C3

• Connective and supportive tissues consist of cells and extracellular material known as the matrix
• The matrix includes connective tissue fibers, ground substance, and tissue fluid
• The main function of connective tissue is to bind, anchor, and provide support for body parts and organs
• Connective tissues also play a role in heat regulation, defense, and repair mechanisms
• All connective and supportive tissues have a mesodermal origin
• The ectoderm of the head region also participates in the formation of connective and supportive tissues
• Embryonic connective tissue or mesenchyme arises from the mesodermal somites and lateral layers of the somatic and splanchnic mesoderm
• All other connective and supportive tissues are derived from mesenchyme
• Classification of Connective and Supportive Tissues:

  • Embryonic connective tissue:
  • Mesenchyme
  • Gelatinous connective tissue
  • Adult connective and supportive tissues:
  • Adult connective tissue:
  • Loose connective tissue
  • Dense connective tissue:
  • Dense irregular connective tissue
  • Dense regular connective tissue (Collagen and Elastic)
  • Reticular connective tissue
  • Adipose tissue (White adipose tissue and Brown adipose)
  • Adult supportive tissue:
  • Cartilage (Hyaline, Elastic, and Fibrocartilage)
  • Bone
  • Notochord
  • Cementum and dentine
• Mesenchyme is composed of irregularly shaped mesenchymal cells with many processes
• Gelatinous connective tissue is found primarily in the embryonic hypodermis and umbilical cord
• Cells of connective tissue include fibroblasts, adipose cells, macrophages, mast cells, plasma cells, and white blood cells
• Fibroblasts synthesize collagen, reticular and elastic fibers, and the extracellular matrix
• Adipose cells store fat and provide protective packing material in and around organs
• Macrophages are phagocytic and ingest bacteria, cell debris, and foreign matter in the connective tissue
• Mast cells synthesize and release heparin and histamine, which mediate inflammation
• Plasma cells synthesize and secrete antibodies (immunoglobulins) into circulation to aid in defense against bacterial infections
• White blood cells defend the organism against bacterial invasion or foreign material
• Collagen fibers are the most abundant and exhibit great tensile strength
• Elastic fibers can be stretched and return to their original size without deformation
• There are five genetically distinct types of collagen: Type I, Type II, Type III, Type IV, and Type V
• Elastin is an amorphous protein of low electron density, with molecules that are randomly coiled and joined by stable covalent cross-links
• The two major stable covalent cross-links in elastin are desmosine and isodesmosine, which are derivatives of lysine
• Elastin is synthesized by fibroblasts and smooth muscle cells as tropoelastin
• Microfibril is the secondary component of elastic fibers, rich in glycoprotein cystine, secreted prior to elastin, providing scaffolding for elastin fibers and sheets
• Reticular fibers are thin fibers forming a delicate net-like framework around capillaries, muscle fibers, nerves, adipose cells, and hepatocytes, serving as scaffolding to support cells in endocrine, lymphatic, and blood-forming organs
• Ground substance in connective tissue is an amorphous, transparent, colorless material with high water content, composed predominantly of various proteoglycans, facilitating diffusion of substances between cells and blood vessels
• Hyaluronic acid, chondroitin sulfates, dermatan sulfate, keratan sulfate, heparan sulfate, and heparin are major types of proteoglycans found in the ground substance of connective tissue
• Adult connective tissues are classified based on the amount, type, arrangement, and abundance of cells, fibers, and ground substance
• Loose connective tissue is loose, irregularly arranged, widely distributed, and serves various functions including support, tissue repair, defense activities, and water metabolism
• Dense connective tissue contains thicker and more densely packed collagen fibers, with fewer cell types and less ground substance
• Reticular connective tissue is composed of stellate reticular cells and a complex three-dimensional network of reticular fibers, found in lymphatic organs and bone marrow
• Adipose tissue, or fat, is a specialized type of connective tissue with two types: white adipose tissue and brown adipose tissue, each with specific functions and characteristics
• Cartilage is a special form of connective tissue that supports soft tissues, consisting of cells and matrix containing collagen or elastic fibers, providing firmness, resilience, tensile strength, and flexibility without distortion
• Cartilage is non-vascular but is surrounded by vascular connective tissue, allowing nutrients to enter and metabolites to leave by diffusion through the matrix
• Cartilage grows by interstitial and appositional growth simultaneously
• Cellular components of cartilage include chondrogenic cells, chondroblasts, chondrocytes, and chondroclasts
• Chondroblast and chondrocytes are stages of maturation of the same cells
• Chondroclasts are multinucleated giant cells responsible for removing cartilage matrix and cells
• Matrix components of cartilage include fibers (collagenous and elastic) and amorphous ground substance (glycosaminoglycans, hyaluronic acid, and keratin sulfate)