deck_16619051 Flashcards
what is integumentary system
The integumentary system consists of the skin and various accessory structures
integument
Can be referred to as skin or integument
Integumentary system overview
.
what percetnage of body weight
12-16 % of total body weight
Largest organ in the body by weight
skin is
Body’s first line of defense against environment
TWO major components of integ system
Cutaneous membrane
Accessory structures
CUTANEOUS MEMBRANE
epidermis
dermis
–> papillary layer
–> reticular layer
(subcutaneous layer)
—> hypodermis
–> not part of cutaneous membrane?
ACCESSORY STRUCTURES
hair shaft
pore of sweat gland duct
tactile (Meissner’s) corpuscle
sebaceous glands
arrector pili muscle
sweat gland duct
hair follicle
Lamellar (Pacinian) corpuscle
Nerve fibres
sweat glands
functions of integumentary system
Protect underlying tissues and organs against impact, abrasion, fluid loss, chemical attack
function vs BLOOD
Acts as a blood reservoir (dermis)
epidermis not vascular, DERMIS VASCULAR
epidermis and cornea
At least four types of tissue. Don’t have a blood supply. One is in your cartilage. Another’s in your eye.
The third’s between your backbones. Between each vertebra. The nucleus pulposus. Is quite avascular.
The last is found all over. The outer part of skin. The epidermis layer. Does not have vessels in.
Fascia is a fifth
function vs temp
Maintain normal body temperature through either vasodilation, vasoconstriction, insulation or evaporative cooling, as needed
function vs excrete
Excrete salts, water, and organic wastes through integumentary glands
sensory function
Detect touch, pressure, pain, and temperature stimuli, and relay the information to the nervous system
functions overview
protect
blood reservoire
temperature hom
excretion
sensory
**
vitamin D
melanin
keratin
Store lipids
skin produce
Synthesizes vitamin D3
Produce melanin, which protects underlying tissue from UV radiation
Produce keratin, which protects against abrasion and serves as water repellent
integumentary system stores
Stores lipids in adipocytes in the dermis
and adipose tissue in the subcutaneous layer (HYPODERMIS)
1) Cutaneous membrane
Epidermis (epi, above)
Composed of stratified squamous epithelium
Dermis
—> Papillary layer ((LOOSE) areolar connective tissue)
—> Reticular layer (dense irregular connective tissue)
Subcutaneous Layer
Subcutaneous Layer
Not technically a layer of the skin
Aka HYPODERMIS or SUPERFICIAL FASCIA
Separates integument from deep fascia
2) Accessory structures
Hairs
Nails
Exocrine glands
Sebaceous glands
Sweat glands
Sensory receptors and
nerve fibers
Arrector pili muscles
Cutaneous plexus (network of blood vessels)
EPIDERMIS
..
Basic Structure of the Epidermis
Superficial, thinner layer of the cutaneous membrane
Epithelial tissue
epidermis structure
Multiple layers (strata) of tightly packed squamous cells
Stratified squamous epithelium
epidermis is
Avascular
There are 4 major cell types in the epidermis:
Keratinocytes
—> The primary cell type in the epidermis
Melanocytes
Langerhans cells
(type of macrophage (WBC))
—> aka INTRAEPIDERMAL MACROPHAGE
Tactile epithelial cells
—> aka MERKEL cells
what does melanin do
Produce melanin, which protects underlying tissue from UV radiation
what does keratinocyte do
Produce keratin, which protects against abrasion and serves as water repellent
KERATINOCYTES
90-95% of epidermal cells
Produce and accumulate keratin (a tough, fibrous protein)
—> protects skin and underlying tissue from mechanical stress, heat, microbes, and chemicals
WHAT ELSE DO KERATINOCYTES PRODUCE
also produce LAMELLAR GRANULES
—> waterproof sealant
MELANOCYTES
produce melanin (pigment)
absorbs damaging ultraviolet (UV) light & contributes to skin colour
transfer melanin to keratinocytes via slender projections that extend between cells (dendrites)
inside keratinocytes, melanin covers & protects nuclear material
WHAT DOES MELANIN DO INSIDE KERATINOCYTES
inside keratinocytes, melanin covers & protects nuclear material
Langerhans Cells (AKA INTRAEPIDERMAL MACROPHAGES)
tissue-resident dendritic cell of the skin
small fraction of epidermal cells
derived from BONE MARROW STEM CELLS (WBC precursor/progenitor)
Tactile Epithelial Cells (aka Merkel cells)
least numerous of epidermal cells
contact a tactile disc (sensory structure)
function in the sensation of touch
EPITHELIAL CELLS THAT TRANSMIT TOUCH TO NERVOUS SYSTEM CELLS (??)
Epidermal layers overview
Entire epidermis lacks blood vessels
…
where do cells get O2/nutrient / recycle waste
Cells get oxygen and nutrients from capillaries in the dermis
how is epidermis structurally organized as a result of lack of BV
Cells with highest metabolic demand are closest to the dermis
how long does it take for new cells to move from deepest stratum layer to most superficial layer of epidermis (skin) ?
Takes about 7–10 days for cells to move from the deepest stratum to the most superficial layer
what happens to cells at superficial layer of epidermis?
Cells in surface layer (STRATUM CORNEUM) remain about 2 weeks before being shed or washed away
stratum corneum
The stratum corneum is the outermost layer of the epidermis and marks the final stage of keratinocyte maturation and development.
Keratinocytes at the basal layer of the epidermis are proliferative, and as the cells mature up the epidermis, they slowly lose proliferative potential and undergo programmed destruction.
epidermal layers – DEEP TO SUPERFICIAL (5 layers)
Stratum basale
Stratum spinosum
Stratum granulosum
Stratum lucidum (only in thick skin)
Stratum corneum
lucidum etymology
Etymology. From Latin tapetum (“tapestry”) and lūcidum (“bright, shining, clear”) the neuter of lūcidum, literally “bright tapestry”.
thin skin
Covers most of body surface
Contains four strata (layers) (NOT LUCIDUM)
Thick skin
Found on palms of hands and soles of feet
Contains five strata (layers)
—> including stratum lucidum
No hair
Stratum basale
1 layer of cuboidal or columnar basal cells (basal keratinocytes)
stratum basale – how attach to basement membrane?
Attached to basement membrane by hemidesmosomes & to other cells via desmosomes
stratum basale – most cells are
Most cells here are basal cells, stem cells that divide to replace more superficial keratinocytes
which other cells present @ Stratum basale?
Also contains Merkel cells and melanocytes
MERKEL CELLS
–> closer to base = closer to nerve cell + plate that it attaches to and sends tactile signals toward
melanocytes?
—> possibly so melanocytes can receive O2/nutrients quicker to produce melanin more effectively
what happens if stratum basale is damaged?
If this layer is damaged, new skin cannot be generated (skin graft necessary)
—> (minor) damage = scars (?)
Stratum spinosum (“spiny layer” or “prickle layer”)
Composed of 8–10 layers of keratinocytes bound together by desmosomes
Provides strength and flexibility
Only looks spiny when on a prepared slide
spinosum etymlogy
The name spinosum is Latin for prickly, spiny,
what does Statum spinosum contain?
Contains Langerhans cells
why spinosum contain langerhans cells?
Langerhans cells are dendritic cells derived from the bone marrow in the stratum spinosum that have an immunologic function. They are identical to tissue macrophages and present antigens to lymphocytes.
CHATGPT
“Location and Function: The stratum spinosum is positioned just above the stratum basale (the deepest layer of the epidermis) and below the stratum granulosum. It’s a good location for Langerhans cells to carry out their function of detecting and processing antigens that penetrate the skin. Langerhans cells are crucial for initiating immune responses by capturing and presenting antigens to T cells.”
CHATGPT
“the stratum spinosum offers a strategic location for Langerhans cells to perform their role in immune defense while maintaining important interactions with other skin cells.”
note keratinocytes of Stratum Spinosum and MELANIN
melanin taken in by keratinocytes (endocytosis) from nearby melanocytes
Stratum granulosum (“grainy layer”)
Composed of 3–5 layers of keratinocytes
Most cells have stopped dividing and started producing KERATIN and KERATOHYALIN
keratohyalin
Keratohyalin is a protein structure found in cytoplasmic granules of the keratinocytes in the stratum granulosum of the epidermis.
keratinocytes in stratum granulosum
Cells grow thinner and flatter
Cell membranes thicken and become less permeable
how is stratum granolosum significant (what does it mark?)
Marks the transition between the deeper, metabolically active strata and dead cells of superficial strata
stratum granulosum and LAMELLAR GRANULES
Contain LAMELLAR GRANULES that release water repellant lipid into cell spaces (of stratums granulosum, lucidum & corneum)
Stratum lucidum (“clear layer”)
Found only in thick skin
3-5 layers of flat, dead cells that appear clear
Flattened, densely packed dead cells filled with KERATIN AND KERATOHYALIN
Adds additional layer of toughness to thick skin
Stratum corneum (cornu, horn)
Outermost, protective region with 15–30 layers of keratinized cells (filled with KERATIN)
what are cells of stratum corneum connected via?
Dead cells still tightly connected by desmosomes
are cells of stratum corneum waterproof? Or water-resistant?
Water resistant, not waterproof
Lose water through insensible perspiration (unable to see or feel) and sensible perspiration (sweat)
SENSIBLE VS INSENSIBLE PERSPIRATION
insensible perspiration (unable to see or feel) and sensible perspiration (sweat)
Epidermal Keratinization
stem cells divide to produce keratinocytes
As keratinocytes are pushed up towards the surface they accumulate keratin
Keratinization ?
replacement of cell contents with keratin
occurs as cells move to the skin surface over 4-6 weeks
they move further away from blood (O2) supply of dermis
gradually they die, are sloughed off, and replaced by cells moving up
NOTE EPIDERMAL GROWTH FACTOR (EGF)
epidermal growth factor (EGF) and other hormone-like proteins play a role in epidermal growth
Epidermal Ridges
Deeper layers of epidermis form epidermal ridges
Adjacent to dermal papillae (papilla, nipple-shaped mound)
Increase surface area for better attachment
Fingerprints vs Epidermal ridges
Pattern of epidermal ridges on surface of fingertips
Unique pattern that does not change during lifetime
Prints of these patterns (fingerprints) used to identify individual
Disorders of the Epidermis
..
Dandruff
excessive amount of keratinized cells shed from scalp
double the normal amount in larger clusters, becomes more visible
Dandruff – causes/ risk factors
Dry skin
Irritated, oily skin
Infections
Psoriasis
chronic skin disorder with genetic link
Cause poorly understood
psoriasis pathophysiology
Rapidly dividing keratinocytes
cells shed in 3 to 5 days as flaky silvery scales
immature keratinocytes produce abnormal keratin
psoriasis, distinctive feature
well-circumscribed (confined?) erythematous plaques with silvery-white scales
psoriasis, commonly found @
commonly found at extensor surfaces (knees, elbows), trunk, and scalp
psoriasis types
Plaque psoriasis
Nail psoriasis
Guttate psoriasis
Plaque psoriasis
Most common type
Described on previous slide
well-circumscribed erythematous plaques with silvery-white scales
commonly found at extensor surfaces (knees, elbows), trunk, and scalp
Nail psoriasis
Psoriasis affecting finger or toenails
causes pitting, abnormal nail growth and discoloration
Nail loss may occur
Guttate psoriasis
usually triggered by a bacterial infection such as strep throat
primarily affects young adults and children
Characterized by small, drop-shaped, scaling spots on the trunk, arms or legs
guttate define
resembling drops or characterized by markings that resemble drops.
gutta = drop
guttatus = speckled
Calluses and Corns
Increased pressure or irritation of the skin leads to HYPERKERATOSIS
Increased keratinocytes in the stratum corneum leads to thickened skin
hyperkeratosis define
abnormal thickening of the outer layer of the skin.
Corns
Smaller, deeper than calluses
have a hard center surrounded by swollen skin
May be painful when pressed
form on the top of the toes or the outer edge of the small toe
calluses are…
where do they develop?
rarely painful
develop on pressure spots, such as the heels, the balls of the feet, the palms and the knees
Dermis overview
Layer between the epidermis and subcutaneous tissue (hypodermis)
Connective tissue layer
Highly vascular
Dermis components
FIBRES:
collagen fibres
elastic fibers
CELLS:
fibroblasts
macrophages
fat cells
hair follicles
Glands
Nerves
Blood vessels
Dermis – fibres
collagen fibres
—> provide tensile strength (resist pushing and pulling)
elastic fibers
—> provide extensibility (ability to stretch) & elasticity (return to original shape)
Dermis – Cells
Fibroblasts
—> secrete ground substance & extracellular matrix
Macrophages
—> phagocytize bacteria & cellular debris
Adipocytes
—> store triglycerides
two distinct layers of the dermis:
- Papillary Region
—> superficial 20% of dermis - Reticular Region
—> deep 80% of dermis
1) Papillary layer of dermis
Named for dermal papillae in this region
—> anchor to epidermis
Composed of areolar tissue
—> thin collagen
—> elastic fibers
Provides cushioning
note way to remember papillary region being compose of AREOLAR CT
areolar etymology
—> “areola (n.) ‘colored circle around a nipple’ (areola papillaris), 1706, from Latin areola, literally “small area,” diminutive of area”
papillary etymology
—> “‘of, pertaining to, or resembling a nipple,’ 1660s, from Latin papilla “nipple” (see papilla) + -ary.”
Note again –> papillary region is like a “cushion” (like breasts)
Note the vasculature in PAPILLARY REGION
Contains:
—> capillary loops that feed epidermis
—> corpuscles of touch
—> free nerve endings for sensations of heat, cold, pain, tickle, and itch
do corpuscles of touch & other nerve endings connect to TACTILE EPITHELIAL CELLS?
presumably yes (?)
2) Reticular layer of dermis
Interwoven meshwork of dense irregular
connective tissue
—> with thick COLLAGEN and ELASTIC FIBRES
why dense irregular
force from various directions
reticular layer contains
blood and lymphatic vessels
nerve fibers
accessory organs (hair follicles, sebaceous and sudoriferous glands)
adipocytes
(note that fat is in dermis (cutaneous) as well as hypodermis (subcutaneous)
compare CONTENTS of papillary vs reticular layer
PAPILLARY
= capillary loops,
corpuscles of touch,
free nerve endings
RETICULAR
= BV, LV,
nn fibres (not just ends)
= accessory organs,
adipocytes
IMPORTANT NOTE ABOUT RETICULAR LAYER OF DERMIS
even though RETICULAR is in the name, it is NOT composed of reticular (LOOSE) CT
It is composed of DENSE IRREGULAR CT
biggest difference of contents between papillary and reticular layers of dermis
reticular layer contains ACCESSORY ORGANS and ADIPOCYTES
reticular layer contains the BV/nn FIBRES – NOT JUST THE loop/ends
disorders of DERMIS
..
Striae (Stretch Marks)
Excessive or quick stretching of the skin leads to dermal scarring
Dermis is torn, replaced with scar tissue
Most fade with time although may always be there
Striae causes, risk factors
Weight gain, muscle gain, or rapid growth
Pregnancy
Excess cortisol (Cushing syndrome)
SUBCUTANEOUS LAYER (aka HYPODERMIS or SUPERFICIAL FASCIA)
Fascia = sheet
In the body, fascia attaches, wraps, and/or separates deep structures
There is superficial and deep fascia
Subcutaneous layer (not part of skin)
Connective tissue that separates skin from deeper structures
Dominated by adipose tissue
—> Protect and support
—> Important energy storage site
Adipose accumulation pattern (men)
Neck, arms, lower back, buttocks
Adipose accumulation pattern (women)
Breasts, buttocks, hips, thighs
where does fat not generally accumulate regardless of gender?
where does it tend to accumulate regardless of gender?
Few cells on back of hands and surfaces of feet
More in abdominal region
the myth of the superficial fascia…
Fascial adhesions
Fascial stretching
Myofascial release
See —>
https://yogainternational.com/article/view/fascia-myths-and-fascia-facts/
summary:
Myth #1: Rolling on foam rollers and other massage tools breaks down fascial adhesions, knots, and scar tissue.
Myth #2: We feel pain in our bodies because our fascia is full of knots, adhesions, and scar tissue.
Myth #3: Our fascia can become dehydrated and rolling on massage tools helps to rehydrate it.
Burns
Burns are significant injuries
Can damage large areas of skin compromising many essential functions
also…
—> Dehydration and electrolyte imbalance can lead to:
—> Kidney impairment and circulatory shock (hypovolemic)
severity of burn depends on
Depth of penetration
Total area affected
severity rated as
Severity is rated as 1st Degree – 3rd Degree burns
First-degree burns
Partial-thickness burns are either first or second degree burns
Only the surface of the
epidermis affected
E.g.
most sunburns
Second-degree burn
Entire epidermis and maybe some of dermis damaged
Accessory structures not affected
Blistering, pain, and swelling occur
—> Infection can develop from ruptured blisters
Healing takes 1–2 weeks
Third-degree burns
Full-thickness burns are considered third degree burns
Destroys epidermis, dermis, and damage extends into subcutaneous layer
Less painful than second-degree burns (*)
—> Burns nervous structures/nociceptors
Extensive burns of this type cannot repair themselves
—> SKIN GRAFTING usually necessary
Evaluating burns in a clinical setting
Depth of burns
—> Assessed with a pin
—> Absence of reaction to pin prick indicates third-degree burn (loss of sensation)
Percentage of skin that has been burned
—> RULE OF NINES
= Method of estimating percentage of surface area affected by burns
= Modified for children (different body proportions)
Emergency treatment of burns
Replacing lost fluids and electrolytes
Providing sufficient nutrients
—> Increased metabolic demands for thermoregulation and healing
Preventing infection
—> Cleaning and covering burn
—> Administering antibiotics
Assisting tissue repair with skin grafts
—> Areas of intact skin are transplanted to cover the burn site
Skin grafts
SPLIT-THICKNESS GRAFT
(transfer of epidermis and superficial portions of dermis)
FULL-THICKNESS GRAFT
(transfer of epidermis and both layers of dermis)
sources of graft
Autograft—patient’s own undamaged skin
—> Best choice if possible; no rejection by immune system
Allograft—frozen skin from a cadaver
Xenograft—animal skin
Factors influencing skin color
Presence of 3 pigments
3 pigments
Melanin
Carotene
Hemoglobin
other factors that determie skin tone
Degree of dermal blood circulation
Thickness and degree of keratinization in the epidermis
Amount of exposure to ultraviolet (UV) radiation
Amount of exposure to ultraviolet (UV) radiation
Can increase pigmentation even though skin color genetically determined
Melanin
Produced by melanocytes in stratum basale
Differences in skin pigmentation are from amount of melanin produced, not from NUMBER/TYPE of melanocytes
melanin is
Packaged into melanosomes (vesicles)
melanosomes go
Melanosomes transferred to keratinocytes
melanosome – VARY how DEPENDING ON SKIN COLOUR ???
Size of melanosomes and point of transfer varies with skin color
2 types of melanin
Eumelanin
Pheomelanin
Eu =
good
pheo =
grey
Eumelanin
Brown, yellow-brown, or black pigment
Pheomelanin
Pink, red or yellow pigment
Hair, freckles, lips, nipples
Melanin made from (structure)
Made from tyrosine
(non-essential amino acid)
phenylketonuria, tyrosine, and skin tone
“Symptoms of untreated PKU include: Eczema. Skin and/or hair discoloration (LIGHTER compared to other members of their family). Small head size (microcephaly).”
“Because tyrosine is made from phenylalanine, people with PKU can be deficient in tyrosine.”
melanin function
Protect genetic material from UV radiation
2) Carotene
orange-yellow pigment
from food
Beta carotene is a precursor of vitamin A
also helps protect the skin
Effects of blood supply on skin color
Hemoglobin is red pigment found in red blood cells
Blood flows to dermis through SUBPAPILLARY PLEXUS
More blood flow to region results in redder color (erythema)
Less blood flow to region initially results in pale color
Sustained reduction of blood flow decreases available oxygen
From surface view, skin has bluish color (cyanosis)
Most apparent in very thin skin (lips, beneath nails)
SUBPAPILLARY PLEXUS
lead to capillary loops of papillary dermis
Erythema
redness of skin due to enlargement of capillaries in dermis
during inflammation, infection, allergy or burns
Cyanosis
bluish color to nail beds and skin
hemoglobin depleted of oxygen looks purple-blue
Pallor
paleness may be due to shock or anemia
Jaundice
Yellowing of the skin due to increased bilirubin
Due to prehepatic, hepatic, or extrahepatic causes
(See notes from 200FT AP/300PT AP)
Albinism
inherited inability to produce melanin d/t mutation in one of the genes involved with melanin production
E.g.
—> melanocytes inability to produce tyrosinase
melanin not present in hair, eyes or skin
affects vision and sunburn easily
Vitiligo
A chronic, usually progressive disorder causing depigmentation
complete or partial loss of melanocytes causing light colored patches
autoimmune condition in which antibodies attack melanocytes
Freckles (ephelides)
Local increase in concentration of melanin (no extra melanocytes)
Genetic component
Darken due to sun exposure
Lighten in the winter
ephelides etymology
Borrowed from Ancient Greek ἔφηλῐς (éphēlis, “a freckle”),
from ἐπ- (ep-, “upon, over, epi-”) + ἥλῐος (hḗlios, “the sun”) + -ῐς (-is, nominal suffix).
Age Spots (liver spots or solar lentigo)
liver spots is misnomer –> nothing to do with liver
accumulations of melanin over time due to long term sunlight exposure
flat blemishes, light brown to black (darker than freckles)
don’t fade in winter, common in adults over 40
lentigo etymology
late Middle English (denoting a freckle or pimple): from Latin, from lens, lent- ‘lentil’.
Moles (melanocytic nevi)
benign over-growth of melanocytes
can be congenital or acquired
Acquired moles are due to a combination of genetics and exposure to UV radiation, but it is poorly understood
may be flat or raised
nevi (nevus) etymology
Nevus (plural: nevi) is the medical term for a mole
“The term originates from nævus, which is Latin for ‘birthmark’”
How to know if a mole is concerning?
atypical or dysplastic nevi may indicate melanoma
The ABCDEs of moles
A = asymmetry
B = borders
C = color
D = diameter
E = evolving
Malignant melanoma
Main cause is UV light exposure
Extremely dangerous
Cancerous melanocytes grow rapidly and metastasize through lymphatic system
malignant melanoma – survival rate depending on detection
If detected early and removed surgically, the 5-year survival rate is 99 percent
If not detected until after metastasis, the 5-year survival rate drops to 14 percent
Basal cell carcinoma (BCC)
Most common form of skin cancer
Originates in stratum basale due to mutations caused by overexposure to UV radiation
basal cell carcinoma appearance
Appears as transparent or pearly white nodule
(Although there is a variety of appearance)
Basal cell carcinoma survival rate
Virtually no metastasis and most people survive
100% 5-year survival rate
Squamous cell carcinoma (SCC)
Second most common form of skin cancer
Originates in squamous cells of the surface layers of the skin
Caused by overexposure to UV radiation
stratum corneum and stratified squamous cells
In the epidermis of skin in mammals, reptiles, and birds, the layer of keratin in the outer layer of the stratified squamous epithelial surface is named the stratum corneum.
Stratum corneum is made up of squamous cells which are keratinized and dead. These are shed periodically.
stratum corneum (cornu = horn)
outer most layer as protection
“horns” protect
squamous cell carcinoma metastasis?
More likely to metastasize than BCC, but still very rare
5-year survival rate is 99%, especially if detected early
Accessory Structures of the Skin
Hair, Sebaceous Glands, Sweat Glands, Nails
Hair follicles
Produce hairs that protect skull
Produce hairs that provide delicate touch sensations
Exocrine glands
Sweat glands
Sebaceous glands
Sweat glands
assist in thermoregulation and excrete wastes
Sebaceous glands
lubricate epidermis
Nails
Protect and support tips of fingers and toes
Hair overview
Hair is composed of dead, keratinized cells produced in a specialized hair follicle
Found almost everywhere on the body
Each hair produced by a HAIR FOLLICLE
where is hair not found
Except palms of hands, sides and soles of feet, sides of fingers and toes, lips, parts of external genitalia
a hair follicle
Complex structure composed of epithelial and connective tissue that forms a single hair
Functions of hair
senses light touch
= hair root plexus
PROTECTION
= head hair: protects scalp from injury & UV light
= eyelashes & eyebrows: protect eyes from foreign particles
= body: prevents abrasions
prevents heat loss
Hair regions
Hair shaft
—> begins deep within hair follicle, but can be seen on the surface
Hair root
—> anchors the hair into the skin
—> Extends from base of follicle to point where hair shaft loses connection with follicle walls
(???)
The hair shaft and root have 3 layers of cells:
Medulla
Cortex
Cuticle
medulla (hair)
maybe absent in thin hair
where pigment cells are
Cortex (hair)
major part of hair shaft
Cuticle (hair)
single layer of thin, flat, heavily keratinized cells
cuticle etymology
from Latin cuticula, diminutive of cutis ‘skin’.
Medulla or core of hair contains ?
Contains flexible, SOFT KERATIN
Cortex contains
Contains thick layers of HARD KERATIN
Gives hair stiffness
Cuticle contains
Contains HARD KERATIN
Thin, but very tough
what about HAIR FOLLICLE
Found in the dermis
Site of hair growth
The hair follicle regulates hair growth
hair follicles are extensions of…
“The hair follicles are downgrowths of the epidermis in which an ordered array of keratinized cells is gradually pushed upward in the form of hair shafts”
“extend into the first and second layer of your skin and sometimes into the third layer (subcutaneous tissue)”
Hair follicle structure
Internal root sheath
External root sheath
Glassy membrane
Connective tissue sheath
hair bulb
hair papilla
Hair matrix
Internal root sheath
Surrounds hair root and deeper portion of shaft
Produced from hair matrix
External root sheath
Extends from skin surface to hair matrix
Glassy membrane
Thickened, clear basement membrane
Connective tissue sheath
Surrounds the epithelial cells of the hair follicle
hair papilla
(connective tissue papilla)
continuous with CONNECTIVE TISSUE SHEATH
hair bulb
expanded base of hair follicle
(contains hair papilla –> AKA connective tissue papilla)
Hair matrix
actively dividing basal cells in contact with hair papilla
(in diagram, arrow basically points towards very base of the hair root (within the medulla))
Associated structures (hair)
..
Root hair plexus
collection of sensory nerves surrounding the base of the follicle
Arrector pili
smooth muscle attached to hair follicle; contraction pulls hair erect
Sebaceous gland
produces secretions to coat hair and skin surface
Hair growth
..
Hairs grow and shed in hair growth cycle in 4 stages
1) Anagen Phase (Active or Growth Phase)
2) Catagen Phase (Regression Phase)
3) Telogen Phase (Resting Phase)
4) Exogen Phase
different lengths of uncut hairs?
(Variations in growth rate and duration of cycle result in different lengths of uncut hair)
(Shed about 50-100 hairs per day)
hair growth phases, etymology
ana = to grow or change in place; functionally similar
cata = reverse, backward, degenerative
telo = complete; completion; finished
= end
exo = outside; external
1) Anagen Phase (Active Phase)
hair matrix cells actively dividing to produce length
lasts 2–6 years
Hair grows at rate of 0.33 mm/day (0.5 inches per month)
2) Catagen Phase (Regression Phase)
hair matrix cells stop dividing
hair follicle atrophies
2-3 weeks in head hair
3) Telogen Phase (Resting Phase)
Lasts 3-4 months
Hair loses attachment to follicle
Becomes club hair
Club hair is shed when follicle is reactivated and new hair formation begins
4) Exogen Phase
Club hair falls out of follicle
Rate of growth & replacement cycle dependent on:
Genetics
Nutrition
Gender (hormones)
hair growth can be affected by
Illness
radiation/chemo, surgery, medicaitons
blood loss
severe emotional stress
hormones (DHT)
Two types of hair
Terminal hairs
Vellus hairs
Terminal hairs
Large, coarse, darkly pigmented
hairs found on scalp, armpit, eyebrows, eyelashes, facial hair, chest, pubic regions
Vellus hairs
Smaller, shorter, delicate
Found on general body surface
what happens to vellus hairs at puberty? (males)
at puberty vellus hair replaced by terminal hair in response to androgens produced in testes & adrenal cortex
terminal vs vellus hair ratio – men vs women
Adult males
95% terminal hair
5% vellus hair
Adult females
35% terminal hair
65% vellus hair
Hair color?
Due to melanin produced by melanocytes
Melanocytes scattered into matrix of hair bulb
Melanin passed into keratinized cortex & medulla cells of hair
melanin type, hair
dark hair: eumelanin
blond/red hair: pheomelanin
gray hair: decreased melanin production d/t progressive decline in tyrosinase
Hair Conditions
..
Alopecia
partial or complete loss of hair
may be caused by genes, aging, endocrine disorders, chemotherapy, skin disease
chemotherapy and hair loss
drugs kill rapidly dividing cells such as hair matrix cells
the 15% of hairs in resting stage are not affected
WHICH HAIRS NOT AFFECTED BY CHEMOTHERAPY
the 15% of hairs in resting stage are not affected
(TELOGEN PHASE – STAGE 3)
Androgenic Alopecia
Male Pattern Baldness
genetically predetermined disorder due to an excessive response to androgens (DHT)
Hirsutism
excessive body hair or body hair in uncommon areas in females or prepubertal males
Hirsutism causes
Poly Cystic Ovarian Syndrome
Cushing syndrome (excess cortisol)
–> note also listed as risk factor for striae (stretch marks)
Congenital adrenal hyperplasia
Functional tumors of the ovaries or adrenal glands (androgen secreting)
Medications
hirsutism etymology
The word is from early 17th century: from Latin hirsutus meaning “hairy”.
Sebaceous glands
Holocrine exocrine glands that discharge an oily lipid secretion onto skin
Located in the dermis
Associated with hair (so absent on palms, soles of feet)
sebaceous glands vs arrector pili muscles
Contractions of arrector pili muscle cause release of SEBUM onto follicle and skin surface
sebum (from sebaceous glands)
Mixture of triglycerides, cholesterol, proteins, and electrolytes
Lubricates and moisten hair shaft and is antimicrobial
Sudoriferous or Sweat glands
Located in dermis
Produce watery secretion
which muscles squeeze sudoriferous (sweat) glands?
Myoepithelial cells (myo-, muscle)
Squeeze gland to discharge secretion
Two types of sudoriferous glands
Eccrine sweat glands
Apocrine sweat glands
sudoriferous etymology
late 16th century (in the sense ‘sudorific’): from late Latin sudorifer (from Latin sudor ‘sweat’) + -ous.
Eccrine sweat glands
Secrete directly onto surface of the skin
Highest number found on palms (~500 glands/cm2 [~3000/in.2]) and soles
Present at birth
Produce watery secretions with electrolytes
Important in thermoregulation and excretion of wastes
Stimulated during emotional stress (cold sweat)
Apocrine sweat glands
Found in axillae, groin, around nipples, and in pubic region
Ducts open into hair follicle
Active after puberty
—> play a role in “body odour”
Produce sticky, cloudy, odorous secretion with complex composition
Strongly influenced by hormones
—> Stimulated during emotional stress & sexual excitement
Include CERUMINOUS glands and mammary glands
ducts open where?
apocrine:
Ducts open into hair follicle
eccrine:
directly onto surface of the skin
secretion quality?
apocrine:
sticky, cloudy, odorous secretion with complex composition
eccrine:
watery secretions with electrolytes
why apocrine has disctinct smell?
due to interaction with bacteria on skin, not secretion itself
Ceruminous Glands
modified sudoriferous glands in external auditory meatus (EAM)
duct opens into external auditory meatus or into ducts of sebaceous glands there
secretory portion in subcutaneous layer
begins to function soon after birth
what does ceruminous gland do?
Produces CERUMEN:
waxy/lubricating
waterproofs canal
barrier to foreign bodies
Conditions of Glands of the Skin
..
Pimples (comedones)
Increased sebum blocks sebaceous duct and hair follicle
Acne
Numerous pimples caused by excessive sebum production or bacterial inflammation of sebaceous glands
Hormonal connection
Impacted Cerumen
abnormal amount of cerumen in EAM can prevent sound from reaching ear drum
May be structural
Accessory Structures: Nails
Thick sheets of tightly packed keratinized epidermal cells
nails function
Protect exposed dorsal surfaces of tips of fingers and toes
Help limit distortion of digits under physical stress
counter-pressure to palmar surfaces of fingers
—> enhance touch perception and manipulations
allow grasping & manipulation of small objects
scratch & groom the body
fingernail parts
Nail body
Nail bed
Lunula
Free Edge
Nail Root
Nail body
Bulk of the visual part of the nail
pink underneath due to capillaries in dermis
Nail bed
Skin underneath the nail
Lunula
white crescent shaped area at proximal end of nail body
capillaries don’t show through the thickened epithelium in this area
Free Edge
may extend past the distal end of the digit
white because absence of capillaries underneath
Nail Root
portion of nail buried in a fold of skin
Eponychium (epi-, over; onyx, nail)
Portion of stratum corneum of nail root extending over exposed nail
Also known as CUTICLE
Hyponychium
Area of thickened stratum corneum under free edge
Nail matrix
proximal portion of the epithelium deep to the nail root
cells divide mitotically to produce new nail cells
growth influenced by age, health, nutritional status, season, time of day and environmental temperature
AGE-RELATED CHANGES TO THE INTEGUMENTARY SYSTEM
Fewer melanocytes
—> In light-skinned people, skin becomes very pale
—> Increased sensitivity to sun exposure, more likely to sunburn
Drier epidermis (decreased sebaceous gland activity)
Thinning epidermis (declining basal cell activity)
Connections between epidermis and dermis weaken
More prone to injury, skin tears, and skin infection
Reduced vitamin D3 production
Causes muscle weakness and brittle bones
Diminished immune response
Declining numbers of dendritic (langerhans?) cells (to about half of levels at age 21)
Increased chance of skin damage and infection
Thinning dermis
Fewer elastic fibers
Sagging and wrinkling are the results
Decreased perspiration
Sweat glands are less active
Greater risk of overheating
Reduced blood supply
Cools skin and stimulates thermoreceptors
Makes person feel cold even in warm room
Slower skin repair
Example: blister repair 3–4 weeks in young adult takes 6–8 weeks in 65- to 75-year-old
Fewer active follicles
Thinner, finer hairs (gray or white from decreased melanocyte activity)
Altered hair and fat distribution
(decreased sex hormone levels)
Vitamin D3 production
UV radiation causes epidermal cells of stratum spinosum and stratum basale to convert steroid to CHOLECALCIFEROL (vitamin D3)
Liver creates intermediate product; then converted to calcitriol by kidneys
Calcitriol allows calcium and phosphate absorption in small intestine
Diet and vitamin D3 production
Naturally from fish, fish oils, and shellfish
Egg yolks
From fortified food products
Inadequate supply of calcitriol leads to impaired bone growth and maintenance
In children, leads to rickets
In adults, leads to decreased bone density
rickets
Flexible, poorly mineralized bones
From not enough sunlight or not enough dietary cholecalciferol (vitamin D3)
Bone matrix has insufficient calcium and phosphate
Uncommon in United States
In adults, leads to decreased bone density
Partially from insufficient dietary intake
Additionally, skin production of cholecalciferol decreases by 75 percent
Increases risk for fractures
Slows healing process
Wound Healing
..
1) Epidermal Wound Healing
abrasion or minor burn
basal cells migrate across the wound
contact inhibition with other cells stops migration
epidermal growth factor (EGF) stimulates basal cells to divide
full thickness of epidermis results from further cell divisions
2) Deep Wound Healing
injury extends to dermis
complex repair process & scar formation
PHASES:
Inflammatory phase
Migratory phase
Proliferative phase
Maturation phase
(Scar tissue formation)
Inflammatory phase
blood clot unites the wound edge
vasodilatation and increased permeability of blood vessels deliver:
—> neutrophils (phagocytic WBC), macrophages (to clean up debris & microbes) and fibroblasts (to produce scar)
Migratory phase
clot becomes scab
epithelial cells migrate beneath scab to bridge wound
fibroblasts begin forming scar tissue
damaged blood vessels begin to regrow
tissue filling wound here is called GRANULATION TISSUE
Proliferative phase
growth of epithelial cells beneath scab
fibroblasts lay down collagen randomly
blood vessel growth
Maturation phase
scab sloughs off when epidermis is restored to normal thickness
collagen fibers become more organized
fibroblasts begin to disappear
blood vessels restored to normal
Scar Tissue Formation = Fibrosis
scar tissue is different from normal tissue (in this case skin):
collagen fibres more densely arranged
decreased elasticity
fewer blood vessels pale
fewer hairs, glands and/or sensory structures
excess scar tissue is raised above epidermal surface
hypertrophic scar: stays within boundaries of original wound
keloid scar: extends beyond wound boundaries into normal tissue
