Epithelia

Question 1

What are the 4 tissue types

Answer 1

Epithelial, connective, nervous, muscle

Question 2

How is epithelial fissure formed

Answer 2

From an uninterrupted layer of cells

Question 3

What’s the function of epithelial tissue

Answer 3

Covers all internal and external body surfaces and forms boundaries between body compartments

Question 4

Cells are joined by various…

Answer 4

Intercellular junctions

Question 5

What is the basement membrane

Answer 5

Separates underlying connective tissue and epithelial cells.
Made of glycoproteins and collagen.
Produced partly from connective tissue cells and partly from epithelial cells

Question 6

How are epithelial cells polarised?

Answer 6

They have an apical (free) surface that’s connected to the outside and a basal surface which is attached to the basement membrane.
Polarisation is particularly present in absorption or secretory cells because the intracellular organelles reflects the directional transport

Question 7

How are epithelial tissues classed?

Answer 7

number of layers of cells in the epithelium
Shape of cells on the apical surface of the tissue
Specialisation of the cell surface

Question 8

How are epithelial cells named based on the number of cells in the layer

Answer 8

Single layer of cells- simple
2 or more layers of cells- stratified
Looks like more than one layer but all cells are connected to the basement membrane- psedostatified

Question 9

Why is there a limit to how thick an epithelial tissue can be?

Answer 9

Epithelial tissue is a vascular (no blood supply) this means nutrients must diffuse through capillaries from the basement membrane

Question 10

How is epithelial tissue classed based on the shape of cells?

Answer 10

Cuboidal- as wide as they are tall
Columnar- taller than they are wide
Squamous- flat, scale like

Question 11

Aspects of columnar cells

Answer 11

Involved in active transport or secretion (GI tract)

Question 12

Aspects of squamous cells

Answer 12

Allow rapid diffusion but fragile

Question 13

What’s transitional epithelium

Answer 13

Apical cells change shape as epithelium is stretched ex. Bladder
Empty- round or dome shaped
Full- stretched or flattened

Question 14

How does specialisations on the surface of the cells affect the classification of epithelial tissue

Answer 14

Ex. Microvilli (increase surface area), cilia (for movement) or presence of protein keratin (waterproofing)

Question 15

4 types of junctions

Answer 15

Tight, zonal adherents, desmosomes, gap junctions

Question 16

Tight junctions

Answer 16

-prevent passage of molecules or ions through the space between epithelial cells. Must enter a cell by active transport or diffusion
- block movement of integral cell proteins between apical and basolateral surfaces.

Question 17

Adhering junctions (Zonula adherens)

Answer 17

Completely surrounds cell providing stability,
Binds cells together at cytoskeleton to create a unit

Question 18

Desmosome

Answer 18

Below adhering junctions and provides strong attachment of cells.
Found in tissues that are exposed to abrasion (skin) or physical stress (heart)
Disc shaped occurring as a row of spots around circumference of cells

Question 19

Gap junctions

Answer 19

Have tiny pores to allow passage of small molecules between adjacent cells.
Means cells can respond to stimuli as a unit rather than individually
FOR INTERCELLULAR COMMUNICATION
Consists of 2 Connexons each made up of 6 connexin units

Question 20

What’s a junctional complex

Answer 20

Tight junction, adhering junction and a desmosome

Question 21

Mesothelium

Answer 21

Simple squamous epithelium lining the major body cavities
Provides a friction free surface by secreting a watery fluid (for movement)
Forms the serous membranes such as the pleura, pericardium and peritoneum

Question 22

Endothelium

Answer 22

Simple squamous epithelium lining the walls of blood vessels, lymphatics and the heart.

Question 23

Blood brain barrier

Answer 23

Restricts the passage of potentially harmful substances from the blood. Achieved through highly selective diffusion through but not between cells.
The endothelial cells metabolise harmful substances to prevent them from travelling to the brain.

Question 24

How does the blood brain barrier make it very difficult to treat brain diseases

Answer 24

Blood brain barrier prevents antibodies from reaching the brain

Question 25

Where are simple cuboidal cells mainly found

Answer 25

Lining tubules and ducts, sites involved in secretion, excretion and absorption.
Ex. Collecting duct of kidneys, salivary glands or pancreas

Question 26

Where would you find the nucleus in a columnar epithelia cell

Answer 26

Central or basolateral

Question 27

How can simple columnar cells be specialised?

Answer 27

Microvilli and goblet cells

Question 28

Microvilli

Answer 28

Increase surface area by about 30x for absorption
Form a striated or a brush border which can be seen under the microscope

Question 29

Goblet cell

Answer 29

Are modified columnar cells found in other cells in the epithelial tissue
Abundant in gastrointestinal and respiratory tracts
Secrete mucus which moistens surface of the respiratory tract

Question 30

Pseudostratified columnar epithelium

Answer 30

Contains 3 cell types : basal, goblet and columnar ciliated. Vary in height and nuclei lie at different heights so looks stratified

Question 31

Cilia

Answer 31

Longer than Microvilli
Move synchronous to provide movement
Can become damaged by common cold, smoking, cold air, old age

Question 32

Why is stratified epithelium tissue not suitable for secretion

Answer 32

Multiple layer doesn’t allow forsecretion

Question 33

Why would stratified squamous epithelium be keratinised

Answer 33

If it needs to be waterproof
Ex, outside layer of skin

Question 34

Desquamation

Answer 34

When surface squamous cells die (sloughed) and replaced by mitosis in the basal cells of the tissue

Question 35

Keratinisation

Answer 35

Epidermis consists mainly of keratinocytes which undergo mitosis in the basal layer of the epidermis. By cell division previously formed cells are pushed to the surface and fill with keratin. These cells’ junctions become filled with a waxy material which causes a lack of nutrients which then become hardened dead keratinised cells