L10: Skin Anatomy and Physiology Flashcards
What are the 3 main layers of the human skin, starting from the outermost layer?
- Epidermis
- Dermis
- Hypodermis
Where are hair follicles found in?
Dermis
What are hair follicles associated with?
Sebaceous gland
What are the physiological processes in the hair follicles?
- 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
What is the outermost layer of the epidermis called?
Stratum corneum
What is the physiological process in the epidermis layer?
- New keratinocytes are produced at the bottom layer of the epidermis
- Keratinocytes travel up the epidermis layer towards the stratum corneum
- Melanocytes transfer melanin to keratinocytes and act as protection against radiation
- As keratinocytes travel up the epidermis, they lose their nucleus and becomes flat and dead
Why is the skin soft, while the nails are hard, even though they are both made up of keratin?
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
What are some properties of the stratum corneum?
- Controlled permeability
- Antimicrobial
- Antioxidant
- Mechanical protection
- UV protection
What is the purpose of having a controlled permeability of the stratum corneum?
To avoid dehydration via trans-epidermal water loss (TEWL) and to prevent ingress of toxic and unwanted substances
What gives the stratum corneum its antimicrobial property?
- 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
What is the typical pH range of the skin?
pH 5.4 to 5.9
Why are newborn babies prone to microbial attacks?
Their skin pH are slightly more neutral than acidic, which makes them unable to effectively fend off microbial attacks
In general, which areas of the body are more prone to microbial attack?
Areas with higher moisture, as they tend to have higher pH (eg. back of wrist, groin)
What is the function of deodorants?
To block bad odour either by covering it with parfum or by decreasing pH to decrease axilliary bacteria
What is are the characteristic ingredients of deodorants?
- Antimicrobials with a positive charge (eg. Benzethonium chloride)
- Antimicrobials with no charge (eg. Chlorhexidine, Triclosan)
- Natural antimicrobials
What is the function of antiperspirants?
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
What are some characteristic ingredients of antiperspirants?
- Aluminium and/or Zirconium chlorohydrate
- Botulinum toxin
What is acne caused by and what is the process of acne formation?
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
What are the consequences of long-term usage of cosmetics on the skin pH and flora?
May neutralise skin pH and promote bacterial growth
May kill normal resident microflora that is beneficial for the skin
What are some antioxidants found in the stratum corneum?
- a- and g-tocopherol (vitamin E)
- ascorbic acid (vitamin C)
- glutathione
What gives the stratum corneum its mechanical barrier property?
- Densely-packed corneocytes
- Lipid-filled gaps
What is the main component of the stratum corneum that confers UV protection?
Melanin
What are the three main entry ways into the skin?
- Transcellular route
- Transappendageal route
- Intercellular route
Which of the skin entry ways is the main route for penetration?
Intercellular route
In order to pass through via transcellular route, what properties must the molecule possess?
Both lipophilicity and hydrophilicity
Why is the transappendageal route a minor entry route?
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
What properties does the molecule need to posses to enter via the intercellular route?
Mainly lipophilic property, to pass through the lipid-filled intercellular gaps
What are chemical penetration enhancers?
Substances that facilitates entry into the skin
