Transcript Integumentary System / Skin

Biology 211
Anatomy & Physiology I
Dr. Thompson
The Integumentary System
The Integumentary System
Skin = Integument
Largest organ in body – 15% of body weight
Skin + accessory organs
(hair, nails, glands)
= Integumentary system
Dermatology = scientific study and medical treatment
of the integumentary system
Exposed to radiation, trauma, infections, chemicals, etc.
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
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
(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
Primary cell type in epidermis = keratinocytes
which produce large amounts of protein keratin
Other cell types:
Melanocytes produce pigment
melanin & transfer it to
keratinocytes
Dendritic or Langerhans cells
(immune cells) protect against
toxins & pathogens
Tactile or Merkel cells
detect touch and pressure;
transfer this information to
sensory receptors in the dermis
Skin Color
Most significant factor is melanin
2 forms: eumelanin (brownish black)
pheomelanin (reddish yellow)
Melanin: produced by melanocytes
accumulates in keratinocytes
Different races:
similar numbers of melanocytes,
different amounts of melanin produced
Also
Carotene = yellow
Hemoglobin in blood = red/pink
Abnormal Skin Color
Albinism = lack of melanin
Erythema = red; increased blood flow, inflammation
Cyanosis = blue; lack of oxyhemoglobin
Pallor = pale; decreased blood flow
Jaundice = yellow; erythrocyte destruction, liver failure
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 (strength)
Elastic (stretchable)
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
Distributed over all skin except: palms of hands
soles of feet
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
Hair
Formed in follicles in dermis
Consists of layers of dead,
highly keratinized keratinocytes
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 pigments called pheomelanin
Blonde color produced by intermediate levels of
pheomelanin and low levels of eumelanin
Texture of hair is due to the 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
Each hair is associated with:
One or more sebacious
(oil) glands
An arrector pili muscle
(smooth 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
Secrete watery sweat for cooling
Apocrine: Located only in axillary, pubic, anal regions
Larger than eccrine glands
Duct opens into opening of hair follicle
Thicker sweat, high content of protein and fats
Contains scent molecules: sexual, fear, etc.
Sweat is usually 99% water with a pH between 4 and 6
Contains significant amounts of sodium, potassium,
calcium, chloride, and trace amounts of other minerals
~ 500 ml/day at rest,
more at warmer temperatures
2,000 ml/hour during moderate
to intense exercise
Modified Sweat Glands
Ceruminous glands in external ear canal.
Secretion combines with sebum to form earwax
Mammary glands in breast
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
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
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
and invade dermis
Highly malignant