Chapter 5 - A&P Lecture

2 layers of skin

• epidermis

• dermis

epidermis

epithelial protective shield

dermis

CT; tough leather layer

subcutaneous tissue

aka hypodermis or superficial fascia

• wraps muscle

• not part of the skin

characteristics of subcutaneous tissue

• mostly adipose tissue with some loose areolar CT

• anchors skin to muscle

• shock absorber and insulator

number of cell types in the epidermis

4 distinct cell types

number of layers in the epidermis

5 layers

4 distinct cell types of the epidermis

• keratinocytes

• melanocytes

• dendritic cells

• tactile epithelial cells

keratinocytes

• bulk

• produce keratin

• desosomes for anchoring and tight junctions to prevent passage of water

keratin

tough protein that gives skin protective function

location of production of keratinocytes

• stratum basale - highly proliferative and make keratin as pushed to surface; by time they reach the surface, they are dead-flat scale like filled with keratin

cause of callus

abrasion increases epithelial proliferation and skin thickens

melanocyte

spider shaped cells

• produce pigment melanin in melanosomes that are transferred to nearby keratinocytes

melanocyte location

deepest layer of epidermis (stratum basale)

melanin

produces pigment shield against UV light that damages DNA

dendritic cells

immune antigen presenters

dendritic cell location

from bone marrow, but migrate to epidermis

tactile epithelial cells

associated with a disclike sensory nerve ending for touch

layers of the epidermis

• stratum basale

• spinosum

• granulosum

• lucidum corneum

stratum basale/germinativum

• deepest layer

• single row of stem cells

• cell divides and daughter cells push up to the next layer

• 10-25% of layer are melanocytes

stratum spinosum (prickly layer)

• several layers thick

• artifact due to desmosomes connected to intermediate filaments

• contains bundles of intermediate filaments consisting of pre-keratin

• dendritic cells most abundant in this layer

stratum granulosum

• 1-5 cell layers thick

• keratinocyte appearance changes as the process of keratinization is occurring

• cells flatten and nuclei and organelles begin to disintegrate

• accumulates two types of granules

• remember nutrients need to penetrate epithelial layer (distance and glycolipid keeps nutrients from passing and cells above granulosum die)

granules in stratum granulosum

• keratohyaline granules

• lamellar granules

• makes skin strong and water tight

keratohyaline

help form keratin in upper layers

lamellar granules

contains water-resistant glycolipid that is secreted into the extracellular space; the glycolipid + tight junctions slow water loss

stratum lucidum

clear layer only present in thick skin

• few rows of flat dead keratinocytes

stratum corneum (horny layer)

• flattened anucleate cells 20-30 cell layers thick

• constantly shed (40 lbs in your lifetime)

contents of stratum corneum

• pre-keratin intermediate filaments

• “glue” from keratohyaline granules

dermis

hide of CT

two layers of dermis

• papillary dermis

• reticular dermis

papillary dermis

• areolar CT containing blood vessels

• dermal papillae that have free nerve endings and tactile corpuscles

• friction ridges contain sweat glands that give us unique finger print pattern

reticular dermis

• dense irregular CT

• 80% of thickness

• most collagen runs parallel to skin

• cleavage lines

• contain flexure lines

cleavage lines of reticular dermis

separations or less dense regions that are important for surgeons because they prevent gaping when cut

flexure lines

folds near joints where dermis tightly secured to deeper structures

pigments of the skin

• melanin

• carotene

• hemoglobin

what makes melanin

tyrosine

melanin

• ranges reddish yellow to brownish black

• color of skin reflects type and amount produced, not # of melanocytes

• absorbs UV rays and dissipates them as heat

• darker skin in areas closer to equator

• more skin damage causes more of this to be produced - get tan

carotene

• in foods like carrots

• accumulates in stratum corneum

vitamin that carotene is converted to

vitamin A - important for eye and skin health

sweat glands/sudoriferous glands location

everywhere but nipples and parts of external genitalia

two types of sweat glands

• eccrine/merocrine (most common)

• apocrine (only about 2000)

secretory cells of sweat glands

associated with myoepithelial cells that contract when stimulated by autonomic nervous system

eccrine location

palms, soles of feet and forehead

secretory part of eccrine gland

coiled in the dermis and duct extends up to a pore at surface of skin

secretion of eccrine glands

sweat - hypotonic filtrate of blood that passes through secretory cells and released by exocytosis

• 99% water, salts, metabolic wastes and dermicidin

function of eccrine glands

temp regulation

apocrine sweat gland location

axillary and anogenital region

• deeper in dermis or sub-q tissue and empty product into hair follicles

type of glands that apocrine glands are

merocrine glands - release product by exocytosis

secretion of apocrine glands

sweat components + fatty substances and protein - yellow color

• odorless, but bacteria decompose the organic components leading to body odor

when apocrine glands functions

function at puberty, but not sure function

• likely sexual scent glands/pheromones

modified apocrine glands

• ceruminous glands

• mammary glands

ceruminous glands

• lining external ear

• secretion mixed with sebum produced sebaceous glands

sebum

sticky bitter substance called cerumen or earwax

• deters insects and blocks foreign material

mammary glands

secrete milk

sebaceous glands

oil glands

• simple, branches alveolar glands

sebaceous gland location

all over body except thick skin of palms and soles of feet

sebaceous gland secretion and what it does

sebum; oily substance

• softens and lubricates hair and skin; prevents water loss from skin

• bactericidal action

holocrine glands

• type of sebaceous gland

• erupt releasing lipid ad cell fragments

arrector pili contraction

forces sebum out of hair follicles to akin surface

when apocrine glands function

during puberty under influence of male sex hormones

skin functions

1. protection

2. body temperature regulation

3. cutaneous sensation

4. metabolic functions

5. blood reservoir

6. excretion

3 types of protection by skin

• chemical barrier

• physical barrier

• biological barrier

chemical barrier of skin

skin secretions and melanin

• acidic pH (acid mantle) retards bacterial growth

• dermicidin in sweat

• bactericida substances in sebum

• keratinocytes also produce antibiotics called defensins

• wounded skin produces cathelicidens - antimicrobial peptides

• melanin - prevents UV damage

physical barrier of skin

brick and mortar

• dead keratin filled kertinocytes - bricks

• glycolipid - mortar

• block penetration of water and water soluble substances into OR out of body

things that can penetrate the skin

• lipid soluble substances (O2, CO2, fat-soluble vitamins, steroids)

• oleoresins (posion ivy/oak)

• organic solvents (acetone, paint thinner)

• salts of heavy metals (mercury/lead)

• some drug agents - penetration enhancers

biological barrier of skin

living

• dendritic cells - antigen presenting cells that trigger immune responses

• macrophages - engluf foreign bodies AND act as antigen presenters

insensible perspiration

resting conditions about 0.5L/day

• continuous, invisible loss of water vapor from the skin and respiratory tract

sensible perspiration

under the influence of nervous system

• bvs dilate and sweat production can increase to 12L/day

skin role when you’re cold

dermal bvs constrict; conserving body heat

cutaneous sensation

sensory receptors - part of the nervous system

• exteroreceptors that respond to stimuli outside of body

metabolic functions of skin

• sunlight converts modified cholesterol to Vit D precursor necessary for Ca++ absorption in the gut

• “disarm” cancer-causing chemicals that penetrate epidermis

• activate some steroid hormones (cortisone to hydrocortisone)

• collagenase - aids natural turnover of collagen, preventing wrinkles

blood reservoir of skin

dermal vascular supply can hold about 5% of body’s entire blood volume; when other parts need blood, they can be shunted away from skin by vasocontriction of dermal bvs

excretion of skin

eliminates trace nitrogen containing wastes - ammonia, urea, and uric acid in sweat

• profuse sweating also eliminates water and salts