Ch 6 Integumentary System

skin

largest organ in the body by weight

• functions to protect from envrionment, intake vitamins, secretion, temperature regulation, sensory reception

integumentary system

the skin and it’s accessory structures (hair, nails, glands, sensory receptors)

• 2 layers: epithelial tissue (epidermis) overlying connective tissue (dermis)

epidermis

outer layer of the skin made of stratified squamous epithelial tissue

• epithelial cells attached to basement membrane between epidermis and dermis

• avascular - receives nutrients via diffusion from vessels in CT below to stratum basale

• 4-5 distinct layers: stratum basale, stratum spinosa, stratum granulosum, stratum lucidem (thick skin ONLY), stratum corneum

• cells on the outer surface have protein keratin → waterproof

• 3 cell types: keratinocytes, melanocytes, dendritic cells

dermis

inner layer of skin made of densre irregular connective tissue (high in elastic fibers - stretchy)

• thicker layer

• where most of the accessories are rooted

• vascular - gives nutrients to epidermis

hypodermis (subcutaneous layer)

located beneath the dermis

• functions as the insulating layer → mostly adipose connective tissue!

• not considered part of the skin, but is attached to dermis

cell cycle in epidermis

as cells grow, they are pushed toward the apical surface, away from nutrient supply (stratum basal) → apoptosis

→ the stratum basale produces 2 daughter cells: one moves through the layers over 25-45 days and dies at the surface, the other remains a stem cell to continue the cycle

→ as they migrate, older cells, keratinocytes, begin to flatten and die

→ as cells reach the outer surface, they become tightly packed, develop desmosomes, form outer layer: stratum corneum

• thickest on palms and soles: lots of dead skin cells that are tightly packed and keratinized (waterproof)

3 cell types of epidermis

keratinocytes, melanocytes, dentritic cells

4-5 layers of epidermis

stratum basale, stratum spinosa, stratum granulosum, stratum lucidum (thick skin ONLY), stratum corneum

Stratum basale

deepest epidermal layer, up agains the dermis attached to the basement membrane

• single row of STEM CELLS

• actively mitotic

  • produces 2 daughter cells: one cell journeys to apical layer 25-45 days and then dies at the surface, one cell remains a stem cell

• friction over time can accelerate cell production and keratin formation → calouses

stratum spinosum

several layers thick, second deepest epidermal layer

• contains web-like system of intermediate pre-keratin filaments (“spindle-like”) attached to desmosomes that help to resist tension

• abundant melansomoes and dendritic cells (immune cells!)

stratum granulosum

thin layer above stratum spinosum - 4-6 cells layers

• cell appearance changes: cells flatten, nuclei and organelles disintegrate, keratinization begins, cells accumulate water-resistant glycolipids (slow-water loss)

cells above this layer begin to die

apoptosis

controlled cell suicide

• changing of cells from stratum basale to stratum corneum

• nucleus and organelles break down

• plasma membrane thickens

• allows cells to slough off as dandruff and dander

• shed 50,000 cells every minutes

stratum lucidum

4th layer of epidermis, only found in thick skin: palms and soles

• thin translucent band superficial to the stratum granulosum

• a few rows of flat, dead keratinocytes

stratum corneum

20-30 rows of dead, flat, anucleate keratinized membranous sacs

• though dead, its cells have a function - take the brunt of the harm so the living cells, tissues, and organs don’t

  • protect deeper cells from environment and water loss

  • protect from abrasion and penetration

  • barrier against biological, chemical, and physical assaults

keratinocytes

cells that produce fibrous protein keratin → waterproofing, especially outer layer

• most abundant in epidermis

• tightly connected by desmosomes

keratin

tough, fibrous, waterproof protein stored in the cells

melanocytes

cells in epidermis that produce dark pigment melanin which gives skin it’s specific color

• absorbs UV light from sunlight and provides skin color via melanosomes (granules)

• 10-25% of cells in the deepest epidermis

• located in stratum basale

• distributed into keratinocytes to protect skin from damaging effects of UV light (DNA damage, fibroblast damage, skin cancer)

hereditary factors affecting skin color

• same number of melanocytes in each person, but vary in the amount of melanin produced (genetically controlled)

• varying distribution and size of melanin granules

• albinos inherit mutation in melanin gene; lack melanin

envrionmental factors affecting skin color

sunlight, UV light from sunlamps, x-rays

physiological factors

• oxygenation in blood of dermal blood vessels

• vasodilation/vasoconstriction of dermal blood vessels

• accumulation of carotene pigment from diet

• jaudice

cyanosis

blueness of skin from deficiency of oxygen in the circulating blood

→ hemoglobin changes color when not attached to an oxygen molecule: turns from red to blue

• can result from airway obstruction (drowning or choking)

• lung diseases (emphysema or respiratory arrest)

• cardiac arrest

jaundice

yellowing of skin and sclera due to excess of bilirubin (yellow pigment) in blood

• cancer, hepatitis, cirrhosis, other compromised liver function

→ put babies in the sun

hematoma

aka bruising: mass of clotted blood showing through skin

pallor

pale or ashen color when there is so little blood flow through the skin that the white color of dermal collagen shows through

• emotional stress, low BP, circulatory shock, color, anemia

→ constricted dermal blood vessels

erythema

abnormal redness of the skin due to dilated cutaneous vessels

• exercise, hot weather, anger, or embarrassment

albinism

genetic lack of melanin that results in white hair, pale skin, and pink eyes

striae

silvery-white scars

• “stretch marks”

• extreme stretching causes dermal tears

blister

from acute, short-term trauma

• fluid filled pocket that separates epidermal and dermal layers

calluses

continued friction/pressure stimulates cells of the epidermis to become increasingly active

• thickening process knows as hyperkeratinosis

dermis

second, largest layper of the skin

strong, flexible dense irregular connective tissue (made of elastic fibers)

• cells: fibroblasts, macrophages, occasionally white blood cells (dendritic cells)

• 2 layers: papillary, reticular

contents: dermal blood vessels, smooth muscle tissue around hair follicles, nerve endings, skeletal muscle

cell types in dermis

fibroblasts, macrophages, whote blood cells (from blood vessels)

papillary layer

top layer of the dermis made of areolar CT, about 20% of dermis

• collagen fibers and blood vessels

• dermal papillae originate here → fingerprints

• phagoctyes patrol for microorganisms

• loose tissue

→ function: allow for diffusion of nutrients and oxygen from blood vessels of lower dermis to epidermis, also allows for white blood cells to climb to the epidermis surface to fight infection

dermal papillae

superficial peg-like projections from the papillary layer of the dermis

• in thick skin → friction ridges in the epidermis → aka fingerprints!

• function: enhance gripping ability, contribute to sense of touch

dermal blood vessels

provide nutrients and oxygen to overlying epidermis

• diffuse through pappillary layer of areolar tissue

smooth muscle tissue of dermis

around hair follicles for movement in response to sensory perception and support

nerve endings in dermis

touch receptors: deep touch/pressue, light touch

free nerve endings: pain, temperature

skeletal muscle in dermis

anchors to the dermis only in the face muscles to form facial expressions!

accessory structures of the skin

hair follicles, nails, sensory receptors, skin glands (sweat and sebaceous)

sebaceous glands

glands found in the dermis and a little in the hypodermis that produce sebum to keep the hair and skin soft and waterproof

• usually found around hair follicles to be produced through the follicle at the epidermis

• absent on palms and soles (for grip! also no hair)

• excess sebum → acne

sweat gland

aka sudoriferous glands

• widespread in the skin

• originate in deeper dermis or hypodermis as ball-shaped coils

• 2 types: eccrine (merocrine glands) that produce sweat, apocrine glands in axillary and groin areas

• modified sweat glands: ceruminous glands, mammary glands

eccrine (merocrine) glands

most numerous sweat gland that opens to a pore in the epidermis

• responds to elevated body temperature by producing sweat to regulate and maintain homeostasis

• abundant on forehead, neck, back

sweat

mostly water + salts and wastes secreted by sudoriferous glands (eccrine and apocrine)

sebum

fatty material produced in sebaceous glands that keeps hair and skin soft and waterproof

skin functions

overall: maintain homeostasis

• protection (physical, chemical, biological)

• barrier against harm

• prevents some water loss

• sensory reception

• excretes wastes

• produces vitamin D

• regulate body temp

the skin as a physical barrier of protection

continuity of the skin!

• flat, dead cells of stratum corneum surrounded by lipids → dead cells are hurt first

• keratin and glycolipids block most water and water soluable substances

• limited penetration of the skin: lipid soluable substances, plant oils, organic solvents, some drugs

what substances are allowed to penetrate the skin

lipid soluable substances

plant oils (poison ivy, etc)

organic solvents

some drugs: transdermal drug methods like nicotine patches, fentanyl patches, hormone patches

the skin as a chemical barrier of protection

skin secretions: low pH slows down bacterial multiplication, sebum and natural antibiotics kill bacteria

melanin: defense against UV radiation damage

how does the skin protect from harmful effects of UV radiation

• melanocytes absorb the UV rays and distribute them into keratinocytes to protect skin cells from harsh and direct rays of UV light, which is a mutagen that can alter DNA, damage fibroblasts, and lead to skin cancer

• dead skin cells of stratum corneum slough off and protect underlying new skin cells

the skin as a biological barrier of protection

dendritic cells of the epidermis and macrophages of dermis present foreign antigens to white blood cells

when body temperature rises

1. thermoreceptors signal hypothalamus

2. vasodilation of dermal blood vessels, vasoconstriction of deep blood vessels

3. sweat glands are activated

when body temperature falls

1. thermoreceptors signal hypothalamus

2. vasoconstriction of dermal blood vessels

3. sweat glands are inactive

4. muscles contract involuntarily (shivering)

methods of heat loss in the body

raditation, conduction, convection, evaporation

raditation

primary method of heat loss through the skin, infrared heat rays escape

conduction

heat moves from skin to cooler objects

convection

heat loss through the skin into circulating air currents

evaporation

sweat changes into gas, carries heat away

→ why we sweat when body temp is elevated!

hyperthermia

abnormally high body temperature

• can occur on a hot, humid day, when sweat cannot evaporate

• when air temperature is high, radiation is less effective (heat moves into body)

  • body may gain heat from hotter air

• symptoms: skin becomes dry, person gets weak, dizzy, nauseous, with headache, rapid pulse

• extreme vasodilation in attempt to regulate temperature can collapse cardiovascular system and can be fatal

hypothermia

abnormally low body temperature

• result from prolonged exposure to cold or illness

• shivering is involuntary skeletal muscle contraction, caused by hypothalamus

• progessess to confusion, lethargy, loss of relfexes, and consciousness

• without treatment, organs shut down → death

fever

temperature set point is purposefully elevated by the immune system to fight infection

• phagocytes release pyrogens in response to presence of bacteria, viruses

• hypothalamus increases set point and raises body temperature

• elevated body temperature helps destroy pathogens

how: construct dermal blood vessels to reduce heat loss through the skin, slows down sweating, causes shivering (to produce more heat)

hypothermia is intentionally induced when

performing surgeries to prevent organ damage from decreased oxygen supply

cutaneous sensation

skin’s role in the nervous system

• receptors in skin respond to external stimuli

• touch receptors and deep pressure

metabolic function

skin produces vitamin D precursor from absorbed UV light

excretion

skin excretes some nitrogen containing wastes via urea

skin cancer

risk factors like excessive exposure to UV lights and chemicals can overwhelm the natural protective responses against skin cancer

3 types: basal cell carcinoma (common, least malignant), squamous cell carcinoma (spreads rapidly), and melanoma (least common, most deadly)

basal cell carcinoma

least malignant skin cancer type,

• most common, 80% of skin cancers

• most often in face

• slow growing

squamous cell carcinoma

skin cancer that arises from keratinocytes of stratum spinosum

• arise most often on head

• grows rapidly, will spread if not caught

melanoma

skin cancer that arises from melanocytes

• highly likely to metastasize

• appears where there is pigment

• 1/3 come from preexisting moles

• ABCD rule

life-span changes in skin

• cell cycle slows → scaly skin, age spots

• epidermis and dermis become thinner

• loss of fat → cold

• wrinkling, sagging

• less sebum → dry skin

• melanin production slows → white hair

• hair thins, less follicles

• impaired nail growth

• sensory receptors decline

• less effective body temp regulation

• dimished vitamin D ability