1. Integumentary System (Skin) 12/14
Protection
Chemical
Low pH secretions (acid) retard bacterial activity
Physical/mechanical barriers
block most water & water- soluble substances
Limited penetration of skin by any substance
Body temperature regulation
Cutaneous sensations--temperature, touch, and pain
Metabolic functions
Synthesis of vitamin D precursor
Prevents dehydration
5. Excretion—nitrogenous wastes and salt in sweat
Lab 4A
BIO 105
BIOL Lab 4A--Skin

2. Consists of three major regions
Epidermis—outermost region
Dermis—middle region
Hypodermis (superficial fascia)—deepest region
not technically part of skin
Mostly adipose tissue
BIOL Lab 5A--Skin

3. Epidermis
Keratinized stratified squamous epithelium with 4 different types of cells and 4-5 layers
Keratinocytes—main cell type; produce keratin (protein)
Melanocytes
Produce melanin pigment—gives skin its coloring– yellowblack
Langerhans cells—macrophages that help activate immune system
Merkel cells—tactile receptors
Nutrients reach epidermis by diffusing through tissue fluid
BIOL Lab 5A--Skin

4. Stratum corneum
Most superficial layer; 20–30 layers of dead cells represented only by flat membranous sacs filled with keratin. Glycolipids in extracellular space.
Stratum granulosum
Three to five layers of flattened cells, organelles deteriorating; cytoplasm full of granules which release lipids and keratohyaline granules which surround keratin.
Stratum spinosum
Several layers of keratinocytes. Cells contain thick bundles of intermediate filaments made of pre-keratin.
Stratum basale
Deepest epidermal layer; one row of actively mitotic stem cells; some newly formed cells become part of the more superficial layers. See occasional melanocytes and epidermal dendritic cells.
BIOL Lab 5A--Skin
Figure 5.2b

5. Layers of Epidermis: superficial  deep Stratum Corneum (Horny Layer)
Outermost layer consisting of rows of dead, flat, keratinized membranous sacs (no nuclei seen in cells)
Dandruff from scalp or “dander” loose flakes that fall off dry skin
Makes up 3/4 of epidermal thickness
Functions
Protection from abrasion and penetration
Waterproofs
Forms a barrier against biological, chemical, and physical assaults—makes skin impermeable to most substances
BIOL Lab 5A--Skin

6. Contains few rows of flat, dead, keratinocytes
Stratum lucidum
found in thick skin e.g. soles of feet, palms, fingertips; not seen in thinner skin.
Contains few rows of flat, dead, keratinocytes
Stratum Granulosum or Granular Layer
Skin layers superficial to this are made up of dying or dead cells;
are too far from blood capillaries to get adequate nutrition and oxygen
Thin; 3-5 layers of flattened cells
Contains cells more resistant to destruction
BIOL Lab 5A--Skin

7. thickest layer of living cells. cells start to flatten out
Stratum Spinosum
thickest layer of living cells.
cells start to flatten out
produce protein keratin and glycolipids that toughen and water-proof skin.
BIOL Lab 5A--Skin

8. Stratum Basale (Basal Layer) Deepest epidermal layer
Firmly attached to dermis
Single row of stem cells
cells undergo rapid division
Takes ~25–45 days for cell to migrate from this layer to surface
BIOL Lab 5A--Skin

9. Dermis-thickest layer Contains strong, flexible connective tissue
Only this layer is vascularized
Cells include fibroblasts, macrophages, and few mast cells and white blood cells
Has nerve fibers, blood vessels and lymphatic vessels
made up of 2 layers:
Papillary – outermost; contains areolar connective tissue; nerve endings for touch and pain
Reticular-innermost; dense irregular collagen, elastic and reticular fibers
BIOL Lab 5A--Skin

10. Papillary layer of Dermis
Areolar connective tissue with collagen and elastic fibers and blood vessels
Looseness of connective tissue allows defensive cells to patrol the area for invaders
Makes dermal papillae which contain:
Capillary loops, Meissner’s corpuscles, Free nerve endings
Epidermal ridges on top dermal papillae make our fingerprints and allow us to grip items better
BIOL Lab 5A--Skin

11. Reticular layer-Collagen fibers provide strength and resiliency
bind with water to keep skin hydrated
Elastic fibers provide stretch-recoil properties
Contains sebaceous and sweat glands, pressure receptors
BIOL Lab 5A--Skin

12. Three pigments contribute to skin color: Melanin
Yellow to reddish-brown to black, responsible for dark skin colors
darker skinned people produce melanocytes with more pigment and their keratinocytes retain color longer than lighter skinned people
Freckles and pigmented moles result from local accumulations of melanin
Carotene
Yellow to orange, most obvious in the palms and soles
Hemoglobin--not a skin pigment but gives the pinkish hue of skin because blood vessels are close to the skin surface
BIOL Lab 5A--Skin

13. Skin Appendages: Sweat Glands
Two main types of sweat (sudoriferous) glands
Eccrine or merocrine sweat glands—abundant on palms, soles, and forehead
Sweat ducts connect to pores
Function in temperature regulation
BIOL Lab 5A--Skin

14. Functional from puberty onward Specialized “sweat” glands:
Apocrine sweat glands—confined to axillary and anogenital areas (animals use smells from these to identify the opposite sex)
Secretion is sweat + fatty substances and proteins; odorless secretion but bacteria feed off it and make odor
Functional from puberty onward
Specialized “sweat” glands:
Ceruminous glands—in external ear canal; secretes cerumen or wax
Mammary glands—secrete milk
BIOL Lab 5A--Skin

15. Sebaceous (Oil) Glands
Widely distributed
Typically located near hair follicles-keep hair moist
Made up of branched alveolar glands
Become active at puberty
Secrete sebum, an oily secretion
Bactericidal
Softens hair and skin
BIOL Lab 5A--Skin

16. Specialized Receptors: Pressure:
Meissner corpuscles—
light touch
In Papillary layer
Pacinian Corpuscles—
deep touch
In Reticular layer
BIOL Lab 5A--Skin

17. Nails
Scalelike modification of epidermis on distal, dorsal surface of fingers and toes
BIOL Lab 5A--Skin

18. Consists of dead keratinized cells
Hair--
Consists of dead keratinized cells
Contains keratin which is tougher and more durable than soft keratin of skin
Root is in skin, shaft projects from the skin
Hair pigments: melanins (yellow, rust, brown, black)
Gray/white hair: decreased melanin production, increased air bubbles in shaft
BIOL Lab 5A--Skin

19. Hair Functions Distribution Alerts body to presence of insects on skin
Helps to keep us warm
Guards scalp against physical trauma, heat loss, and sunlight
Distribution
Entire surface except palms, soles, lips, nipples, and portions of external genitalia
BIOL Lab 5A--Skin

20. Extends from epidermal surface into dermis
Hair Follicle
Extends from epidermal surface into dermis
Sensory nerve endings wrap around each hair bulb or root
Bending of hair stimulates these nerve endings; hair functions as a very sensitive touch receptor
Hair Bulb
Hair grows from the bulb which contains blood vessels and nerves
BIOL Lab 5A--Skin

21. Extends from epidermal surface into dermis
Hair Follicle
Extends from epidermal surface into dermis
Two-layered wall: outer--connective tissue, inner--epithelial tissue
Deep end expands to form hair bulb
Sensory nerve endings wrap around each hair bulb or root
Bending of hair stimulates these nerve endings; hair functions as a very sensitive touch receptor
Hair Bulb
Hair grows from the bulb which contains blood vessels and nerves
BIOL Lab 5A--Skin

22. Arrector pili muscle Smooth muscle attached to follicle
Responsible for “goose bumps”
BIOL Lab 5A--Skin

23. Not technically part of skin Subcutaneous tissue deep to dermis
Hypodermis or superficial fascia (because it is superficial to the fascia which wraps the skeletal muscles)
Not technically part of skin
Subcutaneous tissue deep to dermis
Consists mostly of adipose tissue
This area gets thicker with weight gain
What surgical procedure do some people have to get rid of this fat?
Anchors skin to underlying structures
Is shock absorber
Is an insulator
BIOL Lab 5A--Skin

24. LABWORK 1. List, identify, and describe the major regions of the skin.
2. List, identify, and describe the layers of the epidermis (Pacinian and Meissner’s Corpuscle slides may work best).
3. List, identify, and describe the structures found in the dermis (scalp and corpuscle slides may be best).
BIOL Lab 5A--Skin