H I S T O L O G Y
L E C T U R E
INTEGUMENT
OBJECTIVES:
Upon completion of study of this section the student will be able to:

List the barrier, protection and regulatory functions of the skin.

Indicate the role of epidermal and dermal components in each function.

Distinguish between thick and thin skin. Including location and components found in
each type.

Describe the 5 strata found in the epidermis. Review the development and
organization of each layer.

Discuss the origin and role of melanocytes. Trace the development and fate of the
granule.

Identify the function of Langerhan’s and Merkel’s cells.

Describe the organization and functions of the papillary and reticular layers of the
dermis.

Describe the structure and activities of the hair follicles, sebaceous, eccrine and
apocrine sweat glands.
Integumentary System

refers to the skin plus its appendages.

covers the surface of the body and is composed of two layers: epidermis and dermis.
The deeper fascial layer, the hypodermis, is not considered part of skin.

serves several important functions: protection against injury, desiccation, and
infection; the regulation of body temperature; the absorption of UV radiation for
synthesis of vitamin D; and the reception of sensory stimuli (tactile, thermal, and
pain) from the external environment.

epidermis and dermis interdigitate with each other to form an irregular contour.
Dermal papillae (ridges) project into the epidermis to produce epidermal ridges
(which can be seen on the finger tips with the naked eye).

may also be classified as thick or thin, depending on the thickness of epidermis.
Skin
1. Appendages of Skin

includes sweat glands, hair follicles, sebaceous glands, and nails.
General Structural Plan of Skin
Epidermis
Characteristics

a stratified squamous keratinized epithelium, composed of several strata, which
forms the superficial layer of skin.

is constantly being regenerated by its keratinocytes (every 2 to 4 weeks) via mitotic
activity that occurs mostly at night.

epithelial layers of the epidermis include the following strata: basale, spinosum,
granulosum, lucidum, and corneum:
1. Stratum Basale (germinativum)

is the deepest layer of cells, attached directly to the basal lamina by
hemidesmosomes.

cuboidal to columnar in shape and frequently seen undergoing division.

melanocytes (pigment cells) and Merkel cells are also present in this layer.
2. Stratum Spinosum

consists of a few layers of polyhedral (prickle) keratinocytes.

these cells have extensions, or so-called “intercellular bridges”, where
desmosomes attach the cells to each other.

cells of this layer are mitotically active.

in upper regions of the stratum spinosum are keratinocytes that contain membranecoating granules, which are released into the intercellular spaces and cement the
cells together, “waterproofing” the skin.

Langerhans cells also present in this layer.
3. Stratum Malpighii

refers to the stratum basale and the stratum spinosum grouped together.
4. Stratum Granulosum

the layer of the epidermis where cells accumulate keratohyalin granules and
bundles of intermediate keratin filaments (tonofilaments) and become flattened.

also produce membrane-coating granules.
Keratohyalin Granules

are not enclosed in a membrane but are composed of histidine- and cystine-rich
proteins that appear to bind the keratin filaments together.
Cytoplasmic Aspect

of the plasmalemma of these keratinocytes is thickened by an electron-dense layer,
10 - 12 nm thick, that reinforces it.

is the most superficial layer in which nuclei are present.
5. Stratum Lucidum

a clear homogeneous layer, which is often difficult to distinguish in histological
sections.

nuclei and organelles are not present in this layer, and the cells contain a substance
known as eleidin, which is believed to be a transformation product of keratohyalin.
6. Stratum Corneum

is the outermost layer of the epidermis.

is composed of scale-like dead cells (squames).

each squame is a 14-sided polygon surface layers of cells are constantly being
desquamated, region being desquamated is sometimes referred to as the stratum
disjunctum.
7. Other Cell Types in the Epidermis
Melanocytes

are present in the stratum basale and derived from the neural crest.

synthesize brown melanin pigment in oval organelles called melanosomes.

contain tyrosinase, a UV-sensitive enzyme directly involved in melanin synthesis.

contain long processes that extend between the cells of the stratum spinosum.

by way of these processes, the melanocytes transfer (or inject) melanosomes into
keratinocytes in the stratum spinosum.

this unique mechanism for the transfer of pigment is known as cytocrine secretion.

once melanosomes are within the keratinocytes, they are degraded by lysosomes.

number of melanocytes per unit area of skin varies from one part of the body to
another but is independent of race.
Langerhans Cells

are dendritic-shaped cells derived from the bone marrow.

are present mainly in the stratum spinosum.

contain distinct paddle-shaped membrane-bounded granules (Birbeck granules).

function in presenting antigen to lymphocytes and thereby play a role in contact
allergic responses.
Merkel Cells

are present in small numbers in the stratum basale, near areas of connective tissue
containing blood vessels and nerves.

contain small dense-cored granules that are similar in appearance to those in cells of
the adrenal medulla.

receive afferent nerve terminals and are believed to function as sensory mechanoreceptors.

is composed of thin, loosely arranged fibers and cells.
Dermis
1. Characteristics

layer of skin underlying the epidermis that consists of dense, irregular connective
tissue.

contains collagen (Type I) fibers in abundance and networks of thick elastic fibers.

is divided into a superficial papillary layer and a deeper more extensive reticular
layer, but there is no distinct boundary between them.
2. Papillary layer

is uneven and forms dermal papillae that interdigitate with the basal surface of the
epidermis.

is composed of thin, loosely arranged fibers and cells.

Meissner’s corpuscles (fine-touch receptors) and capillary loops are located in this
layer.
3. Reticular Layer

forms the major portion of the dermis and contains thick, dense, irregular arrays of
collagen fiber bundles and thick elastic fibers.
Encapsulated Nerve Endings

consisting of Pacinian corpuscles (pressure receptors) and Krause’s end bulbs
(cold and pressure receptors) may be present in the deeper regions of the dermis.
Arrector Pili Muscle

are bundles of smooth muscle, attached to hair follicles in the dermis, extend
superficially to underlie sebaceous glands, and insert into the papillary layer of the
dermis.

contraction of arrector pili muscle elevates the hair and produces “goose bumps”.

deep to the reticular layer is the superficial fascia, or hypodermis, a loose connective
tissue, containing many fat cells, that is not considered part of the skin.
Two Types of Skin
1. Thick Skin

has a thick epidermis that is characterized by a prominent stratum corneum.

lines the palms of the hands and the soles of the feet.

lacks hair follicles, sebaceous glands, and arrector pili muscle bundles.
2. Thin Skin

has a thin epidermis with a less prominent stratum corneum.

is present over most of the body surface and contains hair follicles, sebaceous
glands, and arrector pili muscle bundles.

stratum lucidum and stratum granulosum are seldom seen in thin skin, although
individual cells are present that show characteristics of these layers.

the dermis is usually thicker in this area than in thick skin.
Appendages of the skin
1. Hair Follicle

a tubular invagination of the epidermis extending deep into the dermis.

shaft of the hair projects above the surface of the epidermis.

hair consists of a medulla, cortex and cuticle.

root of the hair is embedded in an expanded hair bulb, which is deeply indented by a
papilla (of dermis).

cells in the hair bulb form the inner epithelial root sheath and the medulla.

internal root sheath is an epithelial structure (lying deep to the entrance of the
sebaceous gland) composed of Henle’s layer, Huxley’s layer, and the cuticle.

outer root sheath is a direct continuation of the stratum Malphighii of the epidermis.

the next superficial layer is the glassy (basement) membrane, and the outermost
layer is the connective tissue sheath (dermis).
2. Nail

is located on the distal phalanx of each finger or toe.

is composed of hard keratin lying on a nail bed.

eponychium (cuticle) overlies the crescent-shaped whitish lunula.

hyponychium (keratinized epithelial layer) is located beneath the free edge.

cells in the nail matrix, at the root, are responsible for the growth of the nail.
Glands
Eccrine Sweat Glands

are distributed in skin throughout the body.

are simple tubular coiled glands that have a secretory unit composed of three cell
types: dark cells, clear cells, and myoepithelial cells.
1. Secretory Unit (of eccrine gland):
Dark cells
- line the lumen and contain
secretory granules
Myoepithelial cells
- lie on the basal lamina
scattered beneath the clear cells
Clear cells
- passes intercellular canaliculi
which extend to the lumen of
of the secretory unit
- underlie the dark cells and are
rich in mitochondria and glycogen
2. Duct of Eccrine Gland

is narrow and lined by a stratified cuboidal epithelium.

leads from the secretory unit, through the superficial portions of the dermis, to
penetrate the interpapillary peg of the epidermis and spiral through its layers to
deliver sweat to the outside.

cell type lining the narrow lumen of the sweat duct contains many keratin filaments
and has a prominent terminal web.

in contrast, the basal layer of cells has many mitochondria and prominent nuclei.
Apocrine Glands

are large specialized sweat glands located in various area of the body, such as the
axilla, the areola of the nipple, and the circumanal region.

do not begin to function until puberty and are responsive to hormonal influences.

have a large coiled secretory portion enveloped by scattered myoepithelial cells.

empty their viscous secretory products into hair follicles at a location superficial to
the entry of ducts from sebaceous glands.

are innervated by adrenergic fibers.

apocrine implies that a portion of the cytoplasm becomes part of the secretion, but
electron micrographs have shown that this is not true.
Ceruminous (wax) Glands

of the external auditory canal are also included in this category.
Sebaceous Glands

consist of several sacs (alveoli) that empty into a short duct, which in turn empties
into the neck of a hair follicle.

cells at the periphery of the alveoli are flattened and inactive, but near the ducts
mitosis are common.

daughter cells migrate to the alveolus, produce a secretory product and begin to
break down, releasing an oily secretion known as sebum.

process is known as holocrine secretion (both the disintegrated cells and the
secretory material are discharged).
C L I N I C A L
I N T E G R A T I O N
INTEGUMENT
INTRODUCTION:
Skin is the largest organ in the body. It is made up of epidermis and dermis. Hypodermis is not
part of the skin.
Epidermis is made of 5 layers of cells.
Terms to understand:
HYPERKERATOSIS- hyperplasia of the horny layer of the skin (or the cornea).
PARAKERATOSIS- retention of nuclei in the stratum corneum of the skin.
AUTOIMMUNE- immune response of the body against its own tissues, cells or molecules.
ACANTHOLYSIS- loss of intercellular connections resulting in loss of cohesion between
keratinocytes
ACANTHOSIS- epidermal hyperplasia (S. Spinosum)
COMPLEMENT SYSTEM – group of protein that effect lysis of cells & Ag-Ab complexes,
and cytokine release.
CLINICAL INTEGRATION CASES:
 Psoriasis
 Bullous Pemphigoid
 Pemphigus Vulgaris
 Albinism
 Acne
 Psoriasis:
Common chronic inflammatory condition. Worldwide incidence varies, but prevalent in
European population, rare in Blacks and American Indians. Affects 2% of US population.
Distributed over extensor body surfaces (esp. knee and elbow) scalp and lumbosacral
areas. Equal sex distribution . Etiology – autoimmune ( T- cells stimulation -cytokines)
Etiology – autoimmune( T- cells stimulation -cytokines) Autoimmune T- cells (cytokines)
Histopathogenesis :
Increased epidermal turnover (3 – 5days) ---marked epidermal thickening and increase in
size of epidermal ridges. Abnormal keratinocyte differentiation: loss of S. granulosum. S.
corneum thickening and nuclei retention. Weak junctional complexes in superficial layer (
silvery scales)
Bullous Pemphigoid:
Chronic autoimmune blistering disease: skin & mucous membranes.
Histopathogenesis:
Presence of IgG antibodies specific to hemidesmosomes . Autoantibodies (IgG) bind to
basement membrane and stimulate leucocytic infiltration. Eosinophils release proteases that
degrade hemidesmosomes. Fluid accumulation – blister formation. Subepidermal, nonacantholytic blisters - hard to rupture .
PEMPIGHUS VULGARIS
Pemphix (blister / bubble). Rare autoimmune disorder affecting epidermis and mucosal
epithelium
Histopathogenesis:
Auto-immune disorders.Body attacks self whereby antibodies target a component of
desmosomes (cadherins and desmoplakins). Desmosomes (intercellular bridges) disrupted.
Results in acantholysis. Separation of epidermal cells (S. Spinosum). Atrophy of the prickle
cell layer.
Blisters formation: (easy to rupture)
Complications:
Side effects of systemic medications. Secondary bacterial,viral, or fungal infection . Spread
of infection through the bloodstream (sepsis). Loss of extensive amounts of body fluids &
electrolytes.Fatal if untreated . Dysphagia, if in oral cavity.
ALBINISM:
Genetic , Loss of pigmentation of the skin, hair and eyes. Mutation in genes that regulate
melanin synthesis and distribution of melanocytes. More common in Blacks than
Whites.Presents in neonates. Melanin : Retinal development (RPE) & optic nerve routing.
Types: Ocular + Oculocutaneous
Histopathogenesis:
Hereditary condition (autosomal recessive). Inability of the melanocytes to pick up
tyrosine. Inactivity of the tyrosinase enzyme.
tyrosinase
Tyrosine
DOPA
Melanin
VITILIGO:
Depigmentation disorder. Auto immune.Destruction of melanocytes
Types: Focal, Segmental, Generalized distribution in the body.
ACNE:
Histopathogenesis:
 Disturbance in the normal secretion and flow of sebum; Increase in sebum secretion (androgenic stimulation)
 Obstruction of the outflow tract of the sebaceous gland (keratin plugs).
 Superimposed bacterial infection.
 Chronic inflammation of the sebaceous gland.
CARCINOMAS:
SQUAMOUS CELL CARCINOMA:
Cancer of the skin arising from the squamous cells (keratinized)
Histopathogenesis:
 Malignant tumor of keratinocytes
 Exposure to UV with DNA damage (inactivation of P53 gene)
 Loss of orderly maturation with variability in nuclear size and shape
 Hyperkeratosis and parakeratosis
Types: Superficial or infiltrative
Dermis deeply infiltrated by islands and sheets of malignant squamous cells.
The islands have undifferentiated cells, resembling basal cells, around the perimeter.
Islands show squamous differentiation with formation of squamous pearls or swirls.
BASAL CELL CARCINOMA:
Carcinoma arises from the stratum basale cells.
Histopathogenesis:
 UV light
 Involves the basal cells
 Single arrangement of basal cells surrounding group of tumour cells - (Palisade
arrangement)
MALIGNANT MELANOMA:
Malignant transformation of melanocytes. Causes highest # of skin cancer related deaths in
US. More common in whites, Australia / S. Africa
Etiology- exposure to sunlight (UV): (acute, intermittent, blistering)
Histopathogenesis:
 Increased number of melanocytes with large atypical morphology and haphazardly
arranged at the dermo-epidermal junction.
 May invade the dermis – metastases – fatal.
H I S T O L O G Y
L A B O R A T O R Y
Integument
OBJECTIVES:
Upon completion of study or this section the student will be able to:

Distinguish between the 5 layers of epidermal cells in thick skin and the differences
in these found in thin skin.

Describe the organization of the two layer comprising the dermis.

Detail the structure and subdivisions of the pilosebaceous follicle.

Identity the sweat gland and distinguish the duct from the secretory region. List the
cells found in the secretory region and identify the function of each.
ANNOTATIONS

The skin is comprised of an outer epithelium, the epidermis, and underlying
mesenchymal component, the dermis. The epidermis layer is a stratified squamous
keratinizing epithelium that possesses a scattered population of melanocytes,
Langerhans’ and Merkel’s cells.

The dermis is a relatively dense irregular connective tissue, except for a thin cellular
zone, the papillary layer, that lies directly beneath the epidermis. The major portion
of the dermis, called the reticular layer, contains thick woven bundles of type I
collagen and provides a reinforcing physical substrate for the cellular epithelium.

Epithelial derivatives of the epidermis include hair follicles, sebaceous glands and
sweat glands. These structures descend from the surface epithelium and are
contained within the connective tissue of the dermis.

There are two types of skin: thick skin and thin skin. Thick skin is normally
restricted to the soles (plantar surface) of the feet and palmar surface of the hand,
while all other skin is of the thin type.
Characteristics of each type are described in the table below:
CHARACTERS
THICK SKIN
THIN SKIN
Surface Texture
Alternating ridges and grooves
Smooth
Epidermis/Dermis Interface
Interdigitating ridges
Epidermal Strata
S. Basale, S. Spinosum, S.
Granulosum, S. Lucidum, S.
Corneum
Hairs and Sebaceous Glands
None
Dermal papillae alternating
with epidermal pegs
Same as thick skin, except: no
S. Lucidum. The corneum,
granulosum and spinosum
layers are reduced in thickness
Regionally variable
Sweat Glands
Abundant
Moderate
MICROSCOPIC STUDIES
There will be 2 slides used in this exercise:
1. Skin corpuscle (Thick skin)
2. Scalp human I.s
1. Skin Corpuscle (Thick skin):

Scan the section at lowest magnification and distinguish epithelium of epidermal
surface from the connective tissue in the cut hypodermis region. Starting at apical
surface identify the following three layers
1) epidermis - thick epithelial layer which is separated from underlying dermis by the
“scalloped” layer of tightly packed cuboidal/low columnar cells that comprise the stratum
basale:
2) dermis - is distinguished by the densely woven matrix of collagen bundles and paucity of
nucleated cells;
3) hypodermis - is characterized by the clusters of unilocular adipose cells that are
“encapsulated” by dense connective tissue matrices.

At higher magnification focus upon the epidermis. The stratum corneum is the top
and thickest layer.

It is comprised of stacks of dead keratinocytes that are actually ghosts of former cells
that are filled with tonofibrils (bundles of keratin intermediate filaments) enmeshed in
a matrix derived from keratohyaline granules. The fibrils are not evident because
they stain the same as the surrounding matrix.

In specific regions of the corneum there are columns composed of stacked vesicles.
These vessels are interconnected and represent the “ducts” of the sweat glands that
penetrate the epidermis and exit at skin surface.

As you descend deeper into the epidermis you will encounter a cell layer in which the
keratinocytes characteristically possess basophilic keratohyaline granules.

This region called the stratum granulosum is comprised of several layers of
squamous cells. At the basal surface of the granulosum the cells exhibit a sparse
sprinkling of bluish granules and intact nuclei.

As you follow this layer toward the lumen the granules increase in size and density
also the nuclei begin to show signs of degeneration (i.e., they become pyknotic).
Through a process of autolysis, Iysosomes degrade the cytoplasmic components
leaving only the tonofibrils, keratohyaline matrix and a lipid intracellular cement.

When degeneration is complete, the cells have a glassy appearing cytoplasm and
eosinophilic peripheral margin. These cells (4-5 layers) comprise the stratum
lucidum that lies between the granulosum and overlying corneum.

Beneath the granulosum is the malpighian layer, the cells of which express mitotic
cell divisions (the layer responsible for “growth” of the epidermis). The basal surface
of the malpighian layer is thrown up into folds which form the epidermal ridges that
interdigitate with the underlying dermal ridges. The malpighian layer is actually
comprised of two strata, the stratum spinosum and the stratum basale.

The s. spinosum is multilayered and it’s cells characteristically exhibit large numbers
of desmosomes around their periphery. The desmosomes provide a spiny or prickle
appearance which accounts for the nomenclature of this stratum. Most of the spiny
or prickle layer in your sections do not reveal this character, SO, scan the section
until you find a region where individual keratinocytes possess a “moat-like” clear
zone between themselves and adjacent cells. In these regions you may be able to
identify the spines which represent the macula adherens junctions.

The variable thickness of the Malpighian layer that accounts for the epidermal al
ridges is due to variations in thickness of the s. spinosum. The bottom cell layer
which sits upon the basement membrane, the stratum basale, is only one cell thick.
The basale cells are cuboidal or low columnar, tightly packed and tightly adherent to
the underlying basement membrane via hemidesmosomes.

The variable thickness of the malpighian layer that accounts for the epidermal ridges
is due to variations in thickness of the s. spinosum. The bottom cell layer which sits
upon the basement membrane, the stratum basale, is only one cell thick.

The basale cells are cuboidal or low columnar, tightly packed and tightly adherent to
the underlying basement membrane via hemidesmosomes.

Scan the basale layer and find regions in which the keratinocytes contain
accumulations of brownish melanin granules. In these regions melanocytes are
found between the basale cells and the basement membrane. The melanocytes are
not readily distinguishable since they contain less pigment than the adjacent
keratinocytes. Remember that as melanin is synthesized, the melanosomes are
“injected” into adjacent keratinocytes via a process called cytocrine secretion.

The underlying dermis is thrown up into ridges which serve to increase the
adhesiveness of the epidermis to the dermis by creating a greater surface area.

The dermis is composed of very thick bundles of collagen I that are interwoven into
an irregular matrix.

Interspersed among the collagen bundles is a well developed meshwork of elastic
fibers. There are relatively few fibroblasts scattered among the collagen
bundles.

The zone directly beneath the epidermis, called the papillary layer, should contain
many more cells and blood vessels than the lower and thicker acellular region of the
dermis called the reticular layer. Cellular structures that cross the dermis by
extending between the epidermis and hypodermis include the blood vessels and a
number of epithelial sweat gland ducts.

The sweat glands are simple tubular glands derived from the epidermis that
penetrate the dermis as straight epithelial tubes and become highly coiled at the
dermis-hypodermis interface. The sweat gland ducts are lined by a 2 cell-thick
stratified cuboidal epithelium.

In the coiled secretory regions the ducts also contain two layers, but these are not
well presented in your sections. The secretory regions contain dark cells
(glycoprotein [mucoid secreting cells), clear cells (electrolyte transporting cells) and
a number of myoepithelial cells that sit upon the basement membrane. The darker
staining and narrower ducts are easily distinguished from the secretory regions.

Below the dermis is the hypodermis, which is not part of the skin but is a component
of the superficial fascia. The hypodermis characteristically contains pads of
unilocular adipose (panniculus adiposus) interspersed with dense connective tissue
septa.
Identify and check-off each of the following:
 Epidermis
 Hypodermis
 S. Lucidum
 S. Spinosum
 Malpighian layer
 Reticular layer of dermis
 Melanosomes (In keratinocytes)
 Sweat gland ducts
 Epidermal ridges
 Dermis
 Stratum corneum
 S. Granulosum
 S. Basale
 Papillary layer of dermis
 Fat pads
 Keratohyaline granules
 Sweat gland secretory regions
2. Scalp Human l.s:

The scalp is lined by thin skin. Compare the structure and organization of the
epidermis with that of the thick skin in the previous slide. You should observe that the
stratum corneum is greatly reduced in thickness and that there is no visible stratum
lucidum. The granulosum and spinosum layers are also significantly reduced in
thickness. Could the basal layer also be reduced in thickness?

Rather than the weII-developed ridges between the epidermis and dermis, thin skin
exhibits a scattered population of epidermal pegs (knob-like cellular incursions) that
interdigitate with upward projections of the dermis called dermal papillae.

In your slides, the papillary layer of the dermis is only evident by a difference in the
coarseness of the collagen bundles, they are finer but are also more tightly packed.
Distinguish the papillary layer from the reticular layer. The interface between the
dermis and hypodermis is quite distinct in the scalp because of the amount of
adipose in the superficial fascia.

Penetrating from the epidermis into the hypodermis are a large number of
pilosebaceous follicles comprised of hair and sebaceous glands. Scan the section to
get the best (i.e., most complete sagittal) view of a hair follicle. Since the hairs run so
obliquely, it is difficult to see a complete follicle, so study several sections and
generate mental image of the complete structure.

At the base of the follicle, distinguish the dermal papilla that induces growth of the
hair in the overlying keratinocytes. The epidermis descends into the dermis as a
stratified epithelium that comprises the external root sheath.

Near the apical end of this tubular “gland”, the epithelium bulges and forms alveolar
outpocketings that become the sebaceous glands.

Down the epithelial sleeve near the base of the follicle, the hair evolves from
epidermal cells that lie above the dermal papilla. The cells in this vicinity are
frequently loaded with melanin from melanocytes in the epidermis above the
dermal papilla.

The center of the hair is composed of large polygonal epidermal cells that provide for
the medulla. Medullary cells and surface epidermal cells contain a soft keratin.
Keratinization of the hair occurs a short distance up the shaft from the papilla.

The epidermis cells surrounding the medulla form the densely packed,
spindle-shaped cells of the thicker cortex. Cortex cells synthesize hard keratin.

The outer most layer of the hair is comprised of epidermal cells that form the cuticle.
Near the base of the follicle the cuticle cells form a simple cuboidal sleeve around
the cortex. As you ascend the hair the cutical cells become more columnar in
appearance, with their long axes perpendicular to the shaft. Further up the shaft the
cuticle cells reorganize and form heavily keratinized shingle-like cells that are
oriented with their long axes aligned with that of the hair.

The cuticle, the last of the hair layers to differentiate, creates a hydrophobic barrier
which resists infiltration of the histological embedding media. Consequently, in many
sections the cortex and medullary regions of the hair “fall out” of the sections during
preparation.

The epithelial cells surrounding the hair are the root sheath layers. The external
root sheath runs from the skin’s surface to the dermal papilla. The internal root
sheath only extends from the base to about half way up the shaft where the cells
degenerate and create a space between the hair and surrounding external sheath.

The dermis surrounding the root sheath forms a thin dense connective tissue
sheath. Bundles of smooth muscle, the arrector pili muscles, extend from the
upper dermis to the connective tissue sheath near the middle of the follicle.
Contraction of these muscles causes the hair to stand more vertically in relation to
the skin’s surface.

This process produces the infamous “goose bumps’’ which arise in regard to either
fluctuations in environmental temperatures or emotional rushes. The latter may be
elicited by extremes in inputs that range from those pleasures derived from a sensual
caress to those of uncontrollable fear as might occur in the taking of an histology
exam. Have you realized yet that the physiological experiences of “rushes” are the
same despite whether they are derived from pleasure or from pain.

The sebaceous glands are simple alveoli that are lined squamous keratinocytes. As
the cells divide they stratify and enlarge, increasing the diameter of the gland.

As the cells mature toward the center of the gland they acquire large sebum
inclusions (lipids, which are washed out during preparation). Near the center of the
alveoli, the cells degenerate releasing a mixture of sebum and cytoplasm. This is an
example of holocrine secretion.

Interspersed among the hair follicles are sweat glands. They are fewer in number to
those present in thick skin. ln this preparation the cells within the secretory region are
better preserved than in the previous slide.

Staining differences, though close, can be used to distinguish dark (mucoid) cells
from the clear (transporting) cells. The eosinophilic layer at the base of the
epithelium in the secretory region primarily reflects the cytoplasm of flattened
myoepithelial cells. Which side of the basement membrane are they on?
Identify and check-off each of the following:
 Epidermis
 Hypodermis
 Hair
 Melanin
 Hair cortex
 External root sheath
 Arrector Pili muscle
 Sweat gland secretory unit
 Dermis
 Pilosebaceous follicle
 Dermal Papilla
 Hair medulla
 Hair cuticle
 Dermal sheath around hair
 Sebaceous gland
 Sweat gland duct