New Perspectives in Adipose Tissue (eBook)
490 Seiten
Elsevier Science (Verlag)
978-1-4831-6397-0 (ISBN)
New Perspectives in Adipose Tissue: Structure, Function and Development reviews the state of knowledge on adipose tissue. The book begins with discussions of the anatomy and morphology of adipose tissue. This is followed by separate chapters on the nervous control of circulation and metabolism in white adipose tissue; hormonal regulation of biosynthetic activities in white adipose tissue; hormonal control of lipid degradation; and plasma membrane properties and receptors in white adipose tissue. Subsequent chapters cover topics such as lipoproteins and adipose tissue; brown adipose tissue thermogenesis and energy balance in animals and man; methodological approaches to the study of the adipose tissues; adipose tissue growth following lipectomy; the adipocyte precursor cell; and adipose tissue dysfunction and its consequences. In addition to being authoritative source material, the chapters presented in this book are wide in their coverage and appeal.
The morphology of adipose tissue
Bernard G. Slavin
Publisher Summary
This chapter emphasizes on the morphology of white adipose tissue (WAT) realizing that brown adipose tissue (BAT) is a specialized form of adipose tissue differing in structure and function from WAT. Adipose tissue in mammals is usually characterized as a specialized type of connective tissue consisting mainly of specific lipid-laden cells—adipocytes, surrounded by a collagenous matrix and containing nerves, blood vessels, and the usual complement of connective tissue cells. The chapter describes two types of adipose tissue that are named according to their color characteristics and the form of their adipocytes: (1) white, yellow or unilocular adipose tissue, and (2) brown or multilocular adipose tissue. In most mature mammals, WAT is located diffusely in several distinct anatomical sites, such as subcutaneous, perivascular, intermuscular, peritoneal (mesenteries and omentum), retroperitoneal, synovial, mediastinal, retro-orbital, and intraspinal and medullary (bone marrow). In male rodents, there are large depots of intra-abdominal WAT located adjacent to the epididymis and testes. In general, white adipocytes function to (1) take up mainly fatty acids, glucose and amino acids, (2) synthesize and store lipid in the form of triacylglycerol droplets, (3) hydrolyze the stored lipid, and (4) release free fatty acid into the vasculature. In addition to white adipocytes, one can distinguish macrophages, fibroblasts, mast cells, and occasional white blood cells in WAT. The most notable feature of brown adipocytes is the presence of intracellular lipid droplets of varying size. BAT functions as a thermogenic organ during cold-stress, arousal from hibernation, and in various newborn animals.
2.1 Introduction
Adipose tissue in mammals is usually characterized as a specialized type of connective tissue consisting mainly of specific lipid-laden cells (adipocytes) surrounded by a collagenous matrix and containing nerves, blood vessels and the usual complement of connective tissue cells. Two types of adipose tissue have been described and are named according to their color characteristics and the form of their adipocytes: (1) white, yellow or unilocular adipose tissue (WAT); and (2) brown or multilocular adipose tissue (BAT).
In most mature mammals, WAT is located diffusely in several distinct anatomical sites: subcutaneous, perivascular, intermuscular, peritoneal (mesenteries and omentum), retroperitoneal, synovial, mediastinal, retro-orbital, intraspinal and medullary (bone marrow). In rodents, there are large depots of intra-abdominal WAT located in the male adjacent to the epididymis and testes. Those depots in the female alongside the uterine horns are known as the parametrial fat pads. BAT, on the other hand, resembles glandular tissue and is present in a variety of prenatal, neonatal and adult mammals. Its brownish color is due to a rich vascular supply and numerous large, cytochrome-containing mitochondria within the brown adipocytes. This type of adipose tissue is located mainly in the interscapular and axillary regions with minor accumulations near the thymus gland and great vessels of the thorax and abdomen (Afzelius, 1970). BAT is particularly abundant in all hibernating mammals as well as in some non-hibernating mammals. This chapter places emphasis on the morphology of WAT realizing that BAT is a specialized form of adipose tissue differing in structure and function from WAT.
2.2 White adipose tissue
2.2.1 General histologic features
The histologic appearance of mature WAT has been described by several authors (Fawcett, 1952; Sheldon et al., 1962; Greenwood and Johnson, 1983). Routine fixation and staining of WAT reveal mainly profiles of adipocytes having a spherical to oval shape, often distorted due to extraction of intracellular lipid droplets by the solvents used in tissue processing (Figure 2.1). Staining WAT with common lipophilic dyes (oil red O, sudan, osmium) reveals the large, centrally placed lipid droplet within the adipocyte. In addition to white adipocytes, one can distinguish macrophages, fibroblasts, mast cells and occasional white blood cells in WAT.
Figure 2.1 Plastic section through subcutaneous adipose tissue surrounding the submandibular gland in the rat. Note irregular profiles of white adipocytes which are distorted due to lipid extraction during processing. Arrow points to a peripherally displaced nucleus. × 375. (Reduced to 70% in reproduction)
White adipocytes are organized into lobules which are supported by a loose connective tissue stroma (septa). The use of scanning electron microscopy has demonstrated that each adipocyte is supported intimately by a web of reticulum and collagen fibers which are continuous with the interlobular septae (Mota, 1975). An example of the extensive fibrillar stroma surrounding white adipocytes taken from the epididymal fat depot of a rat fasted for 3 days is seen in Figures 2.2 and 2.3. Collagen and reticulum also surround the neurovascular elements that are present.
Figure 2.2 Scanning electron micrograph of white adipocytes (A) within the epididymal fat pad of a fasted rat. The arrow points to strands of collagen fibers which form a web-like network among the adipocytes. × 1800. (Reduced to 60% in reproduction)
Figure 2.3 High power view of white adipocytes in Figure 2.2. Note the fine fibrillar network surrounding the adipocyte (A). × 3000. (Reduced to 70% in reproduction)
2.2.2 Development
White adipocytes in most fat depots develop from a specific line of connective tissue cells resembling fibroblasts (Napolitano, 1963a; Slavin, 1979; Hausman et al., 1981). The product of lipid synthesis, in the form of triacylglycerol droplets, appears in the rat preadipocyte during the prenatal or postnatal periods. The preadipocyte is characterized by its spindle shape, its high content of rough endoplasmic reticulum and an active Golgi zone (Figure 2.4). Gradually, the intracellular lipid droplets increase in size and number in conjunction with glycogen deposition, and the cell shape changes from a spindle to a sphere (Figure 2.5). The development of adipocytes from endothelial cells in pigs and from pericytes in rats has been suggested by Desnoyers and Vodovar (1977) and Iyama et al. (1979).
Figure 2.4 Typical morphology of a preadipocyte in a developing epididymal fat pad. This cell is spindle-shaped and contains abundant rough endoplasmic reticulum, lipid droplets, mitochondria, and an active Golgi zone (G). A fully-formed external lamina is not yet present. The cell is surrounded by collagen fibers and amorphous fibrillar material. × 21 000. (Reduced to 70% in reproduction)
Figure 2.5 Inguinal adipose tissue from a newborn mouse. Numerous lipid droplets (L) fill the cell. Transient glycogen deposition (GLY) was observed. Note the large increase in the number of mitochondria. × 5600. (Reduced to 60% in reproduction.) From Slavin (1979) by permission from The Wistar Institute Press, Philadelphia
Adipocyte development in the marrow of long bones differs from that in extramedullary sites in that the precursor cell, although spindle-shaped, does not contain significant amounts of rough endoplasmic reticulum, nor are the cells closely surrounded by collagen fibers (Tavassoli, 1974, 1976). In addition, as the medullary adipocyte enlarges due to lipid deposition, there is no concomitant deposition of glycogen as in the case of the extramedullary adipocyte.
The development of white adipocytes had also been studied by the use of a cloned line of cells derived from mouse fibroblasts (Green and Meuth, 1974; Green and Kehinde, 1976). In addition, adipocyte precursor cells isolated from rat, bovine and human adipose tissue stroma and cultured in vitro have been described (Poznanski et al., 1973; Dardick et al., 1976; Van et al., 1976; Van and Roncari, 1977; Plaas and Cryer, 1980). These models of adipocyte differentiation will be covered by other authors in this volume.
2.2.3 White adipocyte morphology
2.2.3.1 Light microscopy
Most white adipocytes contain a single large central lipid droplet surrounded by a peripheral thin rim of cytoplasm, the contents of which cannot be resolved by light microscopy. The nucleus is usually located peripherally as a flattened or pressed structure which forms a peripheral bulge and is partially responsible for the ‘signet-ring’ designation of the white adipocyte (Figure 2.1).
2.2.3.2 Electron microscopy
Fine structural studies of mature and developing white adipocytes have been reported by many investigators (Imaeda, 1959;...
| Erscheint lt. Verlag | 24.4.2014 |
|---|---|
| Sprache | englisch |
| Themenwelt | Studium ► 1. Studienabschnitt (Vorklinik) ► Anatomie / Neuroanatomie |
| ISBN-10 | 1-4831-6397-0 / 1483163970 |
| ISBN-13 | 978-1-4831-6397-0 / 9781483163970 |
| Haben Sie eine Frage zum Produkt? |
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