2. ➢ ILOs:
• Identify the 2 skin layers and their characteristic histological
features.
• Clarify the structural differences between thin and thick skin.
• Know the histological structure of the dermis.
• Describe the composition of the underlying hypodermis.
• Know skin appendages; keratinous and glandular.
• The histological structure of the sebaceous and sweat glands.
• Identify hair and nail structure.
3. ❑ The skin (the integument) is the
largest body organ, about 16%
of the body weight.
❑ Covers underlying soft tissues.
❑ It consists: Epidermis & Dermis.
❑ The dermo- epidermal junction
is formed of dermal papillae,
interdigitate with epidermal
ridges.
What are the 2 layers of skin??
4. ❑ Derived from ectoderm.
❑ Avascular but rich in sensory
nerve endings.
❑ The epidermis is composed of
stratified squamous keratinized
epithelium (keratinocytes).
❑ Other less abundant cell types;
Melanocytes, Langerhans cells,
and Merkel cells.
Epidermis
5. KERATINOCYTES ???
✓ Represents about 85% of the epidermal cell population.
✓ Its main function is to form keratin which is a protective
layer and continuously shed off.
✓ Keratinocytes of epidermis are arranged in 5 layers:
1.Stratum germinativum (Germinal layer)
2.Stratum spinosum (Prickle cell layer)
3.Stratum granulosum (Granular layer)
4.Stratum lucidum (Clear layer)
5.Stratum corneum (Horny layer)
6. E.M:
L.M:
1. Stratum Germinativum (Germinal or Basal Layer):
• Single layer of basophilic
cuboidal or columnar cells
on the basement membrane
at the dermal-epidermal
junction.
• The nuclei are oval and
basal with occasional
mitotic figures.
• Cytoplasm is rich in
cytokeratin intermediate
filament, ribosomes and
few mitochondria.
• The basal cells are
attached to their neighbors
by desmosomes and to the
basal lamina by
hemidesmosomes.
7.
8. E.M:
L.M:
2. Stratum Spinosum (Prickle Cell Layer):
• The thickest layer,
especially in the epidermal
ridges.
• Consists of generally
polyhedral cells, central
nuclei, cytoplasm actively
synthesizing keratins. Just
above the basal layer, some
cells may still divide.
• The cells are adherent to each
other by many desmosomes.
• Cytoplasm full of tonofilaments,
ribosomes and few mitochondria.
• Cells of superficial layer contain
lamellar granules. These granules
contain lipids and lipoprotein and
released by exocytosis into the
intercellular space and cement the
cells together to be impermeable to
water and foreign substance.
9. During routine preparation of
tissue for sectioning, the cells
often retract from each other
except at the desmosomes.
As a result, the cells appear
to have several ‘spines’: this
is the reason for calling this
layer the stratum spinosum.
For the same reason, the
keratinocytes of this layer are
also called prickle cells.
10. E.M:
L.M:
3- Stratum Granulosum (Granular Layer):
• Consists of 3-5 layers
of flat cells with flat
nuclei.
• They contain intensely
basophilic keratohyalin
granules (source of the
amorphous protein
component of soft
keratin).
• Characteristic features
in granular layer cells;
include Golgi- derived
lamellar granules.
lamellar granules undergo
exocytosis, producing a
lipid-rich, impermeable
layer around the cells.
11.
12. E.M:
L.M:
4- Stratum Lucidum (Clear Layer)
• Found only in thick skin,
consists of a thin,
translucent layer of
flattened eosinophilic
keratinocytes held together
by desmosomes.
• It appears as a clear
unstained or lightly stained
homogenous layer.
• Extremely flattened cells.
• Nuclei and organelles
have been lost, and the
cytoplasm consists almost
exclusively of packed
keratin filaments.
13.
14. E.M:
L.M:
5- Stratum Corneum (Horny Layer)
• The most superficial
layer of the epidermis.
• Thicker in thick
skin.
• Acidophilic scaly
layer of flattened dead
non-nucleated
keratinocytes.
• Cytoplasm is replaced by flat
keratin scales (tonofilaments).
• Lipid accumulation in the
intercellular spaces contributes to
the high waterproof properties of this
layer
• Dead cells are continuously shed
off from the surface and replaced
through mitosis of deeper cells.
17. • Melanocytes are derived from
melanoblasts that arise from
the neural crest.
• These cells are responsible for
synthesis of melanin.
• They may be present amongst
the cells of the basal zone, or
at the junction of the
epidermis and the dermis.
1. Melanocytes:
18. L.M:
• Rounded cell
bodies with central
nuclei and long
cytoplasmic processes
passing between
neighboring
keratinocytes.
• In H& E stained
sections they are not
well demonstrated.
EM → → (Protein Synthesizing Cells)
• Abundant RER, mitochondria, prominent Golgi
apparatus and membrane bound (melanosomes).
• Intermediate filaments are present.
• These granules are transferred from one melanocyte to
a number of adjacent keratinocytes to which it is
associated, forming “ epidermal melanin unit” .
• Their nuclei are (euchromatic).
• No desmosomes between melanocytes & keratinocytes.
• Melanin granules are seen as membrane bound
organelles that contain pigment. These organelles are
called melanosomes. Melanosomes bud off from the
Golgi complex. They enter the processes of the
melanocytes. At the ends of the processes, melanosomes
are shed off from the cell and are engulfed by neighboring
19. Function:
1. Synthesis of melanin pigments which is essential to protect the
skin against ultraviolet rays in sunlight.
2. Determines skin color.
NB: The number of melanocytes; nearly the same in all races. Although,
hereditary and racial factors control the amount and size of melanosomes and
the rate of transfer by melanocytes.
20. 2. Langerhans
Cells
L.M:
• Between cells of stratum
spinosum.
• Need supravital stain to be seen.
• Branching or star cells with
multiple cytoplasmic processes.
• Folded & irregular nucleus.
• Pale cytoplasm.
21. EM:
• Cytoplasm is of low electron density with
Golgi apparatus, little ER, abundant
lysosomes and multivesicular bodies.
• Their nuclei are polymorphic and
irregular.
• The most characteristic and unique
feature of Langerhans cells are their
membrane bound tennis paddle-shaped
granules (Birbeck granules).
• No desmosomes, no keratin filaments
and no melanosomes.
22. Function:
(APCs); dendritic cells (DCs). They play important role in
immunity. Microorganisms cannot penetrate epidermis
without alerting DCs and triggering immune response.
NB. These cells are also found in oral mucosa, vagina and
thymus. They belong to the mononuclear phagocyte system.
23. LM:
• Present in the stratum
germinativum near areas of well-
vascularized, richly innervated
connective tissue.
• Naked terminals of myelinated
nerve fibers enter the epidermis
and form disc-shaped expansions
at the base of Merkel cells.
3. Merkel Cells
Derived from the neural crest
(ectodermal in origin).
24. EM:
• Single cells parallel to the basal lamina. Extend their processes between
adjacent keratinocytes to which they are attached by desmosomes.
• Cytoplasm contains perinuclear small dense cored granules !!!!
• It also contains intermediate filaments.
Function
1. Receptors for fine touch sensation.
2. Present all over the body, particularly numerous in the tips of the fingers,
oral mucosa and the bases of the hair follicles.
26. 1. Papillary layer:
Dermis:
• Thin superficial layer.
• Contains epidermal ridges,
dermal papillae (dermo-
epidermal junction).
• Loose CT rich in collagen
fibers III, blood capillaries &
sensory nerve endings or
receptors for touch and
2. Reticular layer:
• Deeper layer of the dermis.
• Dense irregular connective
tissue, fibers running in
different directions.
• Type I collagen fibers and a
network of thick elastic
fibers.
28. Structure:
Hypodermis:
▪ It is a subcutaneous
layer lies under the
dermis (it is not a part
of the skin).
▪ loose connective tissue
rich in fat cells.
Function:
• 1- Attaches skin to underlying
tissue.
• 2- Storage of fat.
• 3- Contains large blood vessels.
29. 1- Skin glands:
a. Sweat glands
b. Sebaceous glands
2- KeratinousAppendages:
a. Hair
b. Nail
Skin Appendages:
31. a. Sweat glands:
1.Eccrine Sweat Glands: 2.Apocrine Sweat Glands:
▪ Present in the dermis of both thick
and thin skin.
▪ Simple coiled tubular glands.
▪ Merocrine gland.
▪ Conduct the secreted sweat.
▪ Duct cells excrete ions, urea, lactic
acid, and some drugs
▪ Present only in axilla, breast, pubic
and perineal regions.
▪ Function after puberty under
hormonal control.
▪ Secretion is a cloudy viscous
odorless fluid secreted by
merocrine mechanism. Once it is
secreted it acquires a "distinctive"
odor as a result of bacterial
degradation.
NB:
Cerminous (wax) glands of external
ear and glands of Moll in the eyelids
are modified apocrine sweat gland.
32.
33. 1.Eccrine Sweat Glands: 2.Apocrine Sweat Glands:
It is embedded in the dermis and
formed of 3 types of cells:
1-Dark cells: secrete mucus.
2-Clear cells: secrete watery
secretion.
3-Myoepithelial cells: present
between secretory cells and their
basement membrane. Their
contraction aid in expressing
gland's secretion into duct system.
The secretory portion:
- It is coiled and embedded
in the dermis.
- Lined by one layer of
cuboidal or columnar
secretary cells.
- enveloped by basal lamina
with myoepithelial cells in-
between.
35. 1.Eccrine Sweat Glands: 2.Apocrine Sweat Glands:
❑ Continuous with the secretory
unit at its base.
❑ Narrows and passes as a spiral
duct to reach the epithelium,
then opens in a sweat pore.
❑ In the epidermis, there is no
epithelial wall of the duct, sweat
makes its own pathway between
epithelial cells.
The conducting portion:
❑It takes a straight course.
❑Lined with cuboidal
cells.
❑Open into the hair
follicles at location
superficial to the entry of
the sebaceous gland
duct.
36.
37.
38. b. Sebaceous glands:
▪ One of the skin appendages
present mainly in the dermis
of thin skin.
▪ Simple alveolar excretory
glands.
▪ Holocrine glands; the entire
cells become part of the
secretion.
39. ❑ Each alveolus is pear
shaped.
❑ It consists of a solid mass
of polyhedral cells.
❑ The outermost cells are
small and rest on a
basement membrane. The
inner cells are larger,
more rounded, and filled
with lipid.
The secretory portion:
❑ Ducts opens into the upper
part of the hair follicle.
❑ It is embedded in the
dermis close to the hair
follicle.
❑ It is lined by stratified
squamous epithelium.
The conducting portion:
40. The secretion of sebaceous glands is called sebum, its oily
nature helps to keep the skin and hair soft.
Function:
Acne vulgaris: very common chronic
inflammatory dermatosis in adolescents of
both sexes. Appear around puberty due to
physiologic hormonal variations.
42. a. Hair:
▪ Keratinized filamentous
structure projecting on the
epidermis.
▪ Each hair is formed of:
1.Shaft: projecting above the
surface of the skin.
2.Root: embedded in the skin.
3.Hair follicle.
43. 1.Shaft of Hair:
It is the part of hair
projecting above the
surface of the skin,
formed of 4 layers:
a. Medulla.
b. Cortex.
c. Cuticle.
d. matrix.
44. 2.Root of Hair:
• The expanded terminal
part of the hair in the
dermis.
• Indented, and its
concavity fits the shape of
dermal papilla.
• Surrounded by hair
follicle.
45. 3.Hair Follicle
• Downgrowth tubular
invagination of the
epidermis extending into
the dermis and
surrounding the hair.
• It is formed of two
sheathes:
- Internal Root Sheath.
- External Root Sheath.
46. - Connective tissue dermal
sheath:
• The part of dermis that
surrounds the hair follicle.
• Epithelium of external root
sheath is separated from the
dermis by a non-cellular
membrane called glassy
membrane which is their
thickened basal lamina.
47. b. Nail:
▪ Scale like modification of
epidermis made of hard keratin.
▪ Parts of the nail:
a) Free edge
b) Body: dense mass of keratinized cells
c) Root
d) Nail folds
e) Eponychium – cuticle
48.
49. 1- Protection against any insults (Keratin in stratum corneum).
2- Water proof-barrier: (lipid-rich extracellular material).
3- Screening against ultraviolet rays: (melanin pigments).
4- Sensation: (sensory nerve endings).
5- Excretion of Na, thermoregulation: (sweat).
6- immunological and defense mechanisms: (Langerhans cell).
Functions of the integumentary system
