Lesson 1

• George: 'Lesson 5. EPITHELIAL TISSUE'
• Epithelium


  • Covers body surfaces, lines body cavities & constitutes glands
  • Creates a selective barrier between the external environment and the underlying Connective Tissue (CT) (e.g. Skin)
  • Facilitates or inhibits the passage of specific substances between external environment & underlying CT
• Epithelial Tissues: Characteristics

  • Cellularity: Composed almost entirely of cells (all cells tightly bound by cell junctions), forming a continuous sheet
  • Avascular: Containing no blood vessels
  • Innervated: Supports nerve fibers
  • Regeneration: Epithelial cells are frequently damaged or lost to abrasion, so they are replaced quickly
  • Polarity: Apical (free) and basal surfaces (attached to underlying connective tissue)
• Epithelial Tissues: 8 Major Functions

  • Protection
  • Sensation
  • Secretion
  • Excretion
  • Diffusion
  • Absorption
  • Contractility
  • Transportation
• Epithelial Tissues: 8 Major Functions - Protection


  Epithelial cells protect underlying tissue from mechanical injury, harmful chemicals and pathogens and dehydration
• Epithelial Tissues: 8 Major Functions - Sensation


  Changes in the environment are detected by specialized epithelial cells found in the skin, eyes, ears, and nose, and on the tongue
• Epithelial Tissues: 8 Major Functions - Secretion


  In glands, epithelial tissue is specialized to secrete specific chemical substances such as enzymes, hormones, and lubricating fluids
• Epithelial Tissues: 8 Major Functions - Excretion


  Epithelial tissues in the kidney excrete waste products from the body and reabsorb needed materials from the urine. Sweat is also excreted from the body by epithelial cells in the sweat glands
• Epithelial Tissues: 8 Major Functions - Diffusion


  Simple epithelium promotes the diffusion of gases, liquids and nutrients. Because they form such a thin lining, they are ideal for the diffusion of gases (e.g. walls of capillaries and lungs)
• Epithelial Tissues: 8 Major Functions - Absorption


  Certain epithelial cells lining the small intestine absorb nutrients from the digestion of food
• Epithelial Tissues: 8 Major Functions - Contractility


  Some very specialized epithelial cells, found in the lining of the heart and respiratory tract, contain the contractile proteins myosin and actin, similar to muscle
• Epithelial Tissues: 8 Major Functions - Transportation


  Some epithelial cells have cilia, short hair-like projections that propel fluid or particulate matter over tissue surfaces
• Epithelial Tissues: Classification

  Each epithelium tissue is given two names: The first name indicates the number of cell layers present. Simple- one layer (used in filtration), Stratified- more than one layer (wear and tear areas), Pseudostratified- one layer that looks like many (areas that need to stretch). The second describes the shape of its cells. Squamous- cells are wider than tall, Cuboidal- cells are as wide as tall, Columnar- cells are taller than wide, Transitional- cells have no specific shape. Ciliated- If the apical edge of the epithelium has cilia
• Organ Epithelial functions

  • Skin - protective function
  • Glands - secretory function
  • GIT - absorptive function
  • Tongue & Nose - sensory function
  • Muscles - contractile function
  • Kidney - excretory function & maintains electrolyte balance
  • Testes - germ cell production
• EMBRYONIC ORIGIN of EPITHELIAL TISSUE
• Germ Layer Give rise to

  • Ectoderm - Epidermis glands on skin, some cranial bones, pituitary and adrenal medulla, the nervous system, the mouth between cheek and gums, the anus
• Embryonic origin of epithelial tissue

  • Germ Layer
  • Ectoderm
  • Mesoderm
  • Endoderm
• Ectoderm gives rise to

  • Epidermis glands on skin
  • Some cranial bones
  • Pituitary and adrenal medulla
  • The nervous system
  • The mouth between cheek and gums
  • The anus
• Mesoderm gives rise to

  • Connective tissues proper
  • Bone
  • Cartilage
  • Blood
  • Endothelium of blood vessels
  • Muscle
  • Synovial membranes
  • Serous membrane lining body cavities
  • Kidneys
  • Lining of gonads
• Endoderm gives rise to


  • Lining of airways and digestive system except the mouth and distal part of digestive system (rectum and anal canal)
  • Glands (digestive glands, endocrine glands, adrenal cortex)
• Embryonic origin of epithelial tissue layers

  1. Ectodermis

  2. Endodermis

  3. Mesodermis
• Ectodermal Derivatives


  • Surface ectoderm: epidermis & its derivatives (hair, nails, sweat glands, sebaceous glands & mammary duct glands
  • Anterior pituitary gland, enamel of teeth, internal ear
  • Corneal epithelium & eye lens
  • Neuroectoderm: neural crest, neural tube
• Mesodermal Derivatives

  • Epith of the kidney & gonads
  • Mesothelium: epith lining the pericardial, pleural & peritoneal cavities
  • Endothelium: epith lining the cardiovascular & lymphatic vessels
  • Adrenal cortex
  • Seminiferous & genital duct epithelium
  • Muscles of the trunk & skeleton
  • Dermis of skin
  • Connective Tissue
  • Spleen
• Endodermal Derivatives

  • Respiratory system epith (trachea, bronchi & lungs)
  • Alimentary system epith (GIT)
  • Liver, GB, pancreas
  • Urinary bladder & urethra
  • Thyroid, parathyroid & thymus gland epith
  • Auditory tube & tonsils
• Classification of epithelial tissue based on number of cell layers
• Classification of epithelial tissue based on shape of cells
• Classification based on Number of cell layers

  • Simple epithelium tissue: One layered
  • Stratified epithelial tissue: More than one layered
• Classification based on Shape of cell

  • Squamous Epithelium: Flattened cells
  • Cuboidal Epithelium: Cubic cells
  • Columnar Epithelium: Column cells
• In stratified epithelium, only the shape of the cells that form the surface layer is used in classifying the epithelium
• In some instances, specialization of the apical cell surface domain can be added in the classification system
• Epithelium classification

  Based on the shape of the cells that form the surface layer
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• Specialization of the apical cell surface domain


  Can be added in the classification system
• Special classification of epithelium

  • Pseudostratified
  • Transitional E. (Urothelium)
  • Endothelium
  • Mesothelium
• Surface modification of epithelial cells

  • Apical domain
  • Lateral domain
  • Basal domain
• Apical/Free Domain


  • Directed towards the external surface or the lumen of an enclosed cavity or tube
• Structures in the Apical Domain

  • Microvilli
  • Stereocilia
  • Cilia
  • Flagella
• Examples of structures in the Apical Domain

  • Microvilli: intestines, kidney tubule
  • Stereocilia: epididymis, hair cells of the ear
  • Cilia: trachea, fallopian tubes
  • Flagella: spermatozoa
• Primary Ciliary Dyskinesia (PCD) is an autosomal recessive hereditary disorder
• PCD in Kartagener’s Syndrome results in dysfunctional cilia, respiratory distress, otitis media, persistent cough, and asthma