NVCC BIO 141 Chapter 6

Functions of the skeletal system

Protection

Mineral Storage/pH homeostasis

Blood Cell Formation: hematopoiesis

Fat Storage: triglycerides

Movement

Support

Compact bone

hard, dense outer layer

resists majority of stresses placed on it

linear compression/twisting

Spongy bone

inner honeycomb-like

resist forces in many directions

holds bone marrow

Long bones

Longer than they are wide, shaft with head at both ends, mostly compact, all bones of limbs except patella, wrist and ankle bones are long bones.

Short bones

Generally cube shaped, contain mostly spongy bones. Includes patella (knee cap), and bones of wrist and ankle.

Flat bones

Thin, flat and usually curved, two thin layers of compact bones surrounds a layer of spongy bones, most bones of the skull, ribs and sternum

Irregular bones

Bones that don't fit into other categories, hip and vertebra

Sesamoid bones

unique irregular bones that are normally found embedded within tendons, close to joints

Diaphysis

shaft of a long bone

Epiphysis

End of a long bone

Epiphyseal Line

remnant of epiphyseal plate

Epiphyseal Plate

Growth plate, made of cartilage, gradually ossifies

Articular Cartilage

covers the surfaces of bones where they come together to form joints

Periosteum

A dense fibrous membrane covering the surface of bones richly supplied with blood vessels and nerves

Endosteum

membranous lining of the hollow cavity of the bone

thinner and lacks fibrous outer layer

Medullary Cavity

marrow cavity

Inorganic components of extracellular matrix of bone

65% of total weight

minerals like calcium salts turned into hydroxyapatite crystal

Organic components of the extracellular matrix of bone

35% of total weight

protein fibers, proteoglycans/glycosaminoglycans: draw water out of blood vessels to matrix to resist compression

glycoproteins: bind different components together

osteocalcin

collagen fibers to resist twisting/stretching

Red Bone Marrow

network of reticular fibers supporting islands of blood forming hematopoietic cells; growth

Yellow Bone Marrow

stores fat as triglycerides; replaces red marrow as adults

Central Canal (compact bone)

blood vessels and nerves lined by endosteum

Perforating Canals (compact bone)

Perpendicular to the central canal

connects neighboring cells

Carry blood vessels into bone and marrow

Canaliculi (compact bone)

Hairlike canals that connect lacunae to each other and the central canal

Lacuna (compact bone)

small cavities in bone that contain osteocytes

Concentric lamellae (compact bone)

layers of bony matrix around a central canal

Interstitial Lamellae (compact bone)

remains of old osteons that broke down as bone grew and remodeled itself

Trabeculae

branching ribs of bone hat project into marrow to reinforce framework

covered by endosteum with no osteons but have concentric lamellae

no central/perforating canals

Osteoblasts

bone forming cells

Osteocytes

mature bone cells found in lacunae

Osteoclasts

large cells that resorb or break down bone matrix

Primary Bone

immature bone

irregularly arranged collagen bundles

abundant osteocytes

little inorganic matrix

mostly replaced

Secondary Bone

Mature bone tissue that replaces immature bone

fully formed lamellae with regularly arranged collagen bundles that are parallel

higher % of inorganic matrix

Intramembranous Ossification

process by which bone forms directly from mesenchymal tissue

flat bones (skull/clavicles)

Endochondral Ossification

Bone forms by replacing hyaline cartilage

Bones are called cartilage (endochondral) bones

Form most of skeleton

Longitudinal Growth

how bones lengthen via division of chondrocytes in epiphyseal plate

Appositional Growth

increase in bone thickness

growth between periosteum and surface

Zone of Proliferation

actively dividing chondrocytes

Zone of Hypertrophy and Maturation

contains mature chondrocytes

Zone of Calcification

dead or dying cartilage cells undergoing rapid calcification

Zone of Ossification

consists of calcified chondrocytes and osteoblasts

Zone of Reserved Cartilage

not directly involved but can divide

Calcitonin

Lowers blood calcium levels from thyroid gland

Parathyroid Hormone

A hormone of the parathyroid gland that regulates the metabolism of calcium and phosphorus in the body.

Vitamin D

promotes calcium ion absorption

Growth Hormone

hormone secreted by anterior pituitary gland that stimulates growth of bones

Thyroid Hormone

modulates activity of growth hormone, ensuring proper proportions

Testosterone

increases wide growth causing men's bones to be thicker

increases calcium salt deposits

increases rate of mitosis in epiphyseal plate causing growth spurts

Estrogen

increases rate of longitudinal bone growth

inhibits osteoclasts causing growth spurts

accelerates closure of epiphyseal state faster than testosterone which is why women are typically shorter

Formation of Bone Matrix

osteoblasts in periosteum/endosteum secreting proteoglycans/glycoproteins that bind calcium ions that eventually crystalize

Reabsorption of Bone Matrix

osteoclasts secrete H+ which is acidic compared to calcium crystals

also secretes enzymes to catalyze reactions to breakdown other molecules which then could be reused

Purpose of Bone Remodeling

maintains calcium ion homeostasis

bone repair

replacement of primary bone with secondary bone

replacement of old brittle bone

bone adaption to tension/stresses

Explain effect of mechanical stress on bone remodeling

stress on bones (amount of compression) stimulates bone growth which increases bone mass