CH6 Bones and Skeletal Tissues

CH6 PowerPoint Notes

^{Skeletal cartilage}

^{is made of cartilage tissue molded to fit its body location and function.}

^Cartilage

• ^{Composed of a lot of water} 

• ^{No nerves or blood vessels} 

• ^{Surrounded by dense irregular connective tissue proper = perichondrium} 

^Hyaline

• ^{Supportive, flexible, resilient with fine collagen fibers} 

• ^{Articular cartilage at joints of moveable bones} 

• ^{Costal cartilage connects ribs to sternum} 

• ^{Respiratory cartilages in larynx and other respiratory passageways} 

• ^Nose 

^Elastic

• ^{More elastic fibers} 

• ^{Epiglottis and outer ear}

^{Fibrocartilage}

• ^{Thick collage fibers} 

• ^{In knee and vertebral discs} 

^{Appositional growth}

^{cartilage forming cells in the perichondrium make matrix and deposit against existing cartilage.}

Interstitial growth

^{chondrocytes in lacunae divide and make matrix.}

Cartilage Growth

^{stops at adolescence when skeleton stops growing.}

^{At times cartilage can become calcified but it is not bone.}

Is cartilage bone?

206 bones

How many bones are there?

Axial

Skull, vertebral column, and rib cage

^Appendicular

Upper and lower limbs and girdles that attach the bones to the axial skeleton.

Shape

• ^{Long bones are longer than wide = limb bones} 

• ^{Short bones are cube-shaped = wrist and anklebones, include sesamoid bones formed in tendon =knee cap} 

• ^{Flat bones are flat and curved = breastplate, shoulder blades, ribs, and most skull bones} 

• ^{Irregular bones have various shapes = vertebrae and hip bones} 

Bone Functions

• ^Support 

• ^Protection  

• ^Movement 

• ^{Mineral reserve for calcium and phosphate} 

• ^{Blood cell formation = hematopoiesis in red bone marrow} 

• ^{Triglyceride storage} 

• ^{Hormone production = osteocalcin for bone formation and protection against obesity and diabetes} 

^{Short, irregular and flat bones}

• ^{External Compact bone with Internal Spongy bone in between = sandwich} 

• ^{Spongy bone (diploe) contains trabeculae with red or yellow bone marrow} 

• ^{Connective tissue membranes outside of compact bone is periosteum and inside compact bone is endosteum} 

• ^{Hyaline cartilage seen at moveable joints} 

^{Long bone} 

• ^{Has shaft, ends and membranes}

• ^Diaphysis

• ^Epiphysis

Diaphysis

shaft or middle area has outer compact bone surrounding medullary or marrow cavity with yellow bone marrow of fat.

^Epiphysis

^{each end with outer compact bone covered by articular cartilage (hyaline) cushions the bone ends during movement and absorbs stress and inner spongy bone.}

^metaphysis

What is between epiphysis and diaphysis?

^{In adult = epiphyseal line}

^{REMNANT of epiphyseal plate made of hyaline cartilage that grows in children to lengthen bone}

^periosteum

• double-layered membrane, covers bone except at joints

• ^{Outer fibrous layer = dense irregular connective tissue proper} 

• ^{Inner osteogenic layer with stem cells that form all bone cells except osteoclasts} 

• ^{Nerve fibers and blood vessels pass into shaft through nutrient foramina} 

• ^{Provides anchoring sites for tendons and ligaments} 

^endosteum

^{Connective tissue membrane lines internal bone surfaces which covers spongy bone and lines canals present with cells similar to periosteum.}

^{the trabecular cavities (strut or thin plate) of spongy bone of long bones and in the diploe of flat bones.}

What is in red bone marrow cavities?

• ^{In infants red bone marrow in all areas of spongy bone + medullary cavity.}

• ^{In adults the medullary cavity contains yellow bone marrow with fat and little red bone marrow in the spongy bone cavities at the ends of long bones.}

Where is red bone marrow in long bones?

Occurs in the red bone marrow housed within flat and irregularly-shaped bones.

Where is the vast majority of hematopoiesis (formation of blood cells) in adults?

• ^{For Muscle, Ligament, and Tendon Attachment} 

• ^{As joints} 

• ^{As passages for blood vessels and nerves} 

• ^{Include projections, depressions and openings} 

What are bone markings for?

Osteogenic/osteoprogenitor cells

^{are actively dividing stem cells that give rise to other bone cells, flat or squamous.}

Osteoblasts are bone-forming cells

^{that can divide and make matrix- initially secrete collagen and calcium binding proteins to form osteoid before mineralization (addition of calcium and others), cube or flat, can form bone lining cells or osteocytes if surrounded by matrix.}

Osteocytes

• ^{are mature bone cells in lacunae which monitor and maintain matrix, sense stress or strain and communicate to bone remodeling cells (osteoblasts and osteoclasts)} 

Endosteal

^{Bone lining cells flat on bone surfaces that maintain matrix, outer surface = periosteal, inner surface}

Osteoclasts

^{for bone resorption, multinucleated, found in depression = resorption bay and have ruffled border.}

^{osteon or Haversian System}

What is the structural unit of a compact/lamellar bone?

Lamella

• ^{many matrix circular tubes}

• ^{collagen fibers run indifferent directions for each osteon in order to handle stress + calcium+ phosphate} 

Yes, they have blood vessels, lymphatic vessels, nerves!

Do Central canals/ Haversian canals have blood vessels?

^{Volkmann’s/perforating canals}

^{run at right angles to the central canals to connect blood vessels, lymphatic vessels, nerves in periosteum to those in central canal and medullary cavity}

^{Osteocytes in lacunae with canaliculi (fine tubes = gap junctions)}

connect the osteocytes to each other and central canal, these are for waste and nutrient exchange.

interstitial lamellae

• Between lamellae of osteons

• NOT part of any osteon

circumferential lamellae

• Under periosteum and above endosteum

• allows withstanding twist

Spongy Bone

• Traceculae are aligned to resist stress

• Irregularly arranged lamellae with osteocytes and canaliculi – NO OSTEONS

Organic and inorganic components

What is the chemical composition of bone?

Organic Components

cells + osteoid (ground substance =proteoglycans +glycoproteins) + collagen) for strength, flexibility, stretch resistance, twist resistance.

Inorganic Components

mineral salts/hydroxyapatite crystals of calcium phosphate in matrix around collagen fibers for hardness and to compression resistance.

Ossification/osteogenesis

bone formation

Ossification/osteogenesis

1. Occurs during formation of skeleton in utero

2. Occurs during bone lengthening growth (some bones stop growing at adulthood), bones maintainability for increasing their width forever

3. Occurs during remodeling and repair

• ^{At week 8 skeleton = hyaline cartilage + fibrous membrane=easier for growth}

When does the bony skeleton form?

Endochondral ossification

• bone replaces hyaline cartilage and produce cartilage/endochondral bone.

• Occurs in almost all bones but clavicles/collar bones and skull

Intramembranous ossification

• bone replaces fibrous membrane and produce membrane bone.

• Forms the cranial bones of skull and collar bone/clavicle

interstitial growth

at epiphyseal plate where cartilage is replaced by bone.

Growth Zone

At epiphyseal plate have cartilage originally (one side closer to epiphysis= resting zone but other side closer to diaphysis.

• bone at epiphyseal plate and ones at bottom closest to diaphysis die leaving spaces that become calcified which are partly destroyed by osteoclasts.

• Then osteoblasts form spongy bone.

What happens when cartilage divides and lengthens?

the epiphyseal plate gets smaller and smaller and eventually, at the end of adolescence, the epiphyseal plate is entirely replaces by bone so that lengthening stops = Epiphyseal Plate Closure (males at 21 yrs and females at 18 yrs)

What happens to the epiphyseal plate as adolescence progresses?

appositional growth

osteoblasts beneath periosteum secrete matrix on the external surface of the bone while osteoclasts on the inner endosteal surface remove some bone to prevent too much weight.

some facial bones (lower jaw and nose)

What bones still grow after adolescence?

giant or dwarf

What happens when there’s an imbalance of growth hormone?

Thyroid Hormones

regulates growth hormone activity

Sex Hormone (testosterone and estrogen)

for growth spurts and changes in bone due to sex, later they are involved in epiphyseal plate closure.

• lots of recycling

• Possibly 1 gram of calcium may enter or leave bone/day

• Spongy bone is replaced every 3-4 years and compact bone is replaced every about every 10 years

• Bone deposition and resorption

Is bone dynamic?

at the surface of the periosteum and endosteum = bone remodeling by osteoblasts and osteoclasts.

the total bone mass remains constant!

Where does bone deposition and resorption occur?

Bone Deposition

New bone matrix by osteoblasts without minerals observed at osteoid seam, it will calcify in a week (calcium and phosphate deposited).

Bone Resorption

By osteoclasts secretion of lysosomal enzymes and H+ and phagocytosis in which the internalized products will enter the blood.

osteoclasts die

What happens after apoptosis?

• Maintaining certain calcium levels in the blood at 9-11 mg/dl

• Mechanical and gravitational forces

• Muscle contraction, nerve signaling, blood clotting all need calcium

• 0-age 10 need 400-800 mg of calcium and from 11-24 need 1200-1500 mg of calcium

What is remodeling of bone due to?

Parathyroid hormone

these glands stimulate osteoclasts to degrade bone and release calcium into blood if blood calcium too low.

(remodels bones)

Calcitonin

halts bone resorption, lowers blood calcium levels and protects the skeleton from excessive calcium loss.

leptin in adipose tissue, SSRIs

What inhibits osteoblast function outside of the thyroid?

Wolff’s Law

bone grows or remodels in response to the demands placed on it.

• weight and muscle pull which cause bones to bend

• Spongy bone trabeculae form struts along lines of compression

• Large, bony projections occur where heavy, active muscles attach

• Remodeling occurs from electrical currents and fluid flow within the canaliculi

How does stress and gravity remodel bones?

Fracture Classification

1. By position of bone ends after fracture: nondisplaced fractures have ends in normal position but displaced are not

2. Completeness of break, complete (all the way through) vs incomplete

3. If penetrate skin = open/compound vs. does not = closed/simple

4. Location

5. Appearance

6. Nature of break

Fracture Treatment and Repair

1. Realign ends = Reduction: if closed hands are used, if open use pins/wires

2. Immobilization by cast or traction to allow healing (6-8 wks for small to medium-sized bones in young adult)

Occurrences During Fracture

1. Hematoma forms = mass of clotted blood and bone cells die, pain, swelling, inflammation

2. Formation of soft granulation tissue/soft callus where capillaries enter hematoma and WBC clean up area, then fibroblasts + cartilage cells + osteogenic cells invade the site to reconstruct the bone

3. New bone appears as bony callus of spongy bone

4. The bony callus is remodeled in which compact bone is made

Osteomalacia in adults and rickets in children

• osteoid produced but not calcium salts = soft and weak bones

• bone deformities and bowing of bones, abnormal length since growth plate never is converted to bone – due to lack of calcium or vitamin D

• To treat: supplement and sun exposure

Osteoporosis

• bone resorption is greater than deposition so bones are light and weak, affects back and hip areas the most.

• Most common in older women as estrogen falls.

• To treat: vitamin D, calcium, exercise, hormones, drugs

Paget’s Disease

• Haphazard bone deposit and resorption

• bone has higher ratio of spongy bone to compact bone than normal causing spotty weaknesses and thickenings

• affects the spine, thigh, skull, and pelvis

• To treat: drugs