Spongy Bone. Spongelike appearance formed by plates of bone called trabeculae. spaces filled with red bone marrow

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1 Spongy Bone Spongelike appearance formed by plates of bone called trabeculae spaces filled with red bone marrow Trabeculae have few osteons or central canals no osteocyte is far from blood of bone marrow Provides strength with little weight trabeculae develop along bone s lines of stress 1

2 Spongy Bone Structure and Stress 2

3 Bone Marrow In medullary cavity (long bone) and among trabeculae (spongy bone) Red marrow like thick blood reticular fibers and immature cells Hemopoietic (produces blood cells) in vertebrae, ribs, sternum, pelvic girdle and proximal heads of femur and humerus in adults Yellow marrow fatty marrow of long bones in adults Gelatinous marrow of old age yellow marrow replaced with reddish jelly 3

4 Intramembranous Ossification Condensation of mesenchyme into trabeculae Osteoblasts on trabeculae lay down osteoid tissue (uncalcified bone) Calcium phosphate is deposited in the matrix forming bony trabeculae of spongy bone Osteoclasts create marrow cavity Osteoblasts form compact bone at surface Surface mesenchyme produces periosteum 4

5 Intramembranous Ossification 1 Produces flat bones of skull and clavicle. 5

6 Intramembranous Ossification 2 Note the periosteum and osteoblasts. 6

7 Stages of Endochondral Ossification 7

8 Endochondral Ossification 1 Bone develops from pre-existing model perichondrium and hyaline cartilage Most bones develop this process Formation of primary ossification center and marrow cavity in shaft of model bony collar developed by osteoblasts chondrocytes swell and die stem cells give rise to osteoblasts and clasts bone laid down and marrow cavity created 8

9 Primary Ossification Center and Primary Marrow Cavity 9

10 Endochondral Ossification 2 Secondary ossification centers and marrow cavities form in ends of bone same process Cartilage remains as articular cartilage and epiphyseal (growth) plates growth plates provide for increase in length of bone during childhood and adolescence by early twenties, growth plates are gone and primary and secondary marrow cavities united 10

11 Secondary Ossification Centers and Secondary Marrow Cavities 11

12 The Metaphysis Zone of reserve cartilage = hyaline cartilage Zone of proliferation chondrocytes multiply forming columns of flat lacunae Zone of hypertrophy = cell enlargement Zone of calcification mineralization of matrix Zone of bone deposition chondrocytes die and columns fill with osteoblasts osteons formed and spongy bone is created 12

13 Fetal Skeleton at 12 Weeks 13

14 LAB 14

15 Pelvic Girdle Girdle = 2 hip bones Pelvis = girdle and sacrum Supports trunk on the legs and protects viscera Each os coxae is joined to the vertebral column at the sacroiliac joint Anteriorly, pubic bones are joined by pad of fibrocartilage to form pubic symphysis 15

16 Pelvic Inlet and Outlet False and true pelvis separated at pelvic brim Infant s head passes through pelvic inlet and outlet 16

17 Os Coxae (Hip Bone) Acetabulum is hip joint socket Ilium iliac crest and iliac fossa greater sciatic notch contains sciatic nerve Pubis body, superior and inferior ramus Ischium ischial tuberosity bears body weight ischial spine lesser sciatic notch between ischial spine and tuberosity ischial ramus joins inferior pubic ramus 17

18 Comparison of Male and Female Female lighter, shallower pubic arch( >100 degrees), and pubic inlet round or oval Male heavier, upper pelvis nearly vertical, coccyx more vertical, and pelvic inlet heart-shaped 18

19 Femur and Patella (Kneecap) Nearly spherical head and constricted neck ligament to fovea capitis Greater and lesser trochanters for muscle attachment Posterior ridge called linea aspera Medial and lateral condyles and epicondyles found distally Patella = triangular sesamoid 19

20 Tibia Tibia is thick, weightbearing bone (medial) Broad superior head with 2 flat articular surfaces medial and lateral condyles roughened anterior surface palpated below patella (tibial tuberosity) distal expansion = medial malleolus 20

21 Fibula Slender lateral strut stabilizes ankle Does not bear any body weight spare bone tissue Head = proximal end Lateral malleolus = distal expansion Joined to tibia by interosseous membrane 21

22 The Ankle and Foot Tarsal bones are shaped and arranged differently from carpal bones due to load-bearing role of the ankle Talus is most superior tarsal bone forms ankle joint with tibia and fibula sits upon calcaneus and articulates with navicular Calcaneus forms heel (achilles tendon) Distal row of tarsal bones cuboid, medial, intermediate and lateral cuneiforms 22

23 The Foot Remaining bones of foot are similar in name and arrangement to the hand Metatarsal I is proximal to the great toe (hallux) base, shaft and head Phalanges 2 in great toe proximal and distal 3 in all other toes proximal, middle and distal 23

24 END OF LAB 24

25 Bone Growth and Remodeling Bones increase in length interstitial growth of epiphyseal plate epiphyseal line is left behind when cartilage gone Bones increase in width = appositional growth osteoblasts lay down matrix in layers on outer surface and osteoclasts dissolve bone on inner surface Bones remodeled throughout life Wolff s law of bone = architecture of bone determined by mechanical stresses action of osteoblasts and osteoclasts greater density and mass of bone in athletes or manual worker is an adaptation to stress 25

26 Dwarfism Achondroplastic long bones stop growing in childhood normal torso, short limbs spontaneous mutation during DNA replication failure of cartilage growth Pituitary lack of growth hormone normal proportions with short stature 26

27 Mineral Deposition Mineralization is crystallization process osteoblasts produce collagen fibers spiraled the length of the osteon minerals cover the fibers and harden the matrix ions (calcium and phosphate and from blood plasma) are deposited along the fibers ion concentration must reach the solubility product for crystal formation to occur Abnormal calcification (ectopic) may occur in lungs, brain, eyes, muscles, tendons or arteries (arteriosclerosis) 27

28 Mineral Resorption from Bone Bone dissolved and minerals released into blood performed by osteoclasts ruffled border hydrogen pumps in membrane secrete hydrogen into space between the osteoclast and bone surface chloride ions follow by electrical attraction hydrochloric acid (ph 4) dissolves bone minerals enzyme (acid phosphatase) digests the collagen Dental braces reposition teeth and remodel bone create more pressure on one side of the tooth stimulates osteoclasts to remove bone decreased pressure stimulates osteoblasts 28

29 Calcium and Phosphate Phosphate is component of DNA, RNA, ATP, phospholipids, and ph buffers ~750 g in adult skeleton plasma concentration is ~ 4.0 mg/dl 2 plasma forms: HPO -2 4 and H 2 PO - 4 Calcium needed in neurons, muscle contraction, blood clotting and exocytosis ~1100g in adult skeleton plasma concentration is ~ 10 mg/dl 29

30 Ion Imbalances Changes in phosphate levels = little effect Changes in calcium can be serious hypocalcemia is deficiency of blood calcium causes excitability of nervous system if too low muscle spasms, tremors or tetany ~6 mg/dl laryngospasm and suffocation ~4 mg/dl with less calcium, sodium channels open more easily, sodium enters cell and excites neuron hypercalcemia is excess of blood calcium binding to cell surface makes sodium channels less likely to open, depressing nervous system muscle weakness and sluggish reflexes, cardiac arrest ~12 mg/dl Calcium phosphate homeostasis depends on calcitriol, calcitonin and PTH hormone regulation 30

31 Carpopedal Spasm Hypocalcemia demonstrated by muscle spasm of hands and feet. 31

32 Hormonal Control of Calcium Balance Calcitriol, PTH and calcitonin maintain normal blood calcium concentration. 32

33 Calcitriol (Activated Vitamin D) Produced by the following process UV radiation and epidermal keratinocytes convert steroid derivative to cholecalciferol - D3 liver converts it to calcidiol kidney converts that to calcitriol (vitamin D) Calcitriol behaves as a hormone that raises blood calcium concentration increases intestinal absorption and absorption from the skeleton increases stem cell differentiation into osteoclasts promotes urinary reabsorption of calcium ions Abnormal softness (rickets) in children and (osteomalacia) in adults without vitamin D 33

34 Calcitriol Synthesis and Action 34

35 Calcitonin Secreted (C cells of thyroid gland) when calcium concentration rises too high Functions reduces osteoclast activity as much as 70% increases the number and activity of osteoblasts Important in children, little effect in adults osteoclasts more active in children deficiency does not cause disease in adults Reduces bone loss in osteoporosis 35

36 Correction for Hypercalcemia 36

37 Parathyroid Hormone Glands on posterior surface of thyroid Released with low calcium blood levels Function = raise calcium blood level causes osteoblasts to release osteoclaststimulating factor (RANKL) increasing osteoclast population promotes calcium resorption by the kidneys promotes calcitriol synthesis in the kidneys inhibits collagen synthesis and bone deposition by osteoblasts Sporatic injection of low levels of PTH causes bone deposition 37

38 Correction for Hypocalcemia 38

39 Other Factors Affecting Bone Hormones, vitamins and growth factors Growth rapid at puberty hormones stimulate osteogenic cells, chondrocytes and matrix deposition in growth plate girls grow faster than boys and reach full height earlier (estrogen stronger effect) males grow for a longer time and taller Growth stops (epiphyseal plate closes ) teenage use of anabolic steroids = premature closure of growth plate and short adult stature 39

40 Fractures and Their Repair Stress fracture caused by trauma car accident, fall, athletics, etc Pathological fracture in bone weakened by disease bone cancer or osteoporosis Fractures classified by structural characteristics break in the skin multiple pieces 40

41 Types of Bone Fractures 41

42 Healing of Fractures 1 Normally 8-12 weeks (longer in elderly) Stages of healing fracture hematoma (1) - clot forms, then osteogenic cells form granulation tissue soft callus (2) fibroblasts produce fibers and fibrocartilage hard callus (3) osteoblasts produce a bony collar in 6 weeks remodeling (4) in 3 to 4 months spongy bone replaced by compact bone 42

43 Healing of Fractures 2 43

44 Treatment of Fractures Closed reduction fragments are aligned with manipulation and casted Open reduction surgical exposure and repair with plates and screws Traction risks long-term confinement to bed Electrical stimulation used on fractures if 2 months necessary for healing Orthopedics = prevention and correction of injuries and disorders of the bones, joints and muscles 44

45 Fractures and Their Repairs 45

46 Osteoporosis 1 Bones lose mass and become brittle (loss of organic matrix and minerals) risk of fracture of hip, wrist and vertebral column complications (pneumonia and blood clotting) Postmenopausal white women at greatest risk by age 70, average loss is 30% of bone mass black women rarely suffer symptoms 46

47 Osteoporosis 2 Estrogen maintains density in both sexes (inhibits resorption) testes and adrenals produce estrogen in men rapid loss after menopause, if body fat too low or with disuse during immobilizaton Treatment ERT slows bone resorption, but increases risk breast cancer, stroke and heart disease PTH (parathyroid hormone) slows bone loss if given daily injection Forteo increases density by 10% in 1 year may promote bone cancer best treatment is prevention -- exercise and calcium intake (1000 mg/day) between ages 25 and 40 47

48 Spinal Osteoporosis 48