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Biology library
Course: Biology library > Unit 36
Lesson 1: Crash Course: Biology- Why carbon is everywhere
- Water - Liquid awesome
- Biological molecules - You are what you eat
- Eukaryopolis - The city of animal cells
- In da club - Membranes & transport
- Plant cells
- ATP & respiration
- Photosynthesis
- Heredity
- DNA, hot pockets, & the longest word ever
- Mitosis: Splitting up is complicated
- Meiosis: Where the sex starts
- Natural Selection
- Speciation: Of ligers & men
- Animal development: We're just tubes
- Evolutionary development: Chicken teeth
- Population genetics: When Darwin met Mendel
- Taxonomy: Life's filing system
- Evolution: It's a Thing
- Comparative anatomy: What makes us animals
- Simple animals: Sponges, jellies, & octopuses
- Complex animals: Annelids & arthropods
- Chordates
- Animal behavior
- The nervous system
- Circulatory & respiratory systems
- The digestive system
- The excretory system: From your heart to the toilet
- The skeletal system: It's ALIVE!
- Big Guns: The Muscular System
- Your immune system: Natural born killer
- Great glands - Your endocrine system
- The reproductive system: How gonads go
- Old & Odd: Archaea, Bacteria & Protists
- The sex lives of nonvascular plants
- Vascular plants = Winning!
- The plants & the bees: Plant reproduction
- Fungi: Death Becomes Them
- Ecology - Rules for living on earth
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The skeletal system: It's ALIVE!
Hank introduces us to the framework of our bodies, our skeleton, which apart from being the support and protection for all our fleshy parts, is involved in many other vital processes that help our bodies to function properly. Created by EcoGeek.
Want to join the conversation?
- Is the book he is holding the same book as all the others but with a different cover?(15 votes)
- Probably. I don't think they would go buying a different book for every video.(4 votes)
- He said that vitamin D is really important in bone regrowth. So why do we wear sunscreen?(9 votes)
- Sunscreen is to prevent the gamma rays that are emitted from the sun from damaging your skin and DNA in your skin cells. If they do, you have a good chance of getting skin cancer, since it is a mutation in the DNA that causes cancers.(10 votes)
- Where is the Femur Bone located in the body?(4 votes)
- It is basically the giant bone located underneath your thigh, under the pelvic bones and right above your knee.(6 votes)
- I herd babys are born with 300 bones and aduts have 206 . how is that possible?(3 votes)
- our bones fuse together to makes the bones longer and larger which makes makes the bones less in quantity in adults(5 votes)
- Do you really need bones to be alive?(2 votes)
- You do not. Although many organisms have either an internal support system (bones) or an external support system (exoskeleton) there are still other organisms without either. Take an amoeba for example. It is a plant-like organism without and internal or external support system, but is still very much alive.(5 votes)
- what is axial skeleton and appendicular skeleton?(2 votes)
- The axial skeleton is the skeletal structure (bones, cartilage, ligaments) that comprises the medial part of a body, also known as the trunk (spine, ribs, skull, etc). In humans, much of the axial skeleton acts as a protective encasement for central nervous system tissue, whereas the apendicular skeleton provides no such function
The appendicular skeleton is the peripheral skeletal structure that includes arms, legs, pelvis (excluding the sacrum), and shoulder. It too, like the axial skeleton, is primarily comprised of bones and is held together with ligaments, with cartilage as the connective tissue that performs various functions essentially relating to making the joints run smoother.(4 votes)
- without a thyroid/parathyroid would you be able to re-grow bones?(2 votes)
- No, you won't be able to. These glands regulate calcium as well as general cellular metabolism and parathyroid gland is especially important in maintaining the normal blood calcium level necessary for re-growth of the bones.
You won't be able to live without parathyroid even for a few days, because calcium is also required for normal function of nervous and muscular systems. Lack of parathyroid hormone can result in tetany, spasm of larinx, and suffocation.(3 votes)
- how does the broken bones heal(2 votes)
- Cells in the bones reproduce until the break is healed.(3 votes)
- Is there a disease where osteoclasts go crazy and slowly break down your bones?(3 votes)
- Osteoporosis, which literally means porous bone, is a disease in which the density and quality of bone are reduced. As bones become more porous and fragile, the risk of fracture is greatly increased. The loss of bone occurs silently and progressively. Often there are no symptoms until the first fracture occurs.
https://www.iofbonehealth.org/what-is-osteoporosis(1 vote)
- What would happen if your osteoclasts stopped working and only the osteoblasts were active?(2 votes)
- You would break down bone but not be able to remodel it. Not such a good idea, if you want to keep your bones working.(2 votes)
Video transcript
- This, my friends, is a walrus baculum. It's basically a penis bone
found in most placental mammals. Interestingly, not in humans. And this is a polar bear skull, which as you can see is more streamlined for
swimming in the water than a grizzly bear skull. And over here we have my
giant friend, the rhino head, which is good for being giant, for fighting off predators
and fighting for, I don't know, why do
rhinos have big heads? And this is the skull
of a pronghorn antelope. It has these horns that come off that are covered in these keratin sheaths that fall off once a year. These are all bones! Parts of skeletons and they're all pretty freakin' awesome, and I'm surrounded by them here at the Philip L. Wright Zoological Museum at the University of Montana. And all of these bones have adapted to help animals survive: the horns on the pronghorn
for mating displays and self-defense; the stream-lined skull of a polar bear for swimming in the water; and the walrus baculum for longevity, I guess? We're used to thinking of our skeletons as being the dead parts of us, because that's what's left
over after all of our, like, stuff that looks like us has rotted away. But the fact is, our bones
make up a vital organ system, and I don't just mean vital in that, without them you would be a sort of, disgusting, dead pile of lumpy mush. But also in the traditional
meaning of vital, meaning it's alive. It protects your vital organs, it makes locomotion possible, it manufactures your blood, and top of it all, it takes care of its own
repair and maintenance. Your skeleton is alive, people, and walrus penises are just the beginning. (upbeat music) So you know what bones are, but maybe you didn't know
that you don't have to be a vertebrate, or even a chordate, to have a skeleton. Jellies and worms, for instance, have hydrostatic skeletons made up of fluid-filled body cavities by squeezing muscles around the cavities, they change their shapes. That can be used to produce movement. Insects have exoskeletons, of course, made of the nitrogenous
carbohydrate chitin. And most mollusks have exoskeletons too, in the form of calcium carbonate shells. But when it comes to skeletons, the winningest formula
has been the endoskeleton. Even though we'd probably
feel a lot safer if we were covered with armored plates like some race of iron men. Having skeletons inside of our bodies has allowed us to grow larger and have much more freedom of movement. It's good stuff. One of the many reasons you don't see ants the size of horses walking around is well, one, it wouldn't be able to breathe, but also a body with such a huge volume would require an exoskeleton that was exponentially thicker and therefore heavier and clumsier to support it. So, endoskeletons allow animals to grow larger by supporting more mass, plus you don't have to worry
about the embarrassment that comes with unsightly molting. As adults, humans have 206 bones, all kinds of shapes and sizes, including three tiny ones in each ear, one weird-shaped one like
a horseshoe in your throat, 27 in your hands, and 26 in each foot. You also have at least 32 teeth, unless you played too much hockey, and even though they're
included in the skeletal system, they don't count as bones because they're made up
of different material, namely dentin and enamel, the hardest material in your body. And you probably think of
the skull as one big bone, but it actually consists
of many separate bones, including eight plates
that cover your brain and 14 others in your face. Face bones. So simple, right? Well, you might want to sit down. You probably already are. But I'm going to because
it's time for biolo-graphy. (piano music) Now you'd think that we'd have nailed down the basics of the human
skeleton a long time ago, because our teeth and
our bones are the biggest and hardest parts of our bodies, and after we leave this mortal coil they're what stick around the longest. It's not like they're super
hard to find and study. Surely all of those ancient physicians who basically invented medical science would have inventoried all of our bones pretty soon after they
figured out that we had bones. Right? If the answer was yes, do you think I'd be sitting here? Most of what we know about
the human skeletal system is thanks to Andries Van Wesel, who was born in what's
now Belgium in 1513. And in those days, if you were like a
kung-fu master of science, you pretty much got your own Latin name, so today, he's known as Andreas Vesalius. Vesalius came from a long line of physicians to kings and emperors and while studying in Paris, he began dorking around in cemeteries and became interested in what's now known as osteology, the study of bones. Perhaps Vesalius' greatest contribution was showing the world that
everything we thought we knew about osteology was wrong. See, back in those days if you wanted to become a doctor, you didn't study bodies or see patients, you read stuff written by ancient Romans whose work was considered indisputable. Because you know, those
guys had long beards and they wore robes. But in his research, Vesalius discovered that Roman
texts about the skeleton, especially the teachings of
the philosopher Dr. Gaelan, were way, way off. See, Roman law prohibited the
dissection of human bodies, so none of those guys ever
actually studied human innards. Instead, they dissected
apes and pigs and donkeys, and used that to make assumptions about the human body. And so for 15 centuries, young doctors were
taught those assumptions. But Vesalius revolutionized osteology and all of medicine by introducing a new practice, every pre-med student's favorite, human dissection. He instructed students
by dismembering corpses in front of them, and cataloging their parts, giving students the first opportunity ever to directly observe the inside of a human body. These new methods drew a lot of attention, particularly from a local judge, who began donating bodies of the criminals that
he executed to Vesalius. Suddenly the dude was up to his cod-piece in pig thieves and murderers, and by the time he was 28, he had done enough
research that he published De humani corporis fabrica On the fabric of the human body, a seven-volume text on human anatomy, including the first comprehensive
description ever made of the human skeleton. Its beautifully detailed illustrations are thought to have been
created in the studio of the Renaissance artist Titian, featuring pictures of flayed corpses positioned in symbolic poses. And many of the volumes, some of which still exist today, are bound in human skin. So the takeaway here is that even though bones are big and hard, the science behind them
is far from obvious. Even though we tend to think of our bones as rigid and fixed, your skeleton is as dynamic as any other of your organ systems. It's built from scratch with
ingredients in your blood, it's grown according
to glands in your head, and probably coolest of all, it's constantly breaking itself down and rebuilding itself, over and over again, for as long as you live. Most new bone tissue
starts out as cartilage, which you may know from
your nose and your ears. It's made of specialized
cells called chondrocytes, and in newly forming bones, these cells start dividing like crazy and secrete collagen and other proteins to form a cartilage model or framework for the bones to form on. Soon blood vessels work their way into the cartilage and
bring plump little cells called osteoblasts. Oste-, which you'll be
hearing a lot of today, just means bone, and blast means germ or bud. The bone building that they
do is called, fittingly, ossification. First, they secrete this gelatinous goo that's a combination of
collagen and a polysaccharide that acts kind of like an organic glue. Then, they start absorbing a
bunch of minerals and salts from the blood and all the
capillaries around them. And, unsurprisingly,
they're especially absorbing calcium and phosphate. And they begin depositing those minerals onto the matrix. With the help of enzymes
secreted by the osteoblasts, these chemicals bond to
form calcium phosphate, which crystallizes to
make your bone matrix. In the end, about two-thirds
of your bone matrix is proteins, like collagen, and the other third is calcium phosphate. Kind of surprising, right? Most of your bone isn't even mineral. And even the part that
is is living tissue, because it's all honeycombed
with blood vessels that allow osteoblasts and
other cells to do their jobs. Unlike an insect's exoskeleton, even the hardest parts
of your bones are alive. Now, even though bone can
take all kinds of forms from big flat plates protecting the brain to the tiny stirrup in your ear, inside they all tend to have
the same basic structure. If you cut one in half, you'd see that the matrix
actually forms in two layers. The outer layer, called the
compact, or cortical bone, is hard and dense and makes up
about 80% of the bone's mass. And the middle, the
spongy or trabecular bone is softer, more porous, and contains the marrow and
fatty tissues and larger bones. The marrow, of course, makes
not only new red blood cells, but almost all of your
different blood cells by a process called hematopoeisis. I'd need, like, about a week of your time and a Greek dictionary to explain how it does this, but suffice it to say that evolution has wisely chosen the
innards of our largest bones to house the blood stem cells that, together, can produce
1 trillion blood cells in you every day. That's 10 to the frickin' twelfth. On the outside, the
larger bones of your body have a similar structure. Have a look here at this femur. That's the biggest bone in your body. The main shaft is called the diaphysis, and each rounded head is an epiphysis. When the bones grow as a child grows, the new tissue forms the
border between the two, a place called the epiphyseal plate. As they did when they formed
the original bone tissue, chondrocytes start to
produce new cartilage here, and the osteoblasts come in and lay down more collagen and calcium phosphate. So as you grow, the ends of your bones are actually growing away from each other, until by the time you're about 25, the last of these plates
in your bones hardens. By the way, this whole
process is stimulated by growth hormones secreted from glands all over your body, but the head honcho, right here, is the pituitary gland
about the size of a pea, nestled at the base of your brain. As adults, this and other glands
produce less growth hormone which slows down our bone lengthening. But, even though lengthening is a limited-time-only process, the thickness and strength of a bone must continually be
maintained by the body. Because, of course,
like all of your cells, bone cells go through
a lot of wear and tear, and need to be able to adjust
to changing conditions. So over the course of each
year of your adult life, about 10% of your skeleton
is completely broken down and then rebuilt from scratch in a process called bone remodeling. Here, the main players are the osteoblasts, again,
and another kind of cell that's kind of the complete opposite, the osteoclasts, or bone breakers. You'd think maybe that the
cells that form bone tissue and the ones that destroy it would be in some kind of constant
battle in your body, but during remodeling,
they work closely together and actually communicate nicely. It's like they're basically frenemies. Remodeling begins when
osteoclasts are sent, by way of hormone signals, through the capillaries to the sites of microscopic fractures
in the bone matrix. Once they're in place, they
secrete an acidic cocktail of hydrogen ions to dissolve
the calcium phosphate into calcium ions, phosphate, and water, and other material that they carry back to nearby capillaries. Then, they secrete enzymes that specialize in digesting collagen. This whole process is called resorption, and when the old bone
tissue has been cleaned up the osteoclasts send
out a hormone shout-out to the osteoblasts, who come in and do their
ossification thing. Bone remodeling is really pretty amazing, and it's all ultimately
regulated by hormones that maintain the levels
of calcium in your blood. The glands that call all the plays during the bone-breaking
part of the remodeling are the parathyroids in your neck. When the calcium in your blood plasma falls below the level of homeostasis, the parathyroid triggers osteoclasts to take calcium out of your bones and release it back into the blood. Likewise, when blood
calcium levels are too high, the parathyroid's cousin the thyroid gland signals osteoblasts to take
calcium out of the blood and lay it down on the bone collagen through more ossification. And remember last week
when we talked about how the kidneys reabsorb
salts and minerals? Well, the thyroid also
regulates how much calcium is reabsorbed in that process, as well as the amount of Vitamin D, because Vitamin D helps
your body absorb calcium through the small intestine, and that is why Vitamin D is all good for your bones and stuff. Now the relation of active osteoblasts to active osteoclasts can change dramatically
under different conditions. The more you stress your bones, the more osteoclasts work to
break down the bone matrix so that it can be reformed. Bone stress can include stuff
like fractures of course, but it can also be less
traumatic and more sustained. Exercise causes stress on the skeleton that helps stimulate bone remodeling, so when you're working out, you're not only building muscle, you're also building bone. So, as you can tell, it's kind of hard to talk about bones without also talking about muscles. And that's what we're going to do on the next episode of
Crash Course Biology. Thank you so much to the Philip
L. Wright Zoological Museum at the University of Montana. Sorry, I just hit you. Check out their tumblr
at umzoology.tumblr.com. It's awesome.