Reading A
The Kidney and Its Working Unit
For m any diners, eating tender ， pale green shoots Of asp aragus is a pleasurable
springtime eve nt ， but the gastronomic experience has a peculiar sequel ： The
next time they urinate ， even if just 20 minutes after e ating, they notice th e
characteristic scent Of asparagus. Achemical in the Od crosses the gut ， enters the
bloodstream, is filtered out by th ekidneys, and appears in the urine with am az ing
speed. Actually, the chemical is acted onno faster than any other compound.
The kidneys are simply marvels atprocessing body fluids and filtering out the
urea; the sodium ， potassium ， or chlorideions ； and the glucose, water， and Other
materials that need to be excreted. The keyto a kidney's rapid functioning lies in
its complicated internal s tru ctu re andin the effcient plumbing system Of which it
is a part.
Th e Kidn eys an d Other Organs of th eExcretory Systern
It is sometimes stated that urination is our most compelling bodily function.
You will probably agre e if you have everbeen hungry, tired ， cold ， an d had a
91
m11 bladder simultaneously and c an recallthe order in which you addressed
those needs. This urgency h as to do withth e necessary waste removal rol e of the
excretory system and with the system'sparticular anatomy.
The main organs Of the excretory system arethe two plump, dark red ， crescent-
shaped kidneys, e ach ab out the size of anadult's fist an d located high in the
abdominal cavity behind the stomach and theliver. For each kidney to carry out
it s vital blood-filtering activities ， it must receive a large, steady fl ow of b100d ·
This it does through the I twin branchesdirectly 0 仃 the body's main
100d vessel ， or aorta. Cleansed b100d then leaves each kidney in large 砸 I
“ th at drains into thebody's largest vein. the kidneys filter and remove
excess water and was t e substances fromthe b100d ， these materialscollect as a
concentrated urine in a central cavity ineach kidney, then flow down a long tube
called a ureter. The two ureters dump urineinto a single storage sac ， th e urinary
bladder, which in an adult c an hold about500 ml (a pint) of fluid. The bladder
c an distend to h 01d a bit more ， but when it is Il ， it causesconsiderable pressure
on nearby nerves and a feeling of urgencythat can temporarily eclipse all other
concerns · During urination ， the urineexits the body through th e urethra ， the
single tube that drains the bladder.
The kidney has three distinct visiblezones; an outer zone: where
initial b100d filtering takes place; acentral zone ， divided into a
number of fan-shaped pyramid regions that help conserve water and valuable
solutes; an d a hollow inner compartment ， where urine collects before
it passes out of the kidney and down theureter. The functional units of the
kid n ey, twisted tubules called nephrons,reach from the outer cortex down into
the central zone and drain into the h0110wcenter.
The Kidney and Its Working Unit
For m any diners, eating tender ， pale green shoots Of asp aragus is a pleasurable
springtime eve nt ， but the gastronomic experience has a peculiar sequel ： The
next time they urinate ， even if just 20 minutes after e ating, they notice th e
characteristic scent Of asparagus. Achemical in the Od crosses the gut ， enters the
bloodstream, is filtered out by th ekidneys, and appears in the urine with am az ing
speed. Actually, the chemical is acted onno faster than any other compound.
The kidneys are simply marvels atprocessing body fluids and filtering out the
urea; the sodium ， potassium ， or chlorideions ； and the glucose, water， and Other
materials that need to be excreted. The keyto a kidney's rapid functioning lies in
its complicated internal s tru ctu re andin the effcient plumbing system Of which it
is a part.
Th e Kidn eys an d Other Organs of th eExcretory Systern
It is sometimes stated that urination is our most compelling bodily function.
You will probably agre e if you have everbeen hungry, tired ， cold ， an d had a
91
m11 bladder simultaneously and c an recallthe order in which you addressed
those needs. This urgency h as to do withth e necessary waste removal rol e of the
excretory system and with the system'sparticular anatomy.
The main organs Of the excretory system arethe two plump, dark red ， crescent-
shaped kidneys, e ach ab out the size of anadult's fist an d located high in the
abdominal cavity behind the stomach and theliver. For each kidney to carry out
it s vital blood-filtering activities ， it must receive a large, steady fl ow of b100d ·
This it does through the I twin branchesdirectly 0 仃 the body's main
100d vessel ， or aorta. Cleansed b100d then leaves each kidney in large 砸 I
“ th at drains into thebody's largest vein. the kidneys filter and remove
excess water and was t e substances fromthe b100d ， these materialscollect as a
concentrated urine in a central cavity ineach kidney, then flow down a long tube
called a ureter. The two ureters dump urineinto a single storage sac ， th e urinary
bladder, which in an adult c an hold about500 ml (a pint) of fluid. The bladder
c an distend to h 01d a bit more ， but when it is Il ， it causesconsiderable pressure
on nearby nerves and a feeling of urgencythat can temporarily eclipse all other
concerns · During urination ， the urineexits the body through th e urethra ， the
single tube that drains the bladder.
The kidney has three distinct visiblezones; an outer zone: where
initial b100d filtering takes place; acentral zone ， divided into a
number of fan-shaped pyramid regions that help conserve water and valuable
solutes; an d a hollow inner compartment ， where urine collects before
it passes out of the kidney and down theureter. The functional units of the
kid n ey, twisted tubules called nephrons,reach from the outer cortex down into
the central zone and drain into the h0110wcenter.
