Organ structure

• Organ


  Made of different tissues coming together to perform a function or functions
• System


  An assembly of organs that are homogeneous with respect to function, structure, embryological origin and prevailing tissue
• Apparatus


  An assembly of organs which concur to a common general function but also have specific functions and morphology and are composed of tissues with dissimilar embryological origin
• Classification of organs


  • Solid or parenchymal
  • Layered
• Solid or parenchymal organs


  • Lack an internal cavity, are parallel and elongated, fibrous and filamentous, have a stroma and a parenchyma
• Layered organs


  • Include hollow organs (visceral or vascular), which delimit a cavity, and the skin
• Solid organs


  • Most are surrounded by a capsule made of dense connective tissue, have a stroma which is a supporting framework, have a parenchyma made of epithelial cells or other types of cells, may possess a hilum
• Parenchymal cells


  • Can be heterogeneously or homogeneously distributed
• Lungs


  • Special solid organs with a tubing system that ends up in the alveoli, have elongated parallel morpho-functional units arranged in bundles and organised by connective tissue
• Hollow organs


  • Have a wall formed by different layers (tunicae) which delimit a lumen or cavity, communicate directly or indirectly with the outside
• Layers of a tubular hollow organ

  • Mucosa
  • Submucosa
  • Muscularis externa
  • Serosa or adventitia
• Non-tubular, saccular organs


  • Have an absent or poorly developed submucosa, have a more difficult to distinguish smooth muscle layer organisation
• Vascular hollow organs


  • Have three layers: tunica intima, tunica media, tunica adventitia, also have an inner and outer elastic lamina
• Skin


  • Largest organ of the human body, made of a squamous stratified epithelium, dermis, and subcutis or hypodermis
• Types of membranes


  • Mucous membranes
  • Synovial membranes
  • Serous membranes
• Mucous membranes


  • Line organs communicating with the outside, humified and lubricated by secretions, made of epithelium and lamina propria
• Synovial membranes


  • Between the articular cavity and the joint capsule, surface layer cells are fibroblast-like synoviocytes and macrophages, underlying tissue is loose connective tissue
• Serous membranes


  • Line ventral body cavities and surround organs, made of mesothelium and loose connective tissue, produce a lubricant liquid to reduce friction