The Skeletal System. Function of Bones Support – form the framework that supports the body and...

The Skeletal System

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

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

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

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

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

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

The Skeletal and Muscular Systems Video

There are 206 bones in the human body

A. The axial skeleton includes the skull and the vertebral column.

Frontal View of the Skull

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

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

Skull: Posterior View

Parietal Bones and Major Associated SuturesForm most of the superior and lateral aspects of the skull

Superior View of the Skull

Posterior View of the Skull

1. Occipital Bone

2. Lambdoidal Suture

3. Parietal Bone

4. Sagittal Suture

5. Coronal Suture

6. Frontal Bone

Lateral View of the Skull

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

Bones of the Skull

Inferior of the Cranial Vault

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)

Inferior View of the Skull

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

Hyoid

1. Greater horns 2.Lesser horns 3. Body

Temporal Bones

Sphenoid Bone

Ethmoid Bone

Wormian Bones

Tiny irregularly shaped bones that appear within sutures

Mandible and Its Markings

Maxillary Bone

Orbits

Nasal Cavity

Paranasal Sinuses

Vertebral Column

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

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)

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

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

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

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

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

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

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

Cervical Vertebrae: The Atlas (C2)

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

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

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

Coccyx

Coccyx (Tailbone)– The coccyx is made up

of four (in some cases three to five) fused vertebrae that articulate superiorly with the sacrum

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

Thoracic Cage

Bony Thorax (Thoracic Cage)

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

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

Structure of a Typical True Rib

Bowed, flat bone consisting of a head, neck, tubercle, and shaft

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

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

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

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

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

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

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

Hand

Skeleton of the hand contains wrist bones (carpals), bones of the palm (metacarpals), and bones of the fingers (phalanges)

Carpus (Wrist) Consists of eight bones

– Scaphoid, lunate, triquetral, and pisiform proximally

– Trapezium, trapezoid, capitate, and hamate distally

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

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

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

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

Ilium: Medial View

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

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)

Pubis: Medial View

Comparison of Male and Female Pelvic Structure

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

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

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

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

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

Fibula

Sticklike bone with slightly expanded ends located laterally to the tibia

Major markings include the head and lateral malleolus

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

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

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

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

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

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

B. The appendicular skeleton includes the bones of the arms and legs and structures associated with them (shoulder, hip, wrist, ankle, fingers, toes).

Upper Limb

Lower Limb

Classification of Bones: By Shape

Long bones – longer than they are wide (e.g., humerus)


Short bones– Cube-shaped bones of

the wrist and ankle– Bones that form within

tendons (e.g., patella)


Flat bones – thin, flattened, and a bit curved (e.g., sternum, and most skull bones)


Irregular bones – bones with complicated shapes (e.g., vertebrae and hip bones)

Shapes of Bones Video

Joints Chapter 8

C. Joints are where two or more bones meet.

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

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

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

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

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

Fibrous Structural Joints: Sutures

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

Fibrous Structural Joints: Gomphoses

The peg-in-socket fibrous joint between a tooth and its alveolar socket

The fibrous connection is the periodontal ligament

Cartilaginous Joints

Articulating bones are united by cartilage Lack a joint cavity Two types – synchondroses and symphyses

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

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

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

Synovial Joints: General Structure

Synovial joints all have the following

– Articular cartilage– Joint (synovial) cavity– Articular capsule– Synovial fluid– Reinforcing ligaments

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

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

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

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

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

Gliding Movement

Angular Movement: Flexion/Extension

Hypertension/Flexion

Dorsiflexion/Plantar flexionAbduction/Adduction/Circumduction

Rotation

Rotation The turning of a bone

around its own long axis

Examples– Between first two

vertebrae– Hip and shoulder joints

Special Movements

Supination and pronation Inversion and eversion Protraction and retraction Elevation and depression Opposition

Supination/Pronation

Inversion/Eversion

Protraction/Retraction

Elevation/Depression

Opposition

Joints Video

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

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

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

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

Gliding Joint

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

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

Synovial Joints: Knee – Other Supporting Structures

Anterior cruciate ligament

Posterior cruciate ligament

Medial meniscus (semilunar cartilage)

Lateral meniscus

Synovial Joints: Knee – Posterior Superficial View

Adductor magnus tendon

Articular capsule Oblique popliteal

ligament Arcuate popliteal

ligament Semimembranosus

tendon

Synovial Joints: Shoulder Stability

Bones and Cartilage Video

Ligaments

D. Ligaments are tough bands of connective tissue that attaches one bone to another.

Tendons

E. Bands of cartilage that binds muscle to bone.

Bursae

E. Bursae act to decrease friction and keep bones and tendons from rubbing against each other.

Structure of Bone

F. Anatomy of a bone:– 1. Compact bone

a. Found in the middle of long bones

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

The medullary cavity is the space within the diaphysis.


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

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

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

Structure of a Flat Bone

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

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

Microscopic 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

– 2. Spongy bone a. Found at the ends of long bone

Cartilage Video

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

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

– 4. Your bones grow in length and diameter. a. Growth occurs are growth plate

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

How Bones Change Video

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

Intramembranous Ossification

Formation of most of the flat bones of the skull and the clavicles

Fibrous connective tissue membranes are formed by mesenchymal cells

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

Stages of Intramembranous Ossification

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

Stages of Endochondral Ossification

Long Bone Growth and Remodeling

Appositional Growth of Bone

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

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

Hormonal Mechanism

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

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

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

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

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

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

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

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


Fibrocartilaginous callus formsGranulation tissue (soft callus) forms a few days after the fractureCapillaries grow into the tissue and phagocytic cells begin cleaning debris

Bones produce blood cells in the red marrow.– a. Found in

1. humerus 2. femur 3. sternum 4. ribs 5. vertebrae 6. pelvis

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


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


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

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


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


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

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

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

Paget’s Disease

Usually localized in the spine, pelvis, femur, and skull

Unknown cause (possibly viral) Treatment includes the drugs Didronate and

Fosamax

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)

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

– 6. Yellow bone marrow contains fat and is found in many bones.

– 7. Bones store minerals. a. Calcium and phosphate needed to form strong

bones.– 1. Found in:

Milk Yogurt Cheese Lettuce Spinach Leafy vegetables

– 8. Bones can become more brittle with age: osteoporosis. Caused by loss of bone volume and content.

The Skeletal System. Function of Bones Support – form the framework that supports the body and...

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