A & P Ch 7

epiphysis is composed of

Outer thin layer of compact bone Inner, more extensive region of spongy bone

sex hormones

estrogen and testosterone; increase rate of cartilage growth and bone formation

Compact bone microscopic anatomy

-Basic functional and structural unit of mature compact bone = osteon (haversian system) -Runs parallel to diaphysis -Gives bone resistance to mechanical stress -3D structure made of: central canal, concentric lamellae, osteocytes in lacunae, canaliculi

Regions of a long bone

-Diaphysis -Medullary cavity -Epiphysis -Metaphysis -Epiphyseal plate or line

red bone marrow (myeloid tissue)

-Hemopoietic (blood cell forming) -Contains reticular connective tissue, developing blood cells, and adipocytes -In children, located in spongy bone of most of bones of body and medullary cavity of long bones -In adults, located in portions of axial skeleton (flat bones of skull, vertebrae, ribs, sternum, ossa coxae (hip bone)), and proximal epiphyses of humerus and femur

Interstitial growth steps

1 and 2. Chondrocytes housed in lacunae undergo MITOTIC cell division; and the result is 2 chondrocytes in 1 lacuna (now called chondroblasts) 3. Chondroblasts each begin to synthesize and secrete their own new cartilage matrix; and are now separated from each other by a matrix border and reside in its own lacuna (now called chondrocyte) 4. The result is two chondrocytes, two lacunae and more cartilage matrix

Four steps of intramembranous ossification

1. Ossification centers are formed when mesenchymal cells cluster and divide and become osteoblasts 2. Osteoid is secreted, then calcified 3. Woven bone (primary 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 the trabeculae of woven bone, on the internal and external surfaces of the bones spaces are filled & bone becomes compact bone; trabeculae in between becomes spongy bone

Activation of Vitamin D to Calcitriol

1. The precursor molecule in keratinocytes of the skin is converted to Vitamin D3 (cholecalciferol) which is released into the blood 2. Vitamin D3 is converted to calcidiol in the liver (when an OH group is added) 3. Calcidiol is converted to calcitriol in the kidney (when another OH group is added)

appositional growth steps

1. Undifferentiated stem cells at internal edge of perichondrium begin to divide 2. New undifferentiated stem cells and committed cells that differentiate into chondroblasts are formed at periphery of old cartilage- they begin to produce and secrete cartilage matrix 3. Chondroblasts push apart and become chondrocytes in its own lacuna

5 zones of interstitial growth

1. Zone of resting cartilage 2. Zone of proliferating cartilage 3. Zone of hypertrophic cartilage 4. Zone of calcified cartilage 5. Zone of ossification

endochondral ossification steps

1. hyaline cartilage models are formed in early embryo; chondrocytes enlarge and surround cartilage begins to calcify; chondrocytes die and disintegrate leaving cavities (no blood flow) 2. a bone collar forms around the hyaline cartilage shaft; the cells of the inner perichondrium differentiate into osteoblasts and these cells from bone matrix (no blood flow) 3. the hyaline cartilage in the center of the shaft calcifies, becoming the primary ossification center; vessels and fibroblasts invade the head of the cartilage; calcified cartilaginous matrix breaks down and fibroblasts convert into osteoblasts and lay down spongy bone; no medullary cavity (blood flow) 4. remodeling and formation of the medullary cavity; osteoclasts break down the spongy bone in the center of the shaft creating the medullary cavity; increased growth in length and diameter 5. secondary ossification centers calcify the epiphyses; capillaries and osteoblasts migrate to the epiphyses and begins to ossify 6. articular cartilage (ends of each side) remains exposed to joint cavities and the epiphyseal plate (growth plate) separates the diaphysis (shaft) from the epiphysis; articular cartilage prevents bone-to-bone contact, and the epiphyseal plate allows bone lengthening

effects of aging on bone tissue

1. loss of bone mass (loss of calcium and minerals causes osteopenia and osteoporosis) 2. brittleness (reduced protein synthesis by osteoblasts results in increase of inorganic minerals in bone matrix)

steps of bone fracture repair

1.) fracture hematoma (blood clot) forms 2.) Fibrocartilage (soft) callus forms (lasts at least 3 weeks) 3.) Hard (bony) callus forms and continues to grow and thicken for several months 4.) Bone remodeled - osteoclasts remove excess material & compact bone replaces primary bone

resorption lacuna (Howship's lacuna)

A depression or pit on the bone surface that usually contains an osteoclast

Periosteum

A two layer, dense fibrous membrane covering the surface of bones (except at their extremities - articular cartilage) and serving as an attachment for tendons and muscles.

Fibrocartilage

A weight-bearing cartilage that withstands compression; forms the intervertebral discs, the pubic symphysis & cartilage pads of the knee joints (menisci)

spongy bone

Also called cancellous or trabecular bone; found in the middle of most compact bones; appears porous; makes up ~ 20% of total bone mass

compact bone

Also called dense or cortical; relatively rigid; appears white, smooth, and solid; makes up ~ 80% of total bone mass

Mature cartilage is __________ and contains no ___________ ____________.

Avascular; nerve endings

PTH and calcitriol interact with

Bone - increase release of calcium from bone into blood by increasing osteoclast activity Kidneys - stimulate kidneys to excrete less calcium and retain more in the blood Small intestine - increase absorption of calcium from small intestine into the blood

Calcium

Ca; essential mineral for muscle contraction, blood clotting, & release of neurotransmitter from nerve cells

Chondrocytes

Chondroblasts encased within the matrix they have produced and secreted Occupy small spaces, lacunae Maintain the matrix

interstitial growth

Chondrocytes divide and secrete new matrix, expanding cartilage from within - 5 zones

zone of proliferating cartilage

Chondrocytes rapidly divide, enlarge slightly, and become aligned within lacuna in columns parallel to diaphysis (stacked coins)

Osteon - Central (haversian) canal

Cylindrical channel lies in center of osteon and runs parallel to it; contains blood vessels and nerves

hyaline cartilage

Costal, articular, epiphyseal plates; provides model during fetal development for formation of skeleton

Osteoblasts

Cuboidal shape; abundant rough ER and Golgi apparatus; synthesize and secrete osteoid; become entrapped within osteoid matrix and differentiate into osteocytes

Calcitonin function

Decreases blood calcium levels by inhibiting osteoclasts & stimulating kidneys to excrete calcium

Perichondrium

Dense irregular connective tissue membrane covering hyaline cartilage (except articular) which helps maintain its shape

Chondroblasts

Derived from mesenchymal cells and produce the cartilage matrix

Other bone classes

External surface generally composed of compact bone covered by periosteum; interior is entirely spongy bone, and no medullary cavity

zone of resting cartilage

Farthest from medullary cavity and nearest the epiphysis and contains chondrocytes distributed throughout cartilage matrix. Secures epiphysis to epiphyseal plate

epiphyseal plate

Growth plate found in metaphysis, thin layer of hyaline cartilage that provides for lengthwise growth of bone; gradually ossifies

Canaliculi

Hairlike canals that connect lacunae to each other and the central canal; house osteocyte cytoplasmic projections that permit intercellular contact and communication; nutrients, minerals, gases, and wastes transported

irregular bones

Have elaborate, complex shapes and don't fit any other category; vertebrae, hip bones, several skull/ facial bones

Bone remodeling is dependent on

Hormones and mechanical stress to bone

Composition of bone matrix

Inorganic salts and organic matrix

Hormones

Molecules released from a cell into the blood and transported throughout the body to affect other cells

storage of mineral and energy reserves

Most of body reserves of calcium and phosphate stored within and then released from bone into blood as needed; potential energy from lipids in stored in yellow bone marrow

Function of bones: lever for movement

Muscles attached to bone contract and exert a pull; bones can alter direction and magnitude of muscular forces

Spongy Bone Microscopic Anatomy

No osteons Open lattice of narrow rods and plates of bone called trabeculae Trabeculae contains parallel lamellae composed of bone matrix Bone marrow when present fills in between the trabeculae

compound fracture

One or both ends of broken bone pierce skin

end of interstitial growth

Only remnant of epiphyseal plate is internal thin line of compact bone called epiphyseal line

perforating canals

Perpendicular to the central canal Connect multiple central canals thus forming a channel for blood vessels and nerves to connect among multiple osteons

bone connective tissue

Primary component of bone, Also called osseous connective tissue, Composed of both cells and extracellular matrix

function of osteoprogenitor cells and osteoblasts

Produce circumferential layers of bone matrix; responsible for growth in bone width

Hyaline cartilage connective tissue

Resilient and flexible; contains a high percentage of water which makes it highly compressible and a good shock absorber

circumferential lamellae

Rings of bone immediately internal to the periosteum (external circumferential lamellae) or external to endosteum (internal circumferential endosteum) Run the entire circumference of the bone

Osteoid

Semisolid, organic, unmineralized bone matrix secreted by osteoblasts Later calcifies as result of salt crystal deposition

sesamoid bones

Short bones along tendons of some muscles; patella (kneecap) is the largest

nutrient foramen

Small opening through compact bone, allows passage of one nutrient artery, one nutrient vein, and sensory nerves into medullary cavity

Phosphate

Structural component of ATP, other nucleotides, and phospholipids; important component of plasma membrane

bone remodeling

The continual process of bone breakdown (resorption) and formation (deposition of new bone); occurs at both periosteal and endosteal surfaces

flat bones

These bones are thin, flat, and may be slightly curved; extensive surface area for muscle attachment; They form the ribs, scapular, sternum and roof of the skull.

zone of hypertrophic cartilage

This layer consists of large, maturing chondrocytes; walls of lacuna thin because chondrocytes resorb matrix as the enlarge

Endosteum

This layer of connective tissue that lines the medullary cavity; contains osteoprogenitor cells, osteoblasts, and osteoclasts.

zone of calcified cartilage

Two or three layers of chondrocytes Deposited minerals kill the chondrocytes and make matrix opaque

Bone is highly_____________, especially in regions containing spongy bone

Vascularized

Serotonin

When levels are too high, osteoprogenitor cells are prevented from differentiating into osteoblasts

Bone formation begins

When osteoblasts secrete osteoid; requires vitamins C and D, calcium, and phosphate

Calcitriol

active form of vitamin D that helps absorb calcium from intestine

medullary cavity

cavity within the shaft of the long bones filled with bone marrow

Osteoclasts are

bone cells that resorb bone tissue; Large, multi-nuclear, phagocytic cells; Derived from fused bone marrow cells; Ruffled border where they contact bone ( increases surface area exposure)

simple fracture

bone does not break through the skin; typically heals in 2-3 months

skeletal system

bones, cartilage, ligaments and other connective tissues that stabilize or connect the bones

Pathological fracture

break in a bone weakened by disease

organic components of bone matrix

collagen and semisolid ground substance of proteoglycans and glycoproteins that suspends and supports collagen fibers; give bone tensile strength by resisting stretching and twisting and contribute to overall flexibility

2 types of bone connective tissue

compact bone and spongy bone

inner layer of periosteum

consists primarily of osteoprogenitor cells, osteoblasts and osteoclasts

articular cartilage

covers the surfaces of bones where they come together to form joints; hyaline; helps reduce friction and absorb shock in movable joints

Ligaments

dense regular connective tissue that anchors bone to bone

Tendons

dense regular connective tissue that connects muscle to bone

Calcification

deposition of hydroxyapatite crystals in bone matrix

Epiphysis

each end of a long bone; the area beyond the epiphyseal plate; expanded knobby region

outer layer of periosteum

fibrous layer of dense irregular connective tissue protects the bone from surrounding structures, anchors blood vessels and nerves to the surface of the bone, and serves as an attachment site for ligaments and tendons.

interstitial lamellae

fill spaces between osteons or leftover parts of osteons that have partially resorbed; incomplete and typically have no central canal

Function of Bones: Support

form the framework that supports the body and cradles soft organs & tissues

Ossification (osteogenesis)

formation and development of bone connective tissue

a break in a bone is called

fracture; 21 different classifications

yellow bone marrow

gradually replaces red bone marrow in adult bones; functions as storage for fat tissue and is inactive in the formation of blood cells

appositional growth

growth in width along cartilage's outside edge - 3 steps

growth hormone (somatotropin)

hormone secreted by anterior pituitary gland that stimulates growth of bones by stimulating liver to release another hormone called insulin-like growth factor (IGF) or somatomedin; both directly stimulate growth of cartilage in epiphyseal growth plate

inorganic components of bone matrix

hydroxyapatites(mineral salts composed of calcium phosphate and calcium hydroxide interact to form crystals), and other salts and ions; crystals harden matrix and account for rigidity and provides for compressional strength

interstitial growth of cartilage

increase in length that occurs within the internal regions of cartilage; 4 steps

short bones

length nearly equal to width (ex. - carpals and tarsals)

Classes of bones

long, short, flat, irregular

long bones

longer than they are wide; most common bone shape

Osteocytes

mature bone cells that maintain the bone matrix and detect mechanical stress on a bone

Four types of cells in bone connective tissue

osteoprogenitor cells, osteoblasts, osteocytes, osteoclasts

Coverings and linings of bone

periosteum and endosteum

Bones

primary organs of the skeletal system

intramembranous ossification

process by which bone forms directly from mesenchymal tissue; produces flat bones of skull, some facial bones, mandible, & central part of clavicle

endochondral ossification

process in which bone forms by replacing hyaline cartilage; 6 steps

Hematopoiesis

production of blood cells; occurs in red bone marrow connective tissue

Osteoporosis

reduction in bone mass sufficient to compromise normal activity

epiphyseal line

remnant of the epiphyseal plate, seen in adult bones

concentric lamellae (compact bone)

rings of bone connective tissue surrounding central canal; adjacent lamella contain collagen fibers oriented at 90 degree angles different from previous and next lamella (gives bone part of it's strength and resilience

parathyroid hormone (PTH)

secreted by the parathyroid glands in response to reduced blood calcium levels; speeds up conversion of calcidiol to calcitriol in kidneys

thyroid hormone

secreted by the thyroid gland and stimulates bone growth by influencing the basal metabolic rate of bone cells

perforating fibers (Sharpey's fibers)

secure periosteum to the underlining bone with thick bundles of collagen that run perpendicular to the duaphysis from periosteum into bone matrix

Cartilage

semi-rigid connective tissue found on the skeleton; a vascular; two types associated with skeleton are hyaline and fibrocartilage

Diaphysis

shaft of a long bone, provides leverage and major weight support; composed of compact bone with spongy bone internally

Lacunae

small cavities in bone that contain osteocytes

bone marrow

soft connective tissue within the medullary cavity of bones; red abd yellow

Diploe (spongy bone)

spongy bone in flat bones of the skull

osteoprogenitor cells

stem cells derived from mesenchyme, located in periosteum and endosteum; divide and one cell matures to become osteoblast

Glucocorticoids

steroid hormones released from the adrenal cortex; high amounts increase bone loss & impair growth at the epiphyseal plate

Function of bones

support & protection, levers for movement, mineral & energy reserve storage, blood cell formation (hematopoiesis)

bone resorption

the breakdown of bone matrix by osteoclasts that is part of the normal development, maintenance, and repair of bone tissue; liberated calcium and phosphate ions enter the blood when blood calcium levels are low

stress fracture

thin break caused by increased physical activity in which the bone experiences repetitive loads

zone of ossification

walls break down between lacunae in columns spaces invaded by capillaries and osteoprogenitor cells from medullary cavity new bone matrix deposited on the calcified cartilage matrix

mechanical stress

weight bearing movement and exercise and is required for normal bone remodeling. Detected by osteocytes and communicated to osteoblasts.

Metaphysis (long bone)

where diaphysis and epiphysis meet; bone widens and transfers forces