Chapter 11
Skeletal System
Points to Ponder
•
•
•
•
•
•
What are the 5 functions of the skeletal system?
What are the parts of a long bone?
How do bones grow, remodel and repair?
How are hormones involved in bone growth?
What is osteoporosis?
How are age, gender and ethnicity determined
through skeletal remains?
• What are the components of the axial and
appendicular skeletons?
• What are synovial joints and what kind of
angular movements to they allow?
Functions of the Skeletal System
1.
2.
3.
4.
Supports the body.
Protects the soft body parts.
Produces blood cells.
Stores minerals (calcium and phosphate) and
fat.
5. Allows for movement by attaching muscles.
Anatomy of a Long Bone
• Diaphysis: Shaft of the
bone; made of compact
bone.
– Large shaft (medullary
cavity) filled with yellow
marrow.
• Epiphysis: Ends of the bone
made mostly of spongy
bone.
– Coated with thin layer of
articular cartilage.
• Articular cartilage: Hyaline
cartilage found on the ends
of long bones.
Anatomy of a Long Bone
• Yellow bone marrow:
Stores fat.
• Red bone marrow: Makes
blood cells; found in spongy
bone and flat bones.
• Periosteum: Living, outer
covering of the entire long
bone composed of fibrous
connective tissue.
– Blood vessels, lymphatic
vessels, nerves.
• Ligaments: Fibrous
connective tissue that
connects bones.
Compact Bone
• Composed of osteons
with a central canal
containing blood vessels.
– Lie in the lacunae
(arranged in concentric
circles around the
central canal).
• Contains living bone cells
(osteocytes) that lie in
the lacunae.
Compact Bone
• Canaliculi (tiny canals)
run through the bone
matrix.
– Connect lacunae with
each other and the
central canal.
• Osteocytes nearest
center of the osteon
exchange nutrients and
wastes with the blood
vessels at the central.
Spongy Bone
• Made of plates
(trabeculae) separated
by uneven spaces; filled
with red bone marrow.
• Lighter than compact
bone, but still made for
strength.
– Trabeculae follow lines
of stress.
Cartilage
• Cartilage: Flexible, gel-like connective tissue
(collagenous and elastic fibers) made of cells
called chondrocytes.
• No nerves or blood vessels; slow to heal.
• 3 main types:
– Hyaline cartilage: Ends of long bones, nose,
ends of ribs, larynx and trachea.
– Fibrocartilage: Disks between vertebrae and
in the knee; stronger than hyaline cartilage.
– Elastic cartilage: Ear flaps and epiglottis;
more flexible than hyaline cartilage.
Bone Growth, Remodeling and
Repair
• Skeleton forms at 6 weeks in fetus development.
• Most bones grow in width and length during
adolescence; some continue until 25.
• Remodeling: Bone changes of size, shape and
strength due to stress on the bone.
Important Cells in Bone Growth,
Remodeling and Repair
• Osteoblasts: Bone-forming cells; promote
deposition of calcium and salts into bone matrix.
• Osteocytes: Mature bone cells that maintain
bone structure; Derived from osteoblasts.
• Osteoclasts: Bone-absorbing cells; break down
calcium and phosphate to return it to the blood.
• Chondroytes: Cartilage-forming cells.
Bone Development and Growth
• Ossification: Formation of bone.
• Occurs in two distinct ways:
1. Intramembranous Ossification: Bone
development between sheets of fibrous
connective tissue; flat bones.
– These bones retain red bone marrow.
– Ex. Skull bones
2. Endochondrial Ossification: Cartilage is
replaced by bone; most bones formed this
way.
Intramembranous Ossification
Endochondral Ossification
• 1st Cartilage model: Chondrocytes lay down
hyaline cartilage in the shape of the future
bones; occurs in embryo.
• 2nd Bone collar formation: Osteoblasts secrete
bone matrix, resulting in a collar made of
compact bone; thickens over time.
• 3rd Primary ossification center: Osteoblasts
are brought interiorly by blood to lay down
spongy bone.
• 4th Secondary ossification sites: Bone centers
in the epiphyses are formed after birth.
• 5th Epiphyseal plate: Growth plate (band of
cartilage) between primary and secondary
ossification center allows bones to lengthen.
Visualizing Endochondral Ossification
How do bones lengthen?
Final Size of the Bones
• When epiphyseal plates close, bone growth no
longer occurs.
– Women: Arm and leg plates close at 16-18
– Men: Arm and leg plates close at 20.
– Other bones may grow to age 25.
• Plate closure is controlled by hormones.
Hormones and Bone Growth
• Growth hormone (GH): Stimulates general
bone growth and growth of the epiphyseal
plates.
– Requires adequate cellular metabolism.
• Diet and thyroid hormone.
• Sex hormones: Increases osteoblast activity
causing “growth spurt” during adolescence.
• Vitamin D: Converted to a hormone to allow
calcium absorption in the intestine.
Bone Remodeling and its
Role in Homeostasis
• Bone remodeling: Bone renewal to keep bones
strong; allows them to respond to stress.
– Rate of up to 18% per year.
• Allows body to regulates the calcium in the blood
through hormones:
** Calcium in blood allows blood to clot!
– Parathyroid hormone (PTH): Stimulates
osteoclasts to dissolve calcium matrix of
bone; Increases blood calcium by
accelerating bone recycling.
– Calcitonin: Decreases blood calcium.
Steps in Bone Repair
• Hematoma (6-8 hrs.): Blood clot formed
between broken bones.
• Fibrocartilaginous callus (~ 3 weeks):
Cartilaginous callus filling the space between
broken bones.
• Bony callus (3-4 months): Cartilaginous callus
is turned to bone to join bones together.
• Remodeling: Osteoblasts build new compact
bone at the periphery; Old bone tissue is
replaced by new bone tissue.
Bone Repair
Health focus: Osteoporosis
• Osteoporosis: Bones are weakened due to a
decreased bone mass.
• Bone reabsorption exceeds absorption usually
by age 40.
• Risk factors: Women, white or Asian, thin,
family history, early menopause, smoking, diet
low in calcium, excessive caffeine or alcohol
consumption and a sedentary lifestyle.
• Can lead to fractures and other complications.
• Can be treated with drugs, hormones and
lifestyle change.
The 206 Bones of the Skeleton
Science focus: Skeletal remains
Characteristics to be determined:
1. Age: approximated through dentition,
studying areas of bone ossification and joint
condition
2. Gender: pelvic bone is best used, thickness
of long bones, skull characteristics
3. Ethnicity: difficult to tell but skull
characteristics are most useful
The Axial Skeleton
• Skull: Made of cranium and facial bones.
• Hyoid bone
• Vertebral column: Vertebrae and
intervertebral disks.
• Rib cage: Ribs and sternum.
The Skull: The Cranium
• Cranium:
– Protects the brain.
– Composed of 8 bones.
– Some contain sinuses.
Bones of the Face and the Hyoid
Bone
• Facial bones:
– Mandible
– Maxillae
– Zygomatic bones
– Nasal bones
• Hyoid:
– Only bone that
does not articulate
with another bone.
The Vertebral Column
• Types of vertebrae:
– 33 vertebrae
• Cervical (7)
• Thoracic (12)
• Lumbar (5)
• Sacrum (5 fused)
• Coccyx (4 fused into
tailbone)
• Intervertebral disks
– Fibrocartilage between
vertebrae.
The Rib Cage
• Ribs: Protects heart and
lungs.
– Flattened bone
originating from the
thoracic vertebrae.
– 12 pairs:
• 7 pr. true ribs
• 3 pr. false ribs
• 2 pr. floating ribs
• Sternum (Breastbone)
The Appendicular Skeleton
• Pectoral girdle and upper limb
• Pelvic girdle and lower limb
The Appendicular Skeleton
• Pectoral girdle:
– Scapula and clavicle.
• Upper limb:
– Arm and hand bones.
The Appendicular Skeleton
• Pelvic girdle:
– Coxal bone
• Lower limb:
– Leg and foot bones
Types of Joints
(Where Bones Meet Bones)
• Fibrous: Usually immovable.
– Ex. Sutures between cranial bones.
• Cartilaginous: Tend to be slightly movable.
– Ex. Intervertebral disks
• Synovial: Freely movable joints.
– Ex. Ball-and-socket hip and shoulder joints;
knee joint.
Anatomy of a Synovial Joint
Summary of Synovial Joints
Movements
•
•
•
•
•
•
Flexion: Decrease in joint angle.
Extension: Increase in joint angle.
Adduction: Body part moves toward midline.
Abduction: Body part moves away from midline.
Inversion: Sole of foot turns inward.
Eversion: Sole of foot turns outward.
Visualizing Synovial Joints Movements