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© 2015 Pearson Education, Inc.

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1 © 2015 Pearson Education, Inc.

2 Skeletal system consists of:
Bone tissue Cartilage Dense connective tissue Soft connective tissue (bone marrow) Adipose tissue Blood Nervous tissue

3 Six Primary Functions of the Skeletal System
Support – forms the framework of the body. Protection – covers or surrounds internal organs Movement – along with the muscles, helps move the body. Mineral storage and homeostasis – calcium, phosphate. Blood cell formation (hemopoiesis) – houses red bone marrow that has stem cells to form RBC, WBC and platelets. Fat storage – bones store fat as yellow bone marrow.

4 Short bone: small, like cubes
carpal and tarsal bones Flat bone: like plates Bones of the cranium, scapula, ribs & hip Long bone: long and thin Bones of arm, forearm, thigh and leg Irregular bone: irregular, complex shape Vertebrae, facial bones Sesamoid bone: bones wrapped inside a tendon – patella Sutural bone: bones found between cranial bones

5 Bone markings are surface features that
help in naming of the bone parts provide information on muscle and ligament attachments, passage of blood vessels and nerves, and bone articulations used as landmarks by physicians to locate some of the internal structures

6 6

7 7 Trochanter Sinus Head Neck Tubercle Head Crest Sulcus Neck Fossa
Foramen Fissure Process Tuberosity Spine Ramus Line Facet Fossa Foramen Tubercle Ramus Trochlea Skull Pelvis Condyle Condyle Femur Humerus 7

8 Structure of a Long Bone Diaphysis (shaft)
Consists of a heavy wall of compact bone (dense bone) Medullary cavity: a cavity in the diaphysis that is filled with bone marrow in adults Epiphysis Two, the wide part at each end that articulate with other bones Mostly spongy (cancellous, trabecular) bone Spaces filled with bone marrow Covered with a layer of compact bone Metaphysis Where diaphysis and epiphysis meet Has the cartilagenous epiphyseal plate before puberty Articular cartilage Covers parts of the epiphysis that articulate with other bones Epiphysis Spongy bone Metaphysis Compact bone Diaphysis (shaft) Medullary cavity Metaphysis Epiphysis The structure of a representative long bone (the femur) in longitudinal section

9 Structure of a Flat Bone
Resembles a sandwich of spongy bone between two layers of cortex (compact bone) Marrow is present, but no large medullary cavity Within the cranium, the layer of spongy bone between the compact bone is called the diploë Diploë (spongy bone) Cortex (compact bone)

10 6-3 Bone (Osseous) Tissue
Bone (Osseous) Tissue is a supportive connective tissue Composed of solid extracellular matrix with dispersed cells Solid matrix: Calcium salt deposits around collagen fibers Cells : Prefix-osteo

11 Bone: Solid Matrix Calcium Salts-Inorganic Mineral component accounts for ~2/3 of bone weight. Calcium phosphate /Calcium hydroxide salts: Hydroxyapatite: Ca10(PO4)6(OH)2 Smaller amounts of calcium carbonate (~10% of mineral) 5% other minerals (fluoride, potassium, magnesium) Crystals are very hard, resist compression But inflexible and brittle. Collagen fibers-Organic Flexible and tough; can take twisting and bending but little resistance to compression Together, calcium salts and collagen fibers in the matrix give bone its strength, flexible and shatter-resistant properties

12 Bone contains four types of cells
Bone CellsCells : Prefix-osteo Bone contains four types of cells Osteoprogenitor (osteogenic) cells Osteoblasts Osteocytes Osteoclasts Cells make up only 2% of bone mass

13 Osteoprogenitor cells:
stem cells that divide and differentiate into osteoblasts. Located in the periosteum & endosteum. Osteoblasts: Produce new bone matrix (collagen fibers and calcium salts) in a process called ossification or osteogenesis Once trapped in matrix, osteoblasts become osteocytes

14 Osteocytes Mature bone cells formed by osteoblasts trapped in matrix Non-dividing cells Maintain bone tissue. Many fingerlike cytoplasmic extensions that pass through canaliculi in lamellae to connect to other osteocytes Osteoclasts Giant multinucleate cells derived from bone marrow myeloid stem cells Break down bone matrix-secrete acid & proteolytic enzymes in a process called osteolysis or resorption

15 Types of Bone Two types: Compact Spongy Compact bone tissue:
80% of bone - Makes up most of the diaphysis of long bone Supports movement and weight of the body Characterized by its dense arrangement

16 6-4 Compact Bone Osteon is the basic unit of compact bone. Composed of: Central canal: contains blood vessels & nerves Lacunae: Tiny cavities each containing one Osteocyte Lamellae: concentric layers of matrix arranged around the central canal (concentric lamellae) Canaliculi: Narrow passageways containing cytoplasmic extensions of osteocytes connect osteocytes to each other, to the central canal and to blood vessels

17 Compact Bone: Lamellae
Concentric lamellae: Found in Osteons, arranged around the central canal Circumferential lamellae: Inner and outer surfaces of dense bone Interstitial lamellae: Between the osteons, irregular shaped (remains of old osteons)

18 Spongy bone: Composed of a network of trabeculae. Lamellae present but not arranged as osteons. Lacunae, osteocytes, canaliculi present. Spaces between trabeculae give bone a “spongy” appearance. Contains bone marrow blood vessels, nerves. Lighter than compact bone Withstand stresses that arrive from many directions

19 Periosteum: Covers the outer surface of the bone (except in areas covered by articular cartilage).
Consists of two layers Outer, dense irregular connective tissue: Protection, Anchor blood vessels & nerves Attachment site for ligaments & tendons Inner, cellular layer containing osteoprogenitors and osteoblasts & osteoclasts: Active in bone growth, repair and remodeling Perforating fibers (Sharpey’s fibers): Collagen fibers that anchor periosteum to bone.

20 Endosteum: Lines the medullary cavity of compact bone
Single layer of reticular connective tissue containing osteoprogenitor cells, osteoblasts and osteoclasts Active in bone growth, repair and remodeling

21 Blood and nerve supply Blood vessels and nerves penetrate the bone through the periosteum at the nutrient foramen Join central canals via perforating canals

22 Bone marrow: Soft connective tissue
Adult Bone Marrow Distribution Red bone marrow Contains hematopoietic (hemopoietic) stem cells for RBC, WBC and platelets. Used in bone marrow transplantation Children contain mostly red bone marrow Medullary cavity & epiphyses of long bones and spongy bone of flat bones Adults, Red bone marrow is restricted to Mostly flat bones -skull, vertebrae, ribs, sternum and ilium Proximal epiphysis of humerus and femur bones.

23 Bone marrow Yellow bone marrow Widespread in adult
Adult Bone Marrow Distribution Yellow bone marrow Widespread in adult Found in medullary cavity and epiphyses of long bones and in spongy bone of flat bones Not found in skull flat bones, vertebrae, ribs, sternum and ilium, proximal epiphysis of humerus and femur bones Consists of Adipose tissue-energy reserves No longer produces blood cells

24 Bone Development Bone formation is called ossification or osteogenesis Begins in fetus with mesenchymal tissue that will undergo transformation to form bones. Two main forms of ossification Endochondral ossification: replacement of a hyaline cartilage “mold” with osseous tissue Intramembranous ossification: development of oseous tissue directly from mesenchyme or fibrous connective tissue

25 Endochondral Ossification
Most bones in body formed this way Bone is formed from a preexisting minature model composed of hyaline cartilage mesenchymal cells differentiate into chondroblast that lay down a cartilage matrix mold of the future bone. Surrounding membrane becomes the perichondrium. Compact and spongy bone will replace this cartilage by the process of ossification At the metaphysis, growth area called epiphyseal plate: cartilage is formed at the epiphyseal side cartilage is ossified on the diaphysis side

26

27 2. Conversion of perichondrium
to the periosteum: production of osteoblasts (no more chondrocytes)

28 Endochondral Ossification
5) Secondary ossification centers 6) The epiphyses fill with spongy bone. During development, bone replaces cartilage except at: Articular cartilage - at the epiphyseal ends (joint cavity)-remains Epiphyseal Plate - Thin cap of cartilage at the metaphysis - Eventually disappears signifying end of bone growth Endochondral Ossification Hyaline cartilage Epiphysis Articular cartilage Metaphysis Spongy bone Periosteum Compact bone Epiphyseal cartilage Diaphysis Secondary ossification center 28

29 Endochondral Ossification
Key point: Action at the metaphysis of growing long bones Chondrocytes at the epiphyseal side divide and enlarge Chondrocytes degenerate on diaphysis side Osteoblasts migrate towards the metaphysis and replace cartilage on the diaphysis side with bone 29

30 Bones grow in length until the epiphyseal plates ossify to become epiphyseal lines.
At puberty, higher levels of sex hormones stimulate osteoblasts resulting in dramatic bone growth. Eventually, osteoblasts produce bone faster than chondrocytes are producing the epiphyseal cartilage: Osteoblasts catch-up! Epiphyseal cartilage (plate) eventually disappears: Long bone stops growing in length between ages (Epiphyseal closure) Visible on X-rays as an epiphyseal line which remains after epiphyseal growth has ended

31 An x-ray showing epiphyseal plate in a child (arrows)
An x-ray showing epiphyseal lines in an adult (arrows) 31

32 Bone Growth Interstitial growth Growth in bone length Expansion and ossification of the cartilage matrix at the metaphysis. Complete between ages Appositional growth Growth in bone width layers of circumferential lamellae are deposited on outer surface of bone along periosteum; osteoclasts of the endosteum enlarge the medullary cavity May continue after end of puberty: strengthen and thicken the long bone with layers of circumferential lamellae At the end of puberty, interstitial growth stops while appositional growth may continue.

33 Appositional growth: Increase Bone Diameter
Bone matrix is removed by osteoclasts Adult Infant Bone matrix is deposited by osteoblasts

34 Intramembranous Ossification
Begins when osteoblasts differentiate within connective tissue (mesenchymal or fibrous) Starts in a fetus…..newborn skull still contains areas where process is not complete -- soft spots (fontanels) Produces dermal bones; Flat bones of skull Mandible Clavicle

35 Intramembranous Ossification
35

36 6-6 Bone Remodeling Bone continually undergoes changes – remodeling- maintains, recycles, and replaces Bone building (by osteoblasts) and bone recycling -osteolysis (by osteoclasts) During Development: deposition > resorption, bones get stronger At maturity: deposition = resorption: Bone structure maintained During aging: resorption > deposition, bones get weaker

37 6-7 Exercise, Hormones, and Nutrition
Effects of Exercise on Bone Exercise, particularly weight-bearing exercise, causes osteoblasts to build bone Mineral recycling allows bones to adapt to stress Heavily stressed bones become thicker and stronger Bone Degeneration Bone degenerates quickly Up to one third of bone mass can be lost in a few weeks of inactivity

38 Normal Bone Growth and Maintenance Depend on Nutritional and Hormonal Factors
Minerals: Calcium and phosphorous; smaller amounts of magnesium, fluoride, iron and manganese needed for remodeling and growth Vitamins: Vitamin C needed for normal production of collagen. Folic Acid and Vitamin B for protein production. Vitamin A stimulates osteoblasts Vitamins K and B12 help synthesize bone proteins

39 Calcitriol (activated vitamin D).
Hormones: Human growth hormone produced by pituitary gland stimulates osteoblasts, increase protein synthesis, and cell division at the epiphyseal plate and periosteum. Thyroid hormones (T3 and T4) promote bone growth via osteoblast stimulation Sex hormones (estrogen and androgens) initially stimulate bone growth by increasing osteoblast activity- growth spurt at puberty- but as their secretion increase, epiphyseal plates become ossified to form epiphyseal lines. Calcitriol (activated vitamin D). Helps absorb calcium and phosphorus from digestive tract Made in the kidneys Synthesized from a related steroid, cholecalciferol (vitamin D3) Insufficient vitamin D can result in rickets in children, or osteomalacia in adults

40 Fig

41 6-8 Calcium Homeostasis The Skeleton as a Calcium Reserve
Bones store calcium and other minerals These calcium ions are vital to several body functions including: Nerve conduction Muscle contraction Blood coagulation Cell-signalling Cofactor for enzymatic reactions

42 Calcium Regulation Calcium ions in body fluids must be tightly regulated: Homeostasis is maintained by parathyroid hormone (PTH) and calcitonin Parathyroid Hormone (PTH) Produced by parathyroid glands in neck Increases calcium ion levels in blood Calcitonin Secreted by parafollicular cells in thyroid gland Decreases calcium ion levels in blood

43 Low Calcium Ion Levels in Plasma
Figure 6-16a Factors That Alter the Concentration of Calcium Ions in Body Fluids Factors That Increase Blood Calcium Levels These responses are triggered when plasma calcium ion concentrations fall below 8.5 mg/dL. Low Calcium Ion Levels in Plasma (below 8.5 mg/dL) Parathyroid Gland Response Low calcium plasma levels cause the parathyroid glands to secrete parathyroid hormone (PTH). PTH Bone Response Intestinal Response Kidney Response Osteoclasts stimulated to release stored calcium ions from bone Rate of intestinal absorption increases Kidneys retain calcium ions Osteoclast more Bone calcitriol Calcium released Calcium absorbed quickly Calcium conserved Decreased calcium loss in urine ↑Ca2+ levels in bloodstream 43

44 HIgh Calcium Ion Levels in Plasma
Figure 6-16b Factors That Alter the Concentration of Calcium Ions in Body Fluids Factors That Decrease Blood Calcium Levels These responses are triggered when plasma calcium ion concentrations rise above 11 mg/dL. HIgh Calcium Ion Levels in Plasma (above 11 mg/dL) Thyroid Gland Response Parafollicular cells (C cells) in the thryoid gland secrete calcitonin. Calcitonin Bone Response Intestinal Response Kidney Response Osteoclasts inhibited while osteoblasts continue to lock calcium ions in bone matrix Rate of intestinal absorption decreases Kidneys allow calcium loss less Bone calcitriol Calcium absorbed slowly Calcium excreted Calcium stored Increased calcium loss in urine ↓Ca2+ levels in bloodstream 44

45 Table 6-2 Hormones Involved in Bone Growth and Maintenance
45

46 6-9 Fractures Fractures Cracks or breaks in bones
Caused by physical stress

47 Figure 6-17 Types of Fractures and Steps in Repair
REPAIR OF A FRACTURE Fracture hematoma Dead bone Bone fragments Spongy bone of external callus Periosteum Immediately after the fracture, extensive bleeding occurs. Over a period of several hours, a large blood clot, or fracture hematoma, develops. An internal callus forms as a network of spongy bone unites the inner edges, and an external callus of cartilage and bone stabilizes the outer edges. 47

48 Figure 6-17 Types of Fractures and Steps in Repair
External callus Internal callus External callus The cartilage of the external callus has been replaced by bone, and struts of spongy bone now united the broken ends. Fragments of dead bone and the areas of bone closest to the break have been removed and replaced. A swelling initially marks the location of the fracture. Over time, this region will be remodeled, and little evidence of the fracture will remain. 48

49 Major Types of Fractures
Closed (simple): skin is not broken Compound (open): fracture projects through the skin Comminuted fractures: presence of multiple bone fragments Greenstick fracture: partial fracture of the bone; one side breaks, the other side bends, typically in children Colles fracture: distal portion of radius, typically after reaching out to cushion a fall Pott’s fracture: fracture at the distal ends of tibia and fibula, common sports injury Stress fractures: microscopic fractures due to repeated stress to bones Hairline: Fine crack in which sections of the bone remain aligned

50 Figure 6-17 Types of Fractures
Colles fracture Greenstick fracture Pott’s fracture 50

51 6-10 Effects of Aging on the Skeletal System
Age-Related Changes Bones become thinner and weaker with age: demineralization of bone and brittleness occurs Demineralization: the loss of bone mass resulting from the loss of calcium and other minerals. Decreased collagen synthesis results in brittleness of bone Osteopenia natural age-dependent loss of bone begins between ages 30 and 40 osteoblast activity declines while osteoclast activity remains the same Women lose 8% bone mass per decade, men-3% The epiphyses, vertebrae, and jaws are most affected. Results in Fragile limbs Reduction in height Tooth loss .

52 Osteoporosis Severe loss in bone mass that compromises normal function Resorption>>deposition-bones more prone to fracture Commonly effects proximal ends of the femur, vertebrae and wrist. Menopausal women more affected due to decreased estrogen levels which is needed to stimulate osteoblast activity Men less affected since androgen production continues late in life Seen also in female athletes with too little body fat who have stopped menstruating, in astronauts, in Scandinavian population, cancer patients Detected by bone scans-Dual Energy X-ray Absorptiometry (DEXA)

53 Figure 6-18 The Effects of Osteoporosis on Spongy Bone
Normal spongy bone SEM  25 Spongy bone in osteoporosis SEM  21 53

54 Osteoporosis: Traditional Treatments
Calcium and vitamin D supplements Increased exercise Estrogen-replacement therapy in menopausal women (may increase breast cancer, stroke, heart disease) Osteoporosis: Newer Treatments SERMs: Selective Estrogen Receptor Modulators (Evista, tamoxifen) Biphosphonate drugs(Fosamax)-destroy osteoclasts Prolia: injected antibody that interferes with formation of osteoclasts

55 Osteoporosis Key is prevention Weight-bearing exercise and diet containing adequate amount of calcium and vitamin D throughout life and especially when young

56 Other Clinical Applications: Abnormalities of Bone Growth and Development

57 Pituitary growth failure
Inadequate growth hormone production in childhood Reduced epiphyseal cartilage activity; abnormally short bones leading to shorter stature Rare in United States; children treated with synthetic human growth hormone Module 5.6 Abnormalities of bone growth and devealopment produce recognizable physical signs Figure 1

58 Gigantism and Acromegaly
Overproduction of growth hormone before puberty-often due to pituitary tumor Produces height over 2.7 m (8 ft. 11 in.) Puberty often delayed Acromegaly Overproduction of growth hormone after epiphyseal cartilages close Bones get thicker, not longer, especially efffects face, jaw, and hands Module 5.6 Abnormalities of bone growth and development produce recognizable physical signs

59 Achondroplasia Common form of dwarfism
Defective endochondral ossification Dominant disorder: Mutation of FGFR3 gene which inhibits cartilage growth at epiphyseal plate Epiphyseal cartilage of long bones replaced by bone early in life Results in short limbs Trunk normal size Module 5.6 Abnormalities of bone growth and development produce recognizable physical signs Figure 2

60 Marfan's syndrome Inherited metabolic condition that results in abnormal connective tissue structure Excessive cartilage formation at epiphyseal plate Results in very tall person with long, slender limbs and cardiovascular problems. Module 5.6 Abnormalities of bone growth and development produce recognizable physical signs © 2013 Pearson Education, Inc. Figure 3

61 Heterotopic Bone Formation
Bone formation in inappropriate places such as within dermis, tendons, or skeletal muscles Caused by abnormal development of osteoblasts in connective tissue Fibrodysplasia ossificans progressiva (FOP) Rare genetic disorder Bone replaces skeletal muscles of back, neck and upper limbs Module 5.6 Abnormalities of bone growth and development produce recognizable physical signs

62 Osteomalacia Caused by a deficiency of Vitamin D Decreased Calcium minerals in the bone matrix; Bones become weak and bend easily. Called Rickets if it occurs in children

63 Paget’s disease: Adult onset bone remodeling disorder; overactive osteoclasts. Abnormal regrowth and brittle bone prone to fracture Osteogenesis imperfecta (Brittle bone disease): genetic disorder that causes deficiency of collagen fibers in the bone matrix; bones become brittle and fracture easily. Osteosarcoma: bone cancer. Osteomyelitis: bacterial infection of the bone.

64 Career corner Orthopedist: Doctors who specializes in diagnosing and treating disorders and injuries related to the musculoskeletal system-commonly treat bone and joint injuries and other bone conditions


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