Glands, Hair, and Nails

Sweat Glands (Sudoriferous Glands)

  • Named from the Spanish infinitive 'sudor,' meaning 'to sweat.'
  • Two types defined by location and structure:

Merocrine Glands

  • Mainly on the body's surface.
  • Release thin, watery sweat.
  • Histology:
    • Easily seen in the skin.
    • Composed of stratified cuboidal epithelial tissue cells.
    • Ducts extend to the skin's surface.
    • Wiggly in nature below the skin.
    • Sweat composition: ~99% water, salty due to water-soluble blood components.
    • Contains Vitamin C (if in excess), some nitrogenous waste (mostly removed via urine), and antibacterial compounds.
    • Pores connect directly to the surface.
    • Function: Thermoregulation (cooling the body).
      • As the body heats, warm water is released.
      • Evaporative cooling occurs as sweat evaporates from the surface.
    • Exocytosis: Sweat released from cells, moves into the gland, and then to the skin's surface.

Apocrine/Holocrine Glands

  • Location: Primarily in axillary (armpit) and anogenital regions.
  • Mechanism of sweat release:
    • Apocrine: The apical surface of the cuboidal cell breaks off, releasing the product.
    • Holocrine: The entire cell breaks down, releasing the product and causing cell death.
  • Other apocrine/holocrine glands:
    • Wax glands in the ear.
    • Mammary glands in breasts (producing breast milk).
    • Oil glands.
  • Function: Active from puberty onwards.
    • Cell pieces released along with sweat are nutritive to bacteria.
    • Bacteria consume cell parts, releasing ammonia, causing odor.

Sebaceous (Oil) Glands

  • Attached to hair follicles.
  • Composed of stratified cuboidal epithelial tissue cells.
  • Active at puberty.
  • Produce sebum (mostly oil).
    • Acts as a natural lubricant for hair, keeping it healthy.
    • Contains antibacterial compounds.
  • Inflammation can lead to acne-like structures during puberty.

Hair

  • Oil glands promote hair health.
  • Functions:
    • Detecting movement (wind, insects).
    • Protection against heat loss and sunlight.
    • Erector pili muscles:
      • Small muscles in the skin that cause hairs to stand up when nervous, scared, or cold.
      • May trap a warm layer of air near the skin.
  • Hair follicle:
    • Formed by the epidermis pushing down into the skin.
    • Composed of stratified squamous epithelial tissue.
    • The base contains the papilla.
      • The papilla is composed of epithelium and connective tissue.
      • Contains blood vessels to nourish the hair.
    • Stratum basale at the bottom (like skin).
    • Melanocytes present for hair color.
  • Hair growth:
    • Cells in the stratum basale grow and are pushed upwards.
    • Cells die as they are pushed upwards, resulting in dead cells at the hair's surface.
  • Hair structure (cross-section):
    • Medulla: The inner layer.
    • Cortex: The middle layer.
    • Cuticle: The outer layer.
    • Split ends occur between the cortex and cuticle when hair breaks down.
  • Hair follicle structure:
    • Inner epithelial tissue layer.
    • Outer connective tissue layer.
  • Types of hair:
    • Vellus hair: Fine hair found all over the body in children and adults.
    • Terminal hair: Coarser hair that grows after puberty, often in the axillary and pectoral areas.
  • Hair Life Cycle:
    • Growth phase (Anagen):
      • Lasts 6-8 years for scalp hair.
      • Hair grows about 22 mm per week.
    • Regressive phase (Catagen):
      • The follicle shrinks, and the hair is pushed out.
    • Resting phase (Telogen):
      • The hair follicle remains, but temporarily, stops growing hair.
      • Lasts for a couple of months.
    • Regeneration phase (New Anagen):
      • The follicle plumps up again and starts to grow a new hair.
  • Growth phase varies in length depending on body location (e.g., arm hair grows for only a few months, eyelashes for a few weeks).
  • Alopecia: Hair thinning.
    • Follicles die with age, especially after 40 in women (often at menopause).
    • Causes include poor diet, famine, illness, and chemotherapy.
    • Male pattern baldness: Hair loss due to genetics and testosterone levels.

Nails

  • Composed of completely dead tissue.
  • Made of stratified squamous epithelial tissue with a high keratin content.
  • Growth:
    • Grows from the bottom (like skin), but in a horizontal direction.
    • Stratum basale is the lowest layer and is mitotically active.
  • Lunule: The white area at the base of the nail.
  • Nail cells die as they move away from the nutritive area and become hard.
  • Nail bed is underneath the nail.
  • Cuticle (eponychium): Another name for the cuticle.