Bones 101

Know your metaphysis from your medullary cavity? Discover the fundamental elements of bone and how structures work together in our latest article.

Why are our bones important?

Bones are a key part of your skeletal system. They have four essential functions:

  1. Support – your bones are joined together to form your skeleton. This supports body movement.
  2. Protect – bones provide the hard protective shield that guards our vital organs.
  3. Produce – inside bones, there is a substance called marrow which comes in two varieties, red and yellow. Red bone marrow contains blood stem cells that can become red blood cells, white blood cells or platelets, whereas yellow bone marrow contains stem cells that can become cartilage, fat or bone2.
  4. Store – bones act as a store for minerals that are used in many systems in the body. These include calcium, phosphorus and vitamin D33

Why are our bones important?

Bones are a key part of your skeletal system. They have four essential functions:

  1. Support – your bones are joined together to form your skeleton. This supports body movement.
  2. Protect – bones provide the hard protective shield that guards our vital organs.
  3. Produce – inside bones, there is a substance called marrow which comes in two varieties, red and yellow. Red bone marrow contains blood stem cells that can become red blood cells, white blood cells or platelets, whereas yellow bone marrow contains stem cells that can become cartilage, fat or bone2.
  4. Store – bones act as a store for minerals that are used in many systems in the body. These include calcium, phosphorus and vitamin D33

External structure of bone

We’re going to be focusing on the structure of long bones, since they are subject to most of the load during daily activities and are crucial for skeletal mobility. 

Long bones appear mostly in the arms and legs, and examples include the femur, clavicle and phalanges. 

Long bones and divided into the following regions:

The diaphysis (shaft) is the middle tubular part of bone, that contributes to most of the bones length. 

The epiphysis is at each end of a long bone. These are enlarged, rounded and filled with spongy bone. Articular cartilage is the smooth, white tissue that covers the epiphysis of bone where they come together to form joints. This allows bones to glide over each other with little friction and acts like a cushion to absorb shock4. In osteoarthritis, the articular cartilage breaks down, leading to joint pain.

The metaphysis is the neck portion of a long bone between the epiphysis and the diaphysis. It contains the growth plate, or epiphyseal plate – a thin disc of cartilage that allows the bone to grow during childhood.

external structure of bone child vs mature

External structure of bone

We’re going to be focusing on the structure of long bones, since they are subject to most of the load during daily activities and are crucial for skeletal mobility. 

Long bones appear mostly in the arms and legs, and examples include the femur, clavicle and phalanges. 

Long bones and divided into the following regions:

The diaphysis (shaft) is the middle tubular part of bone, that contributes to most of the bones length. 

The epiphysis is at each end of a long bone. These are enlarged, rounded and filled with spongy bone. Articular cartilage is the smooth, white tissue that covers the epiphysis of bone where they come together to form joints. This allows bones to glide over each other with little friction and acts like a cushion to absorb shock4. In osteoarthritis, the articular cartilage breaks down, leading to joint pain.

The metaphysis is the neck portion of a long bone between the epiphysis and the diaphysis. It contains the growth plate, or epiphyseal plate – a thin disc of cartilage that allows the bone to grow during childhood.

external structure of bone child vs mature
long bone structure cross section

Internal structure of bone

The image shows a cross-section of long bone. Within bone, there are many different structures carrying out essential functions. 

The periosteum forms a thin membrane of blood vessels and nerves around the bone. Scientists sometimes compare the periosteum of bones to the cambium layer of trees. Just as trees repair themselves and grow in harsh environments, so can your bones.

The outer periosteal layer contributes to the blood supply of your bones and the surrounding muscles. It also contains a network of nerve fibres that transmit messages throughout your body. The inner layer helps to protect your bones and stimulates repair after injury or fracture. 

Sensory nerves within bone work in a very similar way to nerves anywhere else in the body. They respond to stimuli like mechanical loading. Also, the sympathetic nerves regulate autonomic functions related to bone, including remodelling and vascular control5.

Blood vessels in bone provide blood, oxygen and nutrition, and also provide a route for new blood cells to join the circulatory system.

The periosteal artery receives oxygenated blood from the circulation and supplies it to the bone, while the periosteal vein takes blood from the bone and returns it to the circulation and towards the heart to be reoxygenated. 

Osteons are tube-shaped units of bone that run along the length of the bone. They are aligned along lines to stress to help the bone resist bending or fracture. Each osteon consists of lamellae, which are layers of concentric rings of matrix that surround a central canal called the Haversian canal. The Haversian canal allows a pathway for blood vessels and nerve fibres through the bone. 

Perforating canals, also known as Volkmann’s canals, allow blood vessels to channel through bone from the periosteum and interconnect the Haversian canals within osteons. 

The medullary cavity is the hollow part of the bone where red and yellow bone marrow are stored.

Spongy bone, also known as cancellous bone or trabecular bone, forms the ‘filling’ in hollow parts of the bone. It forms a honey-comb like structure to strengthen bone internally and allows marrow to remain in the spaces inbetween.

Compact bone forms the hard external surface of all bones, providing protection and strength. It forms a shell around spongy bone and is the primary component of long bones in the arms and legs, where greater rigidity is needed.

long bone structure cross section

Internal structure of bone

The image shows a cross-section of long bone. Within bone, there are many different structures carrying out essential functions. 

The periosteum forms a thin membrane of blood vessels and nerves around the bone. Scientists sometimes compare the periosteum of bones to the cambium layer of trees. Just as trees repair themselves and grow in harsh environments, so can your bones.

The outer periosteal layer contributes to the blood supply of your bones and the surrounding muscles. It also contains a network of nerve fibres that transmit messages throughout your body. The inner layer helps to protect your bones and stimulates repair after injury or fracture. 

Sensory nerves within bone work in a very similar way to nerves anywhere else in the body. They respond to stimuli like mechanical loading. Also, the sympathetic nerves regulate autonomic functions related to bone, including remodelling and vascular control5.

Blood vessels in bone provide blood, oxygen and nutrition, and also provide a route for new blood cells to join the circulatory system.

The periosteal artery receives oxygenated blood from the circulation and supplies it to the bone, while the periosteal vein takes blood from the bone and returns it to the circulation and towards the heart to be reoxygenated. 

Osteons are tube-shaped units of bone that run along the length of the bone. They are aligned along lines to stress to help the bone resist bending or fracture. Each osteon consists of lamellae, which are layers of concentric rings of matrix that surround a central canal called the Haversian canal. The Haversian canal allows a pathway for blood vessels and nerve fibres through the bone. 

Perforating canals, also known as Volkmann’s canals, allow blood vessels to channel through bone from the periosteum and interconnect the Haversian canals within osteons. 

The medullary cavity is the hollow part of the bone where red and yellow bone marrow are stored.

Spongy bone, also known as cancellous bone or trabecular bone, forms the ‘filling’ in hollow parts of the bone. It forms a honey-comb like structure to strengthen bone internally and allows marrow to remain in the spaces inbetween.

Compact bone forms the hard external surface of all bones, providing protection and strength. It forms a shell around spongy bone and is the primary component of long bones in the arms and legs, where greater rigidity is needed.

References

References