Skeletal tissues contain 3 cartilages

1. hyaline cartilages- provide support, flexibility, and resilience, most abundant type

2. elastic cartilages- similar to hyaline cartilages but contain elastic fibers

3. fibrocartilages- collagen fibers- have great tensile strength

Appositional Growth

(from outside)

cells secrete matrix against the external face of existing cartilage

- increases thickness and remodeling of all bones by osteoblasts and osteoclasts on bone surfaces

Interstitial Growth

chondrocytes divide and secret new matrix, expanding cartilage from within.

- increases length of bones

Axial skeleton

skull, vertebral column and rib cage

Appendicular skeleton

bones of upper and lower limbs

Classifications of bones by shape

1. Long bones- longer than they are wide (limbs bones)
2. short bones- cube shaped (in wrist and ankle). Sesamoid bones (w/in tendons, i.e- patella)
3. flat bones- thin, flat, slightly curved
4. irregular bones- complicated shapes

Functions of Bones

1. Support
2. Protection
3. Movement
4. Storage- minerals (Ca²⁺ and phosphorus) and growth factors
5. Blood cell formation (hematopoiesis) in marrow cavities
6. Triglyceride (energy storage) in bone cavities

Features of bone markings

projections, depressions, and holes or openings that serve as:

• sites of attachment for muscles, ligaments, and tendons
• joint surfaces
• conduits for blood vessels and nerves

Tuberosity

rounded projection

Crest

narrow, prominent ridge

Trochanter

large, blunt, irregular surface

Line

narrow ridge of bone

Tubercle

small rounded projection

Epicondyle

raised area above a condyle

Spine

sharp, slender projection

Process

any bony prominence

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

Meatus

canal-like passageway

Sinus

cavity w/in a bone

Fossa

shallow, basin-like depression

Groove

furrow

Fissure

narrow, slitlike opening

Foramen

round or oval opening through a bone

Periosteum

• outer fibrous layer
• inner osteogenic layer

Osteoblasts

bone-forming cells

Osteoclasts

bone-destroying cells

Osteogenic cells

stem cells

Endosteum

cover spongy bone w/in

short irregular and flat bone

contains osteoblasts and osteoclasts

Red marrow cavities of adults

• trabecular cavities of the heads of the femur and humerus
• trabecular cavities of the diploe of flat bones

Red marrow cavities of newborn infants

medullary cavities and all spaces in spongy bone

lacunae

small cavities that contain osteocytes

Canaliculi

hairlike canals that connect lacunae to each other and the central canal

Volkmann's canals

at right angles to the central canal

connects blood vessels and nerves of the periosteum and central canal

Central (Haversian) canal

contains blood vessels and nerves

Lamellae

weight-bearing; column-like matrix tubes

Trabeculae

located in spongy bone.

align along lines of stress

no osteons; contain irregularly arranged lamellae, osteocytes and canaliculi

Osteoid

organic bone matrix secreted by osteoblasts

ground substance (proteoglycans, glycoproteins)

Intramembranous Ossification

• membrane bone develops from fibrous membrane (no cartilage)
• forms flat bones

Endochondral Ossification

• type of ossification
• requires breakdown of hyaline cartilage prior to ossification

Describe intramembranous ossification process

1. ossification centers appear in the fibrous connective tissue membrane

2. bone matrix (osteoid) is secreted w/in firbrous membrane and calcifies

3. woven bone and periosteum form

4. lamellar bone replaces woven bone, just deep to the periosteum. Red marrow appears.

Describe Endochondral Ossification process

1. bone collar forms around the hyaline cartilage model
2. cartilage in the center of the diaphysis calcifies and then develops cavities
3. the periosteal bud invades the internal cavities and spongy bones begins to form
4. the diaphysis elongates and a medullary cavity forms as ossification continues. Secondary ossification centers appear in the epiphyses in preparation for stage 5.
5. The epiphyses ossify. When completed, hyaline cartilage remains only in the epiphyseal plates and articular cartilages.

Epiphyseal plate cartilage organizes into 4 important functional zones.

1. proliferation (growth)- cartilage undergoes mitosis
2. hypertonic- increasing thickness, older cartilage cells in large
3. calcification- matrix calcifies, cartilage cells die; matrix begins deteriorating, blood vessels invade the cavity
4. ossification (osteogenic) new bone forms

Growth hormone stimulates...

epyphyseal plate activity

Thyroid hormone modulates...

activity of growth hormone

When does bone deposit (bone building) occur?

1. occurs where bone is injured or added strength is needed

Requires a diet rich in protein, vitamin C, D, and A; calcium; phosphorus magnesium; and manganese

Describe process of bone deposit (bone building)

Sites of new matrix deposit are revealed by the

• Osteoid seam- unmineralized band of matrix
• calcification front- the abrupt transition zone between the osteoid seam and older mineralized bone

Describe bone resorption (breaking down) process

• Osteoclasts secrete lysosomal enzymes (digestic organic matrix). Acids convert calcium salts into soluble forms
• Dissolved matrix is transcytosed across osteoclast, enters interstitual fluid and then blood

What controls continual remodeling of the bone?

calcium, phosphorus, mechanical and gravitational forces (body weight)

What is the importance of Calcium?

• transmission of nerve impulses
• muscle contraction
• blood coagulation
• secretion of glands and nerve cells
• cell division

Calcium

controlled by parathyroid hormone (PTH)

• when blood calcium levels decreases
• PTH stimulates osteoclasts to degrade bone matrix and release Calcium.
• Blood calcium levels increases to normalization

Secondarily controlled by calcitonin

• when blood calcium levels increases
• parafollicular cells of thyroid release calcitonin
• osteoblasts deposit calcium salts
• blood calcium levels decreases to normalization

Wolff's law

a bone grows and remodels in response to forces or demands placed upon it.

What are the 4 stages of healing of a bone fracture?

1. hematoma forms
2. fibrocartilages callus forms
3. bony callus formation
4. bone remodeling

Paget's Disease

excessive and haphazard (disorganized) bone formation and breakdown, usually in spine, pelvis femur or skull (not controlled)