The Integumentary System, Part 2 – Skin Deeper: Crash Course A&P #7


Transcript Provided by YouTube:

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Look at all this stuff! Soaps, lotions, conditioners, polishes — all
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from that huge section of your local store that’s dedicated solely to the grooming
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of your skin, hair, and nails. Some might see these things as the trappings
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of vanity. But me? I see them as the tools for the care,
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maintenance, and — sure, sometimes decoration — of the integumentary system.
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Now, true, in spite of what the cosmetics industry may lead you to believe, your integumentary
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system is more than just a place to put eye shadow and hair product in the hopes of attracting a mate.
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This collection of resilient tissues, ranging from the sharp and hard to the soft and fluffy,
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serve a whole panoply of functions, the majority of which you never even notice.
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But, when you do notice what your integumentary system is doing, the results are often uncomfortable
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or ugly or both, and that is what this stuff is mostly for.
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Your sweat glands can make you smell.
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Your oil glands can give you zits.
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Your skin can become either scaly or greasy, and — in rare cases — it can even change color.
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And hair, well, let’s just say it takes a lot of science to tame this mane.
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But each of these tissues — frustrating as they may be at times — has a purpose, and
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without them you’d be cold and vulnerable and dead.
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I’m not gonna lecture you on personal hygiene today. But hopefully by the end of this you’ll
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understand the important functions of your integumentary system, and maybe why it’s
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worth a little bit of time and effort to keep it healthy.
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And hey, it might even score you a date.
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If you recall our recent run-ins with rogue
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nails and tattoo needles, you’ll probably remember that the first and most vital purpose
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of your integumentary system is to act as a protective barrier.
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Your skin, hair, nails and sweat and oil glands all work together to shield you from all the
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things out there that are out to get you: excessive sunlight, infections, abrasions,
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and just, you know, getting poked by sharp sticks and stuff.
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But beyond that, this system is also vital to how you sense the world around you.
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Your skin is loaded with structures that are actually part of your nervous system — called
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cutaneous sensory receptors — they’re what receive stimuli from the outside environment
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and send them to your brain.
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These receptors, or corpuscles, as they’re sometimes called, register all of the different
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sensations that you associate with touch.
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Your tactile corpuscles, for instance, are what make you constantly aware of the tag
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that’s scratching at the back of your neck, while your lamellar corpuscles register the
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sense of pressure, like when someone puts their hand on your shoulder.
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Your hair follicles have receptors, too, which is why you can feel a slight breeze on your
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skin or through your hair.
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Now, on the less-sexy front, your integumentary system also plays a role in the excretion
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of waste, though not as big as a role as we’re often led to believe.
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Most nitrogen-containing wastes like urea, uric acid, and ammonia are disposed of through
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your urine, but small amounts are eliminated through your skin in sweat.
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But despite what you may be told at the beginning of your hot-yoga class, there isn’t much
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evidence that suggests that heavy sweating actually rids your body of any extra toxins
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— if anything, you’re just losing more water.
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When you do exercise, though, you call on another of your skin’s lesser-known functions
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— as a handy blood storage unit.
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About 5 percent of your entire blood volume is retained in your skin at any given time.
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And when you suddenly need more blood supplied to your organs, like when you’re working out,
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your nervous system constricts your dermal blood vessels to squeeze that extra blood into circulation.
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Now, during these times of exertion, both your blood and your sweat glands work together
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to perform a key function: regulating your body temperature.
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Even without exercise, your body oozes out about half a liter of sweat per day, in an
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effort to keep you at a comfortable temperature. That’s just your normal, barely noticeable
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sweat called insensible perspiration.
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But on a hot day, or if you’re on the dance floor exerting yourself, that sweat becomes
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much more noticeable. Such sensible perspiration could produce as much as 12 LITERS of sweat per day!
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Now, if the temperature gets chilly, the surface of your skin can lose a lot of heat, because
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it has so much warm blood behind it. To regulate that heat loss, your dermal blood vessels
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constrict, causing your blood to head deeper into your tissues and help keep your vital organs warm.
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Once things warm up, those blood vessels in the skin gradually relax, and allow that blood
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to return to the surface.
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You’ve probably noticed that if you’re cold for too long, your skin may lose some
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of its color — or even turn pale blue if you’re light-skinned — as that blood retreats
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from the surface.
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And in fact, like a litmus test for your body, changes in the color of your skin can indicate
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a number of homeostatic imbalances.
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Blue skin, or cyanosis, in Caucasian people may indicate heart failure, poor circulation,
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or severe respiratory issues. That’s because blood that’s been depleted of oxygen turns
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darker in color, and when seen through the tissue of lips or skin, it can look bluish.
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A yellowing of the skin, called jaundice, usually signifies liver disorder, as yellow
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bile starts accumulating in the blood stream.
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Reddened skin, or erythema, could indicate a fever, inflammation, or allergy — all of
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these conditions cause blood vessels to expand and more blood to flow to the skin’s surface.
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Of course, human skin color spans a pretty wide spectrum, so some of these conditions
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are easier to diagnose by looking for discolorations of other tissues, like mucous membranes and
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the beds of finger and toenails.
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However light or dark your skin color is, though, you can thank your melanin for it.
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You’ll remember that melanin is a pigment produced by the melanocyte cells in your epidermis.
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Melanin has two forms, producing pigments that range in color from reddish yellow to
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brownish black.
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Because its main job is to protect us from the sun’s ultraviolet rays, it makes sense
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that, in the distant past, the distribution of these different skin tones was not at all random.
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Historically, where solar radiation is more intense, higher concentrations of deep-colored
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melanin became an advantage for the protection it provided.
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But closer to the poles, where those solar rays are weaker and more diffuse, lower concentrations
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of melanin allowed people to collect what sunlight was available, to manufacture vitamin D.
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‘Cause the fact is, we all need some level of sunlight to hit our skin to survive.
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Your bones require vitamin D to keep producing new bone cells, and it’s the only vitamin
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that your body can actually produce on its own. Your skin cells contain a molecule that
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converts to vitamin D when it comes in contact with UV light.
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From there the vitamin heads through your bloodstream to your liver and kidneys where
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it truly becomes activated D, also called calcitriol, which is circulated to all the bones of your body.
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But let’s not just be skin-deep here — your integumentary system also involves your so-called
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skin appendages — your hair, nails, sweat and sebaceous, or oil glands, which can each
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be fascinating as well as frustrating in its own way.
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If you’re like some people I know and you spend a fortune on hair conditioner? That’s
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because your cuticles are out of control.
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All of your hairs, or pili, are basically just flexible strands of dead keratin protein
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cells, like your fingernails.
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And the outermost layer of these dead cells, called the cuticle, looks like it’s made
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of overlapping roof shingles. So what you’re paying the conditioner to do is even out the
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rough surface between those cells of the cuticle to make it look smooth.
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Now if you pluck out a strand of your hair you will be in pain, but you will also have
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the opportunity to notice that it has two main regions — the shaft — where the keratinization
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is complete — and the root — the part inside the follicle where keratinization is still happening.
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Each follicle is just a tube of epidermal cells, and just like in your epidermis, the
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cells at the bottom of each follicle are young and fresh, continually dividing and pushing
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older cells up through the skin and into the open air.
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And your finger- and toenails pretty much grow the same way — starting at the back
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of the nail bed where new cells divide at the root and get pushed forward, creating
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the scaly-hard keratin that you paint with polish and keep trimmed during flip-flop season.
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But there’s probably no other part of the integumentary system that you spend more money
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on trying to control than your sweat and oil glands.
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You’ve got up to three million tiny sudoriferous, or sweat glands distributed throughout your
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body. These guys secrete your salty, watery sweat, and they come in two types: eccrine
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and apocrine.
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Your eccrine sweat glands are more abundant — they’re in your palms, forehead, and
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in the soles of your feet.
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They’re just simple coiled tubes that start in the dermis, extend through a duct, and
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open into a pore on the surface of your skin.
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Your apocrine sweat glands are a slightly different story. You only have about 2000
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of these, and they start cookin’ around puberty, emptying into the hair follicles
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around your armpits and groin.
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These glands secrete a kind of deluxe sweat, with fats and proteins in it. It’s more
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viscous and sometimes yellowish in color. When bacteria on the skin get a hold of this
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sweat, it gets odorific, creating what we generically call body odor.
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Deodorants don’t affect how much you sweat, but they do reduce those smells by attacking
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the stink-making bacteria, while antiperspirants do the opposite, using ingredients like aluminum
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to block your sweat glands and actually keep you from perspiring.
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Some researchers believe these glands may be the human equivalent of other animals’
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musky sex scent glands. So while you might not want to stink up a whole room, a little
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bit of body odor might actually get you a mate.
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Mammary glands, which secrete milk in lactating people, and ceruminous glands, the ones that
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make your cerumen, or earwax, are two other types of modified apocrine sweat glands.
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Finally, your sebaceous, or oil glands are found everywhere but the thick skin in your
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palms and foot soles. Their ducts are smaller on your limbs, but they’re pretty big on
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your face, and neck, and upper chest.
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Most of your sebaceous glands secrete their sebum, an oily substance, into hair follicles
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where it can travel to the surface of your skin.
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And while yes, they cause wicked pimples, their primary goal is to soften and lubricate
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your skin and hair, and help slow water loss from the skin in dry environments.
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Try to remember that the next time you have a break-out before a big date or job interview.
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Maybe it’ll make you feel better. It probably won’t.
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The irony here is that about half of the things I showed at the beginning of this episode
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are used to wash away our natural protective moisturizing oils, while the other half are
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there to add them back through lotions and conditioners!
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Deodorant, though. I think we’re all glad that exists.
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Today you learned how your integumentary system protects your body, senses the outside world,
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helps excrete waste, stores blood, regulates temperature, makes vitamin D, indicates signs
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of poor health, and gives you zits. We also talked about how your hair and nails grow,
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the difference between your eccrine and apocrine sweat glands, and your sebaceous oil glands.
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Thank you for watching, especially to all of our Subbable subscribers, who make Crash
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Course possible for themselves and also to everyone else. To find out how you can become
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a supporter, just go to subbable.com.
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This episode was written by Kathleen Yale, edited by Blake de Pastino, and our consultant,
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is Dr. Brandon Jackson. Our director and editor is Nicholas Jenkins, the script supervisor
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and sound designer is Michael Aranda, and the graphics team is Thought Café.


This post was previously published on YouTube.

Photo credit: Screenshot from video.