2010 Chapter6
TheSkeletalSystem
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EndofChapter6
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BoneFunction
Support Protection Assist in movements Mineral homeostasis Blood cell production
Hemopoiesis in red bone marrow
Triglyceride storage
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TypesofBones
Long bones: longer than wide
Such as thigh, leg, arm, forearm, fingers and toes Most wrist and ankle bones Such as cranial bones sternum, ribs and scapulas
Short bones: almost cube shaped
Flat bones: thin and extensive surface
Irregular bones: do not fit above categories
Such as vertebrae and some facial bones
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MacroscopicStructure
Parts of a long bone
Diaphysis: shaft of long bone; made up mostly of compact bone Epiphysis: broad end of long bone; mostly spongy bone Metaphysis: growth area between diaphysis and epiphysis Articular cartilage: hyaline cartilage at joint Periosteum: fibrous covering over most of bone Medullary cavity (marrow) with fat and blood cells Endosteum: membrane lining medullary cavity
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LongBones
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LongBones
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MicroscopicStructureofBone
Matrix
25% water, 25% collagen fibers, 50% mineral salts Osteogenic cells in periosteum Osteoblasts
Cells
Secrete collagen fibers Build matrix and become trapped in lacunae Become
Osteocytes that maintain bone Osteoclasts are formed from monocytes
Digest bone matrix for normal bone turnover
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HistologyofBones
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CompactBoneStructure
Arranged in osteons (haversian systems)
Cylinders running parallel to long axis of bone Contains blood vessels, nerves, lymphatics
Central canal through center of osteon
Concentric lamellae: layers of matrix Lacunae: lakes between lamellae
Contain osteocytes (bone cells)
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CompactBoneStructure
Canaliculi (little canals)
Contain extensions of osteocytes Permit flow of ECF between central canal and lacunae
Compact bone is covered by periosteum Perforating (Volkmanns) canals
Carry blood and lymphatic vessels and nerves from periosteum They supply central (Haversian) canals and also bone marrow
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HistologyofBones
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SpongyBone
Not arranged in osteons Irregular latticework of trabeculae
These contain lacunae with osteocytes and canaliculi
Spaces between trabeculae may contain red bone marrow Spongy bone is lighter than compact bone, so reduces weight of skeleton
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BoneDynamicsandTissue
Interactions Animation
Bone Dynamics and Tissue
You must be connected to the internet to run this animation.
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BoneFormation
Known as ossification Timeline
Initial bone development in embryo and fetus Growth of bone into adulthood Remodeling: replacement of old bone Repair if fractures occur This initial skeleton model will be replaced by bone tissue beginning at 6 weeks of embryonic life
Mesenchyme (early connective tissue) model
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BoneFormation
Two different methods of ossification each result in similar bone tissue
Intramembranous: bone forms within sheets of mesenchyme that resemble membranes
Only a few bones form by this process: flat bones of the skull, lower jawbone (mandible), and part of clavicle (collarbone)
Endochondrial: mesenchyme forms hyaline cartilage which then develops into bone
All other bones form by this process
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Flat bone of skull
Blood capillary Ossification center Mesenchymal cell Osteoblast
Mandible
Collagen fiber
1
Development of ossification center
Osteocyte in lacuna Canaliculus Osteoblast Newly calcified bone matrix 2 Calcification
Mesenchyme condenses Blood vessel Spongy bone trabeculae Osteoblast
3
Formation of trabeculae
Periosteum
Spongy bone tissue Compact bone tissue
4
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Development of the periosteum
IntramembranousOssification
Four steps
1. Development of ossification center
Mesenchyme cells osteogenic osteoblasts Osteoblasts secrete organic matrix
In lacunae they extend cytoplasmic processes to each other Deposit calcium & other mineral salts Blood vessels grow in and red marrow is formed
1.Calcification: cells become osteocytes
1.Formation of trabeculae (spongy bone)
1.Periosteum covering the bone forms from mesenchyme
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Perichondrium Perichondrium Uncalcified matrix Periosteum Calcified matrix Periosteum (covering compact bone) Medullary cavity
Proximal Proximal epiphysis epiphysis
Hyaline Hyaline cartilage cartilage Uncalcified Uncalcified matrix matrix
Diaphysis Diaphysis
Calcified Calcified matrix matrix
Nutrient artery
Primary ossification center Spongy bone
Distal Distal epiphysis epiphysis
Nutrient artery and vein
Development of 1 Development of cartilage model cartilage model
Growth of 2 Growth of cartilage model cartilage model
3 Development of primary ossification center
4 Development of the medullary cavity
Articular cartilage Epiphyseal artery and vein Uncalcified matrix
Secondary ossification center
Spongy bone Epiphyseal plate
Nutrient artery and vein
5 Development of secondary ossification center
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and epiphyseal plate
EndochondrialOssification
Six Steps 1. Formation of cartilage model of the bone
As mesenchyme cells develop into chondroblasts Cartilage bone grows as chondroblasts secrete cartilage matrix Chondrocytes increase in size, matrix around them calcifies Chondrocytes die as they are cut off from nutrients, leaving small spaces (lacunae)
2. Growth of cartilage model
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EndochondrialOssification
Six Steps 3. Primary ossification center
Perichondrium sends nutrient artery inwards into disintegrating cartilage Osteogenic cells in perichondrium become osteoblasts that deposit bony matrix over remnants of calcified cartilage spongy bone forms in center of the model As perichondrium starts to form bone, the membrane is called periosteum
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EndochondrialOssification
Six Steps 4. Medullary (marrow) cavity
Spongy bone in center of the model grows towards ends of model Octeoclasts break down some of new spongy bone forming a cavity (marrow) through most of diaphysis Most of the wall of the diaphysis is replaced by a collar of compact bone
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EndochondrialOssification
Six Steps 5. Secondary ossification center
Similar to step 3 except that nutrient arteries enter ends (epiphyses) of bones and osteoblasts deposit bony matrix spongy bone forms in epiphyses from center outwards Occurs about time of birth Articular cartilage at ends of epiphyses becomes articular cartilage Epiphyseal (growth) plate of cartilage remains between epiphysis and diaphysis until bone growth ceases
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6. Articular cartilage and epiphyseal cartilage
GrowthinLength
Chondrocytes divide and grow more cartilage on epiphyseal side of the epiphyseal plate Chondrocytes on the diaphyseal side die and are replaced by bone Therefore bone grows from diaphyseal side towards epiphyseal side Growth in length stops between 18-25 years; cartilage in epiphyseal plate is completely replaced by bone (epiphyseal line)
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GrowthinThickness
As bones grow in length, they must also grow in thickness (width)
Perichondrial osteoblasts osteoblasts lay down additional lamellae of compact bone Simultaneously, osteoclasts in the endosteum destroy interior bone to increase width of the marrow
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RemodelingandRepair
Remodeling in response to use
Resorption osteoclasts by and Deposition by osteoblasts Dead tissue removed Chondroblasts fibrocartilage spongy bone deposited by osteoblasts remodeled to compact bone
Repair after a fracture
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TypesofFractures
Partial: incomplete break (crack) Complete: bone broken into two or more pieces Closed (simple): not through skin Open (compound): broken ends break skin
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FactorsAffectingGrowth
Adequate minerals (Ca, P, Mg) Vitamins A, C, D Hormones
Before puberty: hGH + insulin-like growth factors Thyroid hormone and insulin also required Sex hormones contribute to adolescent growth spurt
Weight-bearing activity
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CalciumHomeostasis
Blood levels of Ca2+ controlled Negative feedback loops Parathyroid hormone (PTH) increases osteoclast activity + decreases loss of Ca2+ in urine Calcitonin decreases osteoclast activity
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NegativeFeedback
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Exercise&BoneTissue
Bone strengthened in response to use Bone resorbed during disuse; examples:
During prolonged bed rest Fracture with cast/immobilizer Astronauts without gravity
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DivisionsofSkeletalSystem
Two divisions: axial and appendicular
Axial: bones around body axis
Examples: skull bones, hyoid, ribs, sternum, vertebrae
Appendicular: bones of upper and lower limbs plus shoulder and hip bones that connect them
Examples: collar bone (clavicle), arm (humerus), forearm (radius and ulna), thigh bone (femur)
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Divisionsofthe SkeletalSystem
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Skull&HyoidBone
Eight Cranial bones
Frontal, 2 parietal, 2 temporal, occipital, sphenoid, and ethmoid 2 nasal, 2 maxilla, 2 zygomatic, 2 lacrimal 2 palatine, 2 inferior nasal conchae, 1 mandible,1 vomer
Fourteen Facial bones
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Skull
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Skull
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Skull
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Skull
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SphenoidBone
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EthmoidBone
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EthmoidBone
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UniqueFeaturesofSkull
Sutures: immovable joint between skull bones
Coronal, sagittal, lambdoidal, squamous Located in bones near nasal cavity Allow deformation at birth Calcify to form sutures
Paranasal sinuses: cavities
Fontanels: soft spot in fetal skull
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ParanasalSinuses
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Vertebrae
Functions
Encloses spinal cord Supports head Point of attachment for muscles of back, ribs and pelvic girdle 7 cervical 12 thoracic 5 lumbar 1 sacrum and 1 coccyx
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Regions (from superior to inferior)
NormalCurvesinColumn
Four normal curves
Cervical and lumbar curves are convex (bulge anteriorly) Thoracic and sacral curves are concave (bulge posteriorly)
Curves increase strength, help in balance and absorb shocks
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Vertebral Column
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VertebralColumn
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StructureofVertebra
Body: disc-shaped anterior portion Vertebral arch: posteriorly back from body
With the body, creates a hole called vertebral foramen Transverse process extending laterally on each side Spinous process extending dorsally Two each of superior and inferior articular processes that form joints with vertebrae
Seven processes from this arch
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StructureofVertebra
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CervicalArea
Cervical (C1-C7 from superior to inferior)
Spinous process often bifid with transverse foramina on transverse processes Articulates with head, specialized to support head Lacks body and spinous process Has body and spinous process Called dens (tooth) that creates a pivot for head rotation
C1: atlas
C2: axis
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Cervical Vertebrae
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OtherVertebrae
Thoracic (T1-T12 )
Larger than cervical Have facets for articulations with ribs Largest and strongest; spinous processes short and thick Foundation for pelvic girdle Contain sacral foramina for nerves and blood vessels
Lumbar (L1-L5)
Sacrum (S1-S5 fused into one unit)
Coccyx: 4 coccygeal vertebrae fused into 1
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LumbarVertebrae
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SacrumandCoccyx
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Thorax
Thoracic cage: sternum, costal cartilages, ribs and bodies of T1-T12 Sternum: form by 3 portions fused by about age 25 years:
Manubrium, body, xiphoid process
Ribs: 12 pairs True ribs are #1-7: articulate with sternum directly by costal cartilages False ribs are #8-12: do not articulate with sternum directly by costal cartilages
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Thorax
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PectoralGirdle
Function: attach bones of upper limbs to axial skeleton Clavicles and scapulas: bilateral
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RightPectoral(Shoulder)Girdle
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UpperLimb
Humerus: arm bone
Articulates with scapula (glenoid cavity) at shoulder joint Articulates with radius and ulna at elbow
Ulna: medial bone Radius: lateral bone (thumb side)
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Right Humerus
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RightUlna andRadius
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RightUlnaandRadius
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WristandHand
Carpus (wrist): 8 bones Metacarpals: 5 bones of palm of hand
Number 1-5 starting with thumb Numbered 1-5 metacarpals Each finger except the thumb has proximal, middle and distal phalanges; thumb lacks middle phalanx
Phalanges: 14 bones of fingers
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RightWrist andHand
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Pelvic(Hip)Girdle
Pelvic girdle includes two hip (coxal) bones
Joined anteriorly at pubic symphysis Posteriorly attached to sacrum at sacroiliac joint
Basin-like pelvis is formed by two hip bones (pelvic girdle) + sacrum and coccyx
False (greater) pelvis: broad region superior to pelvic brim; contains abdominal organs True (lesser) pelvis: small region inferior to pelvic brim; contains urinary bladder + internal reproductive organs
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PelvicGirdle(Female)
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PelvicGirdle(Female)
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PartsofEachHip(Coxal)Bone
3 separate bones fuse by age 23 to form a hip bone
Ilium: largest and most superior Ischium: lower posterior part Pubis: lower anterior part
Bones meet at the acetaulum of the hip bone (socket for head of femur)
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Right Hip Bone
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LowerLimb
Femur (thigh bone): largest bone in the body
Articulates with hip proximally and with the tibia and patella distally Head (fits into acetabulum) and greater trochanter at proximal end
Patella: kneecap in anterior of knee joint Tibia: shin bone
Large medial, weight-bearing bone of leg Lateral to tibia and smaller Does not articulate with femur
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Fibula: longest, thinnest bone in body
RightFemur
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RightTibia andFibula
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AnkleandFoot
Tarsus (ankle) has 7 bones
Large talus (ankle bone) and Calcaneus (heel bone) Numbered 1 to 5 from medial to lateral Big toe has proximal and distal phalanges while others have proximal, medial and distal phalanges. Numbered like metatarsals from 1-5
Metatarsals (foot bones)
Phalanges (toe bones)
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Right Foot
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ArchesoftheRightFoot
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MaleandFemaleDifferences
Males usually have heavier bones Related to muscle size and strength Female pelvis is wider and shallower than male pelvis: allows for birth
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AgingandSkeletalSystem
Birth through adolescence: more bone formed than lost Young adults: gain and loss about equal As levels of sex steroids decline with age: bone resorption > bone formation Bones become brittle and lose calcium
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Osteoporosis
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