I.
APHY 101, Lecture 7 – Skeletal System
Overview
 Osteology = Science of Bones
 206 Bones in body on average
II.
Purpose
1. Support & Protect Soft Tissues
 Brain encased in skull
 Heart surrounded by ribs & sternum
2. Motion
 Muscles attach to bone
3. Ca2+ storage
 Constant exchange of Calcium between bone & blood
4. Blood Cell Production
 Red Bone Marrow forms blood cells
III.
Components of Bone
1. Matrix: Hydroxyapitite = Ca10(PO4)6(OH)2, provides hardness
2. Fibers: Collagenous Fibers = provides resilience
3. Cells
1. Osteoblasts
 Build bone by depositing matrix
 Become Osteocytes when surrounded by matrix
2. Osteocytes
 Bone cells; transports nutrients & wastes
3. Osteoclasts
 Breaks down bone
 Releases Calcium into blood
Bone Classification
1. Long Bones – elongated shaft
 Humerus –arm
 Femur – thigh
 Metatarsals – foot
 Phalanges – fingers & toes
2. Short Bones – width = length
 Carpals – wrist
Radius & Ulna – forearm
Tibia & Fibula – legs
Metacarpals – palms
Tarsals – ankle
3. Flat Bones – Plate-like bones
 Sternum & Ribs
 Frontal & Parietal Bones of skull
4. Irregular Bones
 Vertebrae
 Mandible & Maxilla – Lower & upper jaws
 Ethmoid & Sphenoid Bone – Skull
5. Sesamoid Bones
 Develop in tendons
 Patella – kneecap
Structure of Long Bone
A. Epiphysis
a. Enlarged ends of bone
b. Filled with spongy bone
 Trabiculae = bony plates of spongy bone
 Spaces filled with bone marrow
c. Covered with articular cartilage; forms joints
B. Diaphysis
a. Shaft of bone
b. Lined with compact bone
c. Medullary Cavity
 Contains Bone Marrow
 Blood Vessels & Nerves
 Thin layer of spongy bone surrounds cavity
C. Membranes of Bone
a. Periosteum
 Tough vascular membrane covering bone
 Continuous with tendons & ligaments
 Contains blood vessels & nerves
 Houses Osteoblasts
b. Endosteum
 Membrane lining of medullary cavity
 Houses Osteoblasts
Osteon
A. Structural & Functional Unit of Compact Bone
B. Central Canal
 Contains blood vessels & nerves
 Nourishes bone cells
C. Lacuna
 Cavity that houses an osteocyte
D. Osteocyte
 Bone cell that supplies nutrients to bone
E. Canaliuli
 Small canals that radiates from osteocytes towards central canal
 Filled with cell processes
 Nutrients & waste diffuse through cell processes
F. Perforating Canal
 Run transverse to diaphysis
 Convey blood vessels from Periosteum & endosteum towards central canals
Bone Formation
Bone replaces connective tissue in 1 of 2 ways
1. Intramembranous Ossification
a. Typical of flat bones within skull
b. Intramembranous bones originate within sheet-like connective tissue, called
mesenchyme
c. Osteoblasts within mesenchyme deposit bone in all directions
d. Periosteum = thin layer of mesenchyme that remains
2. Endochondral Ossification
a. Development of most bones
i. Begins with a hyaline cartilage model
ii. Remove cartilage to lay down bone
iii. Osteoblasts from Periosteum replace dead cartilage with bone
b. Ossification Centers
i. Primary Ossification center – osteoblasts from Periosteum deposit
compact bone in diaphysis first
ii. Secondary Ossification center – Osteoblasts lay down spongy bone in the
epiphyses
c. Cartilage remains in two regions
i. Epiphyseal Plates – site of bone growth, elongation
ii. Articular cartilage – joints
Growth At Epiphyseal Plates
A. Plate Remains same width during bone growth
1. New cartilage near epiphysis is added to plate
2. Cartilage facing diaphysis is removed
B. 4 Zones of Cartilage
1. Zone of Resting Cartilage = no growth
2. Zone of Proliferating Cartilage = New cartilage is formed by mitosis
3. Zone of Hypertrophic Cartilage = Cartilage enlarges & thickens
4. Zone of Calcified Cartilage = Dead cells & calcified matrix
New Bone