Body fluids problems

Question 1

Lohman reaction

Answer 1

ADP + PCr (phosphocreatine) = ATP + Cr

Buffer to keep ATP high in muscle

Question 2

Why when weightless/ bed rest does
BV reduce
Venus pressure higher despite loss of blood volume
Red cell loss

Answer 2

• High venous pressure as blood pool is focal around heart, increasing cardiac filling, increased CO. Thus heart responds to what is apparent increased volume
• Increased ANP, inducing natriuresis, cardiac receptors stretched, lowering sympathetic drive, vasodilation?, decrease RAAS (also due to low kidney perfusion maybe?), sodium excretion, potassium retainment (causes aldosterone increase later to lower); less ADH secreted, so no thirst and water retention. All contribute to volume loss
• Epo inhibition, due to high PO2 (high CO)

Question 3

Why after long period of bed rest/weightlessness is there an increased tendency for postural hypotension and syncope?

How does counter pressure suit help?

Answer 3

Ordinarily, HR increases, TPR increase and increas ein inotropic state
-These may be hindered due to (1) loss of blood volume (>105) (2) loss of autonomic response (e.g diabetic neuropathy)

-Counter pressure suit prevents fluid translocation to peripheries

Question 4

Why in weightlessness is exercise capacity normal, then on arrival at Earth (standing) is reduced

Answer 4

• In space/bed rest the increase in venous pressure by central pooling, and reduces energy cost associated with exercise
• On earth, reduced blood volume diminishes venous return, and can not increase stroke volume. So CO is markedly reduced.
  Also ome muscle atrophy
  Anaemic also

Question 5

Why does it take only a few day to reverse the postural hypotension, but longer for exercise to return to normal

Answer 5

• Time period for ECF volume increase is hours to days to increase. On earth, the now noticeable lowered CO causes RAAS, ADH, thirst, reduced water excretion etc to increase volume
• Red cell increases however take longer to facilitate, as synthesis takes weeks. Impaired oxygen delivery shows problem with exercise

Question 6

Why are sodium and potassium levels reduced during space flight?

Answer 6

• Expected sodium loss (less RAAS, ANP etc)
• Would expect high potassium, as it does initially. Over time, aldosterone then increases over time, lowering potassium (typically normal in bed rest however)

However adaptation of cardiac receptors, not lowering RAAS as much compared to ANP being high