A&P Chapter 5: Flashcards
skin consists of two distinct regions:
- Epidermis: superficial region
* Consists of epithelial tissue and is avascular - Dermis: underlies epidermis
* Mostly fibrous connective tissue, vascular
Hypodermis (superficial fascia)
- Subcutaneous layer deep to skin
- Not part of skin but shares some functions
- Mostly adipose tissue that absorbs shock and
insulates - Anchors skin to underlying structures: mostly muscles
consists mostly of keratinized stratified squamous
epithelium
epidermis
four cell types found in epidermis
keratinocytes, melanocytes, dendritic (langerhans) cells, tactile (merkel) cells
keratinocytes
- Produce fibrous keratin (protein that
gives skin its protective properties) - Major cells of epidermis
- Tightly connected by desmosomes
- Millions slough off every day
melanocytes
Spider-shaped cells located in deepest epidermis
* Produce pigment melanin, which is packaged into
melanosomes
– Melanosomes are transferred to keratinocytes, where
they protect nucleus from UV damage
Dendritic (Langerhans) cells
- Star-shaped macrophages that patrol deep epidermis
– Are key activators of immune system
tactile (merkel) cells
- Sensory receptors that sense touch
5 layers of skin:
- Stratum basale
- Stratum spinosum
- Stratum granulosum
- Stratum lucidum (only in thick skin)
- Stratum corneum
1.Stratum basale (basal layer)
- Deepest of all epidermal layers (base layer)
- One daughter cell journeys from basal layer to surface,
taking 25–45 days to reach surface
– Cell dies as it moves toward surface - Other daughter cell remains in stratum basale as stem cell
- stratum spinosum (prickly layer)
- Several cell layers thick
– Keratinocytes in this layer appear spikey, so they are called prickle cells
- Stratum granulosum (granular layer)
- Four to six cells thick, but cells are flattened, so
layer is thin
– Cell appearance changes
- Stratum lucidum (clear layer)
- Found only in thick skin
– Consists of thin, translucent band of two to three rows of clear, flat, dead keratinocytes
- Stratum corneum (horny layer)
- 20–30 rows of flat, anucleated, keratinized dead
cells
– Accounts for three-quarters of epidermal
thickness
cells change by going through….
apoptosis (controlled cell death)
apoptosis
– Dead cells slough off as dandruff and dander
– Humans can shed ~50,000 cells every minute
dermis
- Strong, flexible connective tissue
- Fibers in matrix bind body together
two layers of dermis
papillary and recticular
superficial region of dermis
that sends fingerlike projections up into
epidermis
dermal papillea
papillae found on soles and
palms that lie on larger mounds which cause
epidermas to produce epidermal ridges
dermal ridges
peg like projections many contain capillary loops, pain receptors, or touch receptors
dermal papillae
assumed to enhance gripping and enhance sense of touch
epidermal ridges=friction ridges
makes up about 80% of dermal thickess
recticular layer
in reticular layer are caused by many collagen fibers running parallel to skin surface
* Important to surgeons because incisions parallel to cleavage lines heal more readily
cleavage (tension) lines
reticular layer are dermal folds at or near joints
flexure lines
Only pigment made in skin; made by melanocytes
melanin
two forms: reddish yellow to brownish black
*All humans have same number of
keratinocytes, so color differences are due to
amount and form of melanin
* Freckles and pigmented moles are local
accumulations of melanin
carotene
*Yellow to orange pigment
* Most obvious in palms and soles
* Accumulates in stratum corneum and hypodermis
* Can be converted to vitamin A for vision and
epidermal health
hemoglobin
- Oxygenated pigment in erythrocytes
- Pinkish hue of fair skin is due to lower levels of
melanin
excessive sun exposure damaged skin
- Elastic fibers clump, causing skin to become
leathery - Can depress immune system and cause
alterations in DNA that may lead to skin cancer - UV light destroys folic acid
- Photosensitivity is increased reaction to sun
Blue skin color - low oxygenation
of hemoglobin
cyanosis
– Fever, hypertension, inflammation, allergy
erythema (redness)
Anemia, low blood pressure, fear,
anger
pallor (blanching)
Liver disorder
jaundice (yellow cast)
Inadequate steroid hormones in
addison’s disease
bronzing
clotted blood beneath skin
bruises
hair
- Consists of dead keratinized cells
- None located on palms, soles, lips, nipples, and
portions of external genitalia - Functions: Warn of insects on skin, hair on head guards against physical trauma, protect from heat loss, shield skin from sunlight
- Produced by hair follicles
- Contains hard keratin, not like soft keratin found in skin
regions of the hair
shaft and root
area that extends above scalp, where
keratinization is complete
shaft
area within scalp, where keratinization is still
going on
root
three parts of hair shaft:
medulla, cortex, and cuticle
central core of large cells and air spaces
medulla
several layers of flattened cells
surrounding medulla
cortex
outer layer consisting of overlapping
layers of single cells
cuticle
actively dividing area of bulb that produces hair cells
hair matrix
- small band of smooth muscle attached to follicle
- Responsible for “goose bumps”
arrector pili
Dermal tissue containing a knot of
capillaries that supplies nutrients to
growing hair
hair papilla
pale, fine body hair of children and
adult females
vellus hair
coarse, long hair
* found on scalp and eyebrows, at puberty
Terminal hair
hair thinning in both sexes after age 40
* true (frank) baldness
alopecia
nails
- Scale-like modifications of epidermis that
contain hard keratin - Act as a protective cover for distal, dorsal
surface of fingers and toes
thickened portion of bed responsible for nail growth
nail matrix
skin folds that overlap border of nail
nail folds
- nail fold that projects onto
surface of nail body - also called cuticle
eponychium
area under free edge of plate
that accumulates dirt
hyponychium
Also called sudoriferous glands
sweat glands
two main types of sweat glands
- eccrine (merocrine)
- apocrine
eccrine (merocrine)
- Most numerous type
- Abundant on palms, soles, and forehead
- Their secretion is sweat
– 99% water, salts, vitamin C, antibodies,
dermcidin (microbe-killing peptide), metabolic
wastes
aprocrine sweat glands
- Confined to axillary and anogenital areas
- Secrete viscous milky or yellowish sweat that
contains fatty substances and proteins
– Bacteria break down sweat, leading to body odor - begin functioning at puberty
modified apocrine gland
ceruminous gland and mammary glands
lining of external ear canal; secrete cerumen (earwax)
ceruminous gland
secrete milk
mammary gland
sebaceous (oil) glands
- Widely distributed, except for thick skin of palms and soles
- secrete subum
whiteheads
blocked sebaceous glands
acne
usually an infectious inflammation of the
sebaceous glands, resulting in pimples
(pustules)
known as “cradle cap”
seborrhea
function of skin
protection, body temperature regulation, cutaneous sensations, metabolic functions, blood reservoir and excretion of wastes
Skin is exposed to microorganisms, abrasions,
temperature extremes, and harmful chemicals
protection
constitutes three barriers of protection
chemical barrier, physical barrier, and biological barrier
chemical
– Skin secretes many chemicals, such as:
* Sweat, which contains antimicrobial proteins
* Sebum and defensins, which kill bacteria
* Cells also secrete antimicrobial defensin
low pH of skin retards bacterial
multiplication
acid mantle
physical barrier
flat, dead, keratinized cells of stratum corneum, surrounded by glycolipids, block most water and water-soluble substances
biological barrier
– Epidermis contains phagocytic cells
- Dermis contains macrophages
- DNA can absorb harmful UV radiation, converting it to harmless heat
insensible perspiration
Under normal, resting body temperature, sweat glands produce about 500 ml/day of unnoticeable sweat
sensible perspiration
If body temperature rises, dilation of dermal vessels can increase sweat gland activity to produce 12 L (3 gallons) of noticeable sweat (designed to cool body)
Metabolic Functions
- Skin can synthesize vitamin D needed for
calcium absorption in intestine - Chemicals from keratinocytes can disarm
some carcinogens - Keratinocytes can activate some hormones
blood reservoir
- Skin can hold up to 5% of the body’s total blood
volume - Skin vessels can be constricted to shunt blood
to other organs, such as an exercising muscle
Skin can secrete limited amounts of
nitrogenous wastes, such as ammonia, urea,
and uric acid
excretion
less common, but more damaging are:
skin cancer and burns
three major types of skin cancer
basal cell carcinoma, squamous cell carcinoma, and melanoma
basal cell carcinoma
- Least malignant and most common
- Cured by surgical excision in 99% of cases
squamous cell carcinoma
Second most common type; can metastasize
melanoma
Cancer of melanocytes; is most dangerous type
because it is highly metastatic and resistant to
chemotherapy
burns
-Tissue damage caused by heat, electricity,
radiation, or certain chemicals
- To evaluate burns, the Rule of Nines is used
treatment for burns
debridement (removal) of burned skin, antibiotics, temporary covering, and skin grafts
are small fluid-filled blisters that itch, and usually occur around the lips and in the mucosa of the mouth
cold sores
may be triggered by stress, food allergies, lack of vitamins and minerals, hormonal changes or menstrual periods; are contagious
canker sores
delicate hairs in 5th and 6th
month
lanugo coat
sebaceous gland secretion that protects
skin of fetus while in watery amniotic fluid
vernix caseosa
skin thickens and accumulates more subcutaneous fat; sweat and sebaceous gland activity increases, leading to acne
infancy to adulthood
aging skin
– Epidermal replacement slows; skin becomes
thin, dry, and itchy (decreased sebaceous gland activity)
– Subcutaneous fat and elasticity decrease,
leading to cold intolerance and wrinkles
– Increased risk of cancer due to decreased
numbers of melanocytes and dendritic cells
– Hair thinning
ways to delay aging
UV protecton, good nutrition, lots of fluids, and good hygiene
