Transcript The Skin Your In

The Skin You’re In
Basic Facts
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Covers the entire body, ~1.2-2.2 square meters
Weighs 4 to 5 kg, around 7% of body weight
for an adult.
Pliable, yet tough takes a beating everyday!
The Big Layers
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Epidermis: The keratinized stratified
squamous layer consisting of 4-5 distinct
layers with 4 distinct cell types
Dermis: The largest layer mainly made of
tough fibrous connective tissue.
Only dermis has vascular tissue, nutrients
reach epidermis by diffusion
Subcutaneous Tissue (aka: hypodermis) Not
really a layer of skin but shares some of the
skins protective features. Consists mainly of
adipose tissue
Layers of Epidermis
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1. Stratum Basale: Deepest epidermal layer, attached
to the dermis. A single row of growing, mitotic cells.
2. Stratum Spinosum: Several layers thick. Contain
thick bundles of pre-keratin
3. Stratum Granulosum: Thin (3-5) layers where the
keratinocytes change appearance, they start to flatten
and cells part break down. Accumulate two types of
granules
A. Keratohyaline: form keratin in upper layers
B. Lamellated: contain a waterproofing glycolipid
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4. Stratum Lucidum: Clear layer, a thin band
of a few layers of dead keratinocytes, visible
only in thick layers
5. Stratum Corneum: thick 20-30 layers,
where keratin and thick cell membranes
protect the skin. Glycolipids help water-proof
and keratin toughens
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Layers vary based on location and thickness.
In hands and feet where the epidermis is thick,
there is 5 layers. In other areas where it is
thinner, the stratum lucidum is missing and the
other layers are thinner.
Epidermis
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Cell Types
1. Keratinocytes: Most abundant. Made in
the most deep part of the epidermis by cells
undergoing continual mitosis. Pushed up by
the building of new cells. At the surface they
are dead. You lose millions per day and
produce a new epidermis every 25-45 days. In
body areas with lots of friction and use
epidermis production is faster.
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2. Melanocytes: Found deep in the epidermis,
as melanin is made it accumulates in granules
called melanosomes. The melanin granules
then accumulate on the “sunny side” of the
keratinocytes providing UV protection
People all have relatively the same amount of
melanocytes, what determines the skin
pigmentation is the amount of melanin
produced. More melanin, dark skin
pigmentation. Exposure to sunlight can also
increase the amount of melanin produced.
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3. Langerhan’s cells: phagocytes which ingest
foreign debris in the epidermis. They also help
activate the immune system response in the
epidermis.
4. Merkel Cells: Present at the dermisepidermis junction. Associated with sensory
nerve endings in the dermis. Function together
with these endings to make a touch receptor
called Merkel discs.
Dermis
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Made of thick connective tissue. (mainly
dense irregular) Thus it has the cell types
found in connective tissue; macrophages,
fibroblasts, some mast cells and WBC’s
Has nerve fibers, lymphatic vessels, and blood
vessels, and plenty of them
Two Layers
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Papillary Layer: Has areolar connective tissue
with many blood vessels. Has projections that
extend into the epidermis called dermal
papillae. These dermal papillae have:
A. Touch receptors and Meissner’s
Corpsucles
B. Pain receptors
C. Capillary loops
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Larger Mounds of these papillae form thick
dermal ridges in fingers, palms, and soles of
your feet. Fingerprints!!
Reticular Layer
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~80% of the dermis
Mainly Dense Irregular Connective Tissue
Network of blood vessels nourish this layer,
found near the subcutaneous layer.
The matrix has thick bundles of collagen
fibers, in between the thick areas where these
bundles are less dense; these areas are called
cleavage lines.
Glands
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Sweat (sudoriferous) Glands
Eccrine sweat glands: Secretory part lies in a coiled
tubule with a duct leading up to the surface. Sweat is
released by exocytosis by the glands.
Most numerous of sweat glands, literally you have
millions. Main function to control heat/temperature
Heat Controls starts at the head and generally moves
downward. Stress aka Cold sweat starts at the palms,
soles, and armpits, then spreads to other areas
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Apocrine Sweat Glands: Their ducts empty
into hair follicles. Around 2000, largely
around axillary and anogentital areas. Larger
than eccrine glands. Contents are same as
regular sweat, but also protein and fats. The
sweat itself doesn’t smell, but when bacteria
on your skin decompose it, then body odor
occurs.
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Ceruminous glands= produce wax (ears)
Mammary glands = milk
Both are considered specialized sweat glands
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Sebaceous Glands: Oil glands that secrete
sebum. Sebum is usually secreted into a hair
follicle, but sometimes on the surface of the
skin. Helps lubricate and soften hair and skin.
Even provides some bacterial killing action.
Blocked sebaceous glands lead to whiteheads
and if it dries and oxidizes blackheads.
Acne is active inflammation of sebaceous
glands.