The Skeletal System. Function of Bones Support – form the framework that supports the body and...
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The Skeletal System
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Function of Bones
Support – form the framework that supports the body and cradles soft organs
Protection – provide a protective case for the brain, spinal cord, and vital organs
Movement – provide levers for muscles Mineral storage – reservoir for minerals, especially
calcium and phosphorus Blood cell formation – hematopoiesis occurs within
the marrow cavities of bones
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Bone Markings
Bulges, depressions, and holes that serve as: – Sites of attachment for muscles, ligaments, and
tendons– Joint surfaces– Conduits for blood vessels and nerves
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Bone Markings: Projections – Sites of Muscle and Ligament Attachment
Tuberosity – rounded projection Crest – narrow, prominent ridge of bone Trochanter – large, blunt, irregular surface Line – narrow ridge of bone
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Bone Markings: Projections – Sites of Muscle and Ligament Attachment
Tubercle – small rounded projection Epicondyle – raised area above a condyle Spine – sharp, slender projection Process – any bony prominence
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Bone Markings: Projections – Projections That Help to Form Joints
Head – bony expansion carried on a narrow neck
Facet – smooth, nearly flat articular surface Condyle – rounded articular projection Ramus – armlike bar of bone
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Bone Markings: Depressions and Openings
Meatus – canal-like passageway Sinus – cavity within a bone Fossa – shallow, basinlike depression Groove – furrow Fissure – narrow, slitlike opening Foramen – round or oval opening through a
bone
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The Skeletal and Muscular Systems Video
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There are 206 bones in the human body
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A. The axial skeleton includes the skull and the vertebral column.
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Frontal View of the Skull
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The Skull
The skull, the body’s most complex bony structure, is formed by the cranium and facial bones
Cranium – protects the brain and is the site of attachment for head and neck muscles
Facial bones– Supply the framework of the face, the sense organs, and
the teeth– Provide openings for the passage of air and food– Anchor the facial muscles of expression
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Anatomy of the Cranium
Eight cranial bones – two parietal, two temporal, frontal, occipital, sphenoid, and ethmoid
Cranial bones are thin and remarkably strong for their weight
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Skull: Posterior View
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Parietal Bones and Major Associated SuturesForm most of the superior and lateral aspects of the skull
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Superior View of the Skull
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Posterior View of the Skull
1. Occipital Bone
2. Lambdoidal Suture
3. Parietal Bone
4. Sagittal Suture
5. Coronal Suture
6. Frontal Bone
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Lateral View of the Skull
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1.Parietal Bone 2. Coronal Suture 3. Frontal Bone 4. Nasal Bone 5.Vomer 6. Lacrimal Bone 7. Orbital Part of Ethmoid 8. Zygomatic Bone 9. Maxilla 10. Body of Mandible 11. Ramus of Mandible 12.Coronoid Process 13.Mandibular Condyle
14.Mental Foramen 15.Styloid Process 16. External Acoustic Meatus 17. Mastoid Process 18. Zygomatic Process 19.Temporal Bone 20. Greater Wing of Sphenoid 21.Inferior Temporal Line 22. Superior Temporal Line 23.Squamosal Suture 24.Lambdoidal Suture 25.Occipital Bone
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Bones of the Skull
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Inferior of the Cranial Vault
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The bone at the top is the Frontal Bone. The tongue shaped bone below the Frontal Bone is the Ethmoid Bone. Below that is the Sphenoid Bone. To the left and the right in below the Sphenoid Bone are the Left and Right Temporal Bones. In the Occiput at the bottom of the picture you will notice a large opening, called the Foramen Magnum, through which the spinal cord passes. (Photo by Paula Kliewer Photography)
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Inferior View of the Skull
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1.Anterior Palatine Foramen 2. Palatine Process of Maxilla 3. Palatine 4. Greater Palatine Foramen 5.Lesser Palatine Foramen 6. Pterygoid Processes of Sphenoid 7.Zygomatic Process 8. Squamous Part of Temporal Bone 9. Mandibular Fossa 10. Styloid Process 11.Stylomastoid Foramen 12. Mastoid Process 13.Mastoid Foramen 14. Superior Nuchal Line 15. External Occipital Protruberance
16.Median Nuchal Line 17. Inferior Nuchal Line1 8.Foramen Magnum 19. Condyloid Canal 20.Occipital Condyle 21.Hypoglossal Canal 22.Jugular Foramen 23.Carotid Canal
24.Foramen Spinosum 25.Foramen Ovale 26.Foramen Lacerum 27.Vomer 28.Transverse Palatine Suture 29.Median Palatine Suture
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Hyoid
1. Greater horns 2.Lesser horns 3. Body
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Temporal Bones
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Sphenoid Bone
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Ethmoid Bone
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Wormian Bones
Tiny irregularly shaped bones that appear within sutures
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Mandible and Its Markings
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Maxillary Bone
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Orbits
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Nasal Cavity
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Nasal Cavity
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Paranasal Sinuses
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Vertebral Column
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Vertebral Column
Formed from 26 irregular bones (vertebrae) connected in such a way that a flexible curved structure results
– Cervical vertebrae – 7 bones of the neck
– Thoracic vertebrae – 12 bones of the torso
– Lumbar vertebrae – 5 bones of the lower back
– Sacrum – bone inferior to the lumbar vertebrae that articulates with the hip bones
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Vertebral Column: Curvatures
Posteriorly concave curvatures – cervical and lumbar
Posteriorly convex curvatures – thoracic and sacral
Abnormal spine curvatures include scoliosis (abnormal lateral curve), kyphosis (hunchback), and lordosis (swayback)
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Vertebral Column: Ligaments
Anterior and posterior longitudinal ligaments – continuous bands down the front and back of the spine from the neck to the sacrum
Short ligaments connect adjoining vertebrae together
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Vertebral Column: Intervertebral Discs
Cushionlike pad composed of two parts
– Nucleus pulposus – inner gelatinous nucleus that gives the disc its elasticity and compressibility
– Annulus fibrosus – surrounds the nucleus pulposus with a collar composed of collagen and fibrocartilage
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General Structure of Vertebrae
Body or centrum – disc-shaped, weight-bearing region
Vertebral arch – composed of pedicles and laminae that, along with the centrum, enclose the vertebral foramen
Vertebral foramina – make up the vertebral canal through which the spinal cord passes
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General Structure of Vertebrae
Spinous processes project posteriorly, and transverse processes project laterally
Superior and inferior articular processes – protrude superiorly and inferiorly from the pedicle-lamina junctions
Intervertebral foramina – lateral openings formed from notched areas on the superior and inferior borders of adjacent pedicles
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Cervical Vertebrae
Seven vertebrae (C1-C7) are the smallest, lightest vertebrae
C3-C7 are distinguished with an oval body, short spinous processes, and large, triangular vertebral foramina
Each transverse process contains a transverse foramen
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Cervical Vertebrae: The Atlas (C1)
The atlas has no body and no spinous process
It consists of anterior and posterior arches, and two lateral masses
The superior surfaces of lateral masses articulate with the occipital condyles
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Cervical Vertebrae: The Axis (C2)
The axis has a body, spine, and vertebral arches as do other cervical vertebrae
Unique to the axis is the dens, or odontoid process, which projects superiorly from the body and is cradled in the anterior arch of the atlas
The dens is a pivot for the rotation of the atlas
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Cervical Vertebrae: The Atlas (C2)
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Thoracic Vertebrae
There are twelve vertebrae (T1-T12) all of which articulate with ribs
Major markings include two facets and two demifacets on the heart-shaped body, the circular vertebral foramen, transverse processes, and a long spinous process
The location of the articulate facets prevents flexion and extension, but allows rotation of this area of the spine
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Lumbar Vertebrae
The five lumbar vertebrae (L1-L5) are located in the small of the back and have an enhanced weight-bearing function
They have short, thick pedicles and laminae, flat hatchet-shaped spinous processes, and a triangular-shaped vertebral foramen
Orientation of articular facets locks the lumbar vertebrae together to provide stability
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Sacrum
Sacrum– Consists of five fused vertebrae (S1-S5), which
shape the posterior wall of the pelvis– It articulates with L5 superiorly, and with the
auricular surfaces of the hip bones – Major markings include the sacral promontory,
transverse lines, alae, dorsal sacral foramina, sacral canal, and sacral hiatus
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Coccyx
Coccyx (Tailbone)– The coccyx is made up
of four (in some cases three to five) fused vertebrae that articulate superiorly with the sacrum
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Bony Thorax (Thoracic Cage)
The thoracic cage is composed of the thoracic vertebrae dorsally, the ribs laterally, and the sternum and costal cartilages anteriorly
Functions– Forms a protective cage around the
heart, lungs, and great blood vessels
– Supports the shoulder girdles and upper limbs
– Provides attachment for many neck, back, chest, and shoulder muscles
– Uses intercostal muscles to lift and depress the thorax during breathing
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Thoracic Cage
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Bony Thorax (Thoracic Cage)
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Sternum (Breastbone)
A dagger-shaped, flat bone that lies in the anterior midline of the thorax
Results from the fusion of three bones – the superior manubrium, the body, and the inferior xiphoid process
Anatomical landmarks include the jugular (suprasternal) notch, the sternal angle, and the xiphisternal joint
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Ribs
There are twelve pair of ribs forming the flaring sides of the thoracic cage
All ribs attach posteriorly to the thoracic vertebrae
The superior 7 pair (true, or vertebrosternal ribs) attach directly to the sternum via costal cartilages
Ribs 8-10 (false, or vertebrocondral ribs) attach indirectly to the sternum via costal cartilage
Ribs 11-12 (floating, or vertebral ribs) have no anterior attachment
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Structure of a Typical True Rib
Bowed, flat bone consisting of a head, neck, tubercle, and shaft
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Appendicular Skeleton
The appendicular skeleton is made up of the bones of the limbs and their girdles
Pectoral girdles attach the upper limbs to the body trunk
Pelvic girdle secures the lower limbs
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Pectoral Girdles (Shoulder Girdles)
The pectoral girdles consist of the anterior clavicles and the posterior scapulae
They attach the upper limbs to the axial skeleton in a manner that allows for maximum movement
They provide attachment points for muscles that move the upper limbs
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Clavicles (Collarbones)
The clavicles are slender, doubly curved long bones lying across the superior thorax
The acromial (lateral) end articulates with the scapula, and the sternal (medial) end articulates with the sternum
They provide attachment points for numerous muscles, and act as braces to hold the scapulae and arms out laterally away from the body
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Scapulae (Shoulder Blades)
The scapulae are triangular, flat bones lying on the dorsal surface of the rib cage, between the second and seventh ribs
Scapulae have three borders and three angles
Major markings include the suprascapular notch, the supraspinous and infraspinous fossae, the spine, the acromion, and the coracoid process
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The Upper Limb
The upper limb consists of the arm (brachium), forearm (antebrachium), and hand (manus)
Thirty-seven bones form the skeletal framework of each upper limb
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Arm
The humerus is the sole bone of the arm
It articulates with the scapula at the shoulder, and the radius and ulna at the elbow
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Forearm
The bones of the forearm are the radius and ulna
They articulate proximally with the humerus and distally with the wrist bones
They also articulate with each other proximally and distally at small radioulnar joints
Interosseous membrane connects the two bones along their entire length
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Hand
Skeleton of the hand contains wrist bones (carpals), bones of the palm (metacarpals), and bones of the fingers (phalanges)
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Carpus (Wrist) Consists of eight bones
– Scaphoid, lunate, triquetral, and pisiform proximally
– Trapezium, trapezoid, capitate, and hamate distally
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Metacarpus (Palm)
Five numbered (1-5) metacarpal bones radiate from the wrist to form the palm– Their bases articulate with the carpals proximally,
and with each other medially and laterally– Heads articulate with the phalanges
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Phalanges (Fingers)
Each hand contains 14 miniature long bones called phalanges
Fingers (digits) are numbered 1-5, beginning with the thumb (pollex)
Each finger (except the thumb) has three phalanges – distal, middle, and proximal
The thumb has no middle phalanx
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Pelvic Girdle (Hip)
The hip is formed by a pair of hip bones (os coxae, or coxal)
Together with the sacrum and the coccyx, these bones form the bony pelvis
The pelvis– Attaches the lower limbs to the
axial skeleton with the strongest ligaments of the body
– Transmits weight of the upper body to the lower limbs
– Supports the visceral organs of the pelvis
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Ilium
The ilium is a large flaring bone that forms the superior region of the coxal bone
It consists of a body and a superior winglike portion called the ala
The broad posterolateral surface is called the gluteal surface
The auricular surface articulates with the sacrum (sacroiliac joint)
Major markings include the iliac crests, four spines, greater sciatic notch, iliac fossa, arcuate line, and the pelvic brim
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Ilium: Medial View
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Ischium
The ischium forms the posteroinferior part of the hip bone
The thick body articulates with the ilium, and the thinner ramus articulates with the pubis
Major markings include the ischial spine, lesser sciatic notch, and the ischial tuberosity
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Pubis
The pubic bone forms the anterior portion of the hip bone
It articulates with the ischium and the ilium
Major markings include superior and inferior rami, the pubic crest, pubic tubercle, pubic arch, pubic symphysis, and obturator foramen (along with ilium and ischium)
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Pubis: Medial View
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Comparison of Male and Female Pelvic Structure
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Comparison of Male and Female Pelvic Structure
Characteristic Female Male
Bone thicknessLighter, thinner, and smoother
Heavier, thicker, and more prominent markings
Pubic arch/angle
80˚–90˚ 50˚–60˚
Acetabula Small; farther apartLarge; closer together
SacrumWider, shorter; sacral curvature is accentuated
Narrow, longer; sacral promontory more ventral
Coccyx More movable; straighterLess movable; curves ventrally
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The Lower Limb
The three segments of the lower limb are the thigh, leg, and foot
They carry the weight of the erect body, and are subjected to exceptional forces when one jumps or runs
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Femur
The sole bone of the thigh is the femur, the largest and strongest bone in the body
It articulates proximally with the hip and distally with the tibia and fibula
Major markings include the head, fovea capitis, greater and lesser trochanters, gluteal tuberosity, lateral and medial condyles and epicondyles, linea aspera, patellar surface, and the intercondylar notch
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Leg
The tibia and fibula form the skeleton of the leg
They are connected to each other by the interosseous membrane
They articulate with the femur proximally and with the ankle bones distally
They also articulate with each other via the immovable tibiofibular joints
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Tibia
Receives the weight of the body from the femur and transmits it to the foot
Major markings include medial and lateral condyles, intercondylar eminence, the tibial tuberosity, anterior crest, medial malleolus, and fibular notch
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Fibula
Sticklike bone with slightly expanded ends located laterally to the tibia
Major markings include the head and lateral malleolus
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Foot
The skeleton of the foot includes the tarsus, metatarsus, and the phalanges (toes)
The foot supports body weight and acts as a lever to propel the body forward in walking and running
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Tarsus
Composed of seven bones that form the posterior half of the foot
Body weight is carried primarily on the talus and calcaneus
Talus articulates with the tibia and fibula superiorly, and the calcaneus inferiorly
Other tarsus bones include the cuboid and navicular, and the medial, intermediate, and lateral cuneiforms
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Calcaneus
Forms the heel of the foot Carries the talus on its superior surface Point of attachment for the calcaneal
(Achilles) tendon of the calf muscles
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Metatarsus and Phalanges
Metatarsus and Phalanges Metatarsals
– Five (1-5) long bones that articulate with the proximal phalanges
– The enlarged head of metatarsal 1 forms the “ball of the foot”
Phalanges– The 14 bones of the toes– Each digit has three
phalanges except the hallux, which has no middle phalanx
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Arches of the Foot
The foot has three arches maintained by interlocking foot bones and strong ligaments
Arches allow the foot to hold up weight
The arches are:– Lateral longitudinal – cuboid is
keystone of this arch– Medial longitudinal – talus is
keystone of this arch– Transverse – runs obliquely
from one side of the foot to the other
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Developmental Aspects: Fetal Skull
Infant skull has more bones than the adult skull
At birth, fetal skull bones are incomplete and connected by fontanels
Fontanels– Unossified remnants of
fibrous membranes between fetal skull bones
– The four fontanels are anterior, posterior, mastoid, and sphenoid
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B. The appendicular skeleton includes the bones of the arms and legs and structures associated with them (shoulder, hip, wrist, ankle, fingers, toes).
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Upper Limb
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Lower Limb
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Classification of Bones: By Shape
Long bones – longer than they are wide (e.g., humerus)
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Classification of Bones: By Shape
Short bones– Cube-shaped bones of
the wrist and ankle– Bones that form within
tendons (e.g., patella)
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Classification of Bones: By Shape
Flat bones – thin, flattened, and a bit curved (e.g., sternum, and most skull bones)
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Classification of Bones: By Shape
Irregular bones – bones with complicated shapes (e.g., vertebrae and hip bones)
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Shapes of Bones Video
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Joints Chapter 8
C. Joints are where two or more bones meet.
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Joints (Articulations)
Weakest parts of the skeleton Articulation – site where two or more bones
meet Functions of joints
– Give the skeleton mobility– Hold the skeleton together
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Classification of Joints: Structural
Structural classification focuses on the material binding bones together and whether or not a joint cavity is present
The three structural classifications are:– Fibrous– Cartilaginous – Synovial
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Classification of Joints: Functional
Functional classification is based on the amount of movement allowed by the joint
The three functional classes of joints are:– Synarthroses – immovable – Amphiarthroses – slightly movable – Diarthroses – freely movable
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Fibrous Structural Joints
The bones are joined by fibrous tissues There is no joint cavity Most are immovable There are three types – sutures,
syndesmoses, and gomphoses
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Fibrous Structural Joints: Sutures
Occur between the bones of the skull Comprised of interlocking junctions
completely filled with connective tissue fibers Bind bones tightly together, but allow for
growth during youth In middle age, skull bones fuse and are
called synostoses
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Fibrous Structural Joints: Sutures
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Fibrous Structural Joints: Syndesmoses
Bones are connected by a fibrous tissue ligament
Movement varies from immovable to slightly variable
Examples include the connection between the tibia and fibula, and the radius and ulna
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Fibrous Structural Joints: Gomphoses
The peg-in-socket fibrous joint between a tooth and its alveolar socket
The fibrous connection is the periodontal ligament
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Cartilaginous Joints
Articulating bones are united by cartilage Lack a joint cavity Two types – synchondroses and symphyses
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Cartilaginous Joints: Synchondroses
A bar or plate of hyaline cartilage unites the bones
All synchondroses are synarthrotic
Examples include: – Epiphyseal plates of
children– Joint between the costal
cartilage of the first rib and the sternum
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Cartilaginous Joints: Symphyses
Hyaline cartilage covers the articulating surface of the bone and is fused to an intervening pad of fibrocartilage
Amphiarthrotic joints designed for strength and flexibility
Examples include intervertebral joints and the pubic symphysis of the pelvis
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Synovial Joints
Those joints in which the articulating bones are separated by a fluid-containing joint cavity
All are freely movable diarthroses Examples – all limb joints, and most joints of
the body
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Synovial Joints: General Structure
Synovial joints all have the following
– Articular cartilage– Joint (synovial) cavity– Articular capsule– Synovial fluid– Reinforcing ligaments
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Synovial Joints: Friction-Reducing Structures
Bursae – flattened, fibrous sacs lined with synovial membranes and containing synovial fluid
Common where ligaments, muscles, skin, tendons, or bones rub together
Tendon sheath – elongated bursa that wraps completely around a tendon
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Synovial Joints: Movement
The two muscle attachments across a joint are:– Origin – attachment to the immovable bone– Insertion – attachment to the movable bone
Described as movement along transverse, frontal, or sagittal planes
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Synovial Joints: Range of Motion
Nonaxial – slipping movements only Uniaxial – movement in one plane Biaxial – movement in two planes Multiaxial – movement in or around all three
planes
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Gliding Movements
One flat bone surface glides or slips over another similar surface
Examples – intercarpal and intertarsal joints, and between the flat articular processes of the vertebrae
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Angular Movement
Flexion — bending movement that decreases the angle of the joint
Extension — reverse of flexion; joint angle is increased Dorsiflexion and plantar flexion — up and down movement of
the foot Abduction — movement away from the midline Adduction — movement toward the midline Circumduction — movement describes a cone in space
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Gliding Movement
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Angular Movement: Flexion/Extension
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Hypertension/Flexion
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Dorsiflexion/Plantar flexionAbduction/Adduction/Circumduction
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Rotation
Rotation The turning of a bone
around its own long axis
Examples– Between first two
vertebrae– Hip and shoulder joints
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Special Movements
Supination and pronation Inversion and eversion Protraction and retraction Elevation and depression Opposition
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Supination/Pronation
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Inversion/Eversion
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Protraction/Retraction
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Elevation/Depression
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Opposition
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Joints Video
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Hinge Joint:
Hinge joints– Cylindrical projections of
one bone fits into a trough-shaped surface on another
– Motion is along a single plane
– Uniaxial joints permit flexion and extension only
– Examples: elbow and interphalangeal joints
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Condyloid, or Ellipsoidal, Joints
Oval articular surface of one bone fits into a complementary depression in another
Both articular surfaces are oval
Biaxial joints permit all angular motions
Examples: radiocarpal (wrist) joints, and metacarpophalangeal (knuckle) joints
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Saddle Joint
Condyloid, or Ellipsoidal, Joints Oval articular surface of one
bone fits into a complementary depression in another
Both articular surfaces are oval Biaxial joints permit all angular
motions Examples: radiocarpal (wrist)
joints, and metacarpophalangeal (knuckle) joints
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Ball and Socket Joint
A spherical or hemispherical head of one bone articulates with a cuplike socket of another
Multiaxial joints permit the most freely moving synovial joints
Examples: shoulder and hip joints
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Gliding Joint
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Pivot Joint
Rounded end of one bone protrudes into a “sleeve,” or ring, composed of bone (and possibly ligaments) of another
Only uniaxial movement allowed
Examples: joint between the axis and the dens, and the proximal radioulnar joint
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Synovial Joints: Knee
Largest and most complex joint of the body
Allows flexion, extension, and some rotation
Three joints in one surrounded by a single joint cavity
– Femoropatellar– Lateral and medial
tibiofemoral joints
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Synovial Joints: Knee – Other Supporting Structures
Anterior cruciate ligament
Posterior cruciate ligament
Medial meniscus (semilunar cartilage)
Lateral meniscus
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Synovial Joints: Knee – Posterior Superficial View
Adductor magnus tendon
Articular capsule Oblique popliteal
ligament Arcuate popliteal
ligament Semimembranosus
tendon
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Synovial Joints: Shoulder Stability
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Hip
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Elbow
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Bones and Cartilage Video
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Ligaments
D. Ligaments are tough bands of connective tissue that attaches one bone to another.
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Tendons
E. Bands of cartilage that binds muscle to bone.
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Bursae
E. Bursae act to decrease friction and keep bones and tendons from rubbing against each other.
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Structure of Bone
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F. Anatomy of a bone:– 1. Compact bone
a. Found in the middle of long bones
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Structure of Long Bone
Long bones consist of a diaphysis and an epiphysis
Diaphysis– Tubular shaft that forms the axis of long bones– Composed of compact bone that surrounds the
medullary cavity– Yellow bone marrow (fat) is contained in the
medullary cavity
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The medullary cavity is the space within the diaphysis.
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Structure of Long Bone
Epiphyses– Expanded ends of long bones– Exterior is compact bone, and the interior is
spongy bone– Joint surface is covered with articular (hyaline)
cartilage– Epiphyseal line separates the diaphysis from the
epiphyses
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Structure of Long Bone
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Bone Membranes
Periosteum – double-layered protective membrane
– Outer fibrous layer is dense regular connective tissue
– Inner osteogenic layer is composed of osteoblasts and osteoclasts
– Richly supplied with nerve fibers, blood, and lymphatic vessels, which enter the bone via nutrient foramina
– Secured to underlying bone by Sharpey’s fibers
Endosteum – delicate membrane covering internal surfaces of bone
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Structure of Short, Irregular, and Flat Bones
Thin plates of periosteum-covered compact bone on the outside with endosteum-covered spongy bone (diploë) on the inside
Have no diaphysis or epiphyses Contain bone marrow between the
trabeculae
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Structure of a Flat Bone
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Location of Hematopoietic Tissue (Red Marrow)
In infants– Found in the medullary cavity and all areas of
spongy bone
In adults– Found in the diploë of flat bones, and the head of
the femur and humerus
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Microscopic Structure of Bone: Compact Bone
Haversian system, or osteon – the structural unit of compact bone
– Lamella – weight-bearing, column-like matrix tubes composed mainly of collagen
– Haversian, or central canal – central channel containing blood vessels and nerves
– Volkmann’s canals – channels lying at right angles to the central canal, connecting blood and nerve supply of the periosteum to that of the Haversian canal
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Microscopic Bone
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Microscopic Structure of Bone: Compact Bone
Osteocytes – mature bone cells Lacunae – small cavities in bone that contain
osteocytes Canaliculi – hairlike canals that connect
lacunae to each other and the central canal
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Microscopic Structure of Bone: Compact Bone
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– 2. Spongy bone a. Found at the ends of long bone
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Cartilage Video
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Chemical Composition of Bone: Organic
Osteoblasts – bone-forming cells Osteocytes – mature bone cells Osteoclasts – large cells that resorb or break
down bone matrix Osteoid – unmineralized bone matrix
composed of proteoglycans, glycoproteins, and collagen
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Chemical Composition of Bone: Inorganic
Hydroxyapatites, or mineral salts– Sixty-five percent of bone by mass– Mainly calcium phosphates– Responsible for bone hardness and its resistance
to compression
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– 4. Your bones grow in length and diameter. a. Growth occurs are growth plate
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Bone Development
Osteogenesis and ossification – the process of bone tissue formation, which leads to:– The formation of the bony skeleton in embryos– Bone growth until early adulthood– Bone thickness, remodeling, and repair
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How Bones Change Video
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Formation of the Bony Skeleton
Begins at week 8 of embryo development Intramembranous ossification – bone
develops from a fibrous membrane Endochondral ossification – bone forms by
replacing hyaline cartilage
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Intramembranous Ossification
Formation of most of the flat bones of the skull and the clavicles
Fibrous connective tissue membranes are formed by mesenchymal cells
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Stages of Intramembranous Ossification
An ossification center appears in the fibrous connective tissue membrane
Bone matrix is secreted within the fibrous membrane
Woven bone and periosteum form Bone collar of compact bone forms, and red
marrow appears
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Stages of Intramembranous Ossification
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Stages of Intramembranous Ossification
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Stages of Intramembranous Ossification
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Stages of Intramembranous Ossification
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Endochondral Ossification
Begins in the second month of development Uses hyaline cartilage “bones” as models for
bone construction Requires breakdown of hyaline cartilage prior
to ossification
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Stages of Endochondral Ossification
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Long Bone Growth and Remodeling
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Appositional Growth of Bone
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Importance of Ionic Calcium in the Body
Calcium is necessary for:– Transmission of nerve impulses– Muscle contraction– Blood coagulation– Secretion by glands and nerve cells– Cell division
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Hormonal Mechanism
Rising blood Ca2+ levels trigger the thyroid to release calcitonin
Calcitonin stimulates calcium salt deposit in bone Falling blood Ca2+ levels signal the parathyroid
glands to release PTH PTH signals osteoclasts to degrade bone matrix and
release Ca2+ into the blood
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Hormonal Mechanism
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Importance of Ionic Calcium in the Body
Calcium is necessary for:– Transmission of nerve impulses– Muscle contraction– Blood coagulation– Secretion by glands and nerve cells– Cell division
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Response to Mechanical Stress
Wolff’s law – a bone grows or remodels in response to the forces or demands placed upon it
Observations supporting Wolff’s law include– Long bones are thickest midway along the shaft
(where bending stress is greatest)– Curved bones are thickest where they are most
likely to buckle
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Bone Fractures (Breaks)
Bone fractures are classified by:– The position of the bone ends after fracture– The completeness of the break– The orientation of the bone to the long axis– Whether or not the bones ends penetrate the skin
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Types of Bone Fractures
Nondisplaced – bone ends retain their normal position
Displaced – bone ends are out of normal alignment Complete – bone is broken all the way through Incomplete – bone is not broken all the way through Linear – the fracture is parallel to the long axis of the
bone
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Types of Bone Fractures
Transverse – the fracture is perpendicular to the long axis of the bone
Compound (open) – bone ends penetrate the skin
Simple (closed) – bone ends do not penetrate the skin
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Common Types of Fractures
Comminuted – bone fragments into three or more pieces; common in the elderly
Spiral – ragged break when bone is excessively twisted; common sports injury
Depressed – broken bone portion pressed inward; typical skull fracture
Compression – bone is crushed; common in porous bones
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Common Types of Fractures
Epiphyseal – epiphysis separates from diaphysis along epiphyseal line; occurs where cartilage cells are dying
Greenstick – incomplete fracture where one side of the bone breaks and the other side bends; common in children
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Stages in the Healing of a Bone Fracture
Hematoma formationTorn blood vessels hemorrhageA mass of clotted blood (hematoma) forms at the fracture siteSite becomes swollen, painful, and inflamed
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Stages in the Healing of a Bone Fracture
Fibrocartilaginous callus formsGranulation tissue (soft callus) forms a few days after the fractureCapillaries grow into the tissue and phagocytic cells begin cleaning debris
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Bones produce blood cells in the red marrow.– a. Found in
1. humerus 2. femur 3. sternum 4. ribs 5. vertebrae 6. pelvis
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Stages in the Healing of a Bone FractureThe fibrocartilaginous callus forms when:
– Osteoblasts and fibroblasts migrate to the fracture and begin reconstructing the bone
– Fibroblasts secrete collagen fibers that connect broken bone ends
– Osteoblasts begin forming spongy bone– Osteoblasts furthest from capillaries secrete an
externally bulging cartilaginous matrix that later calcifies
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Stages in the Healing of a Bone Fracture
Bony callus formationNew bone trabeculae appear in the fibrocartilaginous callusFibrocartilaginous callus converts into a bony (hard) callusBone callus begins 3-4 weeks after injury, and continues until firm union is formed 2-3 months later
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Stages in the Healing of a Bone Fracture
Stages in the Healing of a Bone FractureBone remodeling
Excess material on the bone shaft exterior and in the medullary canal is removedCompact bone is laid down to reconstruct shaft walls
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Homeostatic Imbalances
Osteomalacia– Bones are inadequately mineralized causing
softened, weakened bones– Main symptom is pain when weight is put on the
affected bone– Caused by insufficient calcium in the diet, or by
vitamin D deficiency
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Homeostatic Imbalances
Rickets– Bones of children are inadequately mineralized
causing softened, weakened bones– Bowed legs and deformities of the pelvis, skull,
and rib cage are common– Caused by insufficient calcium in the diet, or by
vitamin D deficiency
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Homeostatic Imbalances
Osteoporosis– Group of diseases in which bone reabsorption
outpaces bone deposit– Spongy bone of the spine is most vulnerable– Occurs most often in postmenopausal women– Bones become so fragile that sneezing or
stepping off a curb can cause fractures
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Osteoporosis: Treatment
Calcium and vitamin D supplements Increased weight-bearing exercise Hormone (estrogen) replacement therapy
(HRT) slows bone loss Natural progesterone cream prompts new
bone growth Statins increase bone mineral density
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Paget’s Disease
Characterized by excessive bone formation and breakdown
Pagetic bone with an excessively high ratio of woven to compact bone is formed
Pagetic bone, along with reduced mineralization, causes spotty weakening of bone
Osteoclast activity wanes, but osteoblast activity continues to work
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Paget’s Disease
Usually localized in the spine, pelvis, femur, and skull
Unknown cause (possibly viral) Treatment includes the drugs Didronate and
Fosamax
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Developmental Aspects of Bones
Mesoderm gives rise to embryonic mesenchymal cells, which produce membranes and cartilages that form the embryonic skeleton
The embryonic skeleton ossifies in a predictable timetable that allows fetal age to be easily determined from sonograms
At birth, most long bones are well ossified (except for their epiphyses)
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Developmental Aspects of Bones
By age 25, nearly all bones are completely ossified
In old age, bone reabsorption predominates A single gene that codes for vitamin D
docking determines both the tendency to accumulate bone mass early in life, and the risk for osteoporosis later in life
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– 6. Yellow bone marrow contains fat and is found in many bones.
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– 7. Bones store minerals. a. Calcium and phosphate needed to form strong
bones.– 1. Found in:
Milk Yogurt Cheese Lettuce Spinach Leafy vegetables
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Care
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– 8. Bones can become more brittle with age: osteoporosis. Caused by loss of bone volume and content.
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Quiz