1. Biology 322 Human Anatomy I
The Integumentary System

2. The Integumentary System
Skin = Integument
Largest organ in body – 15% of body weight
Skin + accessory organs
(hair, nails, glands) .
= Integumentary system

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
Variable thickness mostly due to dermis:
0.5 mm on eyelids
to 6 mm on back, palms of hand, soles of feet

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

6. (Epidermis)
Stratum Corneum = Many layers of flat, dead, scale-like
cells full of keratin
Stratum Lucidum = One or two layers of dying cells.
Not present in thin skin
Stratum Granulosum = Three or four
layers of cells;
Actively synthesizing
the protein keratin
Stratum Spinosum = Three or four layers
of cells; Some mitosis
Stratum Basale = Single row of dividing cells

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 (dendritic) cells (really macrophages) clean up debris
Merkel (tactile) cells detect touch and pressure; transfer this information to sensory receptors in the dermis

8. Skin Color
Two related forms of melanin:
Eumelanin – Black or brown
Responsible for dark skin or hair
Pheomelanin – Red or pink
Responsible for pink skin
(lips, nipples, glans of clitoris
or penis, freckles)
and red hair
Both synthesized by melanocytes and then transferred to keratinocytes.
Also: Carotene = yellow
Hemoglobin in blood = red/pink

9. - Older ones pushed toward surface by newer cells
(Epidermis)
Keratinocytes move from stratum basale to stratum corneum, dying as they do so. Average = wks
Keratinocytes and stem cells 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

10. 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%

11. Dermis = Dense irregular connective tissue. Thus:
Cells = Fibroblasts / Fibrocytes
Macrophages
Mast cells
Lymphocytes
etc.
Fibers = Collagen (therefore
strong, flexible)
Elastic (therefore
stretchable)

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. 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

14. Hair Distributed over all skin except: palms of hands/fingers
soles of feet/toes
nipples
glans of penis & clitoris
minor labia
Minimal trunk & limb hair
Thicker on scalp to retain heat
Eyebrows enhance facial features, shade eyes
Nostril hair filters dust & other particulates
Pubic hair, axillary hair, anal hair retain pheromones

15. Hair
Formed in follicles in dermis
Consists of layers of dead,
highly keratinized keratinocytes
“Vellus” hair is finer. Covers arms, legs, back, chest, etc.
“Terminal hair” is longer and courser. Scalp, pubic hair,
axillary hair, eyelashes, eyebrows,
male facial hair

16. Shaft
Root
Bulb

17. Medulla: Loosely arranged keratinocytes
Thickest in terminal hair; absent in vellus hair
Cortex: Densely packed keratinocytes
Cuticle: Keratinocytes loosely arranged like scales

18. Black or brown color due to eumelanin produced by melanocytes and transferred to keratinocytes in follicle.
Blond hair has little eumelanin and some pheomelanin
Red hair has little eumelanin and lots of pheomelanin
(the same gene which produces pheomelanin also increases the number of freckles in redheads)
Gray or White hair has little of either eumelanin or pheomelanin

19. Texture of hair due to shape of the hair shaft.
The rounder the hair shaft, the straighter it will be
The flatter the hair shaft, the more curled it will be

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

21. 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.

22. Modified Sweat Glands
Ceruminous glands
in external ear canal.
Secretion combines with
sebum to form earwax
Mammary glands in breast

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

24. 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

26. Burns:
Major cause of accidental death
Classified by depth of tissue involvement
Superficial: involves epidermis only
Partial thickness: involves epidermis
and some dermis
Full thickness: epidermis, dermis,
and deeper tissue
destroyed

27. 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 invade dermis
Moderate malignancy
Malignant Melanoma:
Melanocytes of epidermis
proliferate, invade dermis
Highly malignant