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THE SKIN (INTEGUMENTARY SYSTEM)
Diane Edmondson, PhD
Learning Objectives:
∙ List the basic functions of the skin and describe its overall structure
∙ Describe basic skin embryology
∙ State the names of the layers of the epidermis and how to distinguish them histologically
∙ Explain ultrastructural (electron microscopic) features of the epidermis and the epidermal/dermal junction
∙ Describe the process of keratinization in the epidermis, hair, and nail
∙ Describe the formation of the water barrier in the epidermis
∙ Name the non-keratinocytic cells in the epidermis and state their functions
∙ Explain the structure and components of the dermis, including types of nerves and vascular system
电脑usb接口∙ State the gments and layers of the hair follicle
∙ Describe the relationship between hair size and pha of hair growth
∙ Describe the structure, location, and function of different types of cutaneous glands
∙ Describe the structure and growth of the nail
Key Words: arrector pili muscle, dermal papillae (dermal ridges), dermal sheath, dermis, duct of sweat gland, epidermis, external root sheath, glassy membrane, hair bulb, hair follicle, hair matrix, hair papilla, hair root, hair shaft, hypodermis, internal root sheath, interpapillary pegs (rete pegs), Meissner's corpuscle, melanocytes of epidermis, melanosomes (melanin granules), myoepithelial cell, Pacinian corpuscle, papillary layer of dermis, reticular layer of dermis, baceous gland, stratum basale, stratum corneum, stratum granulosum, stratum lucidum, stratum spinosum, sweat gland
INTRODUCTION
∙ Skin is one of the largest organs in the human body, reprenting 15-20% of total body weight. It rves many functions, including:
英语万能模板 S – SENSATION (it is a receptor for pain, pressure, touch, temperature)
C – CONVERSION (of precursor molecules into vitamin D)
R – REGULATION (of heat)
A – ABSORPTION (of certain lipid-soluble therapeutic substances)
P – PROTECTION (against injury of many kinds) & PREVENTION (of water loss)
E – EXCRETION (of waste products via sweat glands)
The skin can be divided into compartments
EMBRYOLOGY
∙ Epidermis: single-layered ectoderm multilayered periderm stratified squamous epithelium
o Vernix caosa: desquamated periderm/epidermis; slippery; protective and aids in birth
弃之敝屣∙ Dermis: mesoderm menchyme dermis compod of multiple cell types
∙ Hair: epidermal invagination lanugo hairs (fine, lightly pigmented) mature hairs
∙ Melanocytes: neural crest become melanoblasts in menchyme mature in epidermis
EPIDERMIS
∙ Avascular layers of keratinocytic and non-keratinocytic cells
∙ Thickness ranges from 0.1 – 1.0 mm, depending on location
o The terms “thin” and “thick” skin refer to the thickness of the epidermis
o Thin skin = hairy skin (most of the body)
公平英文o Thick skin = hairless skin (glabrous skin on palmar/plantar surfaces, i.e. palms/soles)
KERATINOCYTES
∙ Squamous cells (forming a stratified epithelium) are the major cellular components of the epidermis
∙ Migrate from the basal layer to the superficial surface over a period of about 3-4 weeks
(approximately 26 days)
UPPER LAYERS OF EPIDERMIS
Stratum corneum:
∙ Multiple layers of “flake-like” cells (a.k.a. squames) filled with keratin, without nuclei or organelles
∙ Very thick on palms/soles becau expod to friction
∙ Eventually shed from skin surface
毕设开题报告Stratum lucidum:
∙ Homogeneous zone (eosinophilic or red) between strata corneum and granulosum
∙ Only prent in thick skin
∙ Cells contain eleidin (remains of broken-down keratohyaline granules)大学四年自我鉴定
Stratum granulosum:
∙ 1-3 layers of flattened cells
∙ Contains keratohyaline granules (basophilic or dark purple)
LOWER LAYERS OF EPIDERMIS (stratum Malpighi or Malpighian layer)
Stratum spinosum:
∙ Often the thickest layer
∙ Suprabasal cells are rounder and superficial cells are flatter
Stratum basale:血凝素
∙ Single row of mitotically-active columnar to cuboidal cells which give ri to other keratinocytes
DESMOSOMES
∙ Cells of the stratum spinosum are joined together by desmosomes (a.k.a. macula adherens), which are visible only by electron microscopy
∙ Desmosomes are compod of:
o Desmogleins and cadherins (transmembrane glycoproteins)
o Plaques (compod of desmoplakins): 2 per desmosome (one associated with each cell)
∙ Tonofibrils within the cytoplasm of the cell attach to the plaque
