Lecture 6 - epithelial tissue

• tissue

  • a coherent grouping of cells bound together by intercellular junctions or extracellular matrix
• tissue types

  • epithelium
  • connective
  • muscle
  • nervous

  A) connective

  B) epithelial

  C) muscle

  D) nervous

  
• Epithelium

  • these cells are bound together by intercellular junctions
  • location: lining surfaces of the body (skin), lining of all hollow tubes / organs
  • classification: 1) shape 2) simple vs stratified

  A) epithelium

  B) simple

  C) stratified

  D) pseudo

  
• SIMPLE squamous epithelium cells

  • shape: think of an egg -> flat and thin
  • only have ONE layer of cells
  • these wrap around organs and tubes around the body

  
• STRATIFIED squamous epithelium cells

  • shape: also flat (like simple) but in MULTIPLE LAYERS
  • locations: Lines the skin, vagina, oesophagus, mouth

  A) stratified

  
• Cuboidal epithelial cells

  • shape: short cells with roughly similar length and width
  • note: simple cuboidal is more common than stratified cuboidal
  • simple: single layer
  • stratified: multiple layers

  A) kidney

  B) sweat

  C) absorption

  
• columnar epithelial cells

  • shape: long cylindrical cells, which have nucleus at the base of cell
  • 3 types: simple, stratified, pseudostratified

  A) digestive

  B) respirtatory

  C) microvilli

  
• transitional epithelial cells

  • structure: made of several layers of cells with different heights
  • transitional: cell shape flattens when there's urine and shrinks when no urine
  • location: lines the urinary tract

  
• FEATURES of epithelial tissues

  1. little space between the cells
  2. strong attachment of cells by intercellular junctions
  3. Polarised
  4. Avascular
  5. sits on basement membrane
• epithelial features - "little space between cells"

  • cells are closely packed with minimal extracellular space
  • ensures that barriers are tight and impermeable, protecting against pathogens, toxins etc

  
• epithelial features - "strong attachment by intercellular junctions"

  • Tight junctions- prevent leakage across tissues
  • Adhering junctions- like belts, keep the adjacent tissues well cemented together
  • Gap junctions- allows movement of ions and molecules across the tissue

  A) tight

  B) extracellular

  C) gap

  
• epithelial features - "polarised"

  • polarity: cells have APICAL (upper) and BASAL (lower) surfaces
  • apical - absorption, secretion
  • basal - attaches to the basement membrane

  A) apical

  B) basal

  
• epithelial features - "avascular"

  • epithelial tissues have NO blood vessels, but use DIFFUSION from connective tissues for oxygen & nutrients

  A) connective

  B) basement

  
• epithelial features - "sits on basement membrane"

  • it separates epithelial tissue from underlying connective tissue, ensuring cells sit above the membrane
  • function: a filter, regulates movement of molecules between epithelial cells and connective tissues OR extracellular matrix
  • eg. infection near blood vessel, white blood cells travel past basement membrane to the wound

  A) basement membrane

  B) connective

  
• Cytoskeleton - "maintains cell shape" in different ways

  • INSIDE epithelial cells
  • Microfilaments: It maintains or changes cell SHAPE. Has narrow fibres containing actin (a protein) involved in cell movement.
  • Intermediate filaments: It maintains the cell shape. Formed from different proteins. (eg. prevents skin cells from tearing)
  • Microtubules: It maintains cell shape, helps move organelles. Made from Tubulin subunits (α & β). (eg. movement of vesicle secretion, form spindle fibres invovled in movement of chromosomes in mitosis & meiosis)
• cytoskeleton image
• cytoskeleton image

  A) microtubules

  B) microfilaments

  C) actin

  
• Cilia

  • descr: look like HAIR , attached to the surface of epithelial cells and are 10 micrometers in length
  • function: movement of substances (eg. of eggs in the oviduct, mucous in trachea on top of cilia to cough out)
  • composition: 9+2 MICROTUBULE doublet pattern (each cilium)

  A) basement membrane

  B) goblet cells

  C) lumen

  
• microvilli

  • descr: looks like FINGERS, 1 micrometer in length
  • function: increases SA:volume ratio of cell membrane, enhancing absorption and secretion (eg. small intestine absorbing nutrients)
  • composition: made of actin microfilaments bundled together

  A) actin

  B) plasma membrane

  C) microvilli

  
• Surface specialisation

  • the adaptation of the cell surface (apical- upper) to perform specific functions (absorption, secretion, protection)
  • ie. microvilli, cilia, stereocilia
• Proximal convoluted tubules - kidney

  • structure: twisted structure, increasing SA for reabsorption and secretion
  • function: to reabsorb water and solutes from the filtrate back into the bloodstream
  • composition: microvilli

  
• trachea epithelium

  • pseudostratified columnar (simple) with CILIA (9+2 doublet arrangement)
  • globlet cells producing mucous on the cilia ready to be coughed