Ch 6- Bone Tissue

components of skeletal system

bones, cartilage, ligaments, and tendons

functions of the skeletal system

support, protection, assist in movement, mineral homeostasis, blood cell production, and triglyceride storage

diaphysis

bone shaft or body of bone

epiphyses

distal and proximal ends of bone

metaphysis

located between epiphysis and diaphysis

epiphyseal plate

a layer of hyaline cartilage found in the epiphysis of growing long bones that is responsible for their longitudinal growth

epiphyseal line

bony structure that replaces the epiphyseal plate when bone stops growing

medullary cavity

space within diaphysis that makes long bones lighter; contains yellow bone marrow

red bone marrow

located in spaces within epiphyses; site of homeopoiesis

homeopoiesis

the production of blood cells (RBCs, WBCs, platelets)

yellow bone marrow

located in medullary cavity of long bone; stores triglycerides

periosteum

connective tissue covering the outside of the bone

endosteum

connective tissue covering the inside of the bone

what arteries supply bone

periosteal, nutrient, metaphyseal, and epiphyseal arteries

periosteal arteries

supply periosteum and bone tissue of diaphysis

nutrient artery

travels through nutrient foramen to medullary cavity; supplies bone tissue of diaphysis and part of red marrow of epiphyses

metaphyseal artery

enter metaphyses and supplies bone tissue and red marrow of matephyses

epiphyseal arteries

enter epiphyses and supplies bone tissue and red marrow of epiphyses

extracellular matrix of bone tissue

bone ECM consists of mineral salts (mainly hydroxyapatite) and collagen fibers

calcification

the process by which the extracellular matrix becomes hardened by mineral salts; only occurs when collagen fibers are present

what gives a bone its hardness

mineral salts

what gives a bone its flexibilty

collagen fibers that provide tensile strength (resistance to stretching and pulled apart)

types of bone cells

osteogenic cells, osteoblasts, osteocytes, and osteoclasts

osteogenic cells

the only bone cells that divide; they are stem cells and form osteoblasts

osteoclasts

large cells that breakdown bone; they secrete lysosomal enzymes and acids that breakdown the extracellular matrix

osteocytes

main cells in bone tissue; maintain bone tissue by exchanging nutrients and wastes with blood

osteoblasts

cells that build bone; secrete collagen and other substance to form extracellular matrix

compact bone tissue

dense; forms the exterior of all bone and most of the diaphysis of long bone- protects, supports, and resists stress

microscopic structure of compact bone

osteons with concentric lamellae around a central canal, connected by perforating canals, containing osteocytes housed in lacunae linked by canaliculi, plus interstitial and circumferential lamellae

lacunae

small spaces between lamellae that contain osteocytes

canaliculi

connect lacunae with each other and with central canal; provides routes of oxygen, nutrients, and wastes

osteons

repeating structural units of compact bone; aligned along lines of stress and determine strength of bone

what does an osteon consist of

a central canal, its concentrically arranged lamellae, lacunae, osteocytes, and canliculi

interstitial lamellae

area between osteons that contains lacunae, osteocytes, and canaliculi

circumferential lamellae

encircle bone beneath periosteum or encircle medullary cavity

spongy bone tissue

contains trabeculae, is lighter, and house red marrow

microscopic structure of spongy bone

trabeculae composed of lamellae with osteocytes in lacunae and spaces filled with red marrow

microscopic difference between compact and spongy bone

compact bone is dense and organized into osteons with central canals for strength, while spongy bone has porous trabeculae without osteons, allowing lightness and red marrow storage

osteogenesis/ossification

bone formation that occurs during: embryonic and fetal development, infancy, childhood, adolescence, remodeling of bone, and repair of fractures

intramembranous ossification

bone develops from mesenchymal membrane and forms flat bones of skull and mandible

endochondrial ossification

bone replaces hyaline cartilage; used to form most bones of body

intramembranous vs. endochondrial ossification

intramembranous ossification forms bone directly from mesenchyme, while endochondrial ossification replaces a cartilage model with bone

appositional growth

growth in thickness that occurs by growth at outer surface of bone

interstitial growth

growth in length by division of cartilage on epiphyseal side of epiphyseal plate

interstitial growth vs appositional growth

interstitial growth lengthens bone at the epiphyseal plate (closing after adolescence), while appositional growth increases bone thickness

osteoclast resorption

osteoclasts secrete enzymes and acids that dissolve bone matrix and release minerals

factors affecting bone growth/ remodeling

minerals, vitamins, hormones

fracture

a break in a bone

types of fractures

open (compound) fracture, closed (simple) fracture, comminuted fracture, greenstick fracture, impacted fracture, and stress fracture

open fracture

broken ends of bone protrude through the skin

closed fracture

broken ends of bone do not break through skin

comminuted fracture

bone is broken into pieces

greenstick fracture

partial fracture that occurs in children; one side of bone is broken, other

side is bent

impacted fracture

one broken end of bone driven into the other broken end of bone

stress fracture

microscopic fissures in bone but no visible break due to repeated, strenuous activities such as running, jumping , or aerobic activities

repair of fracture

1. hematoma formation

2. fibrocartilaginous callus formation

3. bony callus formation

4. bone remodeling

hematoma formation

blood leaks from damaged vessels, forming a clot that brings cells for inflammation and healing to the fracture site

fibrocartilaginous callus formation

a soft callus of collagen and cartilage bridges the broken bone ends to stabilize the fracture

bony callus formation

the fibrocartilaginous callus is replaced by spongy bone, forming a hard bony bridge between the broken bone ends

bone remodeling

osteoclasts remove old or excess bone and osteoblasts deposit new bone, restoring the bone’s original shape and strength

function of blood calcium

neuron function, muscle contraction, enzyme regulation, blood clotting

calcium homeostasis

bones act as the calcium reservoir, releasing or storing Ca²⁺ as needed

PTH

produced by parathyroid gland and is secreted when blood calcium levels are low; stimulates osteoclasts and bone resorption

calcitonin

produced by thyroid gland and is secreted when blood calcium levels are high; stimulates osteoblasts and inhibits osteoclasts

exercise effects on bones

increases bone density

aging effects on bones

causes bone loss due to decreased osteoblast activity and hormone levels

osteoporosis

caused by a decrease in blood calcium levels- more calcium is lost from the body than absorbed from the diet

osteomalacia

adult form of inadequate calcification of the extracellular matrix, usually caused by a deficiency of vitamin D; results in pain and tenderness and increased risk of bone fracture

rickets

childhood form of inadequate calcification of the extracellular matrix, usually caused by a deficiency of vitamin D; results in pain and tenderness and increased risk of bone structure

gigantism

the oversecretion of growth hormone prior to puberty

dwarfism

the undersecretion of growth hormone prior to puberty

acromegaly

oversecretion of growth hormone during adulthood; the bones of the hands, feet, and jaws enlarge as well as the nose