Lecture 9 Flashcards
What are tissues?
- specialised cells embedded in an extracellular matrix
- a functional arrangemt of cells
What do tissues form?
Organs
Which forms organs systems which form you
4 key types of tissues
- epithelial tissue (lining/ secretion)
- connective (support) tissue
- muscle tissue (skeletal,smooth,cardiac)
- nervous tissue
Cells have an internal cytoskeleton network of filaments for…
Shape, support and movement
Why do cells secrete extracellular matrix?
For support and structure and regulation of cell communication and behaviour
Cytoskeleton vs ECM staining
Two key functions of the ECM with examples
To maintain differentiated state of cells:
E.g mouse mammary gland epithelium cultured without ECM are flat and don’t produce milk
To maintain normal overall development:
E.g inactivation genes for ECM proteins results in defective skeletal development
Where is epithelial tissue found?
- lines organs and cavities within the body
- covers the external body (epidermis) (including from mouth to anus)
What is the function of epithelial tissue?
- protective barrier
- absorptive and secretory adaptions
Features of epithelial tissue
- has polarity (apical and basal surfaces)
- has basement membrane as a scaffold and anchor to underlying connective (support) tissue
- Avascular (nutrients via diffusion)
- Regenerative (stem cells allow regeneration)
How do u classify epithelium
Based on morphological criteria
- cell shape (squamous, cuboidal, columnar)
- number of cell layers (simple, stratified, pseudo stratified, transitional)
Based on surface specialisations
- micro vili
- cilia
Based on whether surface (covering) or glandular (secretory)
- glandular epithelium can be single cells or grouped into glans to allow focused production of a secreted product
How are epithelial cells connected?
Cellular junctions
3 classifications of cellular junctions that connect epithelial cells
- occluding
- anchoring
- communicating
1 example of an occluding cellular junctions in epithelial cells
- tight junctions (zonula occludens)
3 examples of anchoring cellular junctions
- zonula adherens
- desmosomes
- hemidesmomes
1 example of communicating cellular junctions
- gao junctions
Epithelial cellular junctions
- tight junctions (zonula occludens)
- zonula adherens
- desmosomes
- hemidesmosomes
- gap junctions
What are tight junctions
Tightly bound junctions at apical region
(Protects paracellular pathway)
What do zonula adherens do?
Strengthens attachments to neighbouring cells at apical region
What do gap junctions allow?
Communication between neighbouring cells
What do desmosomes do?
Firmly anchor neighbouring cells together
What do hemidesmosomes do?
Anchors cell to basement membrane
Junctional complex
- ## tight, zonula adherens and desmosomes all in close proximity
(On electron micro-graph, the darker a region is the denser and stronger it is hence the appearance of the desmosome)
When do tight junctions control?
The paracellular pathway
Another name for tight junctions
Zonula occludens
What so tight junctions contain?
- transmembrane proteins
- occludin
- Claudins
(Different proteins in different cells to control what gets through and what doesn’t - changes in different areas of tissue)
Different Claudine = different _______ in different _______
Permeabilities
Tissues
Why are claudins so important - KIDNEYS
In kidney, only specific regions are permeable to Mg2+ ions due to Claudin-16
Mutation to Claudine-16 gene = abnormal claudin-16 resulting in a junction impermeable to ion
This results in low Mg2+ reabsorbiton back into the blood
- magnesium deficiency
- kidney damage/renal failure
What is claudin-1 responsible for?
- waterproof qualities of skin
- mice lacking gene for claudin-1 died at birth due to dehydration
What do zonula adherens do?
- links cytoskeltons to adjacent cells
What do zonula adherens contain?
- actin microfilaments (connects to)
- main transmembrane proteins
- E-Cadherins
What is E-Cadherins linked to?
Matastasis of cancer cells
Malignant cells have lower levels of ________ expression
E-cadherin
Why are Cadherins so important?
Loss of E-cadherins is linked to metastasis of cancer cells
What do desmosomes do? And what do they connect to?
- link cytoskeletoms of adjacent cells
- connect to cytokeratin (intamediate filaments) (stronger then actin)
What do desmosomes contain ?
TRANSMEMBRANE PROTEIMNS Cadherins such as desmoglein
What is pemphigus vulgaris?
- autoimmune disease
- antibodies attack desmoglein 3 which keeps cells bound together (part of a desmosome)
- cells fall apart, skin sloughs off
- Cadherins are imperative for maintaining structural integrity of epithelium
Cadherins are important for mainigning _____ integrity of ______
Structural
Epithelium
What are hemidesmosomes and where are they found?
- modified (half) desmosomes
- found on basal surface of cell
What is the purpose of hemidesmosomes?
- to anchor to basement membrane
(Stop cells peeling off form underlying tissue)
What do hemidesmosomes bind to?
Cytokeratin
What do hemidesmosomes contain? Main transmembrane protein
Integrins
What are gap junctions
Communicating junctions
What do gap junctions contain ? main transmembrane proteins?
- conexins
- form channels called connexons that can open/close
- allow passage of ions and small molecules
What do connexins do?
- form channels called connexons that can open/close
- allow passage of ions and small molecules
Epithelial tissue is _____
Polarised
Epithelial cells have an ____ and ____ surface
Apical
Basal
What are microvili ?
Fingerlike projections of plasma membrane
How long are microvili?
Very short - 0.5 - 1 um
What is the purpose of microvili?
- provides increases surface area e.g for absorption (intestine, kidney)
What is the core of microvili made of?
Parallel actin bundles
What part of microvili can you see under light microscopy?
Brush boarder
What part of microvili can you see through electron microscopy ?
Individual microvili with shape maintained by actin filaments
Two different forms of cilia and what they are for
Non-motile: sensory information
Motile: beat in rhythm to move substances across
- e.g. respiratory tract
- sperm flagellum = modified cilium
How long are cilia
Up to 10um long (half a cell length)
What gives cilia its strength
- has a cytoskeleton composed of a core of microtubules
Apical characteristics of epithelial cells
- cilia
- microvili
What does the basement membrane do?
- binds epithelial cells to connective tissue
- forms barrier but allows nutrients to pass to epithelia, regulated permeability.
- controls growth and differentiation
What is the basement membrane
Sheet-like arrangement of ECM proteins
What is the basement membrane formed by?
- both epithelia and connective tissue
What can you see of the basement membrane under light microscope
- not easily distinguished with H&E staining
- immunocytochemisty can be used to stain specific components (e.g collagen IV labelled with immunogold)
What can you see of the basement membrane under electron microscopy ?
- 3 layers are visible
- lamina lucida
- lamina densa (aka basal lamina)
- lamina fibroreticularis
What are the purpose of basal folding?
Increases surface area on basal surface of cell
What structures allow epithlium to act as a protective barrier?
- junctional complexes - holds epithelium as a sheet
- basement membrane - anchoring sheet and control in permeability through to the underlying tissues
What structures allow epithelial cells to absorb substances from apical surfaces and pass on to underlying tissues?
- microvili
- basal folding
- basement membrane
Practivce questoiuns
