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Cells & Tissues > Epithelium > Flashcards

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
Q

What is the role of cilia on a specialised epithelium?

A

They are hair-like projections which will move substances

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26
Q

What is the role of secretory epithelium?

A

It produces and releases substances

27
Q

what is the role of microvilli on a specialised epithelium?

A

They form the brush border

This increases the surface area of epithelium for absorption

28
Q

In what ways does epithelium provide protection?

A
  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
Q

Which regions of the body are protected by squamous epithelium?

A

Oesophagus, skin, vagina

30
Q

How is epithelium in the gut specialised for absorption?

A

It is specialised for absorption of glucose, ions and water

It has a brush border formed from microvilli which increases the surface area

31
Q

Which type of epithelium is specialised for surface movement?

A

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
Q

What type of epithelium is specialised for gas exchange?

A

Single layer of squamous cells that lines blood vessels - endothelium

It gives a short diffusion distance for gas exchange

33
Q

How do endothelial cells control vascular cell growth?

A

They secrete factors that stimulate angiogenesis

This occurs during normal wound healing and vascularisation of tumours

34
Q

What will the angiogenic factors released by the endothelium do?

A
  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
Q

How is the endothelium involved in the production of prostacyclin?

A

Prostacyclin is formed by endothelial cells from arachidonic acid

This is catalysed by prostacyclin synthase

36
Q

What is the role of prostacyclin?

A

It prevents platelets from adhering to the endothelium to avoid blood clot formation

It is also a vasodilator

37
Q

In what ways can the endothelium modulate smooth muscle activity?

A

Endothelial cells secrete smooth muscle relaxing factors - nitric oxide

They secrete smooth muscle contraction factors - endothelin 1

38
Q

How can the endothelium trigger blood coagulation?

A

Endothelial cells release tissue factor that binds to FVIIa

This activates FXa and initiates the coagulation pathway

39
Q

How are fibrin clots formed?

A

Thrombin converts fibrinogen into fibrin monomers

These self-aggregate to form a soft fibrin clot, cross-linked by FXIII

40
Q

How does the endothelium regulate the traffic of inflammatory cells?

A

The endothelium facilitates transendothelial migration of cells involved in an inflammatory reaction in the surrounding extravascular connective tissue

41
Q

Which type of epithelium is involved in surface lubrication?

A

Mesothelium

It is a simple epithelium that lines all body cavities

42
Q

How does the mesothelium provide surface lubrication?

A

There are spaces within it that contain a protein-rich fluid

This fluid is used to lubricate surfaces which move against each other

43
Q

What are the two ways in which epithelia can provide secretion?

A

There may be isolated epithelial cells e.g. goblet cells

There may be organised multicellular glandular structures (glands)

44
Q

What is an exocrine gland?

Does it have ducts?

A

An exocrine gland secretes a substance onto the surface (epithelium) of an organ

They DO have ducts

45
Q

What is an endocrine gland?

Does it have ducts?

A

An endocrine gland secretes substances directly into the bloodstream

They DO NOT have ducts

46
Q

When classifying exocrine glands, what is the first characteristic that should be identified?

A

If the excretory duct is unbranched, it is a simple gland

If the excretory duct sub-divides, it is branched/compound

47
Q

After identifying if the exocrine gland is simple or compound, how is it described?

A

It may be tubular with branches or tubular with coils

It may be alveolar/acinar

48
Q

What is the mechanism behind mercocrine secretion?

A
  1. protein product is in an intra-cellular vesicle
  2. vesicle fuses with plasma membrane
  3. protein product released by exocytosis
49
Q

How is the fused plasma membrane recycled in mercocrine secretion?

A

It is recycled by endocytosis

None of the cells membrane is lost during this process

50
Q

What is an example of mercocrine secreretion?

A

Pancreatic enzymes released by the exocrine pancreas

51
Q

What is the mechanism behind apocrine secretion?

A
  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
Q

How does apocrine secretion differ from mercocrine secretion?

A

Some of the cell membrane is lost as the protein product is released in apocrine secretion

53
Q

What is the mechanism behind holocrine secretion?

A
  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
Q

What is an example of holocrine secretion?

A

release of sebum from sebaceous glands

55
Q

What is epidermolysis bullosa?

A

An inherited blistering skin disorder

56
Q

What is the mechanism behind epidermolysis bullosa?

A

A gene mutation of the adhesion molecules that stick the epithelium to the basement membrane

57
Q

How are blisters caused in epidermolysis bullosa?

A

The mutation causes abnormal anchoring of the epidermis to the dermis

This causes blisters

58
Q

What is cystic fibrosis caused by?

A

A mutation in the CFTR gene

59
Q

What is the result of a mutation in the CFTR gene?

A

The chloride channel on the apical surface of epithelial cells is defective

60
Q

Which organs are affected by cystic fibrosis?

A

The lungs and exocrine glands (e.g. pancreas)

61
Q

Why are people with cystic fibrosis more vulnerable to infections?

A

There is less water in the mucous so it becomes thick and harder to move

It cannot be expelled so builds up

62
Q

What is congenital ciliary dyskinesia?

A

An autosomal recessive disease that leads to abnormal cilia function

63
Q

What are the consequences of having congenital ciliary dyskinesia?

A
  1. secretions will accumulate

2. can lead to bronchiectasis, sinusitis and situs inversus

Cells & Tissues (4 decks)

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