A&P 1 Lecture - Ch. 6 Bone Tissue

Osseous tissue

bone tissue

a type of connective tissue consisting of a variety of cells and a hard, calcified matrix

Compact bone

densely packed, smooth osseous tissue that encases the entirety of bones forming a hard shell

consists of structural units called osteons

Spongy bone

Consists of a honeycomb of spicules (rods or spines) and trabeculae (thin plates) of osseous tissue

adds strength but minimal weight to bone

Bone marrow

delicate, highly organized organ that fills the spaces between osseous tissue

2 types - red and yellow

Osteogenic stem cells

mitotically active stem cells that can differentiate (mature) into osteoblasts (bone-building cells), or bone-lining cells

found associated with the endosteum and periosteum

Osteoblasts

bone-building cells

function in bone deposition - depositing osteoid into the bone matrix

secrete osteoid (unmineralized bone matrix containing collagen and calcium-binding proteins)

Deposition

the process in which material is laid down

Osteocytes

mature bone cells maintaining the health of the bone matrix

found within lacunae (little-houses) connected to other osteocytes by canaliculi (little canals)

function as mechanical stress sensors and communicate to osteoblasts and osteoclasts to remodel bone

Osteoclasts

giant, multinucleated cells

bone-dissolving cells which breakdown bone matrix and allow the resorption of calcium into the bloodstream

Resorption

the process or action by which something is reabsorbed

Bone-lining cells

cells of the periosteum and endosteum

Osseous tissue matrix

1/3 consists of organic matter (osteoid)

2/3 consists of inorganic matter (calcium and other minerals)

Organic matter of osseous tissue matrix

makes up 1/3 of the matrix

consists of osteoid - substances produced by osteoblasts

includes collagen, glycosaminoglycans, proteoglycans, and glycoproteins

provides flexibility and high tensile strength

organic meaning it's synthesized by living cells

Inorganic matter of osseous tissue matrix

makes up 2/3 of matrix

compounds and minerals that provide hardiness of bone

includes hydroxyapatite (calcium phosphate salt), calcium carbonate, and other minerals

inorganic meaning it's not synthesized by living cells, these minerals are obtained from the environment and diet

Osteomalacia

softening of bone tissue due to a lack of inorganic bone matrix (calcium salts)

caused by a deficiency of vitamin D and/or a deficiency in calcium

Rickets

osteomalacia in children

typically results in bowed legs and other bone deformities

caused by a deficiency of vitamin D and/or a deficiency in calcium

Osteoporosis

literally means porous bone

a deterioration of bone matrix that occurs when bone resorption exceeds bone deposit

mostly affects spongy bone

vertebrae and the neck of the femur become highly susceptible to fractures

commonly in the elderly and 4 times more likely in women due to estrogens association with bone density

Shapes of bones

4 types

long

short

flat

irregular

Examples of long bones

limb bones - humerus, radius, ulna, metacarpals, femur, tibia, fibula, metatarsals, phalanges

Examples of short bones

carpals, tarsals, patella

Examples of flat bones

sternum, scapulae, ribs, skull bones

Examples of irregular bones

vertebrae, coxal bones, some skull bones

Diploe

a special name for spongy bone of short, irregular, and flat bones that is sandwiched between two layers of compact bone on either side

Diaphysis

tubular shaft of a long bone

Medullary cavity

space within the diaphysis of a long bone that contains marrow

Epiphyses

enlarged ends of a long bone

where spongy bone is found filled within marrow

Articular cartilage

hyaline cartilage found at the epiphyses where a bone forms a joint (articulation)

Epiphyseal line

a calcified line that divides the epiphyses from the diaphysis

remnants of childhood epiphyseal (growth) plate

Epiphyseal plate

growth plate of hyaline cartilage found between the epiphyses and diaphysis of a long bone in a growing child

Endosteum

reticular connective tissue that covers the internal surface of bones

covers trabeculae of spongy bone, lines the medullary cavity, and lines canals that pass through compact bone

contains osteogenic stem cells that can differentiate (mature) into other bone cells

Periosteum

double-layered membrane found on the external surface of bones

absent at joint surfaces where articular cartilage is found

contains a fibrous layer - consisting of dense irregular CT, serves as an attachment site for tendons and ligaments

osteogenic layer - inner layer containing osteogenic stem cells

Sharpey's fibers

fibers that anchor the periosteum to bone matrix

Nutrient foramen

hole found on the surface of bone that nerve fibers and blood vessels travel through to penetrate the compact bone

Red bone marrow

site of hematopoiesis (synthesis of blood cells)

in newborns (<1yr) found in all bone cavities

in adults, it's limited to proximal epiphyses of femur and humerus, diploe of flat and irregular bones

Yellow marrow

fatty marrow that replaces red marrow, fills medullary cavities of long bones in adults

Osteoid

unmineralized bone matrix containing collagen and calcium-binding proteins produced by osteoblasts; contributes to the high tensile strength and flexibility of bone

Osteon (Haversian system)

structural unit of compact bone containing lamellae and a central canal

Lamellae

weight-bearing cylinders/rings of bone matrix within an osteon

contains collagen fibers that corkscrew down the cylinders to withstand twisting forces on bone

Central (Haversian) canal

runs through the core of an osteon, contains blood vessels and nerve fibers, supplies the osteon with nutrients and innervation

Perforating (Volkmann's) canals

canals found at right angles (perpendicular) to central canals, allows blood vessels and nerves to penetrate the bone to reach the inner spongy bone

Interstitial lamellae

irregular shaped lamellae that fill gaps between osteons

Circumferential lamellae

superficial rings of compact bone that wrap around the entire surface of the diaphysis of a long bone

think of the circumference of a circle

Lacunae

small cavities or houses that contain osteocytes (mature bone cells)

Canaliculi

tiny canals that connect lacunae together and allow for communication and transport of nutrients and waste between osteocytes

Ossification (osteogenesis)

bone tissue formation/synthesis

begins at week 8 of fetal development

fibrous membranes and hyaline cartilage are replaced by bone tissue

2 types of ossification

intramembranous ossification

endochondral ossification

Endochondral ossification

bone replaces hyaline cartilage

forms all the long bones and most of the skeleton

Intramembranous ossification

bone replaces fibrous membranes

forms flat bones of the skull and clavicles

What age are bone completely ossified and skeletal growth stops?

~25 years old

Steps of endochondral ossification

1. Primary ossification center emerges and a bone collar forms around the diaphysis of the hyaline cartilage model

2. Cartilage calcifies in the center of the diaphysis and then develops cavities

3. The periosteal bud invades the internal cavities and spongy bone forms

4. The diaphysis elongates and a medullary cavity forms; secondary ossification centers appear in the epiphyses;

5. The epiphyses ossify; hyaline cartilage remains only in the epiphyseal plates and articular cartilages

Steps of intramembranous ossification

1. Mesenchymal cells cluster and differentiate into osteoblasts, forming an ossification center

2. Osteoblasts continue to secrete osteoid, which calcifies in a few days; trapped osteoblasts become osteocytes

3. Osteoid is laid down between embryonic blood vessels, forming trabeculae of immature spongy bone

4. Trabeculae just deep to the periosteum are replaced with compact bone; the immature spongy bone in the center is remodeled into the mature spongy bone that is eventually filled with red marrow.

Interstitial (longitudinal) bone growth

how long bones grow lengthwise

occurs at the epiphyseal plate

stimulated by growth hormone

Appositional growth

how bones increase in thickness or width

occurs throughout life, known as bone remodeling

thicken in response to stress on bone such as muscle activity or weight gain

bones thicken due to osteoblasts depositing new bone matrix as circumferential lamellae

Bone elongation at the epiphyseal plate

cartilage growth in which chondrocytes multiply then enlarge pushing the epiphysis away from the diaphysis

Calcification

transformation of hyaline cartilage or fibrous membranes into osseous tissue by the deposition of osteoid and calcium salts

5 zones of epiphyseal plate

resting zone, proliferation (growth) zone, hypertrophic zone, calcification zone, ossification (osteogenic) zone

Resting zone of epiphyseal growth plate

inactive area of epiphyseal growth plate

found furthest from marrow cavity

Proliferation (growth) zone of epiphyseal growth plate

a zone of the epiphyseal growth plate in which chondrocytes are rapidly dividing (proliferating) via mitosis and new cells are stacking on top of each other lengthening the growth plate and pushing the epiphysis away from the diaphysis

Proliferation

rapid increase in numbers

Hypertrophy

increase in size of cells

Hypertrophic zone of epiphyseal growth plate

a zone of the epiphyseal growth plate in which chondrocytes are enlarging lengthening the growth plate and pushing the epiphysis away from the diaphysis

Calcification zone of epiphyseal growth plate

a zone of the epiphyseal growth plate in which chondrocytes die, deteriorate, and matrix is calcified by deposition of calcium salts

Ossification zone of epiphyseal growth plate

a zone of the epiphyseal growth plate in which osteoblasts begin to form spongy bone and marrow invades the new osseous tissue

Bone remodeling

a continuous process of bone deposition and bone resorption

repairs microfractures, releases minerals into the blood to maintain homeostasis, reshapes bones due to mechanical stress, etc.

Bone deposition

carried out by osteoblasts

bone matrix is secreted on the periosteal side of the bone

stimulated by mechanical stress and/or increased concentrations of calcium and phosphate levels

Bone resorption

carried out by osteoclasts

bone matrix is reabsorbed on endosteal side of bone

Wolff's law

bone remodels in response to mechanical stress placed upon them

Importance of calcium in the body

essential for...

nerve transmission

muscle contraction

blood coagulation (clotting)

exocytosis

cell signaling

enzyme reactions

Importance of phosphate in the body

important component of DNA, RNA, ATP, and phospholipids

helps maintain acid-base balance of body fluids

Hormones that regulate blood calcium levels

calcitonin

parathyroid hormone (PTH)

vitamin D (calcitriol)

Vitamin D (calcitriol)

produced by the sequential actions of the skin, liver and kidneys

increases blood calcium levels by enhancing calcium absorption of the small intestine

Parathyroid Hormone (PTH)

increases blood calcium levels

produced by parathyroid glands

produced in response to low blood calcium levels (hypocalcemia)

stimulates osteoclasts to resorb (breakdown) bone releasing calcium into the bloodstream

Calcitonin

decreases blood calcium levels

puts calcium IN bones

produced in response to high blood calcium levels (hypercalcemia)

simulates osteoblasts to deposit calcium into bone

Hypocalcemia

low blood calcium levels

causes hyperexcitability of nerves and muscles

can cause muscle tremors, spasms, or even tetany

Hypercalcemia

high blood calcium level

causes depression of the nervous system, emotional disturbances, muscle weakness

severe cases could result in cardiac arrest

rare condition

Stress bone fractures

bone fractures that are a result of abnormal trauma or overuse

Pathological bone fractures

bone breaks because of underlying disease that has weakened the bone

such as cancer, osteoporosis, etc.

Transverse bone fracture:

bone fracture that runs laterally or side to side

Linear bone fracture:

a bone fracture that runs longitudinally or up and down

Oblique bone fracture

a bone fracture that runs diagonally across a bone

Displaced bone fracture

a bone fracture that causes the bones to misaligned

Nondisplaced bone fracture

bone fracture where the fractured ends retain their normal alignment

Spiral bone fracture

a bone fracture that results from excessive twisting forces

common sports injury

Comminuted bone fracture

bone fragments into three or more pieces

common in the elderly

Greenstick bone fracture

incomplete fracture where one side of the bone breaks and the other side bends

common in children because their bones are more flexible than adults

Simple (closed) bone fracture

a bone fracture in which the bone does NOT penetrate the skin

Compound (open) bone fracture

a bone fracture in which the bone DOES penetrate the skin

Bone reduction

realignment of the bone ends for proper healing

Closed (external) reduction

orthopedic doctor manipulates the bone ends into position through the skin

Open (internal) reduction

bone ends are secured together surgically with pins or wires

Bone fracture repair

1. blood clot (hematoma) forms at the fracture

2. fibrocartilaginous callus forms - fibroblasts secrete collagen matrix, osteoblasts begin forming spongy bone

3. bony callus forms - spongy bone replaces fibrocartilaginous callus

4. bone remodeling occurs - compact bone reconstructs diaphysis walls