Chapter 6 - the integumentary system

functions of skin (6)

resistance to trauma and infection

vitamin D synthesis

sensation

thermoregulation

non-verbal communication

other barrier functions (water, UV)

stem cells

undifferentiated cells that give rise to keratinocytes

located in the deepest layer of epiderm (stratum basale)

keratinocytes

great majority of epidermal cells

synthesize keratin

melanocytes

synthesize pigment of melanin that shields DNA from UV radiation

located in stratum basale, but have branched processes that spread among keratinocytes

tactile cells

touch receptor cells associated with dermal nerve fibers (in basale layer)

dendritic cells

macrophages - originate from bone marrow

protects against pathogens

found in stratum spinosum and granulosum

stratum basale

deepest layer

single layer of stem cells and keratinocytes

a few melanocytes and tactile cells

stratum spinosum

several layers of keratinocytes with desmosomes and tight junctions

spinosum (spindles / spiny)

contains dendritic cells

stratum granulosum

3-5 layers of flat keratinocytes

cells contain dark staining keratohyalin granules

granulosum - granules (small particles)

stratum lucidum

thin, pale layer ONLY in thick skin

keratinocytes packed with clear protein eleidin

stratum corneum

several layers (up to 30), dead skin, keratinized cells

resists abrasion, penetration, water loss

events of stratum granulosum (4)

1. keratohyalin granules release filaggrin

2. cells produce tough envelope proteins beneath their membranes

3. membrane-coating vesicles release lipid mixture (waterproof cell)

4. keratinocytes’ organelles degenerate (cell dies)

filaggrin

a protein that binds keratin into tough bundles

papillary layer

thin zone of areolar tissue near (or inside) dermal papilla.

Allows mobility of leukocytes / other defense cells

rich in small blood vessels

reticular layer

thicker layer of dense irregular connective tissue

stretch marks (striae) - tears in collagen fibers (pregnancy or obesity)

eumelanin

brownish black

pheomelanin

reddish yellow (contains sulfur)

cyanosis

blueness due to lack of oxygen

erythema

redness due to increased blood flow to skin

pallor

paleness due to decreased blood flow to skin

albinism

white skin due to genetic lack of melanin

jaundice

yellowing due to bilirubin in blood

• caused by compromised liver func

hematoma

bruising

• clotted blood under skin

harmful effects of UV

causes skin cancer, breaks down folic acid

beneficial effects of UV

stimulates vitamin D synthesis

friction ridges

fingertips that leave oily fingerprints

unique to each human (not even identical twins have the same fingerprints)

flexion lines (flexion creases)

lines on the flexor surfaces of the digits, palms, wrists, elbows (skin folding during flexion of joints)

hemangiomas

birthmarks!

discolored skin caused by benign tumors of dermal capillaries

freckles / moles

freckles → flat, melanized patches

moles (nevi) → elevated, melanized patches with hair (needs to be watched in case of changes in color and size)

Pilus (plural is pili)

slender filament of keratinized cells growing from a tube in the skin - hair folicle

lanugo hair

fine, downy, unpigmented hair

• on fetus in the last three months of development

vellus hair

fine, pale hair that replaces lanugo

• 2/3 of the hair on women

• 1/10 of the hair on men

• all hair of children except for eyebrows, lashes and scalp hair

terminal hair

longer, coarser, more pigmented

after puberty: forms the axillary and pubic hair

hair bulb

swelling at the base where hair originates

• dermis or hypodermis

  only LIVING hair cells are in or near the bulb

hair root

remainder of the hair in the follicle

hair shaft

portion of hair above the skin surface (hair cells are already dead)

dermal papilla

bud of vascular connective tissue encased by bulb.

ONLY source of nutrition for hair

hair matrix

region of mitotically active cells - directly above papilla

this is the hair’s growth center

hair layers (cross section) (3)

medulla

cortex

cuticle

medulla

core of loosely arranged cells & air spaces

cortex

constitutes bulk of the hair

consists of several layers of elongated keratinized cells

cuticle

composed of multiple layers of very thin & scaly cells that overlap each other

free edges directed upward

hair follicle

contains hair root

has two layers → epithelial root sheath & connective tissue root sheath

epithelial root sheath

extension of the epidermis lying adjacent to hair root

• widens @ deep end into bulge → source of stem cells for follicle growth

connective tissue root sheath

derived from dermis but a bit denser

surrounds epithelial root sheath

hair receptors

1. sensory nerve fibers entwining follicles

2. piloerector muscle (arrector pili)

3. smooth muscle attaching follicle to dermis

   → contract to make hair stand (goose bumps!)

functions of hair (6)

• receptors alert us of parasites crawling on skin

• hair on trunk and limbs kept our ancestors warm

• scalp hair retains heat and protects against sunburn

• pubic and axillary hair signify sexual maturity and aid in transmission of sexual scents

• guard hairs (vibrissae) → nostrils and ear canals

  • eyelashes and brows → nonverbal communication

finger and toe nails

derivatives from stratum corneum

• thin, dead cells packed w/ hard keratin

functions of nails (2)

• improve grooming, picking food apart

  • provide a counterforce to enhance sensitivity of fleshy fingertips to tiny objectsn

nail plate

hair part of nail

1. free edge → overhangs fingertip

2. nail body → visible part

   1. nail root -→ extends proximally under overlying skin

nail fold

surrounds skin rising above nail (ouchie!)

nail groove

separates nail fold from nail plate

nail bed

skin underlying the nail plate

nail matrix

GROWTH ZONE

thickened stratum basale at proximal end of nail

nail growth rates (idk if we need to know this!)

fingernails → 1 mm per week

toenails grow slower

hyponychium

epidermis of the nail bedlan

lunule

opaque white crescent at proximal end of nail due to thickness of matrix

lunule = moon = crescent shape

eponychium

cuticle

apocrine sweat glands

*INACTIVE UNTIL PUBERTY*

• groin, axilla, beards

• ducts lead to hair follicles

• produce sweat that is milky (??) and contains fatty acids

Response to stress and sexual stimulation

(believed to secrete pheromones)

bromhidrosis

body odor ewwwwwww

eccrine (merocrine) sweat glands

most numerous (palms, soles, forehead)

simple tubular glands

watery perspiration that helps cool the body

myoepithelial cells

in apocrine & eccrine glands

• contract in response to stimulation by the sympathetic NS and squeeze perspiration up the duct

what is the pH of sweat?

4-6 (in the acid mantle → no bacteria growth)

what is sweat?

99% water

• begins as a protein-free filtrate of blood plasma produced by the deep secretory portion of gland

  • some NaCl reabsorbed by duct, some NaCl and small solutes remains in sweat

how are some drugs excreted?

through sweat

sebum

oily secretion of sebaceous glands

• keeps skin and hair from becoming dryss

sebaceous glands

flask-shaped

short ducts open into hair follicles

holocrine secretion style

lanolin

sheep sebum (idk why this is in the notes 😭😭)

cerumen (earwax)

waxy secretion combined with sebum and dead epithelial cells

• keeps the eardrum pliable

what does earwax do? (cerumen)

• waterproofs the canal

• kills bacteria

• makes guard hairs sticky to block foreign particles

ceruminous glands

coiled, simple tubular glands in external ear

• modified apocrine glands

mammary glands

produce milk (duhhhh)

• developed only during pregnancy and lactation

what type of gland are mammary glands?

modified apocrine glands

mammary ridges (milk lines)

2 rows of mammary glands in most mammals

• primates kept only 2 glands, but few people have additional nipples along the milk line

basal cell carcinoma

most common type

• least dangerous because it seldom metastasizes

squamous cell carcinoma

• from keratinocytes of stratum spinosum

• usually scalp, ears, lower lip, or back of hand

  • can form a concave ulcer

melanoma

less than 5% of skin cancers

risk factor → family history

deaths from burns result from…? (3)

• fluid loss

• infection

  • toxic effects of eschar

eschar

burned / dead tissue

first degree burn

ONLY EPIDERMIS

• redness, slight edema & pain

second degree burns (partial thickness burn)

epidermis and part of dermis

• red, tan, or white. blistered & painful

• 2 weeks + to heal → may leave scars

third degree burns (full-thickness burn)

all of epidermis, dermis, and some deeper tissues

• requires skin grafts

• needs fluid replacement, infection control, supplemental nutrition