Transcript Skin

Biology 322
Human Anatomy I
Integument
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
Three Layers of skin:
Epidermis: Avascular.
Depends on blood vessels in underlying
dermis for its nutrition
(Epidermis)
= Many layers of flat, dead, scale-like
cells full of keratin
= One or two layers of dying cells
Not present in thin skin
= Three or four layers of cells;
Actively synthesizing protein
keratin
= Three or four layers of cells;
Some cell division
= Single row of dividing cells
(Connective tissue)
Primary cell type in epidermis =
which produce large amounts of protein
Other cell types:
Two related forms of melanin:
Black or brown
Responsible for dark skin or hair
Red or pink
Responsible for pink skin (lips, nipples,
glans of clitoris or penis, freckles) and
red hair
Both synthesized
(Epidermis)
Keratinocytes move from stratum basale to stratum
corneum, dying as they do so. Average = 5 - 6 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
Dermis:
Two Layers:
Dermis = Dense irregular connective tissue. Thus:
Cells =
Fibers =
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
Appendages of the skin
All begin as epidermis of embryo; grow down into dermis
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
Black or brown
Blond
Red
Gray or White
Each hair is associated with:
Sweat Glands
Two specially modified sweat glands:
Sebaceous (oil) glands:
- Branched tubular glands
- Duct opens into opening
of hair follicle
- Secretes sebum,
consisting of lipids,
proteins, ions,
carbohydrates,
Nails:
- Tips of fingers and toes
- Thick layer of densely packed
keratinocytes
- Produced by
Deeper layers of
epidermis =
Average growth:
0.5 mm per week
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