A&P Chapter 7 Skeletal System: Bone Structure and Function

Periosteum

(around) Outer covering(surface) of bone -Outer fibrous layer •dense irregular connective tissue •protects bone from surrounding structures •anchors blood vessels and nerves to bone surface •attachment site for ligaments and tendons -Inner cellular layer •includes osteoprogenitor cells, osteoblasts, and osteoclasts

Endosteum

(within) -Covers all internal surfaces of bone within medullary cavity -Incomplete layer of cells -Contains osteoprogenitor cells, osteoblasts, and osteoclasts

What is Calcium required for?

-.initiation of muscle contraction -.exocytosis of molecules from cells, including neurons - .stimulation of the heart by pacemaker cells d.blood clotting Assisted by two primary hormones regulate blood calcium -Calcitriol (from vitamin D) -Parathyroid hormone (PTH)

intramembranous ossification

-Also known as dermal ossification -Produces: •flat bones of the skull •some of the facial bones •mandible •central part of the clavicle

Bone growth and remodeling

-Begin during embryologic development

Endochondral (cartilage) ossification

-Begins with a hyaline cartilage model -Produces most bones of the skeleton, including: •bones of the upper and lower limbs •pelvis •vertebrae •ends of the clavicle 1.Cartilage model forms 2.Cartilage calcifies •Bone collar forms •Blood vessels develop •Osteoblasts secrete matrix 3.Primary ossification center forms in diaphysis 4.Secondary ossification center forms in epiphysis 5.Bone replaces cartilage (two exceptions) 6.Epiphyseal plate becomes epiphyseal line

Ossification (osteogenesis)

-Bone development -Begins in the embryo (8th week) -Continues through childhood and adolescence -Two types -intramembranous ossification -endochondral ossification

Fractures

-Breaks in bone -Occur as result of unusual stress or impact -Increased incidence with age •due to normal thinning and weakening of bone

Canaliculi

-Channels connecting lacunae and central canal

bone remodeling

-Continual process of bone deposition and resorption -Continues throughout adulthood -Location •Periosteum and endosteum -Occurs at different rates •e.g., distal part of femur replace every 4 to 6 months •e.g., diaphysis of femur not completely replaced over a lifetime -20% of skeleton replaced yearly -Dependent on the coordinated activities of osteoblasts, osteocytes, and osteoclasts -Bone remodels based on the stress placed upon it

Sex hormones

-Estrogen and testosterone -Begin to be secreted in large amounts at puberty

long bones

-Greater in length than width -Have elongated, cylindrical shaft (diaphysis) -Most common bone shape -Ex. •Found in upper and lower limbs •e.g., arm, forearm, fingers, thigh, leg, toes

Red bone marrow (mycloid tissue)

-Hemopoietic (blood cell forming in long bones) -Contains reticular connective tissue, immature blood cells, and fat -In children, •located in the spongy bone and medullary cavity of long bones -In adults, •located in portions of axial skeleton •located in proximal epiphyses of humerus and femur •e.g., skull, vertebrae, ribs, sternum, ossa coxae

Inorganic components

-Made of salt crystalsà primarily calcium phosphate, Ca3(PO4)2 •forms crystals of hydroxyapatite, Ca10(PO4)6(OH)2 •65% of bone mass -Function •Harden the matrix and account for relative rigidity of bones

organic components

-Osteoid à unmineralized matrix of bone (resembling bone) -oid •Secreted by osteoblasts -Function • tensile strength by resisting stretching •Contribute to bone flexibility

Paget's disease

-Results from disruption between osteoclast and osteoblast function -Characterized by excessive bone resorption followed by excessive bone deposition -Larger osteoclasts resorbing bone at higher rate -Newly deposited bone poorly formed -Most commonly affected bones: •pelvis, skull, vertebrae, femur, tibia -Symptoms of bone deformity and pain

Thyroid hormone

-Secreted by thyroid gland -Influences basal metabolic rate of bone cells -Helps regulate normal activity at the epiphyseal plates -Hypothyroidism •low thyroid levels •leads to impaired skeletal growth and other problems

Hormones

-Some altering rates of chondrocyte, osteoblast, and osteoclast activity

growth hormone

-Some altering rates of chondrocyte, osteoblast, and osteoclast activity that makes Somatomedin.

•Bone growth in diameter

-Termed appositional growth only within the periosteum

•Bone growth in length

-Termed interstitial growth

central canal

-blood vessels and nerves traveling here

Osteocytes

-found in lacunae between lamellae

concentric lamellae

-rings of bone around central canal -contain collagen fibers

Four steps of bone fracture repair

1) Fracture hematoma forms from clotted blood •blood vessels torn within periosteum 2) Fibrocartilaginous callus forms •regenerated blood capillaries infiltrating hematoma •fracture hematoma à a connective tissue procallus •fibroblasts producing collagen fibers 3. Hard (bony) callus forms •osteoblasts àproducing trabeculae •forms a hard (bony) callus 4) The bone is remodeled •final phase of fracture repair •compact bone replacing primary bone •usually leaves a slight thickening of bone

Two ways aging affects bone

1. Decreased tensile strength of bone 2. Bone loss of calcium and other minerals

Types of fractures

1. stress factures 2. Pathologic fracture 3. Simple fracture 4. compound fracture

General function of a bone

1.Support and protection 2.Movement 3.Hemopoiesis 4.Storage of mineral and energy reserves •Calcium •Phosphate •Lipids in yellow marrow

bone formation

1.secretion of osteoid 2.Osteoid undergoes calcification •Requirements -vitamin D •enhances calcium absorption from gastrointestinal tract -vitamin C •needed for collagen formation -calcium and phosphate for calcification

Osteoporosis

A condition in which the body's bones become weak and break easily.

Components of osteons

Basic unit of compact bones.central canal, concentric lamellae, osteocytes, canaliculi

What influences bone growth?

Hormones

Short Bone

Length nearly equal to width -E.g., carpal bones (wrist bones) -E.g., sesamoid bones, bones along tendons of muscles -E.g., patella (kneecap), largest sesamoid bone

bone resorption

Osteoclasts breakdown bone tissue then release minerals will be send calcium to the blood if calcium levels are low

irregular bones

Unique shape and function Ex. Vertebrae -Have elaborate shapes -E.g., vertebrae, ossa coxae (hip bones) -E.g., several bones in the skull (ethmoid, sphenoid)

Calcitonin

Will stop or inhibit the bone breaking down activity (osteoclast) in bone connective. -Result: lowers blood calcium levels

components of skeletal system

bone, cartilage, tendons, ligaments

Somatomedin

both directly stimulating growth of cartilage in epiphyseal plate

Simple facture

broken bone not penetrating the skin

Pathologic fracture

occurs in bone weakened by disease

compound fracture

one or both ends piercing overlying skin

Metaphysis (long bone)

region between diaphysis and epiphysis

yellow bone marrow

stores fat. -Product of red bone marrow degeneration -Fatty substance -May convert back to red bone marrow •may occur during severe anemia -condition with reduced erythrocytes (red blood cells) •facilitates the production of additional erythrocytes

components of spongy bone

trabeculae and parallel lamellae

Osteoctyes

•Mature bone cells derived from osteoblasts Maintain bone matrix

Osteoblasts

•Produce osteoid (unmineralized bone matrix) •Periosteum/endosteum

osteoprogenitor cells (Osteogenic)

•Stem cells that make osteoblasts •Periosteum/endosteum

-Compact bone (dense/cortical bone)

•appears white, smooth, and solid •80% of bone mass

Parallel lamellae of spongy bone

•composed of bone matrix •osteocytes resting between lamellae •canaliculi radiating from lacunae

perforating canals (Volkmann's canals)

•contain blood vessels and nerves •run perpendicular to the central canals help connect multiple central canals within different osteons

Diaphysis (shaft)

•elongated, usually cylindrical shaft •provides for leverage and major weight support •compact bone with spongy bone extending inward

medullary cavity

•hollow, cylindrical space within the diaphysis •contains red bone marrow in children •contains yellow bone marrow in adults

epiphyseal plate (growth plate)

•in metaphysis •thin layer of hyaline cartilage •provides for continued lengthwise bone growth • epiphyseal line

Epiphysis

•knobby region at the ends of long bone •proximal epiphysis •distal epiphysis •composed of: -outer thin layer of compact bone -inner region of spongy bone •joint surface covered by thin layer of hyaline cartilage (white and shiny) -termed articular cartilage -helps reduce friction and absorb shock in moveable joints

Osteoclasts

•large, multinuclear phagocytic cells •Break down bone matrix •Periosteum/endosteum

-Spongy bone (cancellous/trabecular bone)

•located internal to compact bone •appears porous •20% of bone mass

trabeculae of spongy bone

•open lattice of narrow rods and plates of bones •bone marrow filling spaces between •provide great resistance to stresses

circumferential lamellae

•rings of bone •run the entire circumference of bone

Stress facture

•thin break caused by increased physical activity •bone experiences repetitive loads (e.g., runners)