Epithelial tissue and cell surface specialisations - lecture 6

Question 1

Define epithelial cells.

Answer 1

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

Question 2

Explain the embryonic origins of epithelial cells.

Answer 2

The three germ layers:
Ectoderm - outer layers e.g. skin, anus.
Mesoderm - inner lining of body cavities, connective tissue.
Ectoderm - inner and outer lining of the GI tract, endothelium.

Question 3

Describe how epithelial cells are classified and what each classification means.

Answer 3

Simple squamous
Simple cuboidal
Simple columnar
Pseudostratified - 1 cell thick, but nuclei at different heights so looks as if it’s stratified.

Stratified/compound squamous
Stratified cuboidal
Stratified columnar
Transitional - stratified, but changes shape e.g. epithelium.

Question 4

Explain the reasons for the different rates of renewal of each type of epithelium.

Question 5

What are the functions of SIMPLE SQUAMOUS epithelium and give an example where it is found.

Answer 5

LUBRICATION e.g. mesothelium.
GAS EXCHANGE e.g. type 1 pheumocytes of pulmonary alveoli.
PRODUCT EXCHANGE - endothelial cells lining heart and capillaries.
BARRIER - Bowman’s capsule, skin, oesophagus, conjunctiva of eye, brain.

Question 6

What are the functions of SIMPLE CUBOIDAL epithelium and give an example where it is found.

Answer 6

ABSORPTION AND CONDUIT - exocrine glands.
ABSORPTION AND SECRETION - kidney collecting ducts.
BARRIER - ovary.
HORMONE SYNTHESIS - thyroid.

Question 7

What is the position, structure and function of the basement membrane?

Answer 7

On the basal side of epithelial tissues.
Provides physical and biochemical cues to the overlying cells.

Question 8

What are the functions of SIMPLE COLUMNAR epithelium and give an example where it is found.

Answer 8

ABSORPTION - small intestine (also contain microvilli to increase SA), colon, gallbladder.
SECRETION - stomach lining, gastric glands, small intestine, colon, cervix.
PROTECTION - exocrine glands, cervix.
LUBRICATION - small intestine and colon.

Question 9

What are the functions of PSEUDOSTRATIFIED epithelium and give an example where it is found.

Answer 9

Pseudostratified ciliated epithelium of the upper respiratory tract - motile cilia and mucus secreting goblet cells.

Lining of male reproductive tract.

Question 10

What are goblet cells?

Answer 10

Cells that have microvilli instead of cilia. They release mucins through exocytocis. Water release is increased by the release of ions.

Question 11

How is cystic fibrosis caused?

Answer 11

There is no CTFR (cystic fibrosis transmembrane conductance regulator) to move Ca2+ out of membranes. This results in very sticky, unmovable mucus.

Question 12

What are symptoms of cystic fibrosis?

Answer 12

CLOGGING OF AIRWAYS - clogging of bronchal passage by sticky mucus.
LIVER - blocking of small bile duct.
PANCREAS - zymogen secretions not released, so can’t digest food properly.
SMALL INTESTINE - food doesn’t move through gut.
INFERTILITY - absence of fine ducts in men and occasionally thick mucus plug in cervix in women.

Question 13

What are the functions of STRATIFIED SQUAMOUS NON-KERATINISED epithelium and give an example where it is found.

Answer 13

Stratified cells are names by the cell type on the surface.
Main role is to PROTECT AGAINST ABRASION e.g. in vagina and epithelium (oesophagus).
REDUCE WATER LOSS, BUT REMAIN MOIST.
Also found in oral cavity, part of anal canal, surface of cornea, inner surface of eyelid.

Question 14

What are the functions of STRATIFIED SQUAMOUS KERATINISED epithelium and give an example where it is found.

Answer 14

Outer squamous cells have lost their nuclei and cornified (become keratinised).
EPIDERMIS OF SKIN is the main site where these are found. A few in oral cavity too.
Protect against abrasion, physical trauma, water loss, microbial ingress and UV light damage.

Question 15

What are the functions of TRANSITIONAL epithelium and give an example where it is found.

Answer 15

URINARY TRACT - flatten by urine and become stretched, are relaxed the rest of the time.
Protect underlying tissue from toxic chemicals and allow stretch.

Question 16

What are serous membranes?

Answer 16

Lines Peritoneum, pleural sacs, pericardial sac.

Thin, 2-part membranes which line certain closed body cavities and envelope the viscera. (They line the cavities around organs, organs don’t lie in them.)
Made of a MESOTHELIUM (simple squamous) with a watery lubricating fluid and a thin layer of connective tissue that attaches epithelium to adjacent tissues.

Question 17

What are mucous membranes?

Answer 17

Lines certain tubes which open to the exterior e.g. GI tract, respiratory tract, urinary tract.

Made out of EPITHELIUM lining, layer of connective tissue (LAMINA PROPRIA), layer of smooth muscle cells( MUSCULARIS MUCOSAE)

Question 18

Explain epithelial cell renewal rates in terms of smoking.

Answer 18

Alveoli - 8 days
Goblet cells - 10 days
Trachea - 1-2 months
Club cells - never

Question 19

How are mucous membranes different fro serous membranes?

Answer 19

Serous membrane has one cell on the surface, mucous membrane has 3 layers.
(Answer given by lecturer).

Question 20

What’s the function of club cells and where are they found?

Answer 20

To PROTECT BRONCHIOLAR EPITHELIUM by secreting uteroglobin.
DETOXIFICATION OF HARMFUL SUBSTANCES inhaled in the lungs.

Act as a stem cell multiplying into ciliated cells to regenerate bronchiolar epithelium.

Found on the airway side of bronchioles.

Question 21

What’s the function of microfold cells and where are they found?

Answer 21

TRAP PATHOGENS.
RAISE AN IMMUNE RESPONSE.
Found in the small intestine very close to lymphatic nodules.

Question 22

What is the function of stereocilia and where are they found?

Answer 22

In the inner ear, they respond to fluid motion for hearing and balance.

Question 23

What are 5 common respiratory conditions linked to smoking?

Answer 23

• Acute bronchitis
• Chronic bronchitis
• Emphysema
• COPD - coronary obstructive pulmonary disease
• Asthma

Question 24

What is acute vs chronic bronchitis?

Answer 24

Acute - cough, mucus production, breathlessness for less than 3 months.

Chronic - chronic inflammation of bronchi that produces a cough and mucus production with at least 2 coughing episodes lasting 3 months or more during a 2 year period. This is the start of irreparable damage to the bronchioles an alveoli.

Both have excess mucus in lung passages.

Question 25

What is emphysema?

Answer 25

Shortness of breath due to permanent widening of air spaces distal to the terminal bronchiole without fibrosis (destruction of air sacs).

Question 26

What is COPD?

Answer 26

Chronic obstructive pulmonary disease. Includes both emphysema and bronchitis.

Question 27

What is asthma?

Answer 27

Wheeze, shortness of breath, chest tightness, cough that may vary over time, variable expiratory airflow limitation. Often has a trigger.
Caused by bronchospasm - tightening of smooth muscle layer in bronchi and bronchioles. Also obstruction from mucus and narrowing of conducting airways.