U2: tissue level

• Terminologies:

  • Tissue: a group of cells with a common origin in an embryo and function together to carry out specialized activities
  • Histology: the study of tissues
  • Pathologist: a physician who examines cells and tissues to diagnose a disease
  • Biopsy: the removal of a sample of living tissue for examination
  • Atrophy: a decrease in the size of cells and tissues/organs
  • Hypertrophy: an increase or enlargement of cells without undergoing cell division
  • Stem cells: immature, undifferentiated cells that divide to replace lost or damaged cells
• Cell junctions:

  • Tight junctions: weblike strands of transprotein membranes that inhibit the passage of substances between cells and prevent leaking out of contents
  • Adherens junction: contains plaque attached to microfilaments and transmembrane glycoproteins called cadherin that resist separation during contractile activities
  • Desmosomes: have plaque and cadherins attached to intermediate filaments (keratin) to prevent separation under tension (skin) and pulling apart during contraction (heart)
• • Hemidesmosomes: similar to desmosomes but linked to the basement membrane instead of adjacent cells; maintain tissue structure
  • Gap junction: has membrane proteins called connexins that enable nerve impulses and signals to travel and allow the travel of nutrients and waste
• Epithelial tissue:

  • Arrangement: continuous sheets tightly packed and held together by many cell junctions
  • Functions: absorbs, protects, excretes, secretes
  • Epithelium: apical surface faces the body surface, cavity, or lumen; lateral surface faces adjacent cells; basal surface adheres to the basement membrane
  • Basement membrane: basal lamina contains laminin and collagen, reticular lamina faces the connective tissue; thickening due to disease can result in poor blood flow
• Connective tissue:

  • Extracellular matrix: material located between widely spaced connective tissues consisting of protein fibers and ground substance
  • Ground substances: support cells and fibers, bind them together, and serve as a medium for exchanging substances; made of H2O and glycosaminoglycans
  • Protein fibers: strengthen and support connective tissue; made of collagen, elastic fibers, and reticular fibers
• Muscular tissue:

  • Pattern: elongated cells called muscle fibers or myocytes that can use ATP to generate force
  • Functions: produces body movements, maintains posture, generates heat
• Nervous tissue:

  • Pattern: branched in the nervous system
  • Functions: exhibits sensitivity to various stimuli, converts stimuli into nerve impulses, conducts nerve impulses
• Fibroblasts:

  • Large, flat cells with branching processes
  • Present in all general connective tissues
  • Most numerous type
• Macrophages:

  • Phagocytes that develop from monocytes, a type of white blood cell
  • Fixed macrophages reside in specific tissues like lungs and spleen
• Plasma cells:

  • Found in many places in the body
  • Most plasma cells reside in connective tissue, especially in the gastrointestinal and respiratory tracts
• Types of cells in connective tissue:

  
  

  Mast cells (mastocytes):

  • Involved in the inflammatory response to injury or infection
  • Can bind to, ingest, and kill bacteria
• Types of cells in connective tissue:

  
  

  Adipocytes:

  • Fat cells that store triglycerides
  • Found under the skin and around organs like the heart and kidneys
• Types of cells in connective tissue:

  
  

  Leukocytes (white blood cells):

  • Not found in significant numbers in normal connective tissue
  • Migrate from blood into connective tissue during an infection
  • Neutrophils gather at sites of infection
  • Eosinophils migrate to sites of parasitic invasions and allergic responses