1. Skeletal System: Bones and Bone Tissue

2. Functions of the Skeletal System 1.Support. Bone is hard and rigid; cartilage is flexible yet strong. Cartilage in nose, external ear, thoracic cage and trachea. Ligaments- bone to bone 2.Protection. Skull around brain; ribs, sternum, vertebrae protect organs of thoracic cavity 3.Movement. Produced by muscles on bones, via tendons. Ligaments allow some movement between bones but prevent excessive movement 4. Storage. Ca and P ions. Stored then released as needed. Fat stored in marrow cavities 5. Blood cell production. Bone marrow that gives rise to blood cells and platelets

3. Components of Skeletal System Bone Cartilage: three types –Hyaline –Fibrocartilage –Elastic We’ve done this I know Tendons and ligaments

4. Hyaline Cartilage Consists of specialized cells that produce matrix –Chondroblasts: form matrix –Chondrocytes: surrounded by matrix; found in lacunae Matrix. Collagen fibers for strength, proteoglycans for resiliency Perichondrium. Double-layered C.T. sheath. Covers cartilage except at articulations Articular cartilage. Covers bones at joints; has no perichondrium Growth

5. Bone Histology Bone matrix. –Organic: collagen and proteoglycans –Inorganic: hydroxyapatite. CaPO 4 crystals If mineral removed, bone is too bendable If collagen removed, bone is too brittle

6. Bone Cells Osteoblasts –Formation of bone through ossification or osteogenesis. Collagen and proteoglycan produced by E.R. and packaged by golgi app. Released by exocytosis. Precursors of hydroxyapetite stored in matrix vesicles, then released by exocytosis. –Ossification: formation of bone by appositional growth. Osteoblasts communicate through gap junctions.

7. Bone Cells Osteocytes. Mature bone cells. Surrounded by matrix, but can make small amounts of matrix to maintain it. –Lacunae: spaces occupied by osteocyte cell body –Nutrients diffuse through tiny amount of liquid surrounding cell and filling lacunae and canaliculi. Then can transfer nutrients from one cell to the next through gap junctions.

8. Bone Cells Osteoclasts. Resorption of bone –Ruffled border: where cell membrane borders bone and resorption is taking place. –H ions pumped across membrane, acid forms, eats Stem Cells. Mesenchyme (Osteochondral Progenitor Cells) become chondroblasts or osteoblasts.

9. Woven and Lamellar Bone Woven bone. Collagen fibers randomly oriented. –Formed During fetal development During fracture repair Remodeling –Removing old bone and adding new –Woven bone is remodeled into lamellar bone Lamellar bone –Mature bone in sheets called lamellae. Fibers are oriented in one direction in each layer, but in different directions in different layers for strength.

10. Cancellous (Spongy) Bone Spongy bone, provides most of the strength in a bone and is filled with marrow.

11. Compact Bone Central or Haversian canals: parallel to long axis Lamellae: concentric, circumferential, interstitial Osteon or Haversian system: central canal, contents, associated concentric lamellae and osteocytes Compact bone is very dense and hard. It is found mainly near the surface of a bone, where it provides great strength.

12. Compact Bone Osteons (Haversian systems) –Blood vessel-filled central canal (Haversian canal) –Concentric lamellae of bone surround central canal –Lacunae and canaliculi contain osteocytes and fluid

13. Bone Shapes Long –Ex. Upper and lower limbs Short –Ex. Carpals and tarsals Flat –Ex. Ribs, sternum, skull, scapulae Irregular –Ex. Vertebrae, facial

14. Structure of a Long Bone Diaphysis –Shaft –Compact bone Epiphysis –End of the bone –Cancellous bone Epiphyseal plate: growth plate –Hyaline cartilage; present until growth stops Epiphyseal line: bone stops growing in length Medullary cavity: In children medullary cavity is red marrow, gradually changes to yellow in limb bones and skull (except for epiphyses of long bones). Rest of skeleton is red.

15. Structure of a Long Bone, cont. Periosteum –Outer is fibrous –Inner is single layer of bone cells including osteoblasts, osteoclasts and osteochondral progenitor cells –Fibers of tendon become continuous with fibers of periosteum. –Sharpey’s fibers: some periosteal fibers penetrate through the periosteum and into the bone. Strengthen attachment of tendon to bone. Endosteum. Similar to periosteum, but more cellular. Lines all internal spaces including spaces in cancellous bone.

16. Structure of Flat, Short, and Irregular Bones Flat Bones –No diaphyses, epiphyses –Sandwich of cancellous between compact bone Short and Irregular Bone –Compact bone that surrounds cancellous bone center; similar to structure of epiphyses of long bones –No diaphyses and not elongated Some flat and irregular bones of skull have sinuses lined by mucous membranes.

17. Bone Development Intramembranous ossification –Takes place in connective tissue membrane Endochondral ossification –Takes place in cartilage Both methods of ossification –Produce woven bone that is then remodeled –After remodeling, formation cannot be distinguished as one or other

18. Intramembranous Ossification Takes place in connective tissue membrane formed from embryonic mesenchyme Forms many skull bones, part of mandible, diaphyses of clavicles When remodeled, indistinguishable from endochondral bone. Centers of ossification: locations in membrane where ossification begins Fontanels: large membrane-covered spaces between developing skull bones; unossified

19. Intramembranous Ossification

20. Endochondral Ossification Bones of the base of the skull, part of the mandible, epiphyses of the clavicles, and most of remaining bones of skeletal system Cartilage formation begins at end of fourth week of development Some ossification beginning at about week eight; some does not begin until 18-20 years of age

21. Endochondral Ossification

23. 6-23 Endochondral Ossification

25. Growth in Bone Length Growth in length occurs at the epiphyseal plate Involves the formation of new cartilage by –Interstitial cartilage growth –Appositional growth on the surface of the cartilage Closure of epiphyseal plate: epiphyseal plate is ossified becoming the epiphyseal line. Between 12 and 25 years of age Articular cartilage: does not ossify, and persists through life Appositional growth only –Interstitial growth cannot occur because matrix is solid –Occurs on old bone and/or on cartilage surface

26. Growth at Articular Cartilage Increases size of bones with no epiphyses: e.g., short bones Chondrocytes near the surface of the articular cartilage similar to those in zone of resting cartilage

27. Fracture of the Epiphyseal Plate

28. Growth in Bone Width

29. 5. Bones are covered by a connective tissue membrane, the___________________, which is capable of laying down fresh layer of bone and thus increasing the diameter of the bone. 6. The main shaft of a long bone is know as its _______________________. 7. The expanded ends of the bone are called_______________________. 6-29

30. Factors Affecting Bone Growth Size and shape of a bone determined genetically but can be modified and influenced by nutrition and hormones Nutrition –Lack of calcium, protein and other nutrients during growth and development can cause bones to be small –Vitamin D Necessary for absorption of calcium from intestines Can be eaten or manufactured in the body Rickets: lack of vitamin D during childhood Osteomalacia: lack of vitamin D during adulthood leading to softening of bones –Vitamin C Necessary for collagen synthesis by osteoblasts Scurvy: deficiency of vitamin C Lack of vitamin C also causes wounds not to heal, teeth to fall out

31. Factors Affecting Bone Growth (cont.) Hormones –Growth hormone from anterior pituitary. Stimulates interstitial cartilage growth and appositional bone growth –Thyroid hormone required for growth of all tissues –Sex hormones such as estrogen and testosterone Cause growth at puberty, but also cause closure of the epiphyseal plates and the cessation of growth

32. Bone Remodeling Converts woven bone into lamellar bone Caused by migration of Basic Multicellular Units –Groups of osteoclasts and osteoblasts that remodel bones Involved in bone growth, changes in bone shape, adjustments in bone due to stress, bone repair, and Ca ion regulation Relative thickness of bone changes as bone grows. Bone constantly removed by osteoclasts and new bone formed by osteoblasts. Formation of new osteons in compact bone –Osteoclasts enter the osteon from blood in the central canal and internally remove lamellae. Osteoblasts replace bone –Osteoclasts remove bone from the exterior and the bone is rebuilt

33. Bone Repair 1.Hematoma formation. Localized mass of blood released from blood vessels but confined within an organ or space. Clot formation. 2.Callus formation. Callus: mass of tissue that forms at a fracture site and connects the broken ends of the bone. –Internal- blood vessels grow into clot in hematoma. Macrophages clean up debris, osteoclasts break down dead tissue, fibroblasts produce collagen and granulation tissue. Chondroblasts from osteochondral progenitor cells of periosteum and endosteum produce cartilage within the collagen. Osteoblasts invade. New bone is formed.

34. Bone Repair, cont. 3.Callus ossification. Callus replaced by woven, cancellous bone 4.Bone remodeling. Replacement of cancellous bone and damaged material by compact bone. Sculpting of site by osteoclasts

35. Calcium Homeostasis Bone is major storage site for calcium The level of calcium in the blood depends upon movement of calcium into or out of bone. –Calcium enters bone when osteoblasts create new bone; calcium leaves bone when osteoclasts break down bone –Two hormones control blood calcium levels- parathyroid hormone (PTH) and thyroid hormone, calcitonin.

36. Calcium Homeostasis

37. Bone Fractures Open (compound)- bone break with open wound. Bone may be sticking out of wound. Closed (simple)- Skin not perforated. Incomplete- doesn’t extend across the bone. Complete- does Greenstick: incomplete fracture that occurs on the convex side of the curve of a bone Hairline: incomplete where two sections of bone do not separate. Common in skull fractures Comminuted fractures: complete with break into more than two pieces

38. Bone Fractures, cont. Impacted fractures: one fragment is driven into the cancellous portion of the other fragment. Classified on basis of direction of fracture Linear Transverse Spiral Oblique Dentate: rough, toothed, broken ends Stellate radiating out from a central point.

39. Bones and Joints Immovable joints like the ones in the skull are held together by joints we may call sutures. Sutures are held together by a thin layer of dense fibrous connective tissue.

40. Slightly movable joints are found between vertebrae. These joints, which are made of cartilage help absorb shock.

41. The most common joints are freely movable joints that are enclosed by a joint capsule composed of connective tissue, and a lubricant, called synovial fluid. Hinge joints can move in one direction wile ball. Ball in socket joints have a full range of movement

42. What are the five main functions of the skeletal system. What are the 3 main Components of Skeletal System What is Bone matrix? What do osteoblasts do? What is an Osteocyte? What do osteoclasts do?

43. Some marrow of long bones is termed "red" marrow. The function of this is to? The shaft of a bone is known as the? The growth zone of a long bone is referred to as the______________ The end of a long bone is referred to as the________________ If the collagen and minerals are removed from a bone, what happens to the bone? Give an example of the following bones Long Short Flat Irregular 6-43

44. Intramembranous ossification Takes place in connective tissue ________________ Endochondral ossification Takes place in __________ How does Calcium Homeostasis work? How are immovable joints held together? Give examples of slightly movable joints. Name two bones that are held together with a ball-in-socket joint. Name two bones that are held together with a hinge joint. 6-44