Lecture 8 - Epithelial Cells & Surface Specialisations

Question 1

What are mucous membranes + what do they line?

What are serous membrane + what do they line?

Answer 1

• Mucous membranes line internal tubes that open to the exterior - e.g.: respiratory, GI and urinary tract.
• Serous membrane line certain closed body cavities that dont open to the exterior and envelop the viscera - e.g.: the peritoneum (surrounds abdominal organs), the pleural sacs, pericardial sac.

Question 2

What are the two parts of a serous membrane?

Answer 2

1) Visceral serosa - closest to organs in the cavity

2) Parietal serosa - lines the outer edge of the cavity

Question 3

Define “epithelia”.
Give examples of 3 main surfaces they line
Which germ layers are epithelial cells derived from?

Answer 3

• Epithelia are sheets of continuous cells of embryonic origin (derived from all 3 germ layers) that covers external surfaces (e..g: skin), internal surfaces that open to the exterior (e.g.: GI tract) and internal surfaces that dont open to the exterior (e.g.: blood vessels).
• All 3 germ layers (ecto, meso and endoderm)

Question 4

What are the 2 main types of epithelial cell types and the subdivisions of each?

Answer 4

1) Simple - i.e.: 1 cell layer
2) Stratified/Compound - e.g.: 2 or more cell layers
All of these can be squamous, cuboidal, & columnar

NB: also get psuedostratified + transitional which are special types.

Question 5

Define squamous, cuboidal and columnar in terms of epithelial cells.

Answer 5

Squamous = flat & flaky
Cuboidal = Height + Width same size
Columnar = Height longer than width

Question 6

Describe the function of simple squamous epithelium + why they’re suited to this function.
Where are simple squamous epithelium often found?

Answer 6

Rapid material exchanger (as they’re very thin and flat) & fluid barriers (due to presence of tight junctions).

• Respiratory space in lungs
• Bowmans capsule (barrier)
• Serosa of heart, lungs and viscera
• In the lymphatic system

Question 7

Describe the function and list locations of simple cuboidal epithelium.

Answer 7

• Absorption + secretion (in exocrine glands and kidney tubules)
• Barrier/covering (in ovary)
• Hormone synthesis, secretion & storage (in thyroid gland)
• Found in pancreatic duct & thyroid gland

Question 8

Describe the function and list the locations of simple columnar epithelium.

Answer 8

Simple columnar epithelium line the crypts of intestinal glands + have microvilli

• Absorption (SI, colon + gall bladder)
• Secretion (stomach lining, gastric glands, SI + colon)
• Lubrication (SI & colon)

Question 9

What is psuedostratified epithelia?

Where is it found + what are its functions?

Answer 9

• All cells make contract with basement membrane but not all reach the apical membrane, giving impression of multiple cell layers and nuclei lying at different levels throughout
• They have motile cilia and goblet cells in URT
• Secretion (respiratory tract)
• Mucus production (respiratory tract)
• Particle trapping and removal (respiratory + nasal cavity)

Question 10

What is stratified squamous epithelium?

Where is stratified squamous non-keratinised epithelium usually found - give examples.

Answer 10

• Epithelium made from variety of different layers, the outermost of which is thin/flat squamous epithelium.
• Stratified squamous non-keratinised epithelium are in areas that are moist and prone to abrasion - e.g.: oral cavity, oesophagus, vagina, anus, cornea etc to protect against it - also protects against water loss.

Question 11

How does stratified squamous non-keratinised epithelium in the vagina maintain a suitably low pH for destroying non-native bacteria and viruses?

Answer 11

They contains large amount of glycogen, which is a substrate for lactobacilli. This produces lactic acid which keeps pH low.

Question 12

What is stratified squamous keratinised epithelium?

What are its functions + where is it most commonly found?

Answer 12

Multiple cell layers with an outermost layer that have lost their nuclei and become cornified - this layer:
- Greatly reduces water loss
- Stops ingress of toxins
- Protects against abrasion
- Stops microbial colonisation (as there is no water)
Most commonly found on epidermis of skin (particularly on foot).

Question 13

What is transitional epithelium?

Where is its main location + what are its functions?

Answer 13

Epithelium that vary in shape/size from cuboidal/columnar to flattened depending on if they’re stretched or relaxed.

• In the urinary tract
• Dispensability in micturition and protection of underlying tissues from toxic chemicals in urine.

Question 14

Name 6 surface specialisations of epithelial cells and describe the functions of each.

Answer 14

Keratin = prevents water loss and protects against abrasion.
Cilia - controls movement of luminal contents
Goblet cells - secrete mucus, moistens + lubricates
Club cells - protects bronchioles and acts as stem cells for respiratory epithelium
Microfold cells = allows rapid sampling of gut microflora
Stereo-cilia = Converts pressure to electrical signals in auditory system

Question 15

What is the epidermis tissue made of?
What are the cells in this layer called?
Where do keratinocytes divide and how long does it take to reach the stratum corneum? How is this changed in Psoriasis?

Answer 15

• Stratified squamous keratinised epithelium
• Keratinocytes - which make keratin to strengthen the epidermis
• At the basal layer, and move up to the stratum corneum in 28-40 days, however only 2-4 days in psoriasis which leads to flaky silvery scales.

Question 16

What are the functions of the epidermis?

Answer 16

• Protect against abrasion and physical trauma
• Prevention of water loss
• Prevention of microbial ingress
• Shielding against UV light damage

Question 17

What are the cell renewal rates for the trachea, alveoli, goblet cells and club cells in the respiratory tract?

Answer 17

Trachea = 1-2 months
Alveoli = 8 days
Goblet cells = 10 days
Club cells = never (once die undergo morphogenesis)

Question 18

Define at least 2 respiratory conditions related to smoking and their causes.

Answer 18

1) Acute bronchitis - cough, mucus production, breathlessness for < 3 months - due to inflammation, swelling and narrowing of lung airways and excess mucus production.
2) Chronic bronchitis - Chronic inflammation of bronchioles, same reasoning but start of irreparable damage to bronchioles and alveoli.
3) Emphysema - shortness of breath, due to permanent widening of airspaces and destruction of airsacs.
4) Asthma - Wheezing, chest tightness and coughing due to bronchospasm (tightened SM layer in bronchioles), obstruction from mucus and narrowing of conducting airways.