Four basic types of tissue  Epithelium  Connective tissue Connective tissue proper (examples: fat tissue, fibrous tissue of ligaments) Cartilage Bone Blood  Muscle tissue  Nervous tissue

 Originate from embryonic tissue called mesenchyme  Most diverse and abundant type of tissue  Cells separated from one another by large amount of nonliving extracellular matrix  Two components  Cells  Extracellular matrix (ECM). o Protein fibers o Ground substance

Cells in Connective Tissue 1. Fibroblasts 2. Adipose (fat) cells 3. Tissue Macrophages** 4. Mast cells** 1. Lymphocytes & Plasma Cells (differentiated B-cells) ** 2. “Leukocytes”** Fixed (permanent residents) ** derived from hematopoietic stem cells and involved in immune function and inflammation Free (transient residents) (specifically, neutrophils, eosinophils, & basophils)

Active fibroblasts

Adipocytes predominate in adipose tissue Single, large lipid droplet Very active cells with many functions: Triglyceride storage and glucose metabolism (insulin and glucagon receptors) Secretion of many bioactive molecules: leptin (regulates satiety)angiotensinogen (blood pressure)steroids (glucocorticoids & sex hormones) growth factors (e.g. insulin-like growth factor, tumor necrosis factor  )cytokines (e.g. interleukin-6) Ross, M. Pawlina, W. Wheater’s Functional Histology: A Text and Atlas. Fifth Edition

Adipocytes Capillaries Nucleus Lipid (fat) droplet Source Undetermined

Monocytes escape from blood vessels into connective tissue where they differentiate into Macrophages Primary function: phagocytosis and antigen presentation University of Michigan Histology Collection

Plasma Cells are mature B lymphocytes that constitutively secrete antibodies White arrows = Golgi regions Black arrows indicate several plasma cells Junqueira and Carneiro. Basic Histology. Tenth Edition Figure 6.5. University of Michigan Histology Collection

Fibers in Connective Tissue  Collagen -Most abundant protein in human body  Reticular Fibers – Specialized type of collagen associated with smooth muscle in organs – Specialized type of collagen associated with smooth muscle in organs  Elastic Fibers – Thin fibers composed of various glycoproteins, including the protein elastin, providing elastic properties to tissues – Thin fibers composed of various glycoproteins, including the protein elastin, providing elastic properties to tissues

Collagen fibers viewed by light microscopy H&E Trichrome University of Michigan Histology Collection

Reticular Fibers University of Michigan Histology Collection

Elastic Fibers elastin stain (“Weigert’s”, “aldehyde fuchsin”, “Verhoeff”): elastic fibers are purple/black

Connective tissue properFluid connective tissueSupporting connective tissue Connective Tissue Dense connective tissue Loose connective tissue LymphCartilageBoneBlood What are the subcategories of the three main categories of connective tissue?

Connective Tissues with Special Properties Reticular connective tissue Adipose connective tissue Elastic connective tissue

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