A&P 1 Seletal system TCC SE Sam Yacoub

Compact bone

also called dense or cortical bone; relatively dense connective tissue that appears white smooth and solid and makes up about 80 percent of bone mass

Spongy bone

also called cancellous or trabecular bone; located internal to compact bone appears porous and makes up about 20 percent of bone mass

General functions of bone

support and protection movement hemopoiesis and storage of mineral and energy reserves

Classification of bones by shape

bones fall into four classes determined by shape long bones short bones flat bones and irregular bones

Long bones

bones greater in length than width with an elongated cylindrical shaft called the diaphysis; the most common bone shape found in the upper and lower limbs and varying in size; example the femur

Short bones

bones classified by shape such as the tarsal bones that are roughly cube shaped

Flat bones

bones classified by shape that are thin and plate-like such as the frontal bone of the skull

Irregular bones

bones classified by shape with complex shapes such as a vertebra

Epiphysis

the proximal or distal end of a long bone

Metaphysis

the region of a long bone between the epiphysis and diaphysis

Diaphysis

the elongated cylindrical shaft of a long bone

Articular cartilage

layer of cartilage covering the epiphysis of a long bone at a joint

Epiphyseal line

remnant of the epiphyseal plate found within the metaphysis

Medullary cavity

central cavity of the diaphysis that contains yellow bone marrow in an adult

Nutrient artery

blood vessel that passes through the nutrient foramen to supply the diaphysis of a long bone

Perforating fibers

collagen fibers that anchor the periosteum to the underlying bone

Periosteum

connective tissue covering the outer surface of bone composed of an outer fibrous layer and an inner cellular layer containing osteoprogenitor cells that help the bone grow in diameter and assist in repair

Endosteum

thin connective tissue membrane lining the medullary cavity and internal bone surfaces containing osteoprogenitor cells osteoblasts and osteoclasts that assists in bone growth repair and remodeling

Diploe

the layer of spongy bone sandwiched between two layers of compact bone within a flat bone of the skull

Red bone marrow

hemopoietic tissue located within spongy bone that produces blood cells; in the adult it is found in the proximal epiphyses of the humerus and femur the diploe of flat bones such as the skull and in the vertebrae ribs sternum and hip bones

Yellow bone marrow

fatty tissue found in the medullary cavity of adult long bones that was red marrow during childhood

Osseous connective tissue

bone connective tissue; the primary component of bone composed of cells and extracellular matrix

Osteoprogenitor cells

one of the four types of cells found in bone connective tissue that give rise to osteoblasts

Osteoblasts

bone cells that form the bone matrix

Osteocytes

mature bone cells that maintain the bone matrix and are found in lacunae

Osteoclasts

large bone cells that resorb bone matrix

Central canal

cylindrical channel at the center of an osteon and parallel to it through which blood vessels and nerves extend

Concentric lamellae

rings of bone connective tissue that surround the central canal of an osteon with collagen fibers oriented 90 degrees from the previous and next lamellae giving bone strength and resilience

Lacunae (bone)

small spaces found between concentric lamellae that house osteocytes

Canaliculi

tiny interconnecting channels within bone connective tissue that extend from each lacuna travel through the lamellae and connect to other lacunae and the central canal housing osteocyte projections that allow intercellular contact and the exchange of nutrients minerals gases and wastes between blood vessels and osteocytes

Perforating (Volkmann) canals

structures in long bone that resemble central canals and carry blood vessels and nerves perpendicular to central canals connecting central canals within different osteons

Circumferential lamellae

rings of bone that run the entire circumference of the bone with external circumferential lamellae running immediately internal to the periosteum and internal circumferential lamellae running internal to the endosteum

Interstitial lamellae

components of compact bone between osteons or partially resorbed osteons that look like they have a bite taken out of them and are incomplete with no central canal

Trabeculae

open lattice of narrow rods and plates of bone found in spongy bone with bone marrow filling the spaces forming a meshwork of crisscrossing bars that provides resistance to stresses; composed of parallel lamellae of bone matrix with osteocytes between lamellae and canaliculi radiating from lacunae

Structure of hyaline cartilage

cells scattered through a matrix of protein fibers embedded in a gel-like ground substance that includes proteoglycans but not calcium making the tissue resilient and flexible with a high percentage of water highly compressible and a good shock absorber while being avascular and containing no nerves

Chondroblasts

cells that produce cartilage matrix

Chondrocytes

chondroblasts encased within the cartilage matrix that occupy small spaces called lacunae and maintain the matrix

Perichondrium

dense irregular connective tissue that covers cartilage and helps maintain its shape

Comparison of bone and hyaline cartilage

bone connective tissue has osteoblasts as the cells that form matrix osteocytes as mature cells mature cells in lacunae calcium present in the matrix and an extensive blood supply while hyaline cartilage connective tissue has chondroblasts as the cells that form matrix chondrocytes as mature cells mature cells in lacunae no calcium present in the matrix and is avascular

Ossification (osteogenesis)

the formation and development of bone connective tissue that begins in the embryo and continues through childhood and adolescence; by the 8th through 12th weeks of embryonic development the skeleton begins forming from intramembranous ossification or endochondral ossification

Intramembranous ossification

process in which ossification centers form within thickened regions of mesenchyme the osteoid undergoes calcification woven bone and surrounding periosteum form and lamellar bone replaces woven bone as compact and spongy bone form; forms the flat bones of the skull

Endochondral ossification

process in which a fetal hyaline cartilage model develops the cartilage calcifies and a periosteal bone collar forms around the diaphysis a primary ossification center forms in the diaphysis bone replaces cartilage except the articular cartilage and epiphyseal plates and secondary ossification centers form in the epiphyses after which the epiphyseal plates eventually ossify and form epiphyseal lines

Interstitial growth

bone growth in length

Appositional growth

bone growth in diameter or thickness

Interstitial growth process

bone growth in length occurs specifically within zone 2 (proliferating cartilage) and zone 3 (hypertrophic cartilage) of the epiphyseal plate pushing the zone of resting cartilage toward the epiphysis as flexible hyaline cartilage permits growth and new hyaline cartilage is replaced by bone similar to endochondral ossification during bone development

Epiphyseal plate

cartilage plate that maintains its thickness during childhood; at maturity the rate of cartilage production slows osteoblastic activity increases and the plate narrows until it disappears stopping interstitial growth and leaving a remnant called the epiphyseal line

Zones of the epiphyseal plate

zone 1 is the zone of resting cartilage zone 2 is the zone of proliferating cartilage zone 3 is the zone of hypertrophic cartilage zone 4 is the zone of calcified cartilage and zone 5 is the zone of ossification

Appositional growth process

occurs within the periosteum as bone matrix is deposited within layers parallel to the surface called external circumferential lamellae which increase in number and cause the structure to increase in diameter while osteoclasts resorb bone matrix along the medullary cavity transforming infant bone into a larger adult version

Bone remodeling

continues throughout adulthood occurring at periosteal and endosteal surfaces of a bone at different rates for example the distal part of the femur is replaced every 4 to 6 months while the diaphysis of the femur is not completely replaced over a lifetime with about 20 percent of the skeleton replaced yearly dependent upon the coordinated activities of osteoblasts osteocytes and osteoclasts and influenced by hormones and mechanical stress

Mechanical stress and bone

mechanical stress from weight-bearing movement and exercise is required for normal bone remodeling and is detected by osteocytes and communicated to osteoblasts increasing synthesis of osteoid and causing an increase in bone strength resulting from skeletal contraction and gravitational forces

Effects of increased and decreased bone mass

increased bone mass results from weight-bearing activities such as weight lifting walking or running and can increase total bone mass while decreased bone mass results from removal of mechanical stress causing reduced collagen formation and demineralization such as decreased strength of unstressed bone in an immobilized fracture

Hormones and bone

molecules released from one cell into the blood that travel throughout the body to affect other cells by binding to cellular receptors of specific cells and initiating specific cellular changes; some hormones alter rates of chondrocyte osteoblast and osteoclast activity affecting bone composition and growth patterns

Growth hormone (somatotropin)

hormone produced by the anterior pituitary gland that stimulates the liver to produce the hormone somatomedin both of which directly stimulate growth of cartilage in the epiphyseal plate

Thyroid hormone

hormone secreted by the thyroid gland that influences the basal metabolic rate of bone cells and regulates normal activity at epiphyseal plates

Sex hormones and bone growth

estrogen and testosterone are secreted in large amounts at puberty and dramatically accelerate bone growth increasing the rate of cartilage growth and bone formation in the epiphyseal plate with bone formation rate greater than cartilage growth until cartilage is eventually replaced with bone and growth stops

Glucocorticoids

a group of steroid hormones released from the adrenal cortex that regulate blood glucose level; high amounts increase bone loss and impair growth at the epiphyseal plate in children requiring monitoring if a child receives high doses such as for asthma

Serotonin (bone remodeling)

a neurotransmitter and hormone for which most bones have receptors that plays a role in the rate and regulation of normal bone remodeling; if levels are too high osteoprogenitor cells are prevented from differentiating into osteoblasts which could be linked to low bone density disorders

Calcium requirements

calcium is required for initiation of muscle contraction exocytosis of molecules from cells including neurons stimulation of the heart by pacemaker cells and blood clotting; two primary hormones regulate blood calcium calcitriol and parathyroid hormone

Calcitriol

the active form of vitamin D produced when the precursor molecule 7-dehydrocholesterol is converted to vitamin D3 (cholecalciferol) in the skin upon UV exposure or obtained from dietary intake then converted to calcidiol in the liver and finally to calcitriol in the kidney; calcitriol stimulates absorption of calcium ions from the small intestine into the blood

Parathyroid hormone (PTH)

hormone secreted and released by the parathyroid glands in response to reduced blood calcium levels that accelerates conversion to calcitriol by the kidney; PTH and calcitriol interact with major organs and act synergistically on bone connective tissue to increase release of calcium from bone into the blood by increasing osteoclast activity

Regulation of blood calcium by PTH and calcitriol

low blood calcium levels are detected by the parathyroid glands which release parathyroid hormone; PTH and calcitriol act synergistically to increase osteoclast activity in bone and decrease calcium excretion in urine at the kidneys while calcitriol increases calcium absorption from the small intestine restoring blood calcium levels to the normal homeostatic range

Calcitonin

hormone that aids in regulating blood calcium levels with a less significant role than PTH or calcitriol; released from the thyroid gland in response to high blood calcium levels and also secreted in response to exercise it inhibits osteoclast activity and stimulates the kidneys to increase loss of calcium in the urine reducing blood calcium levels; it has its greatest effect during periods of greatest bone turnover such as in growing children and its entire function remains unclear

Effects of aging on bone (decreased tensile strength)

aging reduces the rate of protein synthesis by osteoblasts so the relative amount of inorganic material increases making bones become brittle and susceptible to fracture; bone loss of calcium and other minerals makes bones thinner and weaker a condition of insufficient ossification called osteopenia

Osteopenia

condition of insufficient ossification that occurs slightly in all people with age beginning around age 35 to 40 as osteoblast activity declines while osteoclast activity remains at previous levels; the vertebrae jaw bones and epiphyses lose a large amount of mass and women lose more skeletal mass every decade than men

Osteoporosis

reduced bone mass sufficient to compromise normal function occurring in a significant percentage of older women and a smaller percentage of older men contributed to by reduced hormones with age including vitamin D growth hormone estrogen and testosterone

Fracture healing

simple fractures take 2 to 3 months to heal while compound fractures take longer to heal; healing slows with age and some fractures require surgical intervention to heal correctly

Stages of fracture repair

(1) a fracture hematoma forms at the break (2) a fibrocartilaginous (soft) callus forms as blood vessels regenerate (3) a hard (bony) callus forms as primary bone replaces the soft callus (4) the bone is remodeled resulting in compact bone at the fracture site