This document provides an overview of the structure and function of skin and its appendages. It discusses the three layers of skin - the epidermis, dermis and hypodermis - and describes the cellular structure and functions of each layer. It also examines skin appendages like hair, nails, sweat and sebaceous glands. The document is intended as a reference for the anatomy of skin and its related tissues.

1. Skin and Appendages
Dr Laxman Khanal
MS-Human Anatomy
Batch- 2011

2. Introduction
– our largest organ
– Accounts for 12% of body weight…it weighs twice
as much as your brain!
– Varies in thickness at different parts (< 0.5
mm at eyelids to > 5 mm on middle of upper
back)
– Divided into three distinct layers
• Epidermis
• Dermis
• Hypodermis – lies deep to the dermis
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4. Functions
• Barrier against loss of body fluid.
• Protection and excretion
• Sensory function
• Metabolic function
• Temperature regulation
• Adaptation during edema and pregnancy
• Legal and anthropological importance
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5. Structure of skin
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6. Epidermis
• Primarily made up of keratinized stratified
squamous epithelium(keratinocytes)
• gives strength to the skin.
• Varies in thickness from thick skin to thin skin
• It does not have any vascularization, so it
relies on the connective tissues deep to it.
• Also contain melanocytes, merkel’s cells and
Langerhans cell
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7. Layers of epidermis
• Stratum basale (the deepest layer)
• Stratum spinosum
• Stratum granulosum
• Stratum lucidum (only in thick skin)
• Stratum corneum (most superficial layer of
epidermis
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9. STRATUM BASALE
• Consists of single layer of basophilic
columner or cuboidal cells.
• Along with S. spinosum it is component of
Malpighian layer
• Cells are bound to each other by
desmosomes and to basal lamina by
hemidesmosomes.
• All cells contain intermediate keratin
filaments, number of which increases as cells
progress upward.
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10. Stratum Spinosum
• Also contain the dividing cells as in basale.
• Cells contain bundles of intermediate
filament ( tonofilaments) projecting into the
processses of cells which give attachment to
the desmosomes, so giving spined
appearance.
• Tonofilaments provide resistant to the
abrasion so this layer is thicker in the areas
prone to abrasion( thick skin)
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12. Stratum Granulosum
• Consists of polygonal cells , cytoplasm of which is
filled with the basophilic granule , keratohyaline
granules. It is rich in phosphorylated histidine and
cystine.
• Cells contain, lamellated bodies, made up of lipid.
It fuses with the cell membrane and it come out of
cells and function as a intercellular cement or
sealing agent.
• This sealing effect is first evolutionary adaptation
to terrestrial life.
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13. Stratum Lucidum
• more prominent in thick skin . Cellular
organells and nuclei are not prominent.
• It is composed of clear non-nucleated cells.
• In the palms and soles, the stratum lucidum is
present. The tan colored protein blocks the
underlying melanocytes from view
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14. Stratum corneum
• The main difference between thick skin and thin
skin relates to the thickness of the Stratum
corneum.
• These are the dead cells, flaking off. The cells lose
their nucleus and fuse to form squamous
sheets, which are eventually shed from the surface
(desquamation).
• It takes about 40 50 days days for a cell to move
from the stratum basale to the distal edge of the
stratum corneum and shed.
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15. Keratin
• Keratin is a waxy protein substance found in the
epidermis. It also makes up the nails and hairs.
• It can absorb water, so keratin swells when
soaking wet.
• It makes the skin look wrinkled when you are in
the tub too long. The water evaporates when you
dry off, and pulls more water out of your body, so
soaking in the tub will dry your skin out…unless
you put lotion on right away to keep the water in
the epidermal and dermal layers. Lotions will not
penetrate to the dermis, just water.
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16. • Icthyosis – excessive keratinisation of the skin
with autosomal recessive inheritance pattern.
• Grotesque appearance due to icthyosis in
fetus- harlequin fetus.
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17. Melanocytes- neural crest cells
•During the first 3 months
of development, the
epidermis is invaded by
cells arising from the
neural crest.
• These cells synthesize
melanin pigment, which
can be transferred to
other cells of the
epidermis by way of
dendritic processes.
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18. Melanin synthesis
• Stage 1 – tyrosinase
activity in vesicle
• Stage 2- melanosome
with tyrosinase and
filaments of melanin
• Stage 3- more filaments
of melanin
• Stage 4- melanin
completely filled the
vesicles.
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19. • Addison disease – adrenal cortex hypo
function resulting increased in ACTH
production---- increased melanin synthesis.
• Albinism – hereditary condition of inability of
melanocytes to produce melanin.
• Vitiligo- degeneration of entire pool of
melanocytes.
• Nevus and Malignant melanoma
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20. Melanin
• Tyrosine by the action of tyrosinase converted
into the DOPA, which undergo polymerization
to form the melanin.
• it is located in supranuclear position inside the
keratonocytes so that it can prevent the
nuclear damage by the UV radiation coming
from above.
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21. Langerhans cells
• These are star shaped bone marrow derived
cells. Migrated to the skin via blood.
• Present in the S. spinosum of the skin
• These cells are antigen presenting cells so
participate in immune related reaction.
• These are component of SALT.
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22. Merkel’s cell
• Neural crest in origin
• Found in the basal layer of the thick skin . Has
sensory function.
• Expanded terminal disc of free nerve endings
are found just beneath the merkel’s cell.
• These cells also acts as the neuroendocrine
function.
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23. Dermis
• It is connective tissue that support the epidermis
and attaches the epidermis to the hypodermis.
• Its surface consists of many ridges ( dermal
papillae) which interdigitate with epidermal
ridges.
• Dermal papillae are more numerous in the skin
that is more prone to pressure and friction.
• Has 2 layer - Papillary layer and reticular layer
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24. Dermoepidermal junction
• Dermis is consists of the collagen fibers and
elastic fibers which are thicker in reticular
layer and thinner in papillary layer.
• Special collagen fibers extend from the dermal
papillae and inserted in the basal lamina
forming the dermoepidermal junction.
• Loss of this junction lead to pemphigoid
• Loss of intercellular junction lead to
pemphigus.
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25. Papillary layer
• Made up of loose connective tissue having
thin fibers and many cellular structures.
• Has ridges to increase surface area for contact
with the epidermis.
• Along the ridges sweat gland open at regular
interval.
• The papillary layer in the dermis is what forms
our fingerprints.
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26. Reticular layer
• Dense irregular Connective Tissue
• Has bundles of Collagen and Elastic fibers and
less number of cells.
• Arrangement of bundle in the direction of
mechanical force give rise to the cleavage lines of
Langer.
• strongest layer of the Dermis. Gives the area
strength.
• Leather is made of this layer.
• EDS
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27. • The dermis is also the area where all the
glands of the body are located.
• A transdermal patch (nicotine patch, etc) must
diffuse all the way from the epidermis into the
dermis to reach the blood vessels there.
• The blood vessels in the dermis are what give
a pink color to Caucasian people.
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28. Hypodermis
• Consists of loose connective tissue which
helps in sliding the skin over the deep
structure.
• Consists of layer of fat according to the
nutritional status of the person.
• Also called as superficial fascia or panniculus
adiposus
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29. Vessels in skin
• Arteries form the 2 plexuses. One at the
junction of papillary and reticular layer( sub-
papillary plexus) and another at junction of
dermis and hypodermis (cutaneous plexus).
• Veins form the three plexuses – 2 in same
position as for arterial and another in the
middle of the dermis.
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31. Sensory receptors in skin
• Free nerve ending
• Merkel's cells noncapsulated
• Hair follicle receptors
• Pacinian corpuscles
• Ruffini ending capsulated
• Meissener’s corpuscles
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33. Skin color
1) MELANIN: (dark brown pigment).
2) CAROTENE: (a yellowish/orange pigment found only
in plants). Accumulates more in the skins of Asians
and Native Americans.
3) SKIN THICKNESS: blood vessels seen, looks pinker
4) HEMOGLOBIN: The DERMIS contains the blood
vessels that give Caucasians the pink color to the
skin. Even veins are red because blood is red. But
when you look at veins through the adipose layer
(the hypodermis), they look blue.
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34. Condition of skin
• If you rub the skin, it stimulates cell division = callous
• If you rub the skin too hard, the stratum basale tears
away from the basement membrane, and causes a
gap, which fills with fluid: BLISTER.
• The epidermis then dies because it’s too far away
from nutrients. That’s why the top of a blister dries
up
• If the blisters are small (less than 5 mm in
diameter), they are known as vesicles; if they are
larger (greater than 5 mm in diameter), they are
termed bullae
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35. • Psoriasis – decrease in cell turnover time and
increased proliferation of basal layer cells.
Results in greater epidermal thickness and
rapid renewal of epidermis.
• Darkening of the skin to solar radiation-
darkens the preexisting melanin and also
increase the synthesis of melanin.
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36. Skin cancer
Major types
• Squamous cell carcinoma
• Basal cell carcinoma
• Malignant melanoma
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37. Appendages of the skin
• Hairs
• Sebaceous gland
• Sweat gland
• Nails
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38. Hair
• It is keratinized elongated structure derived
from the invagination of epidermis(hair
follicle) .
• By 3rd month first hairs appear over eyebrow
and upper lip.
• It acts for thermoregulation, sensory function.
• Distribution of hair after puberty possesses
distinctive sex differences.
• Made up of shaft and root
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39. Hair
• The hair follicle is a tubular structure
consisting of five concentric layers of epithelial
cells.
• At the base, there is a bulbous expansion, the
hair bulb, enclosing the hair papilla .
• During hair formation inner 3 layer undergo
keratinisation and outer 2 layer form epithelial
sheath.
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41. Stages of Hair growth
• Anangen phase- fast growing phase
• Catangen phase- involution phase
• Telogen phase- rest phase
Types of hairs
• Laungo hairs- foetal hair
• Vellus hairs- infant hair and fine hairs of body
• Terminal hairs- coarse hair
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42. Arrector pili muscle
• extends from the
dermal coat of isthmus
of the hair follicle to the
papillary layer of the
dermis.
• Gives gooseflesh
appearance.
• Cholinergic sympathetic
supply
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43. Nail
• Nails are plates of keratinized epithelial cells
on the dorsal surface of each distal phalanx.
• The nearly transparent nail plate and the thin
epithelium of the nail bed provide a useful
window on the amount of oxygen in the blood
by showing the color of blood in the dermal
vessels.
• Growth rate 1-3mm/month
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44. • Nails develop from thickened areas of
epidermis at the tips of each digit called nail
fields.
• Later these nail fields migrate onto the dorsal
surface surrounded laterally and proximally by
folds of epidermis called nail folds.
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47. Beau’s line
• Transverse depressions
due to disruption of
proximal matrix mitotic
activity.
• Common in coronary
artery
occlusion, hypocalcemia
, malnutrition and
trauma.
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48. Onychomadesis/ nail shedding
• Proximal detachment
of the nail plate from
the proximal nail fold.
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49. Nail pitting
• Punctate depressions
of the nail plate surface.
• Common in psoriasis
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50. Onychorrhexis
• Longitudinal ridging
and fissuring of the
Plate.
• Common in lichen
planus .
• Normal in aging
process.
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51. Leukonychia
• Because of
parakeratotic cells with
in ventral portion of nail
plate, nail appears
whitish.
• May be hereditary or
associated with
congenital disorders.
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52. Koilonychia / spoon shaped nail
• Concave nail due to
upward eversion of
lateral nail edge.
• Common in iron
deficiency anemia, PVS
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53. Splinter hemorrhage
• One of the diagnostic
sign of infective
endocarditis.
• Also common in
vasculitis.
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54. Nail clubbing
• Schamroth's window
test is the test to define
clubbing.
• Lovibond’s angle > 165
degree
• Common in heart
disease, lung disease
and GI disease.
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55. Sebaceous gland
• Holocrine type of branched acinar gland.
• Acinus consists of rounded cells filled with lipid.
• Cell lost by holocrine secretion are replaced by
the proliferation of basal cell of acinus.
• Open either with in hair follicle(common) or on
the skin surface( rare).
• These are not under nervous control.
• Pilo-sebaceous apparatus.
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56. • Gland lies within fibrous
sheath of hair follicle.
• Glandular epithelium
represents the external
root sheath.
• Discharge their
secretion to hair shaft
and then to skin
surface.
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57. Eccrine sweat gland
• Found everywhere in the skin
• Secrets watery secretion –sweat which helps
in thermoregulation.
• It has 2 component- secretory glandular tissue
and duct system . Both are coiled structures.
• Secretory part has 3 types of cells- clear
cells, dark cells and myoepithelial cells.
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58. Sweat gland sebaceous gland
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59. Apocrine gland
• Apocrine glands are mainly confined to the
areolae of the breasts, axillae and genital
regions.
• produce a viscid, milky secretion which
becomes malodorous after the action of skin
commensal bacteria.
• Open into the hair follicle.
• Matured only after the puberty
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60. Apocrine gland ….
• These are much larger in shape than eccrine
glands.
• Innervated by adrenergic nerve ending not by
cholinergic as in eccrine glands.
• Glands of moll of eyelid and ceruminous gland
of ear are modified sweat gland.
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61. References
• Basic histology ( 11th edition) by Luiz Carlos
Junqueira and Jose Carneiro.
• WHEATER’S functional histology(5th edition)
• General anatomy – by AK Dutta
• Langman Medical Embryology (9th edition)
• Various websites.
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