W8- Lecture 43- Epithelial tissue

Question 1

what are epithelia tissues ?

Answer 1

Epithelia are tissues that serve as protective layers and/or secretory components of body organs and systems.

Formed into tightly cohesive cellular sheets.
Form functional units of secretory glands e.g. salivary, mammary, sweat.

Question 2

what are the common attributes that epithelial tissues share ?

Answer 2

Limited intercellular space:
Specialised intercellular junctions hold cell membranes close together – effective barrier – blocks infiltration of fluids between cells.

Single or multiple layers of cells:
Form linings or coverings. Where diffusion/filtration is important, epithelia is a single layer – where protection e.g. abrasion is needed – multiple layers

Free apical surfaces:
All epithelia possess a free apical surface during development or at maturity. The apical surface is where cells of an epithelium face internal lumens.

Basement membrane:
Basal surface attaches to underlying tissues via basement membrane derived from underlying connective tissue.
Epithelia covering or lining tissues are constantly subjected to wear and tear. Mitotic capability enables repair and regeneration.

Question 3

which 2 characteristics are epithelia described by ?

Answer 3

Cells layers:
Simple epithelium
Pseudostratified epithelium
Stratified epithelium

Cell shape:
Squamous cells
Cuboidal cells
Columnar cells
Transitional cells

Question 4

describe the classification of epithelia based on layers

Answer 4

Simple epithelia – one cell thick

Stratified epithelia – many cells thick, but only bottom layer in contact with basement membrane.

Pseudostratified epithelia – appear more than one cell thick, but all cells rest on basement membrane

Question 5

describe the classification of epithelia based on shape

Answer 5

Squamous – flattened cells like paving stones

Columnar – cells are taller than they are wide

Cuboidal – cells are of similar height, depth and width

Transitional – cells in layers which change their shape when they are stretched (only found in urological tract)

Question 6

name two examples of Simple squamous epithelia

Answer 6

e.g. alveoli & capillaries of lungs

Question 7

name an example of Simple cuboidal epithelia

Answer 7

e.g. kidney tubule

Question 8

name an example of Simple Columnar

epithelia

Answer 8

e.g. small intestine

Question 9

name an example of Transitional epithelia

Answer 9

only in urinary tract

stretches to accommodate fluid changes

Question 10

name an example of Keratinised stratified Squamous epithelia

Answer 10

• only found in skin

Question 11

name an example of Stratified Squamous

epithelia

Answer 11

oesophagus

Question 12

name two examples of Pseudostratified

epithelia

Answer 12

• e.g trachea, nasal mucosa

Question 13

name an example of Stratified cuboidal

epithelia

Answer 13

e.g. sweat gland duct

Question 14

name an example of Stratified columnar

epithelia

Answer 14

e.g. Salivary gland duct

Question 15

describe the Basal surface of epithelia

Answer 15

Basement membrane:
Separation from the underlying connective tissue – acts to support epithelia a selectively permeable filter between epithelium and connective tissue.

Anchors epithelium to connective tissue via cell-matrix adhesions.

Basal lamina:
Supportive sheet between epithelium and underlying connective tissue

Question 16

describe the apical surface of epithelia(2)

example of each

Answer 16

Microvilli:
Finger like extensions of the plasma membrane of apical epithelial cell
Increase surface area for absorption (small intestine).

Cilia:
Whip like, motile extensions
Moves mucus, etc, over epithelial surface, in once direction. (trachea and respiratory bronchus).

Question 17

describe the lateral surface of epithelia

Answer 17

Cells are connected to neighbouring cells via cell junctions:

Desmosomes:
Adhesive spots on lateral sides
Involves proteins called cadherins

Tight junctions:
Plasma membrane of adjacent cells fuse
Nothing passes
(GI tract doesn’t let enzymes from gut into blood stream)

Gap junction:
Present in many locations
Lets small molecules pass
(cardiac muscle tissue)

Question 18

what is glandular epithelium ?

Answer 18

Aggregates of epithelial cells clustered together to perform specific secretory or excretory function.

Secrete wide range of products:
Hormones
Enzymes
Milk
Sweat
Mucous
oil

Question 19

what are the two classifications of glands ?

Answer 19

Exocrine
Pour products into ducts that open into lumen of organ or onto the skin

Endocrine
Have no duct system – ductless glands – secrete into empty tissues spaces – eventually enter blood stream

Question 20

what is the most common secretory mechanism ?
examples
impact on cell ?

Answer 20

Merocrine
e.g. salivary gland – secretion passes from cells without damage to plasma membrane – exocytosis

no damage to cell

Question 21

describe how some glands excrete by holocrine mechanisms \
+ example

impact on cell ?

Answer 21

e.g. sebaceous gland – cellular debris part of secretion (sebum)

Involves death of the cell

Question 22

describe how some glands excrete by
Apocrine mechanisms
examples
impact on cell ?

Answer 22

e.g. mammary gland

Apical end pinched off

Question 23

describe the Morphological classification of epithelial cells

Answer 23

Simple – single tube
Compound – branched duct system
Branches
Tubular
Acinar/alveolar (grape like)

Question 24

describe epithelial membranes (4 types)

Answer 24

Epithelial membranes contain epithelium
and an underlying connective tissue:

Mucous membranes – digestive system 
Serous membranes – body cavities
Cutaneous membrane - skin
Synovial membrane - joints
(Synovial membranes contain only connective tissues and line the cavities of synovial joints)

Question 25

describe Serous (serosa) Epithelial membranes

Answer 25

Simple squamous (usually)
Resting on thin layer of loose connective tissue
Found in body cavities
Serous fluid – lubrication

Question 26

describe Mucous (mucosa) Epithelial membranes

Answer 26

Lines cavities open to outside
Mucus cells/glands lumen of digestive (microvilli), reproductive, respiratory systems (ciliated)
Epithelial cells vary in morphology and function.

Question 27

describe Cutaneous membrane Epithelial membranes

Answer 27

The cutaneous membrane is the skin, covering the outer surface of the body
Consists of the epidermis and dermis

Question 28

what two layers does a serous membrane have ?

where are serous membranes found ?

Answer 28

The parietal layer attaches to the body around the organ(thick)
The visceral layer attaches to the organs themselves.(thin + deliacate)

Serous membranes cover the surface of organs that are not exposed to the outside and secrete a watery fluid