A&P Bone Tissue

bone remodeling

the building of new bone tissue and breaking down of old bone tissue

effects of microgravity

loss of 1-2% of bone mass per month especially in the pelvis, backbone, and lower limbs

bone

consists of osseous tissue, cartilage, dense connective tissue, epithelium, adipose tissue, blood, and nervous tissue

osteology

the study of bone structure and the treatment of bone disorders

skeletal system

consists of the framework of bones and their cartilages

tendons

connects muscle to bone

bone tissue weight

18% of the human body

mineral storage in bone

calcium and phosphorus

red bone marrow

A highly vascularized connective tissue located in microscopic spaces between trabeculae of spongy bone tissue

hemopoiesis / hematopoiesis

Blood cell production, which occurs in red bone marrow after birth

what does red bone marrow produce

red blood cells, white blood cells, and platelets

what is red bone marrow composed of

developing blood cells, adipocytes, fibroblasts, and macrophages within a network of reticular fibers

yellow bone marrow

consists of adipose cells, which store triglycerides

long bone

a bone with a greater length than width

diaphysis

the long cylindrical portion of the bone. “body” or “shaft”

epiphyses

the ends of a long bone

metaphyses

regions between the diaphysis and epiphyses. contains a growth plate, hyaline cartilage or the epiphyseal line

epiphyseal line

a line of bone that forms once bone ceases to grow in length, replaces cartilage

articular cartilage

thin layer of hyaline cartilage covering the part of the epiphysis where the bone forms an articulation (joint) with another bone. reduces friction and absorbs shock. limited repair

periosteum

The membrane that covers bone and consists of connective tissue, osteoprogenitor cells, and osteoblasts; is essential for bone growth, repair, and nutrition. RICH IN SENSORY NERVES.

perforating fibers

Thick bundles of collagen that extend from the periosteum into the bone extracellular matrix to attach the periosteum to the underlying bone

medullary cavity / marrow cavity

The space within the body of a bone that contains yellow bone marrow. Also called the marrow cavity.

endosteum

thin membrane that lines the medullary cavity and internal spaces of spongy bone.

functions of bone tissue

support, protection, assists in movement, stores minerals and fats, produces blood cells

extracellular matrix composition

15% water, 30% collagen fibers, 55% crystallized mineral salts

calcification

crystallization of tissue because of the deposition of mineral salts (hydroxyapatite). initiated by osteoblasts

what provides bone its tensile strength

collagen fibers

osteoprogenitor cells

Stem cell derived from mesenchyme that has mitotic potential and the ability to differentiate into an osteoblast. found along the inner osteogenic layer of the periosteum, in the endosteum, and in the canals within bone that contain blood vessels

osteoblasts

bone-building cells. secretes collagen and organic components for bone deposition, initates calcification.

osteocytes

mature bone cells that maintain daily metabolism.

osteoclasts

A large, multinuclear cell that resorbs (destroys) bone matrix. releases lysosomal enzymes that digest minerals and proteins in the extracellular bone matrix.

compact bone tissue

contains few spaces; strongest type of bone tissue. found beneath the periosteum and makes up bulk of diaphysis

osteon

The basic unit of structure in adult compact bone, consisting of a central canal with its concentrically arranged bone lamellae, bone lacunae, osteocytes, and bone canaliculi. Also called a haversian system.

osteonic canal

A circular channel running longitudinally in the center of an osteon (haversian system) of mature compact bone, containing blood and lymphatic vessels and nerves. also called a haversian canal

concentric bone lamellae

circular plates of mineralized extracellular matrix of increasing diameter, surrounding a small network of blood vessels and nerves located in the osteonic canal. similar to rings of a tree

bone lacunae

spaces between concentric bone lamellae that contain osteocytes

bone canaliculi

Small channel or canal, as in bones, where it connects lacunae.

interstitial bone lamellae

fragments of older osteons that have been partially destroyed during bone rebuilding or growth.

perforating / volkmann’s canals

transverse small passageways that blood vessels and nerves from the periosteum penetrate into compact bone

spongy bone tissue

Bone tissue that consists of an irregular latticework of thin plates of bone called bone trabeculae; spaces between bone trabeculae of some bones are filled with red bone marrow; found inside short, flat, and irregular bones and in the epiphyses (ends) of long bones. Also called cancellous or trabecular bone tissue.

“hot spots” in bone scans

increased metabolism. can be a sign of bone cancer, abnormal healing of fractures, abnormal bone growth

“cold spots” in bone scans

decreased metabolism. can be a sign of degenerative bone disease, decalcified bone, fractures, bone infections, pagets disease, rheumatoid arthritis

periosteal arteries

small arteries accompanied by nerves that enter the diaphysis through perforating canals into osteonic canals

nutrient artery

large artery near the center of the diaphysis. passes through the nutrient canal. once into the medullary cavity, it splits into proximal and distal branches towards the ends of the bones

nutrient foramen

a hole in the diaphysis for the nutrient artery to enter

nutrient canal

small canal in the compact bone of the diaphysis

metaphyseal arteries

enters through the metaphyses of a long bone and supplies the red and yellow blood marrow and spongy bone tissue along with the nutrient artery

epiphyseal arteries

enters the epiphyses of a long boneand supplies the red and yellow bone marrow and spongy bone there

ossification or osteogenesis

process of bone formation

intramembranous ossification

bone forms directly within mesenchyme (in fetus) simpler. flat bones of skull, facial bones, mandible, medial part of clavicle

endochondral ossification

bone forms within hyaline cartilage that develops from mesenchyme (in fetus)

steps of intramembranous ossification

development of the ossification center, calcification, formation of bone trabeculae, development of the periosteum

steps of endochondral ossification

development of the cartilage model, growth of cartilage model, development of primary ossification center, medullary cavity development, development of secondary ossification center, formation of articular cartilage and growth plate

cartilage model

hyaline cartilage formed by mesenchyme in fetus development. covered by the perichondrium

perichondrium

membrane that covers cartilage. turns into periosteum if the cartilage turns to bone

interstitial growth

growth from within that causes increase of length

appositional growth

growth from outside, growth in thickness

hypertrophy

increase in size

primary ossification center growth

growth inwards

secondary ossification center growth

growth outwards

zone of resting cartilage

site of small scattered chondrocytes. do not function in bone growth in length

zone of proliferating cartilage

site of medium chondrocytes stacked like coins.

zone of hypertrophic cartilage

site of large, maturing chondrocytes in columns

zone of calcified cartilage

site of mostly dead chondrocytes, only a few cells thick. calcification happens here

factors affecting bone growth and remodeling

minerals, vitamins, hormones

fracture

any break in a bone

stress fracture

a series of microscopic fissures in bone that forms without any evidence of injury to other tissues

reactive phase

blood vessel clotting (fracture hematoma) around site of fracture, swelling and inflammation occur. several weeks

reparative phase 2a

fibrious cartilage callus formation. fibroblasts produce collagen fibers. about 3 weeks

reparative phase 2b

bony callus formation. fibrious cartilage converted to spongy bone. 3-4 months

bone remodeling phase

compact bone replaces spongy bone around fracture site

open (compound) fracture

The broken ends of the bone protrude through the skin. Conversely, a closed (simple) fracture does not break the skin.

comminuted (crumbled) fracture

The bone is splintered, crushed, or broken into pieces at the site of impact, and smaller bone fragments lie between the two main fragments.

greenstick fracture

A partial fracture in which one side of the bone is broken and the other side bends, similar to the way a green twig breaks on one side while the other side stays whole, but bends; occurs only in children, whose bones are not fully ossified and contain more organic material than inorganic material.

impacted fracture

One end of the fractured bone is forcefully driven into the interior of the other.

pott fracture

Fracture of the distal end of the fibula (lateral leg bone), with serious injury of the distal tibial articulation.

colles fracture

Fracture of the distal end of the lateral forearm bone (radius) in which the distal fragment is displaced posteriorly.

vertebral compression fracture

The vertebral body of one or more vertebrae fractures and becomes compressed into a wedge-shape. May be caused by injury, trauma, or more commonly in individuals with osteoporosis.

high-impact intermittent strains

more strongly influence bone deposition than lower-impact constant strains

demineralization

the loss of calcium and other minerals from bone extracellular matrix

demineralization in females

begins after age 30, accelerates after 45; 30% of calcium is lost by age 70. 8% bone mass lost every 10 years

demineralization in males

begins after age 60, 3% bone mass lost every 10 years.

calcium and phosphorus

makes bone extracellular matrix hard

magnesium

helps form bone extracellular matrix

fluoride

helps strengthen bone extracellular matrix

manganese

activates enzyme involved in synthesis of bone extracellular matrix

Vitamin A

Needed for the activity of osteoblasts during remodeling of bone; deficiency stunts bone growth; toxic in high doses

Vitamin C

Needed for synthesis of collagen, the main bone protein; deficiency leads to decreased collagen production, which slows down bone growth and delays repair of broken bones.

Vitamin D

Active form (calcitriol) is produced by the kidneys; helps build bone by increasing absorption of calcium from digestive canal into blood; deficiency causes faulty calcification and slows down bone growth; may reduce the risk of osteoporosis but is toxic if taken in high doses. People who have minimal exposure to ultraviolet rays or do not take vitamin D supplements may not have sufficient vitamin D to absorb calcium. This interferes with calcium metabolism.

Vitamins K and B12

Needed for synthesis of bone proteins; deficiency leads to abnormal protein production in bone extracellular matrix and decreased bone density.

Growth Hormone (GH)

Secreted by the anterior lobe of the pituitary gland; promotes general growth of all body tissues, including bone, mainly by stimulating production of insulin-like growth factors.

Insulin-like growth factors (IGFs)

Secreted by the liver, bones, and other tissues on stimulation by growth hormone; promotes normal bone growth by stimulating osteoblasts and by increasing the synthesis of proteins needed to build new bone.

Thyroid Hormones (T3 and T4)

Secreted by thyroid gland; promote normal bone growth by stimulating osteoblasts.

Insulin

Secreted by the pancreas; promotes normal bone growth by increasing the synthesis of bone proteins.

Sex Hormones (estrogen and testosterone)

Secreted by the ovaries in women and by the testes in men; stimulate osteoblasts and promote the sudden “growth spurt” that occurs during the teenage years; shut down growth at the epiphyseal plates around age 18–21, causing lengthwise growth of bone to end; contribute to bone remodeling during adulthood by slowing bone resorption by osteoclasts and promoting bone deposition by osteoblasts.

Parathyroid Hormone (PTH)

Secreted by the parathyroid glands; promotes bone resorption by osteoclasts; enhances recovery of calcium ions from urine; promotes formation of the active form of vitamin D (calcitriol).

Calcitonin (CT)

Secreted by the thyroid gland; inhibits bone resorption by osteoclasts.

Exercise

Weight-bearing activities stimulate osteoblasts and, consequently, help build thicker, stronger bones and retard loss of bone mass that occurs as people age.

Aging

As the level of sex hormones diminishes during middle age to older adulthood, especially in women after menopause, bone resorption by osteoclasts outpaces bone deposition by osteoblasts, which leads to a decrease in bone mass and an increased risk of osteoporosis.

osteoporosis

Age‐related disorder characterized by decreased bone mass and increased susceptibility to fractures, often as a result of decreased levels of estrogens.