A & P Ch. 7 The Skeletal System

Bones are the

organs of the skeletal system

Composed of many tissues…

bone tissue, cartilage, dense connective tissue, blood and nervous tissue

Bone fx

Support and protect softer tissues, attachment for muscles, store blood-prod. Cells & inorganic salts

All Skeletal Cartilage contains chondrocytes in

lacunae and extracellular matrix

Hyaline cartilage Provides

support, flexibility, and resilience

Most bones start out as

hyaline cartilage!

Hyaline cartilage in

Articular, costal, respiratory, nasal cartilage

Elastic cartilage Similar to

hyaline cartilage, but contains elastic fibers

Elastic cartilage found in

External ear and epiglottis

Fibrocartilage composed of

Thick collagen fibers—has great tensile strength

Fibrocartilage in

Menisci of knee; vertebral discs

Bones of the skeletal system vary greatly in

Size, Shape

Bones are similar in

Structure (three levels), Development, Function

Levels of bone structure

Gross anatomy, Microscopic, Chemical Composition

Bone Classification by Shape

long, short, flat, & irregular

Long Bones

Long and narrow, have expanded ends

Short Bones

Cubelike, length = width, Include sesamoid (round) bones

sesamoid (round) bones

embedded in tendons

Flat Bones

Platelike, with broad surfaces

Irregular Bones

Variety of shapes, Most are connected to other bones

Gross anatomy

Bone textures (Compact and spongy bone)

Compact

Dense outer layer; smooth and solid

Spongy (trabecular)

Honeycomb of flat pieces of bone deep to compact called trabeculae

Compact Bone Consists of

cylindrical units called osteons

Compact bone strength

Strong and solid, Resists compression

Spongy Bone Consists of

branching plates called trabeculae

Spongy bone strength

Somewhat flexible

Parts of a Long Bone

Epiphysis, Diaphysis, Articular cartilage, Compact (cortical) bone, Spongy (cancellous) bone

Epiphysis

expanded end

Diaphysis

bone shaft

Articular cartilage

covers epiphysis

Compact (cortical) bone

wall of diaphysis

Spongy (cancellous) bone

makes up epiphyses

Medullary cavity

hollow chamber in diaphysis; contains marrow

Bone marrow

Red or yellow marrow, lines medullary cavity, spongy bone spaces

Diaphysis

Compact bone surrounding medullary cavity

Epiphyses at

Bone ends, External compact bone; internal spongy bone, Articular cartilage covers articular surfaces Between is epiphyseal line

Epiphyseal line is a Remnant of

Hyaline cartilage, growth plate

TWO Membranes

Periosteum and Endosteum

Periosteum

White, double-layered membrane, Outer fibrous layer of dense irregular connective tissue, Sharpey's fibers secure membrane to bone matrix

Inner Osteogenic layer ___ bone

abuts (in b/n periosteum & bone)

Periosteum Covers

external surfaces except joint surfaces “shrink wrap” (epiphysis, articular cartilage)

Osteogenic layer Contains

primitive stem cells – osteogenic cells

Periosteum contains

Many nerve fibers and blood vessels

Periosteum w/_____ for tendons and ligaments

Anchoring points

Endosteum

Delicate connective tissue membrane covering internal bone surface

Endosteum Lines

canals that pass through compact bone

Endosteum Contains

osteogenic cells that can differentiate into other bone cells

Hematopoietic Tissue in Bones

Red marrow

Red marrow Found within

trabecular cavities of spongy bone and diploë of flat bones (e.g., sternum), medullary cavities and spongy bone of newborns

Red marrow in medullary cavity turns to

yellow marrow w/age

Diploë

holes in spongy bone

Adult long bones have

little red marrow (Heads of femur and humerus only)

Red marrow in

diploë and some irregular bones is most active (hip bones, ends of femur & humerus)

Yellow marrow can convert to

red, if necessary

Mature bone cells are called

osteocytes

Osteocytes occupy (“stuck in”) chambers called

lacunae

Osteocytes exchange nutrients and wastes via

cell processes within canaliculi

bone tissue is a

CONNECTIVE TISSUE!

The extracellular matrix of bone is largely

collagen fibers and inorganic salts

Major cell types

Osteogenic cells, Osteoblasts, Osteocytes, Osteoclasts

Osteogenic Cells (osteoprogenitor cells)

Mitotically active (“true”) stem cells

Osteogenic cells Found in

periosteum and endosteum

When stimulated, ____________ differentiate into osteoblasts or bone lining cells

osteogenic cells

Some osteoprogenitor cells persist as

osteogenic (stem) cells

Osteoblasts

Bone-forming cells

Osteoblasts Secrete

non-mineralized bone (“gooey”) matrix or osteoid…later hardens w/calcium

Bone matric/osteoid Includes

collagen and calcium-binding proteins

Collagen = _______ of bone protein

90%

Osteoblasts are

Actively mitotic

Osteocytes

Mature bone cells in lacunae

Osteocytes Monitor and maintain

bone matrix…Act as stress or strain sensors

Bones thicken b/c of

stress, tension

Osteoclasts

Giant, multinucleate cells for bone resorption

Osteoclasts Derived from

hematopoietic stem cells that become macrophages

Osteoclasts Have

ruffled border

Ruffled border increases

surface area for enzyme degradation of bone and seals off area from surrounding matrix

Bone may breakdown b/c of

Ca+ deficiency…osteoporosis

Compact Bone

Consists of osteons, Osteocytes in lacunae, lamellae, perforating canals, canaliculi

Lamellae

layers of matrix around central canal

Perforating canals join

adjacent central canals

Blood vessels in compact bone provide

nutrients to bone tissue

Osteocytes can pass nutrients through

canaliculi

Collagen fibers in compact bone resists

twisting, withstands stress b/c run in different directions

Central (Haversian) canal runs through

core of osteon

Perforating (Volkmann's) canals are lined with

endosteum at right angles to central canal

Volkmann’s canals Connect

blood vessels and nerves of periosteum, medullary cavity, and central canal

Lacunae—small cavities that contain

osteocytes or chondrocytes

Canaliculi

hairlike canals that connect lacunae to each other and central canal

Organic component includes cells and osteoid

Osteogenic cells, osteoblasts, osteocytes, bone-lining cells, and osteoclasts

Osteoid—1/3 of

organic bone matrix secreted by osteoblasts

Osteoid Made of

ground substance (proteoglycans and glycoproteins), Collagen fibers

Osteoid Contributes to structure

provides tensile strength and flexibility

Cells and osteoid provide Resilience of

bone due to collagen molecules

Inorganic Components of compact bone

Hydroxyapatites (mineral salts), 65% of bone by mass

Hydroxyapatites (mineral salts) Mainly made of

tiny calcium phosphate crystals in and around collagen fibers

Hydroxyapatites are Responsible for

hardness and resistance to compression

bones grow during

DEVELOPMENT, GROWTH / REMODELING, REPAIR (puberty, broken bones, in utero)

Parts of the skeletal system begin to develop during the

first few weeks of prenatal development

Some bones continue to grow and develop into

adulthood