Anatomy Ch. 7: Bones

osteology

study of bones

skeletal system

composed of bones, cartilages, and ligaments

cartilage

all long bones start as cartilage; covers many joint surfaces of mature bones

ligaments

holds bones together at joints; bone to bone connection

tendons

attach muscle to bones

functions of skeletal system: support

limb boned and vertebrae support body; jaw bones support teeth; some bones support viscera (internal organs)

functions of skeletal system: protection

protect brain, spinal cord, heart, lungs, and more

functions of skeletal system: movement

limb movements, breathing, and other bone dependent movements

functions of skeletal system: electrolyte balance

regulate calcium and phosphate levels

functions of skeletal system: blood formation

red bone marrow is the chief producer of blood cells

functions of skeletal system: acid-base balance

buffers blood against large pH changes by altering phosphate and carbonate salt levels

bone (osseous) tissue

connective tissue with the matrix hardened by calcium phosphate and other minerals; only tissue that is solid at room temp

mineralization or calcification

the hardening process of bone

what is a bone made of

bone tissue, bone marrow, cartilage, adipose tissue, nervous tissue, and fibrous connective tissue

long bones

longer than they are wide; rigid levers acted upon by muscles; crucial for movement; ulna, radius, femur

short bones

approximately equal in length and width; glide across one another in multiple directions; completely filled with spongy bone surrounding by one layer of compact bone; carpals and tarsals

flat bones

thin curved plates; protect soft organs; completely filled with spongy bone surrounded by two layers of compact bone; cranium; sternum, scapula, ribs

irregular bones

elaborate shapes that do not fit into other categories; sphenoid bone and vertebrae

compact bone

dense outer shell of bone; ¾ of a bones weight; concentric lamellae around a central canal (blood vessels run through canal)

spongy bone

loosely organized bone tissue; found in center of ends and center of shafts of long bones and the middle of nearly all others; ¼ of a bones weight; almost as strong as compact bone but much less heavy

osteogenic calls

stem cells found in endosteum and inner layer of periosteum; multiply continuously and give rise to most other bone cell types; multi-potent

osteoblasts

bone builders; form single layer of cells under endosteum and periosteum; synthesize soft organic matter of matrix which is hardened by mineralization; stress causes increased number of osteoblasts to reinforce bone

osteocytes

maintenance bone cell; former osteoblasts that have become trapped in the matrix they deposited

lacunae

tiny cavities where osteocytes reside

canaliculi

little channels that connect lacunae; osteocytes use these to contact neighboring cells

strain sensors

when stressed, osteocytes produce signals that regulate bone remodeling (shape and density changes that are adaptive)

osteoclasts

bone-dissolving cells found on bone surface; formed from fusion of stem cells; multiple nuclei; ruffled border for larger surface area; much larger than osteocyte

matrix: organic matter

POLYMER (PROTEIN) PORTION; GIVES FLEXIBILITY; synthesized by osteoblasts; collagen, carbohydrate-protein complexes, such as glycoproteins

matrix: inorganic matter

MADE OF MINERALS; GIVES STIFFNESS; 85% hydroxyapatite (crystallized calcium phosphate salt); 10% calcium carbonate; other minerals (fluoride, sodium, potassium, magnesium)

make up of spongy bone

consists of thing plates of bone called trabeculae which are covered with endosteum; spaces filled with red bone marrow; few osteons; no central canals; trabeculae develop along bone’s lines of stress

red bone marrow

produces blood cells; in nearly every bone in children; in adults, found in skull, vertebrae, ribs, sternum, part of pelvic girdle, and proximal heads of humerus and femur

yellow bone marrow

found in adults; stores fat; can transform to red marrow in event of chronic anemia

ossification or osteogenesis

formation of a bone

intramembranous ossification

produces flat bones and clavicle in fetus; thickens long bones throughout life

embryonic mesenchyme

type of loose, unspecialized connective tissue found in early stage embryos

intramembranous ossification process

osteoid tissue (mineral portion) is deposited into embryonic mesenchyme; tissue is calcified (hardened); spongy bone and periosteum develop; compact bone then develops to surround spongy bone

endochondral ossification stages in a fetus

production of long bones; begins as hyaline cartilage; chondrocytes enlarge to form primary ossification center and periosteum develops; blood vessels invade to form primary marrow cavity and secondary ossification centers form in “epiphysis”

endochondral ossification stage at birth

enlarged primary marrow cavity and appearance of secondary marrow cavity in one epiphysis

endochondral ossification stage in a child

epiphyseal plate forms at the distal end allowing for continuous bone elongation; epiphyses fill with spongy bone and articular cartilage covers each joint surface

endochondral ossification stage in an adult

primary and secondary marrow cavities unite to form a single marrow cavity with a closed epiphyseal plate

achondroplastic dwarfism

long bones lose ability to grow in childhood; bones can grow wider but not longer; normal torso, but short limbs (disproportionate); caused by gene mutation

pituitary dwarfism

lack of growth hormone; normal proportions with short stature; easiest to treat

appositional growth

occurs at bone surface, growing in thickness; part of intramembranous ossification

bone remodeling

absorption and deposition; occurs throughout life (10% of skeleton per year); repairs microfractures, releases minerals into blood, reshapes bones in response to misuse and disuse

Wolff’s law of bone remodeling

architecture of bone determined by mechanical stress placed on it; happens through osteoblasts and osteoclasts; bony processes grow larger in response to mechanical stress

mature bone

metabolically active organ involved in its own maintenance of growth and remodeling

mineral deposition (mineralization)

process in which calcium, phosphate, and other ions are taken from blood and deposited in bone; osteoblasts produce collagen fibers that allow for the growth of minerals; how braces work

mineral resorption

process of dissolving bone and releasing minerals into blood; osteoclasts use hydrochloric acid to dissolve bone minerals; how braces work

phosphate

component of DNA, RNA, ATP, phospholipids, and pH buffers

calcium

needed in neuron communication, muscle contraction, blood clotting, and exocytosis; 2.4 lbs of calcium in adult body and 99% is in bones

hypocalcemia

deficient amounts of calcium in blood; caused by vitamin D deficiency, diarrhea, thyroid tumors, and underactive parathyroid glands; changes membrane potentials, causes overly excitable nervous system, and muscle spasms; laryngospasm can cause suffocation; pregnancy and lactation increase risk

hypercalcemia

excessive calcium levels; makes ion channels less responsive and thus nerves and muscles less excitable; leads to emotional disturbance, muscle weakness, sluggish reflexes, cardiac arrest, or kidney stone formation

calcium homeostasis

depends on a balance between dietary intake, urinary and fecal losses, and exchanges between osseous tissue; regulated by calcitriol, calcitonin, and parathyroid hormone

calcitriol

raises blood calcium levels; increases calcium absorption through the digestive tract (from what we eat), increases resorption of calcium from osteoclasts after breaking down bone, increases reabsorption of calcium in kidneys so less of it is lost in urine; too little calcitriol results in abnormal bone softness (rickets in kids or osteomalacia in adults)

calcitonin

hormone secreted by c cells (clear cells) of thyroid gland; lowers blood calcium by inhibiting osteoclasts reducing bone resorption and stimulating osteoblasts to deposit calcium in bone; more important in children with more active osteoclasts and pregnant/lactating women (fetus elevates blood calcium)

parathyroid hormone

secreted by parathyroid glands on posterior surface of thyroid; released when blood calcium levels are low; raises calcium by increasing osteoclast population and bone resorption, promoting calcium reabsorption in kidneys (so we don’t lose it in urine); raising the effects of calcitriol, and inhibiting collagen synthesis by osteoblasts

anabolic steroids

cause growth to stop; epiphyseal plate closes prematurely; results in abnormally short adult stature

why do girls grow faster than boys

estrogen has stronger effect than testosterone on bone growth

stress fracture

break caused by abnormal trauma to a bone; ex. fall

pathological fracture

break in a bone due to its weakening from a disease ex. bone cancer or osteoporosis

structural characteristics that classify fractures

direction of fracture line, break in the skin, and amount of pieces of bone

nondisplaced fracture

aligned fragments

displaced fracture

shifted fragments; bone needs to be set back into place

comminuted fracture

more than two pieces of bone floating around

greenstick fracture

partial fracture; mostly in young children

compound fracture

broken bone sticks out of skin

healing fractures: step 1

hematoma formation

• hematoma is converted to granulation tissue by invasion of cells and blood capillaries

healing fractures: step 2

soft callus formation

• deposition of collagen and fibrocartilage converts granulation tissue to a soft callus

healing fractures: step 3

hard callus formation

• osteoblasts deposit a temporary bony collar around fracture to unite broken pieces while ossification occurs

healing fractures: step 4

bone remodeling

• small bone fragments are removed by osteoclasts

• osteoblasts deposit spongy bone and then convert it into compact bone

strength of a remodeled bone

bone becomes much thicker and stronger after healing from a fracture; it is not likely to break a bone in the same place twice

closed reduction

procedure in which bone fragments are manipulated into their normal positions without surgery

open reduction

involves surgical exposure of the bone and the use of plates, screws, or pins to realign the fragments

cast

normally used to stabilize and immobilize healing bone

traction

typical treatment for femur fractures to align bone fragments by overriding force of the strong thigh muscles

hip fractures

usually pinned and early walking is encouraged to avoid blood clots; fractures taking more than 2 months to heal may be treated with electrical stimulation which suppresses effects of parathyroid hormone

osteoporosis

most common bone disease; severe loss of bone density; osteoclasts are out competing osteoblasts; bones lose mass and become brittle due to loss of organic matrix and minerals

kyphosis

deformity of spine due to vertebral bone loss; humpback

lordosis

deformity of spine; beer gut creates a lower humpback

estrogen (bone related)

maintains bone density in both sexes; inhibits resorption by osteoclasts

who has greatest risk of osteoporosis

postmenopausal white women because ovaries cease to create estrogen or young female athletes because low body fat causes a decrease in estrogen secretion

best treatment for osteoporosis

prevention; exercise and good bone-building diet between ages 25 and 40

osteopenia

loss of bone mass in any manner