CHAPTER 6

Cutaneous Membrane

skin (epidermis + dermis)

Accessory Structures

hair follicles, nails & exocrine glads

epidermis

superficial stratified squamous epithelium

Dermis

underlying areolar tissue & reticular layer of dense irregular connective tissue

integument

epidermis,demis and accessory structures

layers of the dermis

Papillary layer + Reticular Layer

hypodermis

subcutaneous layer composed of loose connective tissue, interwoven with dermis but not apart of the integumentary layer

7 functions of the epidermis 

1. protection 

2. Excretion

3. regualtion of body temp 

4. synthesis of viatamin D 

5. Storage of lipids 

6. Sensation 

7. Production of melanin 

8. Production of karatin 

epidermis

consists of stratified squamous epithelium which is avascular because superficial cells are inert/dead

main cell type of the epidermis:

keratinocytes

epidermis cell junctions

hemidesmosomes to basal lamina

keratinocytes lifespan

newly formed cells are pushed further and further toward the surface until they are eventually shed 

dermal papillae

the strength of attachment is proportional to the surface area

thin epidermis 

4 layers of keratinocytes that covour most the body

thick epidermis

5 layers of keratinocytes that cover palms and soles

5 layers of the epidermis

stratum corneum,stratum lucidum, stratum granulosum, stratum spinosum, stratum basale

stratum germinativum (stratum basale)

• anchored to basal lamina by hemidesmosomes

• forms epidermal which interlock with dermal papillae

• simple cuboidal/columnar epithelium (keratinocytes)

• provides strong attachment

why do people get calluses ?

Calluses are caused by pressure and wear and tear on your skin’s surface which causes rapid mitosis of skin cells leading to the thickening of the epidermis (protective mechanism) 

why do we get blisters

friction or damage to the epidermis from extreme temperatures (burns, frostbite) a blister forms to protect the underlying tissue from further harm and infection. 

epidermal ridges

ridges ensure good grip of fingers and toes - creates fingerprints ridges and patterns

finger print facts 

• the uniqueness of everyones fingerprint is developed due to genetics in utero 

• everyone has different fingerprints, even identical twins 

• toe prints also have enough uniquness to identify someone

• fingers get pruny when you’re in the water to enhance your grip strength

cell types in stratum germinativum

basal cells - germinative cells (stem cells)

melanocytes - pigment producing cells 

markel cells

sensitive to touch, activate nerve endings by releasing chemicals

stratum spinosum (spiney layer)

8-10 layers joined by desmosomes

includes langerhans (dendritic) cells (phagocytes)

langerhans

play a defensive role in the stratum spinosum by defending against microorganisms and superficial skin cancer

stratum granulosum (grainy layer)

3-5 layers of keratinocytes

cells make large amounts of protein keratin (keratinocytes) and keratohyalin

Keratohyalin

accumulates in granules, promotes dehydration and cross links between karatin fibers 

as cells move up through the stratum granulosum

they get thinner and less permeable creating a tightly interlocked layer of cell, cells begin to die in this layer

at what layer are the cells considered dead?

any layers superior to the stratum granulosum

stratum lucidum

the clear layer only in thick skin

cells are densely packed with keratin & devoid of organelles

stratum corneum

horn

15-30 layers of keritonized, dead cells tightly interconnected by desmosomes keratinized

• Water resistant, insensible water loss (500mL/day

Insensible vs sensible water loss

• Sensible - evaporation 

• Insensible - sweating

Pigments of epithelium 

• Carotene 

• Melanin

Produced by melanocytes in stratum germinativum 

Carotene

an orange/yellow pigment (also found in orange vegetables, can be converted into vitamin A)

• Humans can’t make carotene

Melanin

a yellow/brown pigment (made from tyrosine amino acid)

Melanosomes 

vesicles with melanin packaged into them

Melanosomes turn into

Keratinocytes

Melasosomes in light skinned people

melanosomes get Brocken down in strata germinative and spinosum

Melanosomes in people with dark skin 

melanosomes are Brocken down in strata granulosum 

• Have more melanomas and larger ones 

Function of melanin 

protection from effects of UV radiation, and damage to stratum germinativum 

What is vitiligo?

Vitiligo is a skin condition caused by the autoimmune destruction of melanocytes, the cells that produce melanin, the pigment that gives skin its color

Other effectors of skin colour

dermal circulation and melanosomes 

Dermal circulation 

oxygenated hemoglobin, cold temp, low oxygen 

Oxygenated hemoglobin 

bright red 

• Noticeable in light skinned individuals especially when exercising or flushed (capillaries are dilated)

Cold temp’s effect in dermal circulation 

• Skin capillaries constrict making you look paler (also if blood blow is restricted = paler) 

Low oxygen 

deoxygenated hemoglobin 

Appears dark red &

is blue when seen through pale skin (blue = cyanosis) 

Cholecalciferol 

• (Vitamin D3) - produced by epithelial cells in status spinosum and germinativum in response to sunlight 

• Required for Ca absorption in the digestive tract 

• Liver turns cholecalciferol to a product that the kidneys turn into calcitriol

Calciteriol 

 product formed after the liver converts choleciferol into the product that gets transformed into calcitriol

Ricketts

caused by a vitamin D deficiency results in the bending of abnormally weak and flexible bones under our body 

Vitamin

essential organic nutrient 

Dermis

papillary layer and reticular layer

Papillary layer 

- areolar tissue 

- thrown into folds on the surface = dermal papillae 

- contains capillaries, lymphatics and sensory neurons that supply the surface of the skin 

Lines of cleavage 

• Collagen and elastin in dermis to arranged in parallel bundles 

• Bundles oriented to resist forces normally applied to skin 

    • Establishes lines of cleavage (a line of cleavage will usually remain close and heal with little scarring) 

Severed elastic fibers 

• Lines of cleavage that pull apart from each other making healing longer and may cause scarring 

Cutaneous plexuses 

• Network of arteries and veins between dermis and hypodermis

Dermal Blood supply 

• Dermis is well supplied with blood vessels 

• Network of veins between dermis and hypodermic ; cutaneous plexuses

• These feed into sub capillary plexuses tat supply capillaries extending into papillae = source of O2 & nutrients for epidermis

Nerve cells

regulate blood flow, adjust gland secretion rates and monitor sensory receptors 

Sensory receptors 

respond to light touch, deep pressure, vibration, chemicals, temperatures & damage

appendages of the skin 

hair follicles,hair, nails, sweat glands, sebaceous glands, ceruminous glands

terminal hair

hair on head

specialized TH

eyelash and brow

Vellus Hair

body hair

lunugo

baby hair

hair’s function

insulates and protects scalp

protects nostrils and ear canals 

detects movement through hair plexus sensory nerve 

arrector pili muscle stands up + goose bumps

armpit hair

before/ during puberty - vellus hair

after puberty/adult - terminal hair

phase 1 of hair growth

the active phase lasts 2-5 years. During the active phase, the hair grows approximately 0.33mm/day

phase 2 in hair growth

the follicle begins to undergo regression and transitions to the resting phase

phase 3 of hair growth

during the resting phase the hair loses it’s attachment to the follicle and becomes a club hair

Phase 4 of hair growth

when follicle reactivation occurs, the club hair is shed and the hair matrix begins producing a replacement hair

matrix

produces hair shaft (& inner root sheeths)

cortex

thickest part of the hair shaft, contains the melanin

cuticle

dead, single like cells

sebaceous glands

secrete oil through holocrine secretion

two types of holocrine secretion

simple branched alveolar glands - share duct with hair follicles & squeezed by arrector pili muscle

sebaceous Follicles - not associated with hair follicles

secretion of sebaceous glands 

sebum (lipids + electrolytes + proteins + cholesterol)

functions of sebum

inhibits bacterial growth because of its acidity

lubricates & protects keratinized cells (hair & skin)

newborns vernix caseosa

acne (what is it)

a failure to discharge collected sebum in the form of white/black heads which become inflamed then cause acne

sweat glands 

sudoriferous glands

merocrine

sweat glands (eccrine sweat glands) 

structure - coiled tubular duct

uses exocytosis

sweat secretion is controlled by 

the brain’s thermoregulatory center (hypothalamus) & emotional center (limbic center)

sweats functions

• cooling surface of skin to reduce body temp

• excrete water + electrolytes

• flushes chemicals 

• contains dermicidin (antibiotic protein) to discharge microbes

aprocrine

sweat glands includes ceruminous glands of ear & mammary milk - producing glands

armpit ,pubic region,around nipples

aprocrine secretions 

coiled tubular structures tat open into hair folicles 

sticky, cloudy, oderous, possible sex scent (influenced by horomones)

used as a nutrient for bacteria which intensifies odour

myoepithithelial

cells that are contractile and squeeze the aprocrine gland

apocrine secretion type

merocrine secretions

ceruminous glands

modified apocrine sweat gland in the inner ear 

secretes cerumen (ear wax)

helps to trap foreign particles protecting the ear drum 

basal carcinoma

(most common)

stratum germinative/basale = 2/3 on areas chronically exposed to sun 

cancer of keratinocytes in stratum basale, generally forms with cratered center

squamous cell carinoma

stratum spinosum sun exposed areas

cancer of keratinocytes in stratum spinosum, forms plaques that bleed or ulcerate

melanoma

least common/ most dangerous

can occur anywhere, but sun expossure increases odds 

characteristics :ABCD rule

ABCD Rule for identifying cancer

Asymmetry - irregular shape

Border - irregular 

Colour - mottled

Diameter - more than 5mm

burns

tissue damage caused by :intense heat, electricity radiation (including sunburn) some chemicals

first degree burn

affects only the surface of epidermis; most sunburns, usually limited to redness with minor pain

second degree burns

affects epidermis and upper portions of dermis

• bloistering and swelling and pain 

• heals in 1-2 weeks if no infection 

third degree burns 

affect epidermis,dermis and sometimes hypodermis

major fluid loss (+electrolytes and proteins)

how to treat a third degree burn

within 24 hours

• replace lost fluids and electrolytes 

• provide massive amounts of nutrients 

• protect to try to prevent infection 

skin regeneration after injury

Inflammatory Phase -

Migratory Phase -

Proliferation Phase

Scarring Phase