Download SKIN - Yengage

SKIN
Basic facts about skin
• Largest organ of the body
• Functions include
1.
2.
3.
4.
Barrier
Regulate body temperature and water loss.
Sensory information
Pigments protect from harmful light.
5. Protect against damage to tissues by
chemicals, heat etc.
The 3 layers of skin
• Epidermis
– Stratified squamous
keratinized epithelium
– Grows continuously
• Dermis
– Connective tissue
– Mechanical support
• Hypodermis
(Subcutaneous fascia)
– Contains adipose
tissue
Layers of skin
Layers of the Epidermis
• From basal lamina to free surface:
1. stratum germinativum
2. stratum spinosum
3. stratum granulosum
4. stratum lucidum
5. stratum corneum
Figure 5–3
Epidermis
Layers of the Epidermis
Figure 5.2b
stratum basale
• Is the deepest layer of the epidermis (closest
to the dermis).
• It is found close to the dermal blood supply.
• It consists of a single layer of columnar or
cuboidal cells which rest on the basement
membrane.
• Basal cells are the stem cells of the
epidermis. Their mitotic activity replenishes
the cells in more superficial layers as these
are eventually shed from the epidermis
which are called as keratinocytes.
• So , this layer is also called as stratum
germinativum or germinal layer.
stratum spinosum
• The cells become irregularly polygonal.
• The cells are attached to one another by desmosomes.
• During routine preparation they retract from each other
except at desmosomes so they appear to have numerous
spines. that's why this layer is called as stratum spinosum.
• Some mitosis can be seen in deeper cells of this layer so
this layer also comes under germinative zone.
stratum granulosum
• Consists, in thick skin, of a few layers of flattened
cells which are characterized by presence of
deeply staining granules in cytoplasm .
• The granules in them consist of protein called
keratohyalin.
• The nuclei of cells in this layer are condensed and
darkly stained (Pyknotic).
• Only one layer may be visible in thin skin.
stratum lucidum
• This layer is so called because it appear
homogenous , the cell boundaries are
extremely indistinct.
• Traces of flattened nuclei can be seen in some
cells.
• The stratum lucidum usually cannot be
identified in thin skin.
stratum corneum
• Most superficial layer of skin.
• This layer is acellular.
• It is made up of flattened scale like elements
(squames) containing keratin filaments embedded in
proteins.
• These squames are held together by a glue like
materials containing lipids and carbohydrates.
• Presence of lipids make it highly resistant to
permeation by water.
• Its thickness is greatest in thick skin.
• The superficial layers of skin are constantly shed of
and are replaced by proliferation of cells in deeper
layers.
• Stratum corneum, lucidum and granulosum are
collectively called as zone of keratinization or cornified
zone.
The Dermis
• Made up of connective tissue.
• Richly innervated and vascularized.
• Consists of 2 layers
Papillary layer :- contain connective tissue of
dermal papillae, these papillae are best
developed in thick skin. Papillae contains
capillary loops, and meissner’s corpuscles..
Reticular layer:- consist of bundles of
collagen fibers. It contain number of
elastic fibers, intervals between fibers is
occupied by adipose tissue.
• It rest on superficial fascia through
which it is attached to deeper
structures.
Dermis
Sensory Structures of Dermis
• Deep touch/pressure:
Pacinian corpuscles
• Light touch/pressure: Meisner’s corpuscles
• Warm temperature: Free nerve endings
• Cold temperature: Free nerve endings
• Pain: Free nerve endings
Thin skin
• Average 0.08 mm thickness of
epidermis.
• All over the body except at
palm and soles.
• Hair present
Thick skin
• Up to 6 x thicker
• Palm, soles etc.
• hairless
Thick skin
Stratum corneum
Stratum lucidum
Stratum granulosum
Stratum spinosum
Stratum germinativum
Papillary layer of dermis
Cells of the Epidermis
• Keratinocytes – produce the fibrous
protein keratin
• Melanocytes – produce the brown
pigment melanin
• Langerhans’ cells – epidermal
macrophages that help activate the
immune system
• Merkel cells – function as touch
receptors in association with sensory
nerve endings
KERATINOCYTES
• Basal layer contain keratinocytes which are
derived from stem cells.
• After enter into the stratum spinosum they
undergo further mitosis these are called as
intermediate stem cells.
• Thereafter they does not divide.
Keratin formation
• Basal cells of epidermis contain
numerous cytokeratin filaments.
• As basal cells moves into stratum
spinosum the protein forming
tonofibrils undergoes changes that
convert them to keratin filaments.
• When epidermal cells reach to stratum
granulosum they synthesize keratohyalin
granules.
• Keratin consist of keratin filaments
embedded in keratohyalin.
• Cells in granular layer also show membrane
bound , circular granules that contain
glycoproteins. These granules are called as
keratosomes or lamellated bodies.
• When these cells die the material in these
granules is released and act as a glue that
hold together flakes of keratin.
Skin color depends on :• blood circulation (red cells)
• the pigments carotene and melanin
•Melanin
• Yellow-brown or black pigment.
• Present in cells of basal layer and
adjoining cells of stratum spinosum.
• Produced by melanocytes in stratum
germinativum or at the junction of
epidermis and dermis.
• Melanocytes are derived from melanoblast that
arise from neural crest cells.
• Stored in transport vesicles (melanosomes)
• Melanin granules formed in melanocyte transferred
to keratinocytes through the processes of
melanocytes. Because of the processes of
melanocytes these are also called as dendritic cells.
Melanocyte
FLEXURE LINES
These are certain permanent lines
along which the skin folds during
habitual movements chiefly flexion.
SKIN APPENDAGES
• Hair
• Glands (sweat glands
and sebaceous glands)
• Nails
Hair
• Hair is distributed over the entire skin surface
except
• Palms, soles, and lips
• Nipples and portions of the external genitalia
• Parts of the hair
• Shaft (visible part)
• Cortex (outer layer)- acellular , made up of keratin.
• Medulla (inner layer)- in thick hair it consist of
cornified cells.
• Cuticle- membrane covering hair surface formed by
flattened cornified cells. These cornified elements
contain melanin which is responsible for color of
hair.
• Both in medulla and cortex air bubbles are present
which are also responsible for color of hair. The
amount of air present in hair increases with age and
loss of pigment also . These are responsible for greying
of hairs.
• Root (embedded part)
• Hair bulb (expanded lower end of root)
• Hair papilla (bulb invaginated from below by dermis)
• Hair follicle (tubular sheath which surrounds the root)
The wall of follicle is made up of
three layers
1. Inner root sheath present in
lower part of follicle.
2. Outer root sheath which is
continuous with stratum
spinosum.
3. Connective tissue sheath
derived from dermis.
Hair Follicles
Hair within
follicle
dermis
papilla
Accessory Structures of Hair
• Arrector Pilli :
• involuntary smooth muscle
• causes hairs to stand up
• produces “goose flesh”
• Sebaceous glands :
• lubricate the hair
• control bacteria
Nails
• Scale like modification of the
epidermis on the distal, dorsal
surface of fingers and toes.
• Made of dead cells packed with
keratin
• Produced in a deep epidermal fold
near the bone called the nail root
• Nail body
• the visible portion of the nail
• covers the nail bed
• Lunula
• the pale crescent at the base of the nail
• cuticle
Structure of a Nail
Figure 5.4
Arrector Pili
• Smooth muscle attaches to follicle
• A sebaceous gland lies in the angle between
hair follicle and arrector pili muscle.
• contraction of muscle raises hairs (goose
flesh)
• This occurs during cold and emotional
excitement.
• Second effect of contraction of muscle is
that sebaceous gland is pressed upon and
its secretion are squeezed into hair follicle.
Sebaceous glands
• Connected to hair follicles, but are
found everywhere except palms
and soles.
• Secrete a waxy, oily substance
(sebum)
• Secretion increases at puberty
Sebaceous
gland
sebaceous gland duct
hair follicle
sebaceous
gland
Sweat glands
• Found everywhere
• Excrete water, salt,
metabolic Wastes
• Function – cooling of the
body
Structures of skin: sweat glands
• Duct segment
• less coiled, leads to epidermis
• Stratified cuboidal epithelium
• Secretory segment
• In deep dermis or hypodermis
• Secretory cells
• Myoepithelial cells lie between
secretory cells, contraction expels
sweat
sweat glands and ducts
Developmental Aspects of
the skin
• Epidermis develops from ectoderm
• Dermis and hypodermis develop from
mesoderm
Applied anatomy
Albinism: There is no melanin pigment , usually an inherited
condition.
Dermatitis: There is redness, swelling, itching & exudation.
Thank you