Tissues 2: Epithelial tissues

Question 1

How are epthelial tissue classified?

Answer 1

They are classified by their shape and their layering

Question 2

What are the different shapes for epthelial cells?

Answer 2

squamous (flattened plate-shape) cuboidal columnar

Question 3

What are different types of layering for epithelial tissue?

Answer 3

single layer = simple epithelium multi-layered = stratified epithelium

Question 4

What does simple epithelium mean?

Answer 4

single layer = simple epithelium

Question 5

What does stratified mean?

Answer 5

multi-layered

Question 6

What does simple squamous mean?

Answer 6

Simple = single cell layer; squamous= flattened shape add pic

Question 7

Where are Simple Squamous tissue found?

Answer 7

lung alveolar (air sac) epithelium, mesothelium (lining major body cavities), endothelium lining blood vessels and other blood spaces);

Question 8

What is the role of simple squamous tissue?

Answer 8

form a thin epithelium that allows exchange to occur (e.g. gas exchange in the alveoli

Question 9

What does simple cuboidal mean?

Answer 9

Simple = single cell layer; cuboidal = approx. cube-shaped add pic

Question 10

Where are simple cubiodal tissue found?

Answer 10

e.g. lining kidney collecting duct, and many others ducts

Question 11

What does simple columnar mean?

Answer 11

Simple = single cell layer; columnar = pillar-shaped add pic

Question 12

Where are simple columnar cells found?

Answer 12

enterocytes (intestinal absorptive), many other absorptive and secretory epithelia.

In humans, a simple columnar epithelium lines most organs of the digestive tract including the stomach, small intestine, and large intestine.

Question 13

What are the two types of stratified squamous cells an where are they found? Also comment wheather there nucleus is visable or not.

Answer 13

Two main types:(a) keratinising: epidermis (skin epithelium) (nuclei not visible in surface layer cells) (b) non-keratinising: linings of mouth, oesophagus, anus, cervix and vagina (nuclei are visible in surface layer cells) add pic

Question 14

Define Psuedostratified

Answer 14

Pseudostratified = falsely stratifiedLooks multi-layered, but surface cells have contact with basal lamina. Pseudostratified epithelia are often ciliated add pic

Question 15

Where are psuedostratified cells found?

Answer 15

e.g. airway (trachea and bronchi) epithelium, various ducts in the urinary and reproductive tracts

Question 16

Junctions separate many epithelial membranes into two biochemically and functionally distinct domains.

What are the names of these domains?

Answer 16

the apical domain the basolateral domain

Question 17

What do epithelial functions (secretion, fluid and solute transport, absorption etc. ) all require?

Answer 17

Polarity

Question 18

Why is polarity important for epithelial function?

Answer 18

Epithelial polarity is required to give directionality to epithelial function, i.e. one surface of the epithelium is different from the other.

Question 19

What is different about the plasma membrane of the apical domain and basolateral domain?

Answer 19

These domains have different lipid and protein composition, and have distinct functions.

Question 20

What are tight junctions key for?

Answer 20

Tight Junctions are key for epithelial polarity and function. add pic

Question 21

What is the role of Tight Junctions?

Answer 21

Tight junctions seal the paracellular pathway add pic

Question 22

How do tight junctions allow cells to establish and maintain apical-basolateral polarity

Answer 22

Tight Junctions allow cells to establish and maintain apical- basolateral polarity by preventing the mixing of proteins and lipids between the different plasma membrane compartments.

Question 23

Solutes like glucose, are often pumped across cell layers against a concentration gradient. Why aren’t these gradients lost by diffusion between cells?

Answer 23

This because the paracellular pathway (between cells) is sealed by tight junctions. This has two main outcomes: Concentration differences across cell layers can be maintained. Any solutes crossing the cell layer need to pass through the cells, meaning that the cells control the passage. Strong barriers are particularly required when tissues need to transport against a large concentration gradient. add pic

Question 24

Draw a diagram of an ion/fluid-transporting epithelial cell, outlining the typical organisation. include a capillary in the diagram

Answer 24

add pic

Question 25

How are absorptive and secretory cells arranged in the intestinial epithelium?

Answer 25

Secretory cells (goblet cells) are interspread among absorpative cells (enterocytes)

Question 26

How is tissue organised in the intestinial epithelium? are they stratified squamous?

Answer 26

The intestinial epithelium is simple columnar

Question 27

Draw a diagram showing the typical organisation of an exocrine secretory cell include a capillary in the diagram

Answer 27

add pic

Question 28

Define constitutive?

Answer 28

Constitutive – secretory vesicles, as they are formed, move directly to the plasma membrane and release their contents, e.g. production of plasma proteins by hepatocytes (constitutive endocrine secretion)

Question 29

Define Stimulated

Answer 29

secretory vesicles are stored in the cytoplasm and only fuse with the plasma membrane to release their contents, e.g. the release of adrenaline from cells of the adrenal medulla after a fight-or-flight stimulus (stimulated endocrine secretion); when stomach contents enter the duodenum, pancreatic acinar cells are stimulated to release their digestive enzymes into ducts (stimulated exocrine secretion)

Question 30

How is protective epithelia organised ( its cell shape and layering)

Answer 30

Protective epithelia are usually stratified-squamous (e.g. skin epidermis, lining of the oesophagus).

Question 31

Is this epidermis Keratinised stratified squamous or non-keratinised?

Answer 31

Keratinised add pic

Question 32

What happens when desmosomes go wrong?

Answer 32

This severe blistering, which also affected the mouth and anus, was the result of loss of function of desmosomes. This person started making auto-antibodies to desmosomal cell-cell adhesion molecules, and these reduced desmosome adhesion to make the epidermis fragile. add pic

Question 33

What happens if desmosome function is copramised?

Answer 33

Desmosomes are abundant between the cells of stratified squamous epithelia. If desmosome function is compromised, these epithelia become fragile and easily damaged.

Question 34

What do hemidesmosomes do?

Answer 34

Hemidesmosomes are found in epithelial cells connecting the basal epithelial cells to the lamina lucida, which is part of the basal lamina. attach cells to the basal lamina

Question 35

Place the following in order of cell turnover Cells of the nervous system Fat tissue, heart muscle and bone The lining of the gut

Answer 35

The lining of the gut is replaced every 3-10 days (depending on region). Fat tissue, heart muscle and bone are replaced every 8-10 years. Most cells of the central nervous system are not replaced. If they die, they are lost.

Question 36

Where are the cells located which replace the cells lost from the tips of intestinal villi?

Answer 36

CRYPT OF LEIBERKHUN Cells in the intestinal crypts If we mark a single new cell, we can follow its fate. As the marked cell migrates up the villus epithelium, new cells are constantly being produced by the crypt stem cells….. …..to replace the cells constantly being lost from the villus tip. add pic

Question 37

What can cause inhibition of proliferation of intestinial crypt cells and what are the effects of this?

Answer 37

Chemotherapy Treating mice with the antimetabolite chemotherapy drug, 5-FU, has a profound effect on the architecture of the small intestinal villi. The drug slows down or stops cell division in the crypts. Cell loss from the villus tips continues as normal, but the failure to produce new cells to replace the cells results in a loss of tissue: the villi shorten. This is the reason why chemotherapy can have strong gut side-effects.

Question 38

What diesease is caused by cell proliferation in the colon?

Answer 38

Adenoma (polyp)- benign cancer When there is too much cell proliferation, the rate of cell loss is not sufficient to maintain the normal tissue volume. In the colon, if a cell mutates such that its proliferation is dysregulated, too much tissue is formed. This is a benign tumour called an adenoma (polyp). add pic

Question 39

What leads to the formation of a callus?

Answer 39

: You are applying pressure and abrasion to areas of the skin. This stimulates the cells to divide more rapidly, and the rate of loss from the surface is less than the rate of new cell production, so there is an increase in tissue mass.

Question 40

What virus can cause the hyperproliferation of basal cells of stratified squamous epithelial?

Answer 40

Papilloma virus

Question 41

What disease can the papilloma virus cause

Answer 41

Warts

Question 42

Where do cells that replace cells lost from the epidermis come from?

Answer 42

Surface cells are constantly being lost, but are 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. Each layer replaces the one above as the layers are lost from the surface. add pic

Question 43

What happens if cell loss > cell production?

Answer 43

reduction in tissue mass

Question 44

What happens if cell loss < cell production?

Answer 44

increased tissue mass

Question 45

What happens if cell loss = cell production?

Answer 45

steady state