Skin Anatomy and Types Quiz

Skin Types

• Two types of skin: thick and thin
• Thick: covers palms of hands and soles of feet.
• Thin: covers the rest of the body, mostly hairy.

Skin Layers

• Epidermis:
  • Stratified squamous keratinizing epithelium.
  • Five layers (from deepest to outermost):
    • Stratum basalis
    • Stratum spinosum
    • Stratum granulosum
    • Stratum lucidum
    • Stratum corneum
• Dermis:
  • Papillary layer: loose connective tissue, supports and nourishes the epidermis, contains sensory nerves, lymphatics, and capillaries.
  • Reticular layer: dense irregular connective tissue, tough, fibrous layer, collagen fibers limit stretch, elastic fibers provide flexibility.
• Hypodermis (Subcutaneous Tissue):
  • Loose connective tissue, contains adipose tissue.

Epidermis Layers

• Stratum basalis:
  • Single layer of columnar epithelial cells resting on a basement membrane.
  • Contains many mitotic figures and cells with melanin, which can be either melanocytes or keratinocytes.
• Stratum spinosum:
  • Polygonal cells with central nuclei attached by desmosomes, giving a spiny appearance.
  • Contains membrane-coating granules (Odland bodies).
• Stratum granulosum:
  • Flattened elongated cells containing keratohyalin granules (non-membrane bound).
  • Membrane-coating granules are discharged into the intercellular spaces, forming a skin barrier.
• Stratum lucidum:
  • Prominent in thick skin, not in thin skin.
  • Clear, thin layer of flattened, non-nucleated cells.
• Stratum corneum:
  • Outermost layer of the epidermis.
  • 15-20 layers of dead, flattened, anucleate, keratin-filled keratinocytes.
  • Provides protection against friction and water loss.

Thin Skin

• Covers the body except for palms and soles.
• Has hair, hair follicles, and sebaceous glands.
• Stratum lucidum is absent.
• Stratum spinosum, granulosum, and corneum are thinner than in thick skin.

Epidermal Cell Types

• Keratinocytes:
  • Predominant cell type in the epidermis, originating in the basal layer.
  • Produce keratin and are responsible for the epidermal water barrier by making and secreting lipids.
• Melanocyte:
  • Located in the basal layer.
  • Synthesize melanin in melanosomes and transport it to keratinocytes for UV protection.
• Langerhan's Cells:
  • Found in the stratum spinosum.
  • Branched, star-shaped cells.
  • Contain Birbeck granules in their cytoplasm.
  • Function as antigen-presenting cells, contributing to skin immunity.
• Merkel's Cells:
  • Located in the basal layer.
  • Contain neurosecretory granules near the cell membrane.
  • Function as mechanoreceptors for tactile sensation.

Dermis Components

• Blood Vessels
• Sensory nerve endings
• Sweat glands and their ducts
• Hair follicles
• Sebaceous glands
• Arrector pili muscles

Dermis Structures

• Sebaceous Glands:
  • Secretory epithelial cells produce sebum (an oily secretion).
  • Ducts open into hair follicles, softening hair.
  • Most numerous in hairy areas.
• Sweat Glands:
  • Widely distributed in the skin.
  • Each gland has a coiled body under the skin and a duct opening onto the skin surface (pore).
  • Most numerous in palms, soles, axilla, and groin.
• Arrector Pili Muscles:
  • Small smooth muscle bundles attached to hair follicles.
  • Contraction causes hair to stand and "goose flesh" appearance.

Fingerprints

• Ridges on the epidermis surface formed by projections from dermal papillae.
• Unique pattern in each person.
• Impression made by these ridges are fingerprints.

Hypodermis

• Contains adipose tissue and attaches the dermis to underlying tissues.

Epidermal Appendages

• Structures originating from the epidermis:
  • Hair follicles
  • Sweat glands (eccrine and apocrine)
  • Sebaceous glands
  • Nails

Hair Follicles

• Down growth of epidermal cells into the dermis.
• Base of follicle contains a cluster of cells called the bulb.
• Multiplication of cells in the bulb causes hair growth.
• Root: portion of hair embedded in the follicle.
• Shaft: portion of hair above the skin.

Sweat Glands

• Eccrine Glands:
  • Secrete sweat directly onto the skin surface.
• Apocrine Glands:
  • Secrete fluid into the hair follicle sac, eventually exiting onto the skin.

Sebaceous Glands

• Simple, branched acinar glands.
• Located between the hair follicle and arrector pili muscle.
• Secrete oily substance called sebum through holocrine secretion (entire cell breaks up).
• Absent in palms and soles.

Nails

• Protect the tips of fingers and toes.
• Nail root: embedded in the skin.
• Nail plate: exposed portion.
• Nail grows from a germinal part called the nail bed.

Cutaneous Nerve Endings

• Free Nerve Endings:
  • Detect pain and temperature.
• Merkel's Cells:
  • Tactile sensation in the stratum basale.
• Meissner's Corpuscles:
  • Touch.
• Pacinian Corpuscles:
  • Vibration and pressure.
• Ruffini Endings:
  • Pressure.

Skin Color Sources

• Melanocytes:
  • Produce melanin from tyrosine.
  • Melanin provides UV protection.
  • Responsible for reddish-brown to brown-black color.
• Carotene:
  • Contributes orange-yellow color.
  • Obtained from diet (carrots, tomatoes).
• Hemoglobin:
  • Blood pigment.

Skin Functions

• Excretion:
  • Excretes water and salts in sweat.
• Protection:
  • Protects from bacteria, water, and excess heat and cold.
• Temperature Regulation:
  • Plays a major role in regulating body temperature.
• Sensory Function:
  • Organ for senses of touch, pain, temperature, and pressure.
• Vitamin D Production

Skin Clinical Notes

• Preparation for Surgery:

  • Skin harbors bacteria, so preparation is crucial to avoid infection.
  • Steps include:
    • Shaving hair in surgical area.
    • Washing sebum with soap.
    • Cleaning with an antiseptic.

• Burns:

  • Damage caused by fire, electricity, acids, etc.
  • Damages skin structure, leading to infection and water loss.
  • Classified by severity (depth): First, second, and third degree burns.
    • First degree: epidermis damaged only, heals without scarring.
    • Second degree: epidermis and upper dermis damaged, can heal without scarring if infection is prevented.
    • Third degree: entire skin thickness destroyed, no pain as nerve endings are destroyed, regeneration is not possible, skin grafting is necessary.
  • Rule of Nines: Method to determine the area of a burn by dividing the body into 11 areas, each representing 9% of the total body surface, plus 1% for the perineal area.

• Ulcers:

  • Occur on the skin in various regions.
  • Pressure ulcers occur over pressure points, where skin is compressed between a bony prominence and a hard surface for an extended period.
  • Common in bedridden patients or those confined to wheelchairs.