1. Biology 211 Anatomy & Physiology I
Skin
The Integumentary System

2. The Integumentary System
Skin=Integument
Skin + accessory organs (hair, nails, and cutaneous glands)= Integumentary system
Dermatology=scientific study and medical treatment of the integumentary system
Skin-the most vulnerable organ—exposed to radiation, trauma, infections, injurious chemicals
Lgst. organ—15% body wt

3. Functions of Integumentary System (skin & its products)
Barrier to keep water and solutes in
Barrier to keep bacterial, dirt, etc. out
Protection against abrasion
Contains sensory receptors for touch, temperature, pressure, pain, etc.
Temperature regulation via hair, sweat, & amount of blood flow
Blood reservoir
Synthesis of vitamin D
Excretion

4. Three Layers of skin: Epidermis:
Stratified squamous epithelium; outer layer is "keratinized" or "cornified"
Dermis:
Dense irregular connective tissue
Hypodermis:
Adipose connective tissue (technically not part of system

5. Epidermis: Avascular. Depends on blood vessels in underlying
dermis for its nutrition
Cells formed by mitosis in deepest, or basal, layer, then get pushed into more superficial layers or "stata"

6. (Epidermis)
Stratum Basale = Single row of dividing cells
Stratum Spinosum = Three or four layers of cells;
Some cell division
Stratum Granulosum = Three or four layers of cells;
Actively synthesizing protein
keratin
Stratum Lucidum = One or two layers of dying cells
Stratum Corneum = Many layers of flat, dead, scale-like
cells full of keratin

7. Primary cell type in epidermis = keratinocytes which produce large amounts of protein keratin
Other cell types:
Melanocytes produce pigment melanin & transfer it to keratinocytes
Langerhans cells (immune cells) protect against pathogens and toxins
Merkel cells detect touch and pressure; transfer this information to sensory receptors in the dermis

8. Most significant factor is melanin
Skin Color
Most significant factor is melanin
2 forms (1) eumelanin (brownish black) and (2) pheomelanin (reddish yellow)
Other factors include hemoglobin (red to pink) and carotene (yellow)
Different races have same # of melanocytes, amount of melanin produced differs
Melanin accumulates in keratinocytes

9. Abnormal Color
Cyanosis—blue, lack of hemoglobin
Erythema—abnormal redness, increased blood flow or blood pooling
Pallor—pale, ashen, poor blood flow
Albinism—lack of melanin
Jaundice—yellowing, hi levels of bilirubin (hi rate of erythrocyte destruction
Bronzing—deficiency of glucocorticoids
Hematoma—bruise, blood clot

10. - Keratinocytes in stratum basale (& stratum spinosum)
(Epidermis)
Keratinocytes move from stratum basale to stratum corneum, dying as they do so. Average = wks
- Keratinocytes in stratum basale (& stratum spinosum)
lie along basement membrane; divide by mitosis
- Older ones pushed toward surface by newer cells
- Melanocytes transfer melanin to keratinocytes
- Keratinocytes synthesize large amounts of keratin
and flatten out as they move toward surface
- Older cells die but remain attached to each other
- Cells eventually shed from stratum corneum

11. Dermis: Dense irregular connective tissue
Separated from epidermis (stratified squamous epithelium) by basement membrane
Highly vascular
Highly innervated
Two Layers:
Papillary layer just below epidermis
Reticular layer forms deep 80%

12. Dermis:
Contains many types of sensory receptors for touch, pressure, vibration, pain, temperature, etc.
Some = simple nerve endings
Others = complex structures with multiple cell types

13. Dermis = Dense irregular connective tissue. Thus:
Cells = Fibroblasts / Fibrocytes
Macrophages
Mast cells
Lymphocytes
etc.
Fibers = Collagen (therefore strong, flexible)
Elastic (therefore stretchable)
Weight gain tears collagen fibers producing striae (stretch marks)

14. Appendages of the skin Hair follicles and hair Sweat glands
Sebaceous (oil) glands
Nails on fingers and toes
All begin as epidermis of embryo; grow down into dermis

15. - Distribuled over all skin except: palms of hands
Hair
- Distribuled over all skin except: palms of hands
soles of feet
nipples
glans of penis & clitoris
minor labia
- Formed in follicles located deep in dermis
- Consists of layers of dead, highly keratinized keratinocytes

16. Function of Hair
Trunk and limb hair considered vestigial
Scalp only place where it is thick enough to retain heat
Eyebrows enhance facial features
Vibrassae (guard hair) are used to filter particulates from the ear and nose

17. Shaft
Root
Bulb

18. Medulla: Loosely arranged keratinocytes
Cortex: Densely packed keratinocytes
Cuticle: Keratinocytes loosely arranged like scales

20. Black or brown color due to eumelanin produced by melanocytes and transferred to keratinocytes in follicle. Red color produced by pigment called pheomelanin
Blonde color produced by intermediate levels of pheomelanin and low levels of eumelanin
Texture of hair due to
The rounder the hair shaft, the straighter it will be
The flatter the hair shaft, the more curled it will be

22. Each hair is associated with:
One or more sebacious
(oil) glands
An arrector pili muscle
A plexus of nerves around
the root

23. Sweat Glands - 2 to 3 million - Two types:
Merocrine: Distributed over all skin except nipples
(Eccrine) Simple coiled glands in dermis
Duct leads to sweat pore on surface
Secreted watery sweat for cooling
Apocrine: Located only in axillary, pubic, anal regions
Larger than eccrine glands
Duct opens into opening of hair follicle
Secretes thicker sweat, high content of
proteins and fats. Contains specific scent
molecules: sexual, fear, etc.

24. Sweat is usually 99% water with a pH between 4 and 6
Sweat glands produce 500ml of insensible perspiration (no noticable wetness)daily
Diaphoresis—sweating with wetness (up to 1 l per hr when exercising or in heat)
Two specially modified sweat glands:
Ceruminous—found in the external ear canal. Secretion combines with sebum and dead epidermal cells to form earwax (keeps eardrum pliable, canal waterproof and has a bactericidal effect)
Mammary --milk producing glands found in the female breast (modified apocrine glands)

25. Sebaceous (oil) glands:
- Branched tubular glands
- Duct opens into opening
of hair follicle
- Secretes sebum,
consisting of lipids,
proteins, ions,
carbohydrates,

26. Nails: - Tips of fingers and toes - Thick layer of densely packed
keratinocytes
- Produced by nail matrix at
proximal end, hidden under
eponychium or cuticle
Deeper layers of epidermis = nail bed
Average growth:
0.5 mm per week

27. Nails
Flat nails allow for fleshy, sensitive fingertips
Serve as tools for digging, grooming and manipulation
Useful in medical diagnosis
Iron deficiency—flat or concave
Long term hypoxia (oxygen deficiency)—clubbed

28. Carcinomas (cancers) of the skin:
Basal Cell Carcinoma:
Keratinocytes of stratum basale proliferate, invade dermis
Relatively low malignancy
Squamous Cell Carcinoma:
Keratinocytes of epidermis proliferate
May or may not invade dermis
Moderate malignancy
Malignant Melanoma:
Melanocytes of epidermis proliferate, invade dermis
Highly malignant

29. Burns
Leading cause of accidental death
Classified by depth of tissue involvement
1st degree—involves epidermis only
2nd degree—involves epidermis and some dermis
3rd degree—involves epidermis, dermis and some deeper tissue are destroyed
1st and 2nd degree burns are considered partial thickness burns, and 3rd degree is a full thickness burn