L4: Epithelial cells and surface specialisations

Question 1

What is the difference between a mucous membrane and a serous membrane?

Answer 1

MM→ line certain internal tubes which open to the exteriori

SM→ thin, two part membrane which lines certain closed body cavities and envelop the viscera

Question 2

What does a mucous membrane consist of?

Answer 2

• Epithelium lining lumen of a tube
• Adjacent layer of connective tissue often referred to as the lamina propria
• Third layer consisting of smooth muscle cells, referred to as the muscularis mucosae
  (carries blood and lymphatic vessels and nerves)

Question 3

What does a serous membrane consist of?

Answer 3

• Simple squamous epithelium → exudes watery lubricating fluid → promotes friction free movement
• Thin layer of connective tissue → attaches epithelium to adjacent tissue
  (carries blood and lymphatic vessels and nerves)

Question 4

What does the serous membrane line?

Answer 4

Peritoneum→ envelops many abdominal organs
Pleural sacs→ envelop the lungs
Pericardial sacs→ envelops the heart

Question 5

What are the different layer of the serous membrane called?

Answer 5

Parietal serosa→ outer part (closes to outer edge of cavity)

Visceral serosa→ inner part (closest to organs)

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

What are the different classifications of epithelial cell types?

Answer 7

Simple (one cell layer thick)

• Squamous
• Cuboidal
• Columnar
• Pseudostratified- looks like more than one cell layer as the nuclei are at different levels

Stratified/compound (more than one cell layer thick)

• Squamous
• Cuboidal
• Columnar
• Transitional

Question 8

What is an example of a simple squamous epithelia? What does it allow?

Answer 8

Basement membrane, Bowmans Capsule, Serosa of lungs, heart and viscrea
Provides:
- fast material exchange 
- barrier to fluids 
- barrier to the brain and CNS
- Tissue lubrication

Question 9

What is an example of simple cuboidal epithelia? What are the functions?

Answer 9

Height and width approximately equal
Pancreatic duct, thyroid gland, collecting ducts in kidney
Functions:
- Absorption
- Conduit
- Barrier/ covering
- Hormone synthesis, storage and mobilisation

Question 10

What is an example of simple columnar epithelium? What are the functions?

Answer 10

Heights are significantly greater than their widths
Lining the crypts of Lieberkuhn, stomach lining, gastric glands
Function:
- Absorption
- Secretion
- Lubrication

Question 11

What is a special feature found on the simple columnar epithelium?

Answer 11

Microvilli increase the surface area

Question 12

What is an example of pseudostratified epithelia? What are the functions?

Answer 12

All cells make contact with the epithelial surface, not all cell reach the epithelial surface, nuclei at different levels
Upper respiratory tract (nasal cavity, trachea, bronchi)
Functions:
- Secretion
- Conduit
- Particle trapping and removal

Question 13

What are stratified squamous epithelia cells?

Answer 13

Multiple layers of cells

Outermost are thin squamous epithelial cells

Question 14

What is an example of stratified non keratinised squamous epithelium? What are the functions?

Answer 14

Non keratinised→ epithelium of vagina, oesophagus, oral cavity, anal canal, surface of cornea, inner surface of eyelid
Function:
- Protection against abrasion
- Reduces water loss but remains moist
Found in areas that are moist and subject to varying degrees of abrasion

Question 15

What is an example of stratified squamous keratinised epithelium?

Answer 15

Karatinised→ outer layer of cells lost their nuclei and cornified
→ become squames of keratin 
Outer layer called stratum corneum
e.g. skin→ stratum corneum forms part of the epidermis
Function:
- Reduces water loss and ingress
- Prevents ingress of toxins 
- Protects against abrasion 
- Reduced microbial colonisation
- Shielding against UV light damage

Question 16

What is a keratinocyte?

Answer 16

Special type of epithelial cell
Keratinocyte mitosis occurs in the basal layer
Daughter cells move towards the surface and lose their ability to divide
Synthesis keratin (fibrous protein) → strength of epidermis

Question 17

What is the normal transit time of a keratinocyte? What disease is associated with reduced transit time?

Answer 17

28-40 days
Psoriasis
→ transit time: 2-4 days
→ flaky scaly skin

Question 18

What are the names of two other specialised cells found in the epidermis?

Answer 18

Melanocyte

Langerhan cells

Question 19

What do melanocytes do?

Answer 19

Produce melanin→ skin colour
All have the same number of melanocytes, each person produces different amounts of melanin
Melanosomes transferred to keratinocytes by phagocytosis and transferred to surface

Question 20

What do Langerhan cells do?

Answer 20

Immune cells in the skin
Specialised capacity to present antigens to T lymphocytes
Mediate immune reaction
e.g. allergic contact dermatitis

Question 21

What is significant about the transitional epithelium?

Answer 21

Cells vary from columnar/cuboidal to flattened
Allows for distention and stretch
e.g. bladder

Question 22

There are several different cell surface specialisations what are they? What is there function?

Answer 22

Keratin→ prevent water loss, protection from abrasion
Cilia→ control micro-movement of luminal contents
Goblet cells→ mucus secretions, moistens and lubricates
Club cells→ protection of bronchioles, stem cells for respiratory epithelium
Microfold cells→ found in GALT (immune system function)
Sterocilia→ inner ear, hearing and balance

Question 23

Describe what the goblet cells do? Where they are found?

Answer 23

Release mucins through exocytosis
Increases the water release from cells
Traps dirt/pathogens, moistens and lubricates
Found in epithelium of upper respiratory tract and in intestine
Have microvilli instead of cilia on surface

Question 24

How is cystic fibrosis caused?

Answer 24

Faulty cystic fibrosis transmembrane conductance regulator (CFTR)
Deficiency in chloride ion released
Sticky, immovable mucus
Affects all tissue with mucin and cilia (goblet cells)

Question 25

Which parts of the body are affected by cystic fibrosis?

Answer 25

Airways→ clogging and infection of bronchial passages, obstructs breathing and damages lungs
Liver→ bile duct become blocked, disrupts digestion
Pancreas→ zymogen secretion not released
Small intestine→ non motile stools
Reproductive tracts→ absence of vas deferens in males (infertile), thick mucus plug in cervix in females (infertile)
Skin→ malfunctioning sweat gland, very salty sweat and crystals on surface of skin

Question 26

Describe what club/clara cells are? What do they do?

Answer 26

Airway side of terminal bronchioles→ no cilia and no basal bodies
Protection of bronchiolar epithelium→ secrete uteroglobin
Detoxifying harmful substances→ cytochrome P450 enzymes
Act as stem cells, multiplying and differentiating into ciliated cells to regenerate the bronchiolar epithelium

Question 27

Describe what microfold cells do?

Answer 27

Small intestines only, close to lymphatic nodules

1. Trap pathogens and other molecules
2. Present to underlying dendritic cells for processing
3. Present to lymphocytes and macrophages that reside in basal pocket→ not linked to basement membrane, to raise an immune response or digestion

Question 28

What is unique about the microfold cells?

Answer 28

Have folded extension
Looks like a mushroom cap
Samples the lumen by endocytosis

Question 29

What is a weakness about the M cells?

Answer 29

Weak point in intestinal epithelium

Pathogen exploit them as a portal of entry `

Question 30

Describe the sterocilia? (NOT ESSENTIAL)

Answer 30

Inner ear
- Mechanosensing organelle
- Fluid motion, hearing and balance 
Epididymis and vas deferens
- Absorption of residual sperm 
- Contain actin and myosin filaments→ potential for movement of sperm along ejaculatory tracts

Question 31

Briefly describe cell renewal rates, in terms of smoking and the airway epithelium?

Answer 31

Smoking damages the lungs
Early stage 
1. Normal mucus layer thickens
2. Cilia die off
3. Ciliagenesis- 2 to 4 days 

Chronic stage
1. Goblet cells and basal cells proliferate
2. Club cells (metaplasia) or die
3. Carcinogens induce mutation and malignancy
4. Pneumocytes in the alveoli die → remaining type II cells proliferate to make both type I and II pneumocytes
Fibroblasts lay down scar tissue

Question 32

What are the different cell renewal rates?

Answer 32

Trachea→ 1 to 2 months
Alveoli→ 8 days
Goblet cells→ 10 days
Club cells→ never (once they die they undergo morphogenesis)

Question 33

What are some of the common respiratory disease associated with smoking?

Answer 33

Acute bronchitis→ cough and mucus production, inflammation, swelling and narrowing of the airways
Chronic bronchitis→ same as acute with start of irreparable damage to bronchioles and alveoli
Emphysema→ shortness of breath, permanent widening of airspaces distal to terminal bronchiole without fibrosis
COPD→ emphysema and chronic bronchitis
Astham→ bronchospasm, obstruction from mucus and narrowing of conducting airways→ wheeze, SoB, chest tightness etc…