Epithelial cells and tissues

Question 1

Define tissues

Answer 1

• A group of cells whose type, organisation and architecture and integral to its function
• Made up of cells, extracellular matrix and fluid

Question 2

What is the extracellular matrix?

Answer 2

• Cell deposited material forming part of the extracellular environment
• Generally composed fibrillar (reticular) proteins ie collagen, elastin) embedded in a hydrated gel (proteoglycans or ground substance)

Question 3

What two ways can extracellular matrix be organised and give examples of each

Answer 3

poorly organised - loose connective tissue

highly organised - tendon, bone, basal lamina

Question 4

What are the five main cell types and give examples of each

Answer 4

1. Connective tissue cells - fibroblasts (many tissues), chondrocytes (cartilage), osteocytes (bone)
2. Contractile tissues - (skeletal muscle, cardiac muscle, smooth muscle)
3. Haematopoietic cells - blood cells, tissue-resident immune cells and cells of bone marrow from which blood cells are derived
4. Neural cells - nervous system cells; neurones (carry electrical signals) and glial cells (support cells)
5. Epithelial cells - form continuous layers, these layers line surfaces and separate tissue compartments and have a variety of other functions

Question 5

What type of cancerous tumours do epithelial cells have?

Answer 5

Carcinomas

Question 6

What type of cancerous tumours do mesenchymal cells have?

Answer 6

Mesenchymal (connective tissue and muscle) cancers are sarcomas

Question 7

What type of cancerous tumours do neural cells have?

Answer 7

neuroblastomas (from neurones) or gliomas (from glial cells)

Question 8

What type of cancerous tumours do haematopoietic cells have?

Answer 8

leukaemia’s (from bone marrow cells) or lymphomas (from lymphocytes)

Question 9

How is the epithelial cells organised and where are they found?

Answer 9

Make stable cell-cell junctions to form continuous cohesive layers

Line external and internal body surfaces

Cell-cell junctions are key to the formation and maintenance of epithelial layers

Question 10

What are the three different shapes of epithelial cells?

Answer 10

Squamous - flattened, plate shapes
Columnar - arranged in columns
Cuboidal - cube-like

Question 10

What are the three different shapes of epithelial cells?

Answer 10

Squamous - flattened, plate shapes
Columnar - arranged in columns
Cuboidal - cube-like

Question 11

In what two ways are epithelial cells layered?

Answer 11

Single layer - simple epithelium

Multi-layer - stratified epithelium

Question 12

Where is simple squamous epithelium found? How is it useful?

Answer 12

Lung alveolar sac 
Epithelium mesothelium (lining major body cavities)
endothelium lining blood vessels and other blood spaces

Thin epithelium that allows for gas exchange

Question 13

Where is simple columnar epithelium found? How is it useful?

Answer 13

Typical of surfaces involved in absorption and secretion of molecules

ie enterocytes lining the gut - involved in the take up of digested products

Question 14

Where is simple cuboidal epithelium found?

Answer 14

Typical of the linings found in ducts

ie those lining the kidney ducts

Question 15

Explain the two different types of stratified squamous epithelium

Answer 15

Keratinising -
epithelial cells that produce keratin causing them to die and become thicker, stronger protective structures (skin epithelium-epidermis)
These cells lose their cellular organelles and nuclei

Non-keratinising -
don’t undergo keratinisation and thus retain their nuclei and organelles (mouth, oesophagus, cervix epithelium)

Question 16

What is pseudo stratified epithelium? Where is it found?

Answer 16

Epithelium appears to be multilayered
However surface cells have contact with basal lamina

Airway (trachea and bronchi) epithelium and various ducts in repro and urinary tracts

Question 17

What is epithelial polarity?

Answer 17

Different regions of cell-surface being different from one another, with discretely organised cellular contents

Allowing secretion to only occur in one direction and absorption to occur either apically or basolaterally

Question 18

Why must the pumps, channels and secretory machinery of transporting epithelium be polarised?

Answer 18

If not polarised they can be present in all parts of the cell membrane meaning they are pumping ions both apically and basolaterally so the directional flow is not occurring
Also important for secretion to ensure the direction of secretion is towards the intended target (ie to prevent digestive enzymes secreted going towards the basal aspect)

Question 19

Name the four different types of junctions between cells

Answer 19

Tight. junction
Adherens junction
Desmosomes
Gap junction

Question 20

What is the role of tight junctions and adherens junctions

Answer 20

Tight junction - seals gaps between cells

Adherens junction - Controls formation of other junctions- master junction

Question 21

What is the role of desmosomes and gap junctions?

Answer 21

Desmosomes - spot junctions that form mechanically tough junctions between cells and restrict mechanical stresses

Gap junction - Form pores between cells that allow cells to exchange and share materials
These communicating junctions allow cells to form communities and to synchronise a number of activities

Question 22

What features of transporting epithelium make it suitable to its function?

Answer 22

Plasma membrane contains high conc of ion transporters

Mitochondria lie close to the basal lamina to provide ATP required for active transport at these membranes

Because active transport is mainly confined to the basal membranes, ion and water transport will have directionality - infoldings increase the SA for pumping of these ions

Question 23

Where are absorptive epithelial cells found?

Answer 23

Brush border membrane - absorptive intestinal cells on the villi surface of small intestine

Question 24

What is the function of absorptive epithelial cells?

Answer 24

They contain large amounts of active transporters and channels for uptake of nutrients from the lumen of the gut

As concentration of nutrients increase in cytoplasm of these cells, it diffuses down concentration gradient into basal interstitial space to be collected in capillaries and distributed into circulation

Question 25

What secretory epithelium cells are dispersed in the small intestine?

Answer 25

Goblet cells - mucous secreting

Question 26

Describe the 2 main types of secretion by secretory epithelium

Answer 26

Exocrine (into duct or lumen)

Endocrine (into bloodstream)

Question 27

How are exocrine secretory cells adapted for their function?

Answer 27

Secretory granules in apical cytoplasm as secretion will occur through the apical plasma membrane

Question 28

How are endocrine secretory cells adapted for their function?

Answer 28

Secretory granules found along the basal aspect of the epithelium - contents can be released straight into the blood

Question 29

What is constitutive secretion?

Answer 29

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

Question 30

What is stimulated secretion?

Answer 30

Secretory vesicles stored in cytoplasm that fuse with plasma membrane and only release contents when stimulated ie pancreatic acinar cells releasing their digestive enzymes when food enters the duodenum

Question 31

Give two examples of epithelial proliferation

Answer 31

1. Cells in intestinal crypts replacing cells lost from the tips of intestinal villi
2. Cells of the basal layer of stratified squamous epithelia dividing replace cells lost from the surface

Question 32

How might chemotherapy treatments be responsible for gastro-intestinal disturbances?

Answer 32

Inhibition of intestinal crypt cells results in loss of the finger like intestinal villi and flattening of the intestinal mucosa.
Cell loss from the villus tips continues as normal, but the failure to produce new cells to replace the lost cells results in a loss of tissue and the villi shorten.

Question 33

How are epithelial cells in the epidermis replaced?

Answer 33

Surface cells are constantly being lost and are replaced by new cells being formed in the basal layer which migrate up while undergoing a programme of differentiation that eventually leads them to flattening out and keratinising
Each layer replaces the one above as layers are lost from the surface

Question 34

What is the epidermis?

Answer 34

Keratinising stratified squamous epithelium of our body surface - is the outermost layer of skin on your body.

Question 35

What happens during hyperproliferation of epithelial cells?

Answer 35

results in increased cell numbers and a thickening of cell layers, this is in response to repeated or constant pressure
If the increase in cell production is greater than cell loss from the surface, cells will accumulate creating an increased thick hard layer ie pressure and abrasion to areas can lead to local proliferation leading to hard skin or corns

Question 36

What induces hyper proliferation of epithelial cells?

Answer 36

nfectious agents such as papilloma virus can also induce hyperproliferation. They do this by hijacking the cellular machinery of stratified squamous epithelia and inducing increased cell proliferation, which results in a surface growth eg a wart