Bones – Class 11 | Chapter – 20 | Biology Short Notes Series PDF

Bones: Bone is a rigid tissue that is a component of all animals’ vertebrate skeletons. Bones are responsible for protecting the body’s various organs, as well as producing red and white blood cells. Bones also provide shape and support to the body, as well as aiding in movement.

Functions of Bones

The 206 bones in the human body perform the following functions:

  • Bones provide shape to the body.
  • Bones act as a protection to internal organs like brain, heart, lungs etc..
  • Provides support to the body and anchors muscles.
  • Bones serve as storage space for minerals like calcium and phosphate
  • Bones helps in facilitating body movements.
  • Bones serve as the birthplace for red blood cells.

Types of Bones

The skeletal system of the body is made up of bones, which are primarily responsible for the storage of various macronutrients, providing rigidity, and hosing the bone marrow. Bones are also responsible for the production of red and white blood cells, as well as providing structural outline and movement.

Long Bones: Long bones are distinguished by a shaft, the diaphysis, that is much longer than it is wide. A shaft and a diaphysis connect two epiphyseal ends. The epiphysis is composed primarily of compact bones with a small amount of marrow and is found within the medullary cavity and areas of spongy, cancellous bones at the ends of the bones. The long bones consist of the humerus, ulna, radius, fibula, tibia, femur, metacarpal bones, and phalanges.

Short Bones: The short bones consist of a thin layer of compact bones surrounding a spongy interior that is more or less cuboid in shape. The bones of the wrist and ankles are considered small bones in the human body.

Flat Bones: Flat bones are curved and thin in general. Both the spongy bones and the bone marrow space are covered by two parallel layers of compact bones. Skull bones, ribs, sternum, and scapulae are all members of the flat bones group.

Irregular bones: are made up of thin layers of compact bones that cover a mass of mostly spongy bones. Their bones are complicated and irregularly shaped. The irregular bones are classified based on their bone content rather than their shape. The bones of the spine, pelvis, and a few bones of the skull fall into the category of irregular bones.

Sesamoid Bones: Sesamoid bones are embedded in the tendons. They are located at the ends of the long bones, where the tendons cross. Sesamoid bones reduce friction, which protects the tendons from excessive wear and stress. The sesamoid bones include the patella and the pisiform.

Types of Bone Cells

Bone is thought to be a metabolically active tissue made up of various cell types. When viewed microscopically, bones are composed of hard, homogeneous intercellular material within or upon which we consider four distinct cell types: osteoblasts, osteocytes, osteoclasts, and bone mesenchymal stem cells. 

Osteoblasts are primarily responsible for mineralization and bone tissue formation. They also deposit and synthesize the protein matrix of new intercellular materials on bone surfaces.

Osteoclasts are multinucleated cells that work from the bone’s surface. And aids in bone reabsorption through a direct chemical and enzymatic attack

Osteocytes are trapped within the intercellular material and live in a cavity known as a lacuna, where they communicate with other osteocytes and free bone surfaces via extensive filamentous protoplasmic extensions. Both osteocytes and osteoclasts are involved in bone tissue reabsorption.

Osteoprogenitors are the cells that give rise to both osteocytes and osteoclasts. Undifferentiated mesenchymal stem cells of the bones are found in the loose connective tissue between the condensed fibrous tissue that covers the outside of the bone and the trabeculae that run along the vascular channel.

Mesenchymal stem cells are multipotent stem cells found in bone marrow that play an important role in the formation and repair of skeletal tissues such as cartilages, fat sound in bone marrow, and bones.

List of Bones in Human Body

The Spine 

A fully grown-up adult’s spine has 26 bones, whereas a child’s spine has 36 bones. The 26 spine bones are listed below.

  • The cervical vertebrae are made up of seven bones.There are 12 ones in the Thoracic vertebrae.
  • The lumbar vertebrae are made up of five bones.
  • There is one Sacrum bone. When a child is born, he or she has five bones; however, as the child grows, the bones fuse to form a single bone.


In humans, there are 25 bones in the chest, but there are sometimes additional cervical ribs.

  • The ribs in a pair of twelve have twenty four bones.
  • One or three sternum bones.


The skull is made up of 23 bones. When the middle ear is included, the head will have 29 bones in total. The names and numbers of the bones are listed below.

  • There are eight cranial bones.
  • A single occipital bone
  • Two parietal bones
  • Two temporal bones
  • only one frontal bone
  • A single sphenoid bone
  • A single ethmoid bone
  • There are 15 facial bones in total.
  • Two bones in the nose
  • Two Maxillae (upper jaw bones)
  • Two lacrimal bones
  • Two palatine ribs
  • Two cheekbones
  • Two lower nasal conchas
  • One vomer
  • One bone of the hyoid
  • Only one mandible
  • The middle ear has six bones, three on each side.
  • Two malleus
  • Two incus and
  • Two stapes

Arm and the Hand

The arms have a total of 64 bones. The upper arm bone is made up of six bones in total, three on each side. Two humeri, one pelvic girdle, two scapula bones, and two clavicles. The lower arm is made up of four bones, two on each side: the Ulna and the Radius. The hand has 54 bones, 27 on each side, and the names of the bones are listed below.

  • One carpel
  • Two Scaphoid bones
  • Two lunate bone
  • Two Triquetral bone
  • Two Pisiform bone
  • Two Capitate bone
  • Two Trapezium
  • Two Trapezoid bone
  • Two Hamate bone
  • Ten Metacarpals bones in total with five on each side.
  • Phalanges of the hand
  • Ten Proximal phalanges in total with five on each side.
  • Eight Intermediate phalanges in total with four on each side
  • Ten Distal phalanges in total with five on each side.


The pelvis, also known as the hip bone, is made up of three regions that are joined together to form two coxal bones. Ilium, ischium, and pubis are the names of the two bones. The sacrum and coccyx connect the two hip bones to form the pelvis.

Legs and Feet

The legs are made up of 60 bones. We have two Femur bones, two Patella or knee caps bones, two Tibia bones, and two Fibula bones. We have fifty two bones in total in the foot, with twenty six bones per foot. The tarsus or tarsals are made up of

  • Two Calcaneus or heel bone
  • Two bones in the Talus
  • Two Navicular bones
  • Two Medial cuneiform bones
  • Two Intermediate cuneiform bones
  • Two Lateral cuneiform bones
  • Two Cuboid bones

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