Structure and Function of Human Skin

1. Structure and Function of Human Skin Lianjun Chen Huashan Hospital

2. 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, other contagious diseases

4. OUTLINE • Introduction of the Skin • Microstructure of the skin • Epidermis • The basement membrane zone • Dermis • Subcutis • Appendageal Structure • The function of the skin

5. Introduction • The single biggest organ in the body • Cover an average area of 1.5 m2 • Varying thickness (0.4-4mm) • Different color by the race, age, gender & location • Perform many vital roles

6. Microstructure of the skin • Epidermis • Dermis • Subcutis • The basement membrane zone • Appendageal Structure

8. Epidermis • Derived from ectoderm • The celluar external layer • Keratinocyte • non-keratinocyte • Melanocyte • Langerhans’ cell • Merkel cell

9. Keratinocytes • stratum basale, basal cell layer • stratum spinosum, prickle cell layer • stratum granulosum, granular layer • stratum lucidum • stratum corneum, horny layer

11. Keratohyaline Granules

12. keratinocyte non-keratinocyte keratin + ─ tonofilament + ─ desmosome+ ─ dendritic-shaped ─+

13. Function of the keratinocytes • 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

14. 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

17. Non-keratinocytes • Melanocyte • Langerhans cell • Merkel cell

18. Melanocytes • 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

20. Langerhans’ cells • Langerhans’ cells are originate in bone marrow. They exist in the epidermis above the basal layer . • 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.

21. Langerhans’ Granules

22. Birbeck granules

23. Merkel cells • a kind of neurosecretory cell • located directly above the basement membrane and closely associated with neurites, so called Merkel cell-axon complex.

26. Basement membrane zone • The base of basal cell containing hemidesmosome • The lamina lucida • A clear zone crossed by a fine network of anchoring filaments, largely composed of the structural protein laminin • The lamina densa • An electron dense band, largely composed of type IV collagen • The reticular lamina(collagen VII)

29. Dermis • Derived from mesoderm • Papillary dermis & reticular dermis • Connective tissue • Collagen, elastic fiber, reticulum fiber • matrix (mucopolysaccharides) • blood vessel, lymphatics, nerve ending • Appendageal sructure • apocrine gland, eccrine gland, sebaceous gland, hair follicle, nail, et al

31. Subcutis • It consist largely of fat tranversed by nerves and blood vessels. • The name implies that it is not properly the part of the skin, however, it could be an integrated whole as for the function.

32. Appendages • Hair follicles • Sebaceous glands • Sweat glands • Eccine glands • Apocrine glands • Nails Pilosebaceous units

33. Hair follicles • Classification • Terminal hair Scalp,axillae, pubic,beard eyebrow,eyelash,vibrissa • Vellus • lanugo

34. Hair Anatomy • Infundibulum – surface to entrance of sebaceous duct • Isthmus – sebaceous duct to pilar muscle insertion • Lower segment – Stem,Bulb (matrix and papilla) • Perifollicular sheath (mesenchyme)

35. Infundibulum Isthmus Arrector pili muscle Stem Bulb

37. anagen catagen telogen

38. Sebaceous glands • 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(Fordyce’s spots） • areolas(Montgomery’s tubercles) • prepuce(Tyson’s glands) • eyelids(Meibomian’s glands) • Production of sebum

40. Eccrine glands • Distribution: almost all skin site • Exclude the vermilion border of the lip, nympha, phallus, glans, flexion side of prepuce and nail beds • most abundant on the palms, soles and axillae • Reach to skin surface directly • Under psychological and thermal control

41. Eccrine glands • 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

42. Function of the eccrine gland • Dissipate excessive body heat • Soften horniness • Acidify sweat • Take place of partial renal function • Emulsify lipid • Secrete immunoglobulin • ： • ⑴

43. Apocrine glands • Distribution: generally confined to axillae, areolae and the anogenital region. • reach to the hair follicle instead of skin surface • Becoming active at puberty • Producing a protein-rich secretion , sometimes gives out a characteristic odour.

45. Nails • Consist of a dense plate of hardened keratin between 0.3 and 0.5mm thick • The nail is made up of a nail bed, nail matrix and a nail plate. • The thickened epidermis which underlies the free margin of the nail at the proximal end is called the hyponychium. • Fingernails grow at 0.1 mm per day; the toenails more slowly.

48. Skin is the largest organ in the body by weight and surface area. • Skin is composed by three layers : epidermis , dermis and subcutis. • Epidermis is the outer layer composed mainly of keratinocytes but also melannocytes and Langerhan’s cells. • Dermis is a supportive connective tissue layer comprised mainly of collogen but also containing elastin embbed in a matrix of mucopolysaccharides.

49. Hairs are ketatinized tubes emerging from invaginations of the epidermis called follicles. • Sebaceous glands deliver sebum into follicle lubricating the hair surface. • Eccrine sweat glands are found almost over the entire skin surface and innervated by the sympathetic nervous system,responding to temperature/psychological changes. • Apocrine sweat glands are localized (axillae, nipples,perineum,scalp) and androgen-sensitive. • Nails, like hair, are made largely of keratin.

50. Function of the skin • As a barrier • Provides a protective barrier to: • mechanical,thermal,and other physical injury • the ingress of noxious agents • the excessive loss of moisture and protein(if the skin absent or seriously compromised) • The harmful effect of ionizing radiation especially ultraviolet radiation • Sensation • Rich in nerve ending and specialized sensory receptor