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FLUIDS <=
/span>Unit 18…with som=
e power
concepts(unit 11) Dr. John P.=
Cise,
Professor Of Physics, Austin Community College,1212 Rio Grande St., Austin =
Tx
78701 jpcise=
@austincc.edu & New York Times Oct 20, 2008 by Natalie Angier
The Wonde=
rs of
Blood You’re born with a little over a pint of it, by adulthood
you’re up to four or five quarts, and if at any point you suddenly sh=
ed
more than a third of your share, you must either get a transfusion or prepa=
re
to meet your mortician.Skip to=
next
paragraph
The fluid tissue we c= all blood not only feeds us and cleans us, delivering fresh oxygen and other nutrients to all 100 trillion cells of the body and flushing out carbon dioxide, ammonia and= other metabolic trash. It not only houses the immune system that defends us again= st the world.
Of course, we can’t rely on wind and weather = to keep our hidden seas salubriously churned and aerated, so we have evolved an active respirator and pumping mechanism, the lungs and heart. Our eig= ht pints of blood circulate through the powerhouse duet maybe 60 times an hour= , absorbing recently inhaled oxygen from the honeycombed fabric of the lungs and proceeding into the thickly muscled heart, which then shoots = the enriched fluid outward. Oxygen allocation is the task of the red blood cell= s, which hematology researchers refer to with a mix of affection and awe. “Red cells have enormous capabilities,” said Stanley Schrier of= Stanford University’s School of Medicine. They give up so much to m= ake room for their hemoglobin, the proteins that can latch = onto oxygen and that give blood its brilliant grenadine sheen. Alone among body cells, red cells at maturity jettison their nucleus and DNA to accommodate their cargo. And oh how rough= ly they are treated. A red cell at rest looks like a plump bialy and measures about 8 microns, or .0003 inches, across. Yet to reach every far-flung, oxygen-hungry customer, the cells must squeeze through capillaries less than half their width, which they accomplish by squashing down into threads that then crawl in single file along the capillary wall, pulling themselves forw= ard To ceaselessly shuttle along the body’s 60,000 miles of arteries, veins and capillaries, blood must be fluid, our trusty souvenir sea. Yet even though = we constantly replace components of our blood, directing the aged and the batt= ered to the spleen and liver — the “graveyards for blood cells,̶= 1; Dr. Schafer said — and replenishing them with fresh blood cells forge= d in the bone marrow, the turnover cycle is gradual and we can’t afford to lose everything in one big gush wrought by a predator’s gash. Blood, then, departs from sea water, or, for that matter, from breast milk, another prized body fluid, = in one outstanding way: it is always poised to clot, to relinquish liquidity and assume solidity.
In deciding whether to flow = or clot, blood takes its cues from its surroundings. As blood glides through t= he bulk of its tubular circuitry, the comparatively heavy red cells are driven toward the center of the swirl, said James N. George, a hematologist at the= University of Oklahoma Health Sciences Center, while two other, lighter characters are pushed out to the periphery: the white blood cells that oper= ate as immune warriors, and the platelets, tiny cells that have been called the Band-Aids of the body. Their marginalization is no accident. “They’re surveillance cells,” Dr. George said. “It&= #8217;s almost like they’re scouting for trouble.” White blood cells lo= ok for signs of invasive microbes, while platelets scan for leaks. As long as = the platelets detect the Teflon-like surface of unbroken endothelium, the tissue with which blood vessels are lined, they keep moving.
Question: (a) Convert 8 pints/minute to ft3 =
/second
? (b) Convert 100mm Hg(mercury) of blood pressure ( ave. between 140mm to
70mm)to lb/ft2 (c) Find the average power output of the human he=
art
which pumps 8 pints/minute at a average pressure of 100mm Hg(mercury)? Hints: 1 pint =3D 0.0167 ft<=
sup>3,
60 s =3D 1 min., P =3D (weight density) X height of fluid =3D Dh, Dwat=
er =3D
62.4 lb/ft3 , DHg =3D 13.7 Dwater , 1000 m=
m =3D 1
meter, 3.28 ft/meter, 0.738 ft.lb/s =3D 1 watt, Fluid power =3D Pressure X
[vol/time] =3D P x [vol/time] , units check….P =3D [lb/ft2=
][ft3/s]
=3Dft. lb/s. Answers: (a) ~ 0.0022 ft3/s (b) P =3D ~ 280.4 lb/ft2 (c) 0.8 to 1 watt.