L10: Skin Anatomy and Physiology

Question 1

What are the 3 main layers of the human skin, starting from the outermost layer?

Answer 1

1. Epidermis
2. Dermis
3. Hypodermis

Question 2

Where are hair follicles found in?

Answer 2

Dermis

Question 3

What are hair follicles associated with?

Answer 3

Sebaceous gland

Question 4

What are the physiological processes in the hair follicles?

Answer 4

• Matrix contains rapidly dividing keratinocytes, which produces keratin that makes up the hair shaft
• Melanocytes transfer packets of melanin to the hair follicle matrix keratinocytes, thus giving them colour
• Sebum is produced from sebaceous glands and it keeps the hair shaft moisturized

Question 5

What is the outermost layer of the epidermis called?

Answer 5

Stratum corneum

Question 6

What is the physiological process in the epidermis layer?

Answer 6

1. New keratinocytes are produced at the bottom layer of the epidermis
2. Keratinocytes travel up the epidermis layer towards the stratum corneum
3. Melanocytes transfer melanin to keratinocytes and act as protection against radiation
4. As keratinocytes travel up the epidermis, they lose their nucleus and becomes flat and dead

Question 7

Why is the skin soft, while the nails are hard, even though they are both made up of keratin?

Answer 7

Keratin in the skin is processed into keratohyaline granules, which is a softer type of keratin.

Keratin in nails are usually cross-linked, which confers their rigidity

Question 8

What are some properties of the stratum corneum?

Answer 8

• Controlled permeability
• Antimicrobial
• Antioxidant
• Mechanical protection
• UV protection

Question 9

What is the purpose of having a controlled permeability of the stratum corneum?

Answer 9

To avoid dehydration via trans-epidermal water loss (TEWL) and to prevent ingress of toxic and unwanted substances

Question 10

What gives the stratum corneum its antimicrobial property?

Answer 10

• Acidified pH of around 5.5 (which is partly due to presence of resident microflora); not optimal for growth of most pathogenic bacteria
• Presence of antimicrobial peptides
• Densely-packed cellular layer
• Salty secretions from sweat glands, which creates a hyper-osmotic environment that is unfavourable for most bacteria

Question 11

What is the typical pH range of the skin?

Answer 11

pH 5.4 to 5.9

Question 12

Why are newborn babies prone to microbial attacks?

Answer 12

Their skin pH are slightly more neutral than acidic, which makes them unable to effectively fend off microbial attacks

Question 13

In general, which areas of the body are more prone to microbial attack?

Answer 13

Areas with higher moisture, as they tend to have higher pH (eg. back of wrist, groin)

Question 14

What is the function of deodorants?

Answer 14

To block bad odour either by covering it with parfum or by decreasing pH to decrease axilliary bacteria

Question 15

What is are the characteristic ingredients of deodorants?

Answer 15

• Antimicrobials with a positive charge (eg. Benzethonium chloride)
• Antimicrobials with no charge (eg. Chlorhexidine, Triclosan)
• Natural antimicrobials

Question 16

What is the function of antiperspirants?

Answer 16

Block sweating by temporarily blocking the apocrine sweat glands

When it enters the apocrine sweat gland, it will cause cells at the sweat gland to swell with water

Question 17

What are some characteristic ingredients of antiperspirants?

Answer 17

• Aluminium and/or Zirconium chlorohydrate

- Botulinum toxin

Question 18

What is acne caused by and what is the process of acne formation?

Answer 18

Propionibacterium Acnes

• When sebaceous gland gets clogged, sebum builds up inside the follicle that allows P. acnes to grow rapidly
• Chemicals produced by P. acnes causes inflammation in the follicle and surrounding skin

Question 19

What are the consequences of long-term usage of cosmetics on the skin pH and flora?

Answer 19

May neutralise skin pH and promote bacterial growth

May kill normal resident microflora that is beneficial for the skin

Question 20

What are some antioxidants found in the stratum corneum?

Answer 20

• a- and g-tocopherol (vitamin E)
• ascorbic acid (vitamin C)
• glutathione

Question 21

What gives the stratum corneum its mechanical barrier property?

Answer 21

• Densely-packed corneocytes

- Lipid-filled gaps

Question 22

What is the main component of the stratum corneum that confers UV protection?

Answer 22

Melanin

Question 23

What are the three main entry ways into the skin?

Answer 23

1. Transcellular route
2. Transappendageal route
3. Intercellular route

Question 24

Which of the skin entry ways is the main route for penetration?

Answer 24

Intercellular route

Question 25

In order to pass through via transcellular route, what properties must the molecule possess?

Answer 25

Both lipophilicity and hydrophilicity

Question 26

Why is the transappendageal route a minor entry route?

Answer 26

Enters via the hair follicles, which has variable density in different parts of the body (some parts of the body are devoid of hair follicles)

Molecules needs to have an affinity for the hair follicles

Question 27

What properties does the molecule need to posses to enter via the intercellular route?

Answer 27

Mainly lipophilic property, to pass through the lipid-filled intercellular gaps

Question 28

What are chemical penetration enhancers?

Answer 28

Substances that facilitates entry into the skin