CHAPTER 5

Bones

FUNCTIONS OF THE BONESOur skeletal system provides 5 main functions for our body…

5 MAIN FUNCTIONS OF BONES:

1. Support:“Reinforced Concrete of Body”Forms internal framework that supports

and anchors all soft organsExamples:

Bones of legs act as pillars to support the body trunk when we stand

Rib cage supports the thoracic wall

5 MAIN FUNCTIONS OF BONES:

2. Protection:Bones protect soft body organsExamples

Skull protects brain Vertebrae protect spinal chord Rib cage protects organs of thorax

5 MAIN FUNCTIONS OF BONES:

3. Movement:Skeletal muscles attached to bones by

tendons use the bones as levers to move the body and its parts!

5 MAIN FUNCTIONS OF BONES:

4. Storage:Fat is stored in the internal cavities of

bonesBones itself serves as a storehouse for

minerals…the most important being Calcium and Phosphorous (others are stored as well)

CALCIUM IN THE BONES… A small amount of calcium in its ion form (Ca2+)

must be present in the blood at all times for 1. the nervous system to transmit messages 2. for muscles to contract3. for blood to clot

Most of the body’s calcium is deposited in the bones as calcium salts; the bones are a convenient place to get more calcium ions for the blood as they are used up.

Problems occur if there is not enough OR too much calcium in the blood…hormones control the movement of calcium to and from the bones and blood according to the needs of the body.

5 MAIN FUNCTIONS OF BONES:

5. Hematopoiesis:AKA: Blood cell formationOccurs within the marrow cavities of

certain bones.

CLASSIFICATION

OF BONES

• The adult skeleton is composed of 206 bones

• There are 2 basic types of bone tissue or “osseous”

• There are 4 shape groups as well

2 TYPES OF OSSEOUS (BONE TISSUE):

Compact BoneDenseLooks smooth and

homogenous

Spongy BoneComposed of

small needlelike pieces of bone and lots of open space

4 BONE SHAPE GROUPS: 1. Long bones

Longer than they are wide Have a shaft with heads at both ends Mostly compact bone All the bones of the limbs, except the wrist and

ankle bones are long bones 2. Short bones

Generally cube-shaped Contain mostly spongy bone The bones of the wrist and ankle are short bones Sesamoid bones (which form within tendons) are a

special type of short bone. The best known examples is the patella

4 BONE SHAPE GROUPS: 3. Flat bones

Thin, flattened, and usually curved Have 2 thin layers of compact bone

sandwiching a layer of spongy bone between them

Most bones of the skull, ribs, and the sternum (breastbone) are flat bones

4. Irregular bones Bones that do not fit the preceding categories The vertebrae, which make up the spinal

column, and the hip bones fall into this group

EXAMPLES OF EACH BONE SHAPE IN THE BODY…

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STRUCTURE OF A LONG

BONEGross and Microscopic Anatomy

GROSS ANATOMY OF LONG BONE Diaphysis or

ShaftMakes up most

of the bone’s length and is composed of compact bone

Is covered by periosteum (a fibrous connective tissue membrane)

GROSS ANATOMY OF LONG BONE Epiphyses

Ends of the long bone Consists of a thin layer of compact

bone enclosing an area filled spongy bone

Is covered by articular cartilage instead of periosteum. Articular cartilage is a smooth, slippery surface…friction at joint surfaces is decreased.

In adult bones, there is a thin line of bony tissue spanning the epiphysis that looks a bit different from the rest of the bone in that area called the epiphyseal line which is a remnant of the epiphyseal plate which is a flat plate of cartilage seen in a young, growing bone. Epiphyseal plates cause the lengthwise growth of a long bone. By the end of puberty, when hormones inhibit long bone growth, epiphyseal plates have been completely replaced by bone, leaving only the epiphyseal lines to mark their previous location!

GROSS ANATOMY OF LONG BONE

Medullary Cavity In adults the cavity of the

shaft is primarily a storage area for adipose (fat) tissue.

It is called the yellow marrow or medullary cavity.

However, in infants this area forms blood cells, and red marrow is found there.

In adult bones, red marrow is confined to the cavities of spongy bone of flat bones and the epiphyses of some long bones.

GROSS ANATOMY OF LONG BONE Bone Markings

Bone surfaces are not smooth, but scarred with bumps, holes, and ridges. These “bone markings” reveal where muscles, tendons, ligaments were

attached and where blood vessels and nerves passed. See page 134. 2 types of bone markings

Projections or processes-grow out from bone surface. Depressions or cavities-indentations in the bone.

MICROSCOPIC ANATOMY OF LONG BONE To the naked eye, spongy bone looks open and spiky,

whereas, compact bone looks very dense…. However, when looking at compact bone through a

microscope, one can see that it has a complex structure. It is riddles with passageways carrying nerves, blood vessels and the like, which provide the living bones cells with nutrients and a route for waste disposal.

MICROSCOPIC ANATOMY OF LONG BONE Osteocytes: mature bone cells found in tiny

cavities within the matrix called lacunae. The lacunae are arranged in concentric

circles called lamellae around central “Haversian” canals.

MICROSCOPIC ANATOMY OF LONG BONE Each complex consisting of central canal and matrix rings is called an

osteon, or Haversian system. Central canals run lengthwise through the bony matrix, carrying blood

vessels and nerves to all areas of the bone. Tiny canals, canaliculi, radiate outward from the central canals to all

lacunae. The canaliculi form a transportation system that connects all the bone cells to the nutrient supply through the hard bone matrix…because of this bone cells are well nourished in spite of the hardness of the matrix, and bone injuries heal quickly and well.

MICROSCOPIC ANATOMY OF LONG BONE The communication pathway from the

outside of the bone to its interior (and the central canals) is completed by perforating “Volkman’s” canals, which run into the compact bone at right angles to the shaft.

SUBDIVISIONS OF THE

SKELETONAxial and Appendicular

SUBDIVISIONS OF THE SKELETON

Axial:The bones that

form the longitudinal axis of the body.

Appendicular:The bones of the

limbs and girdles.

SPINE (VERTEBRAL COLUMN)

Extends from the skull to the pelvis where it transmits the weight of the body to the lower limbs.

Formed from 26 irregular bones connected and reinforced by ligaments in such a way that a flexible, curved structure results.

Running through the central cavity of the vertebral column is the delicate spinal cord.

Before birth, the spine consists of 33 separate bones called vertebra, but 9 of these eventually fuse to form the 2 composite bones, the sacrum and the coccyx.

Of the 24 single bones, the 7 vertebrae of the neck are cervical vertebrae, the next 12 are the thoracic vertebrae, and the remaining 5 supporting the lower back are lumbar vertebrae.

The single vertebrae are separated by pads of flexible fibrocartilage-intervertebral discs-which cushion the vertebrae.

The disks and the S-shaped structure of the vertebral column work together to prevent shock to the head when we walk or run. They also make the body trunk flexible

IN ADDITION TO BONES, THE SKELETAL SYSTEM

INCLUDES JOINTS,

CARTILAGES, AND

LIGAMENTS. WE ARE GOING TO LOOK CLOSER AT JOINTS…

JOINTS AKA “articulations” Give the body flexibility and allow

movement to occur. With one exception (the hyoid bone of

the neck), every bone in the body forms a joint with at least one other bone!

Joints have 2 functions:1. They hold the bones together2. Give the rigid skeleton mobility

JOINTS ARE CLASSIFIED IN 2 WAYS-FUNCTIONALLY & STRUCTURALLY

Functional Classification Structural Classification

Focuses on the amount of movement allowed by the joint Synarthroses:

immovable joints Amphiarthroses:

slightly movable joints

Diarthroses: freely movable joints

Based on whether fibrous tissue, cartilage, or a joint cavity separates the bony regions at the joint Fibrous: bones united by fibrous

tissue, Example- Skull sutures Cartilaginous: bone ends are

connected by cartilage, Example-pubic symphysis of pelvis and intervertebral joints of spinal column

Synovial: those in which the bone ends are separated by a joint cavity containing synovial fluid, account for ALL joints of the limbs, examples and more to follow….

TYPES OF SYNOVIAL JOINTS BASED ON SHAPEREFER TO PAGE 166 AS WE DISCUSS!

Plane joint: articular surfaces are flat and only short slipping or gliding movements are

allowed. Hinge joint:

the cylindrical end of one bone fits into a trough-shaped surface on another bone…angular movement is allowed in just one plane (like a door hinge).

Pivot joint: the rounded end of one bone fits into a sleeve or ring of bone…the rotating

bone can turn only around its long axis. Condyloid joint:

“knuckle-like”, the egg shaped articular surface of one bone fits into an oval concavity in another…these joints allow the moving bone to travel from side to side and back and forth but it cannot rotate around its long axis.

Saddle joint: each articular surface has both convex and concave areas, like a saddle…these

joints allow essentially the same movement as the condyloid joint. Ball & Socket joint:

the spherical head of one bone fits into a round socket in another…these multiaxial joints allow movements in all axes, including rotation! They are the most freely moving joints.

DEVELOPMENTAL ASPECTS OF THE SKELETON

Read page 168 starting at “development aspects of the skeleton” through page 169 stopping before “prove it yourself”.

FONTANELS When a baby is born, its skeleton is still

unfinished. In a newborn, the skull has fibrous regions that have yet to be converted to bone.

These fibrous membranes are called fontanels or you may have heard them called “soft spots”. The rhythm of the baby’s pulse can be felt in these areas.

The fontanels allows compression during the birthing process and give room for growth during the later part of pregnancy and infancy.

The fontanels are gradually converted to bone during the early part of infancy and can no longer be felt by 22-24 months after birth.

There are 4 fontanels: Anterior-largest on top of head (one you may

know of) Posterior Mastoid Sphenoid

A FEW INTERESTING, RANDOM PARTS OF SKELETAL SYSTEM

Mandible-lower jaw bone…is the largest and strongest bone of the face.

Hyoid bone-closely related to the mandible, but not really a part of the skull…is unique because it is the only bone of the body that does not articulate directly with any other bone…it is suspended in the mid-neck region, held in place by ligaments!

Phalanges-each hand contains 14 phalanges…there are three in each finger (proximal, middle, and distal) except in the thumb, which only has two (no middle).

HANDS & FEET

ANOTHER INTERESTING

THOUGHT…Male and Female Skeletons are different…the pelvic girdle…Record the differences

listed on page 159 in your text, then refer to your handout.

A FEW COMMON

DISORDERS OF THE SKELETAL

SYSTEM:ScoliosisFracturesArthritis

GoutOsteoporosis

ABNORMAL SPINE CURVATURES

Disorders of the spine may be congenital (present at birth) or result from disease, poor posture, or unequal muscle pull on the spine. There are 3 main types of abnormal spinal curvatures:

1. Scoliosis2. Kyphosis3. Lordosis

FRACTURES For their relatively low mass, bones are

amazingly strong. Despite their remarkable strength, bones are susceptible to fractures, or breaks, all through life.

A fracture is treated by reduction (which is the realignment of the broken bone ends.) Closed reduction: bone ends are coaxed back

into their normal position by the physician’s hands.

Open reduction: surgery is performed and the bone ends are secured together with pins or wires.

After the broken bone is reduced, it is immobilized by a cast or traction to allow the healing process to begin. The healing process is 6-8 weeks, but it is much longer for large bones and for the bones of elderly people (because of their poorer circulation).

Table in your book: pg. 137

ARTHRITIS

Describes over 100 different inflammatory or degenerative diseases that damage the joints.

In all its forms, arthritis is the most widespread, crippling disease in the US… 1 out of 7 Americans suffer its ravages.

All forms of arthritis have the same initial symptoms: pain, stiffness, and swelling of the joint. Then, depending on the specific form, certain changes in the joint structure occur.

CHRONIC FORMS OF ARTHRITIS INCLUDE: Osteoarthritis (OA)

Most common form, typically affects the aged, also called “wear & tear arthritis” Over time, there is a softening, fraying, and eventual breakdown of the cartilage…as

the disease progresses, the bone thickens and extra bone tissue, called “bone spurs” grows around the eroded cartilage and restricts joint movement

Usually slow and irreversible, but is rarely crippling…symptoms are typically controllable.

Rheumatoid arthritis (RA) Onset usually occurs between the ages of 40-50, but may occur at any age. Affects 3

times as many women as men. The course of RA is marked by remissions and flare-ups Autoimmune disease-a disorder in which the body’s immune system attempts to

destroy its own tissue. Current therapy for RA involves many different kinds of drugs and exercise is

recommended…replacement joints or bone removal is a last resort for severely crippled RA patients.

Gouty arthritis “gout” A disease in which uric acid (a normal waste product of nucleic acid metabolism)

accumulates in the blood and may be deposited as needle-shaped crystals in the soft tissues of joints which leads to an agonizingly painful attack that typically affects a single joint, often in the great toe!

Gout is most common in males and rarely appears before the age of thirty…it tends to run in families, so genetic factors are definitely implicated.

Untreated gout can be very destructive; the bone ends fuse and the joint becomes immobilized…fortunately, several drugs are successful in preventing gout attacks.

OSTEOPOROSIS A bone thinning disease that afflicts half of

women over 65 and some 20% of men over the age of 70.

Makes the bones so fragile that even a hug or a sneeze can cause bones to fracture.

The bones of the spine and the neck of the femur are particularly susceptible…vertebral collapse frequently results in a hunched over posture (kyphosis) also known as “dowager’s hump”

Estrogen helps to maintain the health and normal density of a woman’s skeleton, and the estrogen deficiency that occurs after menopause is strongly implicated as a cause of osteoporosis

Other factors may include diet poor in calcium and protein, lack of vitamin D, smoking, and insufficient weight-bearing exercise to stress bones.