Download MBBS (Bachelor of Medicine, Bachelor of Surgery) Dermatology PPT 27 Structure And Fns Skin Lecture Notes
Structure & Functions of Skin
Dermatology
? Dermatology ? defined as `the branch of medicine
concerned with the diagnosis & treatment of skin
disorders'
? However, dermatologists do not confine themselves
purely to a study of intrinsic disorders of the skin
? Must also study internal medicine & the many
environmental & occupational factors that so
frequently cause skin problems
Dermatology
? Probably at least 2000 different skin conditions might
present to the dermatologist; vary enormously in
severity
? Range from cosmetic problems, e.g., dry skin or
wrinkles, through a huge variety of acute or chronic
diseases - disfiguring, itchy or painful, less commonly
fatal to life-threatening conditions
? Certain diseases, if untreated, may prove fatal within
days (e.g., toxic epidermal necrolysis), weeks (e.g.,
pemphigus), months (e.g., malignant melanoma) or
years (e.g., mycosis fungoides)
Dermatology
? The patterns of dermatological diseases / disorders
vary from one country to another
? Even in the same city the work of dermatologists
differ, depending on their particular interests &
expertise & on the social mix of their patients
Dermatology
? Largest organ of the body
? In a 70 - kg person: skin wt- >5 kg; SA = 2 m2
? Consists of a stratified, cellular epidermis & an
underlying dermis of connective tissue
? Epidermis is mainly composed of keratinocytes & is
typically 0.05 ? 0.1 mm in thickness, up to 1.5 mm in
palms & soles
Layers of Skin
? Epidermis: Stratum basale (germinativum)
Stratum spinosum
Stratum granulosum
Stratum lucidum (palms, soles)
Stratum corneum
(Malphigian layer = basal + spinous layers)
? Dermis: Papillary dermis
Reticular dermis
? Subcutaneous Fat
m
HPE Skin - forearm ? very thin epidermis
HPE ? Palm ? stratum lucidum
Different Types of Cells in Epidermis
? Keratinocyte
? Melanocyte
? Langerhans' cell
? Merkel cell
Strata (layers) of Epidermis
? Stratum basale: Columnar / cuboidal cells; large
oval nuclei, dense basophilic cytoplasm
? Stratum spinosum (spinous / prickle cell layer):
Polygonal cells with delicate processes,
desmosomes connect adjacent keratinocytes
? Stratum granulosum: Flattened diamond-
shaped cells filled with coarse basophilic
`keratohyaline' granules
Strata of Epidermis
? Stratum lucidum : Clear layer found in palms
and soles, cells are nucleated, sometimes k/a
transitional cells
? Stratum corneum : Flat, non-nucleated,
eosinophilic layer; cells k/a corneocytes
Dead layer shed during epidermal turnover
Epidermal turnover/ transit time:
? Time taken for a cell to pass from basal layer to
surface of skin
? Apprx. 40 ? 56 days (normal skin)
Melanocyte
? Neural crest derived cells
? Dendritic arborizing cells that synthesize and
secrete melanin containing organelles called
melanosomes
? Located in basal layer; 1:10 ratio
? Epidermal-Melanin Unit: A single melanocyte
supplies melanosomes to 36 keratinocytes (1:36)
? Melanosomes vary in number and size according
to skin type differing skin color
Melanocytes in culture
Melanocyte
? Function of melanin
- Impart colour to skin and hair
- Protect the skin from UV radiation
- Biochemical neutralizer of toxic, free radical
oxygen derivatives
? Melanin: Eumelanin (brown / black) &
phaeomelanin (yellow / red)
Langerhans' cell & Merkel cell
? Langerhans' cell
- Type of macrophage, APCs
- Originate from bone marrow (mesodermal in
origin)
- Role in various immune processes like allergic
contact dermatitis, immune tolerance,
surveillance against neoplasia
? Merkel cell also k/a Merkel-Ranvier cell:
- Oval receptor cells
- Probably derived from keratinocytes
- Associated with sensation of light touch
discrimination of shapes & textures
Dermis
? Papillary dermis ? A thin zone which lies beneath
the epidermis
? Reticular dermis - thick zone which extends from
base of papillary dermis to the surface of
subcutaneous fat
Structure of dermis
? Mainly non-cellular connective tissue
? Constituted of collagen, elastic fibers & ground
substance (mucopolysaccharides, chondroitin
sulphate & glycoproteins)
? Embedded nerves, blood vessels / capillaries,
lymphatics, muscles & pilosebaceous, apocrine
& eccrine units
? Cellular contents include fibroblasts, mast cells,
histiocytes, Langerhans' cells, lymphocytes &
eosinophils
Variation in thickness of skin
? Difference of thickness of the skin is dependent
largely on dermal thickness, with the palms and
soles being thickest (about 1.5 mm) & thinnest
in the eyelids & post-auricular region (about
0.05 mm)
? Children & elderly have thinner skin than adults
? Males have thicker skin than females
Hair
? Hair - a keratinized product of the hair follicle, a tube
-like structure continuous with the epidermis at its
upper end
? Present all over the skin except on vermillion of lips,
palms, soles & skin of nail folds
Types of hair
Types of hair:
1) Lanugo (fine, soft, unpigmented; seen in utero- shed
in 8th-9th month of gestation)
2) Vellus (soft)
3) Terminal (longer, coarse, pigmented)
Also intermediate
After puberty : secondary sexual terminal hair
Hair Cycle
Hair follicles undergo a repetitive sequence of growth
& rest called the hair cycle
Period of active hair growth is Anagen. Duration of
this phase decides the length of hair; In humans, it is
maximum on scalp
Catagen is the regressive phase in which the follicular
activity declines & ceases
The hair stays in the Telogen (resting) phase till the
beginning of next anagen phase
Sebaceous Glands
? Lipid producing holocrine glands
? Arise from the hair follicle at the junction of the
infundibulum & the isthmus
? Distributed al over the body except the palms & soles;
most numerous, large and productive over the face &
scalp
? Mature at puberty are stimulated by various hormones
? Major components of sebum: Triglycerides, wax
esters, squalene, cholesterol esters & cholesterol
Nail
Nail Growth
Functions of nails
Help to grasp & manipulate objects
Help in `pincer grip'
Protect terminal phalanx & fingertip
Serve an aesthetic & cosmetic purpose
Functions of Skin
? Barrier function
? Permeability
? Maintenance of fluid & electrolyte balance
? Thermoregulation- sweating
? Pigmentation
? Immune function
? Sensory receptor
? Endocrine function: Vitamin D synthesis
Thank you!
This post was last modified on 07 April 2022