4. Epithelial Cells

Question 1

What are mucous membranes?

Answer 1

Line certain internal tubes which open to the exterior.
Consists of epithelium lining lumen of a tube, adjacent layer of connective tissue (lamina propria)
Smooth muscle cells - muscularis mucosae

Question 2

What are some examples of mucous membranes?

Answer 2

The GI tract, respiratory tract and urinary tract linings

Question 3

What are serous membranes?

Answer 3

thin, two-part membranes lining closed body cavities
Envelope the viscera.
Secrete a lubricating fluid reducing friction.
Squamous epithelium secretes watering fluid.
Thin layer of connective tissue, attaches epithelium to adjacent tissues.

Question 4

How do serous membranes develop?

Answer 4

Develop into bag-like cavity which they invaginate into. Become surrounded by cavity, not lying within it.
Outer wall parietal, inner wall visceral.
Visceral closest to organs in cavity, parietal outer edge.

Question 5

Describe the structure of the pleurae of the lungs

Answer 5

Each lung has its own serosal membrane surrounding its surface.
Parietal pleura attached to inner layer of ribcage.
Visceral attached to parenchyma of the lung.
Serosal membrane releases moist pleura.
5ml of serum in each membrane.

Question 6

Define epithelia

Answer 6

Sheets of contiguous cells, of varied embryonic origin, that cover the external surface of the body and line internal surfaces including the body’s vessels.

Question 7

Where are epithelial tissues derived from?

Answer 7

From all embryological germ layers.
Ectoderm - epidermis
Endoderm - inner and outer linings of GI tract
Mesoderm - inner linings of body cavities

Question 8

What surfaces contain epithelial linings?

Answer 8

Skin, GI respiratory and genitourinary tract,

pericardial, pleural sacs, peritoneum, blood vessels

Question 9

What are the classifications of epithelial cell types?

Answer 9

Simple, one cell layer thick:
squamous, cuboidal, columnar, pseudostratified
Stratified/compound:
squamous, cuboidal, columnar, transitional

Question 10

Describe the appearances of different simple epithelial tissues

Answer 10

Squamous - squished
Cuboidal - square
Columnar - tall, longer than wide (3x)

Question 11

Describe the appearances of different stratified epithelial tissues

Answer 11

Squamous - several layers of squished
Cuboidal - square
Columnar - taller, longer than wide
Pseudostratified columnar - tall. nuclei are at different levels but still all directly attached to basement membrane
Transitional - different cell types, but characterised by cell type on top surface

Question 12

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

Answer 12

Basement membrane = basal lamina

Sits below simple squamous epithelium

Question 13

What are some examples of simple squamous epithelia?

Answer 13

Bowman’s capsule, lining vein, lung parenchyma

Question 14

What are some functions of simple squamous epithelia?

Answer 14

Fast material exchange and barrier to fluids
Barrier in the brain and CNS
Material exchange and lubrication
Barrier in Bowman's Capsule
Lubrication of lungs, heart and viscera

Question 15

What are some examples of simple cuboidal epithelium?

Answer 15

A single layer of polygonal cells, height and width equal.
Lining of pancreatic duct, surrounded by connective tissue.
Bounds thyroid gland follicles.
Lining collecting ducts of the kidney - lots of basement membranes and connective tissue as barrier.

Question 16

What are some functions of simple cuboidal epithelium?

Answer 16

Absorption and conduit (exocrine glands)
Absorption and secretion in kidney tubules
Barrier, Hormone synthesis and storage

Question 17

What are some examples of simple columnar?

Answer 17

Single layers of cells, heights greater than width.
Basement membrane has nuclei close to basal surface.
Lining the crypts of Lieberkuhn in intestinal glands.
Can contain microvilli - lining small intestine.

Question 18

What are some functions of simple columnar?

Answer 18

Absorption in small intestine and colon
Secretion in stomach lining and gastric glands
Lubrication in small intestine and colon

Question 19

What are some examples of pseudostratified epithelia?

Answer 19

Epithelia in which all cells make contact with the basement membrane, but not all cells reach surface.
Nuclei lie at different levels.
Upper respiratory tract, above basement membrane and connective tissue layers.
Lining of nasal cavity, trachea and bronchi.

Question 20

What are some functions of pseudostratified epithelium?

Answer 20

Secretion and conduit - respiratory tract
Mucus secretion
Particle trapping and removal

Question 21

What are some examples of stratified squamous epithelia?

Answer 21

Multiple layers of cells, outermost are squamous.
Non-keratinised lining vagina and oesophagus.
Part of anal canal, surface of cornea, inner eyelid.

Question 22

What are some functions of non-keratinised stratified squamous?

Answer 22

Protection against abrasion, reduces water loist, remains moist.
In the vagina, cells are rich in glycogen for lactobacilli maintaining low pH, destroys non-native bacteria.

Question 23

What is stratified squamous keratinised epithelium?

Answer 23

Outermost are squamous that have lost their nuclei and become squames of keratin.
Epidermis of skin is primarily this epithelium.
Outermost dead cells known as stratum corneum.

Question 24

What are some functions of the stratum corneum?

Answer 24

Stratum corneum layer greatly reduces water loss.
Prevents ingress of toxins, protects against abrasion.
Reduces microbial colonisation.

Question 25

Describe the structure of the skin.

Answer 25

Top layer is stratum corneum dead squames. Epidermis - avascular epithelia epidermis. Basement membrane, basal cells proliferating closest to membrane brown due to melanin. Dermis - dense irregular connective tissue, made of collagen and elastin bundles in all directions.

Question 26

What are keratinocytes?

Answer 26

Stratified squamous keratinised epithelium is made up of mainly epithelial cells called keratinocytes. Keratinocytes mitosis occurs in basal layer. Daughter keratinocytes move towards surface, differentiate and lose ability to divide. Keratinocytes synthesise keratins - strengthen epidermis.

Question 27

What is the normal transit time of a keratinocyte from basal layer to stratum corneum?

Answer 27

28-40 days | In diseases such as psoriasis, transit time is greatly reduced 2-4 days so stratum corneum is silvery scales.

Question 28

What other cells are present in the epidermis?

Answer 28

Melanocytes, intervals of 1:8 in basal layer. Produce melanin, all have same number but some produce more than others (darker skin) Melanocytes at basal layer, dendritic structure into cell. Langerhans cells, highly specialised capacity to present antigens to T lymphocytes, mediate immune reactions.

Question 29

What are some functions of stratified squamous keratinised epithelium?

Answer 29

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

Question 30

What is transitional epithelium? | Where is it found?

Answer 30

Surface cells vary in shape, different types. Alter between a relaxed and stretched shape. In urinary tract, proximal urethra at tip is keratinocytic.

Question 31

What are some functions of transitional epithelium within the urinary tract?

Answer 31

Distensibility, protection of underlying tissue from toxic chemicals

Question 32

What are some cell surface specialisations?

Answer 32

Keratin prevents water loss, protects against abrasion Cilia controls micro-movement of luminal contents Goblet cells - mucus secretions, moistens and lubricates. Clara cells/club cells protect bronchioles and act as stem cells for respiratory epithelium. Microfold cells, and stereocilia

Question 33

What are goblet cells?

Answer 33

On apical surface, no cilia present instead have microvilli. Release mucins through exocytosis, water release increased by release of ions. Nucleus at bottom of cell, secretory vesicles packed in containing mucin. Epithelium of upper respiratory tract 9+2 actin and myosin arrangement.

Question 34

Describe the symptoms of cystic fibrosis

Answer 34

CTFR mutation - transmembrane conductance regulator Deficiency of chloride ion release results in sticky immovable mucus. Tissues that have mucins and cilia all affected, cannot use mucociliary escalator. Airways - thick mucus, clogged airways, damages lungs Liver - small bile duct blocked, disrupts digestion Pancreas - zymogen secretions not released, digestion Small Intestine - thick motile stools, can kill neonates Reproductive tracts - absence of fine ducts, infertility Skin - malfunctioning of sweat glands, salty sweat, crystals

Question 35

What are clara cells?

Answer 35

On the airway side of the terminal bronchioles, have club like apical surface, no cilia or basal bodies. Protect bronchiolar epithelum. Secrete products e.g. uteroglobin and surfactant. Detoxify harmful substances in the lungs. Contain P450 enzymes in SER. Act as stem cell, to ciliated cells to regenerate epithelium.

Question 36

What are microfold cells?

Answer 36

Only in small intestine and close to lymphatic nodules. Trap pathogens and other molecules. Present these to underlying dendritic cells, that process material to lymphocytes and macrophaes in basal pocket. Have a folded extension like a mushroom cap. Represent a weak point as pathogens can enter here.

Question 37

What are stereocilia?

Answer 37

In the inner ear to respond to fluid motion for hearing and balance. Mechanosensing organelles of hair cells. In epididymis and vans deferens - facilitate absorption of residual sperm body after spermiation complete. Contain actin and myosin filaments, debated whether they can be involved in ejaculation.

Question 38

What are cell renewal rates within the lungs?

Answer 38

In the early stage, normal mucus layer thickens, cilia die off and ciliagenesis takes 2-4 days if stopped smoking. Chronic stage - goblet cells and basal cells proliferate Clara cells die and cannot regenerate. Pneumocytes in alveoli die, fibroblasts lay down scar tissue. Cells in trachea take 1-2 months, alveoli 8 days Goblet cells take 10 days, clara cells always dead.

Question 39

What are some common respiratory conditions related to smoking?

Answer 39

Acute bronchitis - cough and mucus production, reduced lung function, excess mucus, swelling, inflammation At later stages increased risk of serious respiratory diseases. Chronic bronchitis - chronic inflammation, at least 2 episodes lasting 3 months, reduced lung function. Irreparable damage to bronchioles and alveoli. Emphysema - shortness of breath, permanent widening of airspace, destruction of air sacs. Elastase destroys elastin, absence of alpha1 antitrypsin. COPD - emphysema and chronic bronchitis, umbrella term Asthma - wheeze, shortness of breath, chest tightness, due to bronchospasm, tightening of smooth muscle