Tissues

• Tissues


  Collections of specialized cells and the extracellular substances surrounding them
• Histology


  Microscopic study of tissues
• Biopsy


  Removing tissue samples from patients
• Extracellular matrix


  Noncellular substances surrounding the cells
• 4 primary tissue types

  • Epithelial tissue
  • Connective tissue
  • Muscle tissue
  • Nervous tissue
• Tissues


  • Classified by structure, cell shape
  • Relationship of cells to one another
  • Composition of extracellular matrix
• Body structure function can be determined by specific type of tissue
• Blast


  Bud or germ
• Formation of embryonic germ layers

  1. Cells of the epiblast migrate between the two layers

  2. Endoderm - inner layer, forms lining of digestive tract

  3. Mesoderm - middle layer, forms tissues like muscle, bone, blood vessels

  4. Ectoderm - outer layer, forms skin

  5. Neuroectoderm - portion of ectoderm that becomes nervous system

  6. Neural crest cells - groups of cells that break away from neuroectoderm
• Epithelium


  Found both inside and outside the body, primarily a cellular tissue
• Epithelial tissue


  • Mostly composed of cells
  • Covers body surfaces
  • Has an exposed surface
  • Attaches at the basal surface
  • Has specialized cell connection and matrix attachment
  • Avascular
  • Capable of regeneration
• Functions of epithelia


  • Protecting underlying structures
  • Acting as a barrier
  • Permitting the passage of substances
  • Secreting substances
  • Absorbing substances
• Major types of epithelium based on cell layers

  • Simple epithelium - single layer
  • Stratified epithelium - more than one layer
  • Pseudostratified epithelium - appear stratified but single layer
• Types of shapes of epithelial cells

  • Squamous - flat or scale-like
  • Cuboidal - cubed-shape
  • Columnar - taller than wider
• Simple squamous epithelium


  Single flat layer that aids in diffusion, filtration, and some secretion
• Types of simple squamous epithelium

  • Nonkeratinized (moist) - living cells in deepest and superficial layers
  • Keratinized (dry) - living cells only in deepest layers, superficial layers are dead cells containing keratin
• Simple cuboidal epithelium


  Single layer of cube-like cells that carry out active transport
• Simple columnar epithelium


  Single layer of tall, thin cells that perform complex functions
• Pseudostratified columnar epithelium


  Appear to be layered but not, provide protection for the body
• Stratified squamous epithelium


  Thick and layered cells that are capable of dividing and producing new cells, protect against abrasion
• Stratified cuboidal epithelium


  Multiple layers of somewhat cube-shaped cells that protect against infection, secretion, and absorption
• Stratified columnar epithelium


  Multiple layers of cells with tall, thin layers of cube-shaped cells that aids protection and secretion
• Transitional epithelium


  Special type of stratified epithelium that decreases layers when stretched, accommodates fluctuations in volume of fluid
• Transitional epithelium when unstretched vs stretched

  • Unstretched - cube-shaped
  • Stretched - squamous shaped
• Number of cell layers and shapes

  As the number of cell layers increases and the shape of the cell becomes more robust, proportional increase in degree of protection
• Relationship between structure and function of epithelial tissues

  • One layer of flat cells - filtration is more common
  • One layer of cube-like cells - greater secretory capacity
  • One layer of tall, rectangular cells - protects lining on intestine as bacteria cannot penetrate
  • Multiple layers of flat cells - protection against abrasion
• Free surface modifications


  • Smooth free surfaces that reduce friction (endothelium)
  • Folded free surface have increased surface area
  • Microvilli - stationary and found in cells that absorb or secrete
  • Cilia - can move and help move mucus and oocytes
• Cell connections in epithelial tissue

  • Desmosomes - mechanically bind epithelial cells together
  • Hemidesmosomes - bind cells to basement membrane
  • Tight junctions - form barriers and anchor cells together near free surface
  • Adhesion belts - found just below tight junctions, help anchor cells together
  • Gap junctions - allow intracellular communication
• Glands


  Specialized secretory organs composed of epithelium supported by connective tissue
• Major types of glands

  • Endocrine gland - ductless, produce hormones
  • Exocrine gland - produce variety of products that enter ducts
• Structures of exocrine glands

  • Tubular shaped - straight, narrow tube same width as duct
  • Acinar shaped - sac-like structure wider than duct
  • Unicellular - single cells (goblet cells)
  • Simple glands - multicellular with single, nonbranched duct
  • Compound glands - multicellular with branched ducts
• Types of simple exocrine glands

  • Simple tubular: straight tube with no branching
  • Simple branched tubular: several tubular secretory portions branching from single duct
  • Simple acinar: single saclike secretory portions
  • Simple branched acinar: several acinar secretory portions branching
• Types of compound exocrine glands

  • Compound tubular: multiple ducts, each have narrow tubular secretory portions
  • Compound acinar: multiple ducts with sac-like secretory portions
  • Compound tubuloacinar: multiple ducts with several tubular and acinar secretory portions
• Modes of secretion by exocrine glands

  • Merocrine secretion - release by exocytosis
  • Apocrine secretion - release as pinched off fragments of the gland cells
  • Holocrine secretion - shedding the entire cells
• Connective tissue


  Diverse primary tissue type that makes up part of every organ, consists of cells separated by abundant extracellular matrix
• Functions of connective tissue

  • Enclosing and separating other tissues
  • Connecting tissues to one another
  • Supporting and moving parts of the body
  • Storing compounds
  • Cushioning and insulating
  • Transporting
  • Protecting
• Cells of connective tissue

  • Blasts - create matrix (osteoblasts, chondroblasts, fibroblasts)
  • Cytes - maintain matrix (osteocytes, chondrocytes, fibrocytes, adipocytes)
  • Clasts - break down matrix for remodeling (osteoclasts)
  • Mast cells - contain chemicals responsible for inflammation
  • White blood cells - continuously move from blood vessels into connective tissues
  • Macrophages - phagocytic cells
  • Platelets - fragments of hemopoietic cells that function in clotting
  • Undifferentiated mesenchymal cells - adult stem cells
• Major components of extracellular matrix

  • Collagen fibers - most abundant, synthesized by fibroblasts
  • Reticular fibers - short, thin, branching network
  • Elastic fibers - protein that can return to original shape after stretching
  • Ground substance - gel-like mixture of nonfibrous molecules
• Chondrocytes


  Cartilage cells
• Adipocytes


  Adipose cells