Introduction to The Skeletal System

Lesson 2.1

Introduction

• The framework of bones and cartilage that protects our organs and allows us to move is called the skeletal system.

• The branch of medicine that deals with the preservation and restoration of the skeletal system, articulations (joints), and associated structures is called orthopaedics.

Skeleton

• Greek for skeletos, which means “dried up”

• Are bones made of living tissue?

• Bone cells, fat cells, and blood vessels as well as non living minerals and water

The human skeleton

• Adult human made up of _____ bones

• Account for 14% of body weight

• Do we have more or less or the same number of bones at birth? Why? ____ bones

The human skeleton

• The longest bone is the _______

• The smallest bone is the _______ found in the inner ear

• Some parts of the body are made of many bones. Each hand has _____ bones

Differences between males and females?

• Males have longer and thicker arm and leg bones

• Females have a wider ______. Why?

The skeletal system performs the following functions:

• Support

• Protection (for internal organs)

• Movement

• Mineral storage (Calcium and phosphorous)

• Storage of blood cell-producing cells

Structure of the skeleton; Axial • Axial skeleton made up of 80 bones;

the _____ protects the brain

the _________ protects the spinal cord

the________ protects heart and lungs

• Most muscles originate from

axial skeleton since it’s medially

located “core muscles”

Appendicular Skeleton

• Made of 126 bones and include moveable limbs and supporting structures (girdles)

• Upper limbs are attached to the pectoral girdle (shoulder) and the lower limbs are attached to the pelvic girdle (hips)

Consists of:

1. The pectoral gridle (shoulder)

2. Pelvic girdle (hip)

3. The upper limbs

4. The lower limbs

Appendicular skeleton

1.Pectoral Girdle

Consists of: – Scapula (________) – Clavicle (_________)

Allows the upper limb great mobility The sternoclavicular joint is the only point

of attachment between the axial skeleton and the pectoral girdle

Scapula

Clavicle

2. Pelvic Girdle

• Formed by pair of os coxae (hip bones)

• supports the bladder and abdominal contents

• Attachment:– Posteriorly – join with the sacrum – Anteriorly - join to each other anteriorly– Laterally – join to the head of the

______through a cup-shaped acetabulum cavity

Types of Bones

• There are five principal types of bones• • All bones are classified based on shape

1. Long bones (e.g. thighs, legs, toes, arms, forearms,

and fingers)

• greater length than width• consist of a shaft and extremities (ends)• slightly curved for strength• consist mostly of compact bone (dense

bone with few spaces) but also contain considerable amounts of spongy bone (bone with large spaces)

2. Short bones (e.g. wrist, ankle bones)

• Somewhat cube-shaped and nearly equal in length and width

• Spongy except at the surface where there is a thin layer of compact bone

3. Flat bones(e.g. cranial bones, sternum, ribs,

scapulas)

• Generally thin and composed of two more or less parallel plates of compact bone enclosing a layer of spongy bone

• Flat bones afford considerable protection and provide extensive areas for muscle attachment

4. Irregular bones (e.g. vertebrae, and certain facial

bones)

• Have complex shapes and cannot be grouped into any of the other three categories

• They vary in the amount of spongy and compact bone

5. Sesamoid bones

• Are small bones in tendons where considerable pressure develops, for instance, the wrist

• Their number varies greatly from person to person

• All people have at least two sesamoid bones: the patella (kneecap)

Bone Composition

medullary

• Red marrow is where hematopoiesis occurs

• Yellow marrow is made up of adipose (__) tissue

Bone Composition Cont’d

• Bone is very strong for its relatively light weight

• The major components of bone are:– Calcium carbonate– Calcium phosphate– Collagen– Water

Bone Composition Cont’d

• Calcium carbonate and calcium phosphate:– Make up 60-70% of bone weight– Provide much of the bone’s stiffness and resistance to

pressing or squeezing forces

• Collagen (a protein):– Gives bone its characteristic flexibility and contributes to its

ability to resist pulling and stretching forces – With aging, collagen is lost progressively and bone becomes

more brittle.

• Water– Bone consists of much smaller proportion of water than

other body parts

Bone Classification

• According to the degree of porosity, bone can be classified into two general categories:

– Cortical bone (low porosity)

– Spongy or cancellous bone (high porosity)

Cancellous bone Compact Bone

•Porosity •High (Low mineral content and high collagen)

•Low (High mineral content and low collagen)

•Structure •Honey comb •Compact

•Characteristic •Provides more flexibility but is not as stress resistant

•Stiffer and can resist greater stress but less flexible

•Function •Shock absorption due to its better ability to change shape are important

•Withstanding stress in body areas that are subject to higher impact loads

•Location •e.g., vertebrae •Long bones (e.g., bones of the arms and legs)

Effect of Fitness on Bone

• When bones are subjected to regular physical activity and habitual loads, they tend to become denser and more mineralized– e.g. Right forearm of the right-handed tennis player is

more dense than her left one from using it more frequently

• Inactivity works in the opposite direction, leading to a decrease in weight and strength called ______. – e.g. Loss of bone mass has been noted in bed-ridden

patients, inactive senior citizens, and astronauts

Games

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