The Skeletal System

The Skeletal SystemRebecca Stolberg

A Brief IntroductionThe human skeletal system was built standing upright (erect), walking on two legs, as opposed to a construction where four legs are walked upon.By adulthood, the skeletal system is comprised of 206 bones. Bones are one of the hardest structures in the animal body yet they maintain some elasticity.Bones are divided into four classes: long, short, flat and irregular.The skeleton is divided into two parts:The axial skeleton The vertebral column, skull, ribs, and sternumThe appendicular skeleton The limbs

Bones: Why do we have them?SupportThe give the body a structure on which tissues can build upon to create a form.ProtectionSome bones protect organs from damage.MovementMovement using muscles is only possible due to the presence of bone support. StorageBones can store fat and some minerals. Blood cell formationMost of bloods components are made in the bone (marrow).

Bone CompositionCells & TissuesWhat cells are bones made of?There are 5 main types of bone cells:Osteogenic OsteoblastsOsteoclastsOsteocytesBone-lining

Note: Bones are also made of fat cells and nerve cells.

Compact Bone Cells What tissues are bones made of?Bones are made up of three tissue layers:PeriosteumCompact TissueCancellous (Spongy) Tissue

Osteogenic Cells

Osteogenic cells are found in the interior layer of the periosteum. Their purpose is to respond to trauma. Osteogenic cells do so by giving rise to bone making cells, know as Osteoblasts, and bone destroying cells, know as Osteoclasts. Pictured to the left are Osteogenic Stem cells from a human embryo. Osteoblasts & OsteoclastsOsteoblasts are bone forming and effecting cells. The produce bone by producing an organic extracellular matrix that will become mineralized bone. They affect changes in bone structures and are found in the periosteum.

Osteoclasts are large, multinucleated cells that break down (absorb) osseous tissue. They play a large part in the growth, healing and remodeling of bones. They are found in the lacunae, or little spaces, they carve out for themselves.

Osteoclasts and Osteoblasts working together during bone remodeling are called Basic Multicellular Units (BMUs).

Illustrated to the left are Osteoclasts and Osteoblasts from the jaw a calf embryo.

Osteocytes

Osteocytes are sensor cells that are encased in the Osteoblasts. The hardness of a bone comes from the Osteocytes. They are found in the compact bone tissue surrounding the caniculli and Heversian canals. They also sense mechanical stress and trigger bone remodeling. They transport minerals into and out of the bone. Pictured: Ocy=OsteocyteOcl= osteoclastsBone Lining Cells

Bone lining cells are also sensory cells that initiate bone remodeling. Bone cells are made from retired osteoblasts and are found along the bone surface of adults. They regulate the movement of calcium and phosphate out of the bone.

Pictured: Arrow points to bone lining cells.The Periosteum

The periosteum is a fibrous membrane that surrounds the (compact and cancellous) bones accept for where there is articular cartilage. It is incorporated where tendons and ligaments attach to the bone. It allows tendons and ligaments to assert and anchor themselves into the bone. It consists of two layers: the outer formed mainly of connective tissue and the inner layer of finer, elastic fibers that form membrane networks. It is houses osteoblasts.The Compact TissueCompact tissue is the hard part of the bone. However, at a microscopic level, it is actually not made of such densely packed cells. It has canals, canaliculi, which are filled with blood vessels. All of theses canals feed into larger canal known as the Haversian canals. These canals make the bone hollow. Compact bone is made of osteocytes and nerve cells.

12The Cancellous TissueBones get more hallow the closer you get the center of them. Spongy, Cancellous, tissue is not named such because it is spongy, it is named such because of its spongy, lacey appearance. The cancellous tissue in , especially in long bones (i.e. the femur) in adults, house red and yellow bone marrow and is where red blood cells are produced and yellow marrow is stored as fat.

Bone Systems Individual Bones, Bone Systems & the Skeletal SystemLong, Short, Flat and Irregular BonesLong BonesLong bones are located in the limbs, and are made of a shaft and two extremities. The clavicle, humerus, radius, ulna, femur, tibia, fibula, metacarpals, metatarsals, and phalanges are all long bones.Short BonesWhere the skeletal system was intended for strength with small size and limited movement exist small bones. Examples are the carsus and tarsus. The consist only of cancellous tissue surrounded by a thin layer of compact bone. Flat BonesIrregular BonesWhere bones serve a protective purpose or broad muscular attachment exist flat bones. The bones themselves can expand into plates as in the skull and scapula. The sternum and the ribs are also flat bones.Irregular bones is a self explanatory title that describes a small group of bones that do not fit into the proceeding categories. The include the vertebra, sacrum, coccyx, temporal, sphenoid, ethmoid, zygomatic, maxilla, mandible, palatine, inferior nasal concha, and hyoid.The Axial SkeletonThe axial skeleton refers to the 80 bones found in the upper body. Its main function is to protect organs, such as the brain and heart, and provide a structure. The skull, or cranium, houses your brain and provides structure for your mouth, eyes, ears and nose, amongst other things. It is made of 22 cranial and facial bones plus 3 ear bones on each side. Babies have more that will fuse together as they grow. The backbone, or vertebral or spinal column, is a flexible column made up of 26 bones. Babies have 33, but as they mature some fuse together to form the coccyx and others to form the sacrum. The Axial Skeleton also includes the bony thorax consisting of the breastbone ribs and sternum. There main function is to protect the heart and lungs.

The Appendicular SkeletonThe appendicular skeleton refers to al the bones in the arms and legs which are known as appendages and their girdles. The upper appendages, the arms and hands, are made of small, light bones designed to do work. The radius and the ulna created the forearm. The ulna connects with humerus at the elbow joint. The humerus connects to the shoulder via a ball and socket joint. The carpus, or wrist, is made of eight small bones that are connected via gliding joints. The metacarpals expand from there. The human thumb is an example of the metacarpals. From there we have the phalanges, or the fingers, Every finger, but the thumb, has three. The lower appendages, the legs and feet, are structured for support and designed for movements such as running and jumping. The pelvis and femur created the ball-and-socket hip joint, which allows for leg movement. The femur is the longest and strongest bone in the body. The tibia and the fibula make the lower leg and have a restricted range of movement. The feet have tarsus and metatarsus, which are similar to the hands carpals and metacarpals. It would be possible for our feet to be made entirely out of one bone, but the multitude of bones we have allow the feet to accommodate changes in terrain.

The EndFinally, all the bones come together to make the skeletal system (see slides two & three).Works CitedBone Cells. www.mnsu.edu. Minnesota State University Mankato. Web. 26 September 2010.

Gray, Henry. Anatomy of the Human Body. Philadelphia: Lea & Febiger, 1918. Print.

Skeletal System. www.thinkquest.org. Oracle ThinkQuest Education Foundation, 1996. 26 September 2010.

Union College Engineering. Bone Cells. Schenectady, NY, 2010. Print. Web.

Images CitedSkeleton, seen from the front (left) and rear (right). N.d. Elsevier. www.mercksource.com. Web. 26 September 2010.

Sharpey. Transverse section of compact tissue bone. Magnified. N.d. Anatomy of the Human Body. Henry Gray. Philadelphia: Lea & Febriger, 1918. Normal Bone. N.d. Osteonecrosis of the Jaw Center. www.onjcenter.com. Web. 26 September 2010. Amplification of Osteogenic Cells From Human Embryonic Stem Cells. N.d. Society for Biomaterials. www.biomaterials videos.org. Web. 26 September 2010. Klliker. Osteoblasts and osteoclasts on trabecula of lower jaw of calf embryo. N.d. Anatomy of the Human Body. Henry Gray. Philadelphia: Lea & Febriger, 1918. High power view of bone spicules with osteoclasts. N.d. www.outtawa.ca. Web. 26 September 2010. Compact Bone & Spongy (Cancellous Bone). N.d. Sydney Physiotherapy. www.sydneyphysio.com.au. Web. 26 September 2010. Bone Biopsy. N.d. Yale Medical Group. www.yalemedicalgroup.org. Web. 26 September 2010. The Axial and Appendicular Skeleton. N.d. EnCongnitive.com. www.encognitive.com. Web. 26 September 2010. <