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

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 Ossification35

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 Maintenance45

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