• The Functions of the Skeletal System• Bone Classification• Bone Structure• Bone Formation and Development• Fractures: Bone Repair• Exercise, Nutrition, Hormones, and Bone

Tissue• Calcium Homeostasis: Interactions of the

Skeletal System and Other Organ Systems

SKELETAL SYSTEM

I’m all about the osseous tissues.

That’s why I play the Trom-bone.

Osseous Tissue and the Skeletal Structure

•The skeletal system includes:–Bones of the skeleton and associated cartilages–Ligaments and other connective tissues that stabilize and/or connect them

Primary Functions• Framework: support the body’s muscle fat, and skin

(soft tissues). • Protection: Surround vital organs to protect them

Examples• Skull that surrounds brain • Ribs that protect heart and lungs.

• Levers: attach to muscles to help provide movement

• Produce blood cells: produce red and white blood cells and platelets.

• Storage: store most of body’s calcium, supply blood

Structure of bone• Matrix of Bone:

-Combination of the two provides strong bones which are somewhat flexible and resistant to shattering.

2/3 of bone weightis calcium phosphate

1/3 of bone weight is collagen fibers

Cells in Bones

Terms• chondro refers to cartilage

– chondrocyte– endochondral– perichondrium

• osteo refers to bone– osteogenesis– osteocyte– periostium

• blast refers to precursor cell or one that produces something– osteoblast

• cyte refers to cell– osteocyte

• Osteocytes= mature bone cells– recycle the calcium salts in the matrix around them– participate in the repair of damaged bone

• Osteoblasts= responsible for the production of new bone. (osteogenesis) – Elevated local concentrations of calcium phosphate

favorable for calcification

• Osteoclasts= giant cells with 50 or more nuclei. – Derived from circulating monocytes (phoagocytic white

blood cells) – Important in the regulation of calcium and phosphate

concentrations in body fluids

Osteoclast dissolving bone

• Osteoprogenitor= mesenchymal cells that maintain populations of osteoblasts and play an important role in fracture repair

Classification of Bones By Shape

• Long Bones- A long bone is one that is cylindrical in shape, being longer than it is wide. Long bones function as levers; they move when muscles contract.– Examples: humerus, ulna, radius, femur, tibia, fibula).– Keep in mind, however, that the term describes the

shape of a bone, not its size.

• Flat Bones- typically thin and often curved. Serve as points of attachment for muscles and often protect internal organs.– Examples include the cranial (skull) bones, the scapulae

(shoulder blades), the sternum (breastbone), and the ribs. Flat bones

• Short Bones- Short bones are approximately equal in length, width, and thickness

• Examples:– The bones in the wrist and ankle

• Irregular Bones- Bones that do not fall into the category of long, short, or flat are considered irregular bones. Examples:– The vertebrae and some of the skull bones are irregular.

• Sesamoid bones- are small and round, and are located in tendons.

• Examples: – patellae

How Many Bones Does an Adult Have?

206

How Many Bones Does a New Born Baby Have?

270

Divisions of the skeletal system

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•Creates the central axis of the body

•Includes:• Skull• Thorax• Vertebral column

•Contains 80 bones (~40% of skeleton)

Axial Skeleton(Anterior)

Skull, Pelvis, and Vertebral columns are STRUCTURES

NOT BONES!

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Appendicular Skeleton

126 bonesThe bones of the limbs The pectoral girdle The pelvic girdle

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Vertebral Column• “Backbone”• Central axis of skeleton• 5 regions:

– Cervical vertebrae (C1-C7)– Thoracic vertebrae (T1-T12)– Lumbar vertebrae (L1-L5)– Sacral (S)– Coccygeal bone (CO)

Different regions have special characteristics however all have common features

*NOTE THE VERTEBRAE NUMBERING/IDENTIFICATION!

**HINT! HINT!**

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Ribs & Costal Cartilages• 12 pairs (24 total)• One pair articulated with each thoracic vertebrae• 7 True ribs – (T1-T7)

• Attach to sternum via cartilage (vertebrosternal ribs)

• 5 False ribs – (T8-T12) • Do not directly attach to sternum (vertebrocondial ribs)

• 2 Floating ribs – (T11-T12) SUB-TYPE OF FALSE RIB• Not attached to sternum at all (vertebral ribs)

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Upper Limb: Wrist & Hand

• Wrist – region between forearm and hand– 8 carpals

• Hand – attached to carpals– 5 metacarpals– 5 digits– Numbered 1-5 starting with

thumb– 3 phalanges per finger (2

on thumb)– Proximal; Medial; Distal

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Sutures- Immovable joints which tie bones firmly together with denser fibrous connective tissue

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Sutures

Lamboidal (λ)- Joins Parietal to Occipital

Coronal(crown)-Joins Parietal to frontal

Sagittal- joins the two parietal plates

Squamosal (scale-like)- Joins temporal to occipital and parietal

Bone Markings• Bulges, depressions, and holes that serve as sites of

attachment for muscles, ligaments, and tendons, joint surfaces, conduits for blood vessels and nerves.

Bone Structure

Long Bone

Flat Bone

Bone Structures

Compact Bone• Osteon = the functional unit of mature compact bone. (aka

Haversian systems/canals)• Within osteon, osteocytes are arranged in concentric layers

around the central canal.• Central Canals run parallel to the surface of the bone,

contain one or more blood vessels.

•Nutrients diffuse from vessels in central canal•Alternating direction of collagen fibers increases resistance to twisting forces

Isolated osteon:

Spongy Bone• Matrix of spongy bone:

– Forms supportive mesh called trabeculae

– Seem to align along stress lines

– Has no osteons or blood vessels. Nutrients reach osteocytes by diffusion

Gross anatomy of bones

• Diaphysis is the tubular shaft that runs between the proximal and distal ends of the bone

• Medullary cavity- The hollow region in the diaphysis, which is filled with yellow marrow. The walls of the diaphysis are composed of dense and hard compact bone.

• Epiphysis (plural = epiphyses)- The wider section at each end of the bone, filled with spongy bone.– Red marrow fills the spaces in the spongy bone.

• Epiphyseal plate (growth plate)- narrow area where the epiphysis meets the diaphysis .Made of a layer of hyaline (transparent) cartilage in a growing bone.– When the bone stops growing in early adulthood

(approximately 18–21 years), the cartilage is replaced by osseous tissue and the epiphyseal plate becomes an epiphyseal line.

• The outer surface of the bone is covered with a fibrous membrane called the periosteum (peri- = “around” or “surrounding”). The periosteum contains blood vessels, nerves, and lymphatic vessels that nourish compact bone.

WARNING NEXT SLIDE IS GRAPHIC

• The medullary cavity has a delicate membranous lining called the endosteum where bone growth, repair, and remodeling occur.

• (endo- = “inside”; oste- = “bone”),

• Tendons and ligaments also attach to bones at the periosteum. The periosteum covers the entire outer surface except where the epiphyses meet other bones to form joints.

• In this region, the epiphyses are covered with articular cartilage, a thin layer of cartilage that reduces friction and acts as a shock absorber.

Bone Development and Growth

• Determines the size and proportions of our body

• Starts @ 6weeks (cartilaginous) Ends @ ~25 years

Growth of the skeleton

•Sultan Kösen•2.51 m (8 ft 3 in)

•He Pingping•74 cm (2 ft 5 in)

Growth of the skeleton

• Ossification= Formation of bone

• Calcification= deposition of calcium salts within a tissue

2 forms of Bone Growth

• Intramenbranous Ossification deposition of bony matrix in connective tissue membranes

• Endochondral Ossification replacement of cartilage by bone.

Endochondral Ossification

1. Cartilage cells become enlarged in ossification centers– Long bones have three centers:

• 1 at each end (epiphyses)• 1 at the midpoint of diaphysis (shaft)

2. Enlarged cells soon break down leaving spaces filled by osteoblasts (bone forming cells)

3. While organic components of bone are being formed, minerals are being deposited and blood vessels branch throughout the newly forming bone

4. Eventually osteoblasts become osteocytes

Endochondral ossification

Stages 1-3 during fetal week 9 through 9th month

Stage 4 is just before birth

Stage 5 is process of long bone growth during childhood & adolescence

Intramembranous Ossification1. Osteoblasts deposit matrix materials in the

form of calcium salts2. Osteoblasts become osteocytes

Dynamic Nature of Bone• Remodeling- components of bone matrix are

continually being recycled and renewed throughout life as part of normal bone maintenance.

• Young adults remodel 1/5 (20%) of the adult skeleton per year

Dynamic Nature of Bone

• Remodeling- components of bone matrix are continually being recycled and renewed throughout life as part of normal bone maintenance.

• Young adults remodel 1/5 (20%) of the adult skeleton per year

• Diseases and Disorders.

• Bones are adaptable, their shapes reflect the forces applied to them

Exercise Effects on Bone

• Heavily stressed bones become thicker and stronger, bones not subject to ordinary stresses will become thin and brittle

• Moderate amounts of physical activity and weight bearing activities are essential to stimulate normal bone maintenance and maintain adequate bone strength.

Exercise Effects on Bone

Bone markings reflect the stresses

Fracture repair• Bones may crack or break if

subjected to extreme loads, sudden impacts, or stressed from unusual directions.

• Fracture categories:• Displaced/Non-Displaced• Open/Closed.

Displaced/ Non-Displaced

• Displaced fracture- bone ends are not lined up straight.

• Non-Displaced fracture- bone maintains its proper alignment.

Open/Closed

• Closed fracture- bone breaks but no open wound or puncture in the skin.

• Open fracture- bone breaks through the skin. (risk of a deep bone infection) X

WARNING!GRAPHIC CONTENT!

Open/Closed

Closed Fracture Open Fracture

Open Fracture X-Ray of Fracture

A. Fracture Hematoma (i.e. blood clot) forms

Steps in Bone Healing

Steps in Bone Healing

B. Soft Tissue Callus (1st 3 to 4 weeks)- Fibroblasts and osteoblasts migrate in from the periosteum and endosteum- Fibroblasts lay down a collagen matrix - some of the fibroblasts differentiate into chondroblasts (i.e. cartilage-forming cells) and lay down a fibrocartilage splint (i.e. soft tissue callus)

C. Bony Callus (starting 3 to 4 weeks after the injury)- Osteoblasts begin to replace the fibrocartilage splint with spongy and compact bone, forming a bulge that is initially wider than the original bony shaft

Steps in Bone Healing

D. Bone Remodeling- As the patient starts to use (or bear weight on) the bone, the bone starts to remodel along lines of maximal stress (this remodeling process requires the activity of both osteoblasts and osteoclasts

Steps in Bone Healing

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Sutures- Immovable joints which tie bones firmly together with denser fibrous connective tissue

END