Melanocytes/ dental implant courses

References
 Grey`s anatomy,38th
ed
 Oral histology,6th
ed - Tencate
 Oral anatomy, histology & embryology,
3rd
ed – Berkovitz
 Textbook of medical physiology,
10th
ed - Guytonwww.indiandentalacademy.com

Contents
 Introduction
 Embryology
 Structure
 Ultrastructure
 Melanosomes
 Melanogenesis
 Melanin
www.indiandentalacademy.com

Introduction
Two types of cells broadly constitutes the
oral epithelium:
1)Keratinocytes
2)Non-
keratinocytes

Non-keratinocytes -
 Lack desmosomal attachments &
tonofilaments
 Do not participate in the process of
maturation of oral epithelium
 10% of total population of oral epithelium
 Consists of melanocytes, merkel cells,
 Langerhans cells, lymphocyteswww.indiandentalacademy.com

 Stratum basale
(germinativum)
 Single layer of cells on
basal lamina
 Stems cells which give rise
to keratinocytes
 Contain melanin
transferred from
melanocytes
 May see mitotic figures
 Desmosomes and
hemidesmomes

Melanocytes are…
 Melanin pigment forming cells
 Present in epidermis, its appendages, oral
epithelium, some mucous membrane,, parts
of middle and internal ear, etc.
Melanocytes contribute color to the skinMelanocytes contribute color to the skin
and serve to decrease the amount ofand serve to decrease the amount of
ultraviolet light that can penetrate intoultraviolet light that can penetrate into
deeper layers of the skindeeper layers of the skin

They are…
 Capable of producing the brown pigment,
melanin
 Melanin can absorb energy from ultraviolet
(UV) light
 UV light contains high energy photons that
can damage DNA – mutations
 Melanin can prevent damage to DNA, helps
to prevent skin cancer

Melanocytes

Embryology
 Develops from neural crest cells
 Appears in cranio-caudal direction
 Can be identified in epidermis of head in 3rd
month of IU life and in caudal body parts in 4th
fetal month
 Functionally immature during their migration
through the fetal dermis

Structure
 Randomly dispersed cells within basal &
parabasal layer, in people of certain races
found through epidermis
 Small darkly stained nucleus, clear cytoplasm,
no mitotic activity.
 Found wedged between basal cell of
epidermis, at the tips of rete pegs.

 No. of melanocytes varies with body
region and increases with repeated
exposure to light
 Lack desmosomes and tonofilaments
but possess long dendritic processes
that extend in several directions
across several layers of cells

Ultrastructure
 Dendritic nonkeratinocytes lacking desmosomal
attachments with adjacent keratinocytes
 Hang down into superficial dermis and are separated
from the extracellular dermal matrix by the basement
membrane
 Nucleus large ,round and euchromatic

 Cytoplasm has intermediate filaments, prominent
golgi complex, vesicles. endoplasmic reticulum,
mitochondria and melanosomes
 Melanosomes are often aggregated above the
nucleus to form supranuclear caps .
 Melanosomes during their maturation move from
cytoplasm to the dendritic processes .
 At the base where they lie in close apposition with
the lamina densa, show structures resembling
hemidesmosomes.

Development of melanosomes
StageStage ShapeShape SizeSize MelaninMelanin EnzymaticEnzymatic
activityactivity
11 roundround 0.30.3µmµm
in diain dia
absentabsent intenseintense
22 ellipsoidellipsoid 0.50.5µmµm
inin
lengthlength
MelaninMelanin
depositiondeposition
beginsbegins
presentpresent
33 ellipsoidellipsoid 0.50.5µmµm IncreasedIncreased
depositiondeposition
littlelittle
44 ellipsoidellipsoid 0.50.5µmµm Fills entireFills entire
organelleorganelle
absentabsent

 Melanogenesis
 Melanosome - membrane bound vesicle which undergoes a
sequence of 4 developmental stages during which melanin is
synthesized and deposited within it by the tyrosin-tyrosinase
reaction

 Melanin Increase: Sunlight; Addison Disease;
Hemachromatosis
 Melanin Decrease:
 Albinism –Melanocytes present but no tyrosinase.
 Leukoderma (Vitiligo)- Melanocytes absent; destruction of
melanocytes- patchy expansive

Melanin
 The brown color of the skin is due to melanin, which is produced
in the skin itself in cells called melanocytes. These cells are
located in the epidermis.
 In the melanocytes, the melanin is located in membrane-bound
organelles called melanosomes.
 Melanocytes can transfer melanin to keratinocytes - mainly to the
basal cells
 Melanin protects the chromosomes of mitotically active basal
cells against light-induced damage.

Types of melanin
TypeType ColorColor SolubilitySolubility CompositionComposition
EumelaninEumelanin BrownBrown
blackblack
InsolubleInsoluble
in allin all
solventssolvents
NitrogenNitrogen ++++
to otherto other
componentscomponents
PhaeomelaninPhaeomelanin RedRed
yellowyellow
AlkaliAlkali
solublesoluble
Sulphur inSulphur in
addition toaddition to
nitrogennitrogen

The regulation of the production of eumelanin versus
pheomelanin involves the interaction of the melanocortin 1
receptor (MC1R) on the surface of the melanocyte with
melanocyte stimulating hormone (MSH) or with the agouti
signaling protein. The binding of MSH to MC1R results in the
formation of eumelanin while the binding of the agouti protein
to MC1R leads to the production of pheomelanin.

Melanin unit
• Each epidermal melanocyte is
surrounded by a group of keratinocytes
with which it maintains functional
contact- melanin unit
• A melanocyte supplies melanosomes to
app. 30-40 keratinocytes

Functions of melanin
 Absorption of uv light
 Scavenger of damaging free radical
 Can oxidize NADH in vitro and
participate in other oxidation reduction
reactions
 Melanocytes in stria vascularis also
known as intermediate cells
 Melanocytes help proper routing of optic
nerves at the chaisma during early
development of optic cup.www.indiandentalacademy.com

Melanin transfer
 Result of active phagocytosis of the tips of the
melanocytic dendrites by keratinocytes
 In EM, pseudopod-like cytoplasmic projections
of keratinocytes are wrapped around the tips
of the dendrites
 After such projection has enveloped the tip, it
is pinched off
 Melanosomes in pinched-off dendrite are
separated from the cytoplasm of keratinocyte
by plasma membrane of dendrites & of
keratinocytes

 Due to the breakdown of plasma
membrane, the melanosomes are
dispersed in keratinocytes cytoplasm
 In lightly pigmented skin, transferred
melanosomes are found in basal &
parabasal layer
 In Africans,melanosomes are found
throughout the skin including stratum
corneum www.indiandentalacademy.com

Control of melanin pigmentation
Can be analyzed on 2 basis:
 1)Constitutive a) genetics
b) hormones
 2)Facultative a) uv radiations

Genetics:
 Specific genes influence differentiation
of neural crest cells into melanoblasts,
migration of melanoblasts into skin and
differentiation into melanocytes.
 Other genes acting primarily within the
melanocytes control synthesis of
tyrosinase.

Hormones
 Increased ACTH secretion causes
hyper-pigmentation by increasing the
melanocytic activity
 Increased estrogen & progesterone
levels causes hyperpigmentation which
is due to increased melanization of
keratinocytes

 UV radiation: It shows two types of
reactions:
- Immediate tanning
- Delayed tanning

Regional variation
 High conc. Of melanocytes found on face and male
genital app 2000/mm sq, lower trunk about 800/mm sq
 No significant difference exists between density of
distribution of melanocytes for area of skin for lightly &
dark pigmented persons.
 The differnce in degree of pigmentation is due to a
combination of size & no. of dentritic processes and
size of melanosomes and its degree of dispersion
 Related exposure to uv light causes an increase in
concentration of melanocytes and increase in their size
and functional activity

Methods of demonstration
 Silver stains
 Osmium iodide
 DOPA reaction
 Immunohistochemistry

Loss of melanocytes
 Physical causes like burns , trauma
 Ionising radiations
 Chemicals – phenols etc.
 Inflammatory disorders of skin

HYPERMELANOSIS
Condition Location Clinical Features
Racial Any area Diffuse pale to dark brown
discoloration
Oral melanotic
macule
Any area Discrete/diffuse localized
brown to black macule.
Freckles Cheek,temples, nose Small, flat brown to tan
patches
Cholasma Face Localized increase in
pigmentation during
pregnancy.
Mongolian spot Sacral region Bluish grey to brownish area in
sacral region of mongolian
people.

Blue nevus Localized raised blue
black area.
Melanocytic nevus Skin Seen in
adoloscents,flat/slightly
elevated lesion of about 3-
5mm in diameter.
Combined nevus Blue –black circumscribed
area.
Melasma Forehead,cheek,
temples,upper lip
Bilaterally symmetrical
patches seen in females

Albinism
 Vitiligo - partial or complete loss of melanin
in an area

 Malignancy:
Melanoma is a malignant tumour that arises
from a mutant melanocyte. Melanoma occurs
in all races but is most common in people
with fair skin. Most melanomas present as a
dark, mole-like spot that spreads and tends
to have an irregular border. The risk of
melanoma increases with overexposure to
the sun and sunburn.

melanoma

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