1,structure And Function

Medical college of Zhengzhou Universituy

Dermatology & Venereology ZHANG Jiang-an ( 张江安 ) Dept. Of Dermatology Zhenzhou University

Skin Diseases Skin diseases are very common 7% of outpatient visits are for dermatologic complaints

Thousands of skin disorders have been described But only a small number account for the vast majority of patient visits

Skin diseases are divided into two large groups Growths: represents a neoplastic change, squamous cell cacinoma, et al. Rashes: an inflammatory reaction in the skin, psoriasis, et al.

Sexually Transmitted Diseases, STD

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Dermatology & Venereology Part I:

Introduction

Part II: Clinical Dermatology Part III: Sexually Transmitted Diseases Exam

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Introduction the Skin: Basic Structure & Function

Skin The skin is the largest organ in the body weighting an average of 4 Kg and making up about 16% of body weight  covering an area of 2 m2 

Its major function is to act as a barrier against an inhospitable environment  to protect the body from the influences of the outside world 

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Anatomy of normal skin Components of skin 

Epidermis: the outermost layer, the major protective layer



Dermis: the middle layer, the major support layer



Subcutaneous tissue (fat): the innermost layer of the skin

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Cell types seen in the epidermis 

Keratinocytes –



principal cell of the epidermis

Melanocytes – found in the basal cell layer – the pigment-producing cell



Langerhans' cells – An important

immunologically competent cell



Merkel cells – present in small numbers in

the basal cell layer

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Keratinocyte  principal cell of the epidermis – originates from ectodermal – has the specialized function of producing keratin

– plays a role in the immune function of the skin – while differentiating and moving upward through the

epidermis, it changes morphologically 

It flattens out, and eventually the nucleus disappears

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the Layers of the Epidermis

horny layer granular layer prickle cell layer basal layer

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the Layers of the epidermis basal layer (basal cell layer) – the only keratinocytes in normal epidermis which undergo cell division  prickle cell layer (stratum spinosum) – the bulk of the living epidermal keratinocytes  granular layer (stratum granulosum) – contains distinctive dark granules that are composed of keratohyalin  horny layer (cornified layer, stratum corneum) – outer non-nucleated barrier layer 10

I. Basal Cell Layer the innermost layer of epidermis cell division occurs only in this layer

– a proportion of the basal cells proliferate,

differentiate, and move in a stepwise fashion through the full thickness of the epidermis

– It can be considered the “stem cell” of the

epidermis

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Basement membrane zone, BMZ

epidermis BMZ

Stained by PAS

dermis  is

a complex multilayered structure, four layers  divides the epidermis from the dermis  can be observed through PAS stain

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Transit time  It is calculated that the

‘transit time’ for a daughter keratinocyte in the basal cell layer of normal skin to reach the outer surface  It is around 50 –75 days in normal skin  In psoriasis this is reduced to

8-10 days 13

II. Prickle cell layer (Stratum spinosum) lies above the basal cell layer Keratinization begins in this layer – The keratinocytes produce keratin, a fibrous protein

that is the major component of the horny layer

derives its name from the “spines”

( intercellular bridges/ desmosomes) – are extensions from keratin within the keratinocytes – functionally they hold the cells together 14

intercellular bridges

Desmosomes is a special cellular bridges that connect keratinocytes each other. no desmosomes between keratinocytes and melanocytes, or Langerhans’ cells, or Merkel cells

desmosomes

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Pemphigus vulgaris epidermis

dermis

ancantholysis

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II. Prickle cell layer (Stratum spinosum)

lamellar granules 

are the special structure in the epidermis

 are visualized with electron microscopy  extrude into the intercellular space and

ultimately are thought to help form the “cement” that holds together the stratum corneum 17

lamellar granules

Ultrastructure of the epidermis

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Lamellar granules in keratinocyte 19

III. Granular layer (Stratum granulosum) The process of differentiation

continues in this layer 

granular cells – acquire additional keratin – become more flattened – contain distinctive dark granules that

are composed of keratohyalin – also contain lamellar granules

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keratohyalin Cell in granular layer

Ultrastructure of the epidermis

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Keratohyalin constitutes dark granules, which are easily seen on light microscope contains – Profilaggrin

the precursor to filaggrin, the latter plays an important role in the aggregation of keratin filaments in the stratum corneum – involucrin  Play a role in the formation of the cell envelope of the cells in the stratum corneum 

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IV. Horny Layer (Stratum Corneum)

 The cells in the stratum corneum – are dead – are large, flat, polyhedral, plate-like envelops

filled with keratin  They are stacked in vertical layers that range in

thickness from 15 to 25 layers on most body surfaces to as many as 100 layers on the palms and soles.  The cells are held together by a lipid-rich cement in

a fashion similar to “bricks and mortar”, and constitute the major physical barrier of the skin

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horny layer

granular layer

High-power view of granular layer, showing sharp transition from the living but non-dividing epidermal cells and the dead anucleate cornified layer 24

Melanocytes  dendritic, pigment-producing cells located in the basal cell layer  epidermal melanin unit – The dendrites of melanocytes extend for long distances within the epidermis, and any one melanocyte is therefore in contact with a great number of keratinocytes – The dendrites serves as conducts through which pigment granules(melanosomes) are transferred to their neighboring keratinocytes.  protect the skin from ultraviolet radiation

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Epidermal Melanin Unit

Keratinocyte melanosome melanocyte 26

Langerhans' Cells  are

dendritic cells among keratinocytes of the prickle cell layer, they constitute 3% to 5% of the cells in this layer

 at

the light-microscopic level, they are difficult to detect in routinely stained sections

 ultrastructurally

they are characterized by a folded nucleus and distinct intracytoplasmic organelles called Birbeck granules 27

Light Micrograph of Langerhans Cells

Revealed by gold chloride staining, in a vertical section of the epidermis

Stained by ATPase method, in an isolated epidermal sheet 28 viewed from the dermal side

Langerhans' cell

lysosomes

Note 1.indented nucleus

Birbeck granules

2. Birbeck granules rod, and racquet-shaped

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Langerhans' Cells  are

of the monocyte-macrophage lineage and originate in bone marrow.

 are

immunologically competent and may act as antigen presenting cells

 are

the first line of immunologic defense in the skin, and function primarily in the afferent limb of the immune response

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Horny Layer

Prickle Layer

Epidermis

Granular Layer

basal cell layer

Dermis 31

Components of Dermis fibers – collagen – elastic fibers

ground substance cells – the fibroblast – the macrophage – the mast cell 32

Dermis The dermis is a tough but elastic

support structure that contains: – blood vessels to supply nutrition  to regulate temperature 

– lymphatics – free nerve endings 

the most important sensory receptors

– cutaneous appendages

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Skin Appendages eccrine sweet glands apocrine sweet glands hair follicle sebaceous glands nails 34

Diagramatic Cross Section of the Skin

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Skin Appendages

Eccrine Sweet Glands  distributed over the entire body surface  are most abundant on the palms, soles, forehead, and

axillae.

 Secretion of sweat occurs as a result of many factors – heat is a prime stimulus to increased sweating – other physiologic stimuli, including emotional stress, are

important as well.

 to help regulate temperature by excreting sweet onto

the surface of the skin

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Diagramatic Cross Section of the Skin

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Skin Appendages

Apocrine Sweet Glands  are

generally confined to the following sites: axillae, areolae , the anogenital region

 do not begin to function until puberty.  serve no known useful function in humans  they are responsible for body odor, bacterial action

on apocrine sweet causes body odor

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High-power view of secretory cells in apocrine glands showing decapitation pattern of secretion 39

Diagramatic Cross Section of the Skin

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Skin Appendages

Hair Follicle

 are distributed over the entire body surface except

for the palms and soles  Types of hair – vellus hairs (short, fine, light colored) – terminal hairs (long, thick, dark colored)  Hair growth cycles – anagen (growing phase ) – catagen (transitional phase ) – telogen (resting phase )

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Phases of the Growth Cycle of a Hair

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Diagramatic Cross Section of the Skin

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Skin Appendages

Sebaceous Glands

 are part of the pilosebaceous unit and so are found

wherever hair follicles are located.  produce an oily substance termed sebum, which may be useful as a skin moisturizer  from the sebaceous glands, sebum drains into the hair follicle, from which it exits onto the surface of the skin  the size and secretory activity of these glands are under androgen control 44



The pilosebaceous unit, showing the sebaceous gland draining into the hair follicle canal 45

Nails Nails are made of keratin produced

in the matrix Nails facilitate fine grasping and

pinching maneuvers

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normal nail

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Subcutaneous Tissue Insulates the body from cold Cushions deep tissues from blunt

trauma Is a reserve food

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Function of skin

SKIN FUNCTIONS  Protects

from external injury  Literally holds all other organs together  Plays a part in fluid balance. Mainly excretes but can also absorb fluid  Temperature control  An important organ of sensation  Absorb ultraviolet radiation  Metabolizes vitamin D  Synthesizes epidermal lipids which are an important protective barrier  Cosmetic function 50

Key points  Three components of skin – Epidermis, dermis and subcutaneous tissue

 Cell

types seen in the epidermis

– Keratinocytes, Melanocytes, Langerhans' cells, Merkel cells

 The

Layers of the epidermis

– basal layer, prickle cell layer, granular layer, horny layer

 Basement

membrane zone  Skin Appendages include ? – eccrine sweet glands, apocrine sweet glands, hair follicle,

sebaceous glands, nails

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Thank you for your attention!