Skeletal System

Introduction to the Skeleton

Skeletal System Lecture 1: Imagine for a moment that people did not have

skeletons. What comes to mind? Probably that each of us would be a heap on the floor, much like a jellyfish out of water. This image is accurate and therefore reflects the most obvious function of the skeleton; to support the body.

Hey dude. Help a

jellyfish out and put me

back in the water.

FUNCTIONS OF THE SKELETAL SYSTEM

• Provides a framework that supports the body; the muscles that are attached to bones move the skeleton.

• Protects some internal organs from mechanical injury; the rib cage protects the heart and lungs.

• Contains and protects the red bone marrow, one of the hemopoietic (blood-forming) tissues.

• Provides a storage site for excess calcium. Calcium may be removed from bone to maintain a normal blood calcium level, which is essential for blood clotting and proper functioning of muscles and nerves.

TYPES OF BONE TISSUE

• Bone cells are called osteocytes, and the matrix of the bone is made of calcium salts and collagen.

• The calcium salts give bones the strength for its supportive and protective functions.

• The function of osteocytes is to regulate the amount of calcium that is deposited in or

removed from the bone matrix.

• Bone is an organ, it has its own blood supply and is made up of two types of tissue; compact and spongy bone.

• Compact bone is made of haversian systems or

cylinders of bone matrix with osteocytes in concentric

rings (lamellae) around central haversian canals.

• Each haversian system consists of mature osteocytes

arranged in concentric circles around large blood vessels.

• The area surrounding the osteocytes is filled with protein

fibers, calcium, and other minerals.

• Each haversian system looks like a long cylinder.

• Compact bone consists of many haversian systems

running parallel to each other. The network of blood

vessels ensures that the bone tissue receives an

adequate supply of blood. Blood supplies tissues with

oxygen and necessary nutrients.

The Haversian System.

A cousin of the oseton,

Oscaron

• Spongy or cancellous bone has a much different

structure from compact bone.

• Unlike compact bone, spongy bone does not contain

haversian systems. In spongy bone, the bone tissue

is arranged in plates called trabeculae. These bony

plates are separated by irregular spaces, or holes,

and give spongy bone a punched out “Swiss cheese”

appearance.

• The spaces in the bone are important for two

reasons:

– they decrease the weight of the bone, making it

lighter

– and they contain red bone marrow. The red bone

marrow richly supplies the spongy bone with

blood and also produces cells for use throughout

the body.

ANATOMY OF A LONG BONE

The arrangement of compact and spongy

tissue in long bone accounts for its

strength. Long bones contain sites of

growth and reshaping and structures

associated with joints.

The parts of a long bone

include the following:

Diaphysis- The diaphysis is the long shaft of the bone. It is composed primarily of compact bone and therefore provides considerable strength.

Epiphysis- The enlarged ends of the long bone are the epiphyses. The epiphyses of a bone articulates, or meets, with a second bone at a joint. Each epiphysis consists of a thin layer of compact bone overlying spongy bone. The epiphyses are covered by cartilage.

Epiphyseal disc or plate- A growing bone contains a band of cartilage located at the ends of long bones, between the epiphyisis and the diaphysis. This band of cartilage is the epiphyseal plate. It is here that longitudinal bone growth occurs.

Medullary cavity- The medullary cavity is the hollow center of the diaphysis. In infancy, the cavity is filled with red bone marrow for blood cell production. In the adult, the medullar cavity is filled with yellow bone marrow and functions as a storage site for fat; at this stage it is not associated with blood cell production. The inside of the medullary cavity is lined with connective tissue called the endosteum.

Periosteum- The periosteum is a tough fibrous

connective tissue membrane that covers the outside of

the diaphysis. It is anchored firmly to the outside of the

bone on all surfaces except the articular cartiglage. The

periosteum protects the bone, serves as a point of

attachment for muscle, and contains blood vessels that

nourish the underlying bone. Because the periosteum

carries the blood supply to the underlying bone, any

injury to this structure has serious consequences to the

health of the bone. Like any other organ the loss of

blood supply can cause its death.

Articular cartilage- The articular cartilage is found on

the outer surface of the epiphysis. It forms a smooth,

shiny surface that decreases friction within a joint.

Because a joint is also called an articulation, this

cartilage is called articular cartilage.

TYPES OF BONES • Long bones. Long bones are longer than they are

wide. They are found in the arms and legs.

• Short bones. Short bones are shaped like cubes and are found primarily in the wrist and ankles.

• Flat bones. Flat bones are thin, flat, and curved. They form the ribs, breastbone, and skull.

• Irregular bones. Irregular bones are different shaped and are not classified as long, short, or flat. They include the hip bones, vertebrae, and various bones in the skull.

• Sesamoid bones. Sesamoid bones are small round bony masses embedded in certain tendons that may be subjected to compression and tension. The largest sesamoid bone is the patella, which is embedded in the tendon of the quadriceps femoris at the knee.

Short, flat, and irregular bones are all made of

spongy bone covered with a thin layer of

compact bone. Red bone marrow is found

within the spongy bone.

The joint surfaces of bones are covered with

articular cartilage, which provides a smooth

surface. Covering the rest of the bone is the

periosteum.

OSSIFICATION

How does bone form? The 3-month-old fetus has an early skeleton-like framework composed of cartilage and connective tissue membrane. As the fetus matures, the cartilage and connective tissue change into bone. the formation of bones is called ossification. Ossification occurs in different ways in flat and long bones.

Ossification of flat bones • In the fetus, the flat bones consist of a thin

connective tissue membrane. Ossification begins when osteoblasts or bone forming cells, migrate to the region of the flat bones. The osteoblasts secrete calcium and other minerals into the spaces between the thin connective tissue membranes thereby forming bone. This type of ossification involves replacement of thin membrane with bone.

• This is termed intermembranous ossification.

1=connective tissue; 2= osteoblasts; 3= osetocytes;

4=bone spicule

Ossification of long bones • Ossification of long bones occurs as bone tissue

replaces cartilage. The fetal skeleton is comprised largely of cartilage, and the layout of the cartilage in the fetus provides a model for bone formation. As the baby matures, osteoblasts invade the cartilage and gradually replace the cartilage with bone.

• This process continues in each long bone until all but the articular cartilage and the epiphyseal plate have been replaced by bone. By the time the fetus has fully matured, most cartilage of the body has been replaced by bone. Only isolated pieces of cartilage such as the bridge of the nose and the parts of the ribs, remain.

• Termed endochondral ossification

GROWING BONES

Maturation from infancy to adulthood is

characterized by two types of bone

growth. Bones grow longitudinally and

determine the height of an individual.

Bones also grow thicker and become

wider so as to support the weight of the

adult body.

Growing Taller • Longitudinal bone growth occurs at the

epiphyseal plate or growth plate.

• Longitudinal bone growth ceases when the growth plate becomes ossified or hardened. This plate or disc is sensitive to the effects of certain hormones, especially growth hormone and sex hormones.

• GH stimulates growth at the plate, making the child taller. The sex hormones estrogen and testosterone, however, cause the plate to seal or fuse, thereby inhibiting further longitudinal growth.

How Bones Develop

Why are females generally

shorter than males?

The growth plates or epiphyseal plates are

generally more sensitive to the effects of

estrogen than to those of testosterone.

During puberty in the female, the rising levels

of estrogen seal the epiphyseal plate earlier

than testosterone does in males. The effects

of the male hormone, testosterone, are felt at

a later stage. Thus, females stop growing

earlier than males do.

• Because the epiphyseal disc or plate

plays such a crucial role in longitudinal

bone growth, injury to the plate can

severely retard bone growth. A child

who injures the plate in a tibia, for

instance, may end up with that leg

considerably shorter than the non-

injured leg.

Injury and Repair

Fractures of the bones are classified in a number of

ways.

• A simple fracture involves a single fracture line

through a bone.

• A comminuted fracture is one in which the bone

has been fractured into two or more fragments.

• An open fracture is one in which the fractured

bone penetrates the skin.

Can you diagnose what type of fracture this is?

Other fractures, or breaks, include: a greenstick, spiral,

transverse and compressional fracture.

So how do you repair a

fractured bone?

“Can I get a second opinion?”

Dangers of Fractures

1. Loss of blood

2. Damage to soft tissues.

3. Nerve damage

4. Infection

5. Retardation of growth

6. Malformation of normal bone structure

Bone Remodeling Steps involved in repairs of fractures

a. Formation of a fracture hematoma – a clot is formed where blood vessels are broken

b. Fibrocartilaginous callus formation (soft callus) – conversion of the clot into granulation tissue due to invasion of capillaries into the area creating a structure called a procallus. Now, fibroblasts and osteogenic cells invade the procallus giving rise to a fibrocartilaginous callus.

c. Bony callus formation (hard callus) – osteogenic cells differentiate into osteoblasts which produce the trabeculae of spongy bone. Fibrocartilage is converted into bone giving rise to the bony callus. Duration of about six weeks.

d. Bone remodeling – compact bone replaces spongy bone. Controlled by osteoclast activity. Duration lasts about one year.

Here you can see the typical ecchymosis (bruising) that

accompanies a break.

Calcium homeostasis

a. Parathyroid hormone (PTH) – the “anti-bone” hormone

1. Produced by the parathyroid glands

2. Promotes reabsorption of bone matrix….by

3. Increasing the number and stimulating the activity of

osteoclasts.

b. Calcitonin (CT)

1. Secreted by the thyroid gland’s parafollicular cells

2. Functions in several ways simultaneously:

(a) inhibits activity of osteoclasts

(b) speeds blood calcium uptake by bone

(c) accelerates calcium deposition into bones

Skeletal System Disorders

• Leukemia

• Bursistis

• Osteoporosis

• Spina bifida

• Scurvy

• Arthritis

• Rickets

• Talipes equinovarus

• Scoliosis

• Kyphosis

• Fracture

• Dislocation (luxation)

• Subluxation

Leukemia

In people with leukemia, the bone marrow

produces abnormal white blood cells.

The abnormal cells are leukemia cells.

At first, leukemia cells function almost

normally. In time, they may crowd out

normal white blood cells, red blood

cells, and platelets. This makes it hard

for blood to do its work.

An abnormal amount of large WBC’s is one indicator

of leukemia.

Bursitis Wherever your bones, tendons, and ligaments

move against each other, particularly near

joints, the points of contact are cushioned by

small fluid-filled sacs called bursae. By

reducing friction, each of the more than 150

bursae in your body helps the joints operate

smoothly through the full range of natural

movement. But when a bursa becomes

irritated and swollen, it's called bursitis -- or

inflammation of the bursa.

Prepatellar bursitis.

Inflammation of the

patellar bursae directly

over the patella.

Osteoporosis Osteoporosis is a disease in

which bones become

fragile and more likely to

break. If not prevented or

if left untreated,

osteoporosis can progress

painlessly until a bone

breaks. These broken

bones, also known as

fractures, occur typically

in the hip, spine, and wrist.

Spina Bifida

Spina bifida (also called meningocele or myelomeningocele) is a defect that comes from a problem in the very early development of the unborn child. It happens when some of the back bones (vertebrae) do not close over the center tube of nerves (spinal cord). As a result, a soft unprotected area is left, which may bulge through the skin as a dark bag. This 'bag of nerves' is covered by a very thin layer (membrane) which may leak liquid from the spinal cord and brain.

Scurvy

A condition in which there is a lack of vitamin

C in the diet. Vitamin C in necessary in the

development of connective tissues, lipid and

vitamin metabolism, synthesis of

neurotransmitters, immunity and wound

healing. Symptoms include fatigue, joint

aches, bleeding gums, leg rashes and

painful leg edema.

Scurvy was once a problem for sailors who were at sea for

months at a time without fresh fruits in their diets.

Arthritis Nearly 40 million

Americans have arthritis, which causes joints to become inflamed or swollen. There are more than 100 types of arthritis that affect the joints and connective tissues (tendons and ligaments) of the body.

Rickets Rickets is caused by a deficiency in vitamin D.

During growth, human bone is made and

maintained by the interaction of calcium,

phosphorus, and vitamin D. Calcium is deposited

in immature bone (osteoid) in a process called

calcification, which transforms immature bone

into its mature and familiar form. However, in

order to absorb and use the calcium available in

food, the body needs vitamin D. In rickets, the

lack of this important vitamin leads to low

calcium, poor calcification, and deformed bones.

Talipes equinovarus (Clubfoot)

Talipes equinovarus (TEV) is a compound

foot disorder in which the primary

deforming force is in the talus. In the TEV

foot, the talar head and neck excessively

adducted, plantarflexed and medially

rotated with respect to the body of the talus.

TEV may be congenital or acquired due to

neuromuscular diseases or trauma.

Dislocation (luxation)

Forceful displacement of an articulating bone

to an abnormal position, usually

accompanied by damage to tendons,

ligaments, the articular capsule, or other

structures.

A subluxation is a partial dislocation.

The Elephant Man Joseph Merrick, the

Elephant Man, was once considered to have been afflicted with either elephantiasis or neurofibromatosis type I. However, it is now generally believed that Merrick suffered from the very rare Proteus syndrome or perhaps a combination of the two conditions.

Merrick; 1862-1890

Proteus syndrome Named for the Greek god who could change his shape, this rare hereditary disorder is characterized by multiple lesions of the lymph nodes (lipolymphohemangiomas), overgrowth of one side of the body (hemihypertrophy), an abnormally large head (macrocephaly), partial gigantism of the feet, and darkened spots or moles (nevi) on the skin. Merrick's appearance, and especially his skeleton, carry all the hallmarks of the disorder, although apparently an extremely severe case. His head was so large that the hat he wore measured three feet in circumference.

Based on DNA testing and CT

scans, a computerized morph of

what Joseph Merrick would have

looked like had he not suffered

from the disease.