tissues

• There are four types of tissues:

  • Epithelium (covering)
  • Connective (support)
  • Muscle (movement)
  • Nervous (control)
• Connective tissue is extremely abundant throughout the body and is the only tissue type that can provide movement due to its ability to contract
• Tissues are groups of cells with similar structure that perform a common function
• Epithelial tissue lines hollow organs open to the outside of the body, providing a protective boundary
• Nervous tissue is designed to control functions within the body, such as muscles
• Extracellular matrix consists of extracellular protein fibers and ground substance, which includes syrup-like fluid, ECF, interstitial fluid, and tissue fluid
• Epithelia and Glands:

  • Epithelia are sheets of cells that cover body surfaces or line body cavities
  • They occur at interfaces between different environments, providing a boundary
• Functions of epithelial tissue include protection, secretion, absorption, diffusion/filtration, and sensory reception
• Special Characteristics of Epithelia:

  • Cellularity: composed of cells with minimal extracellular material
  • Attachment: anchored to a basement membrane
  • Polarity: free edge (apical) and lower (basal) surface
  • Avascular but innervated: lack blood vessels but receive nerve endings
  • Regeneration: constantly being replaced due to friction resistance
• Epithelial Cell Junctions:

  • Tight junctions: innerlocking proteins that prevent molecules from passing between cells
  • Desmosomes: anchors cells to each other, allowing flexibility and movement
  • Gap Junctions: allow communication between cells
• Classification of Epithelia:

  • Classified by the number of layers of cells and the shape of those cells
  • Number of layers: simple (single layer) or stratified (multiple layers)
  • Shape: squamous (flat), cuboidal (cube-like), columnar (column-like)
• Simple Epithelia:

  • Single layer of cells
  • Important for passive diffusion (squamous) or absorption/secretion (cuboidal or columnar)
  • Special cases include endothelium (found in heart and blood vessels) and mesothelium (lines serosal cavities), psuedostratified columnar (all cells touch basememnt membrane)
• Stratified Epithelia:

  • Consist of 2 or more layers
  • More durable and provide protection
  • Regenerate from below
  • Can be keratinized (waterproofed by dead layer of cells) or non-keratinized
• Transitional Epithelium:

  • Lines the inside of hollow urinary organs and umbilical cord
  • Allows for distention (stretching) and changes shape as needed
• Glands - specialized epithelia:

  • Glands can be cells or organs that secrete substances
  • Exocrine glands have ducts to reach the epithelial surface
  • Endocrine glands are ductless and use blood for transport
• Exocrine gland types of secretions:

  • Serous glands produce thin watery fluids
  • Mucous glands secrete mucin (glycoproteins) that form mucus
  • Mixed glands can produce both serous and mucous secretions
• Connective Tissue:

  • Most abundant type of tissue
  • Functions include connecting cells, forming the skeleton, storing and carrying nutrients, surrounding blood vessels and nerves, fighting infection, heat production, and physical protection
  • Cells in connective tissue are separated by a large amount of nonliving extracellular matrix
  • Connective tissue originates from embryonic tissue called mesenchyme
• Connective tissue originates from embryonic tissue called mesenchyme
• Connective tissue is different from epithelial tissue because cells are separated by extracellular matrix
• Three main categories of connective tissue: connective tissue proper (fibrous), fluid, and supporting
• All connective tissue originates from mesenchyme, which are stem cells waiting to be directed by the body
• Types of cells found in Connective Tissue Proper:

  • Fibroblasts produce fibers and ground substance
  • Macrophages derived from monocytes
  • Mesenchymal cells
  • Leukocytes (WBC)
  • Mast cells release histamine and heparin
  • Adipocytes (fat cells)
• Fibers in Fibrous Connective Tissue:

  • Collagenous fibers are tough and flexible
  • Reticular fibers form a sponge-like framework
  • Elastic fibers allow stretching and recoiling
• Areolar Connective Tissue:

  • Supports and binds tissues
  • Holds body fluids
  • Defends against infection
  • Stores nutrients as fat
  • Aids in waste removal
• Other loose connective tissues:

  • Adipose tissue stores nutrients and is highly vascularized
  • Reticular Connective tissue resembles areolar tissue but only has reticular fibers
• Dense Connective Tissue:

  • Dense irregular connective tissue has thicker collagen fibers
  • Dense regular connective tissue fibers run parallel to the direction of pull
• Cartilage:

  • Resists compression and tension
  • Types include hyaline, elastic, and fibrocartilage
• Bone:

  • Matrix contains inorganic calcium salts and collagen fibers
  • Types include spongy and compact bone
  • Components of Haversian system include osteocytes, periosteum, osteoblasts, and osteoclasts
• Blood:

  • Transports nutrients, wastes, and gases
  • Contains erythrocytes (RBCs), leukocytes (WBCs), and platelets (thrombocytes)
• Membranes:

  • Combination of epithelial tissue and connective tissue
  • Types include cutaneous, mucous, and serous membranes
• Serous Membranes:

  • Line body cavities and cover organs
  • Consist of parietal layer and visceral layer
  • Examples include Pleura (lungs), Pericardium (heart), and Peritoneum (abdominal cavity)