Anatomy and Function of Skin

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Anatomy and Function of Skin
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Importance of the study of skin diseases

• Common and prevalent diseases
• skin beauty and health care
• reflection of the body health
• (paraneoplastic skin diseases)
• Sex Transmitted Disease(STD),AIDS

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I?Introduction

• Skin - the biggest organ of the human body
• Composition of the skin
• Origin of the skin
• Physiologic function of the skin
• Immune system of the skin

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1.Skin-biggest organ of the human body Three
layers of the skin- epidermis, dermis, and
subcutaneous tissue. Its contiguous with the
environment. The skin protects human body against
exogenous harmful factors and maintains the
homeostasis of the inner environment.
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• 2.Composition of the skin
• epidermis
• dermis
• subcutaneous tissue
• blood vessel, lymphatics, nerve ending, apocrine
  gland, eccrine gland, sebaceous gland, hair
  follicle, nail, et al

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• 3.Origin of the skin
• epithelial structures(epidermis, hair follicle,
  sebaceous gland, apocrine unit, eccrine sweat
  unit and nail) are derived from ectodermal.
• melanocyte, nerve and special sensor are derived
  from neural crest.
• dermis, subcutaneous tissue, lymphatics, blood
  vessel, Langerhans cell, mast cell, fibroblast
  and lipocyte are derived from mesodermal.

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4.Physical function of the skin protection,
secretion, discharge, absorption,
thermoregulation, sense
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• 5.Immune system of the skin
• Regulation of immune response cell elements and
  molecular elements
• Immunosurveillance
• Immune tolerance and rejection

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• II?Epidermis
• keratinocyte
• melanocyte
• non-keratinocyte Langerhans cell
• Merkel cell

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keratinocyte
non-keratinocyte Producing keratin
- tonofilament in the
cytoplasm
- desmosome
- Dendritic-shaped cell -

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keratinocytes 1.stratum basalum,basal cell
layer 2. stratum spinosum,prickle cell
layer 3. stratum granulosum,granular layer
4. stratum lucidum 5.stratum
corneum,horny layer
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Function of the keratinocyte ? Continuously
producing keratin and forming horny layer to
protect against various chemical and physical
factors ? participating immune response in the
skin ? secreting cytokines and helping to
activate T lymphocytes
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• desmosome
• attachment plates between adjacent
  keratinocytes in basal layer and prickle layer
• Desmosome transmembrane protein desmoglein,DG
• desmocollin,DC
• Desmosome cytoplasm plakin
• desmoplakin,DP
• plakoglobulin,PG

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Basement membrane zone plasma membrane lamina
lucida basal lamina
reticular lamina
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• non-keratinocytes
• melanocyte
• Langerhans cell, Lc
• Merkel cell
• indeterminate cells

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• 1.melonocyte
• epidermal melanin unit
• melanocytes are derived from the nerual
  crest and reside in the basal layer. Melanocytes
  are dendritic cells and contain large number of
  melanosomes. Any one melanocyte is contact with
  30-40 keratinocytes through its dendrites, form
  the so-called epidermal melanin unit.
• Protective barrier against UV

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• 2.The Langerhans cell
• Langerhans cells are originate in bone marrow
• They exist in the epidermis above the basal
  layer without keratin filament or desmosomes.
  They are characterized by a folded nucleus and
  distinct intracytoplasmic organelles called
  Birbeck granules,resembling a tennis racquet.
• recognition, uptake, processing, and
  presentation of antigens to sensitized T
  lymphocytes.

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? ? ? ? ? ?
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3.Merkel cell a kind of neurosecretory cell,
located directly above the basement membrane and
closely associated with neurites, so called
Merkel cell-axon complex.
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4.Indeterminate cell They are dendritic
cells without melanosomes and Birbeck
granules,but have positive reaction to OKT6.
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• III?Dermis
• collagen
• elastic fiber
• reticulum fiber
• cell(fibroblast?histocyte?mast cell)
• matrix

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IV?Subcutaneous fat tissue Its composed of
loosen connective tissue and lobules of lipocytes.
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V?Appendages 1.eccrine gland 2.apocrine
gland 3.sebaceous gland 4.hair
follicle 5.nail
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• 1. eccrine gland
• Distribution
• They are found at virtually all skin sites
  except at the following sites border of the lip,
  nympha, phallus, glans, flexion side of prepuce
  and nail beds, and most abundant on the palms,
  soles and axillae. They reach to skin surface
  directly.

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• Composition of the eccrine gland
• Coil gland is composed of a single layer of cells
  with two types pale cell and darker-staining
  cell and regulated by cholinergic nerve.
• The duct is composed of a double layer of
  basophilic epithelial cells and divided into
  intraepidermal component and intradermal
  component.

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• Function of the eccrine gland
• ?dissipate excessive body heat
• ?soften horniness
• ?acidify sweat
• ?take place of partial renal function
• ?emulsify lipid
• ?secrete immunoglobulin

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2.apocrine gland generally confined to axillae,
areolae,the anogenital region.It reaches the hair
follicle instead of the skin surface.
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• 3.sebaceous gland
• Distribute throughout all skin sites except palms
  and soles,greatest abundant on scalp, face,middle
  part of the body and vulvae.
• Always associated with upper portion of the hair
  follicles
• Reach skin surface,such as vermilion border of
  the lip(Fordyces spots), areolas(Montgomerys
  tubercles), prepuce(Tysons glands) and
  eyelids(Meibomians glands).

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• Influence factors
• age,sex,race
• temperature
• hormone
• humidity
• anatomical site
• nutrition factor

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lipase of P.acnes or P. ovale in the sebaceous
gland acts on the sebum to produce free fatty
acids which stimulate inflammatory reactions of
hair follicles and surrounded tissue to form
folliculitis.
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Function of the sebum ?emulsify
water ?constituents of vitamin D ?acidification ?e
mulsify lipid
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• 4.hair
• classification
• long hair(armpit hair, scalp hair, pubic hair)
• short hair(eyebrow, eyelashes,vibrissa)
• ??

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• Composition of the hair
• hair shaft
• hair root
• hair bulb
• transection of the hair
• medulla
• cortex
• hair cuticle

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• hair follicle
• inner root sheath
• outer root sheath
• connective tissue sheath
• hair bulbdermal components in the fundus of hair
  follicle

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• 5.nail
• perionychial area
• nail bed
• nail plate

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VI?Blood vessels and lymphatics and nerves of skin
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