JOINTS

The skeletal system is made up of many bones, which are joined at certain points, known as joints. These joints act as "hinge" and are responsible for changing positions of the bones or bringing about movements of the bones. A joint is a point of contact between two bones, between cartilage and bones, or between teeth and bones.

There are various types of joints viz. (1) Fibrous joints: The bones are held together by fibrous connective tissue without synovial cavity. Therefore, it permits no movement, e.g., sutures in skull, (2) cartilaginous joints. The bones are held together by cartilaage, without synovial cavity. These are partially movable, e.g., public symphysis (3) Synovial cavity, united by dense irrgular connective tissue, articular cartilage or by ligaments. These are freely movable, e.g., elbow and ankle joint, radius and ulna, etc.

FUNCTIONS

(a) It provides support to the body. (b) It protects the internal organs. (c) It helps in movement. (d) it maintains mineral balance particularly of calcium and phosphorus , (e) It forms blood cells in red bone marrow. Red bone marrow is a connective tissue within certain bones viz. pelvis, ribs, backbone and ends of arm and thigh bones, which produces RBCs (f) It stores triglycerides. Adipose cells of yellow bone marrow store triglycerides. These are in important chemical energy reserve. (In a newborn, all bone marrow is red and is involved in RBC production but with increasing age much of it changes from red to yellow).