Epithelia

Question 1

Characteristics of epithelia

Answer 1

Avascular
Closely attached to each other (with many specialised junctions)
Functionally distinct surfaces

Question 2

What does the epithelial group consist of

Answer 2

Cells that cover the external body surfaces, line the internal closed cavities, and body tubes that communicate with the exterior
They also form secretory units &a ducts of glands

Question 3

Epithelial fxs

Answer 3

Protection
Absorption
Secretion/excretion
Contractility
Line/cover surfaces of body
Interfaces between diff bio compartment
Form glands and ducts

Question 4

Types of epithelia

Answer 4

Simple

Stratified

Question 5

What is simple epithelia

Answer 5

One cell layer thick
Ideal for secretion diffusion absorption
Range in shape

Question 6

What are stratified epithelia

Answer 6

2+ cell layers thick
Mostly protective fx
Classified according to morphology of surface cells

Question 7

Types of simple epithelia

Answer 7

Squamous
Cuboidal
Columnar
Columnar ciliated
Paeudostratified columnar ciliated

Question 8

Types of stratified epithelia

Answer 8

Squamous
Squamous keratinised
Cuboidal
Columnar
Transitional

Question 9

Eg junctional complexes

Answer 9

Hemidesmosome
Desmosome
Tight junction
Zona adherens (adherens jctn)

Question 10

Simple squamous

Answer 10

Found lining surfaces suitable for diffusion eg alveoli capillary walls lining of pleural pericardial peritoneal cavities
One cell layer thick
Look like fried eggs/flat

Question 11

Simple cuboidal

Answer 11

Found lining ducts and tubules with excretory secretory or absorptive fx eg kidney tubule salivary gland pancreas
Round centrally located nucleus

Question 12

Simple columnar

Answer 12

Line highly absorptive or secretory surfaces eg small intestines stomach gall bladder often interspersed with goblet cells
Nucleus oval shaped and basal border

Question 13

Simple columnar ciliated

Answer 13

Found lining the oviduct cilia beat synchronised

Question 14

Pseudostratified columnar ciliated aka respiratory epithelia

Answer 14

Found in upper respiratory tract
Always ciliated
Interspersed with goblet cells
Nuclei not all situated at basal border
Give appearance of more than one layer

Question 15

Stratified squamous

Answer 15

Found in oral cavity, pharynx, parts of larynx, oesophagus, anal canal, uterine cervix, vagina
Protective fx withstand mech abrasion but no desiccation must be kept moist
Basal layer always cuboidal
Continual new production of cells from basal layer
Variable no of cell layers which change morphology as they move towards the surface and nuclei also become flattened toward the surface

Question 16

Stratified squamous keratinised

Answer 16

In the skin/epidermis
Protective fx withstand mech abrasion and dessication
Process of keratinisation
As they push towards surface they mature then degenerate.
Nuclei become flattened and pyknotic so cell is dead

Question 17

Stratified cuboidal

Answer 17

Found lining ducts eg salivary glands
Usually 2-3 layers
Minimal secretory absorptive fx
Provides more substantial lining compared to simple

Question 18

Stratified cuboidal

Answer 18

Both layers tall - conjunctiva
Basal layers cuboidal - distal urethra, lacrimal sac & duct, salivary gland ducts
Protective fx

Question 19

Transitional epithelia

Answer 19

Urinary tract, bladder
Highly specialised to accommodate stretch
Outer/luminal cells become flattened in a stretched state
Relaxed state 4-5 layers
Stretched state 2-3 layers

Question 20

Other BM names

Answer 20

Basal lamina

External lamina

Question 21

Features of the BM

Answer 21

Secreted by the epithelia

Never penetrated by blood vessels

Question 22

What are the layers of the BM

Answer 22

Lamina lucida
Lamina densa
Lamina fibroreticularis

Question 23

Lamina lucida

Answer 23

Electron Lucent layer next to the epithelial cells

Question 24

Lamina densa

Answer 24

Intermediate electron dense layer (visible by light microscopy)

Question 25

Lamina fibroreticularis

Answer 25

Relatively electron Lucent layer which merged with the underlying CT

Question 26

BM composition

Answer 26

Anchoring filaments Structural glycoproteins Proteoglycans

Question 27

Types of anchoring filament in the BM

Answer 27

``` Collagen 4 (exclusive to BM) Some C 3 (reticulin) found in the lamina fibroreticularis ```

Question 28

Types of structural glycoproteins in BM

Answer 28

Laminin (bind to C 4 and other BM constituents and laminin receptors (shaped glycoproteins) in basal membrane of epithelial cells) Entactin (mediates binding of laminin to C4) Fibronectin (produced by fibroblasts of underlying CT. binds membrane spanning receptor proteins (integrins) and extra cellular components eg collagen, heparin sulphate so play important cell adhesion role)

Question 29

Types of proteoglycans in the BM

Answer 29

Heparan sulphate (extensively hydrated and forming most of bulk of BM)

Question 30

BM fxs

Answer 30

``` Structural (intermediate in attachment of CT to cells Compartmentalises (isolate CT and cells) Filters (regulate movement of substances into the kidneys urinary space within renal corpuscle) Polarity induction ( defines in vivo shape of epithelia (along with mesenchyme below) Tissue scaffolding (guide during regeneration of damaged epithelial tissue) ```

Question 31

Specialisations

Answer 31

Cilia Micro villi Stereo cilia Keratin

Question 32

What are Cilia

Answer 32

Long motile cytoplasmic structures projecting from surface in parallel rows 7-10microm long Seen with light microscope Internal structure made of several micro tubule pairs

Question 33

Cilia fx

Answer 33

Beat wave like to move surface film of mucus or fluid in consistent direction

Question 34

What are microvilli

Answer 34

Relatively short static cytoplasmic projections extending from cell surface forming striated/brush border 0.5-1microm long Not seen individually with light microscope At high electron mag can see the core containing several thin actin filaments

Question 35

Microvilli fx

Answer 35

Size And density related to cells absorptive capacity | They increase the cell surface area

Question 36

What are stereocilia

Answer 36

Microvilli of unusual length Named before electron microscopy showed they have a different internal structure to cilia No micro tubules just filament pus actin skeleton like microvilli Found in epididymis

Question 37

Keratin fx

Answer 37

Prevents desiccation and withstand abrasion

Question 38

Origins of epithelia

Answer 38

3 germ layers of early embryo Ectoderm Endoderm Mesoderm

Question 39

Ectoderm

Answer 39

Give rise to corneal and lens epithelium of eye, epidermis of the skin and its derivatives. Lining of oral and anal canal cavities and cells that produce tooth enamel

Question 40

Endoderm

Answer 40

Give rise to epithelia lining the alimentary tract (- mouth pharynx anus) Respiratory system Intestinal glands (liver gall bladder pancreas) Thyroid, anterior pituitary gland Parathyroid, thymus

Question 41

Mesoderm

Answer 41

Epithelium of urogenital system Provide continuous layer lining blood and lymph vessels (endothelium) and peritoneal and other serous cavities (mesothelium)