Full transcript
0:00Chapter six bones and skeletal tissues part one so skull system has many functions protects and
0:08supports organs of the body including brain the heart the lungs provides a rigid framework for
0:14the body giving its shape and allowing the muscles to pull on those rigid structures to
0:19allow for movement stores minerals especially calcium which is very important for our body
0:24and it produces all blood cells so all blood cells are produced in the red bone marrow and
0:30energy storage the yellow bone marrow is made of adipose tissue so is storing triglycerides fatty
0:38fatty substances hyaline and fibrocartilage are also important in our skeleton cartilages as we
0:47know have little pockets called lacunae within the pockets are the cells the chondrocytes and
0:51then this material surrounding the lacunae is the matrix and that can include collagen
0:59fibers to help give the cartilage strength we can find cartilage in a lot of different areas
1:06in the skeletal system so for instance hyaline cartilage is found on these smooth surfaces of
1:15bones that form joints so smooth surfaces have articular cartilage on them there's the costal
1:22cartilage made of hyaline cartilage attaching the ribs to the sternum the fibrocartilage is
1:28also found in a few places the meniscus of knee the pubic symphysis thick piece of fibrocartilage
1:33attaching the two hip bones the intervertebral discs all big thick pieces of fibrocartilage the
1:40purposes of the cartilage is to provide a smooth surface so at joints a nice smooth surface reduce
1:46friction the cartilage can also resist compressive forces so with in the vertebral column so vertebra
1:53don't hit each other if we sit down really hard because of the fibrocartilage discs and another
1:59feature is they are avascular there are no blood vessels in cartilage so that means cartilage heals
2:05really slowly when damaged locations of hyaline cartilage is the particular cartilage at the ends
2:12of long bones the costal cartilage connecting the ribs sternum and then fibocartilage the
2:17intervertebral discs the menisci in the knee pubic symphysis all right moving on to bone tissue bone
2:25tissue is mostly extracellular material and that extracellular material is 35% organic which is
2:34the collagen fibers and collagen fibers give the bone tissue its flexibility and tensile strength
2:40making very strong able to resist forces and then the other 65% is inorganic material primarily
2:47calcium phosphate these minerals give the bones their hardness as we also can see in compact
2:53bone tissue it has little pockets called lacunae these little dark spots are the lacunae it has
3:01large spaces called the central canals for blood vessels and nerves are found and then lamella are
3:08these layers of tissues so we have these layers of tissues and a ring structure in this case it
3:15would be called the lamella there are four main kinds of bone cells there's the osteoprogenitor
3:23cells these are stem cells osteoprogenitor cells will divide to form osteoblasts osteoblasts are
3:31the cells under the bone tissue that deposit bone tissue they build up the bone by making
3:38more extracellular material that then becomes calcified so osteoblasts build up the bone tissue
3:44when osteoblasts is surrounded by bone tissue and trapped in lacunae they differentiate and
3:50become osteocytes osteocytes their function is to maintain healthy bone tissue so they keep it
3:55healthy and they alert the bones when there are stresses in areas the fourth cell comes from a
4:03different lineage for cells called the osteoclasts osteoclasts absorb the bone material so they break
4:12down the extracellular matrix break down bone tissue when they do that they release calcium
4:17into the bloodstream so you can think of them as cutting or cleaving the bone tissue there are
4:23different kinds of bones we have long bones long bones are much greater in length than width
4:29they always have this middle structure called a diaphysis or shaft examples most of the bones in
4:36the arms and hands and most of the bones in the legs and feet are long bones short bones short
4:43bones are vaguely somewhat cubic so about as wide as they are tall as they are deep kind of they are
4:50found especially in the carpals or the wrists the tarsals and the ankle and patella these are all
4:57short bones there are flat bones flat bones are very thin the layer of compact bone tissues on
5:03the outside and then the spongy bone tissue in the middle flat bones includes the sternum the
5:10ribs and many of the bones of the skull and then irregular bones irregular bones like the vertebra
5:17have complicated shapes so they don't fit in the other three categories very well examples include
5:22the vertebra and the hip bones also the sacrum and coccyx alright there are many bones surface
5:31markings we'll be learning the names of some of them but first I'm going to break them down into
5:34general categories one big category is depressions and openings so for instance fissure fissure is a
5:41very narrow wide slit or opening between bones or in a bone they're providing a passageway for
5:47nerves blood vessels muscles to pass through there are foramen forming our smaller openings
5:55going through a bone they are again passageways they're holes letting blood vessels or nerves on
6:00pass through the bone a fossa is a depression a shallow depression a indention into the bone
6:08surface they're there to fit another structure so in this case these fossa on the humerus making
6:15space for the ulna and radius when we completely bend at the elbow flex at the elbow sulcus sulcus
6:23is a furrow a groove along the surface of the bone again this is providing a space for some
6:31structure this case often tendons or ligaments sometimes blood vessels or nerves there are the
6:39processes that form joints these are the processes that come together to form joints also known as
6:45articulations one example is condyles condyles are smooth rounded knobs at the ends of bones facets
6:54facets are smooth flat surfaces or slightly curved surfaces where bones come together to form joints
7:00and heads heads are large smooth rounded knobs or that project out to help form joints usually what
7:10follows the head is the neck so again these are all smooth surfaces because we don't want rough
7:17friction generating surfaces at joints want to be a smooth movement at these articulations all right
7:24we also have the rough structures these rough structures are attachment points for tendons
7:28and ligaments a crest is a large ridge there's a very rough it's very long process that is an
7:37attachment site we have epicondyles epicondyles are rough projections above condyles a place for
7:45tendons ligaments to attach a spine the spine is a very thin sharp projection sticking out again very
7:53rough so that muscles contacts to it a tuberosity is a large variable sized actually variable sized
8:02rough patch on a bone sometimes really thick sometimes not that obvious the tuberosities
8:08alright moving on to the anatomy of a long bone we can dissect the long bone and find a variety
8:17of structures so for instance what you might call the shaft the middle region of the long
8:22bone is officially known as the diaphysis long cylindrical made primarily of compact bone tissue
8:29within the diaphysis is a cavity or space called the medullary cavity this is where we house yellow
8:38bone marrow and would you find expect to find yellow bone marrow in the frontal bone course
8:44not it isn't a long bone all right at the ends of the bones proximal and distal these ends of
8:52the bones are called the epiphyses so proximal epiphyses and distal epiphyses the epiphysis
9:00have compact bone tissue on the superficial layers so there's outer compact bone tissue forming the
9:08epiphyses and then inside it is the spongy bone material lots of branching out of the bone tissue
9:17and lots of spaces that are filled with blood vessels nerves and red bone marrow so we find red
9:22bone marrow in the epiphyses also the epiphysis have smooth areas these smooth areas are where
9:29joints are formed and that's also where we define articular cartilage also found at the epiphysis
9:35is in adults epiphyseal line calcified structure in children it's called the epiphyseal plate and
9:44it's made of cartilage so for children at the epiphyseal plate which is the growth plate in
9:49adults at the epiphyseal line which is calcified and adults bones no longer grow in length
9:57again at the smooth ends of the epiphyses we have articular cartilage hyaline cartilage that helps
10:05to reduce shocks at the joints surrounding the rest of the outside of the bone is connective
10:11tissue structure called the periosteum it holds blood vessels and nerves tight helps to hold them
10:17next to the bone also so we find osteoprogenitor cells osteoblast and osteoclasts endosteum
10:26endosteum is on the inside lining the inside of cavity lining all these little nooks and crannies
10:32of the spongy bone it is just like the periosteum but by surprise on the inside of the bone
10:40alright here's a close-up of some compact bone tissue as you can see there's these little
10:46circular concentric circular ring structures here's one here's one there's one over here
10:51these reoccurring ring-like structures are called osteons so compact bone tissue has lots and lots
10:58of osteons here's a close-up of an osteon we see in the center is a space called central
11:04canal these will we find blood vessels and nerves each layer each concentric ring of the osteon is
11:12lamella within lamellae we find these little pockets these little pockets are the lacunae
11:17where we find the osteocytes and then there's these teeny tiny little faint lines these are
11:21little canals connecting to the central canal so the nutrients can diffuse to the osteocytes and
11:28waste can diffuse out of the osteocytes back into the bloodstream and these little canals
11:33are called the canaliculi one canaliculus many caniliculi connecting the osteocytes
11:41in the lacunae to the central canal here is a model that we have in lab central canal blood
11:48vessels nerves each layer is lamella in the pockets of the lacunae osteocytes the angry
11:53eyes live in the lacunae and the little faint lines are the canaliculi spongy bone tissue is
12:01obviously formed differently it has all these girders that stretch out and interconnect with
12:07each other and with the contact bone tissue on the outside and these little girders are called
12:13trabeculae so spongy bone tissues made up of mini mini trabeculae when you look at the histology of
12:20spongy bone tissue you still find lamellae so layers of bone tissue thelamellae you still see
12:27the lacunae where the osteocytes live and the little canaliculi but there are no osteons no
12:34central canal no osteon and this is because the girders the trabeculae are thin enough
12:40that they can get everything they need from the blood vessels that are intertwined around
12:44the trabeculae and here is our bone wedge model on the outside is the periosteum on the inside
12:54endosteum here is the trabeculae of spongy bone most of this is compact bone tissue though with
13:00the osteons osteons osteon osteon osteon and the central canals in the center running the length of
13:06the bone we also have perforating canals these are openings carrying blood vessels along the
13:12width the perforating canal with central canals length we can see the little layers or lamella
13:20all right bone formation so we start off with an embryo with embryonic tissue and it is sort of
13:29where the bones will be so that issue goes through the process of intramembranous ossification other
13:34goes through endochondral ossification by first forming hyaline cartilage model so intramembranous
13:40ossification occurs in these flat bones of the skull flat bones of the skull so are sort of
13:47the big sheet of embryonic connective tissue and there'll be many many tiny ossification centers
13:52that will develop where the tissue becomes calcified or osteoblasts start laying down the
13:57bone tissue osteoblasts will spread out forming more bone tissue within the tissue forming there
14:03will be lacunae where osteocytes will develop the calcified bone tissue continues spread through the
14:10sheet getting bigger and bigger and eventually it'll all interconnect giving us a spongy bone
14:17tissue with the trabecula blood vessels will get incorporated and nerves will get incorporated and
14:21then eventually the sheets of spongy bone tissue will develop compact bone tissue on the outside
14:28to surround the spongy bone tissue and also a periosteum will form that's the process of
14:35intramembranous ossification for the bones of the skull and that's going to be the end of part one