The brown adipose tissue shown here consists of small fat cells that are very closely packed with minimal intercellular space. Because of this arrangement, it is hard to define individual cells at this magnification. At higher magnification (not shown), it is possible to identify some individual cells. One cell, whose boundaries could be identified at higher magnification is circumscribed by a dotted line. Each cell contains many small, fat-containing vacuoles surrounded by cytoplasm. Included in this cell is its nucleus (N). As noted, brown adipose tissue is highly vascularized, and in this specimen, one can see numerous blood vessels (BV) as evidenced by the red blood cells that they contain. It is even more difficult to distinguish fibroblasts within the lobule from nuclei of the fat cells. Even at higher magnification (inset), it is difficult to determine which nuclei belong to which cells. A capillary (C) can be identified in the inset. Again, it is recognized by the presence of red blood cells. Where the lobules are slightly separated from one another (arrows), small elongate nuclei can be recognized. These belong to fibroblasts in the connective tissue forming the septa.
KEY DICT, dense irregular connective tissue A, adipocytes BV, blood vessels N, nucleus Cy, cytoplasm MC, mast cells C, capillary SGD, sweat gland ducts
OVERVIEW OF BLOOD / 268 PLASMA / 269 ERYTHROCYTES / 270 LEUKOCYTES / 275 Neutrophils / 275 Eosinophils / 280 Basophils / 282 Lymphocytes / 283 Monocytes / 286 THROMBOCYTES / 286 FORMATION OF BLOOD CELLS (HEMOPOIESIS) / 289 Monophyletic Theory of Hemopoiesis / 289 Development of Erythrocytes (Erythropoiesis) / 293 Kinetics of Erythropoiesis / 295 Development of Thrombocytes (Thrombopoiesis) / 295 Development of Granulocytes (Granulopoiesis) / 295 Kinetics of Granulopoiesis / 296 Development of Monocytes / 298 Development of Lymphocytes (Lymphopoiesis) / 298 BONE MARROW / 298 Folder 10.1 Clinical Correlation: ABO and Rh Blood Group Systems / 273 Folder 10.2 Clinical Correlation: Hemoglobin in Patients with Diabetes / 274 Folder 10.3 Clinical Correlation: Hemoglobin Disorders / 276 Folder 10.4 Clinical Correlation: Inherited Disorders of Neutrophils; Chronic Granulomatous Disease (CGD) / 281 Folder 10.5 Clinical Correlation: Hemoglobin Breakdown and Jaundice / 281 Folder 10.6 Clinical Correlation: Cellularity of the Bone Marrow / 300
Blood is a fluid connective tissue that circulates through the cardiovascular system.
Like the other connective tissues, blood consists of cells and an extracellular component. Total blood volume in the average adult is about 6 L or 7% to 8% of total body weight. The heart’s pumping action propels blood through the cardiovascular system to the body tissues. Blood’s many functions include:  delivery of nutrients and oxygen directly or indirectly to cells, transport of wastes and carbon dioxide away from cells, delivery of hormones and other regulatory substances to and from cells and tissues,  maintenance of homeostasis by acting as a buffer and participating in coagulation and thermoregulation, and  transport of humoral agents and cells of the immune system that protect the body from pathogenic agents, foreign proteins, and transformed cells (i.e., cancer cells).
Blood consists of cells and their derivatives and a protein-rich fluid called plasma.