Skin Research - A Sturdy Multipurpose Shield

Of all the body's vital organs - brain, heart, lungs, liver, kidneys, etcetera - skin weighs the most and has the largest surface area. Unfurled and laid flat, the skin of an average-sized, human adult covers about two square metres - an area roughly equivalent to an oversized beach towel.

Our skin not only protects us against the everyday assaults of the external world - from air and water-borne germs, to extreme heat and cold, to corrosive chemicals and ultraviolet radiation - but also endows us with exquisite sensitivity to touch and temperature. A typical postage-stamp-sized area of skin may hold about 20 blood vessels, 60 or so sweat glands and more than a thousand nerve endings.

The skin's outermost layer, the epidermis, is a sturdy shield of dry, flattened cells filled with keratin - the same tough material that is the main ingredient in hair and nails. On the outside, the epidermis is a killing ground for alien microbes, many of which die on contact with a hostile surface constantly bathed in salty sweat and acidic, oily sebum. Those that gain a foothold must then compete with the many resident species of bacteria that thrive on our skin. Other germs and particles are cast off along with the skin's surface cells, which continuously flake away.

In a deeper layer, behind the keratin shield, basal cells called keratinocytes continuously divide and migrate to the surface to replace shed skin. Positioned strategically throughout the basal-cell community are Langerhans' cells, which search ceaselessly for disease-causing intruders, and melanocytes, which produce the pigment that gives skin its many shades.

Skin's middle layer, the dermis, consists of a thick mass of fibrous connective tissue that provides added resilience to the epidermis. Complex networks of capillaries (microscopic blood vessels) help nourish basal cells, eliminate waste products and regulate the skin's surface circulation. Also, running throughout this elastic collagen mesh are elaborate circuits of nerve fibres that inform the brain about surface pressure, heat and cold. Deeper in the dermis, wrapped around hair shafts, lie the sebaceous glands that oil the skin'ssurface and make it water-resistant. And nearby, sweat glands pump salt-water to the skin's surface to cool an overheated body.

Deeper still, a dense cushion of fat makes up the skin's innermost layer. In addition to its shock-absorbing properties, the fat provides insulation against sudden heat loss from the body's core, as well as serving as a semi-solid medium for such structures as hair roots, large-bore blood vessels and nervous-system junctions.

Unlocking the Mysteries of Wound Healing

Like any fortress, skin repels its foes by presenting a uniformly impenetrable wall. To achieve this ideal state-of-readiness, skin employs a rapid-response system for patching up everyday wounds (such as bruises, cuts, abrasions, punctures and burns). By necessity, skin is an expert at quickly repairing itself.

As might be expected, the various stages of wound healing are immensely complicated, involving pain to signal the alarm, inflammation to begin disaster relief, immune response to fight infection, clotting to stop blood loss, collagen-matrix repair to contract the wound, capillary growth to supply blood to the recovering dermis, and exuberant basal-cell division to create a new epidermis. Much remains to be learned about how different cell populations from different tissues signal each other, how they selectively activate appropriate genes in their respective nuclei, and how those gene products contribute to overall wound repair.

The need to know is urgent, since a process as intricate as wound repair is inherently vulnerable to missteps and malfunctions. Indeed, people who are frail and elderly, or who have weakened immune systems or who have diabetes or poor blood circulation frequently experience wounds that stubbornly refuse to heal. Septic infections, chronic skin ulcers and gangrene are some of the most common complications of impaired wound healing. In contrast, excessive wound healing as a result of burns and scalds presents the equally perplexing problem of disabling and disfiguring scar tissue.

Whether it's too much of a good thing or not enough, chronic problems in wound healing impose a huge burden on Canada's health-care system and cause untold suffering. And their prevalence is expected to increase significantly as Canada's population ages. As a result, IMHA's skin researchers founded the Canadian Interdisciplinary Wound Healing Group given that aberrant wound repair affects so many people and that any new knowledge generated will have broad applications for other skin research. Many diseases that affect the skin share such basic features as surface lesions, rapid cell-division, persistent inflammation and excessive collagen production.

In collaboration with investigators from other Institutes and universities across Canada, IMHA's multi-disciplinary research team will examine the biochemical signals that prompt various cells to multiply and take on specialized repair tasks; how the various cells arrange to travel to the wound site and organize themselves to repair damaged tissue; how infections disturb the normal healing process; how biologically active factors can be integrated into dressings and artificial skin so that they can stimulate proper healing; and how best to apply these insights to needy patients.

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