Bones |structure,functions, cells,


Bones are one-third connective tissue and two third calcium salt. This inorganic calcium salt makes it rigid and hard so that it can afford resistance to compressive and impact forces. The organic connective tissue part makes it tough and flexible so that bone can afford resistance to tensile forces.

Calcium salt present is calcium hydroxyapatite.

And this calcium salt can be removed by putting the bone in acid due to which the bone becomes flexible and can be tied as a knot. If the organic part of a bone is removed by burning then the bone will crumble into small pieces.

However, the bone is very hard and contains high calcium content but then the bone is very much living tissue. Bone is highly vascular and shows a characteristic pattern of growth.




Diseases occur in bones and due to strong forces it fractures but it also has the ability to heal after fractures. Bone has greater regenerative power than any other tissue of the body. Bone disuse leads o Atrophy while bone overuse causes hypertrophy.

Bones in body

Cranium        8
face               14
hyoid             1
ear                  3 bone-in each
sternum          1
Ribs                24
Clavicle          2
Sapula             2
Humerus         2
Ulna                2
Radius             2
carpals            16
metacarpals    10
phalanges        28
Hip bone         2
Femur             2
Fibula             2
Tibia               2
patella             2
Tarsals            14
Metatarsals     10
phalanges       28

The function of the bones

1. It gives shape to the body
2. support the body
3.  resist any form of stress
4.  provide a surface for attachment of muscles
5. levers for muscular action
6. protect delicate organs such as the brain, spinal cord
7. manufacture blood cells
8. store calcium and phosphorus
9. take part in the immune response

What is the structure of a bone?

Bone consist of 30 flexible material and 70% bound material. This composition of bone allows it to be relatively hard and lightweight. 30% of the matrix of the bone consists of collagen fiber named as ossein while the remaining part is ground substance.  The matrix is hardened by calcium hydroxyapatite. Bone is remodeled by osteoblast and osteoclast.

What are bone cells?

Bone consist of many types of cells that are osteoblast, osteocytes, and osteoclasts.


These are mononucleate cells. The osteoblast is bone-forming cells and they are located on the surface of osteon and make a mixture known as osteoids. Osteiids mineralizes to become bones. Osteoblast consists of type I collagen fibers. These cells also manufacture hormones such as prostaglandin that acts in the bone itself.  These cells repair and create new bones.


These cells originate from osteoblast and mostly inactive osteoblasts. Space occupies by these cells are known as lacunae. These cells have many branches that reach out to osteoblast and osteoclast for communication purposes.


These are multinucleate cells and are responsible for bone resorption. These cells contain multiple nuclei that are located on resorption pits. These cells are derived from monocytes stem cells and are capable of phagocytic-activity like macrophages.

What are the types of bones?

There are five main types of bones found in the human body that are long, short, flat, irregular, and sesamoid bones. There is also another classification which we will discuss in another article.


There are a lot of terms used by anatomists to describe the bones. Some of these terms are

Articulation etc

Development of bone

The process of formation of a bone is called ossification. Ossification occurs by two processes that are endochondral ossification and intramembranous ossification. In Intramembranous ossification, bone is formed from the connective tissue while in endochondral ossification bone is formed from the cartilage.  A long bone is mainly formed by endochondral ossification.

Steps of endochondral ossification are
Zone of reverse cartilage
Zone of cell proliferation
Cell hypertrophy
And bone deposition.

What is bone volume?

Bone volume is determined from the rates of bone resorption and bone formation.

Bones diseases

Bone diseases are conditions that affect the bone of the body if occur. Below are some of the bone diseases.

1. Ambe
2. Osteonecrosis
3.  Arthritis
4.  Bone spur
5.   Craniosynostosis
6.   Coffin-Lowry syndrome
7.   Fibrodysplasia ossificans progressiva
8. fibrous dysplasia
9. Fong disease
10. Fracture
11.   Giant cell tumor of bone
12.   Greenstick fracture
13.   Gout
14.   Hypophosphatasia
15.   Hereditary multiple exostoses
16.   Klippel Feil syndrome
17.   Metabolic bone disease
18.   Multiple myelomas
19.   Nail-patella syndrome
20.   Osteitis deformans
21.   Ostitis
22.   osteitis pubis
23.    Cdissecansg osteitis
24.    Osteochondritis dissecans
25.    Osteochondroma
26.    Osteogenesis imperfecta
27.    Osteomalacia
28.    Osteomyelitis
29.    Osteopenia
30.   Osteoporosis
31.   Osteoporosis
32.   hyperparathyroidism
33.    Primary hyperparathyroidism
34.   Renal osteodystrophy
35.    Salter-Harris fractures
36.   Scoliosis
37.  Water on the knee

What is osteology?

Osteology is the study of bones and teeth. For many tasks, osteology is used in anthropology, archaeology, and forensic science.


Fracture in normal bone occurs due to a significant force applied, or due to repetitive trauma. Fractures may also occur in many conditions in which bone becomes weaken. For example, fractures occur in osteoporosis and Paget’s disease. Some fractures are painful but not all fractures are painful. When fractures are serious they also cause serious problems such as flail chest, compartment syndrome, and fat embolism.

X-rays, MRIs, and CT scans are used to investigate fractures and their underlying causes.

What are cortical bones?

Cortical bone is the outer hardest layer of bone and also named as a compact bone. Compact bone is much denser than cancellous bone. Cortical bone forms the cortex and gives the smooth, solid and white appearance to the bone. Cortical bone form 80% mass of adult human bone. Cortical bone consists of an osteon.  In osteon bone cells and the Haversian canal is present.  cortical bone is covered by periosteum and endosteum on its outer and inner surface respectively.

What is a cancellous bone?

Cancellous bone also is known as the spongy bone is the internal tissue of the skeletal bone. This part of the bone is weaker and flexible. Cancellous bone is found at the end of long bones and is the best site for the exchange of calcium ion due to its greater surface area.

Cancellous bone contains red bone marrow where the formation of red blood cells occurs. The functional unit of the cancellous bone is the trabecula.  In trabeculae bone marrow and hematopoietic stem cells are present that give rise to platelets, red blood cells, and white blood cells.

Bone marrow

Bone marrow can be found in bones that hold cancellous tissue. Newborn baby bones are filled with red bone marrow and hematopoietic marrow but as the child grows hematopoietic marrow decreases while marrow adipose tissue increases in quantity.