Epithelia

Question 1

Define epithelia

Answer 1

Sheets of contiguous cells, of varied embryonic origin, that cover the external surface of the body and line the internal surfaces

Question 2

Where is the basement membrane located?

Answer 2

The basement membrane lies between epithelial cells and the subtending connective tissue.

Question 3

What is the structure of the basement membrane?

Answer 3

Thin, flexible, acellular layer
Consists of a basal lamina adjacent to epithelial cells
Variable thickness due the quantity of reticular fibres present

Question 4

What is the function of the basal membrane?

Answer 4

Acts as a molecular and cellular filter

Supports epithelial cells

Question 5

What is the difference between stratified and simple epithelia?

Answer 5

There are multiple layers of cells in stratified epithelia whereas there is only a single layer in simple epithelia.
Only the basal layer of cells in stratified epithelia are in contact with the basal membrane.

Question 6

Describe and give functions and a location of simple squamous epithelia.

Answer 6

Single layer of flattened cells
Bowmans capsule and loop of Henle (kidney), endothelium lining vessels, mesothelium lining cavities and alveoli.
Lubrication, gas exchange, barrier and active transport.

Question 7

Describe and give functions and a location of simple cuboidal epithelia.

Answer 7

Single layer of square cells (transverse) or polygonal (longitudinal)
Thyroid follicles, ducts of exocrine glands, kidney tubules and surface of ovary
Absorption, secretion, conduit, barrier, hormone (synthesis, storage and secretion)

Question 8

Describe and give functions and a location of simple columnar epithelia.

Answer 8

Longer than wide cells with a basally placed nucleus. Hexagonal in longitudinal sections. May have microvilli
Much of GI tract, exocrine ducts, gallbladder, oviducts, ductuli of testis, uterus
Absorption, secretion, lubrication and transport

Question 9

Describe and give functions and a location of pseudo-stratified epithelia.

Answer 9

Cells at all different levels, all touch basal membrane but not all reach the surface. Nuclei at different levels. May have cilia/stereo-cilia
Respiratory tract, epididymus
Secretion, conduit, absorption. Mucus secretion and particle sweeping.

Question 10

Which layer is the naming of compound epithelia based upon?

Answer 10

Most superficial layer

Question 11

Describe and give functions and a location of stratified squamous non keratinised epithelium.

Answer 11

Several layers of flattened cells
Oesophagus, vagina, outer layer of cornea, buccal cavity, anal canal
Protect against abrasion, prevent water loss but remaining moist

Question 12

Describe and give functions and a location of stratified squamous keratinised epithelium.

Answer 12

Layers of flattened cells with the outer most layers dead cells (without nuclei)
Skin
Protect from abrasion, microbes and uv light. Prevent water loss.

Question 13

Describe and give functions and a location of transitional epithelium.

Answer 13

Layers of larger, rounded and occasionally binucleated cells, can be flattened out when stretched.
Urinary passages
Distensible tissues, protection from toxins in waste products

Question 14

Describe and give functions and a location of stratified cuboidal epithelium.

Answer 14

Multiple layers of square cells
Glandular ducts (sweat glands)
Absorption and secretion

Question 15

Describe and give functions and a location of stratified columnar epithelium

Answer 15

Outmost cells columnar, underlying layers cuboidal
Salivary glands, mammary glands, male urethra
Secretion, absorption

Question 16

Why are epithelia renewed at different rates?

Answer 16

Dependent of location and function
Intestine renewed 4-6 days
Epidermis 28 days as keratin is sloughed off
Other not renewed in adulthood unless toxic/physical injury occurs

Question 17

Describe how the structure of microvilli is related to their function?

Answer 17

Projection of cell membrane. Shape supported by actin microfilaments. Protected by dense glycocalyx.
Multiple projections increase surface area creating more surfaces across which absorption can occur
E.g. Small intestine and proximal convoluted tubule in kidney

Question 18

Describe the structure and function of cilia.

Answer 18

Projections of plasma membrane with a core of microtubules in a 9+2 arrangement (9 surround a core 2)
They are able to beat to move material across the cell surface.
E.g. Fallopian tube and respiratory tract

Question 19

Describe the structure and function of stereocilia.

Answer 19

Elongated microvilli which are not motile.
Absorptive function as they increase surface area
E.g. Epididymus