The Skeletal System

1. The Skeletal System Chapter 6 Anatomy and Physiology Mr. Knowles Liberty Senior High School

2. Question of the Day! Do bones remain the same? How do bones “know” when to stop growing? What happens when they don’t?

3. The Skeletal System! Our First System Cells (Osteocytes) Tissues (Osseous Tissue) Organs (Bones) Systems (Skeletal)

4. All C.T. have Three Parts 1. Specialized Cells 2. Extracellular Protein Fibers 3. The Fibers above and a ground substance (usually a liquid)- make up the Matrix that surrounds cells. (most of the volume of C.T.)

5. The Fibers • Collagen Fibers- long, straight, unbranched, fibers of twisted protein; rope-like, very flexible, yet strong. (Tendons and Ligaments)

6. Bone (Osseous Tissue) • G.S. = almost no liquid; collagen fibers + calcium salts (CaPO4 and some CaCO3) • Strong and flexible properties. • Lacunae in matrix contain osteocytes.

7. Bone (Osseous Tissue) • Lacunae organized around a central canal (Haversian canal) which contains blood vessels. • Diffusion cannot occur through calcium salts. • Cytoplasm of osteocytes extend to central canal by canaliculi.

8. A Basic Pattern in Bone Tissue • Lacunae with osteocytes arranged around and connected to a central canal by radiating canaliculi- Osteon • Many osteons in one bone.

10. Bone-Low Mag.

11. Haversian or Central Canal

12. Bone-High Mag.

13. Osteons

14. Bone (Osseous Tissue) • Bone surfaces covered by periosteum- fibrous layer of C.T.; attachment for tendons and ligaments. • Site of appositional growth of bone. • Bone is constantly remodeled- grow thicker with stresses.

17. Anatomy of Bone (4 Parts) 1. Diaphysis- long, tubular shaft, mostly compact bone. 2. Epiphysis- expanded areas at the ends of bone, mostly spongy bone.

21. Anatomy of Bone (4 parts) 3. Marrow Cavity- core of bone with red and yellow marrow. 4. Metaphysis- area that connects the epiphysis and diaphysis. Contains the Epiphyseal plate- area of growth between epiphysis and diaphysis

22. Other Parts to Bone • Periosteum- outermost layer of bone made of cells and fibers. Provides the point of attachment for tendons and ligaments on the outside. Route for vessels to enter the bone. Participates in bone growth and repair.

25. Other Parts of the Bone • Endosteum- a layer of cells that lines marrow cavity; lines trabeculae of spongy bone and central canal of compact bone. Also site of bone growth.

26. Two Types of Osseous Tissue 1.Compact bone- dense bone, solid, more on surface of bone, shaft of bone. Function: osteons are all aligned;strengthen bone, the tissue of bone is parallel to stresses.

27. Two Types of Osseous Tissue 2. Spongy Bone- open network of trabeculae which are struts and plates in the interior of bone (matrix) , light in weight; Function: has no osteons; withstand stress from a variety of directions, reduce the weight of the overall bone.

33. Bone Development • Skeleton begins to develop at 6 weeks after conception, embryo is only 12 mm (0.5 in ) long. • Bone growth continues through the age of 25 yrs. • Bone is continuously remodeled or reshaped.

34. How do bones grow in humans? Can we see bone growth in a developing embryo?

36. The Players in Osteogenesis Ossification- formation of bone is a dynamic process. Osteoblasts- produce new bone matrix. Osteoclasts- produce acids and enzymes to release the stored minerals in the matrix. Osteocytes- mature bone cells that do not divide.

37. Bone Grows in Two Ways • Intramembranous Ossification- bone forms from mesenchyme cells or fibrous connective tissue. Deep layers of the dermis. • Endochondral Ossification- bone replaces a mold of cartilage.

38. Intramembranous Growth Step 1: Mesenchymal cells (stem cells) cluster at a site (ossification center) within the dermis (skin layers) and secrete bone matrix (collagen + Ca +2). These cells will become osteoblasts. Step 2: Bone grows outward in spicules which will become the struts of spongy bone. Vessels grow into area. Step 3: Osteoblasts at the outer edge become less active and become osteocytes.

40. Intramembranous Bones • Dermal bones of the skull- parietal, occipital, etc, the mandible, the clavicle, and the scapula. • Bones that are mostly spongy tissue are made by intramembranous ossification.

41. Osteogenesis Intramembranous ossification- bone growth within C.T. (mandible, parietal) see p. 181, 4th Ed., Martini) Want to see what happens when this growth is uncontrolled? Heterotopic Bone Formation, p. 50 of the A.M.

42. Heterotopic Bone Formation

43. FOP

44. Endochondral Ossification • Endo means inside; -chondros means cartilage. • Bone tissue gradually replaces a cartilage model or mold for the bone. • Most bones form this way; all of the appendicular (limb) skeletal bones.

45. Endochondral Growth • Step 1: Cartilage forms a mold and the chondrocytes grow very large in the center of the mold. Lacunae expand and the matrix thins to struts. Chondrocytes die. • Step 2: Blood vessels grow into the shaft of cartilage; cells of the perichondrium become osteoblasts. The perichondrium now becomes the periosteum.

46. Endochondral Growth • Step 3: Blood supply increases; fibroblasts migrate to the center and become osteoblasts. They start to make spongy bone- Primary Center of Ossification. • Step 4: As bone enlarges, osteoclasts appear and erode the trabeculae in the center- creates the marrow cavity.

48. Show Me the BMU in Action!

49. Endochondral Ossification • Osteoblasts of the diaphysis and chrondrocytes of epiphysis continue to grow; elongate bone. • Epiphyseal Plate is the interface between the two. • At puberty, the osteoblasts overcome chondrocytes; the plate becomes more narrow- epiphyseal line.

50. Fetal Long Bone