1. Unit II: Organization
Integumentary System
Part I
Chapter 5

2. Integumentary System
Body’s largest organ (15% of body wt, 2m2 surface area)
Made of two layers:
Epidermis
Dermis
Accessory Organs
Hair
Nails
Cutaneous Glands
Hypodermis
Below the dermis
Not part of the skin
– 15% of body weight
(keratonized stratified squamous cells)
dermis - (fibrous connective tissue)
4. (adipose connective tissue)

3. Integumentary System
Thick skin – covers the palms, soles, fingers and toes
~0.5mm
stratum corneum is very thick (5 layers)
no sebaceous glands or hair follicles
Thin skin – covers the rest of the body
~0.1mm
thin stratum corneum (4 layers)
hair follicles and glands
Epidermis
Epidermal ridge
Dermis
Dermal papilla
Thick skin
LM x 225
Thin skin
1. thickness of epidermis ~0.5mm thick
Stratum corneum – layer of dead cells
2. thickness of epidermis ~0.1mm

4. Functions of your Skin
Protection of underlying tissues - bears most physical injuries.
Barrier against pathogens - Few microbes can penetrate intact skin.
Acid Mantle - slight acidity of pH 4-6 on the surface
Water proofing
Barrier to ultraviolet light (UV radiation)
Vitamin D synthesis  Calcitriol – needed for bone health
Cutaneous absorption & excretion – O2, CO2, fat soluble vitamins
Sensory - touch, texture, pressure, vibration, and tissue injury
Thermoregulation - thermoreceptors
Communication
Resists and recovers better than any other organ Packed with keratin – tough protein and desmosomes for durability.
Bacteria and fungi colonize on the skin surface but numbers are kept in check by #3
which is unfavorable to the growth of microbes
Keeps the body from absorbing excess water. Prevents body from losing excess water.
Keeps this cancer-causing radiation from reaching deeper tissue layers.
Skin carries out the first step in the synthesis needed for bone development and maintenance. The liver and kidneys complete the process.
1-2% of all blood oxygen, some CO2, many drugs and poisons, fat soluble vitamins all pass through the skin.
Contains nerve endings that react to heat, cold, touch, texture, pressure, vibration, and tissue injury. Some areas have more than others – abundant on face not so much on back.
Keeps us cool as well as retain heat. Nerve endings called thermoreceptors that transmit signals to the brain to increase or decrease blood flow close to the skin surface.
Skeletal muscles insert on dermal collagen fibers and pull the skin to make expressions. Appearance of skin, hair, and nails important to social acceptance.

5. Structure of the Skin Epidermis
Composed of five types of cells:
Stem cells – undifferentiated cells
Keratinocytes – majority of epidermis cells, durability and flexibility
Melanocytes – synthesize pigment (melanin) shields from UV
Tactile (Merkel) – receptors for touch
Dendritic (Langerhans) – stand guard against foreign invaders, phagocytic
Keratinized stratified squamous
2. come from stem cells, synthesize keratin fibrils: fibrous protein that gives epidermis its durability and flexibility
5. Dendritic name – general all over body; Langerhans – specific to skin; and “present” them to the immune system (phagocytic)

6. Layers of the Epidermis
Cells: won’t see stem cells in lab because of when the timing of tissue samples.
5 cells
5 layers of epidermis
Above the dermis
(b) To see this in lab – need to be at x

7. Layers of the Epidermis Stratum basale
Simple cuboidal epithelial cells
4 types of cells: keratinocytes, Melanocytes, Merkel cells, stem cells
Stem cells constantly undergoing mitotic cell division
simple cuboidal to low columnar cells resting on the basement membrane
10-25% of cells melanocytes

8. Layers of the Epidermis Stratum spinosum
8-10 layers of Keratinocytes
Deepest cells undergo mitosis.
Keratin filaments cause the cells to flatten near the surface.
Desmosomes – attach the cells, give spiny appearance
Langerhans cells – arise in bone marrow
consists of several layers of keratinocytes.
Stem cells divide less rapidly.
Keratin filaments/fibers are produced by the keratinocytes.
Desmosomes attach neighboring cells to each other and give cells their spiny appearance – giving it its name spinosum.
Langerhans arise in bone marrow, protect against pathogens.
Keratin protein is incorporated into longer keratin/intermediate filaments

9. Layers of the Epidermis Stratum granulosum
3-5 layers of keratinocytes
Lamellated granules secrete glycolipids
waterproof barrier
forms a barrier between surface cells and deeper layers of the epidermis
cuts off surface strata from nutrient supply
Keratohyalin granules – cross links keratin filaments
Granular layer
consists of 3-5 layers of flat keratinocytes
Contain …
Glycolipids released by lamellated granules in this layer make a waterproof barrier
Keratohyalin granules – used in keratinization = cross linking keratin fibers/filaments  nucleus and organelles disintigrate, cell dies  keratin fibers surrounded by keratohyalin (protein)
keratohyalin  eleidin  keratin

10. Layers of the Epidermis Stratum lucidum
Translucent zone found only in thick skin
Keratinocytes filled with keratohyalin and eleidin
Cells have no nuclei or other organelles
Undergoing dehydration
2. Keratinocytes packed with eleidin - a precursor to keratin
No nutrients to support organelles  dead cells!
4. This layer is pale and featureless because there are no organelles and eleidin doesn’t hold stain well.

11. Layers of the Epidermis Stratum corneum
Consists of up to 30 layers of dead, dead, keratinized cells
outermost layer where surface cells flake off.

12. Life History of Keratinocytes
Produced by stem cells in stratum basale
New cells push others toward surface - keratin filaments
Cells grow flat and fill with keratohyalin
Organelles disintegrate as they pass the water barrier
Cells die and fill with keratin fibers
Exfoliate
New cells are typically formed at night, so you won’t see mitosis in any prepared slide.
It takes about days for a keratinocyte to be pushed up to the surface and flake off. Faster (in an injury or stressed skin - calluses) or slower (in old age).
Water barrier is formed between the granulosum and stratum spinosum.

13. Layers of the Dermis

14. Layers of the Dermis 0.2mm – 4mm thick
Fibrous Connective tissue composed of:
fibroblasts
collagen, elastic fibers: strength and flexibilty
Accessory structures embedded here
Layers
papillary layer – surface layer, thin zone of areolar
Dermal papillae - extensions of the dermis into the epidermis
increase surface area for attachment, create finger prints
reticular layer – thick layer of dense irregular
1. Thickness = 0.2mm to 4mm
2. Fibrous Connective tissue layer made of …
Accessory structures: Cutaneous glands found here as well as hair follicles and nail roots embedded here.
Vascularized with Smooth muscle (arrector pili) associated with the hair follicles which make them stand on end (goosebumps and natural wrinkles) and facial expressions.
3.papillary layer - thin zone of areolar tissue
… forming the ridges of the fingerprints
Reticular layer - thick layer of dense irregular tissue
Boundary is vague. The reticular layer has more collagen fibers which when torn from being stretched too much is what forms stretch marks.
Both layers have collagen and elastic fibers  strength and flexibility

15. Hypodermis Other names: Subcutaneous tissue/ superficial fascia
Mostly adipose
Functions:
Hypodermic injections (subQ)
highly vascular
Limits tissue damage
1. Other names… Binds the skin to underlying tissues. Considered apart of muscular system.
2. Not uniformly distributed. Absent from scalp.
3. energy reservoir
thermal insulation
4. Absorbs drugs quickly.

16. Skin Organs Hair Composed of hard keratin Hair found almost everywhere
2.5 million/75% on general body not head
Not found on thick skin, nipples, lips
differences between sexes or individuals
Texture and color
3 different body hair types:
lanugo -- fine, unpigmented fetal hair
vellus -- fine, unpigmented hair of children and women
terminal hair -- coarse, long, pigmented hair
1. (epidermal cells) but embedded in dermis
2. Differences in sexes is not the number of hairs in a given area but is difference in texture and color of hair
3. Terminal hair – of scalp - eyebrows, eyelashes, pubic hair, male facial hair, and some of the trunk and limb hair.

17. Structure of Hair and Follicle
Cuticle
Cortex
Medulla
Hair matrix
Hair papilla
Hair – keratinized cells
Follicle – oblique tube
Three zones:
bulb = hair originates
vascular tissue (papilla) in bulb
provides nutrients
root = within follicle
shaft = above skin
Three layers in cross section:
Medulla (core): soft keratin
Cortex: thick, hard keratin
cuticle (surface):
thin, hard keratin
Arrector pili
muscle
Hair is filament of keratinized cells (dead!) made of epidermal cells
is oblique tube within the skin (includes everything within skin)
Bulb – hair originates, well nourished  pushed away  dies
root – within follicle
shaft – above skin
4. … abrasion to cuticle = split ends
hair dye changes the color of the cuticle (normally translucent)
Piloerector/arrector pili muscle – smooth muscle; connect follicle to papillar layer; stand hair upright to create a bubble around base to “insulate” – goosebump; sebaceous gland releases sebum at same time
Nerve – wraps around just above bulb

18. Texture and Color of Hair
Straight hair = round
Wavy = oval
Tight curls = flat
Hair color = ratio of
two types of
melanin found in
the cortex
Difference in cross-sectional shape
4. Ratio of pigment in cells of cortex
two types of melanin for hair pigment
gray & white: absence of melanins in cortex and air in medulla

19. Hair Growth Cycle 90% of scalp follicles Detached from Hair falls out
Epidermis
Dermis
Hair matrix
Sebaceous
gland
Old club hair
Piloerector
New hair
Bulge
Club hair
(detached
from matrix)
Club
Dermal papilla
Degeneration
of lower follicle
Hair bulb 2 3
Anagen (early)
(Growing phase, 6–8 years)
Stem cells multiply and follicle grows deeper into dermis;
hair matrix cells multiply and keratinize, causing hair to grow
upward; old club hair may persist temporarily alongside newly
growing hair.
Anagen (mature)
Catagen
(Degenerative phase, 2–3 weeks)
Hair growth ceases; hair bulb
keratinizes and forms club hair;
lower follicle degenerates.
Telogen
(Resting phase, 1–3 months)
Dermal papilla has ascended
to level of bulge; club hair falls
out, usually in telogen or
next anagen. 1
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1. 3 repeating cycles
2. (90% of scalp follicles) grows down into dermis from epidermis
lasts 6-8 years in young adult
3. (lasts 2-3 weeks); club hair being formed (detached from nutrients)
4. (lasts 1-3 months) hair falls out
Hair falls out during catagen or telogen phase.
You have anywhere from scalp hairs that fall out daily.
Development of hair follicle:
Starts in epidermis during development
After further growth becomes embedded in dermis
produced by mesoderm.
90% of scalp follicles Detached from Hair falls out
Grows down from epidermis nutrients

20. Hair Loss and Growth Alopecia - General term for all hair loss
Pattern baldness
sex-influenced trait
males: XdefectY (can’t cover up)
females: XdefectX (no baldness)
expressed only with high testosterone levels
follicles are sensitive to androgens  causes them to shrink when exposed  shorten their lifespan and prevents them from producing hair normally
Hirsutism - excessive hair growth
hormone imbalance (ovary or adrenal cortex tumor)
(loss of hair from head/body sometimes to baldness) = Alopecia mainly results from aging but can be worsened by a number of factors – disease, poor nutrition (iron deficiency), emotional trauma (pulling out hair), hairstyling routines
2. genetic and hormonal (androgens)
3. a. Especially in women and children. Usually associated with menopause.
excess hair where terminal hair not normally present (ex. Beard, chest hair)
Risk factors: ↑ androgens, oversensitivity of follicles to androgen; ↑ insulin in females  stimulates ovaries to produce ↑ androgens  stimulate hair production
Treatment: ↓ insulin levels
Hair implants: take hair from back and put on scalp; living, active follicle that grows

21. Functions of Hair
Body hair - (too thin to provide warmth) - alert us to parasites crawling on skin
Scalp hair - heat retention and sunburn cover
Beard, pubic and axillary hair - sexual maturity and help distribute sexual scents similar to pheromones
Guard hairs - prevent foreign objects from getting in
nostrils, ear canals or eyes
Expression of emotions with eyebrows

22. Skin Organs Fingernail Structure
Body – visible portion
Free edge – grows away from body
Root – embedded in skin; adheres to nail bed
Nail bed – skin under nail
Nail matrix – proximal part of nail bed, growth zone
Nails: non-living material like hair; nearly translucent – pink = dermal blood supply
turn blue = lack of oxygen in the blood

23. Nails Derivative of stratum corneum that grows downward
densely packed cells filled with hard keratin
New cells added by mitosis in the nail matrix
Flat nails allow for fleshy, sensitive fingertips
protect fingertip and surrounding soft tissue from injury
enhances precise delicate movements;
enhances sensitivity (counterforce)
tool
Medical diagnosis
Ex.) iron deficiency = concave nails
Length and growth rate related to the length of the terminal phalanges
3. Most mammals have claws – flat nails are a distinguishing characteristic of primates.
4. Concave - spoonlike
others: dehydration; nutrient deficiency; problems elsewhere in the body
shock – if nailbed doesn’t return to pink within seconds
disease – horizontal ridges
5. … Grow ~3mm a month
3-6 months – regrow completely (fingers)
12-18 months – regrow completely (toes)