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anatomy 241 > Lecture 8 - Cells in Tissues 1, Epithelial tissue and cell membrane specialisations > Flashcards

Lecture 8 - Cells in Tissues 1, Epithelial tissue and cell membrane specialisations Flashcards

1
Q

What are tissues?

A

Speicialised, similar cells embedded in an extracellular matrix
Functional arrangement of cells
Form organs, which form organ systems, which form a functional organism
4 key types = epithelial tissue, connective (support) tissue, muscle tissue, nervous tissue

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2
Q

4 key types of tissues

A

epithelial tissue, connective (support) tissue, muscle tissue, nervous tissue

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3
Q

Cells

A

Cells are the building blocks of the body. Cells are embedded within an ECM, adhesion molecules hold cells together and to surfaces (adhesion molecules are contained within the ECM). Cells have an internal cytoskeletal network of filaments for shape, support and movement. Cells secrete proteins and other molecules that make up an ECM which provides support and structure so it can hold cells in place and regulation of cell communication and behaviour

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4
Q

ECM is crucial to maintain…

A

To maintain differentiated state of cells e.g. mouse mammary gland epithelium cultured without ECM are flat and do not produce milk

To maintain normal overall development e.g. inactivating genes for ECM proteins results in defective skeletal development

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5
Q

Epithelial tissue - features

A

Lines organs and cavities within the body

Covers the external body (epidermis)

Protective barrier - both inside and outside of the body

Absorptive and secretory adaptations - individuals epithelial cells within a covering epithelium are very important in excretory products and epithelial cells also come together to form glands which is its secretory adaption

Classified based on layers, shapes, surface specialisations and function

Has polarity (apical and basal surfaces)

Has a basement membrane as a scaffold and anchor to underlying connective (support) tissue

Avascular (nutrients via diffusion) - no blood vessels directly connecting to them and instead they get nutrients through diffusion

Regenerative (stem cells allow regeneration) - highly regenerative so they have high levels of cell turnover compared to other cell and tissue types and stems cells are largely responsible for this regenerative capacity

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6
Q

Classification of epithelium based on morphological criteria

A

Cell shape (squamous, cuboidal, columnar)

Number of cell layers (simple, stratified, pseudo stratified, transitional)

Pseudostratified - effectively are simple because they have one layer however the nuclei are not in an even line, they are actually disordered across the layer which makes them appear stratified

Stratified = multiple layers of cells lying on top of each other like the epidermis

Transitional epithelium is a type of stratified epithelium, not clear how many layers, can contract and expand in order to adapt to the degree of distension needed

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7
Q

Cell shapes

A

Squamous
Cuboidal
Columnar

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8
Q

Number of cell layers

A

Simple
Stratified
Pseudostratified
Transitional

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9
Q

Pseudostratified

A

effectively are simple because they have one layer however the nuclei are not in an even line, they are actually disordered across the layer which makes them appear stratified

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10
Q

Stratified

A

multiple layers of cells lying on top of each other like the epidermis

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11
Q

Transitional epithelium

A

Transitional epithelium is a type of stratified epithelium, not clear how many layers, can contract and expand in order to adapt to the degree of distension needed

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12
Q

Classification of epithelium based on surface specialisation

A

Microvilli

Cilia

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13
Q

Classification of epithelium based on whether surface (covering) or glandular (secretory)

A

Glandular epithelium can be single cells (goblet cells for example) or grouped into glands to allow focused production of a secreted product

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14
Q

Epithelial cells are connected via

A

cellular junctions

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15
Q

Occluding junctions

A

Tight junctions (zonula occludens)

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16
Q

Anchoring junctions

A

Zonula adherens
Desmosomes
Hemidesmosomes

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17
Q

Communicating junctions

A

Gap junctions

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18
Q

Tight junctions (zonula occludens)

A

Tight junctions (zonula occludens) - find these apically between two cells

general function is to prevent leakage of transported solutes and water and seals the paracellular pathway.

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19
Q

Zonula adherens

A

Zonula adherens - anchors cell via the actin cytoskeleton

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20
Q

Desmosomes

A

Desmosomes - anchor epithelial cells to one another

21
Q

Hemidesmosomes

A

Hemidesmosomes - anchor epithelial cells to the basement membrane

22
Q

Gap junctions

A

Gap junctions - allows cells to communicate with one another

23
Q

Order of junctions (from basement membrane)

A 
Hemidesmosomes
Desmosomes 
Gap junctions 
Zonula adherens 
TIght junctions
24
Q

Junctional complex

A

Junctional complex = symmetrical structures formed between adjacent cells and consists of three components- tight junction, zonula adherens, desmosomes

25
Q

Tight junctions location and function

A

They are at the top/apical surface so they are really controlling the ability of solute molecules to move between our two epithelial cells, selective depending on the tissue type and do allow certain ions and small molecules to move between two epithelial cells on the paracellular pathway therefore selectively permeable

Controls paracellular pathway

26
Q

Tight junctions transmembrane proteins

A

Occludins

Claudins
Very important component of junction
Discovered in 1998
Different Claudins in different tissues allows different molecules to pass between the two epithelial cells

27
Q

Why are claudins important? (tight junctions)

A

Different Claudins= different permeabilities in different tissues

In kidney, only specific regions are permeable to Mg2+ ions due to claudin-16

Mutation in claudin-16 gene = abnormal claudin-16 resulting in junction impermeable to ion

Low Mg2+ reabsorption back into the blood
Magnesium deficiency
Kidney damage/renal failure

200 discovery that claudin-1 responsible for waterproof qualities of skin
Mice lacking gene for claudin-1 died at birth due to dehydration

28
Q

Zonula adherens location and function

A

(below the tight junction)
Links cytoskeletons of adjacent cells
Actin microfilaments

29
Q

Zonula adherens transmembrane proteins

A

E-cadherins
Each epithelial cell individually produces these e-cadherin proteins and they bind to one another and they pass through the plasma membrane of the cell and it binds to the actin filament via another protein called beta-catenin
Band of actin proteins that run around the region of our cells and there are transmembrane proteins that link two cells together via these actin microfilaments

30
Q

Why are cadherins important? (zonula adherens)

A

Loss of E-cadherins linked to metastasis of cancer cells
Malignant cells have lower levels of e-cadherin expression
Māori family from the bay of plenty lost 25 members to stomach cancer over a 30 year period
1998 - DNA analysis revealed mutation in gene encoding e-cadherins
Now able to be screened and receive preventative surgery

31
Q

Desmosomes (macula adherens) location and function

A

Links cytoskeletons to adjacent cells

Connect to cytokeratin (intermediate filaments) - anchoring to intermediate filaments, you can see on the image that the intermediate filaments are coming together at this electron dense plaque which allows the transmembrane protein to meet with the cytoskeleton and we then have a different set of transmembrane proteins that join together to anchor our two different cells together at a desmosome and these are also cadherins but are different to the ones in the previous junction described

32
Q

Desmosomes transmembrane protein

A

Cadherins such as desmoglein - important in the functional capacity of the epithelia as seen through disease that attack desmoglein

33
Q

Pemphigus vulgaris

A

Autoimmune disease
Antibodies attack desmoglein 3 which keeps cells bound together
Cells fall apart, skin sloughs off
Cadherins are important for maintaining structural integrity of epithelium

34
Q

Hemidesmosomes location and function

A

Anchoring epithelial cell to the basement membrane, one electron dense plaque upon which the intermediate filaments can attach
Modified desmosomes
Basal surface of cell
Bind to cytokeratin which is the same as desmosomes

35
Q

Hemidesmosomes transmembrane proteins

A

Main transmembrane protein - integrins

36
Q

Gap junctions location and function

A

Communicating junctions rather than anchoring

37
Q

Gap junctions main transmembrane proteins

A

Connexins
Form channels called connexions that open/cclose
Allow passage of ions and small molecules

38
Q

Epithelial tissue is polarised …

A

Have an apical and basal surface
Linked as sheets through lateral junctions
Linked to basement membrane via junctions
Different specialisations linked to polarity of cell - provides hints as to function (different specialisations at the apical region compared to the basal region due to polarisation

39
Q

Apical characteristics

A

Microvilli and cilia

40
Q

Microvilli

A

Fingerlike projections of plasma membrane
Very short ~0.5-1 µm in length
Provides increased surface area e.g. for absorption (intestine, kidney)
Core of parallel actin bundles
Light microscopy = brush border
Electron microscopy = individual microvilli with shape maintained by actin filaments

41
Q

Cilia

A

Non-motile - sensory information, do not have intrinsic movement within them so they are not actually moving, provide sensation of the extracellular environment and conveys it into the cell
Motile - beat in rhythm to move substances across surface of epithelium
e.g. respiratory tract (mucus and debris moved)
Sperm flagellum = modified cilium
Up to 10µm long (half cell length)
Has cytoskeleton composed of a cord of microtubules (allows a greater range of movement in the cilia)

42
Q

Basal characteristics

A

Basement membrane

Basal foldings

43
Q

Basement membrane

A

Binds epithelial cells to connective tissue
Basement membrane is extracellular so it is formed and maintained as a consequence of products excreted by both epithelial cells and connective tissue cells and they come together to form a sheet like arrangement of ECM proteins (formed and maintained by both epithelia and connective tissue)
Sheet-like arrangement of ECM proteins
Forms barrier but allows nutrients to pass to epithelia. Regulates permeability
Barrier is important to stop any downward growth of epithelial cells (have a high growth and regenerative capacity) and need this basement membrane to stop the epithelial cells from going into the tissue which ultimately protects from things like cancer
Needs to allow nutrients as epithelia is avascular so effectively it is very important in regulating permeability
Controls growth and differentiation

Under light microscope
Not easily distinguished with H&E staining
Immunocytochemistry can be used to stain specific components (e.g. collagen IV labelled with immunogold)

Under EM three layers are visible 
Lamina lucida = connected to the epithelial cell, first layer, Lucida because it is lucid in appearance i.e. it comes out light on EM 
Lamina densa (aka basal lamina) = electron dense region 
Lamina fibroreticularis = another lucid/electron light region, region that actually connects to the fibres of the connective tissues
44
Q

Basal foldings

A

Increases surface area on basal surface of cell

Can give it striped appearance

45
Q

Functional significance

A

Acts as protective barrier
Junctional complexes - hold epithelium as a sheet
For our epithelial cells to work together as a barrier they need to be acting in unison and tightly opposed to one another so our junctional complexes allows out epithelium to work together as a sheet
Basement membrane
Allows epithelium to stay in one place and be anchored there and not pushed down into the underlying tissue

Absorb substance from apical surface and pass on to underlying tissues
Microvilli - increasing surface area for exchange, allowing the absorption of more substances
Basal foldings
Basement membrane

46
Q

Lamina lucida

A

Lamina lucida = connected to the epithelial cell, first layer, Lucida because it is lucid in appearance i.e. it comes out light on EM

47
Q

Lamina densa (aka basal lamina)

A

Lamina densa (aka basal lamina) = electron dense region

48
Q

Lamina fibroreticularis

A

Lamina fibroreticularis = another lucid/electron light region, region that actually connects to the fibres of the connective tissues

anatomy 241 (29 decks)

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