Chapter 6 Skeletal system

• 1) Support
• 2) Protection
• 3) Movement
• 4) Storage
• 5) Blood cell production

• 1) Bone
• 2) Cartilage
• 3) Tendons
• 4) Ligaments

• 1) Hyaline cartilage
• 2) Fibrocartilage
• 3) Elastic cartilage

• Chondroblasts: cells that produce cartilage matrix
• Chondrocytes: chondroblast that has surrounded it self by matrix

Lacuna or lacunae

Contains collagen for strength, proteoglycans for resilience by trapping water.

Double layered sheath of connective tissue covering most cartilage.

Dense, irregular connective tissue with fibroblasts

More delicate than outer layer. Fever fibers and contains chondroblasts

Blood vessels and nerves only penetrate outer layer of perichondrium. They do not penetrate cartilage, so nutrients must diffuse through cartilage matrix to reach chondrocytes

Cartilage that covers the ends of bones at joints. It has no perichondrium, nerves, or blood vessels.

• 1) Appositional growth
• 2) Interstitial growth

Addition of new cartilage matrix on surface of existing cartilage. Chondroblasts in inner perichondrium make new matrix on surface of existing cartilage. When chondroblasts make new cartilage that surrounds them, they are now chondrocytes in a new layer of cartilage.

Addition of new matrix within cartilage. Chondrocytes in matrix divide and make more matrix between cells thus increasing the thickness of cartilage.

35 % organic material (collagen and proteoglycans), 65% organic (hydroxyapatite)

Like reinforced concrete. Collagen= rebar, flexible strength. Mineral= concrete, weight bearing (compression) strength

Genetic disorder that results in too little or poor quality of collagen. It results in brittle bone and fractures are much more likely.

Cells that make new bone matrix. Contain extensive ER, ribosomes, and Golgi apparatuses. Participate in appositional growth and communicate through gap junctions.

• 1) Collagen and proteoglycans packed by golgi into vesicles to be released by exocytosis
• 2) Release matrix vesicles when membrane pinched off to increase calcium and phosphate for hydroxyapatite crystals.

Crystals act like "seeds" to stimulate hydroxyapatite formation and mineralization of matrix.

Mature bone cells. They are osteoblasts that have been surrounded by bone matrix.

They fill lacunae with their cell bodies. Cell processes fill canaliculi keeping cells in contact.

No diffusion through bone matrix. Nutrients pass through gap junctions or fluid in canaliculi and lacunae.

Large, multinuclear cells that resorb bone.

Release H+ to decalcify bone matrix and release enzymes to digest protein component. Some goes into cell through endocytosis.

Embryonic connective tissue. Adult connective tissue is developed from mesenchyme.

Stem cells that become OSTEOBLASTS and CHONDROCYTES. Found in inner layer of perichondrium, periosteum and endosteum.

Stem cells in red bone marrow. Also stem cells from red marrow that make monocytes (WBC)

• 1) Woven bone
• 2) Lamellar bone

Collagen fibers randomly oriented in many directions. Formed during fetal development and repair of fractures.

Osteoclasts resorb woven bone and osteoblasts build new matrix of lamellar bone.

Mature bone, organized into thin layers (3-7 um) called lamellae.

In lacunae sandwiched between layers of lamellae.

• 1) Cancellous bone
• 2) Compact bone

Thin rods/plates of interconnecting bone called trabeculae. Less bone matrix and more space than compact bone. Bear weight and resist stretching/bending.

Component of cancellous (spongy) bone. Each trabecula has several concentric lamellae with osteocytes in lacunae. Can realign if stress lines change in bone due to improper healing fracture.

Blood vessels and bone marrow fit between trabeculae.

Dense bone with blood vessels that enter bone itself. Made of osteons with haversion canals for nerves and blood vessels.

Concentric lamallae, osteocytes and a central haversion canal. Osteocytes lay inside lacunae between concentric lamellar rings. Canaliculi connect lacunae with osteocytes inside.

Circumfrential: thins plates that extend around entire compact bone just underneath periosteum.

Interstitial: In between osteons, remnants of circumfrential and concentric lamellae remodeling.

Canals that run perpendicular to long axis of bone. Connect periosteum, medullary canals and Haversion canals (osteons).

Periosteum or medullary canal --> Volkmann's canals --> Haversion canals --> canaliculi --> osteocyte cytoplasms

Waste go opposite direction

• 1) Long bones (UE and LE)
• 2) Short bones (almost cuboidal, wrist, ankles)
• 3) Flat bones (thin, flat, curved, skull, ribs, sternum, scapulae)
• 4) Irregular bones (vertabrae, facial bones)

• 1) Diaphysis (shaft), made from mostly compact bone, contains medullary cavity
• 2) Epiphysis (ends), made from mostly cencellous bone, contains epiphyseal plate/lines

Cavity in the center of the diaphysis of long bones made of cancellous bone. Filled with red and yellow bone marrow.

Fetal: all red marrow, replaced by yellow marrow just before birth and continues through adulthood. Eventually all long bongs are yellow. Elsewhere in the body, mix of red and yellow.

Proximal ends of humerus and femur

Ileum in the hip is about 50/50 red and yellow.

Cartilage between diaphysis and epiphsis. Site of growth in bone length. When growth stops, epiphyseal plate replaced with epiphyseal lines.

Connective tissue that covers the outside of the bone. Two layers: Outer and inner layers.

Outer fibrous layer is dense irregular collagenous with blood vessels and nerves.

Inner cellular layer is a single layer of bone cells including osteoclasts, osteoblasts and osteochondral pregenitor cells.

Single layer of cells lining inner surface of all cavities within bones (medullary, cavities in cancellous bones and compact bone).

Composed of osteoblasts, osteoclasts, and osteochondral pregenitor cells.

Interior framework of cancellous bone with outer layer of compact bone.

Cancellous bone center surrounded by compact bone. No diaphysis because not elongated.

Processes (projections) of irregular bones possess epiphyseal growth plates and small epiphyses.

Air-filled spaces lined with mucous membranes. Found in flat and irregular bones of skull.

• 1) Intramembranous ossification
• 2) Endochondral ossification

Formation of bone within connective tissue in utero. ~ 8 wks into development.

• 1) Osteochondrial pregenitor cells specialize to become osteoblasts and lay down bone matrix and form center of ossification ontop of collagen fibers of fetal connective tissue membrane forming tiny trabeculae of woven bone
• 2) Trabeculae enlarge as more bone matrix layed down. Cancellous bone forms as trabeculae join together, red marrow develops and cells surrounding developing bone specialize to form periosteum.
• 3) Osteoblasts from periosteum lay down bone matrix to form outer compact bone covering; remodeling turns woven bone into lamellar bone.

Locations in membrane where ossification starts. They expand to form a bone by gradually ossifying the membrane.

Large, membrane covered spaces between developing skull bones. Bones eventually grow together and all fontanels usually closed by age 2.

Formation of bone within cartilage. Most of skeletal system develops this way. Starts with hyaline cartilage model of bone

• 1) Zone of resting cartilage
• 2) Zone of proliferation
• 3) Zone of hypertrophy
• 4) Zone of calcification

Proximal to epiphysis and contains chondrocytes that don't divide rapidly

New cartilage made by chondrocytes using interstitial growth. Chondrocytes divide and form columns like stacked coins.

Chondrocytes from zone of proliferation mature and enlarge

Very thin with hypertrophied chondrocytes and calcified matrix. Chondrocytes die and replaced by osteoblasts from endosteum. Osteoblasts deposit new bone matrix on calcified cartilage matrix (appositional growth)

Rate of cartilage made and bone replacement are equal.

Usually between 12 and 25 yrs old

Similar to epiphyseal plate, but articular cartilage lasts for life, doesn't ossify.

Nutrition, Hormones, Sex hormones

Vitamin D required for Ca absorption. Insufficient fat absorption = Vit D insufficiency because Vit D is fat soluble.

Vitamin D insufficiency in children. Decreased bone mineralization, bowed bones, inflammed joints.

Osteomalacia. Insufficient fat absorption

Growth hormone, testosterone, and estrogen

Excessive bone/cartilage formation at epiphyseal plate. Most common is pituitary gigantism

Growth of connective tissue after epiphyseal plate ossifies and increases diameter of bones especially face and hands.

Low levels of growth hormone. Smaller than average but normal proportions.

• Testosterone and estrogen initially stimulates bone growth at puberty but also stimulate ossification of epihpyseal plate.
• Estrogen causes epiphyseal plate ossification faster

• Most common type of dwarfism.
• Normal sized trunk and head. Shorter than normal limbs.
• Usually caused by spontaneous mutation (during sperm oocyte production) of gene regulating bone growth. Increased inhibition of chondrocyte division at epihpyseal plate.

Basic Multicellular Unit (BMU) containing osteoblasts and osteoclasts resorb and lay new bone. Avg lifespan of BMU is 6 months, renews entire skeleton every 10 years.

Fragment of bone protrudes out of skin

Skin not perforated

Tissues around closed fracture damaged

Doesn't completely extended across bone

Broken into at least 2 fragments

Incomplete fracture on convex side of bone

Incomplete fracture, 2 sections don't separate. Common in skull fractures.

Complete fracture, more than 2 pieces, usually 2 major and 1 smaller fragments

One fragment driven into cancellous portion of other

Along long axis of bone

Perpendicular to long axis of bone

Helical course around bone

Obliquely in relation to long axis.

Rough, toothed, broken ends

Breakage lines radiating from 1 central point

Rate of bone resorbtion greater than bone formation. More common in women. Strong genetic component.

35 yrs of age. Women can lose 50% of cancellous bone. Men can lose 25%.

• 60% of peak bone mass is genetically determined
• 40% attributed to environmental factors

Decreased levels of estrogen increases bone loss. Estrogen inhibits parathyroid hormone (PTH) which is involved in stimulating osteoclasts. After menopause decreased cancellous bone in vertebrae and forearm.

Slowly decreases bone mass after 65. Men have denser bones.

• Supplemental Ca and Vitamin D
• Weight-bearing exercises
• Hormone replacement therapy (now discouraged)
• Selective estrogen receptor modulators
• Calcitonin nasal spray
• Statins

• Increased risk of breast and uterine cancer, MI, CVAs, blood clots
• Decrease PTH= decrease osteoclast activity which slows down bone loss, but does not increase bone mass.

Binds to estrogen receptors in bone but inhibit binding in breast and uterine tissue.

• Inhibit cholesterol synthesis
• Increase osteoblast activity

• 1) Hematoma formation
• 2) Callus formation
• 3) Callus ossification
• 4) Bone remodeling

Mass of blood released from blood vessels that is confined in an organ or space

1st step of bone repair. Clot stops bleeding at fracture site disrupting blood vessels in bone causing ischemia for osteocytes and bone tissue dies.

• 2nd step. Mass of tissue forms at fracture site and connects 2 bone fragments. Callus forms as clot desolves and removed by macrophages.
• Internal and external calluses (cartilage and woven bone)

• 3rd step. Calluses ossified to form woven, canellous bone.
• Similar to fetal bone development.
• Complete in 4-6 weeks.
• Immobilization is critical up to then because refracture of delicate bone matrix is easy.

• Woven bone of internal callus and dead bone adjacent to fracture is replaced by compact bone.
• Osteons from both sides of fracture extend across fracture line and "peg" 2 fragments together.
• Takes a long time.

Usually equal in/out Ca in bone. Parathyroid hormone (PTH) and calcitonin

• Responds to low serum Ca
• Increases osteoclasts activity, Vit D production in kidneys, and calcium absorption in intestines.

• Thyroid gland
• Responds to increased serum Ca
• Decreases osteoclast activity, more Ca stored in bone.