It is Halloween! Your best buddy was chased down by a vampire, and was caught. T

Question

It is Halloween! Your best buddy was chased down by a vampire, and was caught. The vampire 'fed' on your buddy, but your buddy did not taste very good to the vampire, so the vampire only ate 1.5 L of blood before letting your buddy go. Assume that the vampire saliva did not have any components in it that would interfere with the normal physiological response to hemorrhage. Use the table below (describing events related to hemorrhage) Total blood volume (mL) Erythrocyte volume (mL) Plasma volume (mL) normal 1 hour after hemorrhage 18 hours post hemorrhage 5000 2300 2700 4000 1840 2160 4900 1840 3060

Explanation / Answer

1. Hematocrit determines the fraction of blood that is red blood cells.

Hematocrit= Erythrocyte volume/Total blood volume X 100

At normal or t=0, there was no hemorrhage. Hence, the values will be normal for Erythrocyte and total blood volumes.

Hematocrit Normal = 2300/5000 X 100 = 46%

At t=18 hours,

Hematocrit= 1840/4900 x 100= 37.55%

2. Starling Forces direct the passive water exchange between interstitial fluid and the microcirculation in the capillaries. The four starling forces are:

Oncotic pressure refers to the osmotic pressure generated by proteinacious solutes. Colloidal proteins in blood cause blood colloidal osmotic pressure (BCOP). Interstitial fluid colloidal osmotic pressure (IFCOP) is due to colloidal proteins in the interstitial fluid. BCOP is always higher than IFCOP as blood has more colloidal plasma proteins than interstitial fluid.

Hydrostatic Pressure, on the other hand, is the physical force of fluids against their enclosing barriers. Blood hydrostatic pressure is the pressure exerted by blood within blood vessels or heart chambers. If the pressure exerts against the walls of the capillaries, it is capillary hydrostatic pressure (CHP). Hydrostatic pressure in the interstitial fluid is interstitial fluid hydrostatic pressure (IFHP).

Blood from the arteriole first enters a capillary bed. The CHP is high at this stage (around 35 mm Hg). CHP declines as blood moves thorough the capillary. As it reaches the venous end, the CHP drops to approximately 18 mm Hg. BCOP remains constant at about 25 mm Hg throughout the length of the capillary due to presence of plasma proteins. The BCOP is less than the osmotic pressure in the interstitial fluid.

Net filtration pressure (NFP) occurs due to interaction between the hydrostatic and osmotic pressures removing fluid from the capillary. Hence, NHP= CHP - BCOP.

At arterial end of capillary

NFP= CHP- BCOP = 35 mm of Hg- 25 mm of Hg = 10 mm of Hg

At NFP of + 10 mm of Hg, fluid moves out of the capillary at the arterial end. There is filtration occurring at this end.

In the middle of the capillary,

CHP=BCOP at 25 mm Hg

NFP= (25-25) mm of Hg= 0 mm of Hg

There is no net change in fluid volume and fluid movement out of the capillary equal its movement into the capillary.

At venous end of the capillary,

CHP= 18 mm of Hg due to fluid loss. BCOP= 25 mm of Hg.

NFP= (18- 25) mm of Hg= -7 mm of Hg

Re-adsorption occurs as the fluid moves into the capillary

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