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The Skeletal System Prof. Yvette Marris E. Legaspi, RN, MAN

Objectives At the end of the lecture-discussion, you will be able to : • Identify the subdivisions of the skeleton as axial or appendicular. • List at least three functions of the skeletal system. • Name and describe the various types of fractures.

Bones: An Overview

Parts of the skeletal system  Bones (skeleton)

 Joints  Cartilages  Ligaments

Divided into 2 divisions  Axial skeleton  Appendicular skeleton

• At birth, there are over 270 bones in an infant human's body, but many of these fuse together as the child grows, leaving a total of 206 separate bones in an adult.

• The largest bone in the human body is the femur and the smallest bones are auditory ossicles.

Functions of the Bones 1. Support • Form the internal framework of the body • Ribcage supports the thoracic wall • Legs support the torso

2. Protection Bones • protect soft body organs • Skull shields the brain • Ribcage and shoulder girdle protects the heart and lungs

3. Movement • Skeletal muscle attach to bones by tendons • The skeletal muscles use the bones as levers to produce locomotion 4. Storage • The internal cavities of bone store fat • The matrix of bone tissue is a storage medium for minerals • They are found in the form of inorganic salts • two primary minerals: • Calcium • Phosphorus

5. Blood Cell Formation • Certain bones have marrow cavities which contain red marrow • red marrow is the site of hematopoiesis

Classification of Bones • Types of bone tissue • Compact • Spongy • Classification of bone based on structure • Long • Short • Flat • Irregular

Paranasal Sinuses • Hollow parts of bones surrounding nasal cavity • Functions: • Lighten the skull • Resonate and amplify voice

The Hyoid Bone  Only bone that doesn’t articulate with another bone  Moveable base for tongue

Structure of a Long Bone • Diaphysis (Shaft) • Compact bone • Periosteum • Cover and protection • Fibrous connective tissue membrane

• Perforating Fibers , also called Sharpey's fibers • Secure the periosteum to the underlying bone • Medullary Cavity • Yellow Marrow • Adult:Storage for adipose tissue • Infant: forms RBC

• Epiphysis • End of a long bone

• Articular Cartilage • Covers the external surface • Smooth, slippery surface

• Epiphyseal Plate • Cause the lengthwise growth of a long bone • Epiphyseal Line • Remnant of the epiphyseal plate

• Spongy bone • Contains Red Marrow

Bone Markings • It is where muscles, tendons, and ligaments were attached and where blood vessels and nerves passed.

• Two categories: • Projections or processes • Depressions or cavities

• Projections or Processes • Grow out from the bone surface • Depressions or Cavities • Indentations in the bone

Projections That are Sites of Muscle and Ligament Attachment Name

Description

Tuberosity

Large, rounded projection; may be roughened

Crest

Narrow ridge of bone; usually prominent

Trochanter

Very large, blunt, irregularly shaped process. These are found only on the femur

Line

Narrow ridge of bone; less prominent than a crest

Name Tubercle Epicondyle Spine

Process

Description Small, rounded projection or process Raised area on or above a condyle Sharp, slender, often pointed projection or process Any bony prominence

Crest

Epicondyle

Tubercle

Tuberosity

Trochanter

Spine

Projections That Help to Form Joints Name Head Facet

Condyle Ramus

Description Bony expansion carried on a narrow neck Smooth, nearly flat articular surface Rounded articular projection Armlike bar of bone

Head

Facet

Depressions and Openings Allowing Blood Vessels and Nerves to Pass Name

Description

Meatus

Canal-like passageway

Sinus

Cavity within a bone, filled with air and lined with mucous membrane

Fossa

Shallow, basinlike depression in a bone, often serving as an articular surface

Groove

Furrow

Fissure

Narrow, slitlike opening

Foramen

Round or oval opening through a bone

Fissure

Sinus

Foramen

Groove

Microscopic Anatomy of Compact Bone

• Complex Structure • Passageways for • Nerves • Blood vessels • Provides the living bones with nutrients and for removal of wastes

1. Lacunae

• Cavities containing mature bone cells (osteocytes) • Arranged in concentric rings

2. Lamellae • Rings around the central canal

• Sites of lacunae

3. Central (Haversian) canal • Carries blood vessels and nerves to the group of lamella surrounding it • Run lengthwise through the bony matrix

4. Osteon (Haversian System) • Central canal and the lamellae 5. Perforating (Volkman’s) canal • Canal perpendicular to the central canal, run perpendicular to the shaft • Carries blood vessels and nerves

6. Canaliculi

• Tiny canals • Radiate from the central canal to lacunae • Form a transport system to connect all the bone cells to the nutrient supply through the hard bone matrix

Bone Formation, Growth, and Remodeling

• In embryos, the skeleton is primarily hyaline cartilage • During development, much of this cartilage is replaced by bone • Cartilage remains in isolated areas 1. Bridge of the nose

2. Parts of ribs 3. Joints

Bone Growth • Ossification • The process of bone formation • Two Steps • Hyaline cartilage model is covered with bone matrix by osteoblasts (bone forming cells) • The enclosed hyaline cartilage is digested away, opening up the medullary cavity within the newly formed bone

• By birth or shortly after hyaline cartilage models have been converted to bone • EXCEPT for two regions • The articular cartilage • Epiphyseal plates

• Epiphyseal plates allow for growth of long bone during childhood • New cartilage is continuously formed: 1. On the external face of articular cartilage

2. Epiphyseal plate (furthest away from medullary cavity) • Older cartilage becomes ossified: 1. Internal face of articular cartilage 2. Medullary cavity

Long Bone Formation and Growth

Long Bone Growth • Controlled by hormones • Growth hormones • Sex hormones during puberty • Growth ends during adolescence when the epiphyseal plates are completely converted into bone.

Types of Bone Cells • Osteocytes

• Mature bone cells • Osteoblasts • Bone-forming cells • Osteoclasts • Bone-destroying cells

• Break down bone matrix for remodeling and release of calcium • Bone remodeling is a process by both osteoblasts and osteoclasts

Developmental Aspects  At birth, skull bones incomplete  Bones joined by fibrous membranes – fontanelles

 Fontanelles replaced by bone within 2 years • Fetal skull is large compared to total body length

Bone Remodeling • Bones are dynamic and active tissue • Bones are remodeled due to • Calcium levels in the blood • Pull of gravity and muscles on the skeleton • Essential if bones are to retain normal proportions and strength during long bone growth

Bone remodeling – calcium levels • When blood calcium levels drop below homeostatic levels: • PTH is released into the blood (from parathyroid gland) • Activates osteoclasts to break down bone matrix and release calcium into the blood • When blood calcium levels are too high calcium is deposited into the bone matrix as calcium salts.

Bone remodeling – muscle attachment • Bones become thicker and form large projections to increase their strength in areas where bulky muscles are attached • Osteoblasts lay down new matrix and become trapped • Bones of inactive people tend to lose mass.

Rickets • a softening of bones in children due to deficiency or impaired metabolism of vitamin D, magnesium, phosphorus or calcium, potentially leading to fractures and deformity.

Bone Fractures • A break in a bone

• Types 1. Closed (simple) fracture – does not penetrate skin 2. Open (compound) fracture – penetrates through skin

• Bone fractures are treated by reduction and immobilization - Realignment of the bone

Common Types of Fractures

Comminuted Fracture

Compression Fracture

Depressed Fracture

Impacted Fracture

Spiral Fracture

Greenstick Fracture

Repair of Bone Fractures 1. Hematoma (blood-filled swelling) is formed

2. Break is splinted by fibrocartilage to form a callus 3. Fibrocartilage callus is replaced by a bony callus 4. Bony callus is remodeled to form a permanent patch

Stages in the Healing of a Bone Fracture