1. The Integumentary System
Acc. A&P
(Chapter 6 In Text)

2. Integumentary System Epidermis – first true layer
Includes skin and its accessories (hair, nails, etc.)
Skin is the largest organ in the body (12-15% of total body weight)
3 Major Layers:
Epidermis – first true layer
Dermis – second true layer
Subcutaneous layer (aka hypodermis, or superficial fascia)
Protective covering that:
limits water loss
regulates body temperature (homeostasis)
houses sensory receptors
synthesizes chemicals such as Vitamin D
excretes small amounts of some wastes, etc.

3. Epidermis Top layer; made of epithelial cells; avascular
Protects, absorbs, and maintains homeostasis
Rests on basement membrane
Thickest on palms and soles
Composed of keratinized stratified squamous epithelium, consisting of four specialized cell types:
Keratinocytes – the major cell of the epidermis
Melanocytes
Merkel cells
Langerhans’ cells

4. Epidermal Layers Stratum corneum Cohasset, Stratum lucidum Let’s
Stratum granulosum
Stratum spinosum
Stratum basale
Cohasset,
Let’s
Get
Sun
Burned

5. Epidermal Layers Stratum corneum Stratum lucidum Stratum granulosum
Stratum spinosum
Stratum basale
Basement
membrane
Dermis
Dermal papilla
(a)
(b)

6. S. corneum – 20-30 cells thick of dead, kertatinized cells
S. corneum – cells thick of dead, kertatinized cells. (Exposed layer of skin)
S. lucidum (not pictured) covers the S. granulosum
S. granulosum – “grainy layer”
S. spinosum – Intermediate layer, contains spiny-shaped keratinocytes.
S. basale – Mitotically-active
Relatively dry and water-resistant, but not waterproof (not keratinized)
Contains melanocytes
5-10% of this layer.

7. Specialized Cells of the Epidermis: Keratinocytes
Keratinocytes produce keratin
A fibrous, protective protein that waterproofs the skin
Millions of these dead cells are shed daily
Keratin also stiffens epidermal tissue to form fingernails; is found in nails and in hair

8. Specialized Cells of the Epidermis: Melanocytes
Melanocytes are melanin-producing cells located in the bottom layer of the epidermis (the stratum basale)
Melanin is a pigment found in the skin, eyes, and hair
Responsible for skin color
Melanogenesis – occurs after exposure to UV radiation
Process is hormonally-controlled
Higher activity (but same number of cells) in darker-skinned people
Albinos lack the enzyme tyrosinase
Tyrosinase is required for melanocytes to produce melanin from the amino acid tyrosine.

9. Specialized Cells of the Epidermis: Langerhans’ cells
Specialized Cells of the Epidermis: Merkel cells (aka Merkel-Ranvier cells)
Sensitive to touch
When compressed, they release chemicals that stimulate sensory nerve endings
Specialized Cells of the Epidermis: Langerhans’ cells
Part of the immune system; they detect antigens & allow other immune cells to respond (at the lymph nodes)

10. Epidermal Skin Color Heredity and environment determine skin color.
Genetic Factors
Varying amounts of melanin
Varying size of melanin granules
Albinos lack melanin
Physiological Factors
Dilation of dermal blood vessels
Constriction of dermal blood vessels
Accumulation of carotene
Jaundice
Cyanosis due to low oxygen
Environmental Factors
Exposure to UV light
X-rays
Darkens melanin

11. Dermis Anchored to epidermis by basement membrane Vascularized
Contains:
Muscle cells – arrector pili
Nerve cells, specialized sensory receptors
Hair follicles
Glands

12. Dermis – has 2 layers: Papillary layer
Thin, superficial layer; made of areolar & elastic CT
Has Meissner’s (tactile) corpuscles – mechanoreceptor
Has dermal papillae
Innervated and vascularized extensions of the dermis that extend superficially into the epidermis
Responsible for papillary ridges (fingerprints)
Nourishes/forms hair follicles as well
Reticular layer
80% of Dermis; made of dense irregular CT
Hair roots, sebaceous & sweat glands, nails, receptors, blood vessels

13. Sweat
Epidermis
Dermis
Hair shaft
Sweat gland pore
Capillary
Stratum corneum
Stratum basale
Dermal papilla
Arrector pili muscle
Lamellated (Pacinian) corpuscle
Basement membrane
Sebaceous gland
Hair follicle
Sweat gland
Nerve cell process
Adipose tissue
Blood vessels
Muscle layer
Sweat gland duct
Hypodermis T
actile (Meissner’s) corpuscle

14. Subcutaneous layer Not a “true layer” of the skin
Composed of loose CT and adipose tissue
Insulation; contains major blood vessels
Keeps body heat in, and limits entrance of outside heat
Has collagenous and elastic fibers that are continuous with the dermal layer

15. Why care about hair?
Aids with sensory reception (detecting foreign matter on skin)
Insulation (hair on head) – preventing heat loss, protecting from sunlight, and even injury.
Eyelashes – shielding eye from debris
Nose hairs – aid in filtering the air we inhale

16. Accessory Structures: Hair follicles
Each hair develops from a group of epidermal cells at the base of a tube-like depression (a hair follicle)
Follicle extends from the surface into the dermis, which contains the hair root
Three parts of the follicle:
Hair root – contains cells that divide and push older ones to the surface; the older cells move away from the blood supply and keratinize & die.
Hair shaft – dead epidermal cells that extend away from the surface
Hair papilla – contains blood vessels
Melanin – eumelanin (brown/black); pheomelanin (blonde/red)
Arrector pili muscle – attached to hair to allow it to stand up (goose bumps)

17. Hair shaft
Pore
Hair root (keratinized cells)
Arrector pili muscle
Sebaceous
gland
Hair follicle
Region of cell division
Hair papilla
Eccrine sweat gland
Dermal blood vessels

18. Accessory Structures: Nails
Protective coverings on fingers & toes
Three parts:
Nail plate – overlies surface of skin; will naturally extend beyond nail bed and will eventually become worn
Nail bed – skin that is covered by the nail plate
Lunula – white, half-moon shaped at the base of the nail plate
The cells divide from here and give rise to new cells that will become keratinized and become part of the nail plate.
Nail bed
Nail plate
Lunula

19. Accessory Structures: Skin glands
Sebaceous glands:
Usually associated with hair follicles
Holocrine glands that secrete sebum (oil)
Absent on palms and soles
Sweat glands:
Widespread in skin
Originates in deeper dermis, or in the subcutaneous layer
Include ceruminous glands and mammary glands

20. Sebaceous gland Hair follicle Hair Hair shaft Pore Dermal papilla
Duct
Hair shaft
Hair
follicle
Eccrine
sweat
Apocrine
Pore

21. Wounds & Burns Inflammation is a normal response to injury or stress.
Blood vessels in affected tissues dilate and become more permeable, allowing fluids to leak into the damaged tissues.
Inflamed skin may become:
Reddened
Swollen
Warm
Painful

22. Healing of cuts (a) (b) (f) (g) (c) (d) (e) Scar tissue Fibroblasts
Blood cells
Site of injury
Scab
Blood
clot
Healing of cuts

23. Burns
First degree
Superficial partial-thickness (only epidermis is affected)
Heals in several days to two weeks with no scarring
Second degree
Deep partial thickness (destroys some epidermis as well as underlying dermis)
Fluid escapes from damaged dermal capillaries and accumulates beneath the outer layer of epidermal cells, forming blisters
Healing depends on the accessory structures that survive
Third degree
Full-thickness (destroys epidermis, dermis, and the accessory structures of the skin)
All epidermal cells destroyed, healing only occurs if epithelial cells divide and grow inward from margin of the burn
Extensive affected areas may require transplant (autograft from unburned part of body, homograph from cadaver, or a skin substitute – artificial or amniotic membrane from fetus)

24. Anterior and posterior head and neck
Rule of Nines:
Used to estimate total body surface area that is burned.
Anterior
trunk
18%
Posterior
Anterior upper
extremities 9%
Posterior upper
Posterior lower
extremities 18%
Perineum 1%
Anterior and
posterior upper
extremities
posterior lower
36%
100%
posterior trunk
Anterior and posterior head and neck 9%
Anterior head
and neck 41/2%
Posterior head
Anterior lower
41/2%
ANTERIOR
POSTERIOR