Chapter 5 - The Integumentary System

Two other names for skin

cutaneous membrane or integument

In most adults what is the surface area of skin?

about 1.8 square meters (20.83 ft²)

What types of tissue does skin contain?

all four types

two regions of skin

epidermis and dermis

• joined by areolar tissue

Hypodermis

subcutaneous tissue found between skin and underlying structures like muscle

How is the hypodermis attached to dermis?

• Usually by underlying muscle tissue

• Where no muscle present, attaches to bone

  • Ex. flexion creases - skin attaches directly to joints of fingers

Epidermis

• outer and thinner region of skin

• made up of stratified squamous epithelium divided into five separate layers with avascular and tightly packed cells

Stratum Basale

• cells lie just above dermis

• epidermal stem cells constantly divide and produce new cells that are then pushed to surface in 2 to 4 weeks

What happens to blood cells as they get further form dermis

they die off due to lack of oxygen and nutrients

Keratinocytes

• most numerous cells in stratum basale

• make up approximately 95% of cells in this layer

What do keratinocytes do?

• produce and store thick waterproof protein - keratin

• form barrier between environment and body

How do keratinocytes enlarge?

as they move up to stratum spinosum they pack in additional keratin and proteins

Langerhans cells

• macrophages deep in epidermis

• type of white blood cell (leukocyte)

• phagocytize microbes and then travel to lymphatic organs where they stimulate immune system to react

Melanocytes

type of specialized cell located in deeper epidermis

What do melanocytes do?

produce melanin - pigment responsible for skin and hair color

What is variation in skin color due to?

• amount of production and distribution of melanin

• amount of melanocytes are almost the same in every one

What does melanin protect us from?

• UV light

  • more exposure to sun = more production of melanin

albinism

• inability to produce melanin

• lack pigment in skin, hair and eyes

carotene

present in epidermal cells and gives asians yellow-ish hue

hemoglobin

pigment in red blood cells in capillaries of dermis give fair-skinned people pink-ish hue

Free nerve endings

supply pain and temperature sensations to brain

Tactile cells (or Merkel cells)

signal to brain an object has touched the skin

Stratum Spinosum & Stratum Granulosum

immediately superior to stratum basale are two additional layers of cells

Stratum Spinosum cells

• can produce by mitosis

• name comes from spiny appearance caused by keratin filaments

Stratum Granulosum cells

• tightly sealed together form barrier

• squamous cells named for dark staining protein granules found in their cytoplasm

• contain more keratin than stratum spinosum cells

Stratum Lucidium

• only found in thick skin; palms of hands, soles of feet, elbows, etc

• in these areas both stratum lucidum and an extra - thick layer of stratum corneum provide protection from constant friction

Stratum Corneum

• Over much of body keratinization is minimal

• In areas with underlying stratum lucidum, a particularly thick layer of dead, keratinized cells gives extra protection

How is the tough uppermost layer of the epidermis formed?

as cells are pushed toward surface of skin they become flat and hard

What is hardening of stratum corneum caused by?

• keratinization of entire cell, causing uppermost cell layers of epidermis to die

• constantly shed these dead cells

What does keratin do?

protects body from water loss and gain

What does stratum corneum allow us to do?

• live in desert or tropical rainforest without damage to internal cells

• also serves as mechanical barrier to microbial invasion

  • Ex. this function is assisted by secreting of sebaceous glands

Dermis

• deeper and thicker region than epidermis

• composed of dense irregular connective tissue

What does the upper layer of the dermis contain?

• finger-like projection - dermal papillae

  • project into and anchor the epidermis

  • cause ridges in overlying epidermis

  • epidermal ridges (fingerprints) - increase friction and provide better gripping surface

What does the dermis contain?

collagen fibers: stretchy and resistant, prevent tears in skin

elastic fibers: stretch and allow underlying muscle and joint movement, maintain normal skin tension

What do blood vessels in dermis supply?

• oxygen and nutrients to its cells and those of epidermis as well

  • blood rushes to these vessels when we blush

pallor

develops when blood flow to dermal vessels is reduced (pale skin)

cyanotic

develops not adequately supplied with oxygen (perhaps because of lung disease), the person turns “blue“

What do extended periods of diminished blood flow to the dermis cause?

the formation of decubitus ulcers, bedsores

What do sensory nerve fibers in dermis do?

take nerve signals to and from accessory structures of skin

Hypodermis

• areolar and adipose tissue

• fat energy storage form that supplies molecules for cellular respiration

• adipose tissue help insulate body

What does well developed hypodermis give body?

• rounded appearance

• protective padding against external assaults

What does excessive development of adipose tissue in hypodermis cause?

obesity

Hair

found on all body parts except the palms, soles, lips, nipples and portions the external reproductive organs

When is there a noticeable hair in axillary and pelvic regions?

after puberty

Hair in different parts of the body has different…?

growing and resting time periods

Hirsutism

excess body hair

Hair follicles

surround the hair within the skin and are formed from epidermal cells

• located in dermis

Hair matrix

where cell division occurs; hair growth center

• cells become keratinized as they are pushed out, away from blood supply

Hair root

portion of hair within follicle

Hair shaft

portion of hair that continues beyond the skin

Alopecia

hair loss

Androgenic alopecia - male pattern baldness; most common form of alopecia

Alopecia areata - sudden onset of patchy hair loss

Sebaceous (oil) glands

secret into follicle

Arrector pili muscle

smooth muscle attached to hair follicle: create goosebumps

nail root

region at base of nail with special epithelial cells that nails grow from

nail body

visible portion of nail

cuticle

fold of skin that hides nail root

How much do nails usually grow a week?

1 milimeter

What causes pink color of nails?

vascularized dermal tissue beneath nail

lunula

whitish color of half-moo-shaped base

• results from the thicker layer of rapidly reproducing cells in this area

glands

groups of cells specialized to produce and secrete a substance into ducts

sweat glands

• also called sudoriferous glands

• present in all regions of skin

• especially active when person is under stress

As many as __ glands per cm² on the leg, ___ per cm² on palms and soles, and even _______ amounts on fingertips.

90, 400, greater

shape of sweat glands

• tubular

• coiled particularly at origin with dermis

two types of sweat glands

Apocrine glands & Eccrine glands

apocrine glands

open into hair follicles in the anal region, groin and armpits, begin to secrete at puberty

eccrine glands

open onto the surface of the skin, become active when a person is hot, helping lower body temperature as sweat evaporates

ceruminous glands

• modified sweat glands lining opening of ear (external ear canal)

• produce cerumen (earwax)

sebaceous glands

• most associate with a hair follicle

• secret oily substance, sebum, that flows into follicle and then out onto the skin surface

What does the secretion of sebum do?

softens and lubricates hair and skin, helps waterproof both of them

What does sebu do?

weakens or kills bacteria on skin surface because of its low pH, or acidity

What parts of body commonly fail to produce sebum? What does this cause?

• face and back

  • secretions collect and form whiteheads or blackheads

  • if pus-inducing bacteria present, a boil or pimple may result

Skin Protects

• safeguards delicate underlying structures from physical trauma

• melanocytes in stratum basale protect from UV radiation

• sebaceous gland secretions, langerhans cells and outermost layer of dead cells protect against pathogen invasions

Skin Regulates Water

keratinized outer layer of skin is waterproof preventing water loss and water entry

Skin Eliminates Water & Waste

• sweat glands secrete water through sensible & insensible perspiration

  • sensible perspiration - can be felt

  • insensible perspiration - occurs without awareness

• Skin plays minor role in waste elimination

Perspiration contains:

• salts

• ammonia

• urea

• other wastes

Skin Produces Vitamin D

• keratinocytes exposed to sunlight produce vitamin D from precursor molecule

• vitamin D leaves skin, enters liver & kidneys converted to hormone calcitriol

• calcium needed for nervous activity & muscular contraction

• Vitamin D in milk - helps prevent rickets

  • soft & deformed bones

What does calcitriol regulate?

• calcium uptakes by digestive system as well as cellular metabolism of both calcium & phosphorus

• calcium-phosphorus needed for bone development and mineralization

  • deposited in bone - making them strong yet flexible

Skin Gathers Sensory Information From Surroundings

• sensory receptors in dermis & epidermis specialized for:

  • touch

  • hot

  • cold

  • pressure

  • pain

• they supply central nervous system with information about external environment

• fingertips have greatest number of touch receptors - allows fingers to do delicate tasks

• also facilitate communication between people

Skin Helps Regulate Body Temperature - heat

• if body temp rises above normal, the smooth muscle layer blood vessels relax

  • causes blood vessel diameter to increase (vasodilation)

  • allows more blood to move to surface of body and excess heat is released

  • sweat glands are activated when blood moves to surface

• Heat is released when muscles contract & ATP is broken down

Skin Helps Regulate Body Temperature - cold

• when temp cool sweat glands are inactive

  • causes blood vessels to contract, diameter decreases (vasoconstriction)

  • less blood to surface, less heat lost

• skeletal muscles shiver when body temperature falls below normal

• arrector pili shivering insulates animals but not humans

  • our body hair is sparse

• necrosis low body temperature longtime (frostbite)

Hyperthermia

in both heat exhaustion & heat stroke

Heat Exhaustion

• elevated body temp, can sweat

  • dangerous due to body water loss, causing low blood pressure & reduction of important electrolytes

  • if victim not quickly cooled can lead to heatstroke

Heat Stroke

• extremely high body temp - can’t sweat

  • rise to 43 (110 F)

• If not treated fatal

Fever

special case of hyperthermia that can be brought on by immune system response and'/or by infection with a pathogen

Hypothermia

• uncontrollable shivering, incoherent speech, lack of coordination (90-95 F)

• pulse rate slows, hallucinations occur as unconsciousness develops (80-90 F)

• breathing becomes shallow and shivering stops as rigidity sets in

• 50% mortality rate