The Integumentary System: Skin Pigmentation, The Dermis, and The Hypodermis

1. Skin Pigmentation
a. The Properties of Visible Light
i. Visible light is a form of electromagnetic radiation produced by energy sources like the
sun, overhead lights, etc.
ii. Electromagnetic (EM) radiation travels away from its energy source in waves.
1. Wave properties:
a. Wavelength- the distance from the peak of one wave to the peak of the
next wave.
i. For all forms of EM radiation, the shorter the wavelength the higher
the energy, the longer the wavelength the lower the energy.
1. Shorter wavelength forms are all dangerous because the higher
energy forms can damage DNA and cause mutations which
could lead to cancer in the mutated cells.
a. Example: Ultraviolet (UV) radiation, X-rays, and Gamma
rays
ii. For visible light specifically, wavelength is perceived by our brain as
the color of light:
iii. The Visible Light Spectrum:
1. The colors of light from long wavelength to short wavelength:
a. Red (750 nm)-Orange-Yellow-Green (550 nm)-Blue-Indigo-Violet (400 nm)
b. Remember “ROYGBIV”
2. White light- light with a combination of all the visible light wavelengths
b. Pigments
i. Pigments are molecules that absorb some wavelengths (colors) of light and reflect
others.
ii. Example: A Red Pigment- absorbs all the wavelengths (colors) of visible light except red.
The red pigment reflects the red light into your eye and that is why you see it as red.
iii. Example: A Blue Pigment- absorbs all the wavelengths (colors) of visible light except
blue. The blue pigment reflects the blue light into your eye and that is why you see it as
blue.
iv. Example: A Black Pigment- absorbs all wavelengths (colors) of visible light, it does not
reflect any wavelengths (colors). Black is literally the absence of light.
c. The Major Skin Pigments
i. Melanin
1. Melanin is yellow to dark brown pigment produced and secreted by melanocytes
in the S. basale.
a. The melanin is produced and secreted in vesicles called melanosomes that
transfer the melanin to basal cells in S basale and keratinocytes in the S.
spinosum via arm like extensions. The melanin pigment in the basal cells
and keratinocytes accumulates around the nuclei.

b. Melanin is the major skin pigment that determines how dark skin color is
but its primary function is to absorb UV radiation and protect nuclear DNA
from damage and mutation.
2. Darker skin color is due to more melanin secretion not more melanocytes, lighter
skin color is due to less melanin secretion not less melanocytes. Albinism is a
disease that prevents melanin production. Albinos have the lightest skin color,
hair color, and eye color.
a. Melanin also colors hair and the iris of the eye.
3. Skin color affects skin cancer risk
a. Darker skin color = lower risk of developing skin cancer.
b. Light skin color = higher risk of developing skin cancer.
c. Albinos have the highest risk of developing skin cancer.
ii. Hemoglobin
1. Hemoglobin is a protein in red blood cells binds to and carries oxygen (O2) in the
bloodstream that is also a pigment.
a. When hemoglobin is saturated (full) of oxygen it is bright red in color. In
light skinned individuals who do not produce lots of melanin the epidermis
is more transparent and the blood in capillaries produces a visible red color
to skin.
b. If hemoglobin is carrying less than normal oxygen blood becomes darker in
color. This deoxygenated blood appears blue when seen through the
epidermis called cyanosis.
i. Cyanosis- blue color to skin due to lack of oxygen in blood.
1. The lack of oxygen indicated by cyanosis can cause tissue death
due to lack of oxygen so it is an important clinical presentation
and one that should never be ignored.
2. Cyanosis is seen easiest where the epidermis is thinnest: Lips
and nail beds (skin under the fingernails).
iii. Carotene
1. Orange pigment produced and secreted by keratinocytes. Accumulates in the S.
corneum and hypodermis.
2. The Dermis
a. The deep, connective tissue layer of skin.
i. Containing fibroblasts, macrophages, mast cells and, scattered white blood cells
(immune cells).
b. Contains two layers:
i. The Papillary Layer
1. The papillary layer is the superficial 20% dermis (including the dermal papillae). It
is composed of areolar are connective tissue.
2. Contains :
a. Capillary beds
i. Support living cells in the papillary layer and epidermis
b. Sensory receptors
ii. The Reticular Layer

1. The reticular layer is the deep 80% of the dermis. It is composed of dense
irregular connective tissue (with some elastic fibers)
2. Contains:
a. Sensory receptors
b. Hair follicles
c. Exocrine glands
d. Nerves
e. The dermal plexus
i. Arteries and veins between the dermis and the hypodermis.
ii. Control blood flow to and from capillaries in the dermis and
hypodermis
1. Use to help regulate body temperature.
iii. Friction Ridges/Fingerprints and Footprints
1. Epidermal ridges on top of dermal ridges.
2. Create prominent peaks and valleys on palms and soles to increase surface area.
The increased surface area increases friction for better grip.
3. The Hypodermis
a. Not part of skin.
b. The hypodermis is a thick layer of adipose tissue and areolar connective tissue deep to the
dermis.
i. Mostly adipose tissue
ii. This layer stores fat, provides shock absorption, and thermal insulation
iii. The hypodermis is highly vascularized = contains lots of capillaries. Hypodermic needles
deliver drugs to the bloodstream by injecting the drug into this tissue so it can enter the
blood through these capillaries.