Tissues

• Connective tissues are classified based on the structure of cells, composition of the extracellular matrix, and functions of the cells

  
• Epithelial tissue covers body surfaces, is avascular, and has distinct cell surfaces
• The basement membrane is a specialized type of extracellular material secreted by epithelial and connective tissue cells, helping attach epithelial cells to underlying tissues
• Epithelial tissue structures like desmosomes and tight junctions mechanically bind cells together, form permeability barriers, and provide a mechanism for intercellular communication
• Epithelial tissue functions include protecting underlying structures, acting as barriers, permitting the passage of substances, secreting substances, and absorbing substances
• Epithelial tissue can be classified based on cell shape (squamous, cuboidal, columnar) and the number of cell layers (simple, stratified)
• Special types of epithelial tissue include pseudostratified and transitional epithelium
• Pseudostratified ciliated columnar epithelium is almost always ciliated and with goblet cells, found in the lining of the nasal cavity and bronchi of the lungs
• Transitional epithelium is stratified, with cuboidal shape when not stretched and squamous shape when stretched
• Connective tissues enclose and separate other tissues, connect tissues to one another, support and move body parts, store compounds, cushion and insulate, transport, and protect
• The two main types of connective tissue are embryonic and adult connective tissue
• Areolar, adipose, and reticular connective tissues provide loose packing, support, nourishment, thermal insulation, energy storage, and protection of organs
• Dense regular and dense irregular connective tissues have densely packed fibers with relatively little space between them
• Dense regular collagen fibers are oriented in the same direction, while dense irregular fibers are oriented in many different directions
• Cartilage tissues have chondrocytes in lacunae within an extensive matrix, providing flexibility and strength
• Types of cartilage tissues include hyaline, elastic, and fibrocartilage, each with specific characteristics and functions
• Long bones form the embryonic skeleton, providing rigidity with some flexibility, elasticity, and the ability to withstand pressure
• Categories of tissues include:

  • Bone tissue with mineralized matrix made of calcium phosphate and cells called osteocytes in lacunae
  • Blood tissue with liquid matrix (plasma) and formed elements like erythrocytes, leukocytes, and platelets
  • Epithelial tissue, a secretory structure, classified as endocrine glands (no ducts, secrete hormones) and exocrine glands (have ducts)
• Tissues are classified based on the structure of ducts (simple or compound), the formation of tubules or saclike structures, and how products leave the cell (merocrine, apocrine, holocrine)
• Muscle tissue types include:

  • Skeletal muscle (striated, voluntary)
  • Smooth muscle (visceral, involuntary)
  • Cardiac muscle (striated, involuntary)
• Characteristics of muscle tissues:

  • Skeletal: elongated, multinucleated, striated, voluntary, attached to bones and other connective tissues for body movement under voluntary control
  • Cardiac: elongated and branched, 1 nucleus, striated, involuntary, in the heart for heart contraction to pump blood
  • Smooth: spindle shape, 1 nucleus, not striated, involuntary, in hollow organs to regulate organ size, forces fluid through tubes, controls light entering the eye, and produces goosebumps
• Nervous tissue forms the brain, spinal cord, and nerves, composed of neurons (nerve cells) and glial cells that support neurons by nourishing, protecting, and insulating them
• Tissue membranes are thin layers covering structures or lining cavities, including external (skin), mucous, serous, and synovial membranes
• Inflammation is a complex process involving cells and chemicals that occurs in response to tissue damage, mobilizing the body’s defenses and isolating and destroying microorganisms, foreign materials, and damaged cells for tissue repair to proceed
• Steps of inflammation:

  1. A splinter in the skin causes damage and introduces bacteria, activating mediators of inflammation in injured tissues and adjacent blood vessels
  2. Blood vessels dilate and increase in permeability due to activated mediators, causing redness and swelling
  3. White blood cells move to the site of infection, phagocytizing bacteria and debris, leading to pus formation
• Tissue repair involves regeneration or fibrosis, with stem cells playing a crucial role in tissue renewal and repair mechanisms
• Stem cells are self-renewing, undifferentiated cells that can divide throughout life, giving rise to daughter stem cells and differentiated cells, aiding in tissue repair and renewal
• Wound healing involves the formation of a scab, increased production of epithelial cells, fibroblasts producing collagen, and the growth of new blood vessels into the damaged area for tissue repair