connective tissue

• Connective tissues are made up of cells, proteins, and extracellular matrix, with three main types: proper (dense regular, dense irregular, loose), specialized (cartilage, bone, adipose tissue, blood), and fluid (lymph, synovial fluid)

  
• Mesenchyme, an embryonic tissue formed by undifferentiated cells, is the origin of connective tissues
• The extracellular matrix (ECM) in connective tissues is composed of different combinations of protein fibers (collagen, reticular, elastic) and ground substance
• Connective tissue cells include mesenchymal cells, endothelial cells, smooth muscle cells, osteoblasts, chondroblasts, fibroblasts, adipocytes, and hematopoietic stem cells
• Fibroblasts are the most common cells in connective tissue and are specialized for synthesizing collagen, elastin, and other extracellular matrix components
• Adipocytes are fat cells found in adipose tissue, storing energy as triglycerides and regulating energy balance and body weight
• Mast cells have a role in the inflammatory response, innate immunity, and tissue repair
• Plasma cells are responsible for synthesizing antibodies
• Connective tissue fibers include collagen, reticular, and elastic fibers, each with specific functions in the body
• Collagen fibers are the most abundant protein in the human body, while reticular fibers form extensive networks and elastic fibers are found in organs subject to bending or stretching
• Types of connective tissues include embryonic (mesenchyme, mucous) and adult (loose/areolar, dense, specialized)
• Loose connective tissue supports structures under pressure, with a delicate consistency, flexibility, and moderate ground substance
• Dense connective tissue offers resistance and protection, with fewer cells and a predominance of collagen fibers over ground substance
• Connective tissues are made up of cells, proteins, and extracellular matrix, with three main types: proper, specialized, and fluid

  
• Proper connective tissues include dense regular, dense irregular, and loose connective tissue
• Specialized connective tissues include cartilage, bone, adipose tissue, and blood
• Fluid connective tissues include lymph and synovial fluid
• Dense connective tissue is less flexible and more resistant to stress than loose connective tissue, with a clear predominance of collagen fibers over ground substance

  
• In dense irregular connective tissue, collagen fibers are arranged in bundles without a definite orientation
• Dense regular connective tissue has collagen fibers aligned with the linear orientation of fibroblasts in response to prolonged stresses exerted in the same direction
• Reticular tissue provides an architectural framework for hematopoietic and lymphoid organs
• Mucoid tissue, found mainly in the umbilical cord and fetal tissues, has an abundance of ground substance composed chiefly of hyaluronic acid
• Adipose tissue, dominated by adipocytes or fat cells, is important for energy metabolism, thermal insulation, and organ support
• White adipose tissue is specialized for long-term energy storage, while brown adipose tissue is involved in heat production through non-shivering thermogenesis
• Cartilage allows tissues to bear mechanical stresses without permanent distortion and provides shock absorption and sliding areas for joints
• Types of cartilage include hyaline, elastic, and fibrocartilage
• Hyaline cartilage is the most common type, found in the nose, tracheal rings, and where the ribs join the sternum
• Elastic cartilage, similar to hyaline cartilage, contains an abundant network of fine elastic fibers in addition to collagen type II fibrils
• Fibrocartilage is a mixture of hyaline cartilage and dense connective tissue, found in areas like the pubic symphysis and intervertebral disks
• Bone consists of osteocytes, osteoblasts, and osteoclasts, with types including compact and spongy/cancellous bone
• Compact bone is found in the diaphyses of long bones, while spongy/cancellous bone is in the epiphyses
• Microscopically, bone can be primary/woven or secondary/lamellar, with the latter having multiple layers of calcified matrix