved separately in birds and mammals utilizing several gene families, including uncoupling proteins, present in lower vertebrates. Mammalian thermogenic tissue lost contractile functions and expanded its lipid storage capacity, probably to improve function at hibernation temperatures, thus generating confusing resemblances to white adipose tissue. As well as storage and endocrine functions, adipose tissues’ capacities for paracrine interactions, fatty acid sorting and thermogenesis are important in the evolution of mammalian heterothermy, lactation and predominance as herbivores able to thrive on indigestible, poor quality, nutritionally imbalanced diets. Some mammals tolerate high levels of obesity without metabolic impairment, but humans and other apes are not so adapted.