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Histology of Specialized Connective Tissues CT10 Describe adipose tissue: white and brown Adipose tissue is an aggregation of adipose cells organized into lobules by connective tissue. Contains blood vessels, nerves, and lymphatics. Functions: – Stores ene...

Histology of Specialized Connective Tissues CT10 Describe adipose tissue: white and brown Adipose tissue is an aggregation of adipose cells organized into lobules by connective tissue. Contains blood vessels, nerves, and lymphatics. Functions: – Stores energy - Fat is an efficient form of calorie storage because of its calorie density compared to carbohydrates and proteins. – Shock absorber for structures. – Prevents heat loss (insulates the body) and involved in heat production. – Source of water in extreme conditions (from metabolism). – Other endocrine and metabolic functions. Two types: – White or unilocular. – Brown or multilocular. Kierszenbaum A. L. Histology and Cell Biology © Elsevier  Histology of Specialized Connective Tissues CT10 Describe adipose tissue: white and brown Mesenchymal cells or fibroblasts develop into lipoblasts (preadipocytes) that develop into white or brown Adipocytes. White or unilocular adipose tissue: – Each cell contains a single lipid droplet (filled with triglycerides) which gives it a white color in the living state. – Characteristics: Thin ring of cytoplasm surrounding an empty vacuole (left by the dissolved lipid droplet), called Signet ring cell. Eccentrically flatten nucleus – Reticular fibers surrounds the individual fat cells and binds them together. Kierszenbaum A. L. Histology and Cell Biology © Elsevier  Histology of Specialized Connective Tissues CT10 Describe adipose tissue: white and brown White or unilocular adipose tissue: – Abundant in the superficial fascia (hypodermis), partitioned between connective tissue. – Abundant membrane receptors (insulin, growth hormone, norepinephrine & glucocorticoids) that facilitate the uptake and release of fatty acids and glycerol. – Conversion of androgens to estrogens. – Endocrine function – releases Leptin that targets the hypothalamus and other organs. Regulates appetite (Satiety factor). Regulates the amount of adipose tissue. Kierszenbaum A. L. Histology and Cell Biology © Elsevier  Histology of Specialized Connective Tissues CT10 Describe adipose tissue: white and brown Brown or multilocular adipose tissue: – Cells are smaller and the lipids are stored in multiple droplets (multilocular). – It is a ready source of lipids for oxidation, which produces heat. Can oxidize fatty acids at 20 times the rate of white adipose cells. – In the living state the cells appear reddish brown due to the extensive vascularity and abundance of mitochondria that contains cytochrome oxidase. Abundant mitochondrial uncoupling proteins (thermogenin) leads to a high rate of HEAT production. – Found in infants around the neck and interscapular region. Kierszenbaum A. L. Histology and Cell Biology © Elsevier Histology of Specialized Connective Tissues Describe general characteristics of cartilage. Cartilage: – Specialized connective tissue composed of cells, fibers and ground substance. – The extracellular matrix gives cartilage its firmness and strength. – Cartilage is avascular, the large amount of glycosaminoglycans in the matrix permit diffusion between surrounding blood vessels and chondrocytes. – Cartilage also does not contain nerves or lymphatics.  Histology of Specialized Connective Tissues CT14&15 Describe the development and growth of cartilage. Growth of Cartilage (chondrogenesis). Mesenchymal cells transform into chondroblasts. Chondroblasts produce the ECM (fibers and ground substance), and as they become enclosed by matrix they become chondrocytes located in lacunae. The surrounding mesenchyme forms the perichondrium.  Histology of Specialized Connective Tissues CT16 Describe the development and growth of cartilage.. Growth of Cartilage (chondrogenesis). – Interstitial growth: During embryogenesis growth occurs on the inside of young cartilage. Chondrocytes undergo mitosis forming cell nests (isogenous groups). As chondrocytes secrete their territorial matrix they become separated into their own lacunae. – Appositional growth: Growth that occurs from the inner cellular layer (chondrogenic cells) of the perichondrium. Occurs primarily in adult cartilage. Chondroblast derived from the inner cellular layer of the perichondrium undergo mitosis and secrete matrix adding new cartilage to the surface. Kierszenbaum A. L. Histology and Cell Biology © Elsevier  Histology of Specialized Connective Tissues Describe the types of cartilage, their location, and repair of cartilage. CT11, 12,13 Types and location: – Hyaline Cartilage (most prevalent type): Located: – Articular cartilage of synovial joints, tracheal ring, bronchi, nasal septum, laryngeal and costal cartilages in adults. – Most of the fetal skeleton and epiphyseal plates in developing long bones and some other developing bones. Type II Collagen – Elastic Cartilage (found where structures must withstand repeated bending): Located: – External ear, auditory tube (Eustachian tube), epiglottis and laryngeal cartilages. Type II collagen and Elastic fibers. – Fibrocartilage (located where dense connective tissue blends into hyaline cartilage): Found: – Intervertebral discs, articular discs and pubic symphysis. Type I collagen  Histology of Specialized Connective Tissues CT11,12,13 Describe hyaline cartilage. Hyaline Cartilage: ECM: – Has a smooth appearance (hyaline means glassy). – Consists of type II collagen fibers and a ground substance consisting primarily of water (70%) with proteoglycans (rich in GAGs: hyaluronic acid, chondroitin sulfate and keratan sulfate). Chondrocytes: – Oval to round in shape with a basophilic cytoplasm and spherical nucleus. – Usually exist as a single cell in its lacunae or some may be in cell nests (isogenous groups). – Territorial matrix is the newer darker staining matrix surrounding the cell. Perichondrium: – Outer fibrous layer Dense irregular connective tissue. – Inner cellular layer Chondrogenic cells. – Articular cartilage does NOT contain a perichondrium.  Histology of Specialized Connective Tissues CT11,12,13 Describe elastic and fibrocartilage. Elastic cartilage: – The Chondrocytes and the perichondrium are the same as in hyaline cartilage, but the ECM has elastic fibers. Fibrocartilage: – Chondrocytes are the same as in hyaline cartilage, but they are located in an abundance of collagen fibers which looks like lacuna surrounded by dense irregular connective tissue. – Type I collagen (tensile strength). – Low concentration of proteoglycans and water. – There is no perichondrium.  Histology of Specialized Connective Tissues Describe the repair of cartilage. Cartilage Repair after Injury: Repair of cartilage is limited to slight regeneration potential from the chondrogenic cells of the perichondrium (appositional growth). The repair cartilage has a matrix composition of both Type I and Type II.  Histology of Specialized Connective Tissues Classification of Joints Articulations or Joints: Refer to the point of contact between bones.  Histology of Specialized Connective Tissues Classification of Joints Fibrous Joints: Lack a joint cavity and held very close together by dense connective tissue 1. Sutures Found between the bones of the skull. 2. Syndesmosis Forms an interosseous membrane. Found between the shafts of long bones in the extremities. 3. Gomphosis Found at the roots of the teeth and the alveolar process of the maxilla and mandible.  Histology of Specialized Connective Tissues Classification of Joints Cartilaginous Joints: Lack a joint cavity and held very close together by cartilage. 1. Synchondrosis Found in the rib cage and the epiphyseal plate. Bones connected together by hyaline cartilage. 2. Symphysis Found at the intervertebral disc and pubic symphysis Bones connected together by Fibrocartilage cartilage.  Histology of Specialized Connective Tissues Diarthrodial Joints Synovial joints – Articular cavity The articulating bony surfaces are generally not in contact. – Articular cartilage - hyaline cartilage without a perichondrium. – Capsule Fibrous layer Synovial membrane layer: – Synovial cells secrete synovial fluid (hyaluronic acid and Leukocytes).  Histology of Specialized Connective Tissues Osteoarthritis X-Ray Images Osteoarthritis / Degenerative joint Disease: –Most common joint disorder. –Degeneration of articular (hyaline cartilage). Chondrocytes respond to biomechanical and biologic stresses that result in a breakdown of the extracellular matrix. –Structural changes in bone are secondary. – Image Findings: Joint space narrowing Osteophytes Subchondral sclerosis Subluxation and deformity