skin color/ Derivatives

Skin Color

Three Main Pigments Involved in Skin Color

  • The skin color is primarily determined by three main pigments:
    A. Melanin

    • Definition: Melanin is a natural pigment produced by melanocytes, which gives color to skin, hair, and eyes.

    • Cells Producing Melanin: Melanocytes, located predominantly in the basal layer of the epidermis, synthesize melanin.

    • Purpose of Melanin: It provides protection against UV radiation, absorbs harmful rays, and influences skin color.

    • Comparison of Melanocyte Number by Skin Color:

      • Individuals with dark skin have a higher number of melanocytes compared to those with light skin; however, this does not correlate directly with the amount of melanin produced.

    • Definitions:

      • Freckle: A concentrated spot of melanin usually appearing on sun-exposed skin.

      • Nevus (mole): A benign growth of melanocytes creating a pigmented lesion.

    • Vitiligo: A skin condition characterized by the loss of melanin, resulting in white patches on the skin.

    • Albinism: A genetic condition where individuals have little to no melanin due to mutation in the genes responsible for its production. Those with albinism typically have lighter skin, hair, and eyes, and they are sensitive to sunlight.

    B. Carotene

    • Location: Carotene is found in the stratum corneum, the outermost layer of the skin.

    • Color Contribution: Carotene contributes a yellow-orange color to the skin.

    • Associated Vitamin: Carotene is a precursor to vitamin A, which is essential for various bodily functions including vision and immune response.

Chapter 5: Integumentary System

C. Hemoglobin

  • Comparison of Hemoglobin Forms: Oxygenated hemoglobin appears bright red, while deoxygenated hemoglobin appears darker red or blue.

  • Color Contribution: Hemoglobin gives a pinkish hue to fair skin due to its oxygen-carrying capacity.

  • Cyanosis: A bluish discoloration of the skin due to insufficient oxygen in the blood.

Skin Derivatives

A. Hair (Pili)

  • Epidermal Derivative: Hair is primarily made of hard keratin.

    1. Components of Hair: a. Shaft

      • Color Determination: The color of hair is determined by the type and amount of melanin present. b. Root i. Hair Follicle: A structure that surrounds the root of the hair, housing the hair bulb.

        • Function of Hair Follicle: Supports hair growth and provides blood supply.
          ii. Hair Matrix: The area of rapidly dividing cells that generates new hair cells.

        • Function of Hair Matrix: Responsible for producing the hair shaft, as well as contributing to the thickness and structure of hair.

        • Important Note: Different from the matrix of connective tissue, which has a distinct structure and function.
          iii. Hair Root Plexus: A network of sensory nerve endings associated with each hair follicle.

        • Function of Hair Root Plexus: Detects hair movement, contributing to the sensation of touch.

    2. Hair Growth

    • Occurs in the hair matrix at the base of the hair follicle.

    1. Associated Structures:

    • Arrector Pili Muscles: Small muscles attached to hair follicles.

      • Purpose: Causes hair to stand up (piloerection) in response to cold or emotional stimuli.

      • Type of Muscle Tissue: Smooth muscle tissue.

B. Glands

  • Glandular Structure: Glands are composed of epithelial tissue, which is specialized for secretion.

    1. Sebaceous Oil Glands:

    • Typically open into hair follicles and are stimulated by androgens (hormones).

    • Sebum Composition: Sebum is made of fat, cholesterol, and salt, serving to inhibit bacterial growth.

    • Holocrine Secretion:

      • Definition: A type of secretion where the entire cell disintegrates to release its product.

    • Location: Present in all skin areas except for the palms and soles.

    1. Sudoriferous (Sweat) Glands:

    • Produce sweat, composed mostly of water and excretory products.

    • Role: Assist in temperature regulation.

    • i. Merocrine (Eccrine) Sweat Glands:

      • Located on palms and soles, secrete a watery sweat directly onto the skin surface.

    • ii. Apocrine Sweat Glands:

      • Initially thought to use an apocrine method of secretion, but both apocrine and merocrine glands actually utilize merocrine secretion.

      • Product Differences:

        • Merocrine glands secrete a watery fluid for cooling, while apocrine glands produce a thicker, odoriferous fluid that often contains proteins and lipids.

      • Control by Deodorants/Antiperspirants:

        • Deodorants target apocrine gland secretion due to odor, while antiperspirants aim to reduce merocrine gland secretion to lessen sweating.

    1. Ceruminous Glands:

    • Modified sweat glands found in the ear.

    • Cerumen (Earwax): A sticky, waxy substance produced to trap debris and inhibit bacterial growth.

D. Nails

  • Composed of tightly packed keratinized cells (hard keratin). a. Nail Root with Matrix: The area of nail growth. b. Nail Plate: The visible portion of nails that protects tips of fingers and toes.

    • Appearance of Nails: Nails appear pink due to the underlying blood vessels.

    • Clinical Significance: Changes in nail color or texture can indicate underlying health issues.

    • Comparison of Hair and Nails:

      • Similarities:

      1. Both are composed of keratin.

      2. Both structures serve protective functions.

      • Differences:

      1. Hair is primarily a structure of epidermal origin, while nails are flat, keratinized structures with a different growth pattern.

      2. Hair can be colored by melanin, whereas nails do not have coloration due to pigmentation but rather appear pink due to vascularization.

    • Types of Keratin Locations:

    1. Hair

    2. Nails

    3. Epidermis (outer layer of skin).