Skin and the derivatives form integumentary system

1. HISTOLOGY OF THE
INTEGUMENTARY
SYSTEM

2. INTRODUCTION
 Skin and its derivatives and appendages form the integumentary
system. In humans, skin derivatives include nails, hair, and several
types of sweat and sebaceous glands.
 Skin consists of two distinct regions, the superficial epidermis and a
deep dermis.
 The superficial epidermis is nonvascular and lined by keratinized
stratified squamous epithelium with distinct cell types and cell layers.
 Inferior to the epidermis is the vascular dermis, characterized by
dense irregular connective tissue.
 Beneath the dermis is hypodermis or a subcutaneous layer of
connective tissue and adipose tissue that forms the superficial fascia
seen in gross anatomy.
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3. TYPES OF SKIN
There are 2 types of skin:
Thick skin, which is hairless found on the palms and the soles of
the feet, normally composed of five layers.
• It is also called glabrous skin
Thin skin, which is hairy normally composed of four layers
• Thick skin in the soles of feet and palms contain ridges separated
by furrows between them.
• These ridges are used as finger prints in forensic impressions
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5. EPIDERMIS
 The epidermis is primarily made up of keratinized stratified squamous
epithelium
 it gives strength to the skin.
 Varies in thickness from a few cells (eyelids) to dozens of cells thick (palms
and soles of feet)
 It does not have any vascularization (blood supply), so it relies on absorbing
oxygen and nutrients from the blood vessels in the dermis deep to it.
 The nails are made in the epidermis.
 It is made up of five cell layers;
─ Stratum Basale
─ Stratum Spinosum
─ Stratum Granulosum
─ Stratum Lucidum
─ Stratum Corneum
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6. • There are four cell types in the epidermis of skin, with the
keratinocytes being the dominant cells.
• Keratinocytes divide, grow, migrate up, and undergo
keratinization or cornification, and form the protective
epidermal layer for the skin.
• There are other less abundant cell types in the epidermis.These
are the;
─ melanocytes
─ Langerhans cells
─ Merkel’s cells
• These cells are interspersed among the keratinocytes in the
epidermis.
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7. LAYERS OF THE EPIDERMIS
STRATUM BASALE
• It is the deepest, or basal layer, in the epidermis. It consists of;
• a single layer of columnar to cuboidal cells that rest on a basement membrane
separating the dermis from the epidermis.
• Keratinocytes, melanocytes, Langerhans cells & Merkel cells
• The cells are attached to one another by cell junctions, called
desmosomes, and to the underlying basement membrane by
hemidesmosomes.
• Its cells serve as stem cells for the epidermis; thus, much increased mitotic
activity is seen in this layer.
• The cells divide and mature as they migrate up toward the superficial
layers.
• All cells in the stratum basale produce and contain intermediate keratin
filaments that increase in number as the cells move superficially.
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8. STRATUM SPINOSUM
• As the keratinocytes move upward in the epidermis, a second cell layer, or
stratum spinosum, forms.
• It also has Langerhan cells
• This layer consists of four to six rows of cells.
• In routine histologic preparations, cells in this layer shrink.
• As a result, the developed intercellular spaces between cells appear to form
numerous cytoplasmic extensions, or spines, that project from their surfaces.
• The spines represent the sites where desmosomes are anchored to bundles of
intermediate keratin filaments, or tonofilaments, and to neighboring cells.
• The synthesis of keratin filaments continues in this layer that become
assembled into bundles of tonofilaments.
• Tonofilaments maintain cohesion among cells and provide resistance to abrasion of
the epidermis.
NB: stratum basale and spinosum are the only actively dividing cell layers and
together are called the Malpighian layer
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9. STRATUM GRANULOSUM
• Cells above the stratum spinosum become filled with dense basophilic
keratohyalin granules and form the third layer, the stratum
granulosum
• It consists of 3-5 layers of flattened cells
• The granules are not surrounded by a membrane and are associated
with bundles of keratin tonofilaments.
• This combination in cells produces keratin
• The keratin formed by this process is the soft keratin of skin.
• In addition, the cytoplasm of these cells contains membrane-bound
lamellar granules formed by lipid bilayers.
• lamellar granules are discharged into the intercellular spaces of stratum
granulosum as layers of lipid and seal the skin.
• This process renders the skin relatively impermeable to water.
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10. STRATUM LUCIDUM
• It is present in thick skin only
• It lies just superior to stratum granulosum and inferior to
stratum corneum
• Consists of flattened cells.
• It is translucent and barely visible
• The tightly packed cells lack nuclei or organelles and are dead.
• The flattened cells contain densely packed keratin filaments.
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11. STRATUM CORNEUM
• The stratum corneum is the fifth and most superficial layer of skin.
• All nuclei and organelles have disappeared from the cells.
• It primarily consists of flattened, dead cells filled with soft keratin filaments.
• The keratinized, superficial cells from this layer are continually shed or
desquamated and are replaced by new cells arising from the deep stratum
basale.The cells are shed from the surface in about 2 weeks.
• During the keratinization process, the hydrolytic enzymes disrupt the nucleus
and cytoplasmic organelles, which disappear as the cells fill with keratin.
• It takes about 15-30 days for a cell to move from the stratum basale to the stratum
corneum and another 2 weeks for it to shed
• We lose half a million cells per hour; 1.5 grams a day
• That can be a major source of dust in the house
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14. DERMIS
• It is the connective tissue layer that binds to epidermis.
• A distinct basement membrane separates the epidermis from the
dermis.The junction of the dermis with the epidermis is irregular.
• It contains epidermal derivatives such as the sweat glands,
sebaceous glands, and hair follicles.
• The superficial layer of the dermis forms numerous raised
projections called dermal papillae,
• Dermal papillae interdigitate with evaginations of epidermis, called
epidermal ridges.
• This region of skin is the papillary layer of the dermis.
• This layer is filled with loose irregular connective tissue fibers,
capillaries, blood vessels, fibroblasts, macrophages, and other loose
connective tissue cells 14

15. • The deeper layer of dermis is called the reticular layer. This layer is
thicker and is characterized by;
• dense irregular connective tissue fibers (mainly type I collagen)
• less cellular than the papillary layer.
• There is no distinct boundary between the two dermal layers thus papillary
layer blends with the reticular layer.
• Also, dermis blends inferiorly with the hypodermis or the subcutaneous
layer, which contains the superficial fascia and adipose tissue.
 Dermis is highly vascular and contains numerous blood vessels, lymph
vessels, and nerves.
• Certain regions of skin exhibit arteriovenous anastomoses used for
temperature regulation. Here, blood passes directly from arteries into veins.
• The dermis contains numerous sensory receptors. Meissner’s corpuscles are
located closer to the surface of the skin in dermal papillae.
• Pacinian corpuscles are found deeper in the connective tissue of the dermis
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16. Dermal papilla, palm.H&E,272; inset 192
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17. COMPARISON OF THICK & THIN
SKIN
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18. HYPODERMIS
• This is the fat layer. It varies tremendously in thickness:
• Shins = thin
• Buttocks = thick.
• It also contains fibrous tissue, blood vessels and nerves and sits
on top of the muscles.
Functions
1) Stores fat
2) Cushions
3) Insulation from cold because of heat produced by the
larger blood vessels in this layer.
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19. OTHER SKIN CELLS
• In addition to keratinocytes, the epidermis contains three other cell
types:
─ Melanocytes
─ Langerhans cells
─ Merkel’s cells
• Unless skin is prepared with special stains, these cells are normally
not distinguishable with hematoxylin and eosin preparations
Merkel Cells
• Are found in the basal layer of the epidermis and are most
abundant in the fingertips.
• Because these cells are closely associated with afferent (sensory)
unmyelinated axons, it is believed that they function as
mechanoreceptors to detect pressure.
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20. Melanocytes
• Are derived from the neural crest cells.
• They have long irregular cytoplasmic extensions that branch into the
epidermis.
• Melanocytes are located between the stratum basale and the stratum
spinosum of the epidermis and synthesize the dark brown pigment
melanin.
• Melanin is synthesized from the amino acid tyrosine by the melanocytes
• The melanin granules in the melanocytes migrate to their cytoplasmic
extensions, from which they are transferred to keratinocytes in the basal
cell layers of the epidermis.
• Melanin imparts a dark color to the skin, and exposure of the skin to sunlight
promotes increased synthesis of melanin.
• The function of melanin is to protect the skin from the damaging effects of
ultraviolet radiation. 20

21. Langerhans cells
• found mainly in the stratum spinosum.
• They participate in the body’s immune responses.
• Langerhans cells recognize, phagocytose, and process foreign
antigens, and then present them to T lymphocytes for an
immune response.
• Thus, these cells function as antigen presenting cells of the
skin.
Special types of cells in the epidermis,thin
skin.
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22. ACCESSORY STRUCTURES
A. Glands
• Sebaceous glands
• Eccrine sweat glands
• Apocrine sweat glands
B. Hair
• Hair shaft
• Hair follicles
C. Nail
• Nail bed
• Nail matrix
• Eponychium
• Hyponychium
D. Sensory receptors
• Meissner corpuscles
• Free nerve endings
• Pacinian corpuscles
• Merkel cells (Merkel cell neurite complexes or Merkel disks) 22

23. Sebaceous glands
• found in thin skin, usually associated with hair follicles.
• They are most numerous in the skin of the scalp and face.
• Are classified as simple branched acinar glands.
• The secretory cells are lipid producing cells, arranged into several
acini, which open into a short duct.
• Usually, the ducts of sebaceous glands empty their oily secretion,
called sebum, into a hair follicle.
• however, the ducts sometimes open directly onto the surface of the
skin.
• Sebaceous glands release their products by holocrine secretion,
that is, by the disintegration of entire cells.
• Sebum lubricates the skin and coats and protects hair shafts from
becoming brittle.
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24. • Arrector pili muscles are bundles of sympathetically
innervated smooth muscle cells that span between hair
follicles and the papillary layer of the dermis.
• They contract to stand the hair up in response to cold or fear.
The inset shows an acinus of a sebaceous gland and a nearby arrector
pili muscle
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25. Eccrine sweat glands
• Eccrine (merocrine) sweat glands can be found in both thin and
thick skin over most of the body.
• They are more numerous in the palms and soles.
• Eccrine sweat glands produce a clear watery product called
sweat.
• Releasing sweat onto the surface of the skin helps adjust body
temperature as well as aiding in the excretion of metabolic wastes.
Thin skin
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26. Apocrine glands
• are simple coiled tubular glands like the eccrine sweat glands, but their
lumens are larger (about 10 times larger than those of the eccrine sweat
glands)
• Their ducts empty into the superficial regions of the hair follicles.
• The secretory cells of the apocrine glands release their products by
shedding part of their apical cytoplasm( Apocrine secretion)
• Apocrine secretions contain protein, carbohydrate, ammonia and lipid.
• The tubules of the glands are lined by cuboidal or columnar epithelial
cells, depending on the secretory stage.
• Are restricted in location to some specific regions of thin skin, such as
the axilla, the areola (nipple), and the perianal and genital areas.
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28. Hair follicles
• Are structures that produce the hair and maintain hair growth.
• They are cellular structures extending from the epidermis into the
dermis or hypodermis.
• basal region of the hair follicle forms a balloon-shaped structure called
the hair bulb.
• Hair bulb is composed of the hair root and the dermal papilla.
• hair root contains melanocytes and a group of epithelial cells called
the matrix or germinal matrix.These cells are capable of cell
division and give rise to the inner root sheath and to the hair
• The dermal papilla contains capillaries and nerve fibers that
supply the hair follicle
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30. Nail, Finger
• Nail is a translucent, hard, keratinized sheet resting on the tip of
each digit.
• It includes many components:
• The nail plate, the nail itself, which is hard keratin
• The nail root, also called the nail matrix, seen as the lunula in the
living state
• The nail bed, a layer of epidermis beneath the nail plate;
• the eponychium, also called the nail cuticle, which is the junction
zone between the skin of the finger and the nail plate and which
forms a protective seal;
• the perionychium (nail wall), the skin that surrounds the edge of
the nail; and
• the hyponychium, the junction seal between the nail plate and the
skin of the fingertip.
• All of the sealed areas at the edges of the nail plate protect the
delicate nail matrix and nail bed from dehydration and infection.
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32. Nail root (Matrix) and Nail bed
• Nail root is a cellular layer and is also called the matrix or
germinal matrix.
• It contains many layers of epithelial cells, which are responsible
for the production of the nail plate.
• These cells proliferate and become flattened and highly
keratinized and are pushed forward by newly formed cells.
• As they differentiate, the cells finally lose color and shape and
become part of the nail plate.
• The nail plate is similar to the hair shaft, but the pattern of
keratin formation is different.
• The nail bed (equivalent to the epidermis) rests under the nail
plate.The nail bed extends from the nail matrix to the
hyponychium.
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33. • Normally, the nail bed is smooth and allows for healthy nail
growth and a smooth appearance.
• If a nail bed is infected by bacteria or fungus, the nail bed
becomes rough, and an accumulation of organic waste materials
can react with the nail plate and cause the nail to become
thickened and distorted.
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34. PATHOLOGICAL TERMS FOR THE
INTEGUMENTARY SYSTEM
• Acanthosis:Thickening of the stratum spinosum of the epidermis, typically seen in
epidermal hyperplasia.
• Hypergranulosis: Thickening and prominence of the stratum granulosum of the
epidermis, often in response to chronic mechanical irritation of the skin. Hypergranulosis
may also be seen in the declivities of papillary lesions such as verruca vulgaris, or warts.
• Hyperkeratosis:Thickening of the stratum corneum of the epidermis. Orthokeratotic
hyperkeratosis refers to hyperkeratosis without the presence of nuclei.
• Papillomatosis:Fingerlike projections from the epidermal surface, often with
hyperkeratosis, seen in a variety of conditions including verruca vulgaris, or warts.
• Parakeratosis: A form of hyperkeratosis in which nuclei are retained in the stratum
corneum, seen in many conditions including psoriasis.
• Spongiosis:Intercellular edema of the epidermis frequently seen in various etiologies of
dermatitis such as allergic contact dermatitis or irritant dermatitis.
• Ulceration:The discontinuity of an epithelial surface including the epidermis or mucous
membranes.
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35. CLINICAL CORRELATIONS
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40. Cystic Fibrosis
• The sweat of infants with cystic fibrosis (CF) is often salty
and is commonly taken as indicative of this genetic disease.
• CF patients have defects in a transmembrane conductance
regulator (CFTr) of epithelial cells that lead to disruptive
accumulations of thick mucus in the respiratory and
digestive tracts.
• Failure to remove salt from sweat is related to the same
genetic defect.
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41. • If you frequently rub one area of 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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42. Keloid Scars
• Thick, red, sometimes painful scars
• More common in African American, Native American, and Asian
races
• Treatment with cortisone injections
• Keloid scar formers can get internal adhesions also
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43. Stretch Marks
• Is a condition of the dermis
• Caused by sudden weight gain (pregnancy)
• Expansion of skin, collagen fibers in the dermis separate =
stretch marks.
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44. WRINKLES
• Over time, collagen fibers align themselves more and more
as they are always being pulled in the same direction: smile,
frown.
• As you age, the skin begins to sag because the body makes
less collagen, and some is lost from sun exposure.
CELLULITE
• Cellulite is just fat, protruding around fascia fibers
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45. LIPOSUCTION
• This is a surgical procedure where the patient has fat sucked out of
the hypodermis layer.
• Liposuction is dangerous because hypodermis is very vascular, can
bleed too much.
BURNS:
• Three types:
• FIRST DEGREE: Minor burn to the epidermis; sunburn
• SECOND DEGREE:Dermis separates from epidermis; blister
• THIRD DEGREE:Hypodermis is burned. (most severe type of burn)
• 2˚ and 3˚ burns over a large part of the body gives a survival
chance proportional to the amount of skin left. 60% burn = 60%
chance of dying.
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46. DECUBITUS ULCERS (bed sore)
• Epidermis and dermis are destroyed from pressure, underlying tissue
is exposed.
How decubitus ulcers form:
• If you’re sitting down, weight of the body presses against blood vessels,
no blood flow to skin of buttocks. If it goes on longer than a couple of
hours because one can’t move, tissues can’t get oxygen. Ulcer forms,
can get gangrene (tissue death).
• It can also become systemic (bacteria enter the wound, travel in the
blood), which can cause death.
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47. Cellulitis
• Cellulitis is inflammation in subcutaneous layers of the skin, due to
infection.
• Cellulitis can be caused by normal skin flora (bacteria) or by
exogenous bacteria.
• Often occurs where the skin has previously been broken: cracks in the
skin, cuts, blisters, burns, insect bites, surgical wounds, intravenous
drug injection or sites of intravenous catheter insertion.
• Treatment with appropriate antibiotics is needed, and recovery
periods last from 48 hours to six months.
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48. CYANOSIS
• Bluish color to skin.
• Caused by superficial blood vessel constriction in the dermis or
lack of blood flow to skin
• Occurs for two reasons:
• Cold
• Not enough oxygen in body to go around. The oxygen is conserved
for the vital organs, so oxygen to skin and nails is shut down.
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