Pigments of the Skin

Overview of Skin Pigments

• Skin pigmentation is determined by several types of pigments.

Melanin

• Definition: Melanin is the primary pigment responsible for skin color, producing a brownish pigment.

• Types of Melanin:

  • Eumelanin: Brown pigment.

  • Pheomelanin: Reddish pigment.

• Melanocytes:

  • All humans have the same number of melanocytes.

  • The amount of melanin produced determines skin color and darkness.

• Properties of Melanin:

  • Acts as a natural sunscreen.

  • Protects cells from UV radiation.

  • Mechanism:

  • Melanocytes have tentacle-like structures that wrap around keratinocytes to transfer melanin.

  • Keratinocytes arrange melanin on the apical side (the outer surface) away from the nucleus to reflect UV rays instead of absorbing them.

  • This arrangement prevents potential DNA damage from UV exposure, which can lead to mutations, sunburn, or skin cancer.

Effects of Sun Exposure

• Consequences:

  • Prolonged UV exposure can lead to:

  • Skin cancer.

  • Clumping of elastin and collagen fibers in the reticular layer of the dermis leading to skin aging and wrinkling.

• Case Study Example:

  • A truck driver exhibited noticeable skin differences on one side of his face due to sun exposure.

Freckles and Moles

• Formation:

  • Freckles and moles are accumulations of melanin that typically develop after sun exposure.

  • Most babies lack freckles and moles due to limited sun exposure.

• Genetic Predisposition:

  • Some individuals may have a genetic tendency to develop freckles and moles.

ABCDEs of Mole and Freckle Assessment

• Asymmetry (A):

  • A concerning mole is asymmetrical (uneven shape).

• Border (B):

  • Uneven or irregular borders indicated potential risk.

• Color (C):

  • Moles with multiple colors or color gradients (e.g., dark brown to light reddish) are suspicious.

• Diameter (D):

  • Smaller moles are often safer; larger moles pose greater risk.

• Evolving (E):

  • New moles or existing moles that change over time warrant a dermatologist visit.

Keratin

• Definition:

  • Keratin is found in various organisms, including plants such as carrots.

  • It converts to vitamin A, essential for vision.

• Location in Human Body:

  • Found in fat/adipose tissue and the stratum corneum.

  • Can create an orangey color in fat under certain lighting conditions due to carotene content.

Hemoglobin

• Definition:

  • Hemoglobin is the protein responsible for carrying oxygen in red blood cells.

• Appearance:

  • Typically gives skin a pink hue.

• Cyanosis:

  • A condition characterized by a bluish appearance, as seen in the nails of individuals with decreased oxygenated hemoglobin, often due to respiratory diseases like chronic bronchitis or COPD.

Jaundice

• Definition:

  • Jaundice is a symptom rather than a standalone condition, usually indicating liver failure.

• Mechanism:

  • Results from bilirubin accumulation in the blood, being a breakdown product of red blood cells.

  • Bilirubin is typically processed by the liver and excreted through feces or urine.

  • Liver dysfunction inhibits this excretion, causing skin and sclera (whites of eyes) to appear yellow.

Vitiligo

• Definition:

  • Vitiligo is characterized by the loss of melanocytes, leading to depigmented patches on the skin.

• Notable Case:

  • Winnie Harlow, a model with vitiligo, exemplifies this condition.

• Causes:

  • Often linked to autoimmune diseases; however, other causes may exist and the condition remains poorly understood.

Comparison: Vitiligo vs. Albinism

• Vitiligo:

  • Melanocytes are absent (die off).

• Albinism:

  • Presence of melanocytes, but they are non-functional due to genetic conditions.

  • The melanin may either not be produced or fails to enter keratinocytes correctly, leading to a lack of pigmentation.