Q.3 Write a note on cartilage and bone in Human skeleton?

Answer:
Introduction
Overall, the human skeleton is made of bony framework but in certain parts, this frame work is supplemented by cartilage.
Connective Tissue
Both cartilage and bones are types of connective tissues in animals. Most of the connective tissues contain collagen fibres in a matrix.
Explanation
(i) Cartilage
Definition
Cartilage is a dense, clear blue-white firm connective tissue but less strong than bone.
Chondrocytes
The cells of cartilage are called chondrocytes.

Lacuna
Each chondrocyte lies in a fluid space called lacuna present in the matrix of cartilage.
Collagen Fibres
The matrix of cartilage also contains collagen fibres.
No Blood vessels in cartilage in
Blood vessels do not enter cartilage.
Types of Cartilage 

There are three types of cartilage:
1. Hyaline cartilage
2. Elastic Cartilage
3. Fibrous cartilage
1) Hyaline Cartilage:
Hyaline cartilage is strong and flexible cartilage. It is found covering the ends of the long bones, in the nose, larynx, trachea and bronchial tubes.

2) Elastic Cartilage:
Elastic cartilage is similar to hyaline cartilage. It is also quite strong but has  elasticity due to a network of elastic fibers in addition to collagen fibers. It is found in epiglottis and pinna etc.
3) Fibrous Cartilage:
Fibrous cartilage is very tough and less flexible due to large number of their collagen fibers present in knitted form. It is found in intervertebral discs.

(ii) Bone:
Definition
Bone is the hardest connective tissue in body. Bones not only move, support and protect the various parts of body but also produce red and white blood cells and store minerals.
Structure of a bone
1) Compact bone The hard outer layer of a bone is called compact bone.
2) Spongy bone Interior of bone is soft and porous called spongy bone, it contains blood vessels
and bone marrow, Babies are born with about 300 soft bones some of these bones later fuse together, so that the adult skeleton has 206 hard bones.

3) Matrix of bones
Like cartilage, the matrix of bones also contains collagen. But it also contains minerals e.g. calcium and phosphate. Bones contain different types of cells,
4) Osteocyte 
Mature bone cells are called osteocytes.