Skin Layers Flashcards
skin histology, skin layers, layers of the epidermis, structures of the skin, functions of the skin
List the functions of the skin. (6)
protection, sensation, heat regulation, excretion, secretion and absorption
What is sebum? Why is it important?
Sebum: an oily substance that protects the surface of the skin & lubricates both skin and hair.
○ TEWL: protects from trans-epidermal water loss, helps keep skin moisturized
○ Protection against microbes: Sebum is slightly acidic, with a pH of between 4.5 and 6.0. As a result, it helps prevent harmful pathogens, such as bacteria and viruses, from penetrating the skin.
○ Antioxidant transport: Sebum transports fat-soluble antioxidants to the surface of the skin. Antioxidants are natural compounds that protect against the damaging effects of free radicals.
How does the skin protect itself?
○ Acid mantle: protective barrier made up of sebum, lipids, sweat and water that form a hydrolipidic film to protect skin from drying out (TEWL) and exposure to external factors.
○ Fibroblast cells: help rejuvenate and repair skin quickly. Produce collagen (wound-healing & structure) and elastin (elasticity)
○ Melanin: protection from the sun. Melanin protects cell’s nucleus from damage from UV rays
What regulates body temperature?
Vasodilation: protection from heat
□ Blood vessels dilate, perspiration from sweat glands cools the body Vasoconstriction: protection from cold
□ Blood vessels contract, blood flow decreases
□ arrector pili muscle contracts causing goosebumps, hair stands up trapping heat near the body
What are sebaceous glands? What do they produce?
Secretory glands that produce sebum (oil). Very active during puberty and are affected by hormones.
What are the 3 main layers of the skin?
- Hypodermis (deepest)
- Dermis
- Epidermis (superficial)
Name the 5 layers of the Epidermis.
- Stratum germinativum/basal (germinative/basal layer)
- Stratum spinosum (spiny layer)
- Stratum granulosum (granular layer)
- Stratum lucidum (clear layer)
- Stratum corneum (horny layer)
Name the 5 types of cells that make up the epidermis.
- Stem cells: replacement cells (fibroblasts)
- Keratinocytes: compose the majority of the epidermis
- Melanocytes: produce melanin
- Tactile cells: aka Merkel cells, touch receptors
5, Dendritic cells: aka Langerhans cell, immune cells
Describe the germinative layer.
- live layer of the epidermis located directly above the dermis
- cells are constantly undergoing mitosis here, creating new keratinocytes that migrate toward the skin’s surface. (process takes 3-4 weeks)
- melanocytes produce melanin in this layer.
- tactile (merkel cells) also found here
What is melanin? How is it produced? What is this process called?
- Melanin is a dark protein pigment responsible for skin, hair and eye colour.
- Melanogenesis is the highly complex process of melanin production.
Initiated by 3 factors:
- Melanocyte-stimulating hormone (MSH)
- Adrenal corticotropic hormone
- Exposure to ultraviolet (UV) light and irritation
Melanin pathway:
- Damage to DNA triggers melanocyte stimulating hormone to produce melanin (tyrosine {amino acid} + tyrosinase [enzyme])
- Melanocytes produce melanosomes which are transferred into keratinocytes through dendrites
- Melanosomes cluster over the nucleus of the keratinocyte to protect DNA from further damage
What are melanocytes?
Cells that produce pigment granules called melanosomes that produce the melanin protein. Produced in the stratum germinativum.
What are dendrites?
the “arms” or cellular projections that branch out to interact with other cells in the intercellular matrix
What are keratinocytes?
cells that produce keratin in the stratum germinativum
Describe the stratum spinosum.
- aka the spiny layer due to prickly, spine-like cells called desmosomes. Langerhans cells are mostly found here
- largest layer of the epidermis. consists of several layers of keratinocytes. cells continue to change shape here, enzymes create lipids and proteins
What are desmosomes?
keratin filaments that make up the intercellular layer. (hold cells together)
What are Langerhans cells?
immune/guard cells that sense unrecognized foreign invaders and process antigens for removal through the lymphatic system.
Describe the stratum granulosum .
- composed of 3-5 layers of flat keratinocytes containing coarse, dark-staining keratohyalin granules.
- NMF and keratin are produced here
- enzymes destroy desmosomes holding cells together, also causing cell death
what are NMF?
Natural Moisturizing Factors: triglycerides, ceramides, waxes, fatty acids and other intercellular lipids that are excreted from cells to form components of the skin’s waterproofing barrier function of the top layer. Produced in the stratum granulosum
Describe the stratum lucidum.
- a thin, clear layer of dead skin cells named for its translucent appearance.
- thickest on palm and soles, provides grip and forms fingerprints
- cells here release lipid forming bilayers of oil and water.
- keratinocytes in this layer contain clear keratin
Describe the stratum corneum.
-the outermost layer of the epidermis, consisting of up to 30 layers of dead cells called corneocytes. It forms a barrier to protect underlying tissue from infection, water loss, chemical stress, abrasion etc.
What is the squamous layer?
- the most superficial layer of the stratum corneum consisting of flat, scale-like keratinized cells called squamous epithelial cells. it is the visible layer of the skin.
- cells here are constantly being brushed, rubbed, and washed off.
What is desquamation?
the process of dead cells shedding from the stratum corneum. process takes approx. 2-4 weeks.
Describe the dermis.
middle layer of the skin found between the epidermis and hypodermis. it has an essential role in transportation, protection, and repair. Blood vessels, nerves, sweat glands, arrector pili muscle, and hair papillae are found here.
What are the two layers of the dermis?
papillary layer (superficial) and reticular layer (deep)
Describe the papillary layer.
- the top layer of the dermis directly beneath the epidermis, Consists of 10-20% of the dermis. Touch receptors (merkel cells), blood vessels, and capillaries are found here.
- Connects the dermis to the epidermis forming the epidermal-dermal junction.
Describe the structures that form the epidermal-dermal junction.
Dermal Papillae: upward waves, finger-like extensions of the dermis that deliver nutrients to the epidermis via looped capillaries.
Epidermal ridges: downward waves, extensions of the epidermis
Describe the reticular layer.
-deeper layer of the dermis, containing proteins that give skin its strength and elasticity, i.e., collagen and elastin. Makes up to 80% of the dermis
What are fibroblasts?
specialized cells located mainly in the reticular layer of the dermis that produce collagen and elastin.
what is collagen?
a protein substance of complex fibers that gives skin its strength and is necessary for wound healing. part of the dermal substance.
What is elastin?
a fibrous protein that forms elastic tissue, gives skin its elasticity. part of the dermal substance.
what are GAGs?
glycosaminoglycans: large protein molecules and water-binding substances found in between the fibers of the dermis (e.g., hyaluronic acid) . part of the dermal substance.
what are mast cells?
specialized immune cells involved in allergic reactions, numerous around the eye area. found in the dermis
what are leukocytes?
white blood cells that fight infection, located in the dermis
describe the hypodermis
composed of 80% adipose/subcutaneous/fat tissue, deepest layer of the skin beneath the dermis.
- reduces heat loss, stores food to create energy, and provides a protective cushioning for the body.
- layer decreases with age.
what are the three main classifications of nerves in the skin?
a. Sensory (afferent)
b. Motor (efferent)
c. Mixed (sensory & motor)
what are the 5 types of sensory nerves?
a. Meissner’s Corpuscle
b. Krause End Bulbs
c. Ruffini’s Endings
d. Merkel’s Corpuscle
e. Paccinian Corpuscle
what are sudoriferous glands?
sweat glands. Help regulate body temperature and eliminate waste products through excretion of sweat
describe the 2 types of sweat glands
a. eccrine:
- open to skin surface and located all over the body.
- not connected to hair follicles.
- sweat from these glands doesn’t have an offensive odour (99% water with a pH of 4-6, acidic)
b. apocrine:
- found mainly in underarm, genital, anal canal, areola and beard area. become active at puberty
- scent glands that produce pheromones and respond to stress and sexual stimulation.
- produces an alkaline secretion that produces an odour due to interaction with bacteria
- secretes into the hair follicle
