Category: Biology Second Paper Lecture Sheet

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.

The bones of the toes are called phalanges. There are 2 phalanges in the thumb and 3 in the other fingers for a total of 14 phalanges.

The bones of the foot are called metatarsal. Its number is 5. Bones are narrow, long, cylindrical and flat.

The ankle bones are called tarsal. Its number is 7. These are calcaneum, talus, cuboid, navicular and 3 cuneiform (medial, intermediate, lateral).

The next two bones of the femur are the tibia-fibula. The inner thick and large bone is called the tibia. The tibia is a tricuspid bone. Its edges are called ridges. At its upper end there are 2 condyles, 1 condyle, 2 condyles and 1 tuberosity. The lower extremity has 2 elevated parts called malleolus.
The outer thin and slender bone is called the fibula. The fibula looks like a long hexagon. Its head is open. It has the conjunctiva at its upper end and the malleolus at its lower end.

Femur is long, cylindrical, strong and largest bone. It is composed of head, neck and trochanter. Its upper end is the head. There is a lesser and a greater trochanter on either side of the skull. Between the head and the greater trochanter is the trochanteric fossa or hole. The lower end of the femur has two condyles. Between the two condyles are the foramen, the patellar articular surface, and the epicondyles on either side.
At the end of the femur is the triangular patella. The patella is a sesamoid bone. It originates from tendons. The top of the patella attaches to the femur and the bottom to the tibia.

1. It holds the bones of the foot.
2. It gives shape to the hips.
3. Transfers the weight of the body from the spine to the femur.
4. Protects soft organs such as bladder, pelvis etc.

At the junction of ilium, ischium and pubis is a shallow hole called acetabulum. The acetabulum holds the head of the femur.