A&P - Function of Skin

Skin Color Determinants

• Basic Determinants: Skin color is primarily determined by the quantity, type, and distribution of melanin produced by melanocytes.

  • Types of Melanin:

    • Eumelanin: Dark brown to black pigment associated with darker skin types, common in individuals of African descent.

    • Pheomelanin: Reddish or orange pigment, more prevalent in lighter-skinned individuals such as those of Irish or Scottish descent.

Melanin Production

• Production Process: Melanin is synthesized from the amino acid tyrosine in melanocytes.

  • Melanocytes release melanin in packaged vesicles called melanosomes.

  • Keratinocytes (90% of skin cells) ingest melanosomes, which cover their nuclei to protect DNA from UV radiation.

Genetic and Environmental Factors

• Genetics: The type and quantity of melanin produced are genetically determined.

• UV Exposure:

  • Evolutionary trend shows individuals closer to the Equator tend to have darker skin due to higher UV radiation exposure.

  • More melanin provides better protection against UV damage.

Albinism and Melanin Deficiency

• Albinism: A condition characterized by a lack of melanin production.

  • People with albinism (albinotic individuals) cannot produce melanin due to the absence of the enzyme tyrosinase, which catalyzes the conversion of tyrosine to melanin.

Skin Color Variation Mechanisms

• Vitiligo: A condition causing loss of melanin in patches, leading to spots of lighter skin.

• Blood and Skin Color:

  • Skin color can change based on blood flow and hemoglobin levels.

  • For instance, blushing (increased blood flow) leads to temporary redness.

Additional Pigments Affecting Skin Color

• Beta Carotene: A pigment from Vitamin A that can give skin a yellowish-orange tinge if in excess.

• Hemoglobin: The red pigment in blood; increased blood flow can enhance reddish tones in the skin.

• Bile Pigments: Such as bilirubin, can cause yellow discoloration (jaundice) when there’s excess buildup due to liver dysfunction.

Functions of Skin as an Organ

• Protection:

  • Acts as a barrier against microorganisms, chemicals, and physical trauma.

  • Contains melanin to protect against UV exposure.

  • Surface film (composed of skin cells, sebum, and sweat) aids in lubrication and has antibacterial properties.

• Sensation: Detects touch, temperature, pressure, and pain through specialized cells in the skin.

• Flexibility: Skin's elasticity allows for movement without tearing.

• Excretion: Skin serves as an excretory organ, removing waste products like water, ammonia, and urea through sweat.

• Hormone Production:

  • Skin is involved in synthesizing Vitamin D when exposed to UV light.

  • Vitamin D is a hormone that is processed in the skin and further activated in the liver and kidneys.

• Immunity: Skin contains phagocytic cells that destroy pathogens and dendritic cells that trigger immune responses.

• Thermoregulation:

  • Skin plays a crucial role in maintaining body temperature by balancing heat production and loss.

  • Heat production primarily comes from muscle activity, while heat loss occurs through evaporation, radiation, conduction, and convection.

Mechanisms of Heat Loss

• Evaporation: The process of sweat evaporating, which cools the body; particularly vital in high humidity.

• Radiation: The transfer of body heat to the environment without direct contact.

• Conduction: Direct contact between the skin and a cooler object transfers heat away from the body.

• Convection: Heat loss mediated by moving air, enhancing the cooling effect.

Control of Body Temperature

• Hypothalamus: Acts as the control center for thermoregulation, receiving signals about body temperature and initiating appropriate responses to maintain homeostasis, such as sweating or altering blood flow to the skin.