okay in this video we're gonna talk about bone structure so bones are considered organs now we know that bone itself or osseous tissue is a tissue type you find in bones however bone also has nervous tissue cartilage other fibrous connective tissue muscle cells and epithelial cells and you find this all throughout bone therefore we consider bones as an organ themselves although they do contain bony tissue now we can look at bones in terms of different levels so the gross anatomical level which is basically what you can see with the unaided eye just basically visually what a bones look like we can also study bones at their microscopic and chemical levels which is ultimately we're going to focus on mostly in this chapter so there's two major types of boom we got compact bone versus spongy bone compact bone is a dense outer layer that you find on every bone that appears smooth and solid and it forms a nice sort of outer boundary to bones but it's typically kind of thin and deeper and bones you gonna find spongy bone which has made it more of a honeycomb small needle-like flat pieces of bone called trabeculae and these actually have open spaces that are filled with marrow either red or yellow marrow but spongy bone is kind of a lighter material that fills in bones it helps to make a bones lighter and also helps to resist tension in those bones as well now in terms of the structure of short irregular and flat bones you have thin plates of spongy bone or calls called die plow that are covered by compact bone now compact bone is sandwiched between connective tissue membranes called periosteum and endosteum periosteum is what surrounds the outside of compact bone you would find this surrounding the whole outer surface of bones of your body and the purpose of this is is that periosteum sir serves as a nice attachment point for tendons and ligaments it's kind of a dense fibrous tissue now endosteum is actually what covers the inner chambers of bone specifically spongy bone and you find this in the inner surfaces of that those die plow and what endosteum does it essentially nourishes the bone the inside because it's made of a kind of aerial or a type of connective tissue now bone marrow is also scattered throughout the budget spongy bone there's no defined marrow cavity in spongy bone however marrow is sort of distributed on all those spaces you also find that hyaline cartilage can cover the area of bone that's part of a movable joint so in bones that move against each other at a joint you often find highly cartilage cushioning that joint which we call articular cartilage so this is showing example of a flat bone here like your parietal bone if you zoom in on this you find that we have compact bone and compact bone with spongy bone sandwiched in the middle this spongy bone we call diploid and within these spaces you would find red or yellow marrow and endosteum would also line the inner surfaces of these spaces you can see that it's actually is pretty Airy in there there's a lot of space here and it essentially helps to make the bone less dense and therefore not as heavy now in terms of the structure of a typical long bone they all have a diaphysis and an epiphysis the diathesis is the shaft and the bony rounded ends are called the epiphysis the diathesis is a tubular shaft that forms a long axis of the bone consists of compact bone that surrounds a medullary cavity that's typically filled with yellow marrow epiphysis the rounded ends of the long bone that also have compact bone on the outside but they're filled with spongy bone internally and if also find that articular cartilage covers the joint surfaces at these ends as well which helps to form a nice protective cushion between these bones that are articulating you're connecting now between the diaphysis and epiphysis we actually have something called the epiphyseal line the epiphyseal line is the remnant of your growth plate also called the epiphyseal plate in the epiphyseal plate which will go to more detail in a future video but the epiphyseal plate is essentially made of hyaline cartilage and it divides to help form Karlos that becomes bone so looking at the structure of a typical long bone here we see that we have the articular cartilage at the ends or epiphysis and it helps to form a nice protective cushion where these bones would meet other bones and the whole rounded end of the long bone is called the epiphysis the centrally elongated portion is called a shaft or diaphysis you find that in the epiphysis you have a lot of spongy bone which would be filled with red or yellow marrow and then in the diathesis it's actually mostly just a large open cavity called the medullary cavity while medulla means marrow so it makes sense that the medullary cavity is the marrow cavity and in adults it contains a lot of yellow bone marrow which is basically just a lot of triglycerides so it's a way to store fat now the outside of your bones are surrounded by periosteum you can see that here where it's a kind of a dense fibrous tissue that surrounds the outside of the bone and then the inner surfaces would be lined with endosteum as well now bone is highly vascular which is why you see lots of blood vessels diving down into it and it makes sense why it's so vascular because bone is an organ it molds and changes quite a bit in fact the site of new bone growth lengthwise is called the epiphyseal plate now there is no growth plate here because this is an adult's bone and you can see that now it's called the epiphyseal line which is a little line of compact bone that used to be cartilage while this individual was growing this would have been a cartilaginous plate called the epiphyseal plate which forms a nice dividing line between the epiphysis in the diaphysis and in fact you'd find this epiphyseal line on both sides not just the proximal but also the distal epiphysis as well now if you zoom in on the edge of the bone here we find that compact bone lines the outside spongy bone is deeper there pretty just easily identifiable based on the fact that this one looks more dense and compact this one looks more spongy now compact bone is the one that's made of complete osteons you can see that here these sort of circular patterns here called osteons they're like rings on a tree and they essentially help to form the structural unit of compact bone now spongy bone is made of incomplete osteons and the reason why they're incomplete is they used to be from compact bone and this was broken down into something that became more spongy and dipole alike and if this is an area of both as an Arab joint typically gonna find some articular cartilage here which is a little band of hyaline cartilage that can help cushion between this bone and another bone that way you have cartilage bumping up against cartilage which forms a nice protective cushion now in terms of other membranes we have periosteum and endosteum remember periosteum peri means surrounding in ostium is bone so periosteum is a layer of whitish tissue that surrounds the outside of bone and other than the ones that part of it in joints so if there's articular cartilage there's no periosteum there otherwise the periosteum would surround the rest of the bone and there's two layers can we have a fibrous layer in osteogenic layer the fibrous layer is the outermost are more superficial and it consists of a dense irregular connective tissue in sharpies fibers that dive down in the bone is secured to the bony matrix itself now closer to the bone we have an osteogenic layer which is an inner layer so deeper that abuts the bone and contains these osteogenic cells or stem cells the function of osteogenic cells is to interesa Sencha lee help to divide into new bone forming cells to help either repair or replace damaged bone now we also find that periosteum contains on nerve fibers and blood vessels and this can help to nourish bone through nutrient foramen which allow for nerve fibers and blood vessels to dive down deep into bone so endosteum is much different than periosteum for one it's within bone hence the name endo so endosteum is within that bone it lines the inner surfaces of bone and it's more of a delicate connective tissue you know it's not really there for anchoring and support so much as nourishment of the inner lining of the bone and it covers the trabeculae of spongy bone you find this lining canals that pass through compact bone as well and like the periosteum you also find some osteogenic cells here which can help to differentiate into other bone cells especially if the bones been fractured you have another source of stem cells so just the differentiate between the two member we see our periosteum here we have two layers we have the fibrous layer and the osteogenic layer so the fibrous layer is more of a dense fibrous tissue whose function is to serve as attachment or anchoring of other tissues and the osteogenic layer will be right up against the bone this contains stem cells that can help to nourish the bone or at least replenish the bone or help with bone fracture repair inside of bone we have endosteum and endosteum is more of a areolar loose connective tissue that helps to nourish bone from the inside it also contains osteogenic cells that are there to help you know repair bone now what's interesting too is that within the bony chambers we can find red marrow or yellow marrow now red marrow is called that because it has kind of a reddish appearance to it you find this within the trabecular cavity it's a spongy bone of flat bones like your sternum and as well as the heads of your femur and humerus otherwise it's pretty difficult to find red marrow beyond that you find that most spaces within bone actually are filled with yellow marrow in adults however newborns the medullary cavity is and most spongy bone cavities contain red marrow it makes sense because newborns need a lot of blood cells now red marrow can be converted to red I'm sorry yellow marrow can be converted to red if a person becomes anemic so if someone has widespread blood loss their yellow marrow contains stem cells that can divide and then turn into red marrow to help replenish lost blood cells now bone markings are basically sites of muscle ligament and tendon attachment on external surfaces and these are often areas that are involved with joint formation or conduits for blood vessels and nerves so you find that a lot of blood Marquis I'm sorry bone markings are associated with the epiphysis of long bones and they can be things like projections or depressions or openings and they're often going to be passageways for you know nutrients or you know blood vessels to pass through bone or them or they can be attachment points for tendons and ligaments now there's three types of markings we got projections depressions and openings projections are an outward bulge of bone they could be due to increased stress for muscle pull depressions are a Bowl or groove like cut that serves as a passageway for vessels or nerves or plays a role in joints and then openings are basically holes or canals that serve as a passageway for blood vessels and nerves so what this table shows are just some of the different terms we use in anatomy to help differentiate between the different bone markings so these are showing the different types of projections remember projections are usually sites for a muscle and ligament attachment so we find that tuberosities or all those bony features that are large rounded projections that maybe roughened in a crest is more of a narrow Ridge of bone usually kind of prominent trochanter czar very large blunt you regularly shaped processes like the greater and lesser trochanter of the femur again these are projections for muscle attachment we have lines which are more of a narrow or rich so a line is like more of a narrow form of a crest so it's not as prominent tubercles are small rounded projections or processes also for bone or ligament attachment and then epicondyles are raised areas that are above a condyle and a condyle is essentially a smooth area of bone that's for joint articulation or connection in epicondyles are usually just near the condyle and they're also for muscle attachment spines are sharp slender processes and processes are just any raw bony prominence so you'll find is when you go through the gross anatomy of the skeletal system these words show up a lot you know there's different tuberosities of her body different crests and lines and tubercles and what's common is they are these features even though they would have a different name associated with them as well so projections that also helped to form joints are things like heads and facets a head is just a bony expansion on a narrow neck a facet is a smooth nearly flat articular surface and the way I remember facet is think of like a multi-faceted gym where the facet is the smooth kind of flat surface of a gym just like on bones the facets are the smooth and kind of flatter regions now condyles are a rounded articular projection example this is on the mandible here you have the Med tubular condyle which helps to form the temporomandibular joint and then a ramus is an arm like bar of bone so this is showing the mandibular ramus which is basically just a large projection that's arm like it's made of bony tissue now depressions and openings there's lots of different types you have grooves fissures foramen notches mattis's sinuses and fossa now a groove is just a furrow and then a fissure is more of a narrow slit like opening foramina are basically round oval openings and bone which typically allow for the passageway of blood vessels and nerves notches are just indentations and then me a toises or canal like passageways a fossa is just a shallow Basin like depression and bone and if sinus is actually considered a cavity within bones if you look here we can see the frontal sinus which is basically an air-filled cavity deep within your frontal bone just like we have a sphenoid sinus as well which is an air-filled cavity within the sphenoid bone this is showing the paranasal sinuses which are actually associated with your nasal cavity so people talk about a sinus infection we're talking about an infection within these air-filled cavities within the bone