CHAPTER 1
Advanced Dermal Science
The skin
The skin is considered to be the largest organ of the body, which is about 1.5 to 2m squared [1]. It is composed of 3 main layers namely: Epidermis, Dermis and Hypodermis / subcutaneous layer. These layers are designed to serve as a form of protection and thermal regulation for the body. As well as a communication medium between the internal and external environment thus also assisting with the regulation of our immune system and controlled fluid loss `[4].
Epidermis
This is the outermost superficial layer of the 3 layers of the skin mentioned above. It is mainly composed of cells called: keratinocytes and dendritic cells. The thickness of this layer is dependent on the area of the body, for instance the eye lids have the thinnest layer whereas the palms of our hands and souls of our feet have the thickest layers [4].
The epidermis is made up of a further 5 layers listed from the bottom up:
• Stratum basal: is a single layer which is made up of column shaped cells that are tightly packed and is the point of contact with the dermis – it contains active cells that are transported to the surface of the skin through a process known as keratinisation. This layer also contains Melanocytes.
• Stratum spinosum: is the thickest layer composed of up to 10 layers and is made up of squamous cells. You will also find Langerhans cells in this layer. Lamellar granules (which is a type lysosome) of are membrane-bound organelles containing glycoproteins, glycolipids, phospholipids, free sterols, and a number of acid hydrolases, including lipases, proteases, acid phosphatases, and glycosidases [2]. Desmosomes allow for cell-to-cell adhesion between the spinous cells [5]. these desmosomes also help protect against external physical stresses [2].
• Stratum granulosum: the grainy layer which is irregular in shape and size is the reason the thickness is dependent on the area and the proportion to the overlying horny layer [2]. At this stage the cells lose their nuclei which render them as dead and is passed over to the cornified layer.
• Stratum lucidum: this layer is only present in the palms and souls of the feet, which gives it the thickness and transparent colour.
• Stratum corneum: is the most superficial later which is composed of flattened, dead keratinocytes. These cells are then slough off the skin though a process known as desquamation at least every two weeks.
The entire process whereby the basal cells migrate to the stratum corneum is known as keratinisation. This process can take up to 28 days.
The epidermis is also the home to 3 specialised cells:
Melanocytes – produce melanin which is responsible for giving the skin its pigment.
Langerhans cells – is the first point of defence in the skins immune system as they are involved in a veriety of T-cell responses inorder to process antigens found in the epidermis. They can be found in other organs of the body such as: the mouth, oesophagus, vagina and lymphoid organs. [2]
Merkel cells – Are oval – shaped. They are touch receptors that are located in the stratum Basale. The denser the cells are in a region results in higher tactile sensitivity in those areas, therefore Merkle cells are found in great concentration in finger tips, lips, outer root of the hair sheath and on the face. [2]
The Acid Mantle
Also known as hydrolipid film [17] is the invisible acid film that is on the surface of the skin which have the function of preventing bacteria and fungus from growing on the skin. The acid mantle is the perfect mixture of: water, lactic acid, fatty acids (which are secreted from our apocrine and sebaceous glans) and eccrine gland secretions [17]. These form as a protective layer to assist with the metabolism of the skin and balancing the pH of the skin.
The pH of the skin should be between 5.5 and 5.7 (more on the acidic side). The acid mantle helps reinforce the pH of the skin to prevent unhealthy skin conditions however external factors do alter the pH of the acid mantle such as environmental concerns, daily skin care routines, smokers, alcohol consumption… to name a few.
Another important part of this protective layer is the Natural Moisturising Factor (NMF) which is made up collectively of substances that draw water from the atmosphere. NMF also plays a vital role in maintaining the acid mantle of the skin. The amount of NMF in the skin gradually decreases with age and that is when we start seeing signs of pre-mature ageing in the skin, as this is a vital part in maintaining the skin elasticity.
The Dermal – Epidermal Junction
This the section between the epidermis and the dermis. It creates a tight bond between the dermis and the epidermis. Some may say that this layer plays a huge role in ageing.
Structure:
• The basal epidermal cell membrane / Plasma membrane
• Lamina lucida – Rich in laminin and forms an adhesion structure with hemidesmosomes. Hemidesmosomes in the point of connection / biding of the basal layer and the lamina, it is also the link between the extracellular matrix and the intracellular microfilaments.
• Lmina Densa – Thickness varies with age. Consists of type IV collagen, this part is much thicker in males than in females.
• Fibrillar zone – are anchored with fibres that are made up of type VII collagen, this connects the lamina densa to the papillary dermis or may join two parts the lamina densa together.
Functions:
1. Controls cellular and molecular exchanges between the two layers as it is a semipermeable barrier.
2. Plays a role in wound healing due to glycoproteins.
3. Detects and controls cell polarity and direction of growth [2]
Epidermal Appendages
The epidermal appendages involve the eccrine and apocrine glands, ducts and pilosebaceous units, all of which initiate their development at the epidermis as a downward growth. James et al.,2006 showed that areas with higher quantities of pilosebaceous units are able to reepithelialise much quicker after and injury. These areas include the face and scalp [2].
Eccrine sweat glands Apocrine sweat glands
Thermoregulation Scent secretion
Open directly onto the skin Open into pilosebaceous follicle
Smaller in size Larger in size
Located in high volumes on palms of hands and souls of feet. Located under armpits, genital area and around nipples
High amount of sodium Produce thick bioproduct due to protein concentration.
Odourless May have a bad odour
Active in kids Only active from adolescence
[14]
Sebaceous Glands
Is a tiny coiled shaped gland that is attached to the hair follicle and secrets a fatty substance also known as, sebum, it is released into the hair follicle which it travels up and then reaches the external part of the skin [15]. Triglycerides make up almost 50% of sebum.
This also prevents water loss in the skin. Sebum production is controlled by a couple of factors however the most common cause of excess sebum production in the skin is due to the male hormone, testosterone, which causes acne in adolescent teens.
Although sebaceous glands are found all over the body it is found in large amounts in the face and scalp and in least amounts on the palms of hands and souls of feet [ 2/15].
Dermis
The dermis is the middle layer of the three layers that make up the skin. It is a collective layer that includes blood capillaries (where other blood cells may enter due to certain stmuli), oil glands (sebaceous glands), sweat glands (Apocrine and eccrine glands), nerve endings, the hair follicle is also present in the dermis and connective tissue namely;
Collagen:
Elastin and
Fibroblasts (it is higher in number in infants than in adults) [21]. The dermis protects the skin from mechanical injury and also houses sensory receptors which is responsible for tactile responses of the body to extermal stimulation.
The dermis is divided into two parts:
Papillary dermis
This is the thinnest layer and lies on top of the reticular dermis.
Reticular dermis
The reticular layer which is below the papillary layer is the thickest layer containing dense connective tissue.
References
1. Ross and Wilson ANATOMY and PHYSIOLOGY in Health and Illness l 11th EDITION ; Pg354
2. https://www.ons.org/sites/default/files/publication_pdfs/1%20SS%20Skin%20Cancer_chapter%201.pdf
3. https://www.derm-hokudai.jp/shimizu-dermatology/pdf/01-05.pdf
4. https://www.verywellhealth.com/skin-anatomy-1068880
5. https://en.wikipedia.org/wiki/Desmosome
6. https://www.bing.com/images/search?view=detailV2&ccid=yBMzHfMl&id=8125A5C8CF150032CCB0B87BC26FAF43E6817858&thid=OIP.yBMzHfMlph2ehIcKdvFAaAHaF1&mediaurl=http%3a%2f%2fencyclopedia.lubopitko-bg.com%2fimages%2fEpidermis.jpg&exph=484&expw=614&q=epidermis+&simid=608025539288500605&selectedIndex=5&ajaxhist=0
7. https://www.bing.com/images/search?view=detailV2&ccid=vv67XXk9&id=403D3684E4BB8589C730BE39D4ABB61383A9134D&thid=OIP.vv67XXk9OOTTezqIfLKgswHaD2&mediaurl=http%3a%2f%2fwww.molcare-consulting.com%2fwp-content%2fuploads%2fHautengl600dpib.jpg&exph=625&expw=1200&q=Epidermis+Layers&simid=608048946937200748&selectedIndex=16&ajaxhist=0
8. https://healthjade.com/epidermis/
9. https://merkelcell.org/about-mcc/what-is-a-merkel-cell/
10. https://biologiedelapeau.fr/spip.php?article18
11. https://www.cebelia.paris/en/content/31-la-jonction-dermo-epidermique
12. https://emedicine.medscape.com/article/1294744-overview
13. https://emedicine.medscape.com/article/1294744-overview#showall
14. https://www.wisegeek.com/what-is-the-difference-between-eccrine-and-apocrine-glands.htm
15. https://www.britannica.com/science/sebaceous-gland
16. https://www.reddit.com/r/AsianBeauty/comments/4ajksl/skin_basics_161_the_acid_mantle_sweat_and_sebum/
17. https://thenakedchemist.com/understanding-the-acid-mantle/
18. https://thenakedchemist.com/understanding-the-ph-scale/
19. https://www.bing.com/images/search?view=detailV2&ccid=Qm%2fPDmxu&id=585ACD36BA04E9EA3B593D5F21C516DE8C6C9E8D&thid=OIP.Qm_PDmxuXY9nbA4MSiSaLwHaFj&mediaurl=http%3a%2f%2fslideplayer.com%2f7865847%2f25%2fimages%2f22%2fThe%2bDermal-Epidermal%2bJunction.jpg&exph=720&expw=960&q=the+dermal-epidermal+junction&simid=608026192138863742&selectedIndex=4&ajaxhist=0
20. https://medium.com/@fromnature.ca/what-is-nmf-natural-moisturizing-factor-and-why-is-essential-for-your-skin-d55a741b3790
21. https://www.verywellhealth.com/skin-anatomy-1068880
2019-2-21-1550745457