intro human histo lecture

• Histology


  The study of the tissues of the body and how these tissues are arranged to constitute organs, also called Microscopic anatomy or Microanatomy

  
• Tissue


  Derived from the French word "tissu" which means "weave or texture"
• Prior to the late 1700s, "tissue" did not refer to organic, cellular layers, but rather to anything woven or textured
• Tissue


  Came into usage in the English language in the late 1700s, coined by the French scientist Bichat
• Bichat was the first to propose that tissue is a central element in human anatomy
• Bichat's work was done without a microscope
• Other scientists of that period made use of the microscope that had been much improved by the efforts of the Dutch scientist Leeuwenhoek, to delve more deeply into the nature of the weaves or tissues that Bichat had described
• First microscopes


  • Constructed in the Netherlands during the late 1500s
  • Magnification 3 - 9X, images poor
• Robert Hooke examined cork with a microscope and found it was composed of tiny "chambers"
• Hooke called these chambers cells because they reminded him of the small rooms or chambers found in monasteries that, at that time, were described by the the latin word "cella"
• Hooke published this information, as well as the results of other microscopic research he had performed in his Micrographia
• Cell Theory


  Schleiden and Schwann independently hypothesized that all plant and animal tissues are composed of cells, and that cells were the "ultimate" units of living organisms
• Further study revealed that these small cells contained even smaller structures in their cytoplasm
• Initially only the nucleus (nut) of the cell was noted, but it soon became obvious that there was an even smaller structure within the nucleus that was given the name "nucleolus" which means "small nut"
• Stains were not used to examine cells in these early studies, scientists using the microscope relied entirely on differences in refractive index to make structures in tissues visible

  
• Various stains were introduced to increase contrast, e.g. Basophil - granules contain heparin and histamine
• Tissue


  Interwoven masses of cells and extra cellular material
• Cell


  Living, more or less self-sufficient entities that form tissues, surrounded by a membrane
• Organelle


  Membrane bound structures within cells (e.g. mitochondria, golgi bodies, lysosomes)
• Inclusion


  Various non-membrane bound structures within cells (e.g. glycogen granules)
• Tissue structure


  How cells combine together with extracellular material and each other to form a tissue
• Cellular structure


  How a cell is shaped, and how the components inside cells are organized to support that cells specific function
• Sub-cellular structure


  Detailed analysis of organelles and inclusions
• Histochemical structure


  Molecular analysis of cellular structure
• Molecules and structures in cells


  • Energy storage molecules (lipid, protein, carbohydrate)
  • Structural molecules (phospholipids, cholesterol, proteins like tubulin, actin, myosin)
  • Information molecules (DNA, RNA)
  • Catalysts, reaction initiators (enzymes)
  • Antigenicity (interaction of cell molecular structure with immunoglobulins)
• Friedrich Gustav Jacob Henle is credited with creating the first "histology" that was based on a detailed examination of tissues with the microscope
• Henle developed a classification for epithelia: pavement - squamous, cylindrical - cuboidal or columnar, ciliated - having cilia
• Henle also recognized that the epithelium lining the bladder changed shape as the bladder filled - what we call a transitional epithelium today
• Henle was also an anatomist and cytologist - many anatomical, tissue and cellular structures are named after him
• 4 basic types of tissue


  • Epithelial tissue
  • Connective tissue
  • Muscle tissue
  • Nervous tissue
• Differences among 4 Tissue Classes


  • Types and functions of cells
  • Characteristics of the matrix (extracellular material)
  • Relative amount of space occupied by cells versus matrix
• Embryonic Tissues


  • Embryo begins as a single cell that divides into many cells that form layers (strata)
  • Three primary germ layers: ectoderm, endoderm, mesoderm
• Knowledge of cell structure and organization helps with analyzing histological sections under the microscope

  
• Staining patterns differ according to the histochemical properties which are brought about by the molecular structures that mainly make up a tissue
• pH of some organelles can also dictate staining process
• Fibers and filaments are also important to histological examinations
• Plasma Membrane


  Envelops every eukaryotic cell, functions as a selective barrier, keeps constant the ion content, and facilitates interactions of the cell with its environment
• Plasma Membrane

  • Contains integrins, glycolipids, phospholipids, cholesterol, and transmembrane proteins
• Fluid mosaic model of membrane structure


  Describes the structure and function of the plasma membrane
• Nucleus


  The command center of the cell, contains the molecular machinery to replicate the DNA and to synthesize and process all types of RNA