5-4 Epidermal pigmentation

Skin color is one of the most obvious distinguishing characteristics among humans.
The examination of skin color will focus on:
- The impact of pigments in the epidermis.
- The influence of blood flow in the dermis.
- The clinical implications of changes in skin color.

Definition: A pigment produced by melanocytes, which are pigment-producing cells.
There are two types of melanin:
- Pheomelanin: Red-yellow form of melanin.
- Eumelanin: Brown-black form of melanin.
Melanocytes are located in the stratum basale of the epidermis.
Function: Melanocytes manufacture melanin from the amino acid tyrosine and package it into vesicles known as melanosomes.
Melanosomes then transfer pigments to nearby basal keratinocytes until they are destroyed by lysosomes.

In individuals with pale skin, the transfer of melanin occurs mainly in:
- Stratum basale
- Stratum spinosum
In individuals with dark skin, melanosomes are larger and more numerous, and transfer can also occur in:
- Stratum granulosum
The varying sizes and numbers of melanosomes contribute to differences in skin pigmentation.
The ratio of melanocytes to basal cells varies:
- Ranges from 1:4 to 1:20 depending on the body region.
- On average, there are about 1,000 melanocytes/mm² in most body areas, but up to 2,000/mm² in areas like cheeks, forehead, and genital regions.
Important Note: Differences in skin pigmentation do not result from the number of melanocytes but rather from varying levels of melanin synthesis.

Albinism: A condition caused by a deficiency or absence of melanin production.
- Individuals with albinism have normal melanocyte distribution but are incapable of melanin production.
Freckles: Small pigmented areas that appear on relatively pale skin, usually due to overactivity of melanocytes producing melanin.
Lentigos: Similar to freckles but with regular borders and abnormal melanocytes.
Senile Lentigos (Liver Spots): Variably pigmented areas that develop on sun-exposed skin in older individuals with pale skin.

Melanin in keratinocytes provides protection against UV radiation in sunlight.
Response to UV Exposure:
- Melanocytes increase melanin production.
- A small amount of UV radiation is beneficial for producing compounds necessary for calcium ion homeostasis.
- However, excessive UV radiation can damage DNA leading to mutations and increase the risk of skin cancer.
Protection Mechanism: Melanin pigments collect around the nucleus of keratinocytes, acting as a sunshade to protect DNA from UV radiation.
Note: The production of melanin is not fast enough to prevent sunburn on the first day of sun exposure, as synthesis peaks about 10 days after exposure.

UV radiation can cause:
- Burns (sunburns), damaging both epidermis and dermis.
- Cumulative damage can harm fibroblasts, impairing dermis maintenance and leading to premature wrinkling.
- Increased risk of skin cancers due to chromosomal damage in basal cells or melanocytes.

Keratin (KR 10): An orange-yellow pigment that accumulates in epidermal cells and is particularly noticeable in light-skinned individuals.
- Can also be found in fatty tissues in the deep dermis and subcutaneous layer.
Carotene: An orange pigment present in vegetables such as carrots; excessive intake can lead to noticeable skin color changes.
- Health Benefit: Carotene is convertible to Vitamin A, which is important for epithelial maintenance and photoreceptor synthesis in the eyes.

Hemoglobin: A pigment in red blood cells that binds and transports oxygen, giving a reddish tint to the dermal capillaries, which is most visible in light-skinned individuals.
Vasodilation: If blood vessels are dilated, reddish tones become pronounced, especially on cheeks and gums; this happens during increases in body temperature.
Cyanosis: A bluish coloration observed when blood supply is reduced, leading to decreased oxygen levels in the tissues, making the skin, gums, and nail beds appear pale or bluish.
Causes of Cyanosis: Can occur due to extreme cold or cardiovascular/respiratory disorders.

Monitoring skin appearance can assist in diagnosing diseases affecting other body systems.
Jaundice (JWN DIS): Results from the liver's inability to excrete bile, causing yellowish pigmentation to accumulate in body fluids and skin/eyes.
Pituitary Tumors: Can cause excess secretion of melanocyte-stimulating hormone (MSH), leading to increased melanin production and a bronzed appearance.
Addison's Disease: Similar to MSH effects, caused by excessive adrenocorticotropic hormone (ACTH) secretion.
Vitiligo: A condition where individuals lose their melanocytes, resulting in white patches on normal skin; affects about 1% of the population and can be associated with autoimmune disorders.
- No severe health effects but may increase risks for sunburns and hearing loss.

Checkpoint 14: The two major pigments in the epidermis are:
- Melanin: Including pheomelanin (red-yellow) and eumelanin (brown-black).
- Carotene: An orange-yellow pigment.
Checkpoint 15: Skin darkens upon exposure to sunlight due to the increased melanin production by melanocytes.
Checkpoint 16: Areas that appear bluish due to decreased blood oxygen levels include skin, mucous membranes, lips, nail beds, and whites of the eyes, a condition known as cyanosis.