Integumentary System Histology

simplest encapsulated receptor

Ruffini corpuscules

epidermal ridge corresponds to an underlying

dermal papilla

Epidermis

made of keratinized stratified squamous epithelium

Dermis

dense irregular, highly vascularized connective tissue and containing numerous sensory receptors

stratum of Malpighi of epidermis - made of

stratum basale (germinativum) + stratum spinosum

four populations of cells of epidermis

keratinocytes, langherhans cells, melanocytes, merkel cells

Stratum basale of epidermis

single layer of small columnar or cuboidal keratinocytes, has int filaments and desmosomes, stem cell mitotic activity here

Cells are bound to each other in epidermis through

desmosomes

hemidesmosomes connect

epidermal cells to BM

stratum spinosum of epidermis

thickest layer of epidermis with keratinocytes, many int filaments and membrane-coating granules, upward migration of keratinocytes

cytokeratin

fibrillar protein of int filaments, specific to epithelial cells

tonofilaments

cytokeratin bundle groups, many in stratum spinosum of epidermis

spines of stratum spinosum of epidermis

small cytoplasmic processes @ lat membranes of cells, where keratinocytes are attached by many desmosomes

stratum granulosum of epidermis

several layers of keratinocytes (larger), has keratohyaline granules and keratinosomes, cornified cells made

keratohialine granules

composed of filaggrin (nonintermediate protein filament) → induces aggregation of keratins → with formation of coarse keratohyalin granules

Keratinosome

have hydrophobic glycophospholipidic complex

stratum corneum of epidermis

thickest, cells filled with keratin, hard cells will slough off

keratinization of stratum corneum of epidermis

process of evolution, from the basal cell, to the superficial, cornified cell, which is shedding off/sloughed off

stratum lucidum of epidermis

only in thick skin, advanced keratinization process, cells contain densely packed keratin filaments and eleidin

Epidermal growth factor (EGF) and interleukin (IL-1α)

influence the growth and development of keratinocytes

Transforming growth factor (TGF)

suppresses keratinocyte proliferation and differentiation

epidermal permeability barrier

outer multilamellar lipid layer (cross-linked to involucrin)
cornified cell envelope of 3 proteins + keratin-filaggrin komplex
tight junctions between cells of the stratum granulosum (claudin)

Cells that are always present in the epithelium

Melanocytes, Langerhans cells, Merkel cells

melanocytes

produce melanin (melanofilaments), first stored in premelanosome of golgi, matures to melanosome by oxidation of tyrosine to DOPA by tyrosinase, go into keratinocytes

melanoblasts

melanocyte precursor, migrating from the neural crest into the basal layer of the epidermis

Langerhans cells (dendritic cells)

red bone marrow-derived cells, mainly in stratum spinosum, in the epidermis as immunologic sentinels, involved in immune responses, use proteins langerin and CDa1 (Birbeck granules)

Process of langerhans cells

phagocytoses the antigen, presents it to a neighboring T cell or enters a lymphatic vessel, migrates to lymph node, reenter the blood circulation, reach site of epidermal antigen and release proinflammatory cytokines to neutralize the antigen

merkel cells

modified epithelial cells, found in the stratum basale, mechanoreceptors (linked to keratinocytes by desmosomes and with intermediate filaments), many in fingertips, around free nerve endings

_________ ________- contains also neuroendocrine vesicles (VIP, P substance) - thus being part also of the DES

merkel cell

Dermis - contains

fibrocytes, fibroblasts and extracellular matrix, blood and lymph vessels, small number of macrophages, lymphocytes and mast cells

Papillary layer of dermis

superficial, has dermal-epidermal junction through papillae, loose connective tissue provides mechanical anchorage and nutrients to epidermis, contains more ground substance

fine nerve fibers in papillary layer of dermis

Meissner corpuscles (tactile stimulation), Krause end bulbs (respond to cold)

reticular layer of dermis

thick bundles of collagen fibers and coarse elastic fibers, sweat glands ducts, hair follicles and muscles, sebaceous glands

Epidermal-dermal junction/interface - ensures

the anchoring of the two layers, one to each other and their separation through the BM

the connection between the epidermis and the dermis is achieved by

- hemidesmosomes
- cell adhesion molecules
- type VII collagen anchoring fibers

Epidermal-dermal junction in protected vs non protected areas

flat in protected, irregular in non protected with papillary crests

Hypodermis

superficial fascia of loose connective tissue and abundant adipose tissue and smooth + striated muscle fibers

Hypodermis function

mobility of the skin
adipose tissue contributes to thermal insulation, storage of metabolic energy and shock absorber.

nutritive arteries of the skin are found

deep in the hypodermis

Profound subcutaneous plexus

at the epidermal-dermal interface n its branches provide blood supply for the adipose tissue in the hypodermis + dermis

superficial subpapillary plexus

under papillae of dermis, vascularization of superficial dermis + forms capillary loops

anastomotic arterio -venous shunts

in dermis, role in the thermoregulation, blood flow controlled by glomuses

Naked nerve endings

found in the epidermis, light pressure and touch stimuli

peritrichial nerve ending

around the base and shaft of the hair follicle, stimulated by the movement of the hair

Merkel disk

encapsulated receptor, discriminates touch, attached to the Merkel cell found in the stratum basale of the epidermis

Meissner corpuscle

in the dermal papillae of palms, feet, around the lips, mammary gland areola, tactile receptors, made of Schwann cells

Pacinian corpuscle

in the hypodermis, transient vibratory stimuli and is the receptor for deep pressure covered by connective tissue layer

Pilosebaceous unit

produce hair and sebum, a hydrophobic secretory product, which protects hair and accentuates hydrophobic characteristics of keratin

components of pilosebaceous unit

hair follicle (shaft + bulb), accompanied by sebaceous glands and arrector pili muscle

Arrector pili muscle

part of pilosebaceous unit, bundle of smooth muscle fibers, controlled by autonomic sympathetic nervous system

Sebaceous glands

holocrine simple saccular/alveolar glands, secrete lipids - sebum, everywhere except for the palms and soles, release into follicle or surface of skin

Sebaceous glands composed of

secretory portion (in dermis), sometimes excretory ducts (stratified squamous epithelium)

merocrine sweat glands

everywhere except lips and genitalia, simple tubulo-glomerular gland

secretory portion of merocrine sweat gland

lined by a pseudostratified epithelium with clear cells (secrete watery), dark cells (secrete proteins) and myoepithelial cells

excretory canalicular portion of merocrine sweat gland - contains

sweat duct and helical path (opens on its surface at a sweat pore)

heat-regulated vs emotional sweat

heat-regulated under cholinergic control, emotional under adrenergic control

Apocrine sweat glands

scent gland, coiled, tubulo-glomerular glands, merocrine

Moll's glands

apocrine sweat glands at eyelids

ceruminous glands

apocrine sweat glands at external auditory conduct, secrete cerumen

Sweat glands innervated by

sympathetic vegetative nervous system