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Questions and Answers

What occurs during the growth zone of long bone growth?

Bone is resorbed through remodeling.

Cartilage cells undergo mitosis. (correct)

Cartilage cells undergo apoptosis.

Osteoblasts become inactive.

What is formed during the cavitation of the hyaline cartilage stage?

Cartilage degenerates. (correct)

Secondary ossification centers develop.

Bone collar is established.

Medullary cavity appears.

During which stage does the periosteal bud invade the internal cavities?

Ossification of the epiphyses.

Invasion of internal cavities. (correct)

Formation of the medullary cavity.

Formation of bone collar.

Where does the secondary ossification occur in long bones?

In the articular cartilages. Signup and view all the answers

Which of the following defines the osteogenic zone of long bone growth?

New bone formation occurs. Signup and view all the answers

What triggers the formation of ridges in appositional growth of bone?

Secretion of bone matrix by osteoblasts. Signup and view all the answers

During bone remodeling, how does bone increase in diameter?

Through circumferential lamellae formation. Signup and view all the answers

What remains in the epiphyses after the ossification process is complete?

Articular cartilage. Signup and view all the answers

What is the primary function of hyaline cartilage?

To support and offer flexibility Signup and view all the answers

Which type of cartilage is primarily found in the external ear?

Elastic cartilage Signup and view all the answers

What is the role of osteoclasts in bone tissue?

To resorb or break down bone matrix Signup and view all the answers

Which of the following correctly describes the periosteum?

A dense irregular connective tissue membrane Signup and view all the answers

What process occurs during intramembranous ossification?

Bone develops from a fibrous membrane Signup and view all the answers

Which type of bone is characterized by having no diaphysis or epiphyses?

Short bone Signup and view all the answers

What is the primary mineral component found in bone matrix that contributes to its hardness?

Hydroxyapatites Signup and view all the answers

How do chondrocytes inside cartilage grow?

Through division and matrix secretion from lacunae Signup and view all the answers

What is the diaphysis in a long bone?

The tubular shaft of the bone Signup and view all the answers

Which cells are responsible for forming new bone tissue?

Osteoblasts Signup and view all the answers

Which type of bone has a honeycomb structure filled with marrow?

Spongy bone Signup and view all the answers

What type of bone is primarily responsible for blood cell formation?

Long bones Signup and view all the answers

Which feature is NOT associated with fibrocartilage?

Elastic fibers Signup and view all the answers

What separates the diaphysis from the epiphyses in a long bone?

Epiphyseal line Signup and view all the answers

What are the two major types of bone surface markings?

Depressions and processes Signup and view all the answers

Which bones make up the axial skeleton?

80 bones including the skull and vertebral column Signup and view all the answers

What is the function of the vertebral column?

To transmit trunk weight and protect the spinal cord Signup and view all the answers

Which part of the skull is primarily responsible for protecting the brain?

Cranium Signup and view all the answers

What stimulates epiphyseal plate activity during infancy and childhood?

Growth hormone and thyroxine Signup and view all the answers

What characterizes cervical vertebrae compared to other vertebrae?

They contain transverse foramina Signup and view all the answers

What is the primary function of osteoclasts?

Breaking down bone matrix Signup and view all the answers

Which mineral is crucial for muscle contraction and blood coagulation?

Calcium Signup and view all the answers

What is the primary role of the paranasal sinuses?

To lighten the skull Signup and view all the answers

What does Wolff’s law state regarding bone growth?

Bone remodels in response to the forces placed upon it Signup and view all the answers

How many pairs of ribs are considered true ribs?

7 pairs Signup and view all the answers

What is the function of the hyoid bone?

To support the tongue Signup and view all the answers

Which type of fracture is characterized by the bone being broken all the way through?

Complete fracture Signup and view all the answers

What is a common characteristic of comminuted fractures?

The bone fragments into three or more pieces Signup and view all the answers

Which part of the temporal bone is specifically shaped like a bat?

Petrous region Signup and view all the answers

What role does alkaline phosphatase play in bone deposition?

Essential for mineralization of bone Signup and view all the answers

Which of the following describes the occipital bone?

Forms the posterior portion of the cranium Signup and view all the answers

What happens during bony callus formation in the healing stages of a fracture?

New bone trabeculae appear in the fibrocartilaginous callus Signup and view all the answers

Which vertebra allows for the nodding motion of the head?

Atlas (C1) Signup and view all the answers

Which type of bone is cube-shaped and nearly equal in length and width?

Short bones Signup and view all the answers

What are floating ribs?

Ribs that have no anterior attachment Signup and view all the answers

What type of curvature is exaggerated in kyphosis?

Thoracic curvature Signup and view all the answers

What is a primary cause of osteoporosis?

Bone resorption outpacing bone deposit Signup and view all the answers

During which phase of fracture healing does excess material on the bone shaft get removed?

Bone remodeling Signup and view all the answers

Which type of bone is characterized by being thin and composed of two nearly parallel plates?

Flat bones Signup and view all the answers

What is a common characteristic of a greenstick fracture?

Bone bends but does not break completely Signup and view all the answers

Which statement accurately describes parathyroid hormone (PTH)?

Signals osteoclasts to degrade bone matrix Signup and view all the answers

Study Notes

Skeletal Cartilage

Contains no blood vessels or nerves.
Surrounded by perichondrium (dense irregular connective tissue).
Three types:
- Hyaline
- Elastic
- Fibrocartilage

Hyaline Cartilage

Most abundant skeletal cartilage.
Provides support, flexibility, and resilience.
Found in:
- Articular (covering ends of long bones)
- Costal (connecting ribs to sternum)
- Respiratory (making up larynx and reinforcing air passages)
- Nasal (supporting the nose)

Elastic Cartilage

Similar to hyaline cartilage, but contains elastic fibers.
Found in:
- External ear
- Epiglottis

Fibrocartilage

Highly compressed with great tensile strength.
Contains collagen fibers.
Found in:
- Menisci of the knee
- Intervertebral discs

Growth of Cartilage

Appositional: cells in perichondrium secrete matrix against existing cartilage.
Interstitial: lacunae-bound chondrocytes divide and secrete new matrix, expanding cartilage from within.
Calcification of cartilage occurs:
- During normal bone growth
- During old age

Classification of Bones: By Shape

Long bones: longer than they are wide (e.g., humerus).
Flat bones: thin, flattened, slightly curved (e.g., sternum, skull bones).
Irregular bones: bones with complex shapes (e.g., vertebrae, hip bones).

Bone Functions

Support: forms framework that cradles soft organs.
Protection: provides protective case for brain, spinal cord, and vital organs.
Leverage: provides levers for muscles.
Mineral storage: reservoir for minerals (calcium and phosphate).
Blood cell formation: hemopoiesis occurs within marrow cavities of bones.

Gross Anatomy of Bones: Bone Textures

Compact bone: dense outer layer of bone
Spongy bone: honeycomb of trabeculae filled with yellow/red bone marrow.

Structure of Long Bone

Long bones consist of diaphysis and epiphysis
Diaphysis:
- Tubular shaft forming axis of long bones
- Composed of compact bone surrounding medullary cavity/marrow cavity
- Yellow bone marrow (fat) is contained in medullary cavity
Epiphyses:
- Expanded ends of long bones
- Exterior is compact bone (cortex), 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: dense regular connective tissue
- Inner layer: composed of osteoblasts and osteoclasts
- Richly supplied with nerve fibers, blood, and lymphatic vessels, which enter the bone via nutrient foramina.
- Secured to bone by Sharpey’s fibers.
Endosteum: delicate membrane covering internal surfaces of bone

Structure of Flat Bone

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 trabeculae.

Microscopic Structure of Bone: Compact Bone

Haversian System (osteon): structural unit of compact bone.
- Lamella: weight-bearing, column-like matrix tubes composed mainly of collagen.
- Haversian (central) canal: central channel containing blood vessels and nerves.
- Volkmann’s canals: channels lying at right angles to central canal, connecting blood and nerve supply of periosteum to Haversian canal.
Osteocytes: mature bone cells.
Lacunae: small cavities in bone that contain osteocytes.
Canaliculi: hairlike canals connecting lacunae to each other and the central canal.

Cells of Bone

Osteoblasts: bone-forming cells.
Osteocytes: mature bone cells.
Osteoclasts: large cells that resorb or break down bone matrix.

Chemical Composition of Bone: Organic

Osteoid: unmineralized bone matrix composed of proteoglycans, glycoproteins, and collagen.

Chemical Composition of Bone: Inorganic

Hydroxyapatites (mineral salts):
- Sixty-five percent of bone by mass.
- Mainly calcium phosphates.
- Responsible for bone hardness and resistance to compression.

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.
At birth, most long bones are well ossified (except for their epiphyses).
By age 25, nearly all bones are completely ossified.
In old age, bone resorption predominates.
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.

Formation of Bone (Osteogenesis)

Intramembranous ossification: bone develops from a fibrous membrane (most flat bones of skull and clavicles).
Endochondral ossification: bone forms by replacing hyaline cartilage (uses hyaline cartilage as models, requires breakdown of cartilage prior to ossification).

Stages of Intramembranous Ossification

Ossification center appears in 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.

Endochondral Ossification

Begins in the second month of development.
Uses hyaline cartilage as models for bone construction.
Requires breakdown of hyaline cartilage prior to ossification.

Stages of Endochondral Ossification

Formation of bone collar.
Cavitation of the hyaline cartilage.
Invasion of internal cavities by the periosteal bud, and spongy bone formation.
Formation of the medullary cavity; appearance of secondary ossification centers in the epiphyses.
Ossification of the epiphyses, with hyaline cartilage remaining only in the epiphyseal plates and the joint cavity.

Functional Zones in Long Bone Growth

Growth zone: cartilage cells undergo mitosis, pushing the epiphysis away from the diaphysis.
Transformation zone: older cells enlarge, the matrix becomes calcified, cartilage cells die, and the matrix begins to deteriorate.
Osteogenic zone: new bone formation occurs.

Long Bone Growth in Length

Cartilage continually grows and is replaced by bone.

Long Bone Growth and Remodeling

Growth in length: cartilage continually grows and is replaced by bone.
Remodeling: bone is resorbed and added by appositional growth (increase in diameter).

Bone Growth & Remodeling

Endosteum - secretes osteoblasts that elaborate bone matrix beneath the periosteum, narrowing the canal. This process repeats, continuing to enlarge bone diameter.
Hormonal Regulation During Youth:
- Growth hormone & thyroxine stimulate epiphyseal plate activity.
- Androgens & estrogens promote adolescent growth spurts, cause masculinization/feminization of skeletal structures, and later induce epiphyseal plate closure, ending longitudinal bone growth.
Bone Deposition:
- Occurs when bone is repaired or additional strength is needed
- Diet rich in protein, vitamins C, D & A, calcium, phosphorus, magnesium, and manganese is required
- Alkaline phosphatase is essential for bone mineralization
- Osteoid seam: Unmineralized band of bone matrix.
- Calcification front: Abrupt transition zone between the osteoid seam and older, mineralized bone.
Bone Resorption:
- Performed by osteoclasts
- Resorption bays: Grooves formed by osteoclasts as they break down bone matrix.
- Osteoclasts secrete lysosomal enzymes that digest organic matrix and acids that convert calcium salts into soluble forms.
- Dissolved matrix is transcytosed across the osteoclast cell, secreted into interstitial fluid, and then into the blood.
Importance of Ionic Calcium:
- Nerve impulse transmission
- Muscle contraction
- Blood coagulation
- Secretion by glands & nerve cells
- Cell division
Control of Remodeling:
- Two control loops regulate bone remodeling:
  - Hormonal mechanism: Maintains calcium homeostasis in blood.
  - Mechanical & gravitational forces: Act on the skeleton.
Hormonal Mechanism:
- Calcitonin: Released by the thyroid gland and stimulates calcium salt deposit in bone.
- Parathyroid hormone (PTH): Released by the parathyroid gland to stimulate osteoclasts to degrade bone matrix and release calcium into the blood.
Response to Mechanical Stress:
- Wolff’s law: Bone grows or remodels in response to the demands placed upon it.
- Observations support Wolff’s law:
  - Long bones are thickest midway along the shaft where bending stress is greatest.
  - Curved bones are thickest where they are most likely to buckle.
- Trabeculae form along lines of stress.
- Large, bony projections occur where heavy, active muscles attach.
Bone Fractures (Breaks):
- Classified by:
  - Position of bone ends after fracture.
  - Completeness of the break.
  - Orientation of bone to the long axis.
  - Whether or not bone 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: Fracture parallel to the long axis of the bone.
- Transverse: Fracture 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.
- Epiphyseal: Epiphysis separates from diaphysis along the 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 formation: Torn blood vessels hemorrhage, forming a mass of clotted blood (hematoma) at the fracture site. The site becomes swollen, painful, and inflamed.
- Fibrocartilaginous callus formation: Granulation tissue (soft callus) forms a few days after the fracture. Capillaries grow into the tissue and phagocytic cells begin cleaning debris. External callus (fibrous tissue and cartilage) forms.
- Bony callus formation: New bone trabeculae appear in the fibrocartilaginous callus. Fibrocartilaginous callus converts into a bony (hard) callus. Bone callus begins 3-4 weeks after injury and continues until a firm union is formed 2-3 months later.
- Bone remodeling: Excess material on the bone shaft exterior and in the medullary canal is removed. Compact bone is laid down to reconstruct shaft walls.
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 vitamin D deficiency.
- Osteoporosis: A group of diseases where bone reabsorption outpaces bone deposition. 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.

Bone Surface Markings

Bones have unique surface markings serving specific functions.
Markings include:
- Depressions and openings: Allow passage of blood vessels, nerves, and form joints.
- Processes: Projections that form joints or attach ligaments and tendons.

Axial Skeleton

Supports the head, neck, and trunk.
Protects the brain, spinal cord, and thoracic organs.
Composed of 80 bones:
- Cranium
- Vertebral column
- Thoracic cage

The Skull

Consists of cranial and facial bones.
Cranial bones enclose and protect the brain.
Facial bones form the framework of the face, cavities for sense organs, and openings for air, food, and smell.
Sutures join the flat skull bones.

Skull Geography

Facial bones form the anterior aspect, while the cranium forms the rest.
The cranium includes the cranial vault and base:
- Cranial vault contains the forehead.
- Cranial base is the inferior portion.
Internally, bony ridges divide the skull into fossae.

Skull Cavities

The skull contains smaller cavities:
- Middle and inner ear cavities: Located laterally in the cranial base.
- Nasal cavity: Lies within and posterior to the nose.
- Orbits: House the eyeballs.
- Air-filled sinuses: Found in several bones surrounding the nasal cavity.

Skull Openings

The skull has approximately 85 openings:
- Foramina, canals, and fissures.
These openings allow passage for:
- Spinal cord
- Blood vessels serving the brain
- 12 pairs of cranial nerves

Cranial Bones

The cranium is formed by 8 bones:
- Paired: Temporal and parietal.
- Unpaired: Frontal, occipital, sphenoid, and ethmoid.

Frontal Bone

Forms the forehead and roof of the orbits.
Contains the superciliary arches.
Internally contributes to the anterior cranial fossa.
Contains frontal sinuses.

Parietal Bones and Sutures

The parietal bones form the superior and lateral parts of the skull.
The four cranial sutures include:
- Coronal suture: Where parietal bones meet the frontal bone.
- Squamous suture: Where each parietal bone meets a temporal bone.
- Sagittal suture: Where the right and left parietal bones meet.
- Lambdoid suture: Where the parietal bones meet the occipital bone.

Occipital Bone

Forms the posterior portion of the cranium and cranial base.
Articulates with the temporal and parietal bones.
Forms the posterior cranial fossa.
Contains the foramen magnum at its base.
Other features:
- Occipital condyles
- Hypoglossal foramen
- External occipital protuberance
- Superior and inferior nuchal lines

Temporal Bones

Lie inferior to parietal bones.
Form the inferolateral portion of the skull.
Contain four regions: squamous, temporal, petrous, and mastoid.

Sphenoid Bone

Spans the width of the cranial floor.
Resembles a butterfly or bat.
Includes a body and three pairs of processes.
Contains five important openings.

Ethmoid Bone

Lies between the nasal and sphenoid bones.
Forms the medial bony region between the nasal cavity and orbits.

Facial Bones

Unpaired:
- Mandible
- Vomer
Paired:
- Maxillae
- Zygomatic bones
- Nasal bones
- Lacrimal bones
- Palatine bones
- Inferior nasal conchae

Mandible

Lower jawbone, the largest and strongest facial bone.
Composed of two parts:
- Horizontal body
- Two upright rami

Maxillary Bones

Articulate with all other facial bones except the mandible.
Contain maxillary sinuses, the largest paranasal sinuses.
Form part of the inferior orbital fissure.

Other Facial Bones

Zygomatic bones: Form the lateral wall of the orbits.
Nasal bones: Form the bridge of the nose.
Lacrimal bones: Located in the medial orbital walls.
Palatine bones: Complete the posterior part of the hard palate.
Vomer: Forms the inferior part of the nasal septum.
Inferior nasal conchae: Thin, curved bones that project medially from the lateral walls of the nasal cavity.

Special Parts of the Skull

Orbits
Nasal cavity
Paranasal sinuses
Hyoid bone

Nasal Cavity

The nasal cavity is formed of:
- Nasal septum: Divides the cavity into right and left nasal fossae.
- Superior, middle, and inferior nasal conchae: Bony plates that project into the nasal cavity.

Orbits

The orbits are the bony cavities that house the eyeballs.
They are formed by seven bones:
- Frontal
- Sphenoid
- Zygomatic
- Maxillary
- Palatine
- Lacrimal
- Ethmoid

Paranasal Sinuses

Air-filled sinuses located within:
- Frontal bone
- Ethmoid bone
- Sphenoid bone
- Maxillary bones
Lined with mucous membrane.
Lighten the skull.

Hyoid Bone

Located inferior to the mandible.
Does not directly articulate with any other bone.
Acts as a movable base for the tongue.

Vertebral Column

Formed by 26 bones in an adult.
Transmits weight of the trunk to the lower limbs.
Surrounds and protects the spinal cord.
Serves as attachment sites for neck and back muscles.
Held in place by ligaments:
- Anterior and posterior longitudinal ligaments
- Ligamentum flavum

Intervertebral Discs

Cushion-like pads between vertebrae.
Act as shock absorbers.
Composed of:
- Nucleus pulposus: Gelatinous inner sphere.
- Annulus fibrosis: Outer collar of ligaments and fibrocartilage.

Herniated Disc

Occurs when the nucleus pulposus protrudes through the weakened annulus fibrosis.
Causes: Trauma, aging.

Regions and Curvatures of the Vertebral Column

5 major regions:
- Cervical vertebrae (7)
- Thoracic vertebrae (12)
- Lumbar vertebrae (5)
- Sacrum
- Coccyx
4 distinct curvatures:
- Cervical and lumbar curves: Concave posteriorly.
- Thoracic and sacral curves: Convex posteriorly.

Cervical Vertebrae

7 cervical vertebrae (C1-C7) – smallest and lightest.
C3-C7 characteristics:
- Wider body laterally.
- Short, bifid spinous processes (except C7).
- Large, triangular vertebral foramen.
- Transverse processes with transverse foramina.
- Superior articular facets facing superoposteriorly.

The Atlas (C1)

Lacks a body and spinous process.
Supports the skull.
Allows flexion and extension of the neck (nodding 'yes').

The Axis (C2)

Has a body and spinous process.
Dens (odontoid process) projects superiorly.
Participates in rotating the head from side to side.

Thoracic Vertebrae

All articulate with ribs.
Heart-shaped bodies from a superior view.
Demifacets for articulation with ribs (except T1 and T10-T12).
Long spinous processes pointing inferiorly.
Circular vertebral foramen.
Transverse processes articulate with rib tubercles.
Superior articular facets point posteriorly.
Inferior articular processes point anteriorly.

Lumbar Vertebrae

Thick and robust bodies.
Thin, tapered transverse processes.
Thick, blunt spinous processes pointing posteriorly.
Triangular vertebral foramen.
Directly medial superior and inferior articular facets.
Allow flexion and extension but prevent rotation.

Sacrum

Forms the posterior wall of the pelvis.
Consists of 5 fused vertebrae.
Articulates with L5 superiorly and the coccyx inferiorly.
Contains sacral foramina for passage of sacral nerves.

Coccyx

'Tailbone' – formed from 3-5 fused vertebrae.
Offers slight support to pelvic organs.

Bony Thorax

Forms the framework of the chest.
Components:
- Thoracic vertebrae (posteriorly)
- Ribs (laterally)
- Sternum and costal cartilage (anteriorly)
Protects thoracic organs.
Supports shoulder girdle and upper limbs.
Provides attachment sites for muscles.

Sternum

Composed of three sections:
- Manubrium: Superior section articulating with clavicles.
- Body: Bulk of the sternum.
- Xiphoid process: Inferior end.
Contains:
- Jugular notch: Central indentation at the superior border of the manubrium.
- Sternal angle: Horizontal ridge where the manubrium joins the body.

Ribs

All ribs attach to the vertebral column posteriorly.
True ribs (superior 7 pairs): Attach to the sternum by costal cartilage.
False ribs (inferior 5 pairs): Attach indirectly via costal cartilage.
Floating ribs (ribs 11-12): Do not attach to the sternum.

Disorders of the Axial Skeleton

Abnormal spinal curvatures:
- Scoliosis: Abnormal lateral curvature.
- Kyphosis: Exaggerated thoracic curvature.
- Lordosis: Accentuated lumbar curvature.
Stenosis of the lumbar spine: Narrowing of the vertebral canal.

Axial Skeleton Throughout Life

Membrane bones ossify in the second month of development.
Bone tissue grows outward from ossification centers.
Fontanels are unossified remnants of membrane.
The face and skull bones form via intramembranous ossification.
The occipital, sphenoid, ethmoid, and parts of the temporal bones develop via endochondral ossification.

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