Skeletal System Overview

Chapter 7p. 192 – p. 204

What makes up bone?

• Osteocytes (bone forming cells) and extracellular matrix

• Osteocytes are found in lacunae (holes in the bony matrix)

• Extracellular matrix is made up of collagen and inorganic salts

Types of Bones

• Long bones• Short bones• Flat bones• Irregular bones• Sesamoid bones

Long Bones• Epiphysis• Articular Cartilage• Diaphysis

• Spongy bone• Compact bone

Parts of the Long Bone• Periosteum– Vascular, fibrous outer

covering of bone• Endosteum– Lines medullary cavity– Contains bone forming cells

• Medullary Cavity– Hollow region of bone– Continuous with the spongy

bone– Marrow, blood vessels found

here

Spongy Bone

• Trabeculae: branching bony plates– Space between the

bony plates allows for cushion

Compact Bone• Made up of osteons– Circular units with central

blood vessels and nerves– Also called Haversian systems– Resists compression

• Volkmann’s canals– Also known as perforating

canals– Contain larger blood vessels

and nerves– Communicate with surface of

the bone

Osteon

Volkmann’s Canals

Short Bones

• Make up hands and feet

Flat Bones

• Scapula (shoulder blade)• Skull• Ribs

Irregular Bones

• Vertebrae• Facial bones

Sesamoid Bones

• Not always a separate category

• Round bones• Patella

Bone Marrow

Bones under the microscope

Osteoporosis

Bone Development

• Osteogenesis: development of bone• Intramembranous Bone (flat bones)– Unspecialized cells appear at site of new bone

formation– Blood vessels move into these cells and allow cells

to differentiate into osteoblasts• Deposit bony matrix to form spongy bone• Spongy bone would fill in with higher amounts of bony

matrix to form compact bone

Bone Development

• Endochondral Bones– Develop from masses of hyaline cartilage

• Hyaline cartilage lays down basic bone layout• Over time, bone forms over the cartilage

template– Osteoblasts form and secrete bony matrix– Once bony matrix surrounds the osteoblasts, they

are called osteocytes• Endochondral ossification

Bone Development

• Primary ossification center– Bone begins to replace hyaline cartilage in the

diaphysis• Osteoblasts in periosteum deposit compact bone• Secondary ossification centers– Epiphyses– Spongy bone

• Epiphyseal plate – zone of cartilage between diaphysis and epiphysis

Bone Development

Growth at the Epiphyseal Plate• 4 layers– Resting cartilage

• No growth • Closest to the epiphysis

– Proliferating cartilage• Young cells, mitosis

– Zone of hypertrophic cartilage• Older cells

– Zone of calcified cartilage• Dead cells and extracellular

matrix

Growth at the Epiphyseal Plate

• http://www.gla.ac.uk/ibls/US/fab/tutorial/generic/bone5.html

Osteoclasts

• Invade areas of calcified cartilage• Break down extracellular matrix• Osteoblasts then move in – Deposit bony matrix in place of calcified cartilage

Ossification Timetable (p. 200)Age Occurrence

3rd month of prenatal development Ossification of long bones begins

4th month of prenatal development Primary ossification centers are present in long bones

Birth to 5 years Secondary ossification centers present

F: 5-12 years; M: 5-14 years Ossification rapid through ossification centers

F: 15-18 years; M: 17-20 years Bones of upper limb/scapulae completely ossified

F: 16-20 years; M: 18-23 years Lower limbs and hips completely ossified

F: 21-23 years; M: 23-25 years Sternum, clavicles, vertebrae completely ossified

F: by 23; M: by 25 Nearly all bones are completely ossified

Factors Effecting Bone Growth and Repair

• Nutrition• Exposure to sunlight• Hormones• Physical exercise

• Work with a partner to research a factor effecting bone growth and it’s effect on development

• Look up a bone growth disorder, too. (Brief!)

Fractures

• Greenstick – incomplete, across bone (usually in developing bone)

• Fissured – incomplete, longitudinal• Comminuted – complete, shatters the bone• Transverse – complete, right angle to bone axis• Oblique – at an angle other than a right angle• Spiral – caused by excessive twisting of the bone• Compound – bone breaks the skin

Fractures

Bone Repair

• Hematoma forms (blood released from vessels within the bone)

• Formation of spongy bone and fibrocartilage• Bony callus• Osteocytes, osteoblasts and osteoclasts

Functions of the Skeletal System

• Support and Protection• Movement– Origin and insertion of muscle– Origin: immovable end of the muscle– Insertion: movable end – during contraction,

insertion will move toward the origin

Functions of the Skeletal System

• Blood production– Hematopoiesis– Bone marrow – long

bones, spongy bone, larger canals of compact bone

• Red marrow: produces red blood cells, white blood cells and platelets

• White marrow: fatty tissue

Functions of the Skeletal System

• Inorganic salt storage– Salts account for approximately 70% of

extracellular matrix of bone– Mostly calcium phosphate – hydroxyapatite– Also: magnesium, sodium, potassium, carbonate

ions– Will also absorb small amounts of harmful metallic

elements (lead, strontium)