A&P Honors: Ch. 5.8 — Skin as a Barrier

What functions do the skin and its appendages perform?

Protection, body temperature regulation, cutaneous sensation, metabolic functions, blood reservoir, and excretion.

Which is our most vulnerable organ system?

The skin.

Why is the skin our most vulnerable organ system?

It’s exposed to microorganisms, abrasion, temperature extremes, harmful chemicals, and UV radiation.

What are the three types of barriers of the skin?

Chemical, physical, and biological.

What are two examples of chemical barriers?

Skin secretions and melanin.

What is the acid mantle?

The low pH of skin secretions.

What does the acid mantle do?

Retards bacteria’s multiplication.

What natural antibiotics do skin cells secrete? What do they do?

Defensins. They literally punch holes in bacteria, making them leak like sieves.

What does wounded skin release?

Large quantities of protective peptides called cathelicidins.

What do cathelicidins do specifically?

They are particularly effective in preventing infection by group A streptococcus bacteria.

What does melanin do concerning protection?

Provides chemical pigment shield to prevent UV damage to skin cells.

What provide physical barriers?

The continuity of skin and the hardness of its keratinized cells.

What does the outstanding barrier capacity of the skin arise from? What is it compared to?

The structure of its stratum corneum. Bricks and mortar.

What are the bricks and mortar of the skin?

The bricks are the multiple layers of dead flat cells and the glycolipids surrounding them are the mortar.

What three things work hand in hand to ward off bacterial invasion?

Epidermal continuity and acid mantle and chemicals in skin secretions.

What do water-resistant glycolipids of the epidermis block?

They block most diffusion of water and water-soluble substances between cells.

What do water-resistant glycolipids blocking diffusion prevent?

Both their loss form and entry into the body through the skin.

What are some substances that do penetrate the skin in limited amounts?

Lipid-soluble substances

Oleoresins

Organic solvents

Salts of heavy metals

Selected drugs

Penetration enhances

What can passage of organic solvents through the skin into the blood do?

Shut down the kidneys and also cause brain damage.

What can absorption of lead result in?

Anemia and neurological defects.

What are the biological barriers?

The dendritic cells of the epidermis and macrophages in the dermis.

What do dendritic cells do to protect?

They patrol beneath the skin’s surface, engulfing any foreign invaders that have penetrated the epidermis.

Once dendritic cells have captured their prey, what happens? What does this trigger?

They leave the skin and migrate to the nearest lymph node. They show their prey to other immune cells, triggering an immune response.

What do dermal macrophages do to protect?

They dispose of viruses and bacteria that manage to penetrate the epidermis.

Under normal resting conditions how much do sweat glands secrete a day?

500 ml

What is insensible perspiration?

Routine and unnoticeable sweating.

When temperatures ride, what does the nervous system stimulate?

The dermal blood vessels.

When body temperature rises, what does the nervous system simulate dermal blood vessels and sweat glands to do?

It stimulated the dermal blood vessels to dilate and the sweat glands into vigorous secretory activity.

What is sensory persperation?

Visible output of sweat.

What does evaporation of seat form the skin surface do?

Dissipates body heat and efficiently cools the body, preventing overheating.

When the external environment is cold, what does dermal blood vessels do?

Constrict

What do dermal blood vessels’ constriction cause?

Causes the warm blood to bypass the skin temporarily and allows skin temperature to drop to that of the external environment.

What receptors is the skin richly supplied with?

Cutaneous sensory receptors.

What are cutaneous receptors classified as?

Exteroceptors.

Why are cutaneous receptors classified as exteroceptors?

Because they respond to stimuli arising outside the body.

What do tactile corpuscles and tactile epithelial cells do concerning cutaneous sensation?

Allow us to become aware of a caress or the feel of our clothing against our skin.

What do lamellar corpuscles do in relation to cutaneous sensation?

Alert us to bumps or contacts involving deep pressure.

What do hair follicle receptors do concerning cutaneous sensation?

They report on wind blowing through our hair and a playful tug on a ponytail.

What do free nerve endings do concerning cutaneous sensation?

They sense painful stimuli.

When sun bombards the skin, what converts into what?

Modified cholesterol molecules are converted to a vitamin D precursor.

What is done the vitamin D precursor in the conversion from cholesterol?

Transported via the blood to other body areas to be converted to vitamin D.

What important role does vitamin D play?

Allowing the absorption of calcium from the digestive tract.

What can keratinocyte enzymes do?

“Disarm” many cancer-causing chemicals that penetrate the epidermis and activate some steroid hormones.

What is one biologically important protein that skin cells make?

Collagenase.

What is collagenase?

An enzyme that aids the natural turnover of collagen and deters wrinkles.

When other body organs such as muscles, need a greater blood supply, what does the nervous system do? What does this do?

Constricts the dermal blood vessels. This shunts more blood into the general circulation.