Histology
Stanley Shostak
BioSc
1450
Spring 05
Lecture 7. Integumentary
System
= Skin
Basic Structure
External surface: keratinized squamous epithelium
=
epidermis; embryological source of epidermal appendages
Supported by: thick, dense, fibro-elastic CT = dermis;
highly vascular & contains sensory receptors; e.g., pressure
receptors
(Pacinian corpuscles).
Underlying layer: hypodermis or subcutaneous
layer; loose CT; variable amâts adipose tissue; = superficial
fascia
Epidermis
Thick skin: palms of hands and fingers;
soles
of feet
downward folds: epidermal or rete
ridges
(note: ret- = net) between dermal pegs or papillae in
papillary zone of dermis (see below)
keratinocytes: lineage differentiating
cells;
25 to 50 days course of differentiation
melanocytes: usually confined to basal
layer;
have long dendritic processes; ramify; do not establish cell junctions;
cell bodies located btwn basal epi cells and basement mem. premelanosomes
mature to melanosomes; transferred to keratinocytes;
synthesis
promoted by melanocyte stimulating hormone (MSH) from pituitary
tactile disc: Merkel cells: associated
with
free nerve endings; may be part of diffuse neuroendocrine system
dendritic cell = Langerhan's cells: macrophage-monocyte;
antigen presenting cell (= APC); throughout lower epidermal
layers;
long dendritic processes; atopic and other immunologically based skin
disorders;
stimulated: migrate via dermal lymphatic to paracortical zones of
regional
lymph nodes;
5 morphological layers
stratum germinativum or basale (=
stratum malpighi): germinal layer: adjacent to dermis
stratum spinosum or
prickle cell layer: growth and early keratinization; prickles =
desmosomes; prominent nucleoli and cytoplasmic basophilia indicate
protein
synthesis; cytokeratin: (various types) predominant synthetic
product;
aggregates in intracellular fibrils = tonofibrils; converge on
desmosomes;
stratum granulosum or granular layer:
intracellular granules
stratum lucidum (only extremely thick skin):
homogeneous
stratum corneum or cornified layer:
flattened, fused cell remnants; outer keratinized layer; shed
continuously,
replaced from below
Thin skin: stratum corneum reduced; lucidum
and
granulosum virtually gone, spiosum reduced; rete ridges less prominent.
Dermis
mainly fibroblasts plus usual ct elements; two
zones
papillary dermis: upward projections: dermal
papillae and immediate adjacent CT; loose, highly vascular, fine
interlacing
collagen fibers; fine interlacing network fiber of elastin
subpapillary arterial, venous and lymphatic plexuses
and papillary vascular loops
fine axonal connections of free sensory nerve
endings
(to epidermis)
corpuscle of touch = Meissner's corpuscles
lamellated corpuscle = deep pressure receptor
= Pacinian corpuscle
superficial touch receptor = Meissner's
corpuscle
reticular layer: dense, irregular ct:
interlacing arrangement of collagen fibers; coarse, disposed in thick
irregular
bundles; contains blood vessels to subpapillary plexuses from
hypodermal
cutaneous plexuses; elastin in long thick fibers
Skin appendages: epidermal
extensions
Hairy (versus glabrous [hairless and thick])
regions
scalp: robust, thick, densely
collagenous
dermis; hair follicles long and have numerous sebaceous glands,
arrector
pilae, closely packed
body surface: merocrine sweat glands
short;
hair follicles associated with sebaceous glands sparse; finer hairs
axillae and pubic region: hair oriented
obliquely
to skin surface, often curved rather than straight ÷ curled
hair;
apocrine sweat glands common; associated with hair follicles
hair follicle: shaft & bulb; growth
cycle: growing phase, resting phase, club hair.
bulb: whole
epithelial
mass surrounding dermal papilla
shaft: contains hair; 4 keratinizing
concentric
layers formed by bulb; + outermost layer (external root sheath)
nonkeratinizing
downward extension of stratum germinativum of epidermis
inner 3 keratinizing layers = hair
1) medulla: core of hair shaft; not
distinguished
in fine hair
2) cortex: bulk of hair
3) cuticle: hard, thin, surface of
overlapping
plates; prevent matting anchor hair
outer 2 layers = root sheath
4) internal root sheath (& cuticle): lightly
keratinized; disintegrates at level of sebaceous glands
5) external root sheath: not keratinized;
not part of hair formation; separated from CT by glassy membrane
hair bulb: epithelial layers (1 to 4) merge;
hair matrix = mass of cells destined to form hair plus inner
root
sheath; encloses dermal papilla; keratinocytes & melanocytes
vellus: infants, children, females: body
hair
fine and soft;
terminal hair: coarser hair of scalp; male
sex
hormones produced at puberty cause development of further terminal hair
in pubic and axillary regions of both sexes and replacement of vellus
with
terminal hair on male face
dermal papilla: formed by neural crest
cells;
melanocytes abundant; nerve endings
arrector pili: bundle smooth muscle
fibers;
insert on sheath below sebaceous gland and on dermal papillary area
beneath
epidermis
innervated by sympathetic nervous system;
activated
by cold or fear; expulsion of sebum from sebaceous glands
Sebaceous glands: holocrine secretion (of
cells near duct)
Pilosebaceous unit:
outgrowths of external root sheath; lie within CT sheath of hair;
branched
acinar form with; short duct; lipid-filled vacuoles (poorly stained
cytoplasm);
mitosis in basal layer of acini secrete sebum:
also independent of hair follicle in transition
regions: lips, eyelids, glans penis, labia minora & nipples
Sweat glands also glands of Moll (margins of
eyelids) & wax (ceruminous) glands of external auditory canals;
generally
simple, coiled tubular glands; secrete watery fluid
merocrine sweat glands:
innervated by cholinergic fibers;
stimulated
by excessive body heat, fear-provoking stimuli; Note: absent margins of
lip and glans penis
secretory portion: merocrine = eccrine
secretion;
hypotonic with respect to plasma; contains Na+ and Cl-
other ions urea & sm mol. wt. metabolites (a minor mode of
excretion);
myoepithelial cells surrounding secretory portion; dark (may secrete
glycoprotein)
and clear secretory cells (secrete Na+; water follows)
excretory portion: stratified cuboidal
epithelium;
narrower lumen; no myoepithelial cells; resorbs Na+; may
resorb glycoprotein.
sweat pore: located on epidermal ridge
apocrine sweat glands:
odiferous glands & mammary glands
(modified):areolae
of breasts, axilla and genital regions; apocrine secretion;
viscid,
milky secretion discharged into hair follicles; becomes 'malodorous'
after
action of commensal bacteria; become functional after puberty
larger glands; lumen of secretory portion dilated;
low cuboidal cells; eosinophilic cytoplasm; discontinuous layer of
myoepithelial
cells beneath basement membrane
innervated by adrenergic fibers of sympathetic
nervous
system.
fingernail:
nail plate: dense keratinized plate;
slides
distally over rest of nail bed
hyponychium: skin beneath free end of
nail
plate
nail bed: stratified squamous epithelium;
does
not contribute actively to nail growth
nail root: proximal to nail bed; firmly
attached
to distal interphalangeal joint and periosteum of distal phalanx
nail matrix: thickened
epithelium underlying nail root; pronounced epidermal ridges;
proliferation
and differentiation produces nail growth;
lunular: white crescent shaped area at base
of nail; surface appearance distal part of nail matrix
nail fold: skin overlying root of nail;
eponychium: highly keratinized free edge
of nail fold
Skin circulation: adaptations to heat flow
(loss)
plexuses of anastomosing vessels:
cutaneous plexus: deeper plexus; lies at
junction of hypodermis and dermis; supply fatty tissue of hypodermis;
deeper
aspects of dermis & capillary networks enveloping hair follicles,
deep
sebaceous glands, sweat glands
subpapillary plexus: superficial plexus
beneath
dermal papillae; upper aspects of dermis and capillary networks around
superficial appendages; capillary loop in each dermal papilla
arterio-venous shunts: numberous; control
blood flow
glomus body: dermis finger tips and
peripheral
sites prone to excessive cold; highly convoluted segment of
arterio-venous
shunt enveloped by condensed collagenous tissue; thickened (smooth
muscle?)
wall of artery before junction with vein assumes epithelioid appearance
similar lymphatic drainage
last revised: 02-01-05