Viscosity of synovial fluid depends upon –
**Core Concept**
Viscosity of synovial fluid is a critical property that influences joint movement and lubrication. Synovial fluid is a thick, stringy fluid produced by the synovial membrane that lines the joints, and its viscosity plays a crucial role in reducing friction between articular cartilage and bones.
**Why the Correct Answer is Right**
The correct answer is related to the composition of synovial fluid, particularly its concentration of hyaluronic acid (HA). Hyaluronic acid is a type of glycosaminoglycan (GAG) that is responsible for the viscoelastic properties of synovial fluid. The higher the concentration of HA, the higher the viscosity of the synovial fluid. This is because HA molecules have a high molecular weight and can form a network of hydrogen bonds, which contributes to the fluid's thick and stringy texture.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because the pH of synovial fluid does not directly affect its viscosity. While pH can influence the stability of HA molecules, it is not the primary factor determining synovial fluid viscosity.
* **Option B:** This option is incorrect because the temperature of synovial fluid does not significantly affect its viscosity. While temperature can influence the viscosity of some fluids, synovial fluid's viscosity is primarily determined by its HA concentration.
* **Option C:** This option is incorrect because the type of joint does not directly affect the viscosity of synovial fluid. While different joints may have varying amounts of synovial fluid, the viscosity of the fluid itself is determined by its HA concentration.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that synovial fluid viscosity decreases with age, which can lead to increased joint friction and wear. This is why older adults are more susceptible to joint-related injuries and degenerative conditions.
**Correct Answer: D. Concentration of hyaluronic acid (HA).**