1. Histology of the Skin
Kelli A. Hutchens, MD, FCAP
Director of Dermatopathology
Assistant Professor
Loyola University Medical Center
Assistant Director of Mechanisms of Human Disease
Loyola Stritch School of Medicine
2. Objectives
• Identify the epidermis, dermis, and subcutis of the skin
• Name and label the layers five layers of the of the epidermis
• Compare and contrast the anatomic and histologic differences between thick and
thin skin
• Identify (when possible) / or know the location of the following cells:
– Keratinocyte
– Melanoycte
– Merkel cell
– Langerhan cell
• Describe the general function and location of the following components of the
dermal epidermal junction and intercellular space.
– Hemidesmosomes
– Basement membrane
– Basal layer keratinocytes
– Anchoring fibrils
– Desmosomes
• Name and identify the two regions of the dermis
• Identify and classify the following:
– Eccrine gland
– Sebaceous gland
– Apocrine gland
• Compare and contrast the histologic appearance, function, and location of
Pacinian corpuscles versus Meissner’s corpuscles.
4. Epidermis
• Most superficial layer of the skin
• Composed of multiple layers of keratin
containing epithelial cells = keratinocytes with
Melanocytes, merkel cells, and Langerhans
dispersed throughout
• Major functions:
– Maintenance of fluid and electrolyte balance
– Protection from ultraviolet light
– Sensory and immune function
6. Differences between thin & thick skin
Thin Skin
• Palms of hands and soles of
feet = acral skin
• 5 layers thick stratum
corneum with increased
granular layer
• More sensory receptors
• Lack sebaceous glands and
increased eccrine glands
• No hair follicles
Thick Skin
• Entire body except thick
skin areas.
• Less than 5 layers of
stratum corneum with no
stratum lucidum
• Hair follicles present except
lips, labia minora, and glans
penis
7. Epidermis
• Desquamatization:
– Layers of epidermis represent vertical maturation
from undifferentiated basal cells to fully differentiated
cornified cells
– From basal cell to cornified cell takes about 25 days
• Shorter maturation periods seen in inflammatory conditions
such as psoriasis
• Keratin production also changes as the cell matures and
disruption in the mechanism can effect the integrity of the
keratinocytes such as in Haily-Haily and Darier’s Disease.
8. Epidermis
Basement Membrane
Cell to Cell Adherence
Zona adherens: Ca++ dependent
cadherins that connect to actin
Zona occludens: tight junctions
prevent diffusion across cells
Macula adherens: Made of
desmosomes
Gap junctions: communication for
electric / metabolic function
Hemidesmosomes:
connect cells to BM
10. Epidermis: Melanocytes
Melanocytes: clearish
cells in basal layer
with dark nuclei ; ratio
of 1: 10.
Langerhans’s Cells: dendritic cells of the epidermis. Sit in the mid-spinous. Not
visible by light microscopy.
Merkel Cells: located in the stratum basale. Also not visible by light microscopy.
They are receptor cells that establish synaptic contacts with sensory nerves and
contain granules of neurotransmitters.
11. Dermal-Epidermal Junction
• Connects the epidermis and dermis
• It is composed of proteins which provide a
firm connection
– Hemidesmosome: connects basal keratinocytes to
basement membrane
– Basement membrane
• Lamina lucida = collagen types XVII, XIII, laminin 5 & 6
• Lamina densa = collagen type VII
– Anchoring fibrils attach the basement membrane
to the dermis hooking on to collagen VII and
collagen I.
12. Basement Membrane
Lamina Lucida
Lamina Densa
Basal layer keratinocytes
of epidermis
Basement Membrane
Hemidesmosomes
Collagen type XVII, XIII
Laminins 5 & 6
Collagen Type VII
Anchoring Fibrils
Dermis
Collagen type I
14. Dermis
– Two layers
• Papillary dermis = includes the dermal papilla which
project into the epidermis
– The increases contact area preventing epidermal detachment
» Also results in an undulating pattern which vary by
anatomic location and individual resulting in grooves in
the epidermis =dermatoglyphics (fingerprints)
– Capillaries, free nerve endings and encapsulated sensory
receptors called Meissner’s corpuscles.
• Reticular dermis = area between the papillary dermis
and subcutis
16. Dermis
• The dermis is composed of two major types of
fibers:
– Type I Collagen
– Elastic fibers: three types based on microfiber and
elastin content
19. Sebaceous Glands
• Usually associated with
hair follicles
• Simple branched acinar
glands
– Several acini that empty
into single duct
• Holocrine secretion
• Empty “sebum” into hair
follicle
20. Hair Follicle
Outer Root Sheath
Inner Root Sheath
Hair Cuticle
Hair Medulla
Hair Cortex
cross section
(above the level of the bulb)
Papilla
Bulb
Matrix
Connective Tissue Sheath
21. Eccrine Glands
• Merocrine sweat glands
• Release to adjust body
temperature
• Three cell types
– Dark cells: pyramid shaped
with secretory granules line
lumen of tubule
– Clear cells: located toward
basement membrane
– Myoepithelial cells: spindle
shaped contractile cells
22. Apocrine Glands
• Apocrine glands
– Similar to eccrine glands but
larger lumens and ducts empty
onto superficial regions of hair
follicle
– Release product by shedding of
part of cytoplasm = apocrine
snouting
– Influenced by hormones (sexual
scent glands)
– Only found on axilla, areola,
perianal and genital area
23. Subcutis
Pacinian Corpuscle
• Subcutis
– Area deep to the
dermis
– Includes the
hypodermis
• Loose connective tissue
containing adipose
tissue, nerves, sensory
receptors, arteries and
veins
• Provides a flexible
attachment to the
underlying muscle and
fascia
Hair bulb in the subcutis of
the scalp.
Adipocytes
Editor's Notes
Welcome to basic histology of the skin
We will begin with an overview of the skin. On the left is a cartoon and on the right is a full thickness punch biopsy of the skin, stained with hemotoxlin and eosin, aka h&e,. From superficial to deep the major regions of the skin are the epidermis, dermis, and subcutis. You can see the epidermis stains purple/blue while the collagen of the underlying dermis stains a pinkish hue. The remainder of this tutorial will focus on the important histologic points of each of these regions.
The epidermis is the superficial layer of the skin and is composed mainly of epthelilial cells called keratinoocytes. Amongst the keratinocytes three other types of cells reside. Melanocytes, merkel cells, and Langerhans cells. Together these cells act as a both a barrier to external assault such as the radiating effects of ultraviolet light, dynamic membrane insuring fluid and electrolyte balance is maintained, and an immune organ and sensory organ.
The keratinocytes of the epidermis are organized into 4 or 5 layers depending on the regional location. The layers can be easily remembered with the pneumonic cancel lab get some beer. From superficial to deep the layers on thick skin are the strum corneum, stratum lucidum, stratum granulosum, stratum spinosum, and the basal most layer the stratum basale. Proliferation of these basal layer cells into the epidermis can result in the common neoplasm, basal cell carcinoma.
The section of thin skin on the left has all the same layers in the same order with the exception of the stratum lucidum. Both types of skin have a relatively flat surface with a convolted underside due to the papillary dermis insertion into the epidermis. The finger like projections of epidermis that extend into the dermis are called rete ridges.
The differences between thin skin and thick skin are summarized on this chart. The major differences are the antomic location and the increased thickness of thick skin due to the addition of the stratum lucidum and the thickend corneal layer. Thick skin is only found on the palms of the hands and soles of the feet. Another name for thick skin is acral skin as it is found on these acral surfaces. Additional histologic differences listed here include variation in the adnexal structures of the dermis such as increased sensory strutures and a lack of hair follicles on thick skin which is why we don’t have hairy palms, most of us at least. We will discuss these changes again when we look more closely at the adenexal components of the dermis.
The layers of the epidermis are not static but contantly being replaced through the maturation of cells from the basal layer to the cornified layer. This process is called desquamatization. It takes about 25 days fro a cell to move from the basal layer to the cornified layer. Cells move upward to calcium signalling which results in changes in keratin production and subsequent maturation of the cells. Cells of the basal layer make keratins 5 and 14 while cells of the spinous layer make keratins 1 and 10.
The keratinocytes of the epidermis are connected to one another and the basement membrane by specialized attachement proteins. Some of the most clinically important are the desmosomes which are found inbetween keratinocytes. Desmosomes are composed of various types of desmolgliens. When the desmogleins, specifically desmoglien type 3, are attacked by a persons own immune system in diseases such as pemphigus vulgaris the cells will separate from one another and roll up in balls. This process is called acantholysis and results in crusted and blistered skin lesions. Also clinically important are the hemidesmosomes which anchor the cells of the basal layer to a protein structure called the basement membrane. If the hemidesomosomes are not working correctly the epidermis will lift off the dermis forming a subepidermal blister. This is seen in bullous pemphigoid which creates tense skin blisters most common in the elderly.
This is a high power view of the keratinocytes of the stratum spinosum connected to one another by intercellular bridges made up by desmosomal proteins.
Now lets discuss some of the other cells found in the epidermis. Melanocytes are derived from neuroectoderm and function to produce melanin pigment using the enzyme tyrosinase. Melanocytes are clearsih cells with dark angulated nuclei located in the basal layer. They distribute their pigment to neighboring keratinocytes. The neighboring keratinocytes wear pigment like a cap on top of their nuclei. Pigment functions to block out ultraviolet radiation that can cause mutatations and skin cancers. Albinism is a diesease in which melanocytes are unable to produce pigment due to lack of tyrosinase enzyme activity and thus have very high rates of skin cancer. Benign proliferations of melanocytes are called lentigos and nevi while malignant transformation of these cells results in melanoma. Also located within the stratum basale are merkel cells. Merkel cells also are derived from neuroectoderm and function to establish synaptic contacts and contanin very small granules of neurotranmitters. They are not visible by light microscopy. Langerhans cells are dendritic cells and have a role in the immune function of the skin. They are located in the mid-spinous later but are also not visible on light microscopic exam.
Next lets talk about the dermal epidermal junction. The dej is a
Now we willl take a closer look at the dermis. The dermis is the connective tissue layer below the dej
There are two layers of the dermis. The papillary dermis and the reticular dermis. The papillary dermsi is the most superficial layer just below the epidermis. It protrudes as papilla into the epidermis creating an undulating pattern resulting in increased surface area for greater connectiviey between the two regions. Below the papillary dermis is the reticular dermis.
Here is an H&E stained slide showing the epidemris, papillary dermis and superficial part of the reticular dermis. The papillary dermis is invaginating into the epidermis this is called the dermal papilla. Flanking the dermal papilla are the rete ridges. Inside the dermal papilla you cand see capillaries and small sensory structures called meissners corpuscles. Meissners corpuscles are responsible for fine touch descrimination such as telling two coins apart and are found in higher numbers on the finger tips for that reason.
Lets talk more about the fibers of the dermis. The dermis is composed of type I collagen and elastic fibers. There are three types of elastic fibers:
Within the reticular dermis reside the adnexal structures which includes Sebaceous glands, hair follicles, eccrine glands, and apocrine glands.
Let’s take a closer look at some of these structures. The bubbly clear cells forming acini are the sebaceous glands. They are almost always conncected to a neighborhing hair follicle which is where the release their secrtion keeping hair moisturized and sealed. Next to the follicle in this picture you can see a smooth muscle struture called the pilar muscle composed of cigar shaped myocytes that inserts intog the follicle which allows us to get goose bumps. Eccrine sweat glands can also be seen at the base of this picture.
Here is a closer look at the bubbly clear cells called sebocytes whch group together to make up the sebaceus glands acini. SB are considered simple branched acinar glands which means several acini empty into a single duct. Sebocytes literal desingrate to make their secretion product, this is called holocrine secretion.
The hair follicule is separating into anatomic portions. The upper most portion where the hair connects to the epidermis is called the infudibular portion. Below that is the isthmus portion following by the stem and bulbar portion. These regions can be appreciated on the top right. On the bottom right is a hisologic section of the stem and bulbar portion. The bulb is composed of the hair root and the hair papilla. The hari root contains elanocytes that produce pigment for the hair and the matrix which is composed of specialized epethelial cells that theat can divide and give rise to the inner root sheath. The hair papilla contains capillaries and nerve endings that supply the hair. The hair follicle is composed of many layers cells with the epethelium on the outside surrounding a central hair shaft composed of keratin. The outermost layer is the connective tissue shealth. Then there is the
