**6.5 Blood**

*Fads and Facts about Vitamin D*

sitivity reactions) [25]

• Weak immune reactions

**6.2 Muscular system**

muscle) [31]

and protein synthesis [9]

**6.3 Cardiovascular system**

arrhythmias [39]

These changes have been observed:

sympathetic nerve activity [41]

• Loss of arterial pressure gradient [9]

• Redistribution of venous blood volume [40]

described as:

• Increase in virulence of microorganisms [26]

• Hindering of thymopoiesis significantly [27]

authors have not reported significant changes [30].

• More latent viral reactivation [28]

• More allergic symptoms (even sometimes prolonged integumentary hypersen-

• Possibility of increasing opportunistic infections and immunity disorders

There are more reports about immune system alterations [25, 26, 29], but some

The most frequent change is atrophy of skeletal muscles. Alterations are

• Atrophy and loss of function in lower limb muscles (especially the triceps

• Spinal deconditioning (including atrophy of the paraspinal muscle group,

• More damage in plantar flexors than extensors due to a decrease of fiber size

• Significant loss in total body nitrogen and muscle volume in the Mir station [37]

• Alterations in shape and mass of the heart, cardiac function changes, and

• Cephalad fluid shift, not any change in heart rate, a decrease in parasympathetic activity, an increase in output and stroke volume, and no change in

• Decrease in performance of lower extremities muscles [32]

• Reduction of volume and strength in lower limb muscles [36]

• Muscle atrophy greater than 20 days of bed rest [38]

• Atrophy of muscle due to stem cell pool decrease [33]

reduction in curvatures of the spine) [34, 35]

**70**

