The Skeletal System

Chapter 6

Anatomy and Physiology

Mr. Knowles

Liberty Senior High School

Question of the Day!

Do bones remain the same?

How do bones “know” when to stop growing? What

happens when they don’t?

The Skeletal System! Our First System

Cells (Osteocytes)

Tissues (Osseous Tissue)

Organs (Bones)

Systems (Skeletal)

All C.T. have Three Parts

1. Specialized Cells2. Extracellular Protein Fibers3. The Fibers above and a ground

substance (usually a liquid)- make up the Matrix that surrounds cells. (most of the volume of C.T.)

The Fibers

• Collagen Fibers- long, straight, unbranched, fibers of twisted protein; rope-like, very flexible, yet strong. (Tendons and Ligaments)

Bone (Osseous Tissue)• G.S. = almost no liquid; collagen

fibers + calcium salts (CaPO4 and some CaCO3)

• Strong and flexible properties.• Lacunae in matrix contain

osteocytes.

Bone (Osseous Tissue)• Lacunae organized around a central

canal (Haversian canal) which contains blood vessels.

• Diffusion cannot occur through calcium salts.

• Cytoplasm of osteocytes extend to central canal by canaliculi.

A Basic Pattern in Bone Tissue

• Lacunae with osteocytes arranged around and connected to a central canal by radiating canaliculi- Osteon

• Many osteons in one bone.

Bone-Low Mag.

Haversian or Central Canal

Bone-High Mag.

Osteons

Bone (Osseous Tissue)

• Bone surfaces covered by periosteum- fibrous layer of C.T.; attachment for tendons and ligaments.

• Site of appositional growth of bone.• Bone is constantly remodeled- grow

thicker with stresses.

Anatomy of Bone (4 Parts)

1. Diaphysis- long, tubular shaft, mostly compact bone.

2. Epiphysis- expanded areas at the ends of bone, mostly spongy bone.

Anatomy of Bone (4 parts)

3. Marrow Cavity- core of bone with red and yellow marrow.

4. Metaphysis- area that connects the epiphysis and diaphysis. Contains the Epiphyseal plate- area of growth between epiphysis and diaphysis

Other Parts to Bone• Periosteum- outermost layer of bone

made of cells and fibers.Provides the point of attachment for tendons and ligaments on the outside.Route for vessels to enter the bone.Participates in bone growth and repair.

Other Parts of the Bone

• Endosteum- a layer of cells that lines marrow cavity; lines trabeculae of spongy bone and central canal of compact bone.

Also site of bone growth.

Two Types of Osseous Tissue

1. Compact bone- dense bone, solid, more on surface of bone, shaft of bone.Function: osteons are all aligned;strengthen bone, the tissue of bone is parallel to stresses.

Two Types of Osseous Tissue2. Spongy Bone- open network of

trabeculae which are struts and plates in the interior of bone (matrix) , light in weight; Function: has no osteons; withstand stress from a variety of directions, reduce the weight of the overall bone.

Bone Development • Skeleton begins to develop at 6

weeks after conception, embryo is only 12 mm (0.5 in ) long.

• Bone growth continues through the age of 25 yrs.

• Bone is continuously remodeled or reshaped.

How do bones grow in humans?

Can we see bone growth in a developing embryo?

The Players in OsteogenesisOssification- formation of bone is a

dynamic process.Osteoblasts- produce new bone

matrix.Osteoclasts- produce acids and

enzymes to release the stored minerals in the matrix.

Osteocytes- mature bone cells that do not divide.

Bone Grows in Two Ways• Intramembranous Ossification-

bone forms from mesenchyme cells or fibrous connective tissue. Deep layers of the dermis.

• Endochondral Ossification- bone replaces a mold of cartilage.

Intramembranous GrowthStep 1: Mesenchymal cells (stem cells) cluster at a

site (ossification center) within the dermis (skin layers) and secrete bone matrix (collagen + Ca +2). These cells will become osteoblasts.

Step 2: Bone grows outward in spicules which will become the struts of spongy bone. Vessels grow into area.

Step 3: Osteoblasts at the outer edge become less active and become osteocytes.

Intramembranous Bones• Dermal bones of the skull-

parietal, occipital, etc, the mandible, the clavicle, and the scapula.

• Bones that are mostly spongy tissue are made by intramembranous ossification.

OsteogenesisIntramembranous ossification- bone

growth within C.T. (mandible, parietal) see p. 181, 4th Ed., Martini)

Want to see what happens when this growth is uncontrolled? Heterotopic Bone Formation, p. 50 of the A.M.

Heterotopic Bone Formation

FOP

Endochondral Ossification• Endo means inside; -chondros means

cartilage.• Bone tissue gradually replaces a

cartilage model or mold for the bone.• Most bones form this way; all of the

appendicular (limb) skeletal bones.

Endochondral Growth • Step 1: Cartilage forms a mold and the

chondrocytes grow very large in the center of the mold. Lacunae expand and the matrix thins to struts. Chondrocytes die.

• Step 2: Blood vessels grow into the shaft of cartilage; cells of the perichondrium become osteoblasts. The perichondrium now becomes the periosteum.

Endochondral Growth• Step 3: Blood supply increases;

fibroblasts migrate to the center and become osteoblasts. They start to make spongy bone- Primary Center of Ossification.

• Step 4: As bone enlarges, osteoclasts appear and erode the trabeculae in the center- creates the marrow cavity.

Show Me the BMU in Action!

Endochondral Ossification• Osteoblasts of the diaphysis and

chrondrocytes of epiphysis continue to grow; elongate bone.

• Epiphyseal Plate is the interface between the two.

• At puberty, the osteoblasts overcome chondrocytes; the plate becomes more narrow- epiphyseal line.

Fetal Long Bone

Developing Long Bone

Endochondral Ossification

Endochondral OssificationLengthening Bones-• Hyaline chondrocytes die and leave

calcified struts.• Blood vessels grow at edges and

perichondrial cells become osteoblasts.• Osteoclasts- create a marrow cavity by

dissolving struts

Bone GrowthIntramembranous

• Occurs in a layer between dermis (dermal bones).

• Mesenchymal (stem) cells osteoblasts.

• Spongy Bone.

• Skull bones, mandible, scapula, clavicle.

Endochondral • Fills in a cartilage mold

in a center of ossification.• Fibroblasts osteoblasts

in the center of mold.• Osteoclasts form a

marrow cavity.• Compact Bone.• Most other bones; long

bones.

Basic Multicellular Unit (BMU)

• A group of wandering cells that constantly reform or remodel bone.

• Many BMU move throughout the bone’s center and surface.

• Specific sequence of 5 events or steps.

5 Steps to Bone Formation1. Osteoclast Recruitment- osteoclasts arrive at the

site of repair or reformation.2. Resorption- osteoclasts resorb or release the Ca

+2 from the matrix. This forms a cavity in the area (2 weeks).

3. Osteoid Formation- osteoclasts self-destruct and attract osteoblasts to the area. The osteoblasts secrete new collagen and Ca +2 into the cavity.

5 Steps to Bone Formation4. Mineralization- the new osseous

tissue begins to mineralize; Ca +2 fills the cavity.

5. Quiescence- the last osteoblasts develop into osteocytes and remain quiet in the bone tissue. They have long cell processes that can detect mechanical stresses.

Show me Normal Bone Remodeling in Spongy Bone!

When bones don’t stop growing!

Diseases of Bone Growth

• Read bottom of p. 48 – 52 of Martini, F. (1998) Applications Manual. 4th Ed. Prentice Hall: New Jersey.

• Complete the Table on Bone Growth Diseases.

Acromegaly?

Diseases of Bone Growth• Gigantism – overproduction of growth hormone

before puberty, growth plates still open; pituitary tumor.

• Acromegaly – overproduction of growth hormone after puberty, growth plates closed but abnormal growth of cartilage and small bones.

• Marfan’s Syndrome – defect in fibrillin, a protein of C. T. matrix; excessive cartilage at plates that is weak; blood vessels are not as elastic; genetic.

Marfan’s Syndrome?

Achondroplasia

Diseases of Bone Growth

• Achondroplasia – “a’ without, “chondro” cartilage, “plasia” formation – cartilage within the epiphyseal plates grow extremely slow; affects appendicular skeleton more than axial skeleton.

Normal Spongy Bone

Osteoporotic Spongy Bone

Show Me Post-Menopausal Bone in Action

The Skeletal System

Anatomy and Physiology

Chapters 7 and 8

Mr. Knowles

Liberty Senior High School

The Skeletal System

How many bones do women and men have?

206 bones in humans

Two Divisions:Axial Skeleton-

bones of skull, vertebral column,

ribs, and sternum- 80

bones

Appendicular Skeleton-

bones of limbs (appendages), pectoral and pelvic girdles;attach the limbs to the trunk of the body.

Functions of the Skeletal System

1. Support- framework,

2. Storage of Minerals- Ca3(PO4)2, and CaCO3

3. Storage of Lipids- yellow marrow.

Functions of the Skeletal System

4. Blood cell production- red marrow makes erythrocytes, leukocytes, and others.

5. Protection- protect vital organs. Ex. Ribs.

6. Leverage- change magnitude and direction of forces.

Classification of Bones

1. Long bones- long, slender shapes (femur, phalanges)

2. Short bones- boxlike (carpal and tarsal bones)

3. Flat bones- thin, flat bones (sternum, ribs, scapula, parietal)

Short Bones

Carpals

?

Bones of the Skull

Classification of Bones

4. Irregular bones- complex shapes, notched or ridged surfaces [vertebra(ae)]

5. Sesamoid- like a sesame seed, small, flat, and inside joints [patella(ae)]

Vertebra (ae) = irregular bones

The Patella (ae) = a sesamoid bone

Sesamoid Bone in Hand

A Sesamoid Bone

Other Sesamoid

Bones!

Classification of Bones

6. Sutural bones- small, flat, irregular bones of skull (sutural bone in skull)

Many Irregular, Flat, and Sutural

Your Assignment• Finish the handouts over the tissues of

bone.• Identify all bones and structures listed

in the outline (Refer to Table 6-2 on p. 192).

• Classify these bones into the six major types of bones.

What can we learn about a person’s life from their

bones?

G. B. Dyson (2000). The Aleutian Kayak. Scientific American (April) 84-91.