Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Monoclonal antibody wikipedia , lookup
Atherosclerosis wikipedia , lookup
Molecular mimicry wikipedia , lookup
Polyclonal B cell response wikipedia , lookup
Adaptive immune system wikipedia , lookup
Lymphopoiesis wikipedia , lookup
Cancer immunotherapy wikipedia , lookup
Histology Connective Tissues General Concepts Composition 1. Cells. Each type of connective tissue has it own characteristic complement of one or more of a wide variety of cells. 2. Extracellular matrix. Synthesized and secreted by resident “blast” cells specific for each connective tissue type (e.g., fibroblasts and chondroblasts); the matrix is composed of: a. Fibers. Collagen, elastic and reticular b. Ground substance. An amorphous substance that can exist as a liquid, gel, or flexible or rigid solid, conferring unique structural properties to each connective tissue. Functions 1. Provides substance and form to the body and organs 2. Defends against infection 3. Aids in injury repair 4. Stores lipids 5. Provides a medium for diffusion of nutrients and wastes 6. Attaches muscle to bone and bone to bone Types of connective tissue. Classified by the relative abundance, variety, and content of their components 1. Connective tissue proper 2. Cartilage 3. Bone 4. Special. Includes adipose, elastic, reticular, and mucoid connective tissues as well as blood and hematopoietic tissue. Connective Tissue Proper General Concepts 1. Connective tissue proper comprises a very diverse group of tissues, both functionally and structurally. a. Structural functions of connective tissue proper 1) Forms a portion of the wall of hollow organs and vessels and the stroma of solid organs. 2) Forms the stroma of organs and subdivides organs into functional compartments. 3) Provides padding between and around organs and other tissues. 4) Provides anchorage and attachment (e.g., muscle insertions) b. Provides a medium for nutrient and waste exchange c. Lipid storage in adipocytes d. Defense and immune surveillance function via lymphoid and phagocytic cells. 2. All connective tissues are composed of two basic components, which vary widely among different types of connective tissue. The components of connective tissues are: a. Cells (e.g., fibroblasts and macrophages) b. Extracellular matrix 1) Fibers (e.g., collagen and elastic fibers) 2) Ground substance. 12 Histology Connective Tissues Cells of Connective Tissue: 1. Fibroblasts a. Synthesize and maintain fibers and ground substance b. Major resident cell in connective tissue proper c. Active and inactive fibroblasts 2) Active fibroblast a) Large, euchromatic, oval nucleus b) Cytoplasm not usually visible but contains abundant rough endoplasmic reticulum and Golgi c) Elongated, spindle-shaped cells d) High synthetic activity 2) Inactive fibroblast a) Small, heterochromatic, flattened nucleus b) Reduced cytoplasm and organelles c) Low synthetic activity 2. Macrophages a. Derived from blood monocytes; monocytes enter connective tissue from the bloodstream and rapidly transform into macrophages that function in phagocytosis, antigen processing, and cytokine secretion. b. Comprise the mononuclear phagocyte system of the body; include Kupffer cells in the liver, alveolar macrophages in the lung, microglia the central nervous system, Langerhan’s cells in the skin, and osteoclasts in bone marrow c. Structure 1) Heterochromatic, oval nucleus with an indentation in the nuclear envelope and marginated chromatin. 2) Cytoplasm usually not visible unless it contains phagocytosed material. 3. Mast cells a. Mediate immediate hypersensitivity reaction and anaphylaxis by releasing immune modulators from cytoplasmic granules, in response to antigen binding with cell surface antibodies. b. Structure 1) Round to oval-shaped cells 2) Round, usually centrally located nucleus 3) Well-defined cytoplasm filled with secretory granules containing immune-modulatory compounds (e.g., histamine and heparin). 4. Plasma cells a. Secrete antibodies to provide humoral immunity b. Derived from B-lymphocytes c. Structure 1) Oval-shaped cells 2) Round, eccentrically located nucleus with heterochromatin clumps frequently arranged like the numerals on a clock-face 3) Basophilic cytoplasm due to large amounts of rough endoplasmic reticulum 4) Well-developed Golgi complex appears as a distinct, unstained region in the cytoplasm near the nucleus and, for that reason, is often referred to as a “negative Golgi.” 5. Adipose cells (adipocytes, fat cells) a. Store lipids 13 Histology Connective Tissues b. Types 1) Yellow fat (unilocular) a) Each cell contains a single droplet of neutral fat (triglycerides) for energy storage and insulation. b) Minimal cytoplasm, present as a rim around the lipid droplet. c) Flattened, heterochromatic, crescent-shaped nucleus that conforms to the contour of the lipid droplet Can occur singly, in small clusters or forming a large mass, which is then referred to as adipose connective tissue. 2) Brown fat (multilocular) a) Cells contain numerous, small lipid droplets. b) Large numbers of mitochondria c) Present mostly during early postnatal life in humans, abundant in hibernating animals for heat production 6. White blood cells (WBCs, leukocytes): These cells enter and leave the blood stream to migrate through, and function in, connective tissues. The most common WBCs encountered in connective tissue proper are lymphocytes, neutrophils, and eosinophils. For a complete discussion of blood cells a. Lymphocytes (T and B lymphocytes) 1) Small spherical cells with sparse cytoplasm and a round heterochromatic nucleus, often with a small indentation. 2) B cells enter connective tissue where they transform into plasma cells and secrete antibodies. T cells are primarily located in lymphatic tissues and organs; however, T cells can be present in connective tissue proper under certain circumstances (e.g., organ transplantation). b. Neutrophils (polymorphonuclear leukocytes, PMNs) 1) Spherical cells with a heterochromatic nucleus with three to five lobes. 2) Pale-staining cytoplasmic granules. 3) Highly phagocytic cells that are attracted to sites of infection c. Eosinophils 1) Spherical cells with a bilobed nucleus 2) Cytoplasmic granules stain intensely with eosin. 3) Modulate the inflammatory process Extracellular Matrix 1. Fibers Fiber type Composition Properties Collagen Collagen I, II Inelastic, eosinophilic Reticular Elastic Collagen III Elastin Inelastic,branched, argyrophilic Elastic, eosinophilic 2. Ground substance a. Functions 1) Forms a gel-like matrix of variable consistency in which cells and fibers are embedded 2) Provides a medium for passage of molecules and cells migrating through the tissue 14 Histology Connective Tissues 3) Contains adhesive proteins that regulate cell movements b. Components 1) Tissue fluid. Contains salts, ions and soluble protein 2) Glycosaminoglycans (GAGs) a) Long, unbranched polysaccharides composed of repeating disaccharide units, which are usually sulfated. b) Large negative charge of the sugars attracts cations, resulting in a high degree of hydration. The matrix formed ranges from a liquid passageway to a viscous shock absorber. c) GAGs are generally attached to proteins to form proteoglycans. d) Proteoglycan aggregate. Many proteoglycans are attached to hyaluronic acid, which is itself a glycosaminoglycan. 3) Adhesive glycoproteins. For example, fibronectin and laminin. Classification of Connective Tissue A. Connective Tissue Proper 1. Loose (areolar) a. Highly cellular, numerous cell types present. b. Fewer and smaller caliber collagen fibers compared with dense c. Abundant ground substance, allows for diffusion of nutrients and wastes d. Highly vascularized e. Provides padding between and around organs and tissues 2. Dense a. Fewer cells, mostly fibroblasts b. Highly fibrous with larger caliber collagen fibers, provides strength. c. Minimal ground substance d. Poorly vascularized e. Types 1) Dense, irregular connective tissue. Fiber bundles arranged in an interlacing pattern; forms the capsule of organs and the dermis of the skin. 2) Dense regular connective tissue. Parallel arrangement of fiber bundles; restricted to tendons and ligaments. 3. Adipose connective tissue. Consists of accumulations of adipocytes that are partitioned into lobules by septa of connective tissue proper. Provides energy storage and insulation. 4. Blood and hematopoietic (blood-forming) tissues (LAB10) 5. Elastic connective tissue. Regularly arranged elastic fibers or sheets (e.g., the vocal ligament) 6. Reticular connective tissue. A loosely arranged connective tissue whose fibers are reticular fibers. Forms the stroma of hematopoietic tissue (e.g., bone marrow) and lymphoid organs (e.g., lymph node and spleen). 7. Mucoid connective tissue. Embryonic connective tissue with abundant ground substance and delicate collagen fibers; present in the umbilical cord. B. Supportive Connective Tissues 1. Cartilage (LAB 6) 2. Bone (LAB 6) 15