Biology 211
Anatomy & Physiology I
Skin
The Integumentary System
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
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:
Stratified squamous
epithelium; outer
layer is "keratinized"
or "cornified"
Dermis:
Dense irregular
connective tissue
Hypodermis:
Adipose connective
tissue (technically not
part of system
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"
(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
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
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
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
(Epidermis)
Keratinocytes move from stratum basale to stratum
corneum, dying as they do so. Average = 6 - 8 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:
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%
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
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)
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
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
Function of Hair
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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
Shaft
Root
Bulb
Medulla: Loosely arranged keratinocytes
Cortex: Densely packed keratinocytes
Cuticle: Keratinocytes loosely arranged like scales
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
Each hair is associated with:
One or more sebacious
(oil) glands
An arrector pili muscle
A plexus of nerves around
the root
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.
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)
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 nail matrix at
proximal end, hidden under
eponychium or cuticle
Deeper layers of
epidermis = nail bed
Average growth:
0.5 mm per week
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
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
Burns
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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