HISTO LEC - Epithelial Tissues

• Characteristics of Epithelial Tissues:

  • Formed of epithelial cells
  • Provided with Basement membrane
  • Cohesive and relatively strong
  • Avascular - having few or no blood vessels
  • Derived from three germ layers: Endoderm, Mesoderm, & Ectoderm
• Germ Layers:

  • Ectoderm - forms the exoskeleton
  • Mesoderm - develops into organs
  • Endoderm - forms the inner lining of organs
• Epithelial Tissue

  • aggregated polyhedral cells
  • small amount of ECM
  • lining of surface or body cavities
• Connective Tissue

  • several types of fixed and wandering cells
  • abundant amount of ECM
  • strong contraction; body movements
• Nervous Tissue

  • elongated cells with extremely fine processes
  • very small amount of ECM
  • transmission of nerve impulses
• Functions of Epithelial Tissue

  • Covering, lining, and protecting surfaces (Ex. Skin)
  • Absorption (Ex. GI tract)
  • Secretion (Parenchymal Cells and Glands)
• Simple epithelium - single layer
• Simple squamous epithelium

  • Facilitates the movement of the viscera (mesothelium), active transport by pinocytosis (mesothelium and endothelium), and secretion of biologically active molecules (mesothelium)
  • Endothelium of blood vessels
  • Mesothelium of body cavities
  • Bowman’s capsule
  • Thin loop of Henle
• Simple cuboidal epithelium

  Covering and secretion

  Kidney tubules

  Thyroid gland

  Capsule of lens

  • Choroid plexus
• Simple Columnar epithelium

  • Protection, lubrication, absorption, secretion
  • GI Tract: Distal esophagus, Stomach, Small and large intestine
  • Uterus and Fallopian tubes
• Stratified epithelium - two or more layers
• Squamous stratified keratinized (dry)

  • Protection; prevents water loss
  • epidermis
• Squamous stratified nonkeratinized (moist)

  • Protection, secretion; prevents water loss
  • Mouth
  • Esophagus
  • Vagina
  • Anal canal
• Stratified Cuboidal/Columnar

  • Protection and secretion
  • Sweat glands
  • Developing ovarian follicles
• Pseudostratified epithelium

  • Protection, secretion; cilia-mediated transport of particles trapped in mucus out of the air passages
  • Found in respiratory tract
• Transitional epithelium

  • Protection, distensibility (capacity to swell)
  • Found in bladder
• Cell Shape

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• Glandular Epithelium

  • synthesize, store, and release the ff:
  • proteins (eg. in the pancreas)
  • lipids (eg. adrenal, sebaceous glands
  • complexes of carbohydrates and proteins (eg. salivary glands).
• Types of Glands

  Exocrine glands

  • ducts connected to and deliver products to the surface epithelium

  Endocrine glands

  • They lack ducts; capillaries adjacent to them are used to deliver secreted hormone products to target tissues through the blood
• Type of Exocrine Glands

  Merocrine

  secretion releases products, usually containing proteins, by means of exocytosis at the apical end of the secretory cells. Most exocrine glands are merocrine.

  
• Type of Exocrine Glands

  Holocrine

  • secretion is produced by the disintegration of the secretory cells themselves as they complete their terminal differentiation, which involves becoming filled with product.
  • Sebaceous glands of hair follicles are the best examples of holocrine glands.

  
• Type of Exocrine Glands

  Apocrine

  • secretion involves loss of membrane-enclosed apical cytoplasm, usually containing one or more lipid droplets.
  • Apocrine secretion, along with merocrine secretion, is seen in mammary glands.

  
• Types of Merocrine secretion products:

  Serous

  • Watery
  • Parotid gland and sweat glands

  Mucous

  • Viscous and thick
  • Sebaceous gland

  Mucous-serous

  • Submandibular and sublingual gland

  Cytogenic Gland

  • Cell producing glands
  • Ovary and Testes
• Simple glands - Ducts Do Not Branch
• Compound glands - Ducts from Several Secretory Units Converge into Larger Ducts
• Simple Glands

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• Simple Glands

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• Simple Glands

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• Compound Glands

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