Histology of the Skin

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Histology of the Skin Organ system Histology
(Skin and its appendages.)(VAN 3109) by Dr.
Abdulrahman Bello Crc DEPARTMENT OF VETERINARY
ANATOMY,FACULTY OF VETERINARY MEDICINE,USMANU
DANFODIYO UNIVERSITY, SOKOTOE-mail
abccrcfge28_at_gmail.com (2348039687589)
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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

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Overview of the Skin
Epidermis
Dermis
Subcutis
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Epidermisa stratified epithelium
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Epidermis
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.

• Most superficial layer of the skin
• Composed of multiple layers of keratin containing
  epithelial cells
• keratinocytes with Melanocytes,
• merkel cells,
• Langerhans
• dispersed throughout
• Major functions
• Maintenance of fluid and electrolyte balance
• Protection from ultraviolet light
• Sensory and immune function

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Epidermis Layers
Stratum Corneum
Stratum Lucidum
Stratum Granulosum
Stratum Spinosum
Stratum Basale
Rete ridge
Thin Skin
Thick Skin
Stratum Lucindum
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Layers of epidermis

• Stratum basale/germinativum (basal or forming
  layer)
• One layer thick mitotic cells
• 10-25 melanocytes with processes into next layer
• Merkel cells with sensory neurons
• Stratum spinosum (prickly layer)
• Cells appear spiny due to numerous desmosomes
• Many Langerhans cells
• Stratum granulosum (grainy layer
• Cells flatten
• Organelles/nuclei begin to disintegrate
• Keratin precursor granules begin to form
• Lamellated granules with water-proof lipid form
  and will be spewed out between cells
• Stratum corneum (horny layer)
• Cells are deadtoo far from underlying
  capillaries to live
• 20-30 cells thick up to ¾ of dermal thickness
• Keratin, thickened membranes and glycolipids
  between cells provide overcoat for body to
  protect against water loss and other possible
  assaults on body

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Cells in epidermis

• Keratinocytesepidermal cells that make keratin
• Merkel cellsassociated with touch sensory
  neurons
• Langerhans cellsmacrophages (from dermis)
  migrate in to form spider-like immune barrier
• Melanocytes (at border with dermis) make pigment
  to give skin color

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6-9
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• 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
• 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 convoluted 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.

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Differences between thin thick skin

• Thin Skin

• Thick 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

• 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

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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
  15-25 days (spp defference)
• 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 Dariers Disease.

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Figure 6.2a
6-14
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Epidermis
Cell to Cell Adherence
Zona occludens tight junctions prevent diffusion
across cells
Zona adherens Ca dependent cadherins that
connect to actin
Macula adherens Made of desmosomes
Gap junctions communication for electric /
metabolic function
Hemidesmosomes connect cells to BM
Basement Membrane
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The keratinocytes of the epidermis are connected
to one another and the basement membrane by
specialized attachment 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 sub
epidermal blister. This is seen in bullous
pemphigoid which creates tense skin blisters most
common in the elderly.
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Epidermis
Desmosome Intercellular Bridges
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.
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Epidermis Melanocytes
Melanocytes clearish cells in basal layer with
dark nuclei ratio of 1 10.
Langerhanss 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.
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• 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.

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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.

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Basement Membrane
Hemidesmosomes
Basal layer keratinocytes of epidermis
Laminins 5 6
Lamina Lucida
Basement Membrane
Lamina Densa
Collagen Type VII
Collagen type XVII, XIII
Anchoring Fibrils
Dermis
Collagen type I
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Dermis

• Everything below the dermal epidermal junction /
  basement membrane
• Connective tissue layer with contains blood
  vessels, nerves, sensory receptors, adnexal
  structures

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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 Meissners corpuscles.
• Reticular dermis area between the papillary
  dermis and subcutis
• the epidemris,
• papillary dermis
• 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.

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Papillary Dermis
Capillaries
Papillary Dermis
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Dermis

• The dermis is composed of two major types of
  fibers
• Type I Collagen
• Elastic fibers three types based on microfiber
  and elastin content

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Classification of Glands

• Based on the Mode of Secretion
• Merocrine Gland- No loss of Cytoplasm-e.g. most
  of the compound glands e.g. Pancreas
• Also known as Eccrine or Epicrine
• Apocrine Gland- Partial loss of cytoplasm-e.g.
  lactating mammary gland, sweat glands in the
  axilla and external genitalia
• Holocrine Gland- Complete loss of cytoplasm e.g.
  sebaceous and tarsal gland
• Cytocrine Gland- Cells are released as secretion.
  e.g. Testis (spermatozoa)

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Sebaceous Glands
Reticular Dermis
Erector Pili muscle
Hair Follicle
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Dermal Appendages
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.
Sebaceous Glands
Pilar Muscle
Eccrine Glands
Hair Follicle
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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

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Glands and keratinized appendages Is it
dermisor epidermis?

• Sebaceous glands
• Clumps of epithelial tissue distributed within
  dermis
• Secrete sebumoily, fat-based substance that is
  also anti-bacterial
• Located all over body
• Sweat glands
• Microscopic clumps of epithelial tissue
  distributed within dermis, duct extends out
  through dermis to pore (not pores of face
  complexion which are hair follicles)
• More than 2.5 million glands per person
• Eccrine sweat glands, concentrated on hands and
  soles of feet and forehead, secrete sweat to cool
  body, also cold sweat of fear, emotion.
• Apocrine glands, concentrated in armpits and
  groin, analogous with sexual scent glands of
  other animals, odor comes from bacteria that
  concentrate here.
• Ceruminous glands modified sweat glands in ear
  canal produce ear wax
• Mammary glands modified sweat glands in female
  breast produce mothers milk

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Skin Glands
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Hair Follicle
cross section (above the level of the bulb)
Connective Tissue Sheath
Outer Root Sheath
Inner Root Sheath
Hair Cuticle
Hair Cortex
Bulb
Hair Medulla
Papilla
Matrix
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Hair and clawsmodified structures of epidermis

• Claws
• Scale-like epidermal structure
• Cells bind together and have hard keratin
• Grows out from root of nail
• Hair
• Each shaft has three layers of keratinzed cells
  filled with hard keratin
• Flat, ribbon-like shaft produces kinky hair oval
  shaft makes wavy hair round shaft makes coarse
  hair
• Hair color due to amount of melanins of different
  colors made my melanocytes at base of hair
  follicle red hair also has iron-containing
  pigment gray/white hair due to decreased melanin
  production
• Hair follicle
• Fold of epidermal surface into dermis
• Hair grows from here
• Has nerve plexus to give touch/tickle sensation
• Connective tissue sheath derived from dermis
• Hair length due to relationship between active
  and inactive phases of follicle (e.g., eyebrow
  follicles active only three to four months head
  follicles can be continuosly active for years)

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Hairs and hair follicles
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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

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What is it made of?(histologystudy of tissues)

• Skin is organ made up different tissue types
• Layers of skin are two fundamental types of
  tissue organization
• Epidermis epithelium
• Dermis connective tissue

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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

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Subcutis

• 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

Pacinian Corpuscle
Adipocytes
Hair bulb in the subcutis of the scalp.
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