THE SKELETAL SYSTEM

1. THE SKELETAL SYSTEM • Bone structure • Bone Development and Growth • Bone Remodeling • Organization of the Skeleton • Joints • Homeostasis

2. SKELETAL FUNCTION • SUPPORT • PROTECTION • AID IN MOVEMENT: muscle attachment • BLOOD CELL FORMATION: called hematopoiesis. • STORAGE: calcium and phosphate

3. BONE STRUCTURE • Bones are complex organs that are tough but flexible in a healthy individual and are in a state of constant change. • Types of Bone: four basic types • LONG BONES: greater in length than in width This structure is designed to absorb stress from body weight. Long bones are found in the arms, forearms, hands, thighs, legs, and feet.

4. SHORT BONES • Short bones are about equal in length and width, forming a shape that is roughly similar to a cube. • Examples: bones of the wrists and ankles.

5. FLAT BONES • Flat bones are thin and flat, as in the cranium of the head, the ribs, and the sternum.

6. IRREGULAR BONES • Irregular bones have complex shapes that do not fit into any of the previous three categories. • They include the vertebrae and bones of the face.

7. PARTS OF LONG BONES • The long central shaft is known as the diaphysis. It lies between the extreme ends of the bone, which are called epiphyses. • Eachepiphyses forms a joint, or articulation,with another bone. • Along its outer surface where the joint occurs is a thin layer of hyaline cartilage, called the articular cartilage.

8. A sheet of dense connective tissue envelops the bone, except in areas where the articular cartilage is present. • This important tissue is called the periosteum. It is firmly attached to the bone’s outer surface by special protein fibers, and contains a large supply of blood vessels.

9. PERIOSTEUM • It also contains a type of bone cell, the osteoblast, that is active in bone growth and repair. • Functions of the periosteum include bone nourishment, attachment to ligaments and tendons, and bone growth and repair.

10. DIFFERENCE BETWEEN EPIPHYSIS AND DIAPHYSIS:INTERNALLY • epiphysis: a spongy bone lattice network • diaphysis: a tightly packed compact bone • The many small spaces within the spongy-bone network are filled with blood-forming connective tissue known as RED MARROW

11. DIAPHYSIS • In diaphysis, the compact bone borders a central chamber that is continuous with many of the spongy-bone channels. • This large chamber is called the MEDULLARY CAVITY. It is filled with a second type of marrow called, YELLOW MARROW, which is rich in fatty tissue for energy storage.

12. Lining the interior surface of the medullary cavity and extending into spongy bone spaces is a thin membrane known as the ENDOSTEUM

13. BONE COMPOSITION • Bone is composed of bone tissue, cartilage,dense connective tissue, blood-formingtissue,blood vessels, and nerves. • Bone tissue is hard, strong, flexible tissue that is in a state of constant change. • During bone development, canals are provided for the passage of vessels and are maintained throughout life.

14. THREE TYPES OF BONE CELLS • OSTEOBLASTS: known as mesenchymal cells • usually found on the surfaces of bone tissues (within the periosteum) in the bones of adults. • Osteoblasts actively produce matrix (mineral salts and collagen)

15. OSTEOCYTES: Once the osteoblasts become trapped within the chambers (Lacunae), we call them osteocytes. • OSTEOCLASTS: are bone cells that wander throughout bone tissue, secreting a substance that dissolves the mineral salt crystals of the matrix.

16. MICROSCOPIC STRUCTURE OF BONE • Spongy bone consists of numerous thin plates of bone, known as TRABECULAE, that interconnect with one another, leaving spaces in between. • The spaces are filled with RED MARROW, which is the site of blood-cell formation (hematopiesis).

17. BONE DEVELOPMENT and GROWTH • Bone development begins within the first two months of prenatal life. • INTRAMEMBRANOUS bones: the cells develop between thin sheets of connective tissue, or embryonic membrane. • Bones originating from cartilage are called ENDOCHONDRAL bones.

18. In both methods of bone development, the OSTEOBLASTS secrete the new bone matrix composed of collagen and mineral salts. • This secretion of new bone matrix is called OSSIFICATION.

19. INTRAMEMBRANOUS BONES • The development of intramembranous bones begins soon after the formation of embryonic membranes, about the fifth week of life. • Bones that begin as intramembranous bones, develop into flat bones of the skull, the mandibles (lower jaw), and the clavicles (collarbones).

20. ENDOCHONDRAL BONES • Bones that form from cartilage include all but the flat bones of the skull, mandible, and clavicles. • Their development begins around the sixth week of life when clusters of precursor cells transform into cartilage-producing cells, called CHONDROBLASTS.

21. BONE GROWTH • Once an endochondral bone has been formed, it can increase in size in two directions: length and width. • Lengthwise expansion, or interstitial growth, is accomplished at the epiphyseal plate. • A long bone of a growing child will increase in length as long as the chondroblasts in the epiphyseal plate are active.

22. Once chondroblast activity stops, the epiphysis and the diaphysis permanently fuse, and lengthwise growth becomes no longer possible. • Along the area of fusion between epiphysis and diaphysis, a visible line of ossification called the epiphyseal line is formed in the bone.

23. A growing long bone normally undergoes an increase in width, called appositional growth, while it increases in length.

24. BONE REMODELING • Once an individual reaches a certain age, the genetic code commands the pituitary gland to stop the growth process, and growth in height comes to a halt as the epiphyseall plate disappears. • This does not mean the bones become inactive.

25. The process of osteoblast deposition of new bone and reabsorption of bone by osteoclasts continues throughout life. • In fact, every gram of bone tissue in your body will have been recycled at least twice by the time you reach the age of 60 years! • This process is known as BONE REMODELING.

26. Bone remodeling varies in activity from bone to bone, and even from bone area to bone area. • Some bones or bone areas, such as the distal part of the femur, are replaced every five to six months, whereas other bones are replaced much less frequently. • Most bones are not involved in remodeling.

27. In general, the bone areas that receive the greatest stress or injuries undergo more frequent remodeling.

28. ORGANIZATION OF THE SKELETON • The 206 bones of the human body are organized into a single, interconnected frame known as the skeleton. • Two parts: • axial skeleton: contains the bones that lie within the midvetical axis of the body. • appendicular skeleton: bones that lie outside the midvertical axis and are associated with the appendages.

29. AXIAL SKELETON • Skull: consists of the bones of the cranium and the facial bones. • Hyoid bone: a small bone in the anterior part of the neck. • Vertebral column: the backbone. It consists of the vertebrae and sacrum. • Thoracic cage: the bones in the chest region. The sternum and the 12 pairs of ribs that are attached to the vertebral column.

30. APPENDICULAR SKELETON • Pectoral girdle: a frame connecting the upper limbs to the axial skeleton. It contains a scapula and a clavicle on either side of the body. • Upper limbs: the upper appendages, each of which consists of a humerus, a radius, an ulna, carpals, metacarpals, and phalanges.

31. Pelvic girdle: the lower frame connecting the lower limbs to the axial skeleton. It contains two coxal (hip) bones. Together with the lower part of the vertebral column (the sacrum), they from the pelvis. • Lower limbs: the lower appendages, each of which include a femur, a patella, a tibia, a fibula, tarsals, metatarsals, and phalanges

32. SURFACE FEATURES OF BONES • Bone surfaces contain structural features that distinguish one bone from another but do not vary much from person to person. • The features of bones suggest their relationships to skeletal system functions. • They include: projections and depressions that may serve as attachment points for ligaments or tendons, to strengthen the bone,----------------------

33. or for articulation with other bones; openings to permit the penetration of blood vessels or nerves; and spaces for housing body structures. • show “SURFACE FEATURE TERMINOLOGY IN BONES” overhead

34. Bones of the Axial SkeletonSKULL • contains 22 bones • closely adjoined by rigid, narrow joints known as sutures. • chambers that are lined with mucous membranes and are filled with air, called sinuses

35. SKULL • They connect with the nasal cavity to drain fluids, reduce the weight of the skull, and resonate sound from the voice. • Inflammation of the mucous membranes lining the sinuses, which may be caused by an infection, is called sinusitis. • If the amount of swelling is sufficient to block the drainage channels into the nasal cavity, a buildup of fluid pressure can lead to a sinus headache.

36. Five bones of the skull contain sinuses: • the frontal bone • the ethmoid • the sphenoid • and the two maxillary bones.

37. The bones of the skull include 8 bones of the cranium and 13 smaller bones of the face known as facial bones. • Another bone of the skull is the single lower jawbone, the mandable, which hangs from attachments to the cranium.

38. CRANIUM • The cranium encloses and protects the brain within the space it creates, and provides an attachment site for muscles of the scalp, lower jaw, neck, and back. • It consists of eight bones: Frontal bone, Parietal bones, Occipital bone, Temporal bones, Sphenoid bone, Ethmoid bone

39. FRONTAL BONE • the large bone forming the anterior part of the skull above the eyes, or forehead. • Notice the large eye sockets, whose roofs are formed by the frontal bone. These sockets are called orbits. • Also note the small hole above each orbit. This is the supraorbital foramen, through which pass blood vessels and nerves.

40. Within the frontal bone are the frontal sinuses, one above each orbit near the midline.

41. PARIETAL BONES