Bones Lecture

Axial skeleton

80 bones

appendicular skeleton

126

functions of skeletal system

• support

• store minerals and lipids

• produce blood cells

• protection

• leverage

epiphysis

each end of bone

diaphysis contains

medullary cavity

red bone marrow

involved in rbc production

yellow bone marrow

adipose tissue; important as energy reserve

vascular features of bone

• nutrient artery

• nutrient vein

• metaphyseal artery and vein

osteogenic cells

mesenchymal (stem) cells that produce cells that differentiate into osteoblasts

osteoblasts

produce new bony matrix in osteogenesis or ossification

osteoblast produce

osteoid, unmineralized matrix

osteocytes

mature bone cells that cant divide

osteocytes occupy

lacunae

osteoclasts

remove an remodel bone matrix

osteolysis done by osteoclasts

release acids and proteolytic enzymes to dissolve matrix and release stored minerals

Bone matrix

• collagen fibers (1/3 of bone weight)

• Calcium phosphate (2/3 of bone weight)

Appositional growth in bones

increases bone diameter of existing bones

periosteum layers

fibrous outer layer and cellular inner layer

periosteum

wraps the superficial layer of compact bone

periosteum functions

• isolates bone from surrounding tissues

• route for blood and nervous supply

• actively participates in bone growth and repair

perforating fibers

allow for strong attachment

endosteum

• incomplete cellular layer lining medullary cavity

• active during bone growth and repair

endochondral ossification

cartilage gradually replaced by bone

steps in endochondral ossification

• cartilage model enlarges

• blood vessels grow around edge of the cartilage model

• blood vessels penetrate cartilage and enter central region

• growth continues with remodeling

• capillaries and osteoblasts migrate into the epiphyses

• epiphyses fill with spongy bone

• bone grows in length at the epiphyseal cartilage

epiphyseal cartilage

separates epiphysis and diaphysis

Bone growth

At puberty, hormones stimulate increased bone growth, and epiphyseal cartilage is replaced

epiphyseal closure

epiphyseal cartilage narrows until it disappears

epiphyseal line

leaves in adults

steps of intramembranous ossification

• mesenchymal cells cluster and differentiate into osteoblasts

• bone grows out in small struts (spicules)

• blood vessels enter area

• continued deposition of bone by osteoblasts close to blood vessel

• remodeling around blood vessels produce osteons of compact bone

Pituitary growth failure

• inadequate growth hormone production

• abnormally short bones, reduced epiphyseal cartilage

Achondroplasia

short, stocky lims result and trunk is normal size

Marfan syndrome

inherited metabolic condition

excessive cartilage formation

very tall and slender limbs

congenital talipes equinovarus (clubfoot)

may affect one or both feet, feet turn medially and are inverted

Gigantism

disorder causing lengthened bones, overproduction of growth hormone before puberty

Fibrodysplasia ossificans progressiva

gene mutation that causes bone deposition around skeletal muscles, bones develop in unusual places

Acromegaly

bones get thicker not longer (especially in face), overproduction of growth hormone after epiphyseal plates close

Minerals

• inorganic ions contributing to the osmotic balance of body fluids

• vital in many physiological processes

most popular minerals

calcium and phosphate

least prevalent mineral

potassium

calcium controlled by activities in intestines

absorb calcium and phosphate under hormonal control

calcium controlled by activities in bones

• osteoclasts erode matrix and release calcium

• osteoblasts use calcium ti deposit new matrix

calcium controlled by activities in kidneys

varying levels of calcium and phosphate loss in urine under hormonal control

factor that increases blood calcium

PTH

PTH in bones

osteoclasts stimulated to erode matrix, releasing stored calcium

PTH in intestines

calcitriol effects enhanced and calcium absorption increased

PTH in kidneys

increased release of hormone calcitriol, stimulating calcium reabsorption in kidneys

factor that decreases blood calcium levels

calcitonin

calcitonin secreted by

c cells in thyroid gland

calcitonin in bones

osteoclast activity inhibited; calcium deposited in bone matrix

calcitonin in intestines

calcium absorption decreased with decreasing PTH and calcitrol

calcitonin in kidneys

inhibits calcitriol release and calcium reabsorption

release of calcium into blood

weakens bones

deposition of calcium salts

strengthens bones

fracture

crack or break

steps in fracture repair

• fracture hematoma (large clot)

• internal callus (network of spongy bone)

• external callus (composed of cartilage and bone)

• spongy bone formation (dead bone removed and replaced

• compact bone formation, replacing spongy bone

closed or simple fracture

completely internal (no break in skin, seen only on xrays)

open or compound fracture

project through skin, more dangerous to infection

transverse fracture

breaks shaft along long axis

spiral fracture

twisting stresses

displaced fractures

produce new and abnormal bone arrangements

compression fracture

occur in vertebrae subjected to extreme stresses

greenstick fracture

one side of shaft broken or bent (generally in children)

comminuted fractures

shatter affected area, producing fragments

epiphyseal fracture

occur where bone matrix is calcifying

potts fracture

occurs at ankle and affects both medial malleolus and lateral malleolus

colles fractures

break in distal radius