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Basic structure of joint

The joint is the area where the two or more bones are connected in our body structure. Most of the joints are synovial joints, where bones are held together with the ligaments and are lubricated by a fluid called as synovial fluid, secreted by the joint lining. Example, the knee joint is a type of synovial joint and it consists of the following structures: (Figure 7 & 8)

  • Bones: The knee joints is formed by 4 bones joined altogether with ligaments, the thigh bone (femur), the shin bone (tibia), the side bone of tibia (fibula) and the kneecap (patella).
  • Cartilage: It is a C-shaped tissue covering the surface on both ends of the bone at the joints called as articular cartilage, which helps the smooth movement of joint and also act as a shock absorbers.
  • Synovial membrane and fluid: Synovial membrane is present as the lining of joint and makes it a capsule. It secretes a clear, sticky synovial fluid to lubricate it.
  • Ligaments: Strong ligaments connect bones together and surrounds the joint to give support and limit the joint's movement.
  • Tendons: Tendons connect joint bones to muscles and controls its movement.
  • Bursas: These are fluid-filled sacs between bones and helps like cushion in the joint.
  • Meniscus: This is a curved part of cartilage in the knees and other joints.

Constituents of Bones and joint :

If we know the constituents of bone we can ourself assess, what is required for the development and growth of bones and joints. Basically, the bone is made up of osseous tissue formed by organic material 25% and inorganic material 65% along with water (10%) (Figure 9)6

The inorganic constituents of bone contains the bulk of the calcium and phosphate. Magnesium, sodium and potassium minerals are although required in minor quantity, but are equally essential for bone growth and development.Theorganic constituents contains collagen and other polysaccharides (mucoproteins and glycoproteins) and lipids (including phospholipids). There are number of other hormones which helps in the maintenance and growth of bone. It can be of protein in nature like growth

hormones, thyroid, parathyroid, calcitonin and other steroidal hormones like estrogen and testosterone which requires cholesterol i.e fats as the precursor for its synthesis. Although the list is simple but all these compositions are interlinked with number of biochemical reactions which requires many other minerals and micronutrients for the enzymatic reactions. All the above constitution and reactions itself explains, what are the basic requirements for the development and maintenance of the bone growth.

The joints have the similar composition, as these are made up of ligaments as well as bones. The main part of the bone involved in joint is the cartilage. For example in the synovial joints, the cartilage present is the articular cartilage. The articular cartilage is devoid of blood vessels, lymphatics, and nerves and is

generally subjected to a harsh bio-mechanical environment, moreover it has a limited capacity for intrinsic (self /inner) healing and repair. Therefore, the preservation and health of articular cartilage is very important for joint health. Articular cartilage is the highly specialized connective tissue with cells (chondrocytes) and dense extracellular matrix (ECM) (Figure 10), basically composed of water, collagen,proteoglycans, non-collagenous proteins and glycoproteins and functions as a wear-resistant, load-bearing, smooth and frictionless surface. Collagen is one of the two major load-bearing macromolecules present in cartilage. Proteoglycans and glycosaminoglycans are synthesised by one of the endogenous amino-mono- saccharide, Glucosamine, which is inturned synthesized from glucose.

Functions of joints

Basically, the joint is an organ whose main purpose is articulation that is, the movement of this bony frame of our body. These are also the load-bearing structures.Thus, joints helps in the mobility, flexibility and the stability of the body's skeleton. It is remarkable that under such potentially punishing mechanical conditions, most joints functions throughout the life of the individual without evidence of destruction of their major load-bearing areas.

1. https://opentextbc.ca/anatomyandphysiology/chapter/7-1-divisions-of-the-skeletal-system/

2. Gilbert SF. Developmental Biology. 6th edition. Sunderland (MA): Sinauer Associates; 2000.,Chapter 1 section 4; Available from: https://www.ncbi.nlm.nih.gov/books/NBK9974/

3. LARSEN'S HUMAN EMBRYOLOGY, 5TH EDITION; © 2015, 2009 by Churchill Livingstone, an imprint of Elsevier Inc. Chapter 8 Pg. 189

4. Robert J. Peshek, Clinical Nutrition Using the Seven Lines of Defense Against Disease.

5. Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings.

6. Essential Orthopaedics By J Maheshwari; chapter 37; pg 297