Download MBBS Dermatology PPT 27 Structure And Fns Skin Lecture Notes

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