1. Ivyanatomy.com Chapter 7

2. Osteology is the science of bones Bones are a living dynamic tissue: constantly remodeled through life Functions of Bone: Protection – brain is protected by the skull & heart and lungs by the thoracic cage Support & Movement – muscles attach to the skeleton Calcium and Phosphate storage Blood Cell Production – blood cells are produced by red bone marrow

3. Red Bone Marrow – site of blood cell production Locations of Red Bone Marrow: Infant – all bones are filled with red bone marrow Adult – red bone marrow is limited to flat bones (sternum, ribs, skull, hips) and irregular bones (vertebrae) Yellow Bone Marrow – Adipose tissue

4. The cells associated with bones include: Osteocytes = cells that maintain bone. o Osteocytes reside within chambers, called lacunae Osteoblasts = cells that deposit new bone. Once mature, osteoblasts become osteocytes. Osteoclasts = cells that dissolve bone. Osteoclasts originate from white blood cells and they secrete an acid that dissolves the inorganic salts of bone.

5. The extracellular matrix of bones is composed of hydroxyapatite – a calcium phosphate salt that provides the hardness of bones collagen fibers – provides bone with some pliability

7. 1.Long bones = elongated diaphysis Humerus radiusulnametacarpalsphalanges Femur tibiafibula metatarsals phalanges 2.Short Bones = cube-shaped carpals tarsals 3.Flat Bones = plate-like Sternum, ribs, scapula parietal and frontal bones

8. 4.Irregular bones = variety of shapes vertebrae mandible maxilla ethmoid bone sphenoid bone 5.sesamoid (or round) bone = develops within tendons patella

9. Parts of a long bone Epiphysis = expanded end of bone Filled with spongy (cancellous) bone Proximal epiphysis & distal epiphysis Sites of articulation (joint) Diaphysis = shaft of long bone Lined with compact bone Articular cartilage = covers epiphyses Composed of Hyaline cartilage Epiphyseal line = remnant of bone growth (epiphyseal plate)

10. Parts of a long bone Medullary Cavity = chamber within diaphysis Filled with bone marrow, blood vessels and nerves Yellow Bone Marrow in adults Red Bone Marrow in children Endosteum = Membrane that lines medullary cavity Contains dense connective tissue Blood vessels and nerves osteoblasts Periosteum = Tough membrane covering the bone Composed of Dense Connective Tissue Blood Vessels, Nerves, Osteoblasts Continuous with tendons and ligaments

11. Parts of a long bone Compact bone Lines the Diaphysis and a thin layer surrounds the epiphyses Composed of osteons Spongy bone Fills the epiphyses and a thin layer lines the medullary cavity Trabiculae = thin bony plates Osteocytes lie within trabiculae

12. Compact Bone Osteon = Structural & functional unit of compact bone Lamella = concentric rings of bone around a central canal Central Canal (Haversian Canal) Contains blood supply and nerve Aligned parallel to diaphysis Lacunae = bony chamber that contains an osteocyte Osteocyte = maintains the bone Canaliculi = canals connecting osteocytes to the central canal Canaliculi are filled with cellular processes Pathway for nutrient and waste diffusion

13. Osteon continued Perforating Canal (Volkmann’s Canal) conveys blood from periosteum towards the central canal Aligned perpendicular to diaphysis

14. Compact bone is composed of osteons cemented together by bone matrix.

15. Bone Development and Growth Parts of the skeletal system begin to develop during the first few weeks of prenatal development Bone formation = ossification Bones replace existing connective tissue in one of two ways: As intramembranous bones As endchondral bones

16. Intramembranous Ossification Forms broad, flat bones of the skull Formed by replacing layers of embryonic connective tissue (mesenchyme) with bone Osteoblasts within mesenchyme deposit bony matrix in all directions Osteoblasts become osteocytes once surrounded by bone

17. Intramembranous Ossification Intramembranous ossification follows four steps. (a)Mesenchymal cells group into clusters, and ossification centers form. (b)Secreted osteoid traps osteoblasts, which then become osteocytes. (c)Trabecular matrix and periosteum form. (d)Compact bone develops superficial to the trabecular bone, and crowded blood vessels condense into red marrow.

18. Endochondral Bones Most of the bones in the skeleton are endochondral Bone formation begins with a hyaline cartilage model Cartilage decomposes and is replaced by bone.

19. Endochondral Ossification 1.Hyaline cartilage forms model of future bone 2.Cartilage degenerates and periosteum surrounds bone 3.Osteoblasts from periosteum invade the degenerating tissue 4.Osteoblasts beneath periosteum form compact bone at diaphysis = primary ossification center 5.Later, Osteoblasts form spongy bone at epiphyses = secondary ossification center

20. Endochondral Ossification Intramembranous ossification follows four steps. (a)Hyaline cartilage forms model of future bone (b)Cartilage degenerates and periosteum forms around bone (c)Primary ossification center forms compact bone within the diaphysis (e) Secondary ossification centers form spongy bone within the epiphyses (f)Some cartilage remains at the epiphyseal plates & as articular cartilage at the end of bones

21. Endochondral Ossification Two areas of endochondral bone retain cartilage after ossification. 1.Articular cartilage surrounds the epiphyses for joints 2.Epiphyseal plates retain cartilage for bone growth

22. Growth at the Epiphyseal Plate Epiphyseal Plate Band of hyaline cartilage that remains between the two ossification centers Bone growth continues at epiphyseal plates until adulthood. New cartilage is added towards the epiphysis and cartilage is ossified towards diaphysis Once the epiphyseal plates ossify the bones can no longer be lengthened

23. 4 Layers (zones) of growth at epiphyseal Plate 1.Zone of resting cartilage (reserve zone) Cartilage cells near epiphysis Do not participate in bone growth Anchor epiphyseal plate to epiphysis 2.Zone of proliferating cartilage Young chondrocytes undergoing mitosis Adds new cartilage to plate

24. (b) 4 Layers (zones) of growth at epiphyseal Plate 3.Zone of hypertrophic cartilage Older cells enlarge and thicken the epiphyseal plate Osteoblasts invade and calcify the cartilaginous matrix. 4.Zone of calcified cartilage Dead cells & calcium matrix Ossified bone (zone of ossification) Osteoclasts dissolve and phagocytize the matrix Osteoblasts invade the region and deposit new bone.

25. AgeOccurrence 3 rd month prenatal development Ossification begins in long bones4 4 th month prenatal development Most primary ossification centers have appeared in diaphysis of long bones. Birth to 5 yearsSecondary ossification centers appear in the epiphyses of long bones. 5 to 12 years (females) 5 to 14 years (males) Ossification rapidly spreads from the ossification centers 15 to 18 years (females) 17 to 20 years (males) Bones of the upper limbs and scapulae completely ossified. 16 to 21 years (females) 18 to 23 years (males) Bones of the lower limbs and hip bones completely ossified 21 to 23 years (females) 23 to 25 years (males) Bones of the sternum, clavicles, and vertebrae completely ossified. By 23 (females) By 25 (males) Nearly all bones completely ossified.

26. Bone Remodeling Calcium is constantly exchanged between the blood and bone. Bone resorption = Osteoclasts breakdown bone releasing calcium into the blood. Bone resorption occurs when blood [Ca 2+ ] is low and it’s stimulated by parathyroid hormone (PTH). Bone deposition = Osteoblasts deposit new bone from calcium in the blood stream. Bone deposition occurs when blood [Ca 2+ ] is high and it’s stimulated by the hormone calcitonin.

27. Vitamin D – promotes Ca 2+ absorption in small intestine Vitamin D deficiency = softened and deformed bones Osteomalacia in adults Rickets in children Vitamin A – balances bone resorption and deposition Vitamin A deficiency = retards bone development Vitamin C – is required for collagen synthesis. Vitamin C deficiency = results in fragile bones Nutrients that effect bone homeostasis

28. Growth Hormone (GH) Secreted from pituitary gland Promotes bone growth at epiphyseal plates Pituitary Gigantism over secretion of GH during childhood Pituitary Dwarfism insufficient GH during childhood Acromegaly Over secretion of GH as an adult Occurs after epiphyseal plates have sealed Enlargement of hands, feet, nose Hormones that affect bone homeostasis

29. Calcitonin Secreted from thyroid gland Promotes bone deposition Stimulates Osteoblast activity Inhibits Osteoclast activity Parathyroid Hormone (PTH) Secreted from parathyroid glands Promotes bone resorption Stimulates Osteoclast activity Inhibits Osteoblast activity Hormones that affect bone homeostasis Thyroid Gland

30. Blood Calcium Normal Range Increased blood calcium detected by cells in thyroid gland Thyroid Gland secretes Calcitonin Osteoblasts deposit calcium into bones Blood calcium returns to normal Blood calcium level increases Blood calcium level decreases Decreased blood calcium detected by cells in parathyroid gland Parathyroid glands secrete PTH Osteoclasts resorb bone to release Calcium into the blood

31. Sex Hormones (testosterone & estrogen) Promotes long bone growth at puberty Sex hormones also stimulate ossification at epiphyseal plates* *Estrogen has a stronger effect than testosterone on bone ossification, which is why ossification of the epiphyseal plates occurs earlier in development in females than in males. Hormones that affect bone homeostasis

32. Impacts of Exercise and Sunlight on Bone Homeostasis Exercise – especially resistance or strength exercise strengthens bones. Muscles pull on bones, and bones thicken in response. Sunlight – UV rays promote the release of Vitamin D from skin. Circulating vitamin D is activated in the liver, then it promotes the absorption of Calcium from the intestines.

33. Greenstick fracture One side of the bone bends, the other side breaks. Most common in children, because their bones are more pliable than adults. Fissured fracture Longitudinal break on the bone.

34. Transverse fracture Complete break perpendicular to the diaphysis Oblique fracture Complete break at any other angle not perpendicular to diaphysis

35. Comminuted fracture Results in several bony fragments Spiral fracture Results from twisting the bone

36. (a) Hematoma Formation Blood vessels rupture causing severe bleeding. The blood clots, forming a hematoma (b) Cartilaginous Callus Formation Fibroblasts deposit a mass of fibrocartilage (c) Bony Callus Formation Osteoblasts replace the cartilaginous callus with a bony callus (d) Bone Remodeling Osteoclasts and macrophages remove excess bone and debris Repair of a fracture

37. Osteopenia “low bone mass” Progresses towards osteoporosis Osteoporosis “porous bone” Bones develop spaces and canals Bones are fragile and easily broken Common in menopausal women (from the low estrogen levels) Over time, osteoclasts outnumber osteoblasts, and more bone is resorbed than can be deposited. Bone mass decreases as a result. Healthy Bone Osteoporosis Bone

38. Ways to delay or prevent osteoporosis: 1.Exercise daily. 2.Consume enough calcium and vitamin D every day. 3.Do not smoke.

39. Attribution Skeleton illustration Pixabay CC0 Public Domain https://pixabay.com/p-30160/?no_redirecthttps://pixabay.com/p-30160/?no_redirect Classification of bone by shape By BruceBlaus (Own work) [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons https://upload.wikimedia.org/wikipedia/commons/7/77/Blausen_0229_ClassificationofBones.pnghttps://upload.wikimedia.org/wikipedia/commons/7/77/Blausen_0229_ClassificationofBones.png Parts of a long bone By OpenStax College [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons https://upload.wikimedia.org/wikipedia/commons/2/23/603_Anatomy_of_Long_Bone.jpghttps://upload.wikimedia.org/wikipedia/commons/2/23/603_Anatomy_of_Long_Bone.jpg Diagram of Compact Bone By OpenStax College [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons https://upload.wikimedia.org/wikipedia/commons/5/58/624_Diagram_of_Compact_Bone-new.jpghttps://upload.wikimedia.org/wikipedia/commons/5/58/624_Diagram_of_Compact_Bone-new.jpg Diagram of Osteon By BDB [CC BY-SA 2.5 (http://creativecommons.org/licenses/by-sa/2.5)], via Wikimedia Commons https://upload.wikimedia.org/wikipedia/commons/7/75/Transverse_Section_Of_Bone.png https://upload.wikimedia.org/wikipedia/commons/7/75/Transverse_Section_Of_Bone.png Intramembranous ossification By OpenStax College [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons https://upload.wikimedia.org/wikipedia/commons/a/a9/611_Intramembraneous_Ossification.jpghttps://upload.wikimedia.org/wikipedia/commons/a/a9/611_Intramembraneous_Ossification.jpg Endochondral Ossification By OpenStax College [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons https://upload.wikimedia.org/wikipedia/commons/9/97/608_Endochrondal_Ossification.jpghttps://upload.wikimedia.org/wikipedia/commons/9/97/608_Endochrondal_Ossification.jpg Epiphyseal Plate By OpenStax College [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons https://upload.wikimedia.org/wikipedia/commons/1/15/622_Longitudinal_Bone_Growth.jpg https://upload.wikimedia.org/wikipedia/commons/1/15/622_Longitudinal_Bone_Growth.jpg Bone Remodeling By Cancer Research UK (Original email from CRUK) [CC BY-SA 4.0 (http://creativecommons.org/licenses/by-sa/4.0)], via Wikimedia Commons https://upload.wikimedia.org/wikipedia/commons/d/dd/Diagram_showing_bone_remodelling_Fig_CRUK_112.svg https://upload.wikimedia.org/wikipedia/commons/d/dd/Diagram_showing_bone_remodelling_Fig_CRUK_112.svg Types of Fractures By OpenStax College [CC BY 4.0 (http://creativecommons.org/licenses/by/4.0)], via Wikimedia Commons https://upload.wikimedia.org/wikipedia/commons/3/35/612_Types_of_Fractures.jpghttps://upload.wikimedia.org/wikipedia/commons/3/35/612_Types_of_Fractures.jpg Repair of Bone Fracture By OpenStax College [CC BY 3.0 (http://creativecommons.org/licenses/by/3.0)], via Wikimedia Commons https://upload.wikimedia.org/wikipedia/commons/1/12/613_Stages_of_Fracture_Repair.jpghttps://upload.wikimedia.org/wikipedia/commons/1/12/613_Stages_of_Fracture_Repair.jpg Normal and Degraded Bone By Gtirouflet (Own work) [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons https://upload.wikimedia.org/wikipedia/commons/8/8e/Bone_normal_and_degraded_micro_structure.jpg https://upload.wikimedia.org/wikipedia/commons/8/8e/Bone_normal_and_degraded_micro_structure.jpg