The Integumentary System
BIO 231
Anatomy and Physiology
The Skin or Integument
Surface area - 1.2 to 2.2
M2
4-5 kg or 9-11 lbs.
7% total body weight
1.5- to 4.0 mm thick
Layers
Epidermis - epithelial
cells
Dermis - fibrous
connective tissue
Vascularized
Hypodermis - mostly
adipose & some areolar tissue
Skin Layers
Cells of the Epidermis
Keratinocytes - produce
fibrous protein keratin
Joined by desomosomes
From the stratum basale
Eventually pushed to the
surface as they fill with & die
Cells of the Epidermis
Melanocytes - produce
melanin
In deepest layer of the
epidermis
Spider shaped
Keratin is transferred as
melanosomes to nearby keratinocytes
Melanin accumulates on
the “sunny”side of the nucleus - shielding it from UV radiation
Cells of the Epidermis
Langerhans Cells
Star shaped - frombone
marrow
Actually macrophages -
immune function
Merkels cells
At the epidermal-dermal
junction
Associated with disclike
sensory ending
combination - Merkels
disc -
Layers of the Epidermis
Thick skin - palms,
fingertips, and soles of the feet
Five layers
Thick skin - rest of the
body
Strata lucidum missing
Other layers reduced in
thickness
Layers of the Epidermis
Stratum Basale - basal
layer
Deepest layer
Rapidly dividing cells
Also called stratum germinativum
10-25% of the cells are
Occasionally Merkel cells
are found
Layers of the Epidermis
Stratum spinosum -
prickly layer
Keratinocytes - flatten
and appear irregular or spiny in shape (prickle cells0
Spines are an artifact of
tissue preparation
Scattered about are
Langerhans’ cells and melanin granules
Layers of the Epidermis
Startum Granulosum
Thin layer (3 to 5 cells
thick)
Keratinocytes drastically
change appearance
Cells flatten and nuclei
& organelles begin to
Accumulate
keratinohyaline (form keratin)and lamellated granules (containa waterproofing
glycolipid spewed into the extracellular space
Cells membranes thicken
Layers of the Epidermis
`Stratum Lucidum - clear
layer
Thin band above the
stratum granulosum
A few rolls of of clear
flat dead kearinocytes
Only in thick skin
Layers of the Epidermis
Stratum corneum
Outermost layer
20 to 30 cells thick
Keratin and thicken
membranes protect skin against abrasion and penetration
Glycolipid between cells the layer
All cells are dead
Average person sheds 18
kg (40 lbs) of skin flakes in a lifetime
Dermis
Second major skin region
Strong flexible
connective tissue
Fibroblasts, macrophages,
some mast cells, & white blood cells
Matrix heavily embedded
with collagen, elastin and reticular fibers
Richly supplied with
nerve fibers, blood vessels and lymphatic vessels
Major portion of hair
follicles, oil and sweat glands are derived from epidermis but reside in the
Dermis
Two layers - thin
superficial papillary layer - areolar connective tissue
Rich with collage and
elastin fibers and blood vessels
Superior surface has
projections called dermal papillae
Associated with sensory
endings
On the palms and soles
the dermal papillae set atop large mounds
- dermal ridges
This elevates epidermis
into epidermal ridges
Sweat glands open on the
ridges - leave trace of sweat - detected as fingerprints
Dermis
Reticular layer - deeper
80% of the thickness of
the dermis
Thick bundles of that run in various planes - most parallel
to surface
Less dense regions -
lines of cleavage ot tension lines
Incisions made parallel
to these lines - skin gapes less and heals more readily
Flexure lines - dermal
folds found near joints
Skin Structure
Sweat (Sudoriferous)
Glands
Over entire body surface
except nipples & parts of the external genitalia
2.5 million per person
Eccrine sweat glands -
most numerous on palms, soles and forehead
Simple coiled tubular
gland - opens with a funnel shaped pore at the surface
Contains 99% water &
traces of salts, vitamin c, antibodies, urea, uric acid, ammonia, and lactic
acid (attracts )
pH 4 to 6
Sweat (Sudoriferous)
Glands
Apocrine glands -
axillary and anogenetial areas - larger
Same components of sweat
+ fatty substances and proteins - more viscous
Odorless but on the skin surface decompose the
secretions - becomes musky unpleasant odor
Activated by stress &
pain - activity also increased by sexual foreplay
Sweat (Sudoriferous)
Glands
Ceruminous glands -
lining of ear canal- secreate cerumen - earwax - may deter insects & block
entry of foreign material
Mammary glands - secrete
milk - discussed later
Sebaceous Glands
Simple alveolar glands -
no visible lumen
Genrally small - except
large on face neck and upper chest
Secrete oily substance
called sebum
Generally secreted into a
hair follicle or occasionally a pore of the skin
Has bactericidal action
Secretion stimulated by
androgens - thus activity at puberty
Cutaneous Glands
Hair (Pili)
Composed of largely dead,
keratinized cells
Dominated b y hard
keratin - tougher & more durable - individual cells do not flake off
Three concentric layers
of keratinized cells
Medulla of large
cells& spaces
Cortex of several layers
of cells
Cuticle - single layer of
overlapping cells - like shingles
Hair pigment form
melanocytes at base of the hair follicle - transferred to cortical cells
Hair Follicle
From epidermal surface
into the dermis
Deep end - hair bulb
Root hair plexus -
network of sensory nerve endings surrounding the hair bulb - responds to hair
movement
Hair papilla - extends
into the hair bulb - contains capillaries
- supplies nutrients to the hair
Arrector pilli - - pulls the follicle into an upright
position - goose flesh
Hair Follicle Structure
Hair Follicle Structure
Types of Hair
Vellus hair- fine pale hair of children and
adult females
Terminal hair - coarser,
longer hair of the eyebrows, scalp
At puberty terminal hair
appear in the axillary & pubic regions of both sexes and on the face, chest
and typically the arms and legs of males
Stimulated by
Nails
Scalelike modification of
the epidermis
Correspond to hooves
& claws of other animals
Hard kerratin
Nail matrix of the nail
bed is responsible for nail growth
Structure of a Nail
Burns
Tissue damage inflicted
by intense heat , electricity, radiation of certain chemicals
All these denature cells
proteins & cause cell death in the affected areas
The major threat of burns
id loss of body fluids
As fluid seeps out -
dehydration and elctrolyte imbalance occurs
This can result in renal
shutdown, circulatory
Fluids must be replace
immediately
Rule of Nines
Used to estimate the
volume of fluid lost by computing the percentage of surface burned
Body divided into 11
areas - each accounting for 9% of the body surface - area around the genetials
accounts for 1%.
Rule of Nines
Classification of Burns
First-degree burns - only
epidermis is damaged
Local redness, swelling
& pain
Typically heal in 2 to 3
days without special attention
Second-degree burns -
injure epidermis and upper region of the
Symptoms mimic those of
first-degree burns - but blisters may also occur
Skin regeneration occurs
usually in 3 to 4 weeks
Both of the above are
often called partial-thickness burns
Classification of Burns
Third-degree burns (full-thickness burns) - involve the
entire thickness of the skin
Affected area maybe gray-white, cherry red or
blackened
Initially little or no
edema
Skin is common treatment
Burns are considered
critical if
1. Over 25% second-degree
burns
2. Over 10% third-degree
3. Third-degree burns on
the face, hands or feet