The joint cavity containing oily and slippery fluid called synovial is called synovial joint. It is 7 types. namely-
(i) Pivot (atlas joint)
(ii) Hinge joint (elbow joint)
(iii) Ball and Cotoral Joints (Skandha/Femur Joints)
(iv) Flat joint (Carpal joint)
(v) Saddle (metacarpal joint)
(vi) Ellipsoid Joint (Carpal Joint)

Bone joints containing cartilage are called amphiarthrosis joints. It is of two types. namely-
(i) Symphysis (pubis symphysis)
(ii) Synchondrosis (joint of cartilage)

The joint where the bones are joined by fibrous connective tissue is called fibrous connective tissue. It is of three types. namely-
(i) Suchar (Treaty of Ten)
(ii) Syndesmosis (tibia-fibula joint)
(iii) Gomphosis (joint of teeth and jaws)

The junction of two or more bones or cartilages is called a joint. There are three types of joints.
1. Fibrous or Synarthrosis Joint: The joint where the bones are joined by fibrous connective tissue is called fibrous connective tissue. It is of three types. namely-
(i) Suchar (Treaty of Ten)
(ii) Syndesmosis (tibia-fibula joint)
(iii) Gomphosis (joint of teeth and jaws)
2. Cartilaginous/Amphiarthrosis/Cartilaginous Joints: Bone joints containing cartilage are called amphiarthrosis joints. It is of two types. namely-
(i) Symphysis (pubis symphysis)
(ii) Synchondrosis (joint of cartilage)
3. Synovial joint: The joint cavity containing oily and slippery fluid called synovial is called synovial joint. It is 7 types. namely-
(i) Pivot (atlas joint)
(ii) Hinge joint (elbow joint)
(iii) Ball and Cotoral Joints (Skandha/Femur Joints)
(iv) Flat joint (Carpal joint)
(v) Saddle (metacarpal joint)
(vi) Ellipsoid Joint (Carpal Joint)

1. Structure of the body: Bones form the structure of the body and give specific shape to the body.
2. Preservation: The soft parts of the bony body protect the heart, lungs, brain, spinal cord, etc.
3. Movement: Skeletal muscles control body movement through contraction and expansion.
4. Red blood cell production: Red blood cells are produced from the bone marrow.
5. Immunity: Stabilized reticuloendothelial system increases the body’s immune system.
6. Breathing and Hearing: Some parts of the spine change and help in breathing and hearing.
7. Mineral salt storage: Bone stores calcium, phosphorus, potassium etc. About 97% of the body’s calcium is stored in bones.
8. Accumulation of toxic elements: If there are toxic elements in the body like lead, arsenic, etc., the bones store them.
9. As a junction: Acts as a junction of muscles, ligaments and tendons.
10. Pressure and ionic balance: Maintains internal pressure and ionic balance of the body.
11. Hormonal action: Osteocalcin hormone is produced from the bone marrow. This hormone regulates blood sugar and fat levels.
12. Chemical energy storage: As we age, some red bone marrow turns into yellow bone marrow. Bile bone marrow contains adipose cells. Adipose cells store chemical energy.

Haversian canals, lamellae, lacunae and canaliculi are collectively called Haversian canals or osteons. The structure of pure bone or osteon is described below-
1. Haversian Duct: The duct located in the unstable center is called Haversian duct. It contains veins, arteries and lymphatics. The Haversian ducts are connected to each other by the ducts of Vochmans.
2. Lamellae: 5-15 layers surround the Haversian canal. Each layer is called lamellae. It contains calcium, phosphorus and collagen.
3. Lacuna: Each lamella has small cavities. Each cavity is called a lacuna. Each lacuna contains bone cells called osteocytes or osteoblasts or osteoclasts.
4. Canaliculi: Each lacuna is surrounded by several fine canals. These ducts are called canaliculi. Lacunae are connected to each other by canaliculi. It transports nutrients and waste materials.
5. Medullary cavity: The cavity in the unstable center is called the medullary cavity. It is filled with red or yellow pulp

The inelastic cells that have less calcium and more marrow and are soft like a sponge are called spongy bones. Its structural and functional unit is called trabeculae. It has numerous kuthuri or voids. They are like sponge or honeycomb called cancellous or trabecular bone. Each trabecula is composed of osteocytes, lamellae, lacunae and canaliculi. Blood vessels from the unstable periosteum enter the trabeculae and supply nutrients to the bone cells. Haversianism does not exist. Carotid bones of mammals, large bony extremities, flat bones and all bones of birds are spongy in nature. Almost all bones in children are spongy. 20% of the total weight of the human body is spongy bone.

The unstable cells which have more calcium and less marrow and are strong are called compact bone. Pure bones have the Haversian system. At the center of the Haversian system is the Haversian groove. Haversian ducts are surrounded by circular lamellae. The lamellae contain lacunae of tiny cavities. The lacunae are surrounded by tiny canaliculi. Lacunae communicate with each other by canaliculi. Haversian ducts are interconnected by transverse ducts. These transverse channels are called Volkmann’s canal. The unstable cavity is called the marrow cavity. The marrow cavity is filled with red or yellow marrow. Fixed bones like femur, tibia-fibula, humerus, radius-ulna etc. 80% of the total weight of the human body is bone.

Bones are divided into two categories. namely-
1. Compact bone: The unstable cells which have more calcium and less marrow and are strong are called compact bone. Pure bones have the Haversian system. At the center of the Haversian system is the Haversian groove. Haversian ducts are surrounded by circular lamellae. The lamellae contain lacunae of tiny cavities. The lacunae are surrounded by tiny canaliculi. Lacunae communicate with each other by canaliculi. Haversian ducts are interconnected by transverse ducts. These transverse channels are called Volkmann’s canal. The unstable cavity is called the marrow cavity. The marrow cavity is filled with red or yellow marrow. Fixed bones like femur, tibia-fibula, humerus, radius-ulna etc. 80% of the total weight of the human body is bone.
2. Spongy bone: The inelastic cells that have less calcium and more marrow and are soft like a sponge are called spongy bones. Its structural and functional unit is called trabeculae. It has numerous kuthuri or voids. They are like sponge or honeycomb called cancellous or trabecular bone. Each trabecula is composed of osteocytes, lamellae, lacunae and canaliculi. Blood vessels from the unstable periosteum enter the trabeculae and supply nutrients to the bone cells. Haversianism does not exist. Carotid bones of mammals, large bony extremities, flat bones and all bones of birds are spongy in nature. Almost all bones in children are spongy. 20% of the total weight of the human body is spongy bone.

Bone is the strongest organ of the body made up of organic and inorganic materials. The volatile matrix consists of 40% organic matter and 60% inorganic mineral salts. Contains collagen and asimucoid (mucopolysaccharide) as organic matter. Inorganic materials include calcium carbonate, calcium phosphate, calcium chloride and magnesium phosphate. Bones are hard because they contain calcium salts in the matrix. It contains 97% calcium. The ossified membrane is called periosteum. The periosteum is attached to the bone by Sharpey’s fibers. The lining of the unstable medullary cavity is called the endosteum.
The process of bone formation is called ossification. The largest bone in the human body is the femur and the smallest bone is the stapes. There are three types of bone cells. Osteocytes, osteoblasts and osteoclasts.