This document discusses the key cell types found in oral epithelium, including melanocytes, Langerhans cells, and Merkel cells. It provides details on their location, origin, structure, functions, and role. The basal lamina, which forms the interface between epithelium and connective tissue, is also examined. It is comprised of collagen types IV and VII, laminins, nidogen, and perlecan which provide a scaffold and regulate cellular functions.

1. Dr. P. Poornima,
First Year Postgraduate

2. NON-KERATINOCYTES/ CLEAR CELLS
•Histologic sections - clear cells.
•10% of the population in the epithelium
•Depending on the position of clear cells in the epithelium. They
are further divided into:
 low level clear cells (Melanocytes & Merkel cells) and
 high level clear cells (Langerhans cells)

3. MELANOCYTE
•Melanocytes - basal layer of epithelium.
•Only cells that synthesize the pigment melanin, which is
packaged in, Melanosomes.
•Oral mucosal melanocytes are present in unipolar,
bipolar, or multiple-dendritic forms, with marked
variation in cell size and complexity of dendritic
systems.

4. History:
•Becker in1927 - dendritic cells - basal layer of oral epithelium.
•Oral Mucosal Melanocytes - gingival - Landlaw & Cahn in
1932.
Origin:
•From the neural crest.

5. •Number of melanocytes in the oral epithelium is the same
regardless of racial/ethnic origin.
•The colour of oral mucosa is determined by several factors:
•Number, size, and distribution of melanosomes
•Type of melanins,
•Masking effect of heavily keratinized epithelium.
•Degree of vascularization of tissues and by level of
haemoglobin in blood

6. Embryonic development of melanocytes:
Influenced by a number of signaling molecules produced
by neighbouring cells:
•Wnt,
•ET‐3,
•BMPs,
•SF & c‐Kit ligand,
•HGF
•Cadherins

7. The keratinocyte-melanocyte unit
•The ratio of melanocytes to keratinocytes ranges from 1:10 to
1:15.
•Each unit consists of one melanocyte and a group of about 36
keratinocytes.

8. Melanosome
•Is membrane‐bound organelle in which melanin
biosynthesis & storage take place
Melanosome biogenesis: 4 morphologic stages

10. Melanosomal transport:
Within melanocytes:
•Melanosomes are transferred from cell centre -melanocytes
dendrites - through microtubules
•The transport is controlled by 2 classes of
microtubules‐attached motor proteins kinesins & dyneins.
•Centrifugal movement by kinesin, Centripetal movement
by dynein

11. To keratinocytes:
1)Exocytosis
2)Cytophagocytosis
3)Fusion of melanocyte & keratinocyte plasma membrane
4)Shedding of melanosome‐filled vesicles followed by
phagocytosis of the vesicles by keratinocytes
Regulation of melanocyte function:
UV irradiation

12. Functions of melanocytes:
•Determines the colour of skin, hair and eyes
•Provides protection from stressors
•Capacity to sequester metal ions and to bind certain drugs
and organic molecules

13. Langerhans cell
Langerhans cells (LC) are dendritic, antigenpresenting cells
(APC), function as the “outermost arm” of the immune
system.
located suprabasally, constitute 2-8%
History:
•Paul Langerhans in 1868.
•In 1961,ultra-structural characteristics - Birbeck.et.al.
•The Birbeck‘s granule serves as element for
morphological identification of the LCs.

14. Origin:
•From bone marrow

15. Location

16. Ultrastructure:
•12 microns, cleaved or folded nucleus, absence of
tonofilaments and desmosomes.
•Birbeck granules – size- 100 nm to 1 μm - “tennis racket”
•seen in continuity with the cytoplasmic membrane and are
often clustered near the Golgi apparatus.
•Two hypotheses explaining their origin:
• Arise from the Golgi apparatus.
•Arises from invaginations of the cytoplasmic
membrane.

17. •The Birbeck granules seem to be specific markers of LCs.
•Based on electron microscopy, two types of LCs:
•Type – I
•Type – II

18. Life cycle of Langerhans cell

19. Merkel cell
folded nucleus, a clear, organelle-rich cytoplasm with
peripheral protrusions among the epithelial cells, few
desmosomal attachments
found in basal and spinous layer of epithelium, concentrated
at base of retepegs.
History:
In 1875, Friedrich Sigmund Merkel, in base
of rete pegs of the epidermis of pig snout
skin called -‘Tastzellen’ (touch cells).

20. Origin:
Two hypotheses concerning origin of MCs:
(1)Neural crest origin hypothesis and
(2)Epidermal origin hypothesis
Evidence from experiments, in birds -neural crest derived,
in mammals - epidermal origin.
Merkel’s cell located in the
region of the stratum basale,
associated with nerve axon

21. Ultrastructure:
•In stratum basale of the epithelium.
•approximately 10 μm in diameter.
•specialized neural pressure sensitive receptor cell.
•commonly seen in masticatory mucosa, but absent in
lining mucosa.
•MCs differ from other non-keratinocytes – not dendritic.

22. High numbers in the lip, anterior hard palate and gingiva.
The regions richer in MCs are involved in tactile
perception.
In oral mucosa in recognition of particle size and texture
during mastication.
More numerous in the sun-exposed skin than in covered
skin.

23. • MCs shows lobulations or spine-like protrusions –
microvilli, upto 50, 2.5 mm in length.
•The spine-like protrusions of highly variable length
attached to the neighboring keratinocytes by
relatively few, small desmosomes

24. Ultrastructure:
•Dense-core secretory granules.
•Granules measures about 80-120 nm or100-140 nm in
diameter.
•Cytoplasm shows loosely arranged intermediate
filament cytoskeleton.
•possesses a characteristic intranuclear rodlet
•make contact with nerve terminals to form
MC-neurite complexes.

25. Electron micrograph of Merkel cell in the basal layer of oral epithelium.
The cytoplasm of this cell is filled with small, dense vesicles situated
close to an adjacent unmyelinated nerve axon. Arrowheads point to the
site of the basal lamina.

26. Basal Lamina
It is the interface between epithelium and the connective
tissue.

27. •Basal lamina is made up of :
• Lamina lucida: 20 – 40 nm thick –BP 180,integrins,
laminin-5
•Lamina densa: 20 – 120 nm thick- Type IV collagen,
laminins, perlecan, nidogen
•Lamina fibroreticularis:Collagen Type VII

29. Functions of basament membrane:
•Scaffold for tissue organization and template for tissue
repair.
•Selective permeability barrier.
•Physical barrier
•Firmly link an epithelium to its underlying matrix
•Regulate cellular functions.

33. Lamina densa is constructed of type IV collagen molecules
assembled to form a meshwork
Laminin-1 also undergoes self assembly to form a
meshwork.
The two networks combine through the interaction of
nidogen bridges to create a scaffold
The biochemical bond formed between integrins and
laminin-5 in tha basal lamina densa

36. •Type VII collagen forms special anchoring fibrils
•Looplike formations of Type VII collagen fibrils originate
and terminate in the lamina densa
•Collagen types VI and XV are also localized to the
basement membrane zone

37. Constituents of Basal lamina includes:
• Collagens: Type IV and Type VII
• Cell surface proteoglycans : Syndecan and Epican
• Noncollagenous components: Laminins, Nidogen,
Perlecan

38. Type IV Collagen:
•Type IV collagen is a nonfibrillar collagen
•Type IV procollagen molecules are heterotrimers
•Each chain–collagenous domain – about 1400 aminoacids
•Several short, non collagenous segments that impart
flexibility
•Made up from two α1 (IV) chains and one α2 (IV) chain.
•Connected to perlecan, nidogen, and BPAG-2.

39. Type VII Collagen
•Composed of three identical α chains
•Type VII collagen is made by epithelial cells and by
fibroblasts of the lamina propria.

40. Cell surface proteoglycans
Syndecan
syndecan – 1 is capable of forming attachments to
fibronectin, collagen types I, III, and V and tenascin

41. Noncollagenous components of Basal lamina
Nidogen

42. Perlecan
•Main producers – Fibroblasts
•Binds to fibronectin, nidogen and laminin

43. Laminins
•Primary organizer of the sheet structure, and early in
development, basal laminae consist mainly laminin.
•Large, flexible, extracellular, cross shaped adhesion proteins
consisting of three long polypeptide chains ( α, β, and γ).