the dynamic natural skin care: function

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Monday, October 13

Melanocytes function

Home › Melanocyte-stimulating hormone › Function of melanin › What are melanocytes › Melanocytes function.

What are the functions of melanocytes?

The classic melanocytes function is melanin pigment synthesis.

The non-classical, non-cutaneous melanocytes dispersed across the body carry out a variety of functions depending on their locations. They may retain common lineage signature function of melanin pigment synthesis. The type of melanin pigment (eumelanin or pheomelanin) produced and their relative proportion in the skin decides one's skin color.

Melanocyte precursors cells differentiate and migrate from the neural crest via the mesenchyme into the epidermis and hair follicles. Classical melanocytes are pigment producing cells, which are found in the dermis, epidermis and hair follicles. During development they follow the dorsolateral migratory pathway. Nonclassical melanocytes migrate to several non-cutaneous sites. Interacting continuously with the surrounding tissues, they makeup local populations having different functions. The non-cutaneous sites include eyes, inner ear, brain, leptomeninges and heart.

Classical melanocytes functions

In many species of animals the melanocytes have evolved to provide camouflage from prey and predators. In humans, protection against UV radiation has evolved as one of the primary functions of the pigment producing cells. Skin pigmentation, being the most apparent display of human polymorphic traits, defines ethnicity and race.

UV radiation causes cellular damage and DNA damage. The cap-like melanin pigment accumulation above the nucleus of the keratinocyte, protects the nucleus from the DNA damage. The antioxidative and redox signaling activity during of the melanogenesis process neutralizes the harmful free radicals in the skin. The hair color is also due to the pigment deposit in the hair shaft. Grey hair appears when the melanocytes in the hair follicle stop producing and depositing melanin.

The highly reactive quinone intermediates produced during melanogenesis have antibacterial and antifungal properties. The post inflammatory hyperpigmentation by the melanocytes dampens the inflammatory response and suppresses inflammation. They also interact with Langerhans cells and regulate skin immune response.

Nonclassical melanocytes functions

The presence of the melanocytes and melanin is necessary for the proper functioning of inner ear, eyes, heart and brain.

Melanocytes function in eyes

Pigment cells are found in retinal pigment epithelium (RPE) and uveal tract in the eyes.

RPE
RPE melanin is essential for the development of neural retina. RPE cells are thought to produce melanosomes only during the prenatal period. RPE melanin protects the neural retina from reactive oxygen species and macular degeneration. RPE also provides visual acuity.

Uveal melanocytes
The uvea, the middle layer of eye, is divided into choroid, ciliary body and iris. All the three parts have pigment cells. The pigment cells of the iris impart the eye color to an individual. The pigment in the choroid is believed to protect the cells from oxidative damage by free radicals.

Functions of melanocytes of the inner ear

The pigment producing cells are found in the cochlea and the vestibular organ. The lack of these cells or lack of inner ear melanocyte function can lead to deafness.
Cochlear melanocytes are present within the stria vascularis and the modiolus. They are essential for the proper development and function of cochlea.
The vestibular labyrinth of the inner ear also has pigment cells. It is believed that they may be associated with balance perception.

The melanocytes of the heart

These group of cells are found in the valves and septa of the heart. Cardiac pigment cells, though appear not essential for heart activity, are found to trigger atrial arrhythmia. They may be regulating Ca levels and redox signaling.

Functions of the melanocytes of the brain

These cells are found in the sympathetic cephalic ganglia and leptomeninges. The melanocytes are also found along cerebral capillaries. The ventrolateral surfaces of the medulla oblongata are covered by the pigment cells. Endocrine and redox activity are attributed to these cells. The pigment present is brain-specific neuromelanin.

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Reference:
1.Tsatmali M, Ancans J, Thody AJ. Melanocyte function and its control by melanocortin peptides. J Histochem Cytochem. 2002 Feb;50(2):125-33.
2.Gertrude-E. Costin, Vincent J. Hearing. Human skin pigmentation: melanocytes modulate skin color in response to stress. The FASEB Journal vol. 21 no. 4 976-994.

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Alopecia areata totalis.
Alopecia areata universalis.
Post inflammatory hypopigmentation.
Piebaldism.

Current topic in dynamic skin care: Melanocytes function.

Get glowing skin complexion. Remove acne scars and blemishes from face.

Wednesday, September 17

Melanin in skin - Function of melanin

Home › Melanin pigment › Function of melanin - Melanin in skin.

The primary function of melanin is in skin pigmentation. Melanin has other important roles in the human body such as, sunlight absorption and sun screening, protection from ultraviolet radiation, charge-transfer redox activity, free radical scavenging, antimicrobial immune defense, immunomodulation and ion chelating.

Melanin in skin

Melanins are a broad spectrum of very common natural pigment compounds found in both the plant and animal kingdoms. It is a complex molecule derived from the amino acid tyrosine via the intermediate product L-DOPA, by the action of the tyrosinase enzymes. There are three basic types of melanin, namely, eumelanin, pheomelanin, and neuromelanin. Variation in human skin color is a result of density and relative proportions of contributing melanins.

Function of melanin

In plants and invertebrates, melanin is involved in immune defence. In certain pathogenic microbes, bacteria and fungi, these pigments function as defence mechanisms against the host's immune responses.

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Though many other functions are attributed to melanins in plant and animal kingdoms, herein we will consider their functions related to the human body.

Skin pigmentation: Melanin, whose primary function is in pigmentation, has many more important functions to perform in the human body.

Protection from UV radiation: Melanin functions as a sunscreen and as a broad spectrum sun radiation absorbent. The absorbed energy causes redox reactions, and both eumelanin and pheomelanin form free radical species. Eumelanin, being more photostable scavenges the originated oxidative species and neutralizes them. However, pheomelanin being more photolabile may not neutralize all the oxidative free radicals. Free radicals have the potential to cause DNA damage. Hence, fair individuals, having high amounts of pheomelanin, are more prone to skin cancers on sun exposure.

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Melanin in the eyes: Melanin in the iris, protects the retina from excessive light and photodamage. By absorbing the scattered light within the eyeball, it also helps in improving the visual acuity. Melanin in the retinal pigment epithelium (RPE) has antioxidant properties and neutralizes the photooxidative species. The antioxidative activity wanes with aging and one of causes of macular degeneration is oxidative stress.

Melanin in the ears: The melanin pigment is present in the inner ear with no known function. In Waardenburg syndrome, deafness occurs along with reduced inner ear pigmentation. In the inner ear, the loss of melanocytes in stria vascularis of cochlear duct is associated with loss of hearing.

Melanin in the brain: The substantia nigra pars compacta is a part of the midbrain, which appears darker than the surrounding areas due to the presence of neuromelanin in dopaminergic neurons. Degeneration of the pigmented neurons or depigmentation is found in persons affected with Parkinson's disease. It is hypothesized that neuromelanin may be neutralizing the oxidative stress and chelating the toxic metal ions in the brain. The decrease in neuromelanin, as observed in Parkinson's disease may be the cause of the associated degenerative symptoms.

Melanins also function as chelating agents. They can chelate metal ions, including toxic species, and protect the cells from damage. Melanins can also bind with a number of organic molecules and neutralize their damaging effects.

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Melanins behave as semiconductors. Thin melanin films having multifarious electrical and optical properties can be made by spray deposition. Having interesting biophysical properties, melanin opens up many new biotechnological applications.

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Reference:
1.Michaela Brenner, Vincent J. Hearing. The Protective Role of Melanin Against UV Damage in Human Skin. Photochem Photobiol. 2008; 84(3): 539–549. 2.F. Solano. Melanins: Skin Pigments and Much More—Types, Structural Models, Biological Functions, and Formation Routes. New Journal of Science, vol. 2014, Article ID 498276, 28 pages, 2014. doi:10.1155/2014/498276. 3.Burkhart, C. G. and Burkhart, C. N. The mole theory: primary function of melanocytes and melanin may be antimicrobial defense and immunomodulation (not solar protection). International Journal of Dermatology, 44: 340–342.

Interesting topics:
Terminal hair.
Hypertrichosis definition.
Eyelash hypotrichosis.
Short anagen syndrome.
Anagen effluvium causes.
Anagen phase.
Stages of hair growth.
Scleromyxedema.
Alopecia mucinosa.
Alopecia barbae treatment.
Alopecia totalis causes.
Alopecia areata universalis.

Current topic: What is the function of melanin in skin.

Get glowing skin complexion. Remove acne scars and blemishes from face.

Sunday, January 20

Stratum granulosum definition - Stratum granulosum layer function

Home › Know your skin › Epidermis › Definition and function of stratum granulosum layer
Stratum granulosum is a well defined region of epidermis found under the lucidum layer in the palms and soles and under corneum in the other areas of the skin.

As granulosum has visible granules, it is also known as granular layer. Among the five sublayers of epidermis of skin, granulosum is in the middle having spinosum and lucidum layers on the inner and outer sides.

Definition of stratum granulosum

Stratum granulosum is defined as "the layer of epidermis just under the stratum corneum or (on the palms and soles) just under the stratum lucidum; contains cells (with visible granules) that die and move to the surface." by wordnetweb.princeton.edu/perl/webwn.

Structure and function of stratum granulosum

Skin structure showing granulosum layer of epidermis

Skin structure showing stratum granulosum

In the regions of the body, where the skin is thin, there is no clear cut differentiation between granulosum and lucidum tiers. Under the microscope, this tier appears grainy and consists of 2-5 cell thickness. These grainy, granular or granulosum cells are the keratinocytes, which have migrated from the lower spinosum. These are the last layer of living cells which are in the process of losing their nuclei and dying.

These squamous cells have many basophilic granules called keratohyalin granules which are small and are not bound by membrane. Filaggrin, a type of protein, is found in large quantities in theses cells and is believed to bundle keratin. Lipid containing lamellar granules are present which are bound by membrane. These membrane-bound granules secrete the contents to extracellular space by exocytosis (peni-cytosis) and give rise to sheets of waterproof fatty barrier. This barrier function also prevent nutrients diffusion from the lower cells, leading to death of cells.

Tuesday, January 8

Stratum lucidum definition - Function of stratum lucidum layer

Home › Know your skin › Epidermis › Definition and function of stratum lucidum layer
Stratum lucidum is a well defined epidermal layer found under the corneum region of the skin of the palms and soles. Main function of this stratum is to help the skin handle friction and also waterproof it.

It is a thin transitional layer of epidermis found between the 'horny' and 'granular' layers. However in the rest of the body where the skin is thinner, this stratum does not appear differentiated from the granular region.

Stratum lucidum definition according to Merriam-Webster is: "a thin somewhat translucent layer of cells lying superficial to the stratum granulosum and under the corneum especially in thickened parts of the epidermis (as of the palms or the soles of the feet).

1.Epidermal skin showing stratum lucidum

Stratum lucidum is defined as "the layer of epidermis immediately under the corneum in the skin of the palms and soles" by wordnetweb.princeton.edu/perl/webwn

Skin structure showing stratum lucidum

This transparent or translucent layer is composed of three to five tiers of dead keratinocytes. Here these cells do not have distinct boundaries and are flattened. These dead keratinocytes contain a clear intermediate form of keratin called eleidin. The presence of melanosomes may determine the level of its darkness. They are surrounded by fatty substance, probably as the result of the exocytosis of lamellar bodies in the previous tiers. The presence of the oily substance is responsible for the waterproofing function. This barrier function makes the inner regions fairly impermeable to water from outside as well as preventing loss of water from inner cells. Another probable function of this tier is in reduction of friction.

Monday, January 7

Stratum spinosum - Prickle cell layer - Functions of stratum spinosum

Home › Know your skin › Epidermis › Functions of stratum spinosum (Prickle cell layer)
Stratum spinosum or prickle cell layer of the epidermis has the vital function of Keratinization. Prickle cell layer is the fourth tier from the exterior and is situated between stratum granulosum and germinativum (basale).

The basale and spinosum keratinocytes are together denoted as Malpighian layer. This prickle tier ranges between 5-10 keratinocytes in thickness and the keratinocytes are modified basal keratinocytes having large nuclei which contain very prominent nucleoli.

Keratinization process begins in stratum spinosum. The large pale staining nuclei of prickle layer, function actively to synthesize cytokeratin, a type of fibrillar protein. Cytokeratin builds up within the keratinocytes and aggregate together to form tonofibrils. These tonofibrils form desmosomes which radiate from the keratinocytes forming points of intracellular connections between adjacent prickle keratinocytes. However it is to be noted that there is no continuity of cytoplasm through the 'prickles' of adjacent spinosum keratinocytes.

The name spinosum denotes the prickle or spiny appearance of the keratinocytes due to the radiating desmosomes. This net-like prickle tier provides protection to the underlying tissues. This net-like spinosum also gives some elasticity and flexibility to the epidermis. The prickle cells tier is thicker in areas of skin subject to frequent abrasion such as palms and soles.

One of the important function of the spinosum keratinocytes is the production of lamellar bodies having polar lipids, free sterols, phospholipids and enzymes. Bipolar lipids are produced and retained by these prickle keratinocytes, whose function is prevention of loss of moisture from the skin.

This spinosum layer contains Langerhans cells which are macrophages with the function of protection against pathogens. Langerhans macrophages contain Birbeck granules also known as Birbeck bodies, which are rod shaped with a striated appearance. Birbeck granules function in receptor-mediated endocytosis and phagocytosis. The origin of Langerhans cells is in the bone marrow and they migrate to this prickle region of epidermis. As these polyhedral spinosum keratinocytes approach the granulosum tier they get gradually flattened. Mitosis (cell division function), which occurs continuously in the basale epidermis is nearly absent in these spinosum keratinocytes.

Illustration of Prickle cell layer (stratum spinosum)

Stratum spinosum layer in epidermis of skin.

Layers of epidermal skin
stratum spinosum (Prickle cell layer)

Like the keratinocytes of basale region, spinosum keratinocytes are also susceptible to mutations caused by sunlight and can become malignant. Prickle cell carcinoma is found in fair-skinned individuals who have a history of longer term sun exposure.

Saturday, January 5

Stratum corneum layer in skin - Function of stratum corneum cells

Home > Know your skin > Epidermis > Function of the stratum corneum cell layer in the skin

Stratum corneum, the outermost layer of the epidermis, has the skin barrier function and is formed by the death of keratinocyte cells. The stratum corneum (SC) is multi layered and is composed of dead, anucleated, flattened corneocytes.

The stratum corneum has a thickness between 10 and 40 μm and may contain 15-20 layers. These corneocytes are embedded within the multiple lamellar sheets of lipid matrix formed by specialized lipids.

Formation of stratum corneum and desquamation

Epidermis is the outermost layer of skin and it consists of five sublayers. Its main function is to protect underlying tissues and organs from pathogens, toxic agents, oxidants, dehydration, chemicals, environment, ultraviolet radiation and physical stress. Epidermis functions very dynamically and renews continuously.

A continuous process of cell proliferation takes place in the lowermost layer of epidermis known as basale layer. These cells moving outwards undergo maturation and after a number of changes become keratinocyte cells . Eventually these cells die and form the stratum corneum to function as a barrier and get replaced and shed by the desquamation process.

Stratum corneum layer cells in skin-function

Function of stratum corneum
layer cells in skin

The process of living keratinocytes undergoing transformation into non-living corneocytes is called cornification. As the living keratinocyte cells die, they lose the nuclei and organelles. Their cell membranes undergo changes and ceramides replace them and a cornefied envelope of structural proteins is linked to them.

Desmosomes (corneodesmosomes) which are molecular complexes of cell adhesion proteins and cell linking proteins, bind these corneocytes in the outer st. corneum. As these protein complexes move towards outer region of st. corneum, protein degrading proteases, break them up which leads to desquamation.

Function of stratum corneum

This layer functions as a barrier protecting the inner layer of epidermis from dehydration and also from invasion of pathogens. Stratum corneum contain a dense network of a protein known as keratin. Keratin keeps the epidermis hydrated by absorbing moisture as well as by preventing water evaporation.

The st. corneum by the nature of its structure, makes the epidermis elastic and a glutenous protein bond pulls the epidermis back to its original natural shape.

Another important action of S. corneum is in providing protection from mechanical injuries. To carry out this action, this layer is typically thicker in palms and soles. To some extent it helps in the absorption of moisturizers, holding them back from immediate loss.

Effects of defects in stratum corneum

The formation of corneocytes and their desquamation in a regulated manner is very essential for the maintenance of healthy skin. Any failure or set back in these regulated processes can give rise to skin disorders and ailments. A collection of low-molecular-weight water-soluble components, known as the natural moisturizing factor (NMF) present in st. corneum act as a humectant absorbing moisture by direct contact and also from atmosphere.

These barrier and moisturizing properties can be deranged by intrinsic factors like skin diseases and excessive sebum production or xerosis. Extrinsic factors like weather, temperature, low humidity, surfactants and chemicals can also impair the moisturizing barrier. Mental and physical stress can also have effects on the function of stratum corneum cell layers by the increase in the circulating stress hormones in the skin.

Sunday, December 30

Hypodermis layer - Function of hypodermis

Home › Hypodermis layer - Hypodermis function
Hypodermis, also known as subcutaneous tissue, has important functions. Hypodermis layer lies immediately below the dermis.

It is the lowermost layer of our integumentary system. Though hypodermis is not part of the skin, it is very essential for anchoring the skin to the body. Though both dermis and hypodermis are derived from mesoderm, unlike dermis, this layer is not derived from dermatome region.

Subcutaneous tissue layer has many types of cells in it like fibroblasts, fat cells (adipocytes) and leukocytes. Fibrous bands and elastins are found in this region of integumentary system, anchoring the cutaneous layer (skin) to the deep fascia fat. Sudoriferous glands (sweat glands), papilla region of hair root and pacinian corpuscle (a type of nerve ending) are found in the junction of dermis and hypodermis.

Blood vessels and lymphatic vessels traverse this region, carrying the blood and lymph to the dermis. At the junction of dermis and subcutaneous tissue, arteries form deep cutaneous plexus. Its function is to supply oxygen and nutrients to the tissues in the hypodermis, dermis, hair follicles, sebaceous glands and sweat glands.

The thickness of hypodermis varies considerably in respect of body area, nutritional status, age and gender of the individual. In thin areas of the skin like eyelids, genitals, and nipples, it is nearly absent. With aging drastic changes take place in the hypodermis. It begins to thin out and disintegrate causing deep wrinkles, folds and sagging of the facial skin.

The fat storing cells, adipocytes, are grouped together in lobules separated by connective tissue. Hormones in adults have effect on the pattern of hypodermis fat distribution function. In men fat tends to accumulate over the abdomen, torso and shoulders and in women fat accumulates on the breasts, waist, hips, buttocks and thighs. In weight loss there is usually changes in the amount of lipid content of the adipocytes and not in their number.

The adipose fat also functions as a cushion and padding against pressure and friction, absorbing shocks from impacts to the skin. Fats stored in this layer also functions as energy reserve and the fat is put back into circulation when needed. Another function is in providing thermal insulation to the inner body to slow down heat loss. This helps in the regulation of body temperature. Children and elderly people have less storage of adipose fat in their subcutaneous tissue and are more sensitive to cold.

Panniculus carnosus, a layer of flat sheets of striated muscle is found in hypodermis. Their function in humans is seen in some muscles of facial expression, dartos muscle (dartos fascia or tunica dartos) lying beneath the skin of scrotum, palmaris brevis muscle in the ulnar side of hand and platysma muscle found in the neck.

Human skin structure and function
hypodermis layer

In many regions of hypodermis vestigial panniculus carnosus is present and is usually covered by panniculus adipose fatty layer. The function of elastin fibers found in the hypodermis layer is in giving elasticity to skin

Saturday, August 14

Skin care - Skin physiology - Function of epidermis

Physiology of skin - Function of epidermis → function of dermis

Human skin has two important and main layers, dermis and epidermis with different physiology and function.

Epidermis, the outermost layer of skin, functions as a chemical and physical barrier between the interior of the body and external environment.

Its physiology and function include secretion, excretion, insulation, protection and pigmentation. Dermis is the deeper layer and its main action is to provide structural support to the skin.

Skin physiology: function of epidermis in protection

The main action of bottom most layer of epidermis, which lies adjacent to dermis, is the cell multiplication.
The new cells progressively move towards the outer layers, simultaneously maturing and differentiating.

The physiology and shape of the cells also changes and by the time they reach the top most layer, they are flattened, lacking nuclei they become lifeless.
At this stage they are called corneocytes and are filled with keratin proteins capable of water retention and also lipids.
The outer most layer, which contains 10-30 layers of stacked corneocytes, is called Stratum Corneum and is semi-permeable, becoming a barrier between the interior of the skin and external surroundings.
Epidermis physiology also includes functions as physical barrier protecting the internal tissues from bacterial invasion, physical abrasion and ultraviolet rays.

Skin physiology: function of epidermis in thermoregulation, excretion and sensation

In hot weather, skin physiology is tuned to produce sweat.
Sweat on reaching the epidermis surface, evaporates cooling the surface by the latent heat of evaporation.
In response to low temperatures, sweat is decreased and blood flow to the skin is increased to maintain the temperature.
Besides removing excess water and temperature control, the sweating process also removes smaller quantities of waste salts and many organic compounds.
The nerve fibers (Merkel cells) reach upto the outer most layer of dermis and stratum basale and pick up sense signals of touch, temperature, pain and pressure.

Skin physiology: function of epidermis in immunity

Certain specialized cells of epidermis, Langerhans cells, have immune functions.
Though these cells originate from bone marrow, they migrate to epidermis layers.
These dendritic cells have Birbeck granules.
They interact with white blood cells (helper T cells) and help in destroying the invading organisms.
Apart from detection of foreign bodies, Langerhans' cells, have a major role in the physiology of allergies.

Skin physiology: function of epidermis in skin coloration

The black-brown melanin pigment, is produced by the melanocytes present in basal layer of epidermis.
Melanocytes comprise up to 10% of the cells in epidermis.

skin layers

Epidermis and dermis
The slender projections of melanocytes extend to keratinocytes and help in the transfer of melanin granules.
Melanin granules apart from imparting color to skin also protect it from UV rays.
Melanin granules clump on the surface side of keratinocytes, protecting the nucleus from UV light and genetic damage.
The scattering and absorbing of Uv rays by melanin protects the internal cells by blocking free radical formation and damage.

Thus with multiple functions, epidermis plays a major role in skin physiology.

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