BIO 168 Ch. 6 & 8 Exam

Bone: Supports…

Body and soft organs

Bone: Protection

Brain, spinal cord, and vital organs

Bone: Anchorage

Levers for muscle action

Bone: Mineral storage

Mostly calcium and phosphorus

Bone: Blood cell formation

Hematopoiesis; occurs in red bone marrow of certain bones

Bone: Triglyceride storage

Energy source and stored in bone cavities

Bone: Hormone production

Osteocalcin: helps regulate insulin secretion, glucose homeostasis, and energy expenditure

Appendicular skeleton

Consists of the bones of the upper and lower limbs and the girdles that attach the limbs to the trunk

Axial skeleton

Includes the bones of the skull, vertebral column, and rib cage

Differentiate between the general functions of the axial and appendicular regions of the skeleton

Axial is for protection and support, while appendicular helps with movement

Bone Shape: Long bones

Longer than wide with a medullary cavity extending the length of the shaft

Ex: most limb bones

Bone Shape: Short bones

Cube shaped bones

Ex: wrist and ankle bones

• Sesamoid bones form within tendons. Ex. patella; vary in size and number in different individuals

Bone Shape: Flat bones

Thin, flat, slightly curved

Ex. sternum, ribs, most cranial bones

Bone Shape: Irregular bones

Complicated bones

Ex. vertebrae and hip bones

What bone class do most of the limb nones fall into?

Long bones

Bone structure

They contain different types of tissues

• Bone (osseous) tissue dominates

• Also contain nervous tissue, cartilage, dense connective tissue, muscle cells, and epithelial cells in its blood vessels

Three levels of structure: gross, microscopic, chemical

Compact bone

Dense outer layer on every bone that appears smooth solid

Spongy bone

Made up of a honeycomb of small, needle-like or flat pieces of bone called trabeculae

• Open spaces between trabeculae are filled with red or yellow bone marrow

Structure of short, irregular, and flat bones

• Consist of thin plates of spongy bone (diploe) covered by compact bone

• Compact bone sandwiched between connective tissue membranes (periosteum, endosteum)

• Bone marrow is scattered throughout spongy bone; no defined marrow cavity

• Hyaline cartilage covers area of bone that is part of a moveable joint

Periosteum

Covers outside of compact bone

Endosteum

Covers inside portion of compact bone

Structure of a typical long bone

• All long bones have a shaft (diaphysis), bone ends (epiphyses), and membranes

Diaphysis

Tubular shaft that forms long axis of bone

• Consists of compact bone surrounding central medullary cavity that is filled with yellow bone marrow in adults

Epiphyses

Ends of long bones that consist of compact bone externally and spongy bone internally

• Articular cartilage covers articular (joint) surfaces

Epiphyseal line

Between diaphysis and epiphysis

• Remnant of childhood epiphyseal plate where bone growth occurs

Structure of long bone periosteum

White, double-layered membrane that covers external surfaces, except joints

• Fibrous layer: outer layer consisting of dense irregular connective tissue consisting of Sharpey’s fibers that secure to bone matrix

• Osteogenic layer: inner layer abutting bone and contains primitive osteogenic stem cells that gives rise to most all bone cells

• Contains many nerve fibers and blood vessels that continue on to the shaft through nutrient foramen openings

• Anchoring points for tendons and ligaments

Structure of long bone endosteum

• Delicate connective tissue membrane covering internal bone surfaces

• Covers trabeculae of spongy bone

• Lines canals that pass through compact bone

• Like periosteum, contains osteogenic cells that can differentiate into other bone cells

Hematopoietic Tissue in Bones

Red bone marrow is found within trabecular cavities of spongy bone and diploe of flat bones, such as sternum

• In newborns, medullary cavities and all spongy bone contain red bone marrow

• In adults. RBM is located in heads of femur and humerus, but most active areas of hematipoiesis are flat bone diploe and some irregular bones (such as hip bone)

• Yellow bone marrow can convert to red, if person becomes anemic

Bone markings

Sites of muscle, ligament, and tendon attachment on external surfaces. Areas involved in joint formation or conduits for blood vessels and nerves

3 Categories of bone markings:

• Projections - sites of muscle and ligament attachment

• Surfaces - form joints

• Depressions and openings - for blood vessels and nerves

Sites of muscle and ligament attachment: Tuberosity

Large rounded projection; may be roughened

Sites of muscle and ligament attachment: Crest

Narrow ridge of bone; usually prominent

Sites of muscle and ligament attachment: Trochanter

Very large, blunt, irregularly shaped process (only ex. is femur)

Sites of muscle and ligament attachment: Line

Narrow ridge of bone; less prominent than a crest

Sites of muscle and ligament attachment: Tubercle

Small rounded projection or process

Sites of muscle and ligament attachment: Epicondyle

Raised area on or above a condyle

Sites of muscle and ligament attachment: Spine

Sharp, slender often pointed projection

Sites of muscle and ligament attachment: Process

Any bony prominence

Surfaces that help form joints: Head

Bony expansion carried on a narrow neck

Surfaces that help form joints: Facet

Smooth, nearly flat articular joint surface

Surfaces that help form joints: Condyle

Rounded articular projection; often articulates with a corresponding fossa

Depressions and opening (nerves and BV): Groove

Furrow

Depressions and opening (nerves and BV): Fissure

Narrow, slitlike opening

Depressions and opening (nerves and BV): Foramen

Round or oval opening through a bone

Depressions and opening (nerves and BV): Notch

Indentation at the edge of a structure

Depressions and opening (Other): Meatus

Canal-like passageway

Depressions and opening (Other): Sinus

Cavity within a bone, filled with air and lined with mucous membrane

Depressions and opening (Other): Fossa

Shallow, basin-like depression in a bone often serving as an articular surface

5 Major cell types of bone tissue

Each is a specialized form of the same basic cell type

1. Osteoprogenitor (osteogenic) cells

2. Osteoblasts

3. Osteocytes

4. Bone-lining cells

5. Osteoclasts

Osteoprogenitor cells

• Also called osteogenic cells

• Mitotically active stem cells in periosteum and endosteum

• When stimulated, they differentiate into osteoblasts or bone-lining cells

• Some remain as stem cells

Osteoblasts

• Bone forming cells that secrete unmineralized bone matrix called osteoid

• Osteoid is made up of collagen and calcium-binding proteins

• Collagen makes up 90% of bone protein

• Osteoblasts are actively mitotic

Osteocytes

• Mature bone cells in lacunae that no longer divide

• Maintain bone matrix and act as stress or strain sensors

• Respond to mechanical stimuli such as increased force on bone or weightlessness

• Communicate information to osteoblasts and osteoclasts (cells that destroy bone) so bone remodeling can occur

Bone-lining cells

• Flat cells on bone surfaces believed to also help maintain matrix (along with osteocytes)

• On external bone surface, lining cells are called periosteal cells

• On internal surfaces, they are called endosteal cells

Osteoclasts

• Derived from same hematopoietic stem cells that become macrophages

• Giant, multinucleate cells function in bone resorption (breakdown)

• When active, cells are located in depressions called resorption bays

• Cells have ruffled borders that serve to increase surface area for enzyme degradation of bone. This also helps seal off area from surrounding matrix

What does compact bone consist of?

Also called lamellar bone

• Osteon (Haversian system)

• Canals and canaliculi

• Interstitial and circumferential lamellae

Compact bone: Osteon

• The structural unit of compact bone

• Consists of an elongated cylinder that runs parallel to long axis of bone (tiny weight bearing pillars)

• An osteon cylinder consists of several rings of bone matrix called lamellae

• Lamellae contain collagen fibers that run in different directions in adjacent rings. Withstands stress and resist twisting. Bone salts are found between collagen fibers

Compact bone: Central (Haversian) canal

Runs through core of osteon. Contains blood vessels and nerve fibers

Compact bone: Perforating (Volkmann’s) canals

Canals lined with endosteum that occur at right angles to central canal. Connect blood vessels and nerves of periosteum, medullary cavity, and central canal.

Compact bone: Lacunae

Small cavities that contain osteocytes

Compact bone: Canaliculi

Hairlike canals that connect lacunae to each other and to central canal. Enables communication between all osteocytes of osteon and permit nutrients and wastes to be relayed from one cells to another

Compact bone: Interstitial lamellae

• Lamellae that are not part of osteon

• Some fill gaps between forming osteons; others are remnants of osteons cut by bone remodeling

Compact bone: Circumferential lamellae

• Just deep to periosteum, but superficial to endosteum, these layers of lamellae extend around entire surface of diaphysis

• Help long bone resist twisting

Structure of spongy bone

• Appears poorly organized but is actually organized along lines of stress to help bone resist any stress

• Trabeculae, like cables on a suspension bridge, confer strength to bone

• No osteons are present, but trabeculae do contain irregularly arranged lamellae and osteocytes interconnected by canaliculi

• Capillaries in endosteum supply nutrients

Organic components of bone

• Rebar = flexible

• Includes osteogenic cells, osteoblasts, osteocytes, bone-lining cells, osteoclasts, and osteoid

• Osteoid: makes up 1/3 of organic bone matrix, is secreted by osteoblasts. It consists of ground substance and collagen fibers, which contribute to high tensile strength and flexibility of bone

• Bone resilience is due to collagen molecules that stretch/break to prevent fractures, they can reform

Inorganic components of bone

• Concrete = hardness

• Hydroxyapatites: calcium phosphate crystals that are responsible for hardness and resistance to compression

• Bone is half as strong as steel in resisting compression and as strong as steel in resisting tension

• Lasts long after death because of mineral composition and can reveal info about ancient people

Ossification (osteogenesis)

• Process of bone tissue formation

• Formation of bony skeleton begins in month 2 (week 😎 of development

• Postnatal bone growth occurs until early adulthood

• Bone remodeling and repair are lifelong

Endochondral ossification

• Bone forms by replacing hyalin cartilage, referred to as cartilage (endochondral) bones

• Form most of skeleton below skull except clavicles

• Uses previously formed hyaline cartilage models

• Requires breakdown of hyaline cartilage prior to ossification

• Begins at primary ossification center in center of shaft

• Blood vessels infiltrate perichondrium, converting it to periosteum

• Mesenchymal cells specialize into osteoblasts

5 Steps of Endochondral ossification

1. Bone collar forms around diaphysis of cartilage model

2. Central cartilage in diaphysis calcifies, then develops cavities

3. Periosteal bud invades cavities, leading to formation of spongy bone - bud is made up of blood vessels, nerves, RBM, osteogenic cells and osteoclasts

4. Diaphysis elongates, and medullary cavity forms - secondary ossification centers appear in epiphyses

5. Epiphyses ossify - hyaline cartilage remains only in epiphyseal plates and articular cartilages

Intramembranous ossification

• Bone develops from fibrous membrane

• Bones are called membrane bones

• Begins with fibrous connective tissue membranes formed by mesenchymal cells

• Forms frontal, parietal, occipital, temporal, and clavicle bones

4 Steps of Intramembranous ossification

1. Ossification centers are formed when mesenchymal cells cluster and become osteoblasts

2. Osteoid is secreted, then calcified

3. Woven bone is formed when osteoid is laid down around blood vessels, resulting in trabeculae. Outer layer of woven bone forms periosteum

4. Lamellar bone replaces woven bone and red bone marrow appears

Postnatal Bone Growth

• Long bones grow lengthwise by interstitial (longitudinal) growth of epiphyseal plate

• Bones increase thickness through appositional growth

• Bones stop growing during adolescence (some facial bones continue to grow slowly though life)

Growth in length of long bones

• Interstitial growth requires presence of epiphyseal cartilage in the epiphyseal plate

• Epiphyseal plates maintains constant thickness - rate of cartilage growth on one side balanced by bone replacement on other

• Epiphyseal plate closure occurs when epiphysis and diaphysis fuse

• Bone lengthening ceases 18 for grills and 21 for boils

• Epiphyseal plate consisits of 5 zones

1. Resting zone

2. Proliferation (growth) zone)

3. Hypertrophic zone

4. Calcification zone

5. Ossification zone

1. Resting zone

Area of active cartilage on epiphyseal side of epiphyseal plate that is relatively inactive

2. Proliferation (growth) zone

• Cartilage cells undergo mitosis on diaphysis side of epiphyseal plate

• New cells formed move upward, pushing epiphysis away from diaphysis, causing lengthening

3. Hypertrophic zone

• Older cartilage cells enlarge

• Area with older chondrocytes closer to diaphysis

• Cartilage lacunae enlarge and erode, forming interconnecting spaces

4. Calcification

Surrounding cartilage matrix calcifies; chondrocytes die and deteriorate

5. Ossification zone

• Chondrocyte deterioration leaves long spicules of calcified cartilage at epiphysis-diaphysis junction

• Spicules are then eroded by osteoclasts and are covered with new bone by osteoblasts

• Ultimately replaced with spongy bone

• Medullary cavity enlarges as spicules are eroded

Hormonal regulation of bone growth

• hGH: stimulates infant/childhood epiphyseal plate cavity

• Thyroid: control HGH

• Testosterone + estrogens at puberty: growth spurts and can end growth (epiphyseal plate closure)

• Excesses or deficits of any hormones cause abnormal skeletal growth

Bone remodeling

• Replaces 5-10% of bone every year. Spongy (every 3-4 years), Compact (every 10 years)

• Consists of bone deposit and bone resorption

• Occurs at surfaces of both periosteum and endosteum

• Remodeling units: packets of adjacent osteoblasts and osteoclasts coordinate remodeling process

Bone Resorption

• Function of osteoclasts

• Break down matrix by using enzymes and protons

• Osteoclasts also phagocytize demineralized matrix and dead osteocytes

• Osteoclast activation involves PTH (parathyroid hormone) and immune T cell proteins

Bone deposition

• New bone matrix is deposited by osteoblasts

• Osteoid seam: band of unmineralized bone matrix that marks area of new matrix

• Calcification front: abrupt transition zone between osteoid seam and older mineralized bone

Control of bone remodeling

• Maintaining Ca2+ homeostasis: hormonal negative feedback loop involving PTH main Ca2+ in the blood. Calcitonin does the opposite

• Keeping bone strong: mechanical and gravitational forces acting on bone drive remodeling to keep bone strong

Wolf’s Law

Bones grow or remodel in response to demands placed on them

Stress usually

Fractures

Breaks

• During youth, most fractures result from trauma

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

Fracture classification: Position of bone after fracture

• Nondisplaced: ends retain normal position

• Displaced: ends are out of normal alignment

Fracture classification: Completeness of break

• Complete: broken all the way through

• Incomplete: not broken all the way through

Fracture classification: Whether skin is penetrated

• Open (compound): skin is penetrated

• Closed (simple): skin is not penetrated

Types of fractures: Comminuted

• Bone fragments into 3 or more pieces

• Common in older folks with brittle bones

Types of fractures: Compression

• Crushed

• Common in porous bones (osteoporotic bones) subjected to extreme trauma like a fall

Types of fractures: Spiral

• Ragged break occurs when excessive twisting forces are applied to a bone

• Common sports fracture

Types of fractures: Epiphyseal

• Epiphysis separates from the diaphysis along the epiphyseal plate

• Tends to occur where cartilage cells dying and calcification of the matrix is occuring

Types of fractures: Depressed

• Broken bone portion is pressed inward

• Typical of skull fracture

Types of fractures: Greenstick

• Bone breaks incompletely like a twig. One side of the sheft breaks while the other side bends

• Common in children whose bones have more organic matrix and more flexible than adults.