Bone Tissue

functions of the skeleton

support, protection, movement, electrolyte balance, acid-base balance, blood formation

another name for bone

osseous tissue

calcification

hardening process of bones(mineralization)

shapes of bones

long bones, short bones, flat bones, irregular bones

shaft

(diaphysis) cylinder of compact bone

marrow cavity of the shaft

medullary cavity, is lined w/ endosteum(osteogenic cells and reticular connective tissue)

enlarged ends of bones

epiphyses, spongy bone covered by compact bone, is enlarged to strengthen joint and attach ligament

the joint surface of bones is____

covered w/ articular cartilage

nutrient foramen

blood vessles that penetrate bone

periosteum

outer fibrous layer of collagen, inner osteogenic layer of bone forming cells

endosteum

thin layer of reticular connective tissue and osteogenic cells

epiphyseal plate

growth plate

types of bone cells

osteogenic, osteoblasts, osteocytes, osteoclasts

bone matrix

dry weight, 1/3 organic, 2/3 inorganic matter

organic matter of bone matrix

collagen, glycosaminoglycans, proteoglycans, and glycoproteins

inorganic matter of bone matrix

85% hydroxyapatite, 10% calcium carbonate, 5% other minerals(fluoride, potassium, magnesium)

combination of organic and inorganic matter of bone matrix_____

provides for strength and resilience

minerals in bone matrix...

resist compression

collagen in bone matrix...

resists tension

osteon

basic structural unit of compact bone

cylinders of osteons are formed...

from layers(lamellae) of matrix around central canal(osteonic canal)

in osteons, collagen fibers...

alternate between right and left handed helices from lamella to lamella

canaliculi

tiny cell processes that allow osteocytes to connect to each other and their blood supply

perforating canals

Volklmann canals, vascular canals perpendicularly joining central canals

trabeculae

spongelike appearance formed by plates of bone called trabeculae

spaces of spongy bone filled w/

red bone marrow

trabeculae have few...

osteons or central canals(no osteocyte is far from blood of bone marrow)

the trabeculae provides...

strength w/ little wieght, develop along bone's lines of stress

bone marrow

soft tissue that occupies marrow cavity

this type of marrow is hemopoietic

red bone marrow

hemopoietic

produces blood cells

yellow bone marrow

fat at center, no longer produces blood

intramembranous ossification

condensation of mesenchyme into trabeculae

embryonic connective tissue

mesenchyme

during intramembranous ossification, osteoblasts on trabeculae...

lay down osteoid tissue(uncalcified bone)

during intramembranous ossification_______ is deposited in the matrix forming bony trabeculae of spongy bone

calcium phosphate

during intramembranous ossification, osteoclasts...

create marrow cavity and form compact bone at surface

during intramembranous ossification, surface mesenchyme...

produces periosteum

during endochondral ossification...

bone develops from pre-existing model, most bones develop this process, formation of primary ossification center and marrow cavity in shaft of model

during primary ossification of endochondral ossification

bony collar is developed by osteoblasts, chondrocytes swell and die, stem cells give rise to osteoblasts and clasts, bone is laid down and marrow cavity is created

the secondary ossification centers and marrow cavities of endochondral ossification

form in ends of bone through same process as primary ossification centers

the secondary ossification centers and marrow cavities of endochondral ossification cartilage...

remains as articular cartilage and epiphyseal growth plates

growth plates

provide for increase in length of bone during childhood and adolescence

by early twenties, growth plates...

are gone and primary and secondary marrow cavities are united

zone of reserve cartilage(bone elongation)

hyaline cartilage

zone of proliferation(bone elongation)

chondrocytes multiply forming columns of flat lacunae

zone of hypertrophy(bone elongation)

cell enlargement

zone of calcification(bone elongation)

mineralization of matrix

zone of bone deposition(bone elongation)

chondrocytes die and columns fill w/ osteoblasts, osteons formed and spongy bone is created

during bone growth and remodeling...

bones increase in length, bones increase in width(appositional growth)

bones are remodeled...

throughout life

bones increase in length by...

interstitial growth of epipyseal plate, epipyseal line is left behind when cartilage is gone

when bones increase in width...

osteoblasts lay down matrix in layers on outer surface and osteoclasts dissolve bone on inner surface

Wolff's law of bone

architecture of bone is determined by mechanical stresses(action of osteoblasts and osteoclasts)

mineralization is a....

crystallization process

during mineralization

osteoblasts produce collagen fibers spiraled the length of the osteon, minerals cover the fibers and harden the matrix

when minerals cover the fibers and harden the matrix...

ions are deposited along the fibers; ion concentration must reach the solubility product for crystal formation to occur

abnormal calcification

(ectopic) may occur in lungs, brain, eyes, muscles, tendons or arteries(arteriosclerosis)

during mineral resorption from bone...

bone is dissolved and minerals are released into the blood

when bone is dissolved and minerals are released into the blood...

performed by osteoclasts(ruffled border), hydrogen pumps in membrane secrete hydrogen into space between the osteoclast and bone surface, chloride ions follow by electrical attraction, hydrochloric acid dissolves bone minerals, enzyme digest the collagen

dental braces reposition teeth and remodel bone

create more pressure on one side of the tooth, stimulates osteoclasts to remove bone, decreased pressure stimulates osteoblasts

Phosphate is a component of ...

DNA, RNA, ATP, phospholipids, and pH buffers

how much phosphate in adult skeleton

750g

plasma concentration of phospate

4 mg per dL

calcium is needed in ...

neurons, muscle contraciton, blood clotting and exocytosis

how much calcium in adult skeleton

1100g

plasma concentration of calcium

10mg per dL

ion imbalances in the bones are caused through...

changes in phosphate levels(little effect) and changes in calcium levels(can be serious)

hypocalcemia

deficiency of blood calcium, causes excitability of nervous system if too low(muscle spasms, tremors)

hypercalcemia

excess of blood calcium, binding to cell surface makes sodium channels less likely to open, depressing nervous system(muscle weakness and sluggish reflexes)

calcium phosphate homestasis...

depends on calcitriol, calcitonin, and PTH hormone regulation

carpopedal spasm

hypocalcemia demonstrated by muscle spasm of hands and feet

calcitriol, PTH, and calcitonin...

maintain normal blood calcium concentration

calcitriol

activated vitamin D, behaves as a hormone that raises blood calcium concentration

calcitriol is produced by the following process

UV radiation and epidermal keratinocytes convert steroid derivative to cholecalciferol(D3), liver converts it to calcidiol, kidney converts that to calcitriol(Vitamin D)

calcitriol behaves as a gromone that raises blood calcium concerntration by....

increasing intestinal absorption and absorption from the skeleton, increases stem cell differentiation into osteoclasts, promotes urinary reabsorption of calcium ions

lack of calcitriol causes...

abnormal softness(rickets) in children and osteomalacia in adults

calcitonin

secreted(C cells of thyroid gland) when calcium concentration rises too high

functions of calcitonin

reduces osteoclast activity as much as 70%, increases the number and activity of osteoblasts, reduces bone loss in osteoporosis

calcitonin is important in children

because osteoclasts are more active in children

deficiency of calcitonin does not

cause disease in adults

Parathyroid hormone

released w/ low calcium blood levels, glands located on posterior surface of thyroid

function of PTH

causes osteoblasts to release osteoclast-stimulating factor(RANKL) increasing osteoclast population, promotes calcium resorption by the kidneys, promotes calcitriol synthesis in the kidneys, inhibits collagen synthesis and bone deposition by osteoblasts

sporatic injection of low levels of PTH

causes bone deposition

other factors affecting bones

hormones, vitamins, growth factors

bone growth is_____during puberty and stops when_______ closes

rapid, epiphyseal plate

during the growth rate at puberty

hormones stimulate osteogenic cells, chondrocytes, and matrix deposition in growth plate

teenage use of anabolic steroids causes

premature closure of growth plate and short adult stature

pathological bone fracture

in bone weakened by disease(osteoporosis, bone cancer)

types of bone fractures

open, greenstick, comminuted, linear, transverse, oblique, spiral, colles, pott

healing time of fractures

8-12 weeks in normal adults

stages of bone healing

fracure hematoma, soft callus, hard callus, remodeling

fracture hematoma

clot forms, then osteogenic cells form granulation tissue

soft callus

fibroblasts produce fibers and fibrocartilage

hard callus

osteoblasts produce a bony collar in 6 weeks

remodeling

spongy bone replaced by compact bone

closed reduction

fragments are aligned w/ manipulation and casted

open reduction

surgical exposure and repair w/ plates and screws

electrical stimulation used on fractures...

if 2 months necessary for healing

orthopedics

prevention and correction of injuries and disorders of the bones, joints, and muscles

osteoporosis

bones lose mass and become brittle(loss of organic matrix and minerals), risk of fracture, pneumonia, blood clotting

greatest risk to osteoporosis

menopausal white women

osteogenic cells

stem cells that develop from fibroblasts and then give rise to other bone cells

osteoblasts

bone forming cells

osteocytes

former osteoblasts that have become trapped in the matrix they deposited

osteoclasts

bone dissolving cells found on the bone surface