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Presentation on theme: "BONES AND SKELETAL TISSUES"— Presentation transcript:


2 SKELETAL CARTILAGES Skeletal cartilages:
Made of some variety of cartilage Consists primarily of water High water content accounts for its resilience Ability to spring back to its original shape after being compressed Contains no nerves or blood vessels Surrounded by a layer of dense irregular connective tissue called the perichondrium Acts like a girdle to resist outward expansion when the cartilage is compressed Contains the blood vessels from which nutrients diffuse through the matrix to reach the cartilage cells This mode of nutrient delivery limits cartilage thickness

Hyaline Elastic Fibrocartilage All three types have the same basic components: Cells called chondrocytes Encased in small cavities (lacunae) within an extracellular matrix containing a jellylike ground substance and fibers

4 HYALINE CARTILAGE Looks like a frosted glass when freshly exposed
Provides support with flexibility and resilience Most abundant skeletal cartilage Chondrocytes appear spherical Only fiber type in the matrix is fine collagen fibers


6 HYALINE CARTILAGE Includes: Articular cartilages: Costal cartilages:
Cover the ends of most bones at movable joints Costal cartilages: Connect the ribs to the sternum (breastbone) Respiratory cartilages: Form the skeleton of the larynx (voicebox) Reinforces other respiratory passageways Nasal cartilages: Support the external nose


8 ELASTIC CARTILAGE Looks very much like hyaline cartilages, but they contain more stretchy elastic fibers and so are better able to stand up to repeated bending


10 ELASTIC CARTILAGE More flexible than hyaline Located only in the:
External ear Epiglottis of the larynx: Flap that bends to cover the opening of the larynx each time we swallow


12 FIBROCARTILAGE Highly compressible and have great tensile strength
Perfect intermediate between hyaline and elastic cartilages Consist of roughly parallel rows of chondrocytes alternating with thick collagen fibers


14 FIBROCARTILAGE Occur in sites that are subjected to both heavy pressure and stretch: Padlike cartilages (menisci) of the knee Discs between vertebrae


16 Growth of Cartilage Growth occurs in two ways:
Appositional growth (growth from the outside) results in outward expansion due to the production of cartilage matrix on the outside of the tissue Cartilage-forming cells in the surrounding perichondrium secrete new matrix against the external face of the existing cartilage tissue Interstitial growth (growth from inside) results in expansion from within the cartilage matrix due to division of lacunae-bound chondrocytes and secretion of matrix Lacunae-bound chondrocytes divide and secrete new matrix, expanding the cartilage from within

17 Growth of Cartilage Typically, cartilage growth ends during adolescence when the skeleton stops growing Under certain conditions—during normal bone growth in youth and during old age—calcium salts may be deposited in the matrix and cause it to harden, a process called calcification NOTE: calcified cartilage is NOT bone

206 named bones of the human skeleton are divided into two groups: Axial skeleton: Forms the long axis of the body Protect, support, or carry other body parts Includes: Skull Vertebral column Rib cage Appendicular skeleton: Bones of the upper and lower limbs, and the girdles (pectoral/shoulder and pelvic/hip) that attach them to the axial skeleton Help us to get from place to place (location)


Classified by shape: Long Short Flat Irregular


22 Long Bones Longer than they are wide:
Have a definite shaft and two ends Consist of all limb bones except patellas, the carpels (wrist), and tarsals (ankles) Named for their elongated shape, NOT their overall size Example: the three bones in your fingers (digits) are long bones, even though they are very small


24 Short Bones Somewhat cube-shaped Include: Carpals: wrist
Tarsals: ankle Sesamoid bone: Shaped like a sesame seed Special type of bone that forms in a tendon Example: patella Vary in size Some clearly act to alter direction of pull of a tendon Functions of others is not known


26 Flat Bone Thin, flattened and often curved Include: Most skull bones
Sternum (breastbone) Scapulae (shoulder blades) Ribs


28 Irregular Bones Complicated shapes that do not fit in any of the previous classes Example: Vertebrae Coxae (hip bone)


30 FUNCTIONS OF BONES Besides contributing to body shape and form, our bones perform several important functions: 1. Support 2. Protection 3. Movement 4. Mineral storage 5. Blood cell formation

31 Support Bones provide a framework that supports the body and cradles its soft organs Examples: Bones of the lower limbs act as pillars to support the body trunk Rib cage supports the thoracic wall

32 Protection Fused bones at the skull protect the brain
Vertebrae surround the spinal cord Rib cage helps protect the vital organs of the thorax

33 Movement Skeletal muscles, which attach to bones by tendons, use bones as levers to move the body and its parts As a result, we can walk, grasp objects, and breathe

34 Mineral Storage Bone is a reservoir for minerals
Most important are calcium and phosphates Stored minerals are released into the bloodstream as needed for distribution to all parts of the body: Deposits and withdrawals of minerals to and from the bones go on almost continuously

35 Blood Cell Formation Most blood cell formation (hematopoiesis) occurs in the marrow cavities of certain bones

36 Bone Structure Because bones contain various types of tissue, bones are organs: Bone (osseous) tissue Nervous tissue in their nerves Cartilage tissue in their articular cartilages Fibrous connective tissue lining their cavities Muscle and epithelial tissues in their blood vessels

37 Gross Anatomy Bone markings are projections, depressions, and openings found on the surface of bones that function as sites of muscle, ligament, and tendon attachment, as joint surfaces, and as openings for the passage of blood vessels and nerves

38 Names of Bone Markings Projections (bulges): grow outward from the bone surface Projections that sites of muscle and ligament attachment: Tuberosity: elevated round swelling Large and rounded May be roughened Crest: elongated prominence Narrow ridge Usually prominent Trochanter: to run Very large Blunt Irregularly shaped ONLY in the femur Line: Less prominent than crest Tubercle: little swelling Small and rounded Epicondyle: above a knuckle (condyle) Raised area on or above a condyle Spine: Sharp, slender, often pointed projection Process: Any bone prominence

39 Names of Bone Markings Projections That Help to Form Joints: articulation Head: Bony expansion carried on a narrow neck Facet: small face Smooth, nearly flat articular surface Condyle: knuckle Rounded articular projection Ramus: branch Armlike bar of bone

40 Names of Bone Markings Depressions and openings:
Allow blood vessels and nerves to pass Meatus: passage/opening Canal-like passageway Sinus: curve, hollow Cavity within a bone, filled with air and lined with mucous membrane Fossa: furrow or shallow depression Shallow, basinlike depression in a bone Often serves as an articular surface Groove: ditch Furrow Fissure: slender deep furrow Narrow, slitlike opening Foramen: passage/opening Round or oval opening through a bone

41 Bone Textures Compact: Spongy Bone:
All bones have a dense outer layer consisting of compact bone that appears smooth and solid Spongy Bone: Internal to compact bone is spongy bone, which consists of honeycomb, needle-like, or flat pieces, called trabeculae (little beam) In living bones the open spaces between trabeculae are filled with red or yellow bone marrow

42 Compact/Spongy Bone

43 Typical Long Bone Structure
All long bones have the same general structure: Diaphysis: dia (through) / physis (growth) Tubular shaft Forms the long axis of the bone Constructed of a relatively thick collar of compact bone that surrounds a central medullary cavity or marrow cavity In adults, the medullary cavity contains fat (yellow marrow) and is called the yellow bone marrow Epiphyses: epi (upon) / epiphyses (singular) The ends of the bone Consist of internal spongy bone covered by an outer layer of compact bone Joint surfaces of each epiphysis is covered with a thin layer of articular (hyaline) cartilage, which cushions the opposing bone ends during joint movement and absorbs stress


45 Typical Long Bone Structure
Epiphyseal line: sometimes called the metaphysis Located between the epiphyses and diaphysis in an adult Is the remnant of the epiphyseal plate, a disc of hyaline cartilage that grows during childhood to lengthen the bone


47 Typical Long Bone Structure
Membranes: Periosteum The external surface of the entire bone except the joint surfaces is covered by a glistening white, double-layered membrane called the periosteum (peri=around / osteo=bone) Outer fibrous layer is dense irregular connective tissue Inner osteogenic layer abutting the bone surface consists primarily of: Bone-forming cells: osteoblasts Bone-destroying cells: osteoclasts


49 Typical Long Bone Structure
Membranes: Periosteum Richly supplied with nerve fibers, lymphatic vessels, and blood vessels, which enter the diaphysis via a nutrient foramen Secured to the underlying bone by perforating (Sharpey’s) fibers Tufts of collagen fibers that extend from its fibrous layer into the bone matrix Provides anchoring points for tendons and ligaments At these points the perforating fibers are exceptionally dense


51 Typical Long Bone Structure
Membranes: Endosteum (within bone) The internal surface of the bone is lined by a connective tissue membrane called the endosteum Covers the trabeculae of spongy bone and lines the canals that pass through the compact bone Like the periosteum, the endosteum contains both osteoblasts and osteoclasts


53 Structure of Short, Flat, and Irregular Bones
Short, flat, and irregular bones consist of thin plates of periosteum-covered compact bone on the outside, and endosteum-covered spongy bone inside, which houses bone marrow between the trabeculae (no marrow cavity is present) Not cylindrical No shaft or epiphyses Called the diploe (folded) Arrangement resembles a sandwich


55 Location of Hematopoietic Tissue in Bones
Hematopoietic tissue of bones, red bone marrow, is located within: The trabecular cavities of the spongy bone in flat bones The trabecular cavities of the spongy bone of the epiphyses in the long bones Red bone marrow is found in: All flat bones Epiphyses, and medullary cavities of infants In adults, distribution is restricted to flat bones and the proximal epiphyses of the humerus and femur Hence, blood cell production in adult long bones routinely occurs only in the head of the femur and humerus Red marrow found in the diploe of flat bones (such as the sternum) and in some irregular bones (such as the hip bones) is much more active in hematopoiesis These are the sites used for obtaining red marrow samples Yellow marrow in the medullary cavity can revert to red marrow if a person becomes very anemic and needs enhanced red blood cell production

56 Microscope Anatomy of Bone
Although compact bone looks dense and solid, a microscope reveals that it is riddled with passageways that serve as conduits for nerves, blood vessels, and lymphatic vessels


58 Microscope Anatomy of Bone Compact Bone
The structural unit of compact bone is the osteon, or Haversian system Each osteon is an elongated cylinder oriented parallel to the long axis of the bone Tiny weight –bearing pillars Group of hollow tubes of bone matrix, one placed outside the next like the growth rings of a tree trunk In diagram: osteon are drawn as if pulled out like a telescope to illustrate the individual lamellae Each matrix tube is a lamella (little plate), and for this reason compact bone is often called lamellar bone Although all of the collagen fibers in a particular lamella run in a single direction, the collagen fibers in adjacent lamella always run in opposite directions This alternating pattern is beautifully designed to withstand torsion (twisting) stresses—the adjacent lamella reinforce one another to resist twisting


60 Microscope Anatomy of Bone Compact Bone
Collagen fibers are not the only part of bone lamellae that are beautifully ordered Tiny crystals of bone salts align with the collagen fibers and thus also alternate their direction in adjacent lamellae Running through the core of each osteon is: The Central (Haversian) Canal that containing small blood vessels and nerve fibers that serve the needs of the osteon’s cells Perforating (Volkmann’s) Canals lie at right angles to the long axis of the bone, and connect the blood and nerve supply of the periosteum to that of the central canals and medullary cavity BOTH Haversian and Volkmann Canal are lined with endosteum


62 Microscope Anatomy of Bone Compact Bone
(b):Osteocytes (spider-shaped mature bone cells) occupy lacunae (small space, cavity, or depression occupied by cells) at the junctions of the lamellae Hair-like canals called canaliculi connect the lacunae to each other and to the central canal Tie all the osteocytes in an osteon together, permitting nutrients and wastes to be relayed from one osteocyte to the next throughout the osteon Although bone matrix is hard and impermeable to nutrients, its canaliculi and cell-to-cell relays (via gap junctions) allow bone cells to be well nourished Function is to maintain the bone matrix: If they die, the surrounding matrix is resorbed (remove-assimilated)


64 Microscope Anatomy of Bone Compact Bone
Not all the lamellae in compact bone are part of osteons (c): Lying between intact osteons are incomplete lamella called interstitial lamella These either fill the gaps between forming osteons or are remnants of osteons that have been cut through by bone remodeling (a): Circumferential lamellae are located just beneath the periosteum, extending around the entire circumference of the bone Effectively resist twisting of the long bone


66 Spongy Bone Lacks osteons
Trabeculae (honeycomb network) align along lines of stress and help the bone resist stress as much as possible These tiny bone struts are as carefully positioned as the flying buttresses of a Gothic cathedral Irregularly arranged lamella and osteocytes interconnected by canaliculi Nutrients reach the osteocytes by diffusing through the canaliculi from capillaries in the endosteum surrounding the trabeculae




70 Chemical Composition of Bone
Organic components: Cells (osteoblasts, osteocytes, and osteoclasts) Osteoid: nonliving Composed of secretions from the osteoblasts which contribute to the flexibility and tensile strength of bone that allows the bone to resist stretch and twisting Ground substance: proteoglycans and glycoproteins Collagen fibers: Bonds in or between collagen molecules break easily on impact dissipating energy to prevent the force from rising to a fracture value In the absence of continued or additional trauma, most of the bonds reform

71 Chemical Composition of Bone
Inorganic components: Make up 65% of bone by mass Consist of hydroxyapatite (mineral salts) that is largely calcium phosphate, which accounts for the hardness and compression resistance of bone Present in the form of tightly packed tiny crystals surrounding the collagen fibers in the extracellular matrix Because of the salts they contain, bones last long after death and provide an enduring “monument” Healthy bone is half as strong as steel in resisting compression and fully as strong as steel in resisting tension (stretching)

72 BONE DEVELOPMENT Ossification and osteogenesis are synonyms meaning the process of bone formation (os=bone / genesis=beginning) In embryos: leads to the formation of the skeleton Early adulthood: bones increase in length Throughout life: bones are capable of growing in thickness Adults: ossification serves mainly for bone remodeling and repair

73 Formation of the Bony Skeleton
Before week 8, the skeleton of a human embryo is constructed entirely from fibrous membranes and hyaline cartilage Bone tissue begins to develop at about this time and eventually replaces most of the existing fibrous or cartilage structures When a bone develops from a fibrous membrane, the process is intramembranous ossification, and the bone is called a membrane bone Bone development by replacing hyaline cartilage is called endochondral ossification (endo=within / chondo=cartilage), and the resulting bone is called a cartilage (endochondral) bone

74 Intramembranous Ossification
Results in the formation of cranial bones of the skull (frontal, parietal, occipital, and temporal bones) and the clavicles All bones formed by this process are flat bones Four Major Steps: 1, 2, 3, 4

75 Intramembranous Ossification

76 Intramembranous Ossification

77 Endochondral Ossification
Replaces hyaline cartilage, forming all bones below the skull except for the clavicles Begins in the second month of development Five Steps: 1,2,3,4,5

78 Endochondral Ossification
1. Initially, osteoblasts secrete osteoid, creating a bone collar around the diaphysis of the hyaline cartilage model

79 Endochondral Ossification

80 Endochondral Ossification
2. Cartilage in the center of the diaphysis calcifies: Because calcified cartilage matrix is impermeable to diffusing nutrients, the chondrocytes die and deteriorate forming cavities

81 Endochondral Ossification

82 Endochondral Ossification
3. The periosteal bud (nutrient artery and vein, lymphatics, nerve fibers, red marrow elements, osteoblast, and osteoclasts) invades the internal cavities and spongy bone forms around the remaining fragments of hyaline cartilage

83 Endochondral Ossification

84 Endochondral Ossification
4. The diaphysis elongates as the cartilage in the epiphyses continue to lengthen and a medullary cavity forms through the action of osteoclasts within the center of the diaphysis

85 Endochondral Ossification

86 Endochondral Ossification
5. The epiphyses ossify shortly after birth through the development of secondary ossification centers When complete, hyaline cartilage remains only at two places: On the epiphyseal surfaces (articular cartilages) Junction of the diaphysis and epiphysis, where it forms the epiphyseal plates

87 Endochondral Ossification

88 Postnatal Bone Growth During infancy and youth:
Long bones lengthen entirely by interstitial growth of the epiphyseal plates All bones grow in thickness by appositional growth

89 Growth in Length of Long Bones
Side of the epiphyseal plate cartilage facing the epiphysis, the cartilage is relatively quiescent and inactive Side of the epiphyseal plate cartilage abutting the diaphysis organizes into a pattern that allows fast, efficient growth (osteogenic zone) As the cells divide the epiphysis is pushed away from the diaphysis Long bone lengthens


91 Bone Growth

92 Growth in Length of Long Bones
During growth, the epiphyseal plate maintains a constant thickness because the rate of cartilage growth on its epiphyseal-facing side is balanced by its replacement with bony tissue on its diaphysis-facing side

93 Bone Growth

94 Growth in Length of Long Bones
As adolescence draws to an end, the chondroblasts of the epiphyseal plates divide less often and the plates become thinner and thinner until they are entirely replaced by bone tissue Longitudinal bone growth ends when the bone of the epiphysis and diaphysis fuses This process, called epiphyseal plate closure, happens at about 18 years of age in females and 21 years of age in males However, an adult bone can still increase in diameter or thickness by appositional growth if stressed by excessive activity or body weight

95 Growth in Width (Thickness)
Growing bones widen as they lengthen Increases in thickness by appositional growth


97 Growth in Width (Thickness)
Osteoblast beneath the periosteum secrete bone matrix on the external bone surface Osteoclasts on the endosteal surface of the diaphysis remove bone There is normally slightly less breaking down than building up This unequal process produces a thicker, stronger bone but prevents it from becoming too heavy

98 Appositional Growth

99 Hormonal Regulation of Bone Growth
During infancy and childhood, the most important stimulus of epiphyseal plate activity is growth hormone from the anterior pituitary, whose effects are modulated by thyroid hormone, ensuring that the skeleton has proper proportions as it grows At puberty, male and female sex hormones (testosterone and estrogen) are released in increasing amounts Initially these sex hormones promote the growth spurt typical of adolescence, as well as the masculinization or feminization of specific parts of the skeleton Ultimately these hormones induct the closure of the epiphyseal plate ending longitudinal bone growth

100 BONE HOMEOSTASIS Every week we recycle 5 to 7% of our bone mass, and as much as half a gram of calcium may enter or leave the adult skeleton each day Spongy bone is replaced every 3-4 years Compact bone, is replaced approximately every 10 years This is fortunate because when bone remains in place for long periods the calcium crystallizes and becomes very brittle—ripe conditions for fracture When we break bones (most common disorder of bones), they undergo a remarkable process of self-repair

101 Bone Remodeling In the adult skeleton, bone deposit and bone resorption (removal) occur BOTH at the surface of the periosteum and the surface of the endosteum These two processes constitute bone remodeling: They are coupled and coordinated by remodeling units (osteoblasts and osteoclasts) Osteoblast: bone forming cells Osteoclast: large cells that resorb or break down bone matrix In adult skeletons, bone remodeling is balanced bone deposit and removal, bone deposit occurs at a greater rate when bone is injured, and bone resorption allows minerals of degraded bone matrix to move into the blood

102 Bone Remodeling Bone deposit: involves osteoblasts
Occurs wherever bone is injured or added bone strength is required Optimal bone deposit requires: Healthy diet rich in proteins Vitamin C Vitamin D Vitamin A Minerals: calcium, phosphorus, magnesium, and manganese

103 Bone Remodeling Bone Resorption: accomplished by osteoclasts
Move along a bone surface, digging grooves called resorption bays as they break down the bone matrix Secretes: Lysosomal enzymes that digest the organic matrix Hydrochloric acid that converts the calcium salts into soluble forms that pass easily into solution May also phagocytize the demineralized matrix and dead osteocytes

104 Control of Remolding Regulated by two control loops:
A negative feedback hormonal mechanism that maintains Ca2+ homeostasis in the blood Calcium is important in many physiological processes: Nerve impulses Muscle contraction Blood coagulation Secretion by glands, nerve cells Cell division Responses to mechanical and gravitational forces acting on the skeleton Daily calcium requirement is: mg from birth until the age of 10 mg from ages 11 to 24

105 Hormonal Mechanism Mostly used to maintain blood calcium homeostasis, and balances activity of parathyroid hormone (PTH) and calcitonin (thyroid)

106 Hormonal Mechanism Increased parathyroid hormone (PTH) level stimulates osteoclasts to resorb bone, releasing calcium to the blood Osteoclasts are no respectors of matrix age They break down both old and new matrix ONLY osteoid (unmineralized matrix), which lacks calcium salts, escapes digestion As blood concentrations of calcium rise, the stimulus for PTH release ends


108 Hormonal Mechanism Calcitonin (Thyroid):
Secreted when blood calcium levels rise Inhibits bone resorption Encourages calcium salt deposit in bone matrix, effectively reducing blood calcium levels As blood calcium levels fall, calcitonin release wanes



111 Hormonal Mechanism These hormonal controls act not to preserve the skeleton’s strength or well-being but rather to maintain blood calcium homeostasis In fact, if blood calcium levels are low for an extended time, the bones become so demineralized that they develop large, punched-out-looking holes Thus, the bones serve as a storehouse from which ionic calcium is drawn as needed

112 Response to Mechanical Stress and Gravity
Wolff’s Law: Response to mechanical stress (muscle pull) and gravity serves the needs of the skeleton by keeping the bones strong where stressors are acting A bone’s anatomy reflects the common stresses it encounters: Example: a bone is loaded (stressed) whenever weight bears down on it or muscles pull on it Tends to bend the bone Compresses the bone on one side and subjects it to tension (stretching) on the other side Both forces are minimal toward the center of the bone (cancel each other out)


114 Wolff’s Law 1. Long bones are thickest midway along the diaphysis, exactly where bending stresses are greatest (bend a stick and it will split near the middle 2. Curved bones are thickest where they are most likely to buckle 3. Trabeculae of spongy bone form trusses, or struts, along lines of compression 4. Large, bony projections occur where heavy, active muscles attach Bones of weight lifters have enormous thickenings at the attachment sites of the most used muscles Also explains the featureless bones of the fetus and the atrophied bones of bedridden people—situations in which bones are not stressed

115 Control of Remolding Skeleton is continuously subjected to both hormonal influences and mechanical forces The hormonal loop determines whether and when remodeling occurs in response to changing blood calcium levels Mechanical stress determines where it occurs Example: When bone must be broken down to increase blood calcium levels, PTH is released and targets the osteoclasts Mechanical forces determine which osteoclasts are most sensitive to PTH stimulation, so that bone in the least stressed areas (temporarily dispensable) is broken down

116 Bone Repair Fractures are breaks in bones:
Due to trauma to bones or thin, weaken bones

117 Classification of Fracture
Position of the bone ends after fracture: Nondisplaced: bone ends retain their normal position Displaced: bone ends are out of normal alignment Completeness of break: Complete: bone is broken through Incomplete: bone is not broken through Greenstick: bone breaks incompletely (like green twig breaks) Only one side of the shaft breaks; the other side bends Orientation of the break relative to the long axis of the bone: Linear: parallel fracture Transverse: break is perpendicular to the bone’s long axis

118 Classification of Fracture
Whether the bone ends penetrate the skin: Open (compound): penetrates the skin Closed (simple): does not penetrate the skin Location: Arm, leg, etc. Epiphyseal: epiphysis separates from the diaphysis along the epiphyseal plate Depressed: skull bones pushed in External appearance Nature of break: Comminuted: bone fractures into 3 or more pieces Spiral: angular

119 Bone Repair Repair of fractures involves four major stages:
1. Hematoma formation: mass of clotted blood Because blood vessels are damaged Bone cells deprived of nutrients die at the site Tissue at the site become swollen, painful, and inflamed


121 Bone Repair 2. Fibrocartilaginous callus formation:
Formation of soft granulation tissue (soft callus) Capillaries grow into the hematoma Phagocytes invade the area Fibroblasts: Produce collagen fibers that span the break and connect the bone ends Osteoblasts: Begin forming spongy bone


123 Bone Repair 3. Bony callus formation:
New bone trabeculae begins to form and is gradually converted to bony (hard) callus


125 Bone Repair 4. Remodeling of the bony callus:
Excess material on the diaphysis exterior and within the medullary cavityis removed Compact bone is laid down to reconstruct the shaft walls


127 Bone Repair New Methods
1. Electrical stimulation of fracture 2. Ultrasound treatments 3. Free Vascular fibular graft 4. VEGF: vascular endothelial growth factor 5. Nanobiotechnology 6. Bone Substitutes

Imbalances between bone deposit and bone resorption underline nearly every disease that affects the adult skeleton

129 Osteomalacia Soft bones
Includes a number of disorders in adults in which the bone is inadequately mineralized Osteoid is produced, but calcium salts are not deposited, so bones are soft and weak Main symptom is pain when weight is put on the affected bones Cause: insufficient calcium or by a vitamin D deficiency (helps to absorb calcium) Treatment: drink vitamin D-fortified milk and exposing the skin to sunlight which stimulates production of vitamin D

130 Rickets Inadequate mineralization of bones in children caused by insufficient calcium or vitamin D deficiency Treatment: drink vitamin D-fortified milk and exposing the skin to sunlight which stimulates production of vitamin D Because young bones are still growing rapidly, rickets is much more severe than adult Osteomalacia Bowed legs, deformities of the pelvis, skull, and rib cage are common

131 Osteoporosis Refers to a group of disorders in which the rate of bone resorption exceeds the rate of formation Bones become so fragile that something as simple as a hearty sneeze or stepping off a curb can cause them to break Bones have normal bone matrix (intercellular material of a tissue), but bone mass is reduced and the bones become more porous and lighter increasing the likelihood of fractures Spongy bone of the spine is most vulnerable, and compression fractures of the vertebrae are common Femur, particular the neck, is also very susceptible to fracture (broken hip)

132 Osteoporosis Older women are especially vulnerable to osteoporosis, due to the decline in estrogen after menopause Other factors that contribute to osteoporosis include: A petite body form Insufficient exercise or immobility to stress the bones A diet poor in calcium and vitamin D Abnormal vitamin D receptors Smoking: Reduces estrogen levels Hormone-related conditions: Hyperthyroidism Diabetes mellitus

133 OSTEOPOROSIS (a): Normal Bone (b): Osteoporotic Bones

134 Paget’s disease Is characterized by excessive bone deposition and resorption, with the resulting bone abnormally high in spongy bone High ratio of spongy bone to compact bones It is a localized condition that results in deformation of the affected bone Weaken of a region of a bone Cause: unknown

The skeleton derives from embryonic mesenchymal cells, with ossification occurring at precise times Most long bones have obvious primary ossification centers by 12 weeks At birth, most bones are well ossified, except for the epiphyses, which form secondary ossification centers Throughout childhood, bone growth exceeds bone resorption; in young adults, these processes are in balance; in old age, resorption exceeds formation




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