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?

What are the functions of the skeletal system?

1. Supports the body

2. Protects the soft body parts

3. Produces blood cells

4. Stores minerals (calcium and phosphate) and fat

5. Allows for movement by attaching muscles

11.1 Overview of the skeletal system

What is the anatomy of a long bone?

• Diaphysis – shaft of the bone made of compact bone and filled with yellow marrow

• Epiphysis – ends of the bone made mostly of spongy bone

• Articular cartilage – hyaline cartilage found on the ends of long bones

• Yellow bone marrow – stores fat• Red bone marrow – makes blood cells

found in spongy bone and flat bones

• Periosteum – living, outer covering of fibrous connective tissue

• Ligaments – fibrous connective tissue that connects bones

11.1 Overview of the skeletal system

More detail on bone…

• Compact bone– Composed of osteons with

a central canal containing blood vessels

– Contains living bone cells called osteocytes chambers called lacunae

• Spongy bone– Made of plates with spaces

filled with red bone marrow

11.1 Overview of the skeletal system

Where are the 3 types of cartilage found?

• Cartilage – flexible connective tissue categorized based on the type and arrangement of matrix fibers

• 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

11.1 Overview of the skeletal system

What are the important cells in bone growth, remodeling and repair?

• Osteoblasts – bone-forming cells

• Osteocytes – mature bone cells that maintain bone structure derived from osteoblasts

• Osteoclasts – bone-absorbing cells

• Chondroytes – cartilage-forming cells

11.2 Bone growth, remodeling and repair

How does bone develop?

Ossification - the formation of bone in two distinct ways:

1. Intramembranous ossification - bone development between sheets of fibrous connective tissue; used in flat bones

2. Endochondrial ossification – cartilage is replaced by bone; used by most bones

11.2 Bone growth, remodeling and repair

How does endochondral ossification occur?

1st Cartilage model – chondrocytes lay down hyaline cartilage in the shape of the future bones

2nd Bone collar formation – osteoblasts secrete bone matrix and results in a collar made of compact bone

3rd Primary ossification center – osteoblasts are brought interiorly by blood and lay down spongy bone

4th Secondary ossification sites – bone centers in the epiphyses formed after birth

5th Epiphyseal plate – a cartilage band that acts as a growth plate that allows bones to lengthen

11.2 Bone growth, remodeling and repair

Visualizing endochondral ossification

11.2 Bone growth, remodeling and repair

How do bones lengthen?

11.2 Bone growth, remodeling and repair

How do hormones affect bone growth?

• Growth hormone (GH) – stimulates general bone growth and the epiphyseal plates

• Sex hormones – increases growth during adolescence

• Vitamin D – converted to a hormone to allow calcium absorption in the intestine

11.2 Bone growth, remodeling and repair

What is bone remodeling and what is its role in homeostasis?

• Bone remodeling – bone renewal at a rate of up to 18% per year

• Remodeling allows bones to respond to stress

• Regulates the calcium in the blood through hormones:– Parathyroid hormone (PTH) – increases blood

calcium by accelerating bone recycling– Calcitonin – decreases blood calcium

11.2 Bone growth, remodeling and 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

11.2 Bone growth, remodeling and repair

Steps in bone repair • Hematoma (6-8 hrs.) – blood clot formed between

broken bones

• Fibrocartilaginous callus (~ 3 weeks) – cartilaginous callus forms between broken bones

• Bony callus (3-4 months) – cartilaginous callus is turned to bone

• Remodeling – old bone tissue is replaced by new bone tissue

11.2 Bone growth, remodeling and repair

Bone repair11.2 Bone growth, remodeling and repair

The 206 bones of the skeleton

11.3 Bones of the axial 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

11.3 Bones of the axial skeleton

The axial skeleton• Skull – made of cranium and facial bones

• Hyoid bone

• Vertebral column – vertebrae and intervertebral disks

• Rib cage – ribs and sternum

11.3 Bones of the axial skeleton

The skull – the cranium

• Cranium– Protects the brain– Composed of 8 bones– Some contain sinuses

11.3 Bones of the axial skeleton

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

11.3 Bones of the axial skeleton

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

11.3 Bones of the axial skeleton

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– Known as the breastbone

11.3 Bones of the axial skeleton

The appendicular skeleton

• Pectoral girdle and upper limb

• Pelvic girdle and lower limb

11.4 Bones of the appendicular skeleton

The appendicular skeleton

• Pectoral girdle – Scapula and clavicle

• Upper limb – Arm and hand bones

11.4 Bones of the appendicular skeleton

The appendicular skeleton

• Pelvic girdle – coxal bone

• Lower limb– Leg and foot bones

11.4 Bones of the appendicular skeleton

Types of joints (where bones meet bones)

• Fibrous – usually immovable such as the sutures between cranial bones

• Cartilaginous – tend to be slightly movable such as the intervertebral disks

• Synovial – freely movable joints such as the ball-and-socket hip and shoulder joints and the knee joint

11.5 Articulations

Anatomy of a synovial joint

11.5 Articulations

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

11.5 Articulations

Visualizing synovial joints movements11.5 Articulations