[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:07.40,0:00:11.41,Default,,0000,0000,0000,,The largest organ in your body\Nisn't your liver or your brain.
Dialogue: 0,0:00:11.41,0:00:16.28,Default,,0000,0000,0000,,It's your skin, with a surface area\Nof about 20 square feet in adults.
Dialogue: 0,0:00:16.28,0:00:19.42,Default,,0000,0000,0000,,Though different areas of the skin\Nhave different characteristics,
Dialogue: 0,0:00:19.42,0:00:22.04,Default,,0000,0000,0000,,much of this surface performs\Nsimilar functions,
Dialogue: 0,0:00:22.04,0:00:26.15,Default,,0000,0000,0000,,such as sweating, feeling heat and cold,\Nand growing hair.
Dialogue: 0,0:00:26.15,0:00:28.10,Default,,0000,0000,0000,,But after a deep cut or wound,
Dialogue: 0,0:00:28.10,0:00:31.75,Default,,0000,0000,0000,,the newly healed skin will look different\Nfrom the surrounding area,
Dialogue: 0,0:00:31.75,0:00:36.48,Default,,0000,0000,0000,,and may not fully regain all \Nits abilities for a while, or at all.
Dialogue: 0,0:00:36.48,0:00:41.10,Default,,0000,0000,0000,,To understand why this happens, we need to\Nlook at the structure of the human skin.
Dialogue: 0,0:00:41.10,0:00:43.04,Default,,0000,0000,0000,,The top layer, called the epidermis,
Dialogue: 0,0:00:43.04,0:00:47.22,Default,,0000,0000,0000,,consists mostly of hardened cells,\Ncalled keratinocytes,
Dialogue: 0,0:00:47.22,0:00:49.14,Default,,0000,0000,0000,,and provides protection.
Dialogue: 0,0:00:49.14,0:00:52.19,Default,,0000,0000,0000,,Since its outer layer is constantly being\Nshed and renewed,
Dialogue: 0,0:00:52.19,0:00:54.08,Default,,0000,0000,0000,,its pretty easy to repair.
Dialogue: 0,0:00:54.08,0:00:57.24,Default,,0000,0000,0000,,But sometimes a wound penetrates\Ninto the dermis,
Dialogue: 0,0:00:57.24,0:01:00.66,Default,,0000,0000,0000,,which contains blood vessels,\Nand the various glands and nerve endings
Dialogue: 0,0:01:00.66,0:01:03.56,Default,,0000,0000,0000,,that enable the skin's many functions.
Dialogue: 0,0:01:03.56,0:01:06.75,Default,,0000,0000,0000,,And when that happens, it triggers the\Nfour overlapping stages
Dialogue: 0,0:01:06.75,0:01:09.80,Default,,0000,0000,0000,,of the regenerative process.
Dialogue: 0,0:01:09.80,0:01:14.84,Default,,0000,0000,0000,,The first stage, hemostasis, is the skin's\Nresponse to two immediate threats:
Dialogue: 0,0:01:14.84,0:01:16.45,Default,,0000,0000,0000,,that you're now losing blood,
Dialogue: 0,0:01:16.45,0:01:20.26,Default,,0000,0000,0000,,and that the physical barrier of \Nthe epidermis has been compromised.
Dialogue: 0,0:01:20.26,0:01:23.01,Default,,0000,0000,0000,,As the blood vessels tighten to minimize\Nthe bleeding,
Dialogue: 0,0:01:23.01,0:01:25.26,Default,,0000,0000,0000,,in a process known as \Nvasoconstriction,
Dialogue: 0,0:01:25.26,0:01:28.95,Default,,0000,0000,0000,,both threats are averted by forming\Na blood clot.
Dialogue: 0,0:01:28.95,0:01:33.14,Default,,0000,0000,0000,,A special protein known as fibrin forms\Ncrosslinks on the top of the skin,
Dialogue: 0,0:01:33.14,0:01:38.45,Default,,0000,0000,0000,,preventing blood from flowing out\Nand bacteria or pathogens from getting in.
Dialogue: 0,0:01:38.45,0:01:41.90,Default,,0000,0000,0000,,After about three hours of this,\Nthe skin begins to turn red,
Dialogue: 0,0:01:41.90,0:01:44.83,Default,,0000,0000,0000,,signaling the next stage, inflammation.
Dialogue: 0,0:01:44.83,0:01:47.73,Default,,0000,0000,0000,,With bleeding under control\Nand the barrier secured,
Dialogue: 0,0:01:47.73,0:01:52.08,Default,,0000,0000,0000,,the body sends special cells to fight any\Npathogens that may have gotten through.
Dialogue: 0,0:01:52.08,0:01:54.96,Default,,0000,0000,0000,,Among the most important of these\Nare white blood cells,
Dialogue: 0,0:01:54.96,0:01:56.73,Default,,0000,0000,0000,,known as macrophages,
Dialogue: 0,0:01:56.73,0:02:02.00,Default,,0000,0000,0000,,which devour bacteria and damage tissue\Nthrough a process known as phagocytosis,
Dialogue: 0,0:02:02.00,0:02:05.72,Default,,0000,0000,0000,,in addition to producing growth factors\Nto spur healing.
Dialogue: 0,0:02:05.72,0:02:08.08,Default,,0000,0000,0000,,And because these tiny soldiers \Nneed to travel
Dialogue: 0,0:02:08.08,0:02:10.19,Default,,0000,0000,0000,,through the blood to \Nget to the wound site,
Dialogue: 0,0:02:10.19,0:02:13.60,Default,,0000,0000,0000,,the previously constricted \Nblood vessels now expand
Dialogue: 0,0:02:13.60,0:02:16.25,Default,,0000,0000,0000,,in a process called vasodilation.
Dialogue: 0,0:02:16.25,0:02:18.44,Default,,0000,0000,0000,,About two to three days after the wound,
Dialogue: 0,0:02:18.44,0:02:23.24,Default,,0000,0000,0000,,the proliferative stage occurs, when \Nfibroblast cells begin to enter the wound.
Dialogue: 0,0:02:23.24,0:02:25.68,Default,,0000,0000,0000,,In the process of collagen deposition,
Dialogue: 0,0:02:25.68,0:02:29.75,Default,,0000,0000,0000,,they produce a fibrous protein \Ncalled collagen in the wound site,
Dialogue: 0,0:02:29.75,0:02:33.93,Default,,0000,0000,0000,,forming connective skin tissue\Nto replace the fibrin from before.
Dialogue: 0,0:02:33.93,0:02:37.72,Default,,0000,0000,0000,,As epidermal cells divide to reform\Nthe outer layer of skin,
Dialogue: 0,0:02:37.72,0:02:40.61,Default,,0000,0000,0000,,the dermis contracts to close the wound.
Dialogue: 0,0:02:40.61,0:02:43.22,Default,,0000,0000,0000,,Finally, in the fourth stage \Nof remodeling,
Dialogue: 0,0:02:43.22,0:02:47.60,Default,,0000,0000,0000,,the wound matures as the newly deposited\Ncollagen is rearranged and converted
Dialogue: 0,0:02:47.60,0:02:49.43,Default,,0000,0000,0000,,into specific types.
Dialogue: 0,0:02:49.43,0:02:52.12,Default,,0000,0000,0000,,Through this process,\Nwhich can take over a year,
Dialogue: 0,0:02:52.12,0:02:55.23,Default,,0000,0000,0000,,the tensile strength of the new skin\Nis improved,
Dialogue: 0,0:02:55.23,0:02:58.64,Default,,0000,0000,0000,,and blood vessels and other connections\Nare strengthened.
Dialogue: 0,0:02:58.64,0:03:02.10,Default,,0000,0000,0000,,With time, the new tissue \Ncan reach from 50-80%
Dialogue: 0,0:03:02.10,0:03:04.57,Default,,0000,0000,0000,,of some of its original healthy function,
Dialogue: 0,0:03:04.57,0:03:08.82,Default,,0000,0000,0000,,depending on the severity of the initial \Nwound, and on the function itself.
Dialogue: 0,0:03:08.82,0:03:11.10,Default,,0000,0000,0000,,But because the skin\Ndoes not fully recover,
Dialogue: 0,0:03:11.10,0:03:15.75,Default,,0000,0000,0000,,scarring continues to be a major clinical\Nissue for doctors around the world.
Dialogue: 0,0:03:15.75,0:03:18.59,Default,,0000,0000,0000,,And even though researchers have made\Nsignificant strides
Dialogue: 0,0:03:18.59,0:03:20.69,Default,,0000,0000,0000,,in understanding the healing process,
Dialogue: 0,0:03:20.69,0:03:23.87,Default,,0000,0000,0000,,many fundamental mysteries\Nremain unresolved.
Dialogue: 0,0:03:23.87,0:03:27.45,Default,,0000,0000,0000,,For instance, do fibroblast cells arrive\Nfrom the blood vessels,
Dialogue: 0,0:03:27.45,0:03:30.04,Default,,0000,0000,0000,,or from skin tissue adjacent to the wound?
Dialogue: 0,0:03:30.04,0:03:32.62,Default,,0000,0000,0000,,And why do some other mammals, \Nsuch as deer,
Dialogue: 0,0:03:32.62,0:03:37.30,Default,,0000,0000,0000,,heal their wounds much more efficiently\Nand completely than humans?
Dialogue: 0,0:03:37.30,0:03:39.83,Default,,0000,0000,0000,,By finding the answers to these questions\Nand others,
Dialogue: 0,0:03:39.83,0:03:44.79,Default,,0000,0000,0000,,we may one day be able to heal ourselves\Nso well, that scars will be just a memory.