A+P TEST 2: SKELETAL TISSUE

How many bones are you born with?

270

What are the two regions of the skeleton

Axial skeleton and appendicular skeleton

How many bones do you have by adulthood

206

What are the different shapes of bones?

Long, Short, Flat and Irregular bones

Long bones

• Longer than wide

• All limb bones except → patella, wrist bones and ankle bones

Short Bones

-Cubed shaped

• Wrist and ankle bones

• Sesamoid bones which includes the patella

Flat Bones

• Thin, flattened and curved

  • Sternum

  • Scapulae

  • Ribes

  • Most of the skull bones

Irregular bones

Do not fit any of the other bone classification

• vertebrae

• hip bones

Compact Bone

external layer

• appears to be solid and smooth

• relatively dense

• covers areas where there may be spongy bone

Spongy Bone

• honeycomb structure (mesh like )

• Open spaces between the traceculae are filled with marrow

• Spicules : delicate slivers of bone , spines or rods

Trabeculae

small needle-like or flat pieces

Contain irregularly arranged lamellae and osteocytes interconnected by Canaliculi

• Aligned along stress lines

Diaphysis

Shaft that forms the axis of the bone

Medullary Cavity

central canal surrounded by a collar of compact bone , contain bone marrow

True or False: The Shaft of the Long bone is thicker

TRUE

Epiphyses

• bone ends

• surface is covered by articular cartilage

• Thin layer of compact bone

• Interior contains spongy bone

In childhood the epiphyses and the diaphysis are separated by an

Epiphyseal plate, which become fused to form an epiphyseal line in adulthood

Metaphysis

refers to the epiphyseal plate or epiphyseal line

Periosteum

Double layered membrane that surrounds the bone

What are the two layers of the periosteum

Fibrous layer —> outer layer consisting of dense irregular connective tissue

Osteogenic layer —> inner layer of the periosteum consisting of osteoblasts and osteoclasts

The periosteum is richly supplied by…

Lymphatic vessels, nerve fibers and blood vessels

Perforating Fibers

Tuffs of collagen fibers that extends from fibrous layer to the bone

Endosteum

Delicate connective tissue membrane

-covers trabeculae of spongy bone

• covers canal system of compact bone

True or false, bone marrow is present in spongy bone

True

Where is red bone marrow ( red marrow cavities) found

In the trabecular cavities of long and short bones

In infants what bone marrow is present ?

Red bone marrow In spongy bone

Where is blood produced in bones

in the head of the femur and humerus and flat bones and some some irregular bones

True or false: Yellow marrow can’t convert back to red marrow cavities during anemia

False

Osteogenic cells

• Endosteum / periosteum

• Gives rise to osteoblast

Osteoblast

• synthesizes organic matter of matrix \ later hardens

• Reinforces bone

• Secrete osteocalcin ( insulin secretion)

Osteocytes

• Former osteoblast

• matured bone cells that occupy lacunae at junctions of lamellae

• Trapped in matrix they produced ( lacunae)

• Canaliculi - connect lacunae

  • cytoplasmic process

• Reabsorbs / deposits bone matrix

Osteoclast

Bone dissolving ( crush, chew) surface of bone

• Developed from bone cell stem cells

• Bone remodeling

Why does the ruffed border face the bone

To increase the surface area of the osteoclast and resorption bays

What’s makes up bone ?

Osteoid and hydroxyapatite’s

Osteoid

Makes up 1/3 of matrix ( mass)

• Ground substance and collagen fibers

Hydroxyapatites

Calcium phosphate

• Gives bone exceptional hardness

Osteon or Haversian system

Structural unit of compact bone

Osteon

Elongated cylinder that runs parallel to the long axis of the bone

• Weight bearing pillars

• Growth rings called lamella

Haversian or central canal

Runs through the Osteon and contains small blood vessels

Perforating canals ( volkmann)

Run perpendicular to and interconnect the central canal

Concentric lamellae

Layers of matrix around central canal

Interstitial lamellae

Incomplete lamellae lying between Osteons

Circumferential lamellae

Located deep to the periosteum and endosteum

Canaliculi

Tiny canals that connect osteocytes to each other and to central canals

Intermembranous Ossification

Process of developing bone from fibrous membrane

Forms the flat bones : clavicles and the cranial bones of the skull

• Frontal, temporal , occipital, and parietal

Before 8 weeks what does the skeleton look like

Fibrous membrane

Mesenchyme

Sheet of vascular tissue

What do the mesenchyme cell do

The mesenchyme condenses, the cells of mesenchyme line up around the vessels

• Become osteoblast

• Secrete Osteoid tissue

  • soft collagenous

  • Resemble bone but not calcified

What happens during mineralization of intramembranous ossification

Osteoid tissue hardens and continues to trap vessels and osteoblast in the hardening matrix

• Process is occurring in adjacent tissue ; forms periosteum

• Hardening matrix starts to take shape of trabeculae

• Osteoblast are constantly depositing bone

  • fill in the spaces between trabeculae

  • create zone of compact bone

  • give rise to flat bone

Endochondral ossification

• Occurs in all other bones beside the clavicle

• Begins in the second month of development

• Patterns are made of hyaline cartilage

Primary ossification center

Usually the center of cartilage shaft where ossification begins

Stage 1 of endochondral ossification

• Mensenchymal cells form hyaline cartilage covered in perichondrium

• Perichondrium produces chondrocytes and model grow in thickness

Stage 2a of endochondral ossification

• Perichondrium becomes vascularized and becomes periosteum

• Osteoblast are produced and deposit collar of bone around diaphysis of cartilage model

• Bone collar signals primary ossification center to form ~9 week fetus

Stage 2b of Endochondral Ossification

• In the primary ossification center, chondrocytes hypertrophy → signaling surrounding matrix to calcify

• Chondrocytes becomes trapped by impermeable matrix

• Chondrocytes can’t get nutrients, and die ; creating cavities

Stage 3 of endochondral ossification

Cavities invaded by periosteal bud

• Bud contains arteries, veins, nerves, Osteogenic cells and osteoclast

• Osteogenic cells become osteoblast

  1. secrete Osteoid on calcified cartilage and makes early spongy bone

  2. ~ week 12 fetus

Stage 4 of endochondral ossification

• Osteoclast break down bone in center of diaphysis → forms medullary cavity

• Diaphysis elongate as cartilage at epiphyses grow, calcifies and is dissolved by osteoclast

• Secondary ossification center forms in one or both epiphyses

• Bone at birth

Stage 5 of endochondral ossification

• Periosteal buds enters second ossification and begins to form spongy bone

• Secondary ossification is similar to primary ossification but no medulla cavity is formed

• Childhood to adolescence

Stage 6 of endochondral ossification

Epiphyses ossify

• The only cartilage remaining in the bone is articular cartilage

• Late to early teens , early twenties

Interstitial growth

• Growth in length occurs due to active cartilage at the epiphyseal plate ( elongation due to cartilage growth )

• Growth from within

What is the growth zone in bone ?

Epiphyseal plate

• Replaces bone, multiplies, and it’s only SOME

• Closure when cartilage is gone → epiphyseal line

Appositional growth ( width

Osteoid tissue deposition on the surface of bone

• Continuous growth of diameter and thickness

• Intramembranous ossification

• Osteoblast secrete Osteoid tissue → become trapped in calcified tissue

• Circumferential lamellae

• Osteocytes in endosteum enlarge marrow cavity

What is required for growth in length of bone

Epiphyseal cartilage in epiphyseal plate

What are the five zones of the epiphyseal plate

1. Reserve cartilage ( resting)

2. Proliferation (growth)

3. Cell hypertrophy

4. Calcification

5. Bone deposition ( ossification)

Resting ( reserve cartilage)

Resting chondrocytes

Proliferation ( growth) zone

Chondrocytes undergo mitosis

Cell hypertrophy zone

• Chondrocytes become bigger

• Lacunae wall thin ; begins to erode

Calcification zone

• Matrix become temporary calcified

• Chondrocytes die

Near end of adolescence; chondroblast divide

Less often

When the epiphyseal plate start to this

It’s then replaced by bone

epiphyseal plate closure occur when….

Epiphysis and diaphysis are fused

When does bone lengthening stops ?

In females ~ 18 years of age and in male ~21 years of age

Achondroplastic dwarfism

Chondrocytes in the proliferation and hypertrophic zone fail to grow

What can influence or modify bone growth?

Nutrition and hormones

• lack of calcium, protein, and other nutrients during growth and development can cause bones to be small

Vitamin D in bone

• Necessary for absorption of calcium from intestine

• Can be eaten or manufactured in the body

Vitamin C in bone

• Necessary for collagen synthesis by osteoblast

• Lack of vitamin c cause wounds not to heal, teeth to fall out

Growth Hormone (GH)

• Infancy / childhood

• From anterior pituitary

• Stimulate interstitial cartilage growth and appositional bone growth

Thyroid Hormone

• required for growth of all tissues

• Modulates GH = proper proportions

Sex hormones

• Such as estrogen and testosterone

• Causes growth at puberty

• Causes closure of epiphyseal plate and the cessation of growth

To much GH =

gigantism

Too little GH or TH

some type of dwarfism

Bone remodeling

• constant bone deposit and bone resorption

• Process is coordinated by osteoblast and osteoclast

• Controlled by hormonal and mechanical stress

If deposition =resorption , bone mass….

Remains the same

About how much of you bone mass is recycled each week

5-7%

• trabecular bone is replaced every 3-5 years

• Cortical bone is replaced every 10 years

What is calcium required for

• Nerve impulses

• Muscle contraction

• Blood clotting

• Mitosis

Hypocalcemia

Too little calcium→ can cause hyperexcitability or muscle spasm

Hypercalcemia

Too much calcium → non responsiveness ( muscle and nerves)

Bone deposition

• Accomplished by osteoblast

• Calcium ( and others) taken from blood stream → deposited into bone

• Bone deposit occur when the bone is injured or requires more strength

Bone resorption

• Accomplished by osteoclast

• Lysosomal enzymes digest organic matrix ( hydrogen pumps and chloride ions)

• Hydrochloric acid coverts calcium into a soluble form

• Calcium enter bloodstream

Parathyroid hormones

• Produced in the parathyroid gland

• Responds to low blood calcium levels

• Stimulate osteoclast and inhibits osteoblast

• Increase renal absorption of calcium from urine

  • encourages the body to keep calcium in blood instead of eliminating it as waste

Calcitonin

• Produced in thyroid gland

• Responds to high blood calcium levels

• Stimulates osteoblast and inhibits osteoclast

Is calcium homeostasis a negative or positive feedback loop

Negative feedback loop

• Falling calcium levels in bloodstream

• Rising calcium levels in bloodstream

Wolff’s Law

Bone grows ( via remodeling) in response to the mechanical stresses placed on it

• More stress = more bone/ high response

• Less stress = less bone / low response

Vigorous exercise =

increased mechanical stress = thicker stronger bones

• This is important for handedness and strength training

• Fetus/ bed bound patients → less mechanical stress = resorption = dramatically weaker bones

• Example : bone spurs in response of continuous stress

Bones disorders

Imbalances between deposit and bone resorption underlie nearly every disease that affects the human skeleton

• Osteomalacia

• Osteoporosis

• Paget’s disease

Osteomalacia

• Bone is poorly mineralized ( calcium salts inadequately deposited )

• Problem : soft, weak bones

• Cause: vitamin d deficiency or lack dietary calcium

• Rickets

Osteoporosis

• resorption exceeds deposit

• Matrix is normal, but bone mass declines

• Common result in veterbral and hip fractures

• Risk factors : post menopausal women ( estrogen levels decline)

• Treatment : vitamin d supplements, calcium and weight bearing exercise

Paget’s disease

• Excessive, haphazard bone deposition and resorption

• Problem : high ratio of spongy bone to compact bone ; reduced mineralization

• Cause: unknown, maybe viral

• Treatment : calcitonin and biphosphonates

Fractures

• Are breaks

• During youth , most fracture result from trauma

• In old age, most result from weakness of bone due to bone thinning

hematoma formation

• Bleeding at site of fracture leads to formation of hematoma

• Bone cells deprived of nutrients die

• Area swells, inflames and becomes painful

Fibrocartilaginous callus formation

• Capillaries invade hematoma followed by fibroblast and osteoblast

• Phagocytic cells clear debris

• Fibroblast differentiate into chondroblast and form cartilage matrix

Bone callus formation

• Within a week the FC callus begins to be converted into bone

• Trabeculae appears

• FC callus converted into bone callus of spongy bone

• Goes on for about 8 weeks