SAQMG2

If astronauts spent long periods in the weightless environment of outer space then they may suffer from bone atrophy if they do not undertake exercises that will help to stress their bones.

Bone hypertrophy means an increase in bone tissue and bone atrophy means a decrease in bone tissue.

Fatigue fractures are also commonly known as stress fractures and march fractures.

A fatigue fracture is caused by a load being applied repeatedly over a short period of time.

A greenstick fracture is characterised by an incomplete fracture with one side bent and the other buckled.

Children are prone to greenstick fractures because their bones contain a greater proportion of collagen than adult bones which gives their bones a greater amount of flexibility.

The amount of cancellous bone is reduced with ageing.

Bone tissue strength decreases by around 15% from age 25 to 85 years.

Hyaline, elastic and fibrocartilage.

Articular cartilage is found in synovial joints.

Chondrocytes manufacture, secrete and maintain the organic matrix.

There are three main layers in articular cartilage.

The main layers are: superficial tangential, middle and deep.

Articular cartilage is attached to bone by means of the collagen fibrils that extend from the deep zone into the underlying bone tissue.

Articular cartilage is strongest when a tensile load is applied parallel to the orientation of the collagen fibrils.

The ratio of equilibrium tensile modulus in normal articular cartilage to osteoarthritic cartilage is 7.2 (from 10.1/1.4) and 2.1 (from 4.5/2.1) in the superficial and middle zone respectively.

A porous filter is used to allow the expelled interstitial fluid to escape.

The compressive aggregate modulus is directly proportional to the proteoglycan content per wet weight.

The loading conditions in the creep and stress relaxation experiments differ in that in the former a constant stress is applied and in the latter a constant strain rate is applied until a certain strain is achieved and is then maintained.

The permeability of articular cartilage decreases with increasing compressive stress.

The coefficient of friction of articular cartilage is generally much less than that for artificial joints.

The arithmetical mean deviation of articular cartilage is generally much greater than that for the components of artificial joints.

Five factors on which the viscosity of articular cartilage is dependent are: concentration of salt in solution, hydrogen ion concentration, temperature, shear rate and amount of joint degeneration.

At a low shear rate of 0.1 s-1 the viscosity of synovial fluid is 125 times greater in a normal specimen compared to a rheumatic specimen (from 10/0.08 = 125).

In hydrodynamic lubrication the two surfaces are moving over one another whilst in squeeze film lubrication the two surfaces are moving towards one another.

In boosted lubrication small molecules, including water, are forced into the articular cartilage.

The lubricating glycoprotein which covers the surface of articular cartilage is called lubricin.

Lubricin plays a vital role in boundary lubrication.

The three variables are: magnitude of the applied load, viscosity of the lubricant and relative velocity of the surfaces.

The viscosity of synovial fluid is partially dependent on the relative velocity - generally decreasing with increasing relative velocity (shear rate).

Six important functions of the skin are: temperature regulation, protection, reception of stimuli, synthesis of chemicals and hormones, excretion, and immunity.

Fat-soluble vitamins, hormones and drugs are all substances that can be absorbed through the skin.

Dermatology is the medical speciality that deals with the diagnosis and treatment of the skin.

The ratio of total body mass to skin mass is 12 to 1.