The Skeletal System

1. The Skeletal System Support Protection Movement

2. Topics covered • Structure and development • Remodel and repair • How bones fit together to make the skeleton • How joints enable bones and muscles to work together • Problems with the skeletal system

3. Skeletal system consists of 3 types of connective tissue • Bones – the hard elements • Ligaments – dense, fibrous connective tissue that binds bone to bone • Cartilage – special connective tissue of fibrous & elastic collagen in a gel-like fluid called “ground substance”

4. Long bone

5. ligaments

6. Cartilage

7. Bones: The hard elements • Most bone mass consists of nonliving extra cellular crystals of calcium minerals • Also consists of: • Living bone cells, nerves and blood vessels (bones bleed when they are cut or broken!)

8. 5 Bone Functions • Support • Movement • Protection • Formation of blood cells • Mineral storage

9. 1. Support • Bones form the structure (skeleton) to which the skeletal muscles are attached • http://kidshealth.org/misc/movie/bodybasics/bodybasics_knee.html

10. 2. Movement • Bones support and interact with muscles making movement possible

11. 3. Protection • As hard elements bones surround and protect many delicate internal organs

12. 4. Blood cell formation • Certain bones contain cells that are responsible for making different types of blood cells

13. 5. Mineral Storage • Calcium, phosphates which are important to metabolic function • http://www.octc.kctcs.edu/GCaplan/anat/Notes/API%20Notes%20H%20Skeletal%20System.htm

14. Long bones • Longer than wide • Cylindrical shaft called diaphysis • Enlarged knobs at each end called epiphysis • Compact bone forms the shaft and covers each end • Central cavity of the shaft is filled with yellow bone marrow (primarily fat for energy)

15. Epiphysis • Inside each epihysis is spongy bone that is less dense than compact bone making it light, but strong • Spongy bone is a lattice work of hard relatively strong trabeculae (L. little beams) made of calcium, minerals and living cells

16. Long bone special function • Upper arms and legs (humerous and femur) contain spaces between the trabeculae that are filled with red bone marrow. • Stem cells in the red marrow are responsible for the production of red and white blood cells and platelets

17. Outer surface - periosteum • Bones are covered by tissue called periosteum that contains specialized bone forming cells: osteocytes (Gk. Bone & cells) • Osteocytes are arranged in rings in cylindrical structures called osteons (sometimes called Haversian systems)

19. Periosteum cont’d • As bone develops and hardens osteocytes become trapped in chambers called lacunae – but stay in touch with each other via canals called canaliculi. • Canaliculi are used to pass nutrients between adjacent osteocytes to nurture bone cells when far from blood vessels

20. Osteocytes in lacunae • Waste products diffuse in the opposite direction and are removed by the blood vessels for transport to urinary system

21. Osteocytes in trabeculae • In spongy bone osteocytes don’t need canals for nutrients and waste transportation – the trabeculae structure gives the osteocytes access to nearby blood vessels in the red marrow • http://cellbio.utmb.edu/microanatomy/bone/compact_bone_histology.htm

22. Ligaments hold bones together • Attach bone to bone • Packed collagen fibers all oriented in the same direction • Confer strength to certain joints while permitting movement of bones in relation to each other

23. Cartilage lends support • Fibers of collagen and elastin in a ground substance of mostly water • Smoother and more flexible than bone • Found where support under pressure is needed and where some movement is necessary

24. 3 types of cartilage • Fibrocartilage – found in areas requiring ability to withstand high pressure & tension (intervertebral discs, menisci of knees) • Hyaline cartilage – forms the embryonic structures that become bones; covers the end of mature bones in joints • Elastic cartilage – highly flexible (ears, epiglottis

25. Development of bone • Chondroblasts – cartilage forming cells of earliest stages of fetal development • At 2-3 months in utero the cartilage models begin to dissolve and are replaced by bone = ossification • When chondroblasts die the matrix they produced breaks down making room for blood vessels

26. Development continued • The blood vessels carry osteoblasts (Gk bone + to form) into the area where the matrix was from the periosteum. • Osteoblasts secrete osteoid (a mixture of proteins and collagen) that becomes the strong internal structure of the bone • Osteoblasts also secrete enzymes that help form hydroxyapatite (crystals of hard mineral salts around the osteoid matrix)

27. Eventually mature osteocytes become embedded in hardened lacunae where they maintain the bone matrix • Bones continue to lengthen throughout childhood and adolescence because of the growth plate (epiphyseal plate) in each epiphysis • As bone lengthens the plates at each end grow farther apart • Bones also grow in width as osteoblasts lay down bone just below periosteum

28. Bone development controlled by hormones • Growth hormone during preadolesence • Sex hormones during puberty stimulate growth plates at first • By 18 in women and 21 in men the same sex hormones signal the growth plates to stop growing • Growth plates close but bones can still grow wider

29. Remodeling and repair • Bone is either forming or disintegrating as long as you live • Osteoclast (Gk: bone + to break) is another type of bone cell that cuts through mature bone tissue and dissolves the hydroxyapatite and digests the osteoid matrix • Released calcium and phosphate ions enter the blood

30. Bone remodel & repair • Where bone has been removed osteoblasts are attracted to lay down new osteoid matrixes and stimulate new deposits of hydroxyapatite crystals

31. Bones change size, shape & strength • Compression causes tiny electrical currents (jogging) within the bone that stimulate bone-forming activity of the osteoblasts • So new bone is laid down in areas under high compressive stress and bone is reabsorbed in areas of low stress

32. Weight-bearing exercise increases bone mass! • Jogging, weight lifting causes your bones to become stronger & more dense • Homeostasis of bone structure depends on a balance of the activities of the osteoblasts and osteoclasts • Osteoporosis – great loss of bone mass due to imbalance of the activities of the 2 types of bone cells

33. Your body will take minerals from your bones if blood levels are low • PTH will stimulate osteoclasts to dissolve bone • About 10% of bone is remodeled or replaced each year in young adults

34. Repair - fractures • First a blood clot or hematoma forms at the break site as the bone bleeds • Inflammation, swelling and pain immobilize the area • Repair begins within days as fibroblasts migrate to the area • Some become chondroblasts and together with fibroblasts make a callus

35. Repair • The callus appears between the broken ends of the bone • Osteoclasts arrive and clear fragments of original bone as well as the blood cells of the hematoma • Finally osteoblasts arrive to lay down new matrix and start hydroxyapatite formation & callus becomes bone

36. Repair • Bones rarely break in the same place twice because the repaired area is thicker than the original bone • The repair process slows with age and applications of weak electrical current can increase the rate of healing – perhaps by attracting osteoblasts

37. The skeleton protects, supports and permits movement • Classification of 206 bones: • Long bones – limbs, finger • Short bones - wrists • Flat bones – cranium, sternum, ribs • Irregular bones – coxal (hip), vertebrae

38. 3 functions of skeleton • Support of soft organs • Protection from injury (skull) • Permits flexible movement (joints0

39. Skeletal organization • Axial skeleton – skull, vertebral column, ribs, sternum • Appendicular skeleton – pectoral girdle, pelvic girdle, limbs

41. Axial – Skull bones • Cranial – flat bones enclose and protect brain • Frontal bone: forehead and upper ridges of eye sockets • Parietal bones: upper left and right sides of skull • Temporal bones: lower left and right (ears)

43. Skull bones cont’d • Sphenoid bone: back of the eye sockets • Ethmoid bone: contributes to eye sockets and helps to support the nose • Occipital bone: curves underneath to form the back & base of the skull • Foramen magnum (L. great opening): where vertebrae connects to skull

45. But wait, there’s moreSkull bones! • Facial bones - front • Maxilla – forms part of eye sockets and sockets to anchor upper row of teeth • Palatine bones – hard palate (roof of mouth) • Vomer bone – behind palatine & part of nasal septum

47. But wait, there’s moreSkull bones! • Zygomatic bones: cheek bones & outer portion of eye socket • Nasal bones: underlie the upper bridge of nose (space between maxilla & nasal bones is the nasal cavity) • Lacrimal bones: inner eye sockets with tear duct (drains to nasal cavity)

49. All skull bones joined tightly except for mandible (speak & chew) • Mandible: lower jaw w/ sockets for teeth • Sinuses are air spaces which make the skull lighter and give the human voice its tone and resonance • Each sinus is lined with tissue that secretes mucus & connects to nasal cavity by small passageways