Bone Anatomy

Question 1

What is the bone made of?

Answer 1

Each bone is a complex living organ that is made up of many cells, protein fibers, and minerals.

Question 2

Where are new blood cells produced?

Answer 2

New blood cells are produced by the red bone marrow inside of our bones.

Question 3

How many bones make up the adult skeleton system?

Answer 3

206 individual bones

Question 4

What are the two main bone divisions?

Answer 4

Bones are divided into the axial skeleton and the appendicular skeleton

Question 5

Where does the axial skeleton run?

Answer 5

The axial skeleton runs along the body’s midline axis and is made up of 80 bones

Question 6

What makes up the axial region?

Answer 6

Skull
Hyoid
Auditory ossicles
Ribs
Sternum
Vertebral column

Question 7

What makes up the appendicular skeleton?

Answer 7

The appendicular skeleton is made up of 126 bones in the folowing regions:

Upper limbs
Lower limbs
Pelvic girdle
Pectoral (shoulder) girdle

Question 8

What percent of the body mass does the skeleton account for?

Answer 8

The skeleton makes up about 30-40% of an adult’s body mass.

Question 9

What is the bone made of?

Answer 9

Roughly half of the bone matrix’s mass is water, while the other half is collagen protein and solid crystals of calcium carbonate and calcium phosphate.

Question 10

Where are living bone cells found?

Answer 10

Living bone cells are found on the edges of bones and in small cavities inside of the bone matrix. These cells make up very little of the total bone mass

Question 11

The living bone cells allow bones to

Answer 11

Grow and develop
Be repaired following an injury or daily wear
Be broken down to release their stored minerals

Question 12

What are the 5 types of bones?

Answer 12

Long
Short
Flat
Irregular
Sesamoid

Question 13

What are long bones?

Answer 13

Long bones are longer than they are wide and are the major bones of the limbs. Long bones grow more than the other classes of bone throughout childhood and so are responsible for the bulk of our height as adults. A hollow medullary cavity is found in the center of long bones and serves as a storage area for bone marrow. Examples of long bones include the femur, tibia, fibula, metatarsals, and phalanges.

Question 14

What are short bones?

Answer 14

Short bones are about as long as they are wide and are often cubed or round in shape. The carpal bones of the wrist and the tarsal bones of the foot are examples of short bones.

Question 15

What are flat bones?

Answer 15

Flat bones vary greatly in size and shape, but have the common feature of being very thin in one direction. Because they are thin, flat bones do not have a medullary cavity like the long bones. The frontal, parietal, and occipital bones of the cranium—along with the ribs and hip bones—are all examples of flat bones.

Question 16

What are Irregular bones?

Answer 16

Irregular bones have a shape that does not fit the pattern of the long, short, or flat bones. The vertebrae, sacrum, and coccyx of the spine—as well as the sphenoid, ethmoid, and zygomatic bones of the skull—are all irregular bones.

Question 17

What are Sesamoid bones?

Answer 17

The sesamoid bones are formed after birth inside of tendons that run across joints. Sesamoid bones grow to protect the tendon from stresses and strains at the joint and can help to give a mechanical advantage to muscles pulling on the tendon. The patella and the pisiform bone of the carpals are the only sesamoid bones that are counted as part of the 206 bones of the body. Other sesamoid bones can form in the joints of the hands and feet, but are not present in all people.

Question 18

At birth, what are the 3 parts of the long bone separated by?

Answer 18

hyaline cartilage

Question 19

What are the ends of the long bones called?

Answer 19

Each end bone is called an epiphysis (epi = on; physis = to grow)

Question 20

What is the middle bone of the long bones called?

Answer 20

The middle bone is called a diaphysis (dia = passing through)

Question 21

How do the epiphyses and diaphysis bones grow?

Answer 21

They grow towards one another and eventually fuse into one bone. The region of growth and eventual fusion in between the epiphysis and diaphysis is called the metaphysis (meta = after)

Question 22

Once the long bone parts have fused together, where is the only hyaline cartilage left?

Answer 22

The only hyaline cartilage left in the bone is found as articular cartilage on the ends of the bone that form joints with other bones. The articular cartilage acts as a shock absorber and gliding surface between the bones to facilitate movement at the joint.

Question 23

What is the outside of a bone called?

Answer 23

The outside of a bone is covered in a thin layer of dense irregular connective tissue called the periosteum. The periosteum contains many strong collagen fibers that are used to firmly anchor tendons and muscles to the bone for movement. Stem cells and osteoblast cells in the periosteum are involved in the growth and repair of the outside of the bone due to stress and injury. Blood vessels present in the periosteum provide energy to the cells on the surface of the bone and penetrate into the bone itself to nourish the cells inside of the bone. The periosteum also contains nervous tissue and many nerve endings to give bone its sensitivity to pain when injured.

Question 24

What is deep to the periosteum?

Answer 24

Deep to the periosteum is the compact bone that makes up the hard, mineralized portion of the bone. Compact bone is made of a matrix of hard mineral salts reinforced with tough collagen fibers. Many tiny cells called osteocytes live in small spaces in the matrix and help to maintain the strength and integrity of the compact bone.

Question 25

What is deep to the compact bone?

Answer 25

Deep to the compact bone layer is a region of spongy bone where the bone tissue grows in thin columns called trabeculae with spaces for red bone marrow in between. The trabeculae grow in a specific pattern to resist outside stresses with the least amount of mass possible, keeping bones light but strong. Long bones have a spongy bone on their ends but have a hollow medullary cavity in the middle of the diaphysis. The medullary cavity contains red bone marrow during childhood, eventually turning into yellow bone marrow after puberty.

Question 26

What is an articulation?

Answer 26

An articulation, or joint, is a point of contact between bones, between a bone and cartilage, or between a bone and a tooth. Synovial joints are the most common type of articulation and feature a small gap between the bones. This gap allows a free range of motion and space for synovial fluid to lubricate the joint.

Question 27

What's a fibrous joint?

Answer 27

Fibrous joints exist where bones are very tightly joined and offer little to no movement between the bones. Fibrous joints also hold teeth in their bony sockets.

Question 28

What are cartilaginous joints?

Answer 28

Cartilaginous joints are formed where bone meets cartilage or where there is a layer of cartilage between two bones. These joints provide a small amount of flexibility in the joint due to the gel-like consistency of cartilage.

Question 29

What is the skeletal systems primary function?

Answer 29

The skeletal system’s primary function is to form a solid framework that supports and protects the body's organs and anchors the skeletal muscles. The bones of the axial skeleton act as a hard shell to protect the internal organs—such as the brain and the heart—from damage caused by external forces. The bones of the appendicular skeleton provide support and flexibility at the joints and anchor the muscles that move the limbs.

Question 30

What do bones of the skeletal system act as?

Answer 30

The bones of the skeletal system act as attachment points for the skeletal muscles of the body. Almost every skeletal muscle works by pulling two or more bones either closer together or further apart. Joints act as pivot points for the movement of the bones. The regions of each bone where muscles attach to the bone grow larger and stronger to support the additional force of the muscle. In addition, the overall mass and thickness of a bone increase when it is under a lot of stress from lifting weights or supporting body weight.

Question 31

What is Hematopoiesis?

Answer 31

Red bone marrow produces red and white blood cells in a process known as hematopoiesis. Red bone marrow is found in the hollow space inside of bones known as the medullary cavity. Children tend to have more red bone marrow compared to their body size than adults do, due to their body’s constant growth and development. The amount of red bone marrow drops off at the end of puberty, replaced by yellow bone marrow.

Question 32

What do bones store?

Answer 32

The skeletal system stores many different types of essential substances to facilitate growth and repair of the body. The skeletal system’s cell matrix acts as our calcium bank by storing and releasing calcium ions into the blood as needed. Proper levels of calcium ions in the blood are essential to the proper function of the nervous and muscular systems. Bone cells also release osteocalcin, a hormone that helps regulate blood sugar and fat deposition. The yellow bone marrow inside of our hollow long bones is used to store energy in the form of lipids. Finally, red bone marrow stores some iron in the form of the molecule ferritin and uses this iron to form hemoglobin in red blood cells.

Question 33

Growth and Development

Answer 33

The skeleton begins to form early in fetal development as a flexible skeleton made of hyaline cartilage and dense irregular fibrous connective tissue. These tissues act as a soft, growing framework and placeholder for the bony skeleton that will replace them. As development progresses, blood vessels begin to grow into the soft fetal skeleton, bringing stem cells and nutrients for bone growth. Osseous tissue slowly replaces the cartilage and fibrous tissue in a process called calcification. The calcified areas spread out from their blood vessels replacing the old tissues until they reach the border of another bony area. At birth, the skeleton of a newborn has more than 300 bones; as a person ages, these bones grow together and fuse into larger bones, leaving adults with only 206 bones. Flat bones follow the process of intramembranous ossification where the young bones grow from a primary ossification center in fibrous membranes and leave a small region of fibrous tissue in between each other. In the skull these soft spots are known as fontanels, and give the skull flexibility and room for the bones to grow. Bone slowly replaces the fontanels until the individual bones of the skull fuse together to form a rigid adult skull. Long bones follow the process of endochondral ossification where the diaphysis grows inside of cartilage from a primary ossification center until it forms most of the bone. The epiphyses then grow from secondary ossification centers on the ends of the bone. A small band of hyaline cartilage remains in between the bones as a growth plate. As we grow through childhood, the growth plates grow under the influence of growth and sex hormones, slowly separating the bones. At the same time the bones grow larger by growing back into the growth plates. This process continues until the end of puberty, when the growth plate stops growing and the bones fuse permanently into a single bone. The vast difference in height and limb length between birth and adulthood are mainly the result of endochondral ossification in the long bones.