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Epithelium Flashcards

1
Q

What is epithelium?

A

Epithelium is the layer or layers of cells that cover body surfaces or line body cavities

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2
Q

What germ cell layers make up epithelium?

A

All 3 layers -

endoderm, mesoderm and ectoderm

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3
Q

Which body surfaces are lined by epithelium?

A

All body surfaces are lined by epithelium except:

  1. articular cartilage
  2. tooth enamel
  3. the anterior iris
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4
Q

What does the epithelium sit upon?

A

A layer of connective tissue called the basal lamina

The basal lamina is part of the basement membrane

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5
Q

How are epithelial cells stuck together?

What are the different surfaces of the epithelial cell?

A

Through intra-cellular junctions/complexes

It has polarity as it has apical and basal surfaces

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6
Q

How does epithelium get nutrients and why?

A

It relies on diffusion for nutrients as it is avascular

It doesn’t have a blood supply

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7
Q

What are the 7 main functions of epithelium?

A
  1. absorption
  2. surface movement
  3. secretion of substances
  4. gas exchange
  5. surface lubrication
  6. sensation
  7. protection
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8
Q

What is the role of adhesion complexes?

A

They glue cells together and to the basement membrane

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9
Q

What are tight junctions?

A

These are occludin/claudin seals to protein movement

They seal epithelial cells in a narrow band just below their apical surface

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10
Q

What is the function of tight junctions?

A
  1. limit passage of molecules and ions through the space between cells
  2. maintain the polarity of cells and osmotic balance
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11
Q

Where are Adherens junctions located?

A

Below the tight junctions

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12
Q

What are adherens junctions?

A

transmembrane proteins that connect across cell cytoskeletons

Their cytoplasmic face is linked to the actin cytoskeleton

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13
Q

What is the function of gap junctions?

A

Small channels which allow for intercellular exchange of ions and small molecules

They are involved in cell signalling

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14
Q

What are desmosomes?

Where are they located?

A

They are intercellular junctions that provide strong adhesion between cells

They are below the Adherens junction and above the gap junction

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15
Q

What is the function of desmosomes?

A

They give mechanical strength to tissues as they are intracellularly linked to the intermediate filament cytoskeleton

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16
Q

What is the function of hemidesmosomes?

A

They provide attachment to the basal lamina

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17
Q

What are the three stages involved in classifying epithelia?

A
  1. look at the number of layers of cells

is there a single layer or multiple layers?

  1. look at the shape of the cells

are they flat, cubed or columnar?

  1. do the cells have any specialisations or adaptations?
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18
Q

What is simple epithelium?

A

Epithelium made of one layer of cells

It can be squamous (flat), cuboidal or columnar

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19
Q

What is pseudo-stratified epithelium?

A

It is a simple epithelium made of columnar cells

The cells are different heights so it looks like multiple layers

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20
Q

Where is pseudo-stratified epithelium found?

A

In the upper airways - cilia/goblet cells

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21
Q

What is stratified epithelium?

A

It consists of multiple layers

it can be squamous, columnar or cuboidal

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22
Q

What is transitional epithelium?

A

It is a type of stratified epithelium

It has multiple layers but changes shape from columnar to flat

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23
Q

Where is transitional epithelium found?

A

In the bladder and urinary tract

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24
Q

What are the 4 main specialisations seen in epithelia?

A
  1. ciliated
  2. secretory
  3. with microvilli
  4. keratinising
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25
What is the role of cilia on a specialised epithelium?
They are hair-like projections which will move substances
26
What is the role of secretory epithelium?
It produces and releases substances
27
what is the role of microvilli on a specialised epithelium?
They form the brush border This increases the surface area of epithelium for absorption
28
In what ways does epithelium provide protection?
1. it prevents dehydration of cells 2. it prevents chemical and mechanical damage to cells 3. it is multi-layered for strength 4. it forms tight seals between cells 5. it is replicative so can replace damaged cells
29
Which regions of the body are protected by squamous epithelium?
Oesophagus, skin, vagina
30
How is epithelium in the gut specialised for absorption?
It is specialised for absorption of glucose, ions and water It has a brush border formed from microvilli which increases the surface area
31
Which type of epithelium is specialised for surface movement?
Cilia move in a co-ordinated way to provide unidirectional movement They move mucus in the airways, sperm in the testes and ova in the fallopian tube
32
What type of epithelium is specialised for gas exchange?
Single layer of squamous cells that lines blood vessels - endothelium It gives a short diffusion distance for gas exchange
33
How do endothelial cells control vascular cell growth?
They secrete factors that stimulate angiogenesis This occurs during normal wound healing and vascularisation of tumours
34
What will the angiogenic factors released by the endothelium do?
1. some induce endothelial cell proliferation and migration 2. some activate endothelial cell differentiation 3. some induce a secondary cell type to produce angiogenic factors
35
How is the endothelium involved in the production of prostacyclin?
Prostacyclin is formed by endothelial cells from arachidonic acid This is catalysed by prostacyclin synthase
36
What is the role of prostacyclin?
It prevents platelets from adhering to the endothelium to avoid blood clot formation It is also a vasodilator
37
In what ways can the endothelium modulate smooth muscle activity?
Endothelial cells secrete smooth muscle relaxing factors - nitric oxide They secrete smooth muscle contraction factors - endothelin 1
38
How can the endothelium trigger blood coagulation?
Endothelial cells release tissue factor that binds to FVIIa This activates FXa and initiates the coagulation pathway
39
How are fibrin clots formed?
Thrombin converts fibrinogen into fibrin monomers These self-aggregate to form a soft fibrin clot, cross-linked by FXIII
40
How does the endothelium regulate the traffic of inflammatory cells?
The endothelium facilitates transendothelial migration of cells involved in an inflammatory reaction in the surrounding extravascular connective tissue
41
Which type of epithelium is involved in surface lubrication?
Mesothelium It is a simple epithelium that lines all body cavities
42
How does the mesothelium provide surface lubrication?
There are spaces within it that contain a protein-rich fluid This fluid is used to lubricate surfaces which move against each other
43
What are the two ways in which epithelia can provide secretion?
There may be isolated epithelial cells e.g. goblet cells There may be organised multicellular glandular structures (glands)
44
What is an exocrine gland? Does it have ducts?
An exocrine gland secretes a substance onto the surface (epithelium) of an organ They DO have ducts
45
What is an endocrine gland? Does it have ducts?
An endocrine gland secretes substances directly into the bloodstream They DO NOT have ducts
46
When classifying exocrine glands, what is the first characteristic that should be identified?
If the excretory duct is unbranched, it is a simple gland If the excretory duct sub-divides, it is branched/compound
47
After identifying if the exocrine gland is simple or compound, how is it described?
It may be tubular with branches or tubular with coils It may be alveolar/acinar
48
What is the mechanism behind mercocrine secretion?
1. protein product is in an intra-cellular vesicle 2. vesicle fuses with plasma membrane 3. protein product released by exocytosis
49
How is the fused plasma membrane recycled in mercocrine secretion?
It is recycled by endocytosis None of the cells membrane is lost during this process
50
What is an example of mercocrine secreretion?
Pancreatic enzymes released by the exocrine pancreas
51
What is the mechanism behind apocrine secretion?
1. protein product is in a vesicle that approaches the apical membrane 2. the apical membrane pinches off with loss of some of the apical membrane
52
How does apocrine secretion differ from mercocrine secretion?
Some of the cell membrane is lost as the protein product is released in apocrine secretion
53
What is the mechanism behind holocrine secretion?
1. secretory product accumulates in cytoplasm 2. cell disintegrates to release the product 3. this is cell suicide as the product is released into the surrounding environment
54
What is an example of holocrine secretion?
release of sebum from sebaceous glands
55
What is epidermolysis bullosa?
An inherited blistering skin disorder
56
What is the mechanism behind epidermolysis bullosa?
A gene mutation of the adhesion molecules that stick the epithelium to the basement membrane
57
How are blisters caused in epidermolysis bullosa?
The mutation causes abnormal anchoring of the epidermis to the dermis This causes blisters
58
What is cystic fibrosis caused by?
A mutation in the CFTR gene
59
What is the result of a mutation in the CFTR gene?
The chloride channel on the apical surface of epithelial cells is defective
60
Which organs are affected by cystic fibrosis?
The lungs and exocrine glands (e.g. pancreas)
61
Why are people with cystic fibrosis more vulnerable to infections?
There is less water in the mucous so it becomes thick and harder to move It cannot be expelled so builds up
62
What is congenital ciliary dyskinesia?
An autosomal recessive disease that leads to abnormal cilia function
63
What are the consequences of having congenital ciliary dyskinesia?
1. secretions will accumulate | 2. can lead to bronchiectasis, sinusitis and situs inversus

Cells & Tissues (4 decks)

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