Skeletal System

1. Skeletal System Our support system

2. Two Types of Bone • There are two types of bone • Compact bone • The outer more dense portion of bone • Composed of cylinder of dense white osseous tissue

3. Sponge Bone • Despite its name it is relatively hard and strong • Name given because of the appearance of its cross section. • It provides support for bone marrow and reduces the density of bone

4. All bone is covered in periosteum which is a tough membrane that contains a network of blood vessels to supply nutrients, and nerves which signal pain. • Periosteum also works with tendons and ligament to attach bone together.

5. Histology and Bone Growth • Osteoprogenitor cells • non-specialized cells found in periosteum, endosteum, and central canal of compact bones; can turn into other types of cells as needed

6. Osteoblasts • cells that actually form bones; arise from non-specialized osteoprogenitor cells and are cells that secrete a matrix of calcium with other minerals that give bone its typical characteristics

7. Osteocytes • considered mature bone cells that started as osteoblasts; osteoblasts surround themselves with matrix to then become mature osteocytes • Osteoclasts • believed to originate from a type of white blood cell called monocyte found in red bone marrow; job is to tear down bone material and help move calcium and phosphate into blood; and aids in remodeling

9. Osteon: consisting of concentric bone layers called lamellae and the central canal • Lamellae: A thin layer of calcified matrix around a central canal • Central Canal: hollow tube with central to an osteon and provides an opening for blood vessels and nerves into the bone.

11. Osteocytes live in little “caves” called lacuna. • From their lacuna osteocytes reaches through canaliculior little tunnels to connect with one another or a blood supply.

12. Anatomy of a long Bone

13. Long bones are made up of a diaphysis and two epiphysis. • Proximal • Closer to the trunk • Distal • Further from the trunk

14. Long bones contain both yellow and red bone marrow. • Yellow marrow is located in the shafts of the long bones. • Yellow bone marrow contains mostly fat cells and works as an energy reserve • Red Marrow is found in spongy bone, the ends of long bones, Ribs, vertebrae, the sternum and the pelvis. • From specialized stem cells it produces red blood cells, platelets, and white blood cells.

15. Bone Growth • Most bones develop from cartilage • In the second month of fetal development, much of the skeleton is made of cartilage during, and in the third month, osteocytes begin to develop and release minerals that lodge in the spaces between the cartilage cells, turning the cartilage to bone. • Ossification: the process by which cartilage is slowly replaced by bone as a result of the deposition of minerals • Many area remain cartilage to lend flexibility and support to the body.

17. Bone Growth • There are two forms of bone growth intramembranous ossification and endochondral ossification. • Intramembranous ossification is how flat bones form • Endochondral is how long /short bones form

18. Endochondral Ossification • First there is a cartilage model that forms • Next osteoblasts are produced by the perichondrium and they form what is known as a bone collar around the middle of the cartilage • Encircling it like a napkin ring; providing physical reinforcement • What was perichondrium is now periosteum • Primary ossification center arises • Blood vessels penetrate the bony collar and will the primary ossification center into the primary marrow cavity. And the secondary ossification cent shows up.

19. Endochondral Ossification • The secondary ossification cent becomes hollowed out by the same process as the primary one creating a secondary marrow cavity in the epiphysis. • At the time of birth infant bones primarily look like step four. • During infancy and childhood, the epiphyses fill with spongy bone. • Cartilage is then limited to the articular cartilage covering each joint and the epiphyseal.

21. Bone Elongation and Appositional Growth • Bones continue to develop after a person’s birth • During early childhood and late adolescence bone cells gradually replace the cartilage of the epiphyseal plate in long bones • Such as the one on the arms and legs • Epiphyseal plate is composed of cartilage cells that divide and form columns, pushing older cells toward the middle of the bone • As older cells die the are replaced by new bone cells.

24. After a late adolescents the epiphyseal plate ossifies.

25. Appositional Growth (or widening of the bone)is where new bone is layed on the outside of the bone by osteoblasts and old bone is being broken down by osteoclast in the middle.

27. Joints • Joint: the place where two bones meet • Three major types of joints: • Fixed • Semimovable • Movable

28. Joints • Joint: the place where two bones meet • Three major types of joints: • Fixed • Semimovable • Movable

29. Fixed Joint • Fixed joints prevent movement • Found in the skull where they permit no movement of those bones • Small amount of connective tissue in a fixed joint also helps absorb impact to prevent the bones from breaking

30. Semimovable Joints • Semimovable joints permit limited movement • Found in the vertebral column; allow the body to bend and twist • Also found in the rib cage; connect the upper ten pairs of ribs to the sternum

31. Movable joints • Movable joints enable the body to perform a wide range of movements and activities • Include: • Hinge • Ball-and-socket • Pivot • Saddle • Gliding

32. Movable Joints • Hinge joint: found in the elbow • Ball-and-socket: shoulder joint • Pivot joint: formed between the top two vertebrae in the neck • Saddle: found at the base of each thumb • Gliding: fount between the small bones of your foot

34. Joint Structure • Joints are subjected to a great deal of pressure and stress, but their structure is well suited to meet these demands • Bones that come into contact are covered with cartilage • Protects against friction

35. Joint Structure • Ligaments: tough bands of connective tissue • Hold the bones of the joint in place • Synovial fluid: lubricating substance that helps protect the ends of bones from damage by friction

36. Joint Structure • Knee joint is the most susceptible because it carries the body’s weight

37. Joint Structure • Arthritis: used to describe disorders that cause painful, swollen joints • Two forms of arthritis: • Rheumatoid arthritis: develops when the immune system begins to attack body tissues • Osteoarthritis: degenerative joint disease in which cartilage becomes thinner and rougher, so bones rub against each other