2. Epithelial tissues

Question 1

Epithelia are classified by

Answer 1

Shape

Layering

Question 2

What shapes can Epithelia take?

Answer 2

Squamous (flattened plate-shape)
Cuboidal
Columnar

Question 3

What are the types of layering in Epithelia?

Answer 3

Single layer = simple epithelium

Multi-layered = stratified epithelium

Question 4

Where is simple squamous epithelium found?

Answer 4

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

Question 5

Where is simple cuboidal epithelium found?

Answer 5

Lining kidney collecting duct

Many other ducts

Question 6

Where is simple columnar epithelium found?

Answer 6

Enterocytes (intestinal absorptive)

Many other absorptive and secretory epithelia

Question 7

Where is keratinising stratified squamous epithelium found?

Answer 7

Epidermis (skin)

nuclei not visible in surface layer cells

Question 8

Where is non-keratinising stratified squamous epithelium found?

Answer 8

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

Question 9

Where is pseudostratified epithelia found?

Answer 9

Airway (trachea & bronchi)

Various ducts in the urinary and reproductive tracts

Question 10

Epithelia functions require …

Answer 10

Polarity

Must be directional

Question 11

Epithelial layer surfaces

Answer 11

Apical surface at lumens (open) surface

Basal surface in contact with ECM

Question 12

Basal & Lateral membrane of Epithelia are usually grouped

Answer 12

Basolateral membrane

Question 13

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

Answer 13

Belt junctions

Question 14

2 Types of cell-cell junctions between Epithelial cells

Answer 14

• Zonulae (continuous belts)

* Maculae (discrete spots)

Question 15

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

Answer 15

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

Question 16

Where are desmosomes (spot adhering junctions) often found?

Answer 16

Scattered throughout lateral membrane

Question 17

What do Gap Junctions do?

Answer 17

Act as regions of direct communication between adjacent cells

Question 18

What do cell-cell junctions do?

Answer 18

Give epithelia mechanical integrity

Act to seal intercellular pathways of the layer

Question 19

Tight junctions seal the paracellular pathway

Answer 19

Prevents things passing between membrane of adjacent cell

Question 20

Paracellular

Answer 20

Passing/ situated beside/between cells

Question 21

Transcellular

Answer 21

Passing through cells

Question 22

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

Answer 22

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

Question 23

Zonula occludens are also known as

Answer 23

Tight junctions

Question 24

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

Answer 24

Concentration differences across cell layers can be maintained

Question 25

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

Answer 25

The tighter the seal

Question 26

Which pathways do tight junctions seal?

Answer 26

``` Paracellular pathways (Gate function) ```

Question 27

What is the fence function of tight junctions?

Answer 27

TJ's segregate apical and basolateral membrane polarity

Question 28

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

Answer 28

Apical membrane contains many ion/ water channels | Basal membrane has many infoldings and mitochondria for active transport

Question 29

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

Answer 29

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

Question 30

Secretory tissues: The pancreas has both ... and ... functions

Answer 30

Exocrine | Endocrine

Question 31

Exocrine

Answer 31

Secretion into lumen or duct

Question 32

Endocrine

Answer 32

Secretion into bloodstream

Question 33

Example of exocrine secretors

Answer 33

Goblet cells | Pancreateic acinar cells

Question 34

Direction of movement in exocrine secretions

Answer 34

Basal to Apical

Question 35

Direction of movement in endocrine secretions

Answer 35

Apical to Basal

Question 36

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

Answer 36

Constitutive | Stimulated

Question 37

Constitutive secretory cells

Answer 37

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

Question 38

Stimulated secretory cells

Answer 38

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

Question 39

Example of constitutive endocrine secretion

Answer 39

production of plasma proteins by hepatocytes

Question 40

Example of stimulated endocrine secretion

Answer 40

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

Question 41

Example of stimulated exocrine secretion

Answer 41

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

Question 42

What type of epithelia do protective epithelia usually constitute of?

Answer 42

Stratified squamous

Question 43

Give 2 examples of protective epithelia

Answer 43

Skin epidermis | Lining of oesophagus

Question 44

How does protective epithelia perform its function?

Answer 44

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

Question 45

What are the 2 forms of stratified squamous epithelia?

Answer 45

Keratinising | Non-keratinising

Question 46

What is keratinising stratified squamous epithelia?

Answer 46

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

Question 47

What is non-keratinising stratified squamous epithelia?

Answer 47

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

Question 48

What are the 3 main layers in skin?

Answer 48

Epidermis Dermis Hypodermis

Question 49

What type of epithelial cells does the epidermis have?

Answer 49

Keratinising stratified squamous epithelial layer

Question 50

What is the main function of the epidermis?

Answer 50

Act as a barrier to environment

Question 51

What do defects in cytokeratins or cell junctions lead to?

Answer 51

Blistering diseases as a result of damage to fragile epidermal cells

Question 52

What do desmosomes mechanically link?

Answer 52

Cells to each other and the ECM (via hemidesmosomes)

Question 53

What happens if desmosome function is compromised?

Answer 53

Epithelia become fragile and easily damaged

Question 54

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

Answer 54

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

Question 55

Cell turnover in tissues

Answer 55

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

Question 56

How often is the lining of the gut replaced?

Answer 56

Every 3-10 days

Question 57

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

Answer 57

8-10 years

Question 58

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

Answer 58

Most are not replaced | If they die they are lost

Question 59

Cell turnover in epithelia

Answer 59

Consistent | Whole population replaced over relatively short periods

Question 60

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

Answer 60

Cell division by stem cells in the intestinal crypts

Question 61

Epithelial-turnover in the small intestine

Answer 61

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

Question 62

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

Answer 62

Reduce cell proliferation | Increase cell proliferation

Question 63

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

Answer 63

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

Question 64

What occurs when there is too much cell proliferation?

Answer 64

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

Question 65

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

Answer 65

Too much tissue is formed: a benign tumour | = Adenoma (polyp)

Question 66

Although adenomas are not malignant...

Answer 66

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

Question 67

Cell turnover in epidermis

Answer 67

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.

Question 68

Examples of infectious agents that affect the turnover of the epidermis

Answer 68

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

Question 69

If cell loss = cell production

Answer 69

Tissue is in steady state

Question 70

If cell loss > cell production

Answer 70

Reduction in tissue mass results

Question 71

If cell loss < cell production

Answer 71

Increase in tissue mass

Question 72

Changes to steady state of cell turnover can be...

Answer 72

Physiological | Pathological

Question 73

Examples of physiological change in cell turnover are seen in...

Answer 73

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