Epithelial Tissue Types and Functions

• Epithelial tissue is one of the four basic tissue types

Lecture Outline

• Simple Epithelium
• Stratified Epithelium
• Glandular Epithelium

Tissue Definition

• A collection of cells performs a similar function

Epithelial Tissues

• Line internal cavities and body surfaces
• Form boundaries
• Protect against the external environment
• Form glands

Epithelial Cell Locations

• Covering and lining epithelium such as Epidermis of skin; lining of the respiratory, reproductive, urinary, & GI tracts
• Glandular epithelium such as Secreting portions of glands, thyroid, adrenal, and sweat glands

Epithelial Tissue Roles

• Forms boundaries and protection
• Secretion
• Absorption
• Excretion
• Filtration

Characteristics of Epithelial Tissue

• Tightly packed sheets of cells
• Can be single or multiple layers
• Avascular

Cell Biology Re-cap

• Epithelium includes
  • Cilia
  • Narrow extracellular space
  • Microvilli
  • Apical region of an epithelial cell
  • Cell junctions in tight, adhesive belt, desmosome and gap junctions
  • Basal region of basal lamina and reticular fibers
  • Basement membrane Connective tissue Nerve ending Capillary

Basement Membrane Re-cap

• Epithelial cells connect to hemidesmosome
• Lamina lucida connected to basal lamina
• Lamina densa connected to reticular lamina

Simple vs Stratified Epithelium

• Simple is in one layer and consists of squamous, cuboidal, or columnar cells.
• Stratified has two or more layers and consists of squamous, cuboidal, or columnar cells.

Simple Epithelium General

• Single layer
• Involved in diffusion, osmosis, filtration, filtration, and secretion

Simple Squamous Epithelium

• Like thin floor tiles
• Consists of a simple squamous cell
• Has a basement membrane and connective tissue

Simple Cuboidal Epithelium

• Shaped like cubes/hexagons
• May have microvilli
• Involved in Secretion and absorption
• Consists of a simple cuboidal cell
• Has a basement membrane and connective tissue

Simple Columnar Epithelium

• Involved in protection, secretion, and absorption
• Apical surface may have microvilli or cilia
• Cell nuclei lie towards the basal surface
• Non-ciliated in GI tract like the stomach and intestinal lining
• Ciliated in portions of the respiratory and genitourinary tract

Stratified Epithelium

• Has 2 or more layers, for protection

Combining Cell Arrangement and Shape

• Stratified squamous epithelium consists of squamous cells apically, but basal layers vary from cuboidal to columnar. Nuclei are centrally located, and for protection.
• Stratified cuboidal epithelium consists of two layers, nuclei centrally located and spherical and involved with absorption and secretion

Other Cell Arrangement

• Stratified columnar epithelium has a single layer of columnar cells on several layers of cuboidal or many-sided cells. Nuclei is basal and oval for protection and secretion
• Transitional epithelium varies depending on stretch with apical cells often large, round, and bi-nucleated. The nuclei are centrally located for distention, which occurs in the bladder, ureter, and urethra

Transitional Epithelium

• Changes from cuboidal to flat as organs stretch, like the bladder
• Connected to an Apical surface through Basement membrane to the Connective tissue

Pseudostratified Epithelium

• Mucus in goblet cell and ciliated columnar cell
• Contains cilia, basement membrane, basal cell, and connective tissue

Simple Squamous Epithelium

• Has a central nucleus
• Found at filtration and diffusion sites
• Lines Aveoli, Bowman's capsules of kidneys

Simple Cuboidal Epithelium

• Has central nucleus for secretion and absorption
• Is dominant in the: thyroid gland, kidney tubules, glandular ducts
• Consists of simple cuboidal epithelium
• Has nucleus of simple cuboidal cell, lumen of duct, and connective tissue.

Simple Cuboidal Epithelium in Kidney Tubules

• Kidney tubules contain simple cuboidal epithelium
• Has nucleus of simple cuboidal cell and lumen of tubule

Simple Non-ciliated Columnar Epithelium

• Microvilli increase SA
• Goblet cells secrete mucus.
• Lines GI tract, glandular ducts and gallbladder
• For secretion and absorption
• Mucus in goblet cell and nucleus of absorptive cell
• nonciliated simple columnar epithelium and lumen of jejunum.

Ciliated Simple Columnar Epithelium

• Cilia at Apical Surface helps ‘waft’ substances
• Goblet cells in some regions such as the respiratory tract
• Upper respiratory tract, fallopian tubes, brain ventricles
• Secretion and aid in movement

Pseudostratified Columnar Epithelium

• Nuclei at different levels for ciliated lines and airways
• Secretion and aid movement
• Mucus in goblet cell, cilia Lumen of trachea.
• Pseudostratified ciliated columnar epithelium

Stratified Squamous Epithelium (Keratinized)

• Apical layer squamous cells
• Deep cell layers variable in shape
• Dead cells sloughed off at Apical surface
• Keratinized - apical layer and several layers deep to it contain keratin (fibrous protein)
• For protection, and is the Superficial layer of the skin

Stratified Squamous Epithelium (Non-keratinized)

• Lines ‘Wet’ Surfaces: mouth, vagina, oesophagus for Protection

Stratified Cuboidal Epithelium

• Rare - oesophageal glands for Protection and limted secretion/absorption
• Stratified cuboidal epithelium with Nucleus of stratified cuboidal cell
• Connective tissue, Lumen of duct

Stratified Columnar Epithelia

• Also rare, Part of urethra, ducts of oesophageal glands for Protection and secretion

Transitional Epithelium

• Permits distension.
• Lines urinary bladder, ureter and urethra

Clinical - COPD

• Clinical significance to COPD

Clinical Smear Tests

• Papanicolaou Smear or Pap smear is Done by Sloughing off cells from wall of cervix to Detect cellular changes or pre-cancerous cells
• Recommended for women over 25

Glandular Epithelia

• Epithelium includes covering, lining and glandular types
  • The lining epithelium can be the Epidermis of skin or can line the reproductive, urinary & GI tracts
  • The Glandular Epithelium is the secreting portion of glands like thyroid, adrenal, and sweat glands

Glandular Epithelia Defined

• Collection of epithelial cells specialized for secretion, either scattered cells or complete organs

Endocrine Glands

• Secrete into interstitial fluid
• Secretions enter interstitial fluid and diffuse into blood
• Hormones regulate many physiological processes, maintaining homeostasis
• Includes the Pituitary, Islets of Langerhans (pancreas) & adrenal glands

Exocrine Glands

• Secrete into ducts
• Glandular secretions includes mucus, earwax, sweat, saliva, digestive enzymes and oil
• Exit Secretions through a DUCT
• The Duct empties onto the surface epithelium or into the lumen of an internal passageway
• Sweat and salivary glands are exocrine

Functional Classification of Secretions

• Merocrine Glands (Salivary, pancreas): secretions released from secretory vesicles by exocytosis
• Apocrine Glands (Mammary gland): accumulate secretion at apical cell surface and cell ‘pinches’ off releasing secretion
• Holocrine Glands (sebaceous gland): Secretory cell matures, then ruptures releasing product

Structural Classification of Exocrine Glands

• Shape of secretory portion can be Tubes or tubular, Blind pockets or Alveolar, or both Tubuloalveolar

Structural Classification of Exocrine Glands Ducts

• They can have a singular duct or an If duct divides, it becomes compound

Explore epithelial tissue, one of the four basic tissue types. Learn about simple, stratified, and glandular epithelium. Discover their roles in forming boundaries, secretion, absorption, excretion, and filtration.