Introduction to the Skeletal System. Support: Bones support the weight of the body and structures such as the head and face Protection: Bones protect.

Chapter 7 Part 1Introduction to the Skeletal System

Support: Bones support the weight of the body and structures such as the head and face

Protection: Bones protect delicate organs such as the brain and spinal cord, heart and lungs

Muscle Attachment & Movement: Bones act as levers to which muscles are attached

Blood Production: Blood cells are produced within red bone marrow (hematopoeisis)

Store Minerals: Minerals such as calcium and phosphorus, etc. are stored in bone matrix

All About Bones

Many tissues are contained within bones◦ Bone tissue◦ Nervous tissue (nerves)◦ Blood vessels (and blood)◦ Cartilage ◦ Dense connective tissue

Tissues Within Bones

There are 5 types of bones: Long (ex: femur) Short (ex: carpals) Flat (ex: scapula) Irregular (ex: vertebrae) Sesamoid (ex: patella)

Five Types of Bones

Those classified as Long Bones must meet this criteria:◦ Must have a body (diaphysis) that is longer than it

is wide; Diaphysis must have a hard covering (periosteum) made of compact bone

◦ Must have growth plate (epiphysis) at either end; Epiphysis must contain marrow and be made of spongy bone with a thin covering of compact bone

Example: femur, humerus

Long Bones

Epiphysis: Expanded end of bones that form joints with adjacent bones◦ Covered by articular cartilage (hyaline) at the

joint Diaphysis: The long shaft of the bone

◦ Covered in compact bone

Long Bone Structure

The epiphysis is at the end of long bones. The epiphyseal plate is the part of the

epiphysis where lengthwise bone growth occurs.

Usually referred to as ‘the growth plate’. The epiphyseal plates fuse in early

adulthood and no further lengthening of the bones occurs.

Epiphyseal Plate

The diaphysis is the long, shaft portion of a long bone.

The diaphysis contains a hollow medullary cavity that is lined with endosteum and filled with marrow.

A tough layer of vascular connective tissue, called the periosteum, covers the bone and is

continuous with ligaments and tendons.

Diaphysis & Periosteum

Bone Marrow There are two types of bone marrow:

◦ Red Bone Marrow-responsible for the production of red blood cells, white blood cells and blood platelets; is found in spongy bone (epiphysis)

◦ Yellow Bone Marrow-stores fat and is not active in blood cell production; found in the medullary cavities

Bone Marrow Transplant Clip

Ends of long bones: ◦ Epiphyses

Shaft of long bones:◦ Diaphysis

Inner cavity of long bones:◦ Medullary Cavity

Outer covering of bones:◦ Periosteum

Inner covering of medullary cavity:◦ Endosteum

REVIEW

Osteoblasts are cells that build bone tissue◦ They become active in connective tissue

membranes and deposit bone matrix around themselves-this leads to the branching appearance of spongy bone

Osteoclasts destroy bone tissue by secreting acid that dissolves the inorganic bone matrix

These two cells usually work well together but malfunctions can lead to bone cancer

Blast vs. Clast

Bone cells called osteocytes are located within spaces called lacunae that lie in concentric circles around Haversian canals that contain blood vessels, and nerves

These systems are organized into columns called osteons that are cemented together

Microscopic Structure of Compact Bone

These osteonic/Haversian systems contain blood vessels & nerve fibers and extend longitudinally through bone

Osteonic canals are interconnected by transverse perforating canals (Volkmann’s canals).

Microscopic Structure of Compact Bone (continued)

Scientists like to name things after themselves…

Haversian canals=central canals◦ run longitudinally through bone

Volkmann’s canals=perforating canals ◦ these are transverse canals that run between

individual Haversian systems

Canals, canals, canals

Osteocytes are scattered in no particular order and pass nutrients and wastes back and forth in passageways in the matrix called canaliculi.

Important sites for spongy bone include: ◦ the skull ◦ the ribs◦ the vertebrae ◦ the sternum

Microscopic Structure of Spongy Bone

Compact bone ◦ Osteocytes and extracellular matrix cluster

around Haversian canals◦ Many of these units cemented together makes up

compact bone Spongy bone

◦ Also composed of osteocytes and extracellular matrix, but the units do not aggregate around canals

◦ They form cross connections called trabeculae

Compact vs Spongy Bone

The intercellular material consists of collagen and inorganic salts.◦ Calcium Phosphate & Calcium Carbonate

Most bones contain a mixture of compact and spongy bone◦ the epiphyses of long bones all contain spongy

bone covered by compact bone◦ the diaphysis of a long bone is made of compact

bone

Similarities

Bone Development & Growth Bones begin to form during the first few

weeks of prenatal development Bones form in one of two ways

◦ Intramembranous bones originate between sheet-like layers of connective tissues

◦ Endochondral bones begin as masses of cartilage that ossify

1. Membrane like layers of connective tissue appear at the site of future bones (ex: skull)2. Cells differentiate into osteoblasts3. Osteoblasts deposit bony matrix around themselves4. Cells outside the developing bone give rise to the outer periosteum 5. Osteoblasts on the inside of the bone form the outer compact covering over spongy bone6. Osteocytes form when extracellular matrix completely surrounds osteoblasts

Intramembranous Bone Formation

1. Hyaline Cartilage forms at the site of future bones2. Cartilage grows and begins to change3. Blood vessels invade the tissue 4. Osetoblasts form spongy bone at the primary ossification center of the diaphysis5. Secondary ossification occurs in the spongy bone of the epiphyses6. The epiphyseal plate separates the two ossification centers7. Accumulation of the bone cells forces the death of the cartilaginous cells

Endochondral Bone Formation

8. Bones continue to lengthen while cartilaginous cells of the epiphyseal plate are active9. Bone growth ceases when the primary and secondary ossification centers meet

Endochondral Bone Formation (continued)

Epiphyseal (growth) plates are responsible for lengthening bones while increases in thickness are due to intramembranous ossification underneath the periosteum.

A medullary cavity forms in the region of the diaphysis due to the activity of the cells called osteoclasts.

In summation…

Osteoclasts and osteoblasts remodel bone tissue throughout life

Hormones that regulate blood calcium (PTH-Parathyroid Hormone and calcitonin) help control resorption and deposition of bone matrix

Homeostasis of Bone Tissue

Bones shape, support, and protect body structures

Bones aid in body movement Bones house tissues that produce blood

cells and store salts

Bone Function

Supporting weight: bones of the lower limbs, pelvis, and backbone

Protecting the senses: bones of the skull protect the eyes, ears, and brain

Vital organ protection: bones of the thoracic cavity and pectoral girdle protect the heart and lungs

Reproductive organs: protected by the pelvic girdle

Support & Protection

Blood cell formation begins in the yolk sac As a fetus grows, blood cells are

manufactured in the liver and spleen◦ The liver does not perform digestive processes

because the fetus does not consume meals directly, but receives nourishment from the mother via the placenta

After birth, blood cells form in bone marrow◦ Which kind?

Hematopoiesis

The thyroid gland regulates blood calcium levels via two hormones

When blood calcium is low, parathyroid hormone (PTH) stimulates osteoclasts to break down bone tissue to release calcium salts

When blood calcium is too high, calcitonin stimulates osteoblasts to form bone tissue, storing excess calcium salts

Inorganic Salt Storage

Bones are good accumulators of heavy metals such as lead, radium, or strontium (bad news)

Poison Storage

The use of lead-based paints for homes, children's toys and household furniture has been banned in the United States since 1978

Lead-based paint is still on walls and woodwork in many older homes and apartments

Lead is sometimes found in toys and other products produced abroad

Lead Poisoning

A fracture is a break in a bone Blood vessels within the bone and the

periosteum rupture forming a 1)hematoma Fibrocartilage fills in the gap between the

ends of the broken bone with a 2)cartilaginous callus

Osteoblasts and osteoclasts go to work and the cartilaginous callus breaks down and a 3)bony callus fills the space

Fractures

Bone healing can be aided by doctors◦ First cast used in Philadelphia in 1876◦ More recently, screws and plates have been

used to internally align healing bones parts◦ Rods, wires and nails are used by surgeons

today They are lighter and smaller and usually built of

titanium

Fractures (continued)

Greenstick: an incomplete fracture usually occurring in the developing bones of children

Types of Fractures

Compound: a severe fracture in which the bone breaks through the skin

Types of Fractures

Comminuted: a fracture in which the bone is broken into several pieces

Types of Fractures