week 6

• What is a tissue?

  Coherent grouping of cells

  
  

  Bound by cell junctions or ECM
• What makes up the ECM?


  Fibres and ground substances
• Fibres in the ECM


  Collagen

  Reticular

  Elastic
• How are epithelium bound together?

  Extraceullar junctions
• Where are epithelial cells?

  On tissues that form the surfaces of the body, externally and internally

  
  

  Gastrointestinal system, lining of circulatory systems, renal system (kidneys), uterus, urinal system
• Endothelial cells


  cells lining the blood vessels
• Endometrium


  inner lining of the uterus

  
  

  It is epithelium
• What are the functions of epithelial cells?

  - Protection (of tissues)

  - Absorption (in gut)

  - Secretion (sweating)

  - Excretion
• The six characteristics of epithelial cell

  1. Very little space between cells

  2. Strong attachments between cells - intercellular junctions

  3. Surface specialisations

  4. Oriented/polarised

  - Free apical surface and adhere to basement membrane

  5. Avascular (but have nerve endings)

  6. Sit on a basal lamina
• Lack of space between epithelial cells


  Unlike other cells, they are very close together

  
  

  Helps lumen form nice tubes
• Strong attachments of epithelial cells


  Intracellular junctions

  
  

  Can be on the cells lateral surface, or on the cells basal surface
• Epithlial cells attachment on the cells lateral surface

  - Tight junctions (zonula occludens) - Zonula adherens

  - Desmosone (macula adherens)

  - Gap junctions

  - Infoldings of membranes
• Attachment of the cells basal surface

  - Hemidesmosome
• Surface specialisations of epithelial cells

  Cytoskeletal components that push through the plasma membrane
• Epithelial cells apical surface

  1. Microvilli

  2. Cilia

  3. Stereocilia
• Major components of the cytoskeleton

  Microtubules (cilia, spindle fibres, organelles)

  
  

  Microfilaments/actin (cytokinesis, under plasma membrane, muscle contraction)

  
  

  Intermediate filaments
• How long are cilia?

  10 microns
• How long are microvili?

  1 micron
• Microvili


  Projections that increase the cell's surface area

  
  

  Very important for the small intestine and the kidney, as it helps with re-absorption

  
  

  Made up of acttin
• Are actin filaments outside the cell?

  No - it looks like they are sitting on the top but they are actually inside and are pushing up

  
  

  Cell surface specialisations are therefore cytoskeleton, as they are INSIDE the cell
• Why are epithelial cells orientated/polarised?

  It means that they can form surfaces and tubes, means that they are highly arranged
• How are epithelial cells orientated?

  There are always a lumen (except for skin, where lumen is the outside)

  
  

  Base

  
  

  Apex
• Why are there epithelial cells avascular?

  They have underlying connective tissue which have blood vessels

  
  

  But it does have nerve endings
• Why do epithelial cells sit on a basal lamina?

  It helps with cell adhesion, orientation and shape

  
  

  Normal epithelial cells never cross the basal lamina
• Another name for basal lamina

  Basement membrane
• Components of the basal lamina


  Secreted by epithelial cells

  
  

  Has collagen, laminin (glycoprotein), proteoglycan
• Where do epithelial cells come from?

  From any of the three germ layers
• Endoderm epithelial cells

  GI tract, respiratory tract
• Mesoderm epithelial cells


  Linings of the inner body cavities (e.g. circulatory system)
• Ectoderm epithelial cells


  Skin (epidermis)
• Why can epithelial cells morph into shapes?

  Because they are joined together, have an apex and a base, can proliferate

  
  

  They can become specialised, form branches and be multilayered
• What controls the fate of the epithelia?

  Interaction with mesenchyme
• Epithelial cells are characterised according to:

  Number of layers (simple, stratified)

  
  

  Shape of the most superficial cell (squamous, cuboidal, columnar)
• Single squamous epithelium


  single layer of flat cells. lines blood vessels, including capillaries, where gas exchange occurs
• Simple cuboidal epithelium


  Single layer of cube shaped cells

  
  

  Found in some ducts or glands
• Simple columnar epithelium


  Made up of a single layer of tall cells that fit closely together

  
  

  Part of digestive tract
• Stratified squamous epithelium


  Multiple layers of flat cells

  
  

  Good for protection

  
  

  In skin, vagina, anus, cheek
• Pseudostratified epithelium


  Looks like it is a multilayered epithelium, but it is not

  
  

  This is because the nuclei are at different layers throughout the peithelium

  
  

  Found in trachea and male epithelial system
• Transiional epithelium


  Found exclusionary in urinary tract

  
  

  It transitions form fat, columnar, cumboidal cells when the bladder or uretha is relaxed

  
  

  Then transitiosn to be flat when the bladder is full - contracted
• Complex stratified epithelium


  Lots of partions in the epithelium

  
  

  Supports the developing germ cells, between sertoli cells

  
  

  Complex, multi layered epithelium