FSC unit 2 skin

Overview of Hair Anatomy and Function

• Three primary areas covered in the section:

  • Hair structure (separate from follicle)

  • Exocrine glands

  • Nail anatomy

Hair Structure

• Hair is composed of tightly packed keratinized squamous epithelial cells.

  • These cells are long dead but tightly packed together.

• Visible part of hair is known as the hair shaft; it extends above the skin surface.

• The hair root penetrates into the dermis or subcutaneous layer.

Key Terms

• Medulla: Innermost part of hair; often referenced in human anatomy for inner parts of organs.

• Cortex: Surrounds the medulla; makes up the majority of the hair structure.

• Cuticle: Outer protective layer surrounding the hair.

• Arrangement used to categorize other organs (e.g., lymph nodes, adrenal glands, kidneys).

Hair Thinning and Medulla Loss

• Thinning hair often correlates with the loss of medulla.

• Observation: Running hands through hair may reveal thinner strands where medulla is missing, indicating potential pathology or aging.

Hair Follicle Structure

• The complete hair structure, known as the hair follicle, contains hair and other important layers:

  • Associated sebaceous glands produce an oily substance (sebum) that keeps hair moisturized.

  • The arrector pili muscle, which contracts via sympathetic nervous system activation, causes hair to stand erect (e.g., during fight or flight).

• The hair matrix is responsible for the generation of hair cells.

  • Contains a limited number of stem cells, contrasting with the abundance of stem cells in the epidermis.

  • Cells in the matrix receive nutrients and oxygen from the hair papilla and other mechanisms.

Components of Hair Follicle

• Other structures include:

  • Epithelial root sheath: Inner lining that continues from the epidermis.

  • Dermal root sheath (connective tissue sheath): Provides outer structure and support.

  • Glassy membrane: A transparent barrier that anchors the external sheath to the connective tissue layer.

Hair Growth Phases

• Hair grows at approximately $0.33$ mm per day.

• Three main phases of hair growth:

  • Active phase (anagen): Lasts 2-5 years; hair grows vigorously.

  • Regression phase (catagen): Lasts 2-3 weeks; the matrix activity decreases.

  • Resting phase (telogen): Lasts about 3 months, resulting in club hairs that can detach from the follicle.

Alopecia

• A condition characterized by hair loss, often due to T cell activation and immune system issues, adversely affecting the hair matrix.

• Treatment: Hydrocortisone injections to suppress immune response, allowing facilitation of hair growth.

• Alopecia refers specifically to patchy hair loss, distinct from male pattern baldness.

Types of Hair

• During fetal development, lanugo (nonpigmented hair) develops.

• Vellus hair: Fine body hair, often referred to as peach fuzz.

• Terminal hair: Coarse, pigmented hair that develops during puberty (e.g., scalp, eyebrows, lashes).

• Eyelashes and eyebrows are genetically programmed to grow to a certain length.

• Melanin in hair:

  • Two types:

  • True melanin: Responsible for black hair.

  • Pheomelanin: Responsible for blonde and red hues.

• As aging progresses, melanocytes stop producing melanin in hair, leading to grey or white hair.

Glands Associated with Skin

• Focus on the various glands:

  • Sebaceous glands: Simple branched acinar glands connected to hair follicles, producing sebum that keeps hair and skin moist.

  • Sudoriferous glands (sweat glands):

  • Merocrine sweat glands (eccrine): Small vesicular secretions involved in thermoregulation, found in palms, soles, forehead.

    • Controlled by nervous system activation.

  • Apocrine sweat glands: Larger secretions high in proteins and lipids found in armpits, groin, and areolae, contributing to body odor.

• Ceruminous glands: Modified sweat glands found in the external ear, releasing cerumen for lubrication and protection against pathogens.

Nail Anatomy

• Nails are highly packed, keratinized squamous cells, similar to hair.

• Main structures:

  • Nail body: Visible part of the nail.

  • Free edge: Part extending beyond the fingertip.

  • Nail root: Contains cells that are born near the bone.

  • Lunula: White crescent shape near the nail root.

  • Eponychium: Cuticle over the lunula.

  • Hyponychium: Skin connection under the free edge of the nail.

Skin Pathology and Aging

• Basal Cell Carcinoma: Most common skin cancer; least malignant; mutation leads to increased mitosis in stratum basale.

• Squamous Cell Carcinoma: Second most common; occurs in stratum spinosum; should be caught early.

• Melanoma: Least common but most dangerous; manifested by increased mitosis in melanocytes.

• ABCDE for cancer identification:

  • A: Asymmetry

  • B: Border irregularity

  • C: Color (darker indicates danger)

  • D: Diameter (larger size may indicate malignancy)

  • E: Evolving characteristics

Effects of Aging on Skin

• Aging leads to:

  • Decreased sebum production and skin dryness.

  • Thinning of epidermis and dermis.

  • Decreased pigmentation leading to grey or white hair.

  • Slower healing processes and increased susceptibility to pathogens.

  • Reduced thermoregulation capabilities.

Conclusion

• Importance of understanding skin anatomy and pathology for identifying health issues, facilitating clinical assessments and treatments.