Skin colour and human interactions pigmentation

Human skin color ranges from the darkest brown to the lightest hues. Differences in skin color among individuals is caused by variation in pigmentation, which is the result of genetics (inherited from one's biological parents), exposure to the sun, disorders, or some combination thereof. Differences across populations evolved through natural selection or sexual selection, because of social norms and differences in environment, as well as regulations of the biochemical effects of ultraviolet radiation penetrating the ski

1. Skin Color

Skin color is determined by (a) the amount of

blood, (b) pigments, (c) oxygenation level of the
blood, (d) all of these

3. Which pigments contribute to skin
color?
» Melanin, carotene, and hemoglobin

4. Melanin

» Melanin is the only pigment made in the skin.

» Polymer (large macromolecule with repeating
units)

» Ranges in color from yellow to reddish-brown
to black

>“

5. Human skin color

» Comes in different colors
» Distribution is not random -
> Darker-skinned people found nearer the equator

(where greater protection from the sun is needed)
> Lighter-skinned people found near poles
> Melanocytes of black and brown skinned
people produce many more and darker
melanosomes than lighter skinned people

Freckles and pigmented moles - accumulation of
melanin

>“

6. What’s in a tan?

> Melanocytes are stimulated to greater activity

» Prolonged buildup of sun causes buildup of
melanin

> Buildup helps protect DNA of viable skin cells
from UV by absorbing the light and
dissipating energy as heat.

>“

7. The long and the short of it...

» Sun's rays contain two types of ultraviolet
radiation that reach your skin: UVA and UVB.
° UVB radiation burns the upper layers of skin (the
epidermis), causing sunburns.
UVA radiation is what makes people tan. UVA rays
penetrate to the lower layers of the epidermis, where
they trigger cells called melanocytes to produce melanin.
Melanin is the brown pigment that causes tanning.
» Melanin is the body's way of protecting skin from
burning.
Darker-skinned people tan more deeply than lighter-
skinned people because their melanocytes produce more
melanin. But just because a person doesn't burn does
not mean that he or she is also protected against skin
cancer and other problems.

8. HW: Read Homeostatic Imbalance,
TB 157 bottom center

» Write a summary about melanin’s protective
effects - to be shared in class tomorrow.

9. Carotene

> Yellow to orange pigment found in certain
plant products (carrots)

» Accumulates in stratum corneum and fatty
tissue of hypodermis

» Obvious in palms and soles of where stratum
corneum is the thickest

>“

10. Fair skin ES

» Pinkish hue of fair skin reflects crimson
» Color of oxygenated hemoglobin
> Fair skin people have small amounts of

melanin, epidermis is nearly transparent thus
showing the hemoglobin color.

>“

11. HW: Read Homeostatic Imbalance,
TB 157 bottom right

» Write a summary of what you read: (to be
shared in class tomorrow)
° Redness or erythema
> Pallor or blanching
> Jaundice or yellow cast
» Bronzing
> Black and blue marks or bruises
* hematomas

12. And just a little more HW

» TB Questions page 173 - write the question
and correct answer:
1, 2, 3, 4,5, 6,7