3.2 Functions of the Skin

Flashcards covering the functions of the skin as discussed in the lecture, including thermoregulation, protection, sensation, excretion, absorption, and vitamin D synthesis.

Skin

The body's largest organ, constantly multitasking to protect, balance, and help sense the world, performing vital functions every moment of the day.

Integumentary System

The system comprising the skin's layers, cells, and accessory structures

Thermoregulation of the skin

The skin's ability to help regulate body temperature. It does this through two main mechanisms when temperature changes occur.

When you're hot:

• Eccrine sweat glands increase sweat production.

• Evaporation of sweat from the skin surface carries heat away, cooling the body.

• Dermal blood vessels dilate (vasodilation), bringing more blood to the surface to increase heat loss.

• When you're cold:

• Eccrine sweat glands decrease sweat production.

• Blood vessels constrict (vasoconstriction), reducing heat loss by limiting blood flow to the skin.

• Skeletal muscles may contract continuously when you shiver to generate heat.

• Erector pili muscles attached to hair follicles contract, causing goosebumps and trapping a thin layer of warm air near the skin.

Eccrine sweat glands

Glands that increase sweat production when hot to lower body temperature through evaporation, and decrease production when cold.

Vasodilation

A process where blood vessels in the dermis dilate (widen) to bring more blood to the surface and increase heat loss from the body.

Vasoconstriction

A process where blood vessels constrict (narrow) to decrease blood flow to the skin and conserve body heat.

Physical barrier (skin)

The skin's role in defending against microbes, ultraviolet radiation, physical injury, chemicals, and dehydration.

Stratum corneum

The outermost layer of the skin, packed with tough, dead, keratinized cells that form a protective waterproof shield.

Acidic pH of sweat

A characteristic of sweat that helps slow bacterial growth on the skin.

Bacterial chemicals

Substances from sebaceous secretions that help kill microbes on the skin surface.

Dendritic cells

Immune cells located in the epidermis that help get rid of foreign invaders.

Macrophages

Immune cells located within the dermis that help get rid of foreign invaders.

Melanin

A pigment produced by melanocytes that absorbs and disperses ultraviolet radiation, protecting deeper skin layers from DNA damage.

Melanocytes

Cells that produce the pigment melanin.

Topical treatments

Medicinal applications to the skin, effective because of the skin's ability to absorb lipid-soluble substances.

Cortisone creams

Lipid-soluble topical treatments that reduce inflammation by preventing histamine release.

Adhesive patches

Devices used to deliver drugs intentionally through the skin for slow, controlled release into the bloodstream.

Vitamin D synthesis

A process that begins in the skin when exposed to UV rays, activating a precursor molecule.

Precursor molecule (Vitamin D)

A molecule in the skin activated by UV sunlight, later modified by the liver and kidneys to produce active Vitamin D.

Calcitriol

The most active form of Vitamin D, produced after the skin's precursor molecule is modified.

Calcium absorption

A process vital for bone maintenance, regulated by Vitamin D.

Homeostasis

The maintenance of internal body balance, a vital role played by the skin.

Protection and barrier functions of the skin:

• The skin acts as a physical barrier defending against:

  • Microbes, ultraviolet radiation, physical injury, chemicals, and dehydration.

• Stratum corneum (outermost layer):

  • Packed with tough, dead, keratinized cells that form a protective waterproof shield.

  • Rich in keratin and surrounded by lipids to form a water-resistant seal that minimizes transepidermal water loss (TEWL).

• Water balance and entry prevention:

  • The skin helps keep the body hydrated overall and limits water entry into the skin during showers and swims.

• Chemical and microbial defense on the surface:

  • The acidic pH of sweat slows bacterial growth on the skin.

  • Bactericidal chemicals from sebaceous secretions help kill microbes.

• Immune defense:

  • Dendritic cells in the epidermis and macrophages in the dermis help the immune system remove foreign invaders if microbes breach the skin.

• Pigment and UV protection:

  • Melanin, produced by melanocytes, absorbs and disperses ultraviolet radiation to protect deeper skin layers from DNA damage.

Sensory reception of the skin

• The skin is loaded with sensory receptors that detect:

  • Pressure, vibration, temperature, pain, and light touch.

• Signals are sent to the brain so fast you can react in milliseconds (e.g., jerking your hand away from a hot stove).

• The skin helps you stay connected to your environment and respond to it instantly, whether it's the feel of fabric, a paper cut, or the warmth of sunlight.

Excretion of the skin:

• Excretion:

  • The stratum corneum is nearly waterproof, and about 400\,\mathrm{mL} of water evaporates through it daily.

  • Sweat also eliminates small amounts of urea, ammonia, salts, and carbon dioxide (\mathrm{CO_2}).

Absorption of the skin:

• Absorption:

  • The skin can absorb certain lipid-soluble substances such as vitamins A, D, E, and K, some medications, and even small amounts of oxygen and carbon dioxide (\mathrm{O2} and \mathrm{CO2}).

  • Harmful substances can also be absorbed, including acetone, heavy metals (lead, mercury, arsenic), and irritants from poison ivy or poison oak.

• Topical treatments:

  • Lipid-soluble substances on the skin can reduce inflammation by preventing histamine release from mast cells (e.g., cortisone creams).

  • Drugs can be delivered through the skin using adhesive patches, allowing slow, controlled release into the bloodstream.

Everyday skincare and decisions relate to the skin’s barrier and thermoregulatory functions (e.g., sunscreen, hydration, winter skin care).

Vitamin D synthesis

• The synthesis of vitamin D begins in the skin when exposed to ultraviolet rays from sunlight.

• A precursor molecule in the skin is activated by UV, then modified by the liver and kidneys to produce calcitriol, the most active form of vitamin D.

• Vitamin D plays a role in calcium absorption and bone maintenance; without the skin's initiation of this process, calcium absorption and bone health would be impaired.

UV exposure has practical implications for vitamin D synthesis and bone health