Bones

**Axial Skeleton -** Cranium, vertebral column, ribs, sternum **Appendicular Skeleton -** shoulder girdle, arms, hands, pelvic girdle, legs, feet =Learn the Skeleton:= http://www.youtube.com/watch?v=p-RpCoBe4wI
 * __ 1. Identify the axial and appendicular subdivisions of the skeleton __**

The skeleton serves five functions in the human body. =Skeletal System Structures and Functions : http://www.youtube.com/watch?v= TnY6l9hMOew= **__ 3. Identify and classify different types of bone __**
 * __ 2. Describe the functions of the skeletal system __**
 * **Support** - gives the body its structure by providing a very strong framework. It also allows for posture; without bones, we could not stand up straight.
 * **Protection** - bones are very hard and therefore are good at protecting. Examples: the brain is protected by the spongy bone sandwich in the skull, the ribs protect vital organs in the thoracic cavity, the vertebrae surround and protect the spinal cord.
 * **Mobility** - bones can articulate with each other when pulled on by muscles because of our joints.
 * **Storage** - the bone ECM stores calcium and phosphorous salts and yellow bone marrow stores lipids.
 * **Hematopoiesis** - red bone marrow produces new blood cells. Red bone marrow is found in young bones. As we age, red bone marrow is converted into yellow bone marrow except in the ribs, sternum, and skull, pelvis, shoulder blades, vertebrae, and the cancellous ends of the femus and humerus.
 * **Long bones** - longer than they are wide. They consist of an epiphysis and diaphysis. Ex. femus, clavicle, radius
 * **Short bones** - approximately as wide as they are long. Ex. carpals and tarsals
 * **Flat bones** - flat and generally protective. Ex. ribs, skull
 * **Irregular bones** - these do not fit into the other categories. Ex. vertebrae
 * [|Sesamoid bones] - bones enclosed in a tendon. Ex. patella, certain metacarpals and metatarsals.

**__ 4. Describe some common bone markings and describe their function __** There are several different types of bone markings. Bone markings typically reveal where muscles, tendons, and ligaments were attatched and where blood vessels and nerves passed. There are two categories of bone markings; projections or processes, which grow from the bone surface, and depressions or vaities which are indentations in the bone. One bone marking, found only on the femur is a **trochanter**. A trochanter is a very large, irregulary shaped process (any bony prominence). The trochanter is part of the ball-and-socket joint connecting the femur with the pelvis, thus its function is to allow movement of the leg. A general example of a **process** would be the odontoid process in the axis, which fits into the bodyless atlas of the vertebra. Another common bone marking is **head**. The head is a bony expansion carried on a narrow neck. The function of the head, is similar to the trochanter, and allows bones to connect to one another, thus allowing movement. A **fossa**, which is found in the humerous (coronoid fossa) is a shallow, basin-like depression that often serves as an articular surface. One example of this is the coronoid fossa of the humerous fits with the semi-lunar notch of the Ulna, forming a joint, and allowing movement. Another kind of bone marking is a **foramen**, which is a round or oval opening through a bone. An example of a foramen is found in the pelvis (obturator foramen). Foramen genrally allow large vessels, or other tubelike structures to pass through them and avoid having to go around bones to reach their destination.


 * __5. Explain the process of homeostasis by describing how the body maintains blood calcium levels__**

Blood Calcium levels should always remain between 9mm of blood Ca/100 mL blood and 11mm of blood Ca/100mL blood. When there is too much Calcium in the blood a whole sequence of events occurs. First the increase will be picked up by chemoreceptors found in the hyperthalimus. Impulses will then be sent to the thyroid gland, which is the control center, in this case. The thyroid then sends a hormone called calcitonin to the bone matrix. In the bone matrix, osteoblasts will deposit the calcium in the extra cellular matrix which in turn lowers blood calcium levels. The blood will then return to homeostatic levels through what is called negative feedback. A similar process occurs when there is too little calcium in the blood. This decrease in blood calcium levels will once again be picked up by chemoreceptors, however, this time in the hypothalimus. The hypothalimus will then send impulses to the parathyroid gland which will send a parathyroid hormone (PTH) to the bone matrix. When this hormone is sent, three things occur. First, there is an increase in calcium reabsorbtion in the kidneys. Next, there is an increase in calcium absorbtion in the intestines. Finally, osteoclasts (not osteoblasts) relase calcium from the extra cellular matrix into the blood. This process will then cause an increase in blood calcium levels and blood will once again return to homeostatic levels through negative feedback.

Osteoblasts and osteoclasts play a key role in bone remodeling. When a bone is being constantly used, it needs to be remodeled so it can be stronger in order to support the body when it is being strained. In this situation, the osteo//blasts//, which are located in the periosteum (the nutrient sheath of the bone), help increase bone mass. Conversely, when a bone is not being used often, the bone is remodeled so it is smaller, since its size is unnecessary. In this case, the osteo//clasts// help break down the extracellular matrix of the bone, a process known as bone resorption. Osteo//cytes//, on the other hand, are vital for the bone to sustain itself as living tissue. Osteocytes are the most common cell in human bones. They are derived from osteoblasts, and are found in clusters known as osteons. Osteocytes are connected by canniculi, which help transfer materials such as minerals and waste.
 * __6. Distinguish between osteoblast, osteoclast and osteocyte function__**

The long bone of the body is distinguished by a long central shaft with two articulation points at end end. Some examples of long bones are the femur, tibia, fibula, humerous, ulner, and radius. The long bone is made up of both compact bone and spongy bone. The epiphysis of the long bone provides the body with movement and support. The epiphysis is made up of spongy bone and contains an epiphysial line, or growth plate. The spongy bone of the epiphysis allows allows it to articulate with other bones. The articular cartilage of the long bone provides provides support and movement. Comprised of smooth, light and avascular tissue, the articular cartilage of the bone allows for movement between the areas where the bones meet. The medullary cavity is responsible for hemopoetic blood cell production because it contains red marrow, which yields white and red blood cell production. The diaphysis of the bone is a long shaft comprised of compact bone that gives support to the bone and rest of the body. The periosteum is a nutrient sheath that covers the outside of the bone and protects the bone and gives the entire skeletal system protection from dangerous pathogens. The nutrient arteries, or branches, is a nutrient rich area of the bone that provides storage and protection of blood vessels and nutrients. The yellow marrow of the long bone is responsible for the storage of lipids.
 * __8. Relate the structure of long bone to its function__**

The bone matrix, also known as the Haversian System, is the microscopic system that makes up compact bone. The Haversian system is made up of coccentric circles, or lamallee, that circle around the haversian canal. Each lamallee contains a number of osteocytes, which are simply bone cells. Osteocytes are surrounded by laccnae and are connected to each other by canniculi, which helps exchange nutrients and metabolic waste. In addition, the ECM is also an important part of the bone matrix. The ECM provides support to the bone because it is comprised of strong fibers. Its strength also allows the bones to perform its function of support to the entire body. The ECM is also important for the storage of calcium and phosphorus salts, which can be used at any time by way of the homeostasis process. The bone matrix is also important part of the homeostatic process that regulates blood calcium levels in the body. If the blood calcium levels are too high, the bone matrix will receive calcitonin from the thyroid gland. In the bone matrix, the ECM will receive calcium and thus lower the blood calcium levels. If blood calcium levels are too low, the bone matrix will receive a parathyroid hormone from the parathyroid gland. In the bone matrix, the ECM will release calcium into the blood. http://www.youtube.com/watch?v=gc1SnqTz0Is The process of bone remodeling occurs quite frequently in the human body; without us even knowing it. Bone is often remodeled based on how much it is used, (the fibula being remodeled in soccer players for instance because of all of the strain put on it) but for the most part it is simply a maintenance process. Bone remodeling begins when osteoclasts are signaled to activate (a process called activation) and to begin to break down the calcium and phosphorous salt deposits stored in the extra cellular matrix of the bone in a process called bone resorption. When the necessary bone is removed, osteoblasts, which are used to build bones begin to fill the gaps created by the osteoclasts in a process known as formation. In the future we may be able to be control bone remodeling, as a result osteoporosis would be a thing of the past because osteoclasts could simply be switched off when they cease to serve a positive function. Also, broken bones could be healed much faster because we could increase the number of osteoblasts working on repairing the bone. [|Good Video] (scroll down to bone remodeling).
 * __9. Explain the role of the bone matrix__**
 * __10. Describe the mechanism of bone remodeling and predict how bone remodeling will impact the skeleton in the future__**

Two types of bone fractures are simple fractures and compound fractures. A simple fracture occurs when the bone does not penetrate the skin (closed). A compound fracture occurs when the bone does penetrate the skin (open). Compound fractures are dangerous because they greatly increase the chance of osteomyelitis, which is the bacterial infection of the exposed bone. Patients that have a compound fracture are given a large amount of antibiotics to prevent this. Two other subdivisions of fractures are incomplete fractures and complete fractures. An incomplete fracture occurs when a bone is fractured but does not seperate into different pieces while a complete fracture occurs when a bone is broken into different pieces. One type of incomplete fracture is a hairline or stress fracture. This thin crack in the bone is often the result of stress. Shinsplints are examples of hairline fractures. Greenstick is another type of incomplete fracture. It involves the splitting of a bone such as a branch from a sapling might split if bent. Greenstick occurs primarily in young bones, which are less ossified and contain more collagen in the ECM. One type of complete fracture is a spiral fracture, where the bone is twisted and broken into two pieces. Spiral fractures are common amongst sports injuries and are not too difficult to fix. Another type of complete fracture is a comminuted fracture, where a bone is broken into many pieces, rather than simply two pieces. Comminuted fractures are more common in osteoporotic, or brittle, bones. An impacted fracture is also a type of complete fracture. It occurs when a bone is broken and the two pieces of the same bone are forced into each other. Before healing, the two pieces must be pulled apart. Impacted fractures are often due to falling. Compression fractures are another type of complete fracture and involve different bones being forced into each other. Before healing, bones involved in compression fractures must also be pulled apart. A compression fracture could happen in the vertebrae. An avulsion is a fracture (usually complete) that takes place when a muscle tears off a piece of bone. This is more common in young athletes. Two other classifications of fractures are transverse and oblique. Both usually apply to complete fractures and describe the angle of the fracture. A transverse fracture is a break from one side of the bone striaight to the other. An oblique fracture is a break from one side of the bone diagonally to the other.
 * __11. Identify and describe the various types of bone fractures__**

__** Bone healing involves four major stages. When a bone is fractured, blood vessels running through the bone break and become disrupted, causing blood to swell in the area and form a **hematoma**. Because the bloodstream cannot get any blood to smoothly move in and out of the broken blood vessels, many living cells in the area are cutoff from receiving any nutrients or expelling any of their wastes. Consequently, cell death, known as **necrosis**, occurs at the site of the fracture. As the hematoma continues to swell, **phagocytes** come in to remove the cells that have died. This process, which is commonly known as the inflammatory process, also removes any debris or bacteria from the fracture site that can cause infection. The next stage after the formation of the hematoma is the formation of a **soft fibrocartilage callus** that develops over the site of the fracture. This callus, as well as **osteoblasts** that come into the area, help to heal and build new bone by laying down a **matrix of Calcium and Phosphorus salts**, **collagen fibers**, and **cartilage**. This matrix fills in the broken area of the bone and over time, continues to harden and become stronger so that the bone can continue healing. New blood cells form **granulation tissue** so that new trabeculae can be laid down and made stronger. The fibrocartilage callus is eventually replaced by a hard, **bony callus** made of spongy bone. This occurs as more and more **osteoblasts** migrate into the area to build bone. During the bone remodeling stage, the bone is restored close to its original shape, structure, and strength, based on the mechanical stresses that are place on it. A strong permanent "patch" forms at the fracture site, blood vessels are formed and the spongy bone has ossified.
 * __12. Describe the stages of bone healing
 * a) Hematoma Forms:**
 * b) Soft Callus Forms:**
 * c) Bony Callus Forms:**
 * d) Bone Remodeling:**