Functions of the Skeletal System Summary Questions

BONE TISSUE AND THE

SKELETAL SYSTEM

Bone is a living tissue.

• Unlike the bones of a fossil made inert by a process of mineralization, a child’s bones will continue to grow and develop while contributing to the support and function of other body systems. (credit: James Emery)

 

Introduction

Chapter Objectives

After studying this chapter, you will be able to:

• List and describe the functions of bones
• Describe the classes of bones
• Discuss the process of bone formation and development
• Explain how bone repairs itself after a fracture
• Discuss the effect of exercise, nutrition, and hormones on bone tissue
• Describe how an imbalance of calcium can affect bone tissue

 

Bones make good fossils.

• While the soft tissue of a once living organism will decay and fall away over time, bone tissue will, under the right conditions, undergo a process of mineralization, effectively turning the bone to stone.
• A well-preserved fossil skeleton can give us a good sense of the size and shape of an organism, just as your skeleton helps to define your size and shape.
• Unlike a fossil skeleton, however, your skeleton is a structure of living tissue that grows, repairs, and renews itself.
  • The bones within it are dynamic and complex organs that serve a number of important functions, including some necessary to maintain homeostasis.

 

6.1 | The Functions of the Skeletal System

By the end of this section, you will be able to:

• Define bone, cartilage, and the skeletal system
• List and describe the functions of the skeletal system

 

Bone, or osseous tissue, is a hard, dense connective tissue that forms most of the adult skeleton, the support structure of the body.

• In the areas of the skeleton where bones move (for example, the ribcage and joints), cartilage, a semi-rigid form of connective tissue, provides flexibility and smooth surfaces for movement.

 

The skeletal system is the body system composed of bones and cartilage and performs the following critical functions for the human body:

• supports the body
• facilitates movement
• protects internal organs
• produces blood cells
• stores and releases minerals and fat

 

Support, Movement, and Protection

The most apparent functions of the skeletal system are the gross functions -those visible by observation.

• Simply by looking at a person, you can see how the bones support, facilitate movement, and protect the human body.
  • Just as the steel beams of a building provide a scaffold to support its weight, the bones and cartilage of your skeletal system compose the scaffold that supports the rest of your body.
• Without the skeletal system, you would be a limp mass of organs, muscle, and skin.

 

Bones also facilitate movement by serving as points of attachment for your muscles.

• While some bones only serve as a support for the muscles, others also transmit the forces produced when your muscles contract.
• From a mechanical point of view, bones act as levers and joints serve as fulcrums.
  • Unless a muscle spans a joint and contracts, a bone is not going to move.

 

 

Bones act as levers when muscles span a joint and contract.

 

Bones also protect internal organs from injury by covering or surrounding them.

• For example, your ribs protect your lungs and heart, the bones of your vertebral column (spine) protect your spinal cord, and the bones of your cranium (skull) protect your brain.

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The cranium completely surrounds and protects the brain from non-traumatic injury.

 

Orthopedist

An orthopedist is a doctor who specializes in diagnosing and treating disorders and injuries related to the musculoskeletal system.

• Some orthopedic problems can be treated with medications, exercises, braces, and other devices, but others may be best treated with surgery.

 

An orthopedist will sometimes prescribe the use of a brace that reinforces the underlying bone structure it is being used to support.

 

While the origin of the word “orthopedics” (ortho- = “straight”; paed- = “chil ”), literally means “straightening of the child,” orthopedists can have patients who range from pediatric to geriatric.

• In recent years, orthopedists have even performed prenatal surgery to correct spina bifida, a congenital defect in which the neural canal in the spine of the fetus fails to close completely during embryologic development.

 

Orthopedists commonly treat bone and joint injuries but they also treat other bone conditions including curvature of the spine.

• Lateral curvatures (scoliosis) can be severe enough to slip under the shoulder blade (scapula) forcing it up as a hump.
• Spinal curvatures can also be excessive dorsoventrally (kyphosis) causing a hunch back and thoracic compression.
  • These curvatures often appear in preteens as the result of poor posture, abnormal growth, or indeterminate causes.
  • Mostly, they are readily treated by orthopedists.
• As people age, accumulated spinal column injuries and diseases like osteoporosis can also lead to curvatures of the spine, hence the stooping you sometimes see in the elderly.

 

Some orthopedists sub-specialize in sports medicine, which addresses both simple injuries, such as a sprained ankle, and complex injuries, such as a torn rotator cuff in the shoulder.

• Treatment can range from exercise to surgery.

 

Mineral Storage, Energy Storage, and Hematopoiesis

On a metabolic level, bone tissue performs several critical functions.

• For one, the bone matrix acts as a reservoir for a number of minerals important to the functioning of the body, especially calcium, and phosphorus.
  • These minerals, incorporated into bone tissue, can be released back into the bloodstream to maintain levels needed to support physiological processes.
  • Calcium ions, for example, are essential for muscle contractions and controlling the flow of other ions involved in the transmission of nerve impulses.
• Bone also serves as a site for fat storage and blood cell production.
  • The softer connective tissue that fills the interior of most bone is referred to as bone marrow.
  • There are two types of bone marrow: yellow marrow and red marrow.
    • Yellow marrow contains adipose tissue; the triglycerides stored in the adipocytes of the tissue can serve as a source of energy.
    • Red marrow is where hematopoiesis—the production of blood cells—takes place.
      • Red blood cells, white blood cells, and platelets are all produced in the red marrow.

The head of the femur contains both yellow and red marrow.

• Yellow marrow stores fat.
• Red marrow is responsible for hematopoiesis.

 

6.2 | Bone Classification

By the end of this section, you will be able to:

• Classify bones according to their shapes
• Describe the function of each category of bones

 

The 206 bones that compose the adult skeleton are divided into five categories based on their shapes.

• Their shapes and their functions are related such that each categorical shape of bone has a distinct function.

Bones are classified according to their shape.

 

Long Bones

A long bone is one that is cylindrical in shape, being longer than it is wide.

• Keep in mind, however, that the term describes the shape of a bone, not its size.
• Long bones are found in the arms (humerus, ulna, radius) and legs (femur, tibia, fibula), as well as in the fingers (metacarpals, phalanges) and toes (metatarsals, phalanges).
• Long bones function as levers; they move when muscles contract.

 

Short Bones

A short bone is one that is cube-like in shape, being approximately equal in length, width, and thickness.

• The only short bones in the human skeleton are in the carpals of the wrists and the tarsals of the ankles.
• Short bones provide stability and support as well as some limited motion.

 

Flat Bones

The term “ flat bone” is somewhat of a misnomer because, although a flat bone is typically thin, it is also often curved.

• Examples include the cranial (skull) bones, the scapulae (shoulder blades), the sternum (breastbone), and the ribs.
• Flat bones serve as points of attachment for muscles and often protect internal organs.

 

Irregular Bones

An irregular bone is one that does not have any easily characterized shape and therefore does not fit any other classification.

• These bones tend to have more complex shapes, like the vertebrae that support the spinal cord and protect it from compressive forces.
• Many facial bones, particularly the ones containing sinuses, are classified as irregular bones.

 

Sesamoid Bones

A sesamoid bone is a small, round bone that, as the name suggests, is shaped like a sesame seed.

• These bones form in tendons (the sheaths of tissue that connect bones to muscles) where a great deal of pressure is generated in a joint.
• The sesamoid bones protect tendons by helping them overcome compressive forces.
• Sesamoid bones vary in number and placement from person to person but are typically found in tendons associated with the feet, hands, and knees.
• The patellae (singular = patella) are the only sesamoid bones found in common with every person.

 

Bone Classifications

Bone Classifications	Features	Function(s)	Examples
Long	Cylinder-like shape, longer than it is wide	Leaverage	Femur, tibia, fibula, metatarsals, humerus, ulna, radius, metacarpals, phalanges
Short	Cube-like shape, approximately equal in length, width, and thickness	Provide stability, support, while allowing for some motion	Carpals, tarsals
Flat	Flat Thin and curved	Points of attachment for muscles; protectors of internal organs	Sternum, ribs, scapulae, cranial bones
Irregular	Complex shape	Protect internal organs	Vertebrae, facial bones
Sesamoid	Small and round; embedded in tendons	Protect tendons from compressive forces	Patellae

 

 

YOU WILL NEED TO MEMORIZE THE MAIN HUMAN BONES: 

Here is a list of the bones on the test:

• Cervical Vertebrae
• Calcaneus - heal
• Ribs
• Skull
• Carpals - wrist
• Tarsals - ankle
• Phalanges - fingers and toes
• Thoracic Vertebrae
• Sternum
• Clavicle
• Lumbar vertebrae
• Sacrum
• Scapula
• Patella - kneecap
• Coccyx - tailbone
• Metacarpals - hand
• Femur
• Metatarsals - foot
• Humerus
• Ulna
• Tibia
• Fibula
• Radius
• Phalanges - fingers and toes
• Pelvis

 

 

 

 

 

 

 

 

 

As well as these bones of the Skull: 

• Frontal
• temporal
• occipital
• parietal
• zygomatic arch
• mandible
• maxilla
• nasal
• mastoid process

 

 

Watch This Video to START LEARNING:

How to learn the human bones. (Links to an external site.)