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CONNECTIVE TISSUE II ADIPOSE TISSUE Marylee.M.Kott, M.D Reading : Gardner and Hiatt Chapter 3; Klein and McKenzie, pp77-85 (Though not much here on adipose); Junqueira Chapter 6, p123 Objectives: Recognize brown and white adipose tissue in the light microscope Know their respective functions. Key Words: White adipose tissue, brown adipose tissue I. Fat cells or adipocytes Found in aggregates of varying sizes, constituting adipose tissue. Aggregates may only be apparent in layers or groups of cells seen microscopically. Adipose tissue accounts for 20-25% of the weight of women, 15-20% of the male's weight. Two separate categories of adipocytes which differ in distribution, histological appearance, and function: 1. white adipose tissue 2. brown adipose tissue The mature fat cell (unilocular adipocytes) is in actuality larger in relation to other cell types. II. Development of Fat cells: Undifferentiated mesenchymal cells are transformed into lipoblasts Lipoblasts accumulate fat and give rise to mature fat cells. When the body mobilizes a large amount of lipid, mature unilocular fat cells return to the lipoblast stage. Undifferentiated mesenchymal cells also give rise to a variety of other cell types, including fibroblasts. III. White Adipose Tissue (WAT: unilocular fat): The predominant type of fatty tissue in humans Consists of fat cells with a single large lipid inclusion. Cells may occur singly or in groups. White fat is ubiquitously distributed throughout the body, padding and insulating the organs.
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Geographic deposition determined by age, sex and hormonal status. White fat also functions as an energy reservoir, providing a low-weight, high calorie form of energy (relative to glycogen), without thermogenic properties . Photomicrograph of unilocular adipose tissue of a young mammal. Arrows show nuclei of adipocytes (fat cells) compressed against the cell membrane. Note that, although most cells are unilocular, there are several cells (asterisks) with small lipid droplets in their cytoplasm, an indication that their differentiation is not yet complete. IV. Brown Adipose Tissue (BAT: multilocular fat): Uncommon in adult humans. Sole purpose appears to be heat generation in mammals, in which it functions upon arousal from hibernation, survival after birth, and during cold stress. The main site of non-shivering heat production under conditions of cold stress. Brown fat is widely distributed in the first decade of life in the human, becoming
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