Anatomy & Physiology I - EXAM 2

EXAM 2 -SKELETAL

What is Bone?

A connective tissue made of

osteoblasts (secrete osteoid)

osteocytes (osteoblasts trapped in matrix for maintenance, repair, and sensing mechanical stress)

osteoclasts (break down ECM and remodel)

What is Osseous Tissue?

Specialized connective tissue that is dense, more durable than cartilage.

Highly vascular w/ organic and inorganic components to resist compression/tension

Functions of Skeletal System?

1. Support

2. Protection

3. Muscle attachment

4. Energy and mineral reserves

5. Hematopoiesis (blood production)

What is the ECM made of?

Composite material is organic and inorganic

Organic: osteoid (collagen, carb, protein) for tensile strength

Inorganic: hydroxyapetite (calcium, phosphorus, oxygen) for compressive strength

Why is Bone Harder/More Durable than Cartilage?

Its extracellular matrix is mineralized.

What is the Primary Protein Found in the Bone ECM?

Collagen protein fibers

What Does the Organic Portion of the Osseous ECM Provide?

Resistance to stretch

Tensile strength

Flexibility

What Does the Inorganic Portion of the Osseous ECM Provide?

Resistance to compressive force

Hardness

Rigidity

Rickets Disease (and Osteomalacia)

Inadequate calcification in ECM through lack of Vit D, Ca, or P

Leads to softening of bones and deformity (bow legs)

Osteogenesis Imperfecta

Congenital collagen defect

Brittle bones with easy fractures

Types of Fractures

Stress Fracture: abnormal trauma

Pathological Fracture: bone weakened by disease process

What is Cortical Bone?

Compact bone organized into osteons w/ concentric lamellae of ECM

Central canal for neurovasculature

Oriented parallel to direction of compressive stress; alternating collagen direction provides multidirectional stability to resist torsion

What is Cancellous Bone?

Organized into trabeculae w/out osteons

Strong, lightweight with space sometimes filled w/ red bone marrow

What are the Periosteum and Endosteum?

Both are dense irregular connective tissue, highly innervated/sensitive, produce osteoblasts

Periosteum: external covering

Endosteum: internal covering

Describe a Long Bone

Cancellous bone internally w/ red bone marrow

Articular cartilage externally

Epiphysis: enlarged end

Diaphysis: shaft made of cortical bone w/ medullary cavity for yellow bone marrow

What are Flat, Short, and Irregular Bones Made of? Examples?

Cancellous bone surrounded by cortical bone to protect underlying structures

No medullary cavity

Short: Metacarpals/tarsals

Irregular: os coxae, skull, vertebrae, hyoid

Flat: sternum

Sesamoid: patella (largest)

Cancellous bone is laid down in branching projections called __________________.

Trabeculae

Cortical bone is organized into ______ with concentric ______ of ECM.

Osteons, lamellae

What are the Two Types of Bone Formation?

Intramembranous & Endochondral

When does Ossification Begin?

Embryonic Week 8

Describe Intramembranous Ossification. What bones?

Cranial bones, facial bones, and clavicle

1. Primary ossification center forms in fetal connective tissue

2. Osteoblasts develop and secrete osteoid. Cancellous bone trabeculae form around blood vessels.

3. Crystals incorporate, turning osteoblasts into cytes. Surrounding tissue becomes periosteum now surrounding bone.

4. Periosteum forms superficial cortical bone, which crowd blood vessels to create red marrow.

Describe Endochondral Ossification. What bones?

Long bones

1. Hyaline cartilage cells differentiate into chondrocytes and perichondrium form.

2. Capillaries penetrate cartilage and perichondrium transforms into periosteum. Bony collar and primary ossification center develops.

3. Chondrocytes die and osteoclasts break down to form medullary cavity (LONG BONES ONLY)

4. Bony collar expands and secondary ossification centers develop at epiphyses. Osteoblasts form cancellous bone from cartilage. Cartilage remains at epiphyseal (growth) plate and articular cartilage at joints.

What is Primary Bone?

“Woven bone”

Quickly laid down in irregular collagen fibers (no osteons w/ parallel orientation, so less durable)

Minimal inorganic matrix

Eventually resorbed

What is Secondary Bone?

“Lamellar bone”

Produced slowly

Fully formed osteons with parallel collagen orientation

Higher % inorganic matrix so stronger

Describe Two Types of Bone Marrow.

Red - Hemapoietic tissue

Every bone in children

Head and trunk in adults

Yellow - Fat storage

Limbs in adults

Describe Longitudinal Bone Growth.

Occurs at epiphyseal plate

Chondrocytes divide to push epiphysis away from diaphysis

Cartilage matrix ossifies

What Are the Five Zones of Cartilage?

1. Zone of Reserve Cartilage (inactive chondrocytes)

2. Zone of Proliferation (rapid division)

3. Zone of Hypertrophy (increase in size)

4. Zone of Calcification (dead chondrocytes in calcified matrix)

5. Zone of Ossification (osteoblasts ossify calcified cartilage)

What Marks the End of Longitudinal Growth?

Cartilaginous tissue is overtaken by ossification, and epiphyseal plate closes

Women - 18 y/o

Men - 21 y/o

What is Achondroplasia?

Failure of cartilage growth in epiphyseal plate (ONLY LONG BONES)

Can be spontaneous mutation or hereditary

Describe Appositional Bone Growth.

Occurs at periosteal surface in between layers of periosteum and endosteum (SIMILAR TO INTRAMEMBRANOUS OSS)

Periosteal osteoblasts secrete new matrix (superficial cortical bone)

Osteoclasts erode medullary cavity to bone width remains proportional

What Hormones Regulate Growth?

Growth Hormone, Estrogen, Testosterone

What does Growth Hormone Do?

Increase chondrocyte division at epiphyseal plate

Increase osteogenic cell activity

Stimulate osteoblasts in periosteum

What does Testosterone Do?

Increase appositional growth

Increase chondrocyte cell division

What does Estrogen Do?

Inhibit osteoclast activity

Accelerates epiphyseal closure

What are the Functions of Skeletal Remodeling.

Occurs on periosteal and enosteal surfaces

• Reshape bone during growth

• Reshape in response to use

• Repair damage

• Release minerals into blood

How does Skeletal Remodeling Occur?

• Deposition

  • Osteoblasts secrete osteoid w/ collagen fibers in spiral along osteon

  • Ca and P crystalize on collagen to form hydroxyapetite

• Resorption

  • Osteoclasts dissolve bone and return minerals to blood

How is Skeletal Remodeling Regulated?

Calcium homeostasis is required for neuron signaling, muscle contraction, and clotting

Calcitriol, Calcitonin, and Parathyroid Hormone

Describe the Three Hormones Responsible for Regulating Remodeling.

Calcitriol (active Vit D)

• raises blood calcium by promoting small intestine absorption, skeletal resorption, reducing kidney excretion

Calcitonin

• secreted by thyroid to inhibit osteoclasts and stimulate osteoblasts (hypercalcemia)

PTH

• inhibits osteoblasts, stimulates osteoclasts, reduces kidney excretion, and promotes calcitriol synthesis (hypocalcemia)

What is Wolff’s Law?

Bones will remodel according to habitual demand. (Compact bone thickest in diaphysis, large projections for muscel attachment)

What are the Step to Healing a Fracture?

1. Inflammatory Response (blood clot with fibroblasts, chondrocytes, osteoblasts/clasts, macrophages)

2. Soft Callus (fibroblasts secrete collagen and chondrocytes to produce fibrocartilage and repair periosteum/endosteum)

3. Hard Callus (osteoblasts produce bony collar in 4-6 weeks, similar to endochondral ossification)

4. Remodeling (clasts break down fragments and blasts build cancellous bone and ossifies to give cortical bone)

Explain How Aging Effects the Skeletal System.

When younger, deposition > resorption

When older resorption > deposition

What is Osteoporosis?

Excessive resorption of bone with loss of density

Cancellous bone of vertebra and femur most vulnerable, often related to decline in estrogen

Risks: smoking, diabetes, nutrition, activity

Tx: estrogen replacement, medication, supplements, weight training

Prevention: calcium rich diet, vit D, reduced alcohol and carbonated drinks

What are the Specific Carpals You Need to Know?

Pisiform - sesamoid bone developed by age 12 (distal to ulna)

Scaphoid - most frequently fractured by FOOSH injuries (distal to radius)

What are the Types of Joints?

Fibrous Joints - joined by dense connective tissue (sutures)

Cartilaginous - joined by cartilage, slightly mobile (pubic symphysis, costochondral)

Synovial Joints - cavity enclosed by capsule covered by cartilage, great mobiilty

Describe the Construction of a Synovial Joint.

• Superficial Fibrous Layer

  • dense connective tissue merged with periosteum and ligaments

• Deep Synovial Layer

  • produced fluid to reduce friction

Cushioned and supported by ligaments and hyaline cartilage

Describe the Types of Synovial Joints

Plane Joint - flat surfaces glide over one another (carpals, tarsals)

Hinge - convex end articulates with C-shaped depression (elbow, knee)

Pivot - rounded portion partially enclosed in ligament (atlanto-axial, radioulnar)

Ball & Socket - rounded head fits into depression (shoulder, hip)

Describe a Shoulder (glenohumeral) Dislocation.

Detachment of humeral head form glenoid fossa

Inferior displacement most common from superior blow

Causes damage to soft tissue

Compare the Shoulder and Hip

Shoulder - shallow glenoid fossa, loose muscular connection, greater mobility

Hip - deep acetabulum, strong ligament connections, greater stability

What are the Ligaments of the Knee?

Medial and Lateral Menisci - cushion and stabilize

Medial and Lateral Collateral Ligaments - prevent lateral deviation

Anterior Cruciate Ligament - prevents hyperextension

Posterior Cruciate Ligament - prevents posterior tibia displacement

The Ankle is Made of What Joints?

Talotibial and Talofibular (hinge) Joints