Tissues

• Tissues


  Functionally related groups of cells that work together
• Types of tissues


  • Epithelial
  • Connective
  • Muscle
  • Nervous
• Epithelial tissue


  • Covers a body surface or lines a body cavity
  • Forms most glands
  • Functions: Protection, Absorption & Secretion, Filtration, Forms slippery surfaces
• Epithelial tissue characteristics


  • Cellularity - cells in close contact with little intercellular space
  • Specialized contacts - junctions for attachment and communication
  • Polarity - apical and basal surface
  • Support by connective tissue - contributes to basement membrane
  • Avascular - nutrients must diffuse
  • Innervated
  • High capacity for regeneration
• Lateral surface features of epithelial cells

  • Adhesion proteins link plasma membranes of adjacent cells
  • Special cell junctions: Tight junctions, Gap junctions, Desmosomes
• Tight junctions


  Close off intercellular space, prevent molecules passing between cells
• Desmosomes


  Two disc-like plaques connected across intercellular space, proteins interdigitate into extracellular space, intermediate filaments insert into plaques
• Gap junctions


  Passageway between two adjacent cells, let small molecules move directly between neighboring cells
• Simple epithelium


  One layer of cells
• Stratified epithelium


  More than one layer of cells

  
• Squamous epithelium


  Cells wider than tall, plate or "scale" like
• Cuboidal epithelium


  Cells as wide as tall, cube-like
• Columnar epithelium


  Cells taller than wide, column-like
• Pseudostratified columnar epithelium


  All cells originate at basement membrane, only tall cells reach apical surface, nuclei at varying heights

  
• Simple squamous epithelium


  • Single layer of flat cells with disc-shaped nuclei
  • Functions: Passage of materials by diffusion and filtration, Secretes lubricating substances
  • Locations: Renal corpuscles, Alveoli of lungs, Lining of heart, blood and lymphatic vessels, Lining of ventral body cavity

  
• Simple cuboidal epithelium


  • Single layer of cube-like cells with large, spherical central nuclei
  • Functions: Secretion and absorption
  • Locations: Kidney tubules, Secretory portions of small glands, Ovary & thyroid follicles

  
• Simple columnar epithelium


  • Single layer of column-shaped (rectangular) cells with oval nuclei
  • Some bear cilia at apical surface, May contain goblet cells
  • Functions: Absorption, Secretion of mucus, enzymes, and other substances, Ciliated type propels mucus or reproductive cells
  • Locations: Non-ciliated - Lines digestive tract, gallbladder, ducts of some glands, Ciliated - Lines small bronchi, uterine tubes, uterus

  
• Pseudostratified columnar epithelium


  • All cells originate at basement membrane, only tall cells reach apical surface, may contain goblet cells and bear cilia, nuclei at varying heights
  • Functions: Secretion of mucus, propulsion of mucus by cilia
  • Locations: Non-ciliated - Ducts of male reproductive tubes, Ducts of large glands, Ciliated - Lines trachea and most of upper respiratory tract

  
• Stratified epithelia


  • Contain two or more layers of cells, Regenerate from below, Major role is protection
• Stratified squamous epithelium


  • Many layers of cells, squamous in shape at apical layer, deeper layers cuboidal or columnar
  • Keratinized - Surface cells dead and full of keratin, Non-keratinized - Moist lining of body openings
  • Functions: Protects underlying tissues in areas subject to abrasion
  • Locations: Keratinized - Epidermis, Non-keratinized - Esophagus, mouth, vagina

  
• Glandular epithelium


  Ducts carry products of exocrine glands to epithelial surface, May be unicellular or multicellular

  
• Goblet cells


  • Produce mucin, Mucin + water = mucus, Protects and lubricates many internal body surfaces
• Multicellular exocrine glands


  Classified by structure of duct and mode/type of secretion (merocrine, apocrine, holocrine)
• Connective tissue


  Most diverse and abundant tissue, Main classes: Connective tissue proper, Blood, Cartilage, Bone, Components: Cells, Matrix (protein fibers, ground substance), Common embryonic origin - mesenchyme
• Classes of connective tissue

  • Loose connective tissue
  • Dense connective tissue
  • Adipose tissue
  • Cartilage
  • Bone
  • Blood
• Skeletal muscle tissue


  • Long, cylindrical cells, Multinucleate, Obvious striations
  • Functions: Voluntary movement, Manipulation of environment, Facial expression
  • Locations: Skeletal muscles attached to bones
• Smooth muscle tissue


  • Spindle-shaped cells with central nuclei, Arranged in sheets, No striations
  • Functions: Propels substances along internal passageways, Involuntary control
  • Locations: Mostly walls of hollow organs
• Cardiac muscle tissue


  • Branching cells, Uni-nucleate, Intercalated discs
  • Function: Contracts to propel blood into circulatory system
  • Location: Walls of heart
• Nervous tissue


  Transmits electrical signals from sensory receptors to effectors, Main components: Brain, spinal cord, nerves, Contains neurons and supporting neuroglial cells
• Rectum


  The last part of the colon that stores feces until defecation
• Anal sphincter


  Controls defecation
• Appendix


  • A vestigial attachment of the cecum
  • Located between the small and large intestine
• Summary of Digestive Enzymes

  • Salivary amylase
  • Pepsin (protease)
  • Trypsin (protease)
  • Lipase
  • Nuclease
• Salivary amylase


  Breaks down starch
• Pepsin


  Breaks down proteins
• Trypsin


  Breaks down polypeptides into peptides
• Lipase


  Breaks down fats into fatty acids and glycerol
• Nuclease


  Breaks down nucleic acids into nucleotides
• pH


  Optimal pH for each enzyme
• The presence of large numbers of mitochondria in the cells lining the small intestine allows them to absorb nutrients