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Tissues > 2. Epithelial tissues > Flashcards

2. Epithelial tissues Flashcards

1
Q

Epithelia are classified by

A

Shape

Layering

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2
Q

What shapes can Epithelia take?

A

Squamous (flattened plate-shape)
Cuboidal
Columnar

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3
Q

What are the types of layering in Epithelia?

A

Single layer = simple epithelium

Multi-layered = stratified epithelium

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4
Q

Where is simple squamous epithelium found?

A

Lung alveolar
Mesothelium (lining major body cavities)
Endothelium lining blood vessels and other blood spaces

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5
Q

Where is simple cuboidal epithelium found?

A

Lining kidney collecting duct

Many other ducts

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6
Q

Where is simple columnar epithelium found?

A

Enterocytes (intestinal absorptive)

Many other absorptive and secretory epithelia

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7
Q

Where is keratinising stratified squamous epithelium found?

A

Epidermis (skin)

nuclei not visible in surface layer cells

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8
Q

Where is non-keratinising stratified squamous epithelium found?

A

Linings of mouth, oesophagus, anus, cervix and vagina (nuclei are visible in surface layer cells)

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9
Q

Where is pseudostratified epithelia found?

A

Airway (trachea & bronchi)

Various ducts in the urinary and reproductive tracts

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10
Q

Epithelia functions require …

A

Polarity

Must be directional

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11
Q

Epithelial layer surfaces

A

Apical surface at lumens (open) surface

Basal surface in contact with ECM

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12
Q

Basal & Lateral membrane of Epithelia are usually grouped

A

Basolateral membrane

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13
Q

What can segregate the epithelial plasma membrane into apical & basolateral domains?

A

Belt junctions

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14
Q

2 Types of cell-cell junctions between Epithelial cells

A
  • Zonulae (continuous belts)

* Maculae (discrete spots)

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15
Q

Usually, cell-cell junctions are arranged as an apical junctional complex containing a…

A

Tight Junction nearest the apex and an Adherens junction just below it

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16
Q

Where are desmosomes (spot adhering junctions) often found?

A

Scattered throughout lateral membrane

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17
Q

What do Gap Junctions do?

A

Act as regions of direct communication between adjacent cells

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18
Q

What do cell-cell junctions do?

A

Give epithelia mechanical integrity

Act to seal intercellular pathways of the layer

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19
Q

Tight junctions seal the paracellular pathway

A

Prevents things passing between membrane of adjacent cell

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20
Q

Paracellular

A

Passing/ situated beside/between cells

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21
Q

Transcellular

A

Passing through cells

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22
Q

Tight Junctions allow cells to establish and maintain apical- basolateral polarity by…

A

Preventing the mixing of proteins and lipids between different plasma membrane compartments

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23
Q

Zonula occludens are also known as

A

Tight junctions

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24
Q

What is the consequence of paracellular pathways (between cells) being sealed by tight junctions?

A

Concentration differences across cell layers can be maintained

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25
Q

The more elaborate the network of contacts in a tight junction…

A

The tighter the seal

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26
Q

Which pathways do tight junctions seal?

A 
Paracellular pathways
(Gate function)
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27
Q

What is the fence function of tight junctions?

A

TJ’s segregate apical and basolateral membrane polarity

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28
Q

Describe the membrane in transporting epithelia e.g. distal convoluted tubules

A

Apical membrane contains many ion/ water channels

Basal membrane has many infoldings and mitochondria for active transport

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29
Q

What increases efficiency of absorption? How can this be achieved?

A

Increasing surface area
Make it longer
Fold the lining to form structures e.g. villi
Create tubular protrusions e.g. microvilli

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30
Q

Secretory tissues: The pancreas has both … and … functions

A

Exocrine

Endocrine

31
Q

Exocrine

A

Secretion into lumen or duct

32
Q

Endocrine

A

Secretion into bloodstream

33
Q

Example of exocrine secretors

A

Goblet cells

Pancreateic acinar cells

34
Q

Direction of movement in exocrine secretions

A

Basal to Apical

35
Q

Direction of movement in endocrine secretions

A

Apical to Basal

36
Q

Other than endocrine and exocrine, how else can secretory cells be classified?

A

Constitutive

Stimulated

37
Q

Constitutive secretory cells

A

secretory vesicles, as they are formed, move directly to plasma membrane and release their contents

38
Q

Stimulated secretory cells

A

secretory vesicles stored in cytoplasm and only after signal fuse with plasma membrane to release their contents

39
Q

Example of constitutive endocrine secretion

A

production of plasma proteins by hepatocytes

40
Q

Example of stimulated endocrine secretion

A

release of adrenaline from cells of adrenal medulla after fight-or-flight stimulus

41
Q

Example of stimulated exocrine secretion

A

when stomach contents enter duodenum, pancreatic acinar cells are stimulated to release their digestive enzymes into ducts

42
Q

What type of epithelia do protective epithelia usually constitute of?

A

Stratified squamous

43
Q

Give 2 examples of protective epithelia

A

Skin epidermis

Lining of oesophagus

44
Q

How does protective epithelia perform its function?

A

Can form thick layers that protect underlying tissues from various physical and chemical insults
e.g. heat, cold, solvents (alcohol), abrasion

45
Q

What are the 2 forms of stratified squamous epithelia?

A

Keratinising

Non-keratinising

46
Q

What is keratinising stratified squamous epithelia?

A

Cells of upper (surface) layers are “dry”
because the cells have hardened and died
Their nuclei are not visible

47
Q

What is non-keratinising stratified squamous epithelia?

A

upper (surface) layer is “wet”
because cells are alive
Their nuclei are visible.

48
Q

What are the 3 main layers in skin?

A

Epidermis
Dermis
Hypodermis

49
Q

What type of epithelial cells does the epidermis have?

A

Keratinising stratified squamous epithelial layer

50
Q

What is the main function of the epidermis?

A

Act as a barrier to environment

51
Q

What do defects in cytokeratins or cell junctions lead to?

A

Blistering diseases as a result of damage to fragile epidermal cells

52
Q

What do desmosomes mechanically link?

A

Cells to each other and the ECM (via hemidesmosomes)

53
Q

What happens if desmosome function is compromised?

A

Epithelia become fragile and easily damaged

54
Q

What do cervical smear tests sample? What is looked for?

A

Cells of the non-keratinising stratified squamous epithelium of the uterine cervix
Looking for abnormal nuclei, size and shape

55
Q

Cell turnover in tissues

A

A balance between cell proliferation and cell death is key to maintaining architecture of tissues.

56
Q

How often is the lining of the gut replaced?

A

Every 3-10 days

57
Q

How often is fat tissue, heart muscle and bone replaced?

A

8-10 years

58
Q

How often are most of the neuronal cells of the CNS replaced?

A

Most are not replaced

If they die they are lost

59
Q

Cell turnover in epithelia

A

Consistent

Whole population replaced over relatively short periods

60
Q

What is responsible for the renewal of surface epithelial cells in the intestine?

A

Cell division by stem cells in the intestinal crypts

61
Q

Epithelial-turnover in the small intestine

A

New cells are constantly being produced by the crypt stem cells, to replace the cells constantly being lost from villus tip.

62
Q

How does disturbing the balance of cell proliferation/loss affects tissue dynamics?

A

Reduce cell proliferation

Increase cell proliferation

63
Q

How does Antimetabolite chemotherapy drug, 5-FU effect cell turnover in the intestines?

A

Slows/ stops cell division in crypts
Cell loss from villus tips continues as normal
Failure to produce new cells to replace loss means villi shorten

64
Q

What occurs when there is too much cell proliferation?

A

Rate of cell loss is not sufficient to maintain normal tissue volume

65
Q

What happens if a cell mutates so proliferation is dysregulated in the colon?

A

Too much tissue is formed: a benign tumour

= Adenoma (polyp)

66
Q

Although adenomas are not malignant…

A

They have a high risk of acquiring more mutations that switch to cancer

67
Q

Cell turnover in epidermis

A

Surface cells are constantly being lost
Replaced by new cells being formed in the basal layer which migrate up while undergoing a programme of differentiation that eventually leads to them flattening out and keratinising.

68
Q

Examples of infectious agents that affect the turnover of the epidermis

A

Warts result from infection of epidermal keratinocytes by 1 of the family of HPV
Virus hijacks cell proliferation machinery and increases cell proliferation.

69
Q

If cell loss = cell production

A

Tissue is in steady state

70
Q

If cell loss > cell production

A

Reduction in tissue mass results

71
Q

If cell loss < cell production

A

Increase in tissue mass

72
Q

Changes to steady state of cell turnover can be…

A

Physiological

Pathological

73
Q

Examples of physiological change in cell turnover are seen in…

A

Cyclic production and loss of endometrial epithelial lining of uterus in menstrual cycle.
The large increase, during pregnancy, in number and size of epithelial glands of breast and their loss after weaning

Tissues (11 decks)

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